An Introduction to Organic
Chemistry
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
An Introduction to Organic Chemistry
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 1
Time Allowed:
54 minutes
Score:
/45
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1 In 1869 Ladenburg suggested a structure for benzene, C6H6, in which one hydrogen atom is
attached to each carbon atom.
CH
HC
CH
CH
HC
CH
Ladenburg structure
A compound C6H4Cl 2 could be formed with the same carbon skeleton as the Ladenburg structure.
How many structural isomers would this compound have?
A
3
B
4
C
D
5
6
2 There are three structural isomers with the formula C5H12.
Which formulae correctly represent these three structural isomers?
A
CH3CH2CH2CH2CH3
CH3CH2CHCH3CH3
CH3CH3CCH3CH3
B
CH3CH2CH2CH2CH3
CH3CH2(CH)CH3CH3
C(CH3)4
C
CH3CH2CH2CH2CH3
CH3CH(CH3)CH2CH3
CH3C(CH3)2CH3
D
CH3CH2CH2CH2CH3
CH3CH(CH3)CH2CH3
CH3CH2CH(CH3)CH3
3 How many geometrical (cis-trans) isomers are there of hex-2,4-diene, CH3CH=CHCH=CHCH3?
A
none; hex-2,4-diene does not show geometric isomerism
B
2
C
3
D
4
4 The free radical substitution reaction between methane and chlorine involves initiation,
propagation and termination stages.
Which row is correct?
involved in
initiation stage
radical produced in
a propagation stage
A
heterolytic fission
H•
B
heterolytic fission
CH3•
C
homolytic fission
H•
D
homolytic fission
CH3•
5 Corticosterone is a hormone involved in the metabolism of carbohydrates and proteins.
O
OH
CH3
HO
CH3
O
corticosterone
How many chiral centres are there in one molecule of corticosterone?
A
5
B
6
C
7
D
8
6 Use of the Data Booklet is relevant to this question.
Which compound has an Mr of 84 and will react with HBr to give a product with an Mr of 164.9?
A
B
O
7 Considering only structural isomers, what is the number of alcohols of each type with the formula
C5H12O?
8 In the hydrolysis of bromoethane by aqueous sodium hydroxide, what is the nature of the
attacking group and of the leaving group?
9 In this question, structural isomerism and stereoisomerism should be considered.
How many isomeric aldehydes have the formula C5H10O?
A
3
B
4
C
5
D
6
10 The following compounds are found in the seaweed Asparagopsis taxiformis.
Which compound could show both cis-trans isomerism and optical isomerism?
A
Cl
Br
Br
Cl
H
Br
C
C
C
B
Br
C
H
C
I
Br
Br
C
H
Br
O
H
C
D
C
C
Cl
Cl
Br
C
Br
Cl
C
H
C
C
Br
H
I
C
H
11 Pentane, C5H12, is reacted with chlorine in the presence of ultraviolet light. A compound R is
found in the products. R has molecular formula C5H10Cl 2. Each molecule of R contains one chiral
carbon atom.
Which two atoms of the pentane chain could be bonded to chlorine atoms in this isomer?
A
1 and 3
B
C
1 and 5
2 and 3
D
2 and 4
12 When heated with chlorine, the hydrocarbon 2,2-dimethylbutane undergoes free radical
substitution.
In a propagation step a free radical X• is formed.
CH3
CH3CH2
C
CH3 + Cl • → X• + HCl
CH3
How many different forms of X• are possible?
A
1
B
2
C
3
D
4
13 What is true of every nucleophile?
A
It attacks a double bond.
B
It has a lone pair of electrons.
C
It is a single atom.
D
It is negatively charged.
14 How many isomers, including structural and stereoisomers, with the formula C4H8 have structures
that involve π bonding?
A
1
B
2
C
3
D
4
15 A carbanion is an organic ion in which a carbon atom has a negative charge. A carbocation is an
organic ion in which a carbon atom has a positive charge.
What is involved in the mechanism of the reaction between aqueous sodium hydroxide and
2-bromo-2-methylbutan
2A
heterolytic bond fission followed by an attack by an electrophile on a carbanion
B
heterolytic bond fission followed by an attack by a nucleophile on a carbocation
C
homolytic bond fission followed by an attack by an electrophile on a carbanion
D
homolytic bond fission followed by an attack by a nucleophile on a carbocation
16 Which stage in the free radical substitution of methane by chlorine will have the lowest activation
energy?
A
CH3• + Cl 2 → CH3Cl + Cl •
B
Cl • + Cl • → Cl 2
C
Cl • + CH4 → CH3• + HCl
D
Cl 2 → Cl • + Cl •
17 Which compound exhibits stereoisomerism?
A
CH3CHCl CH3
B
CH3CHCl CH2Cl
C
CH3CCl 2CH3
D
CH2Cl CH2CH2Cl
18 Including structural and stereoisomers, how many isomers are there of C2H2Br2?
A
2
B
3
C
4
D
5
19 Including structural and stereoisomers, how many isomeric products are produced when alcoholic
KOH reacts with 2-chlorobutane?
A
1
B
2
C
3
D
4
20 An organic compound J reacts with sodium to produce an organic ion with a charge of –3.
J reacts with NaOH(aq) to produce an organic ion with a charge of –1.
What could be the structural formula of J?
A
HO2CCH(OH)CH2CO2H
B
HO2CCH(OH)CH2CHO
C
HOCH2CH(OH)CH2CO2H
D
HOCH2COCH2CHO
21 How many isomeric esters have the molecular formula C4H8O2?
A
B
2
C
3
D
4
22 Carvone is found in spearmint.
CH3
O
H
C
C
C
H2C
CH2
C
C
H 3C
H
CH2
carvone
How many σ and π bonds are present in this molecule?
σ
π
A
13
3
3
B
22
2
2
C
22
2
2
D
25
5
5
5
23 An alkene has the formula CH3CH=CR CH2CH3 and does not possess cis-trans isomers.
What is R ?
A
H
B
Cl
C
D
CH3
C2H5
24 Menthol is an important compound extracted from the peppermint plant.
CH3
OH
H 3C
CH3
menthol
How many chiral centres are there in one molecule of menthol?
A
1
B
2
C
3
D
4
25 High-energy radiation in the stratosphere produces free-radicals from chlorofluoroalkanes,
commonly known as CFCs.
Which free-radical is most likely to result from the irradiation of CHFCl CF2Cl ?
A
CHFCl CFCl
B
CHCl CF2Cl
C
CHFCF2Cl
D
CFCl CF2Cl
26 The formula CH3 can represent an anion, a cation or a free radical. Species with the molecular
formula CH3 can act as an electrophile, a free radical or a nucleophile depending on the number
of outer shell electrons on the central carbon atom.
How many outer shell electrons must be present for CH3 to act in these different ways?
27 The diagram shows the structure of the naturally-occurring molecule cholesterol.
H 3C
CH3
H
H
CH3
H
H
HO
cholesterol
Student X claimed that the seventeen carbon atoms in the four rings all lie in the same plane.
Student Y claimed that this molecule displays cis-trans isomerism at the C=C double bond.
Which of the students are correct?
A
both X and Y
B
neither X nor Y
C
X only
D
Y only
28 How ma
ny isomers with the formula C5H10 have structures that involve π bonding?
A
3
B
4
C
5
D
6
29 Methyl isocyanate, CH3NCO, is a toxic liquid which is used in the manufacture of some
pesticides.
In the methyl isocyanate molecule, the sequence of atoms is H3C — N
C
O.
What is the approximate angle between the bonds formed by the N atom?
A
N
B
C
N
O
H3C
C
C
O
N
C
O
H 3C
H 3C
H3C
104°
D
109°
120°
N
C
O
180°
30 The use of sucrose in food processing depends in part on osmotic pressure, symbol Π.
In dilute solution, Π varies with concentration in a similar way to gas behaviour.
The equation Π V = nRT can be used, where n is the number of moles of solute molecules
contained in volume V at temperature T. The number of moles of solvent molecules should be
ignored.
Under aqueous acidic conditions sucrose is hydrolysed.
C12H22O11 + H2O → CH2OH(CHOH)4CHO + CH2OH(CHOH)3COCH2OH
sucrose
glucose
What can be deduced from this hydrolysis equation?
the osmotic pressure
glucose and fructose are
A
decreases
optical isomers
B
decreases
structural isomers
C
increases
optical isomers
D
increases
structural isomers
fructose
31 The molecule shown is optically active.
Cl
Cl
H
Cl
H
H
C
C
C
C
C
H
H
H
Cl
Cl
H
C
H
H
How many chiral carbon atoms are present in this molecule?
A
1
B
C
2
3
D
4
32 What is involved in the mechanism of the reaction between aqueous sodium hydroxide and
1-bromobutan
1-
A
attack by a nucleophile on a carbon atom with a partial positive charge
B
heterolytic bond fission and attack by a nucleophile on a carbocation
C
homolytic bond fission and attack by an electrophile on a carbanion
D
homolytic bond fission and attack by a nucleophile on a carbocation
33 Which compound exhibits both cis-trans and optical isomerism?
A
CH3CH=CHCH2CH3
B
CH3CHBrCH=CH2
C
CH3CBr=CBrCH3
D
CH3CH2CHBrCH=CHBr
34 When heated with chlorine, the hydrocarbon 2,2-dimethylbutane undergoes free radical
substitution.
In a propagation step the free radical X• is formed.
CH3
CH3CH2
C
CH3 + Cl ● → X● + HCl
CH3
How many different forms of X• are possible?
A
1
B
2
C
3
D
4
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
C
B
A
1, 2 and 3
are
correct
1 and 2
only are
correct
D
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
35 Propanone and hydrogen cyanide react together by this mechanism.
H3C
C
H3C
O–
H3C
O
CN–
C
H3 C
H3C
H
C
CN
CN
OH
H3 C
+
CN
Which statements about this mechanism are correct?
1
CN– is an electrophile.
2
It is an addition reaction.
3
Heterolytic bond breaking is involved.
36 Which statements about the photochemical chlorination of ethane are correct?
1
A propagation step in the mechanism is C2H5• + Cl 2 → C2H5Cl + Cl •.
2
Butane is present in the products.
3
The initiation step is the heterolytic fission of chlorine.
CN–
37 Use of the Data Booklet is relevant to this question.
Free-radicals play an important part in reactions involving the destruction of the ozone layer and
the substitution of alkanes by chlorine.
Some free-radicals contain two unpaired electrons. Such species are called diradicals.
Which species are diradicals?
1
O
2
Cl
3
CH3
38 During the bromination of methane, the free radical CH3• is generated. A possible terminating
step of this reaction is the formation of C2H6 by the combination of two free radicals.
What could be produced in a terminating step during the bromination of propane?
CH3
1
CH3CH2CH2CHCH3
CH3
2
CH3CHCHCH3
CH3
CH3
3
CH3CH2CHCH2CH3
39 An organic compound Y, molecular formula C6H14O, may be oxidised to compound Z, molecular
formula C6H12O2.
What could be the structural formula of Y?
1
CH3CH2CH(CH2OH)CH2CH3
2
(CH3)3CCH2CH2OH
3
CH3CH2CH(CH3)CH2CH2OH
40 Which statements about the photochemical chlorination of ethane are correct?
1
Hydrogen gas is one of the products.
2
A propagation step in the mechanism is C2H6 + Cl • → C2H5• + HCl.
3
The initiation step is the homolytic fission of chlorine.
41 Sorbitol is an artificial sweetener used to sweeten chocolate which is suitable for diabetics.
OH
H
C
H
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
H
OH
sorbitol
Which functional groups can be produced when this molecule is subjected to oxidation under
suitable conditions?
1
aldehyde
2
carboxylic acid
3
ketone
42 Disaccharides, C12H22O11, are important in the human diet. For example, sucrose is found in
pastries and lactose occurs in milk products.
Both of these compounds can be hydrolysed.
sucrose + H2O → CH2OH(CHOH)4CHO + CH2OH(CHOH)3COCH2OH
glucose
fructose
lactose + H2O → CH2OH(CHOH)4CHO + CH2OH(CHOH)4CHO
glucose
galactose
Which statements about these hydrolysis products are correct?
1
Glucose and fructose have structural isomers.
2
Glucose and galactose are optical isomers.
3
Glucose and galactose are ketones.
43 Which statements about bond angles are correct?
1
The bond angle in SO2 is smaller than the bond angle in CO2.
2
The bond angle in H2O is smaller than the bond angle in CH4.
3
The bond angle in NH3 is smaller than the bond angle in BF3.
44 Which pairs of homologous series have the same C:H ratio in their general formulae?
1
aldehydes and ketones
2
carboxylic acids and esters
3
alkenes and ketones
45 The definitions of many chemical terms can be illustrated by chemical equations.
Which terms can be illustrated by an equation that shows the formation of a positive ion?
1
first ionisation energy
2
heterolytic fission
3
enthalpy change of atomisation
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An Introduction to Organic
Chemistry
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
An Introduction to Organic Chemistry
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
82 minutes
Score:
/68
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) –OH or hydroxyl groups (allow alcohol groups)
[1]
(ii) alkenes or C=C (double) bonds or carbon double bonds
[1]
(iii) CH3CH(OH) or CH3CO- groups
[1]
(b) V is CH3CH(OH)CH=CH2
[1]
W is CH3CH=CHCH2OH
H
[
(c) compound V shows optical isomerism
(ecf for 'geometric(al)' if candidate's V is capable of cis-trans)
CH3
C
H2C
CH
[1]
CH3
HO
OH
C
H
H
CH
CH2
[1]
(d)
OH
OH
OH
or
CH3CH(OH)CH(OH)CH2OH
H
[
[Total: 8]
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2
(ii)
(a
(i) Na reacts with –OH or hydroxyl / alcohol groups
[1]
Fehling's solution reacts with –CHO or aldehyde groups
[1]
2
(b) alkene or C=C or carbon double bond or phenol or phenylamine
[1]
1
(c)
CH3CH2CH(OH)CHO
3CH(OH)CH2CHO
H
2CH2CH2CHO
OH
CHO
CHO
HO
CHO
OH
[1] + [1] +
3
the CH3CH(OH) group or the CH3CO group or methyl secondary alcohol or
methyl ketone
(d)
d)
[1]
(ii) CH3CH(OH)CH2CHO
HO
2
(e)
e)
optical isomerism
(ii)
H
OH
CHO
[1]
HO
H
CHO
[1]
2
[Total: 10]
3
Types of reaction used must come from the list in the question.
organic reaction
type of reaction
reagent(s)
CH3CH2CH2CH2Br →
nucleophilic
CH3CH2CH2CH2NH2
substitution
CH3CH2CH2CH2OH→
free radical
Br2
BrCH2CH2CH2CH2OH
substitution
or Br2 in an organic solvent
NH3
(1)
(1)
not Br2(aq)
CH3COCH3 →
nucleophilic
HCN
CH3C(OH)(CN)CH3
addition
or HCN and CN–
or NaCN/KCN + H+
CH3CH(OH)CH2CH3
elimination
conc. H2SO4
→ CH3CH=CHCH3
not dehydration
or P4O10 or Al2O3 or H3PO4
(1)
(1)
[Total: 11]
4
(a
(i) carboxylic acid or alcohol present or
carboxylic acid and alcohol present
not acid or carboxyl or hydroxyl
ydr
(ii) carboxylic acid not present or
only alcohol present
(1)
(iii) alkene or >C=C< present
(1)
[3]
(b)
b)
each correct structure gets (1)
(ii) pair 1
pair 2
(4 × 1)
geometrical or cis-trans or E/Z isomerism
(1)
optical isomerism – accept chiral compounds
(1)
[6]
#1
#2
[Total: 9]
5
(a
(i) C2H5O
(1)
(ii)
(1)
1)
(b)
b) (
functional group isomerism
or structural isomerism
(1)
do not allow 'functional isomerism' or positional isomerism
(ii)
compound
ompou
of isomerism
P
cis-trans or geometrical
T
optical
(1 + 1)
(c)
c) (
[3]
dehydration/elimination
ehy
(ii) conc. H2SO4 / P4O10 / Al2O3 / H3PO4 / pumice
(1)
(iii) CH2=CHCH=CH2
(d)
d) (
allow CH2=C=CHCH3
(1)
1)
CH3CH2CH(OH)CH2CH3
(1)
(ii) steam
conc. H2SO4
with H3PO4 catalyst or
then water
(1 + 1)
only allow condition mark if reagent mark has been given
(iii) Cr2O72– /H+ or
MnO4–/H+
(1)
1)
[Total: 12]
6
(a
(i) C=C double bonds / alkenes
(ii) –OH groups / accept alcohols or acids
(iii) CH3CO– or CH3CH(OH)– groups
(iv) carbonyl, >C=O, groups / accept aldehydes and ketones
(b)
4 × [1]
[4]
O
CO2H
O
D
D
E
E
2 × [1]
[2]
(c) isomers of C
OH
OH
cis
cis
trans
trans
correct structure (excl. stereochemistry)
cis and trans drawn correctly
type of isomerism is cis-trans or geometrical isomerism
[1]
[1]
[1]
[3]
[Total: 9]
7
(a
reaction 1
free radical substitution (1)
reaction 2
elimination (1)
(b) (i) in reaction 4
[2]
CH3C(OH)(CN)CH3 (1)
(ii) in reaction 3
I– (1)
(iii) in reaction 3
or in reaction 4
CH3I
CH3COCH3 (1)
(c) a species which has a lone pair of electrons
or which reacts with an electron deficient (δ+) centre in a molecule (1)
(d) in reaction 3
in reaction 4
OH– (1)
CN– (1)
(e) π bonding is electron rich (1)
[3]
[1]
[2]
[1]
[Total: 9]
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An Introduction to Organic
Chemistry
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
An Introduction to Organic Chemistry
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
82 minutes
Score:
/68
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The two compounds V and W are isomers with the molecular formula C4H8O, and show the following
properties and reactions.
●
●
●
●
Both compounds react with sodium metal, and both decolourise bromine water.
Compound V forms a yellow precipitate with alkaline aqueous iodine, whereas compound
W does not.
When reacted with cold KMnO4(aq), both V and W produce the same neutral compound
X, C4H10O3.
Both V and W exist as pairs of stereoisomers.
(a) Suggest which functional groups are responsible for the reactions with
(i) sodium,
.............................................................................................................................................
(ii) bromine water,
.............................................................................................................................................
(iii) alkaline aqueous iodine.
.............................................................................................................................................
[3]
(b) Suggest structures for V and W.
V
W
[2]
(c) State the type of stereoisomerism shown by compound V and draw the structures of the
stereoisomers.
type of stereoisomerism .............................................................................................................
structures of stereoisomers
isomer 1
isomer 2
[2]
(d) Suggest the structure of the neutral compound X.
X
[1]
[Total: 8]
2
Although now remembered for his music, the Russian composer Alexander Borodin was a chemist.
He is credited with the discovery of the aldol reaction, a product of which is compound J.
J shows the following properties:
●
●
●
●
●
its molecular formula is C4H8O2,
it is neutral,
it reacts with sodium metal,
it reacts with Fehling's solution,
it does not react with aqueous bromine.
(a) Suggest which functional groups are responsible for the reactions with
(i) sodium,
.............................................................................................................................................
(ii) Fehling's solution.
.............................................................................................................................................
[2]
(b) The result of the bromine test shows a functional group is absent from compound J.
Suggest the identity of this functional group.
.............................................................................................................................................. [1]
(c) In the boxes below, draw three possible straight-chain structures for J that fit the above
results, and that are structural isomers of each other.
K
L
M
[3]
(d) Compound J reacts with alkaline aqueous iodine to give a pale yellow precipitate.
(i) Which functional group does this reaction show that J contains?
.............................................................................................................................................
(ii) Which of your three structures K, L or M contains this group and is therefore J?
.............................................................................................................................................
[2]
(e) Compound J exists as stereoisomers.
(i) Name the type of stereoisomerism shown by J.
.............................................................................................................................................
(ii) Draw two structures of J to illustrate this stereoisomerism.
[2]
[Total: 10]
3
Organic chemistry is the chemistry of carbon compounds. The types of organic reactions that
you have studied are listed below.
addition
elimination
hydrolysis
oxidation
reduction
substitution
Addition and substitution reactions are further described as follows.
electrophilic
nucleophilic
free radical
Complete the table below.
Fill in the central column by using only the types of reaction given in the lists above.
Use both lists when appropriate.
In the right hand column give the formula(e) of the reagent(s) you would use to carry out the
reaction given.
organic reaction
type of reaction
reagent(s)
CH3CH2CH2CH2Br →
CH3CH2CH2CH2NH2
CH3CH2CH2CH2OH →
BrCH2CH2CH2CH2OH
CH3COCH3 →
CH3C(OH)(CN)CH3
CH3CH(OH)CH2CH3 →
CH3CH=CHCH3
[Total: 11]
4
Compound X has the molecular formula C4H8O2.
(a)
a)
Treatment of X with sodium metal produces a colourless flammable gas.
What does this result tell you about the functional groups that could be present in X?
....................................................................................................................................
....................................................................................................................................
(ii) There is no reaction when X is treated with sodium hydrogencarbonate, NaHCO3.
What does this result tell you about the functional groups that could be present in X?
....................................................................................................................................
....................................................................................................................................
(iii) When X is shaken with aqueous bromine the orange colour disappears.
What does this result tell you about the functional groups that could be present in X?
....................................................................................................................................
....................................................................................................................................
[3]
(b) The molecule of X has the following features.
●
●
●
The carbon chain is unbranched and the molecule is not cyclic.
No oxygen atom is attached to any carbon atom which is involved in π bonding.
No carbon atom has more than one oxygen atom joined to it.
There are five possible isomers of X which fit these data. Four of these isomers exist as
two pairs of stereoisomers.
(i) Draw displayed formulae of each of these two pairs.
pair 1
pair 2
(ii) These four isomers of X show two types of stereoisomerism.
State which type of isomerism each pair shows.
pair 1 .......................................................................
pair 2 .......................................................................
[6]
[Total: 9]
5
The structural formulae of six different compounds, P – U, are given below.
CH3CH=CHCH2CH3
CH3CH2COCH2CH3
CH2=CHCH2CH2CH3
P
Q
R
CH3CH2CH2CH2CH2OH
HOCH2CH2CH(OH)CH3
CH3CH2CH2OCH2CH3
S
T
U
(a) (i)
What is the empirical formula of compound T?
.................. ...............................................................................................................
(ii)
Draw the skeletal formula of compound S.
[2]
(b) (i)
Compounds S and U are isomers.
What type of isomerism do they show?
............................................................ .....................................................................
(ii)
Two of the six formulae P – U can each be drawn in two forms which are known as
stereoisomers.
Which two compounds have formulae that can be drawn in two forms?
What type of stereoisomerism does each show?
Identify each compound by its letter.
compound
type of stereoisomerism
[3]
(c) Compound S can be converted into compound R.
(i)
What type of reaction is this?
............................................. ....................................................................................
(ii)
What reagent would you use for this reaction?
............................................ .....................................................................................
(iii)
Write the structural formula of the compound formed when T undergoes the same
reaction using an excess of the reagent you have used in (c)(ii).
.............................................................................................................................. [3]
(d) Compound P may be converted into compound Q in a two-step reaction.
CH3CH=CHCH2CH3 step 1
P
(i)
(ii)
intermediate
step 2
CH3CH2COCH2CH3
Q
What is the structural formula of the intermediate compound formed in this sequence?
Outline how step 1 may be carried out to give this intermediate compound.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(iii)
What reagent would be used for step 2?
......................................... .................................................................................... [4]
[Total: 12]
6
Compound C has the molecular formula C7H14O. Treating C with hot concentrated acidified
KMnO4(aq) produces two compounds, D, C4H8O, and E, C3H4O3. The results of four tests
carried out on these three compounds are shown in the following table.
result of test with
test reagent
compound C
compound D
compound E
Br2(aq)
decolourises
no reaction
no reaction
Na(s)
fizzes
no reaction
fizzes
I2(aq) + OH–(aq)
no reaction
yellow
precipitate
yellow
precipitate
2,4-dinitrophenylhydrazine
no reaction
orange
precipitate
orange
precipitate
(a) State the functional groups which the above four reagents test for.
(i)
Br2(aq)
..................................................................................................................................
(ii)
Na(s)
..................................................................................................................................
(iii)
I2(aq) + OH–(aq)
..................................................................................................................................
(iv)
2,4-dinitrophenylhydrazine
..................................................................................................................................
[4]
(b) Based upon the results of the above tests, suggest structures for compounds D and E.
D, C4H8O
E, C3H4O3
[2]
(c) Compound C exists as two stereoisomers.
Draw the structural formula of each of the two isomers, and state the type of
stereoisomerism involved.
type of stereoisomerism .......................................................
[3]
[Total: 9]
7
Organic reactions involve substances which may be
atoms, molecules, ions or free radicals.
We also apply the terms
electrophilic, nucleophilic, addition, elimination and substitution
to organic reactions.
Consider the following reactions.
CH4 + Cl 2
CH3Cl + HCl
reaction 1
CH3CH2OH
CH2=CH2 + H2O
reaction 2
CH3I + OH–
CH3OH + I –
CH3COCH3 + HCN
CH3C(OH)(CN)CH3
reaction 3
reaction 4
(a) Using the terms mentioned above, state as clearly as you can the nature of each of the
following reactions.
reaction 1 .......................................................................
reaction 2 .......................................................................
[2]
(b) By considering the four reactions above, suggest a formula for each of the following
substances.
In each case, state which reaction you are considering.
(i)
one substance that is an addition product
reaction.......
(ii)
one substance that is a leaving group
reaction.......
(iii)
addition product
leaving group
one substance that behaves as an electrophile
reaction.......
electrophile
[3]
(c) What is meant by the term nucleophile?
..........................................................................................................................................
.................................................................................................................................... [1]
(d) Reactions 3 and 4 involve nucleophiles.
For each reaction, give the formula of the nucleophile.
reaction 3
reaction 4
[2]
(e) One characteristic reaction of ethene is its ability to decolourise bromine.
CH2=CH2 + Br2
BrCH2CH2Br
In this reaction, ethene behaves as a nucleophile.
Suggest an explanation for how ethene can behave in this way.
..........................................................................................................................................
.................................................................................................................................... [1]
[Total: 9]
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An Introduction to Organic
Chemistry
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
An Introduction to Organic Chemistry
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 2
Time Allowed:
52 minutes
Score:
/43
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Organic nitrates in photochemical smog can cause breathing difficulties.
The diagram shows an example of an organic nitrate molecule.
H
H
1
3
C
H
2
C
O
O
NO2
O
What is the correct order of the bond angles shown in ascending order (smallest first)?
A
1→2→3
B
2→1→3
C
3→1→2
D
3→2→1
2 A dimer, X, is stable when solid but a dynamic equilibrium is set up in solution.
X(aq)
2Y(aq)
A solution of X has an initial concentration of 0.50 mol dm–3. When equilibrium has been reached
[X(aq)] has fallen to 0.25 mol dm–3.
The changes in [X(aq)] and [Y(aq)] are plotted against time until equilibrium is reached. The value
of Kc is then calculated.
Which graph and value for Kc are correct?
Kc / mol dm–3
graph
0.5
X
0.4
A
concentration 0.3
/ mol dm–3
0.2
1
Y
0.1
0
time
0
0.5
X
0.4
B
2
concentration 0.3
/ mol dm–3
0.2
Y
0.1
0
time
0
0.5
X
0.4
C
1
concentration 0.3
/ mol dm–3
0.2
Y
0.1
0
time
0
0.5
D
2
X
0.4
concentration 0.3
/ mol dm–3
0.2
Y
0.1
0
0
time
3 How many structural isomers are there of trichloropropane, C3H5Cl 3?
A
B
3
C
4
D
5
6
4 Which of the compounds shown have chiral carbon atoms?
1
2
CH3
3
4
OH
O
CH3
OH
A
1, 2
B
1 and 4 only
C
2 and 3 only
D
2, 3 a
5 Which compound would undergo nucleophilic addition?
A
bromoethane, C2H5Br
B
ethanal, CH3CHO
C
ethane, C2H6
D
ethene, C2H4
CH3
CH3
6 In recent years a number of athletes have been banned from sports because of their illegal use of
synthetic testosterone, a naturally occurring hormone in the body.
CH3
OH
CH3
O
testosterone
How many chiral centres are present in a testosterone molecule?
A
1
B
2
C
3
D
6
7 The compound known as ‘gamma-linolenic acid’ is found in significant amounts in the seeds of
the Evening Primrose plant. There is evidence that the compound may help patients with
diabetes.
CH3(CH2)4CH=CHCH2CH=CHCH2CH=CH(CH2)4CO2H
gamma-linolenic acid
How many cis-trans isomers does gamma-linolenic acid have?
A
3
B
6
8 What always applies to a nucleophile?
A
It attacks a double bond.
B
It has a lone pair of electrons.
C
It is a single atom.
D
It is negatively charged.
C
8
D
12
9
The antidote molecule shown can help to prevent liver damage if someone takes too many
paracetamol tablets.
H
x
H
H
H
C
N
y
S
C
represents a
lone pair
z
H
H
H
What is the order of decreasing size of the bond angles x, y and z?
10 The drug cortisone has the formula shown.
CH2OH
CO
CH3 OH
O
CH3
O
In addition to those chiral centres marked by an asterisk (*), how many other chiral centres are
present in the cortisone molecule?
A
0
B
1
C
2
D
3
11 The presence of 11-cis retinal, C20H28O, in cells in the eye is important for vision.
The structure of retinal includes an aldehyde group, a cyclohexene ring and a long aliphatic side
chain, in which a carbon-carbon double bond exists between carbons numbered 11 and 12.
Which pair of statements about 11-cis retinal could be correct?
total number of
>C=C< double bonds
arrangement around
the adjacent carbons
11 and 12
R2
R1
A
5
B
C
H
H
R1
H
5
C
C
C
H
R2
R1
R2
6
D
C
C
C
H
H
R1
H
6
C
C
R2
H
12 What is the least number of carbon atoms in a non-cyclic alkane molecule that has a chiral
centre?
A
7
B
8
C
9
D
10
13 Which equation represents a valid propagation step in the free radical reaction between ethane
and chlorine?
A
C2H6 + Cl • → C2H5Cl + H•
B
C2H5Cl + Cl • → C2H4Cl • + HCl
C
C2H6 + H• → C2H •5 + HCl
D
C2H5• + Cl • → C2H5Cl
14 Which pair of reaction types is illustrated by the reaction sequence below?
CH3CH=CHCH3
HI in CH3CO2H
CH3CH2CHICH3
A
electrophilic addition and electrophilic substitution
B
electrophilic addition and nucleophilic substitution
C
nucleophilic addition and electrophilic substitution
D
nucleophilic addition and nucleophilic substitution
NaOH(aq)
CH3CH2CH(OH)CH3
15 Trichloroethene is widely used as a dry-cleaning agent.
H
Cl
C
Cl
C
Cl
With which of the following does trichloroethene react to give a chiral product?
A
B
Br2
C
HCl
D
NaCN(aq)
NaOH(aq)
16 Which compound is both chiral and acidic?
A
H
B
CO2H
C
OH
CH2Br
HCO2CH
CH3
C
H
CH3
D
C
CO2H
CH(OH)CO2H
CH2CO2H
17 Sorbitol is a naturally-occurring compound with a sweet taste. It is often used as a substitute for
sucrose by the food industry.
The diagram shows its structure.
H
H
H
C
O
H
H
C
O
H
O
C
H
H
C
O
H
H
C
O
H
H
C
O
H
H
How many chiral centres are present in sorbitol?
A
1
B
2
C
3
D
4
18 Which hydrocarbon can form a monochloro-substitution derivative which shows both chirality
and cis-trans isomerism?
A
CH3CH=CH2
B
(CH3)2C=CH2
C
CH3CH=C(CH3)2
D
CH3CH=CHCH2CH3
19 Glucose, C6H12O6, is a product of photosynthesis.
It has the following structure.
H
C
O
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
How many chiral centres does the molecule have?
A
1
B
2
C
4
D
6
20 The compound 1,2-dichloroethene, C2H2Cl 2, has been used as an industrial solvent for a number
of compounds including fats, camphor and caffeine.
Which statement about this compound is incorrect?
A
The compound can be catalytically hydrogenated.
B
The compound is a planar molecule.
C
The compound shows cis-trans isomerism.
D
The compound shows optical isomerism.
21 Lycra is a polyurethane fibre used in the fashion industry. It is a polymer made from two
monomers, one of which has the following formula.
O=C=N–(CH2)n –N=C=O
What is the O–C–N bond angle in this molecule?
A
90 °
B
109 °
C
120 °
D
180 °
22 Which molecules, each with a linear carbon chain, can have an optically active isomer?
A
I and II only
B
I, II and III only
C
II and III only
D
I, II and IV only
I
II
III
IV
C3H6BrI
C3H4BrI
C3H6I2
C3H4Br2
23 In which pair do the isomers have identical boiling points?
A
CH3CH2CH2CH2OH
a
3)2CHCH2OH
B
CH3(CH2)4CH3
and
3)2CHCH(CH3)2
CH3
CH3
C
C
H
Cl H 2 C
CH2Cl
Cl
H
CH3
D
C
H
C
and
CH3
Cl
CH3
CH3
and
C
H
C
H
C
H
24 Warfarin is used as a rat poison.
O
O
C
C
C
CH
CH2
C
OH
CH3
O
warfarin
How many chiral centres are present in the warfarin molecule?
A
B
0
C
1
D
2
3
25 The structures below show isomers of C6H12.
1
2
CH3
C
CH3
CH3
C
C
C2H5
H
3
H
C2H 5
C 2H 5
C
C
CH3
4
CH3
H
C
C
CH3
In which pair are the members cis-trans isomers of each other?
26 Which alkene could exist in cis and trans forms?
A
CH3CH2CH2CH
B
CH3CH2CH
C
CH3CH2C
CH
CH2
CH3
D
CH3CH
C
CH3
3
CH2
3
C 2H 5
H
CH3
C
CH3
27 When gaseous chemicals are transported by road or by rail they are classified as follows.
flammable
non-flammable
poisonous
Which gas is non-flammable?
A
butane
B
hydrogen
C
oxygen
D
propene
28 The diagram shows the structure of vitamin C.
HO
OH
C
O
C
C
CH CH
O
CH2OH
OH
How many chiral centres are there in one molecule?
A
1
B
2
C
3
D
4
29 What is the number of isomers of C2H2Cl2 including cis-trans isomers?
A
2
B
3
C
4
30 Which of these always applies to a nucleophile?
A
It attacks a double bond.
B
It has a lone pair of electrons.
C
It is a single atom.
D
It is negatively charged.
D
5
31 Compound P displays cis-trans isomerism and gives a red-brown precipitate with Fehling’s
solution.
What is P?
A
B
CH2CHO
H
C
C
C
H
COCH3
H
CH3
CH3
CH3
CH3
H
C
D
H
C
H
C
Br2
B
Na
C
NH3
D
CN –
H
C
CHO
32 What can behave as an electrophilic reagent?
A
C
H
C
CHO
33 Which molecule does not have a chiral centre?
A
B
CO2H
CO2H
H
C
OH
H
C
OH
HO
C
H
H
C
OH
CO2H
CH3
C
D
OH
OH
OH
OH
C
C
HO
HO
CH3
CO2C2H5
34 How many structural and cis-trans isomers are there for dichloropropene, C3H4Cl2?
A
3
B
5
C
6
D
7
35 The isomers, citric acid and isocitric acid, are intermediates in the Krebs cycle of the oxidation of
glucose in living cells.
CH2CO2H
CH2CO2H
C(OH)CO2H
CHCO2H
CH2CO2H
CH(OH)CO2H
citric acid
How many chiral centres does each acid possess?
isocitric acid
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
D
1 only
is
correct
No other combination of statements is used as a correct response.
36 Which structural formulae represent 2,2-dimethylpentane?
1
(CH3)2CHCH2CH(CH3)2
2
(CH3)3CCH2CH2CH3
3
CH3CH2CH2C(CH3)3
37 Which reactions are examples of nucleophilic substitution?
1
CH3CH2Br + OH– → CH3CH2OH + Br–
2
H+
CH3I + H2O 
→ CH3OH + HI
3
CH3CH2CH2Cl + NH3 → CH3CH2CH2NH2 + HCl
38 The chlorine free radical takes part in the destruction of the ozone layer.
Which statements about this free radical are correct?
1
It is formed by the heterolytic fission of the covalent bond in a chlorine-containing molecule.
2
It has a single unpaired electron.
3
It has the same electron arrangement as a chlorine atom.
39 Aspirin is a widely-available pain-killer, whose properties have been known for centuries. The
structure of aspirin is shown.
OH
C
O
O C CH3
O
Which functional groups are present in aspirin?
1
alcohol
2
carboxylic acid
3
ester
40 Monopotassium citrate is used as an emulsifying agent in powdered milk and in powdered soups.
It may be represented by the formula shown.
CH2CO2H
HO
C
CO2– K+
CH2CO2H
Which statements about monopotassium citrate are correct?
1
It can form optical isomers.
2
It can act as a dibasic acid.
3
It can form esters with both acids and alcohols.
41 In which pairs are the members stereoisomers of each other?
1
CH3
CH3
C
C
Br
Br
Cl
H
2
CH3
C
Br
C
C
H
C
H
H
H
CH3
CH3
Br
C
H
3
H
Cl
CH3
Br
C
C
Cl
H
C
Br
Cl
42 For the reaction
(CH3)3SiCl + C2H5O– → (CH3)3SiOC2H5 + Cl –
which statements are likely to be true?
1
It involves nucleophilic attack by C2H5O–.
2
Cl – is displaced by C2H5O–.
3
The oxygen-carbon bond is not broken.
43 What will always be a characteristic of a compound containing a single carbon atom with four
different groups bonded to it?
1
It will have an optical isomer.
2
It will have a chiral centre.
3
It will have a structural isomer.
Save My Exams! – The Home of Revision
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An Introduction to Organic
Chemistry
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
An Introduction to Organic Chemistry
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 2
Time Allowed:
80 minutes
Score:
/66
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) C2H5O
(ii)
(1)
OH
(1)
(iii)
compound
ompou
of isomerism
A
cis-trans or geometrical
D
optical
allow one mark if both A and D are correctly identified
but in both cases, the type of isomerism is incorrect
(1 + 1)
(b)
b) (
dehydration/elimination
ehy
(ii) conc. H2SO4/P4O10/Al2O3/pumice etc.
(1)
but
(iii) CH2=CHCH=CH2/butadiene/buta-1,3-diene
(c)
c) (
[4]
CH3CH2CH(OH)CH3
(ii) steam
conc. H2SO4
with H3PO4 catalyst or
then water
(iii) Cr2O72– /H+
(d) functional group isomerism
or structural isomerism
not positional isomerism
[3]
(1)
(1 + 1)
(1)
1)
(1)
[1]
[Total: 12]
2
organic reaction
CH3CHO →
type of reaction
reagent(s)
(1)
HCN
(1)
or HCN and CN–
free radical
(1)
Br2
CH3CH2CHBrCH3 substitution
(1)
nucleophilic
CH3CH(OH)CN addition
CH3CH2CH2CH3 →
(1)
or Br2 in an organic solvent
CH3CH(OH)CH3 →
elimination
(1)
not Br2(aq)
(1)
conc. H2SO4
(1)
KMnO4/MnO4 –
(1)
CH3CH=CH2
CH3CH=CH2 →
addition
CH3CH(OH)CH2OH or oxidation
(1)
[10]
[Total: 10]
3
•
heterogeneous: different phases/states
•
(heterogeneous): adsorption onto the surface
•
the correct allocation of the terms heterogeneous and homogeneous to the two exemplar
•
•
example of heterogeneous, e.g.
equation, e.g.
Fe (in the Haber process)
N2 + 3H2
2NH3
•
•
•
example of homogeneous, e.g.
equation, e.g.
how catalyst works, e.g.
Fe3+ (in S2O82- + I-)
S2O82- + 2IFe3+ + I-
or
homogeneous: same phase/state
2SO42- + I2
Fe2+ + ½I2
[OR example:
FeCl3 (in Friedel-Crafts or chlorination etc. with CH3Cl, Cl2, Br2)
C6H5 Cl + HCl
equation,
C6H6 + Cl2
FeCl4- + Cl+ ]
FeCl3 + Cl2
mode of action
Total = [8]
__________________________________________________________________________
Question
4
(a)
Mark Scheme
Bond breaking =
Bond forming =
Enthalpy change =
(b) (i)
(ii)
3
(c
Mark
C=O
C–H
= 740
= 410
= 1150 kJ
[1]
C–C
C–O
O
O–H
= 350
= 360
= 460
= 1170 kJ
[1]
= –20 kJ mol–1
[1]
1150 – 1170
Total
[3]
Stereoisomerism = (molecules with the same molecular formula and)
same structural formula but different spatial
arrangements of atoms
[1]
Chiral centre =
[1]
[2]
(Planar) carbonyl so (equal chance of nucleophile) attacking either side
[1]
[1]
M1 = lone pair AND curly arrow from lone pair to carbonyl C
M2 = partial charges on C=O AND curly arrow from bond (=) to Oδ–
M3 = structure of intermediate including charge
M4 = lone pair AND two correct curly arrows (from lone pair to H AND from
H—C to C)
M5 = CN–
[1]
[1]
[1]
[1]
[1]
[5]
(CN– regenerated so) catalyst
[1]
[1]
atom with four different atoms/groups attached
(i)
(ii)
[12]
5
(a
(i)
(ii)
A = CH3CH2CH2CH2CHO
[1]
B = CH3CH2CH(CH3)CHO
[1]
C = (CH3)2CHCH2CHO
[1]
D = (CH3)3CCHO
[1]
CH3
CH3
HC
H3CCH2
(b) (i)
(ii)
CH
H2
CHO
[4]
H2
O HC
[1+1]
[1+1]
CH2CH3
Fehling’s / Benedict’s OR Tollens’ OR dichromate OR manganate
Warm / heat
Fehling’s / Benedict’s =(Brick)-red ppt
Tollens’ = silver / mirror OR grey/black precipitate
with the aldehyde / A-D
Dichromate = orange to green
Manganate = purple to colourless
[1]
[1]
(2,4-)DNP(H) / Brady’s reagent
[1]
Orange / yellow / red-orange / yellow-orange ppt
[1]
[1]
[3]
[2]
[11]
6
(a
(i) same molecular formula
but different structural formula/structure (1)
(ii) asymmetric C atom/chiral centre present (1)
>C=C< bond present (1
[3]
(b) NaO2CCH(OH)CH(OH)CO2Na (1)
[1]
(c) no because there is no chiral carbon atom present (1)
[1]
35.8 4.5 59.7
:
:
this mark is for correct use of Ar values (1)
12
1
16
C : H : O = 2.98 : 4.5 : 3.73
C : H : O = 1 : 1.5 : 1.25 this mark is for evidence of correct calculation (1)
gives empirical formula of W is C4H6O5
(d) (i) C : H : O =
(ii) C4H6O5 = 12 × 4 + 1 × 6 + 16 × 5 = 134
molecular formula of W is C4H6O5 (1)
[3]
29.4 ×100
= 0.0294 (1)
1000
1.97
n(W) =
= 0.0147 (1)
134
no. of –CO2H groups present
0.0294
= 2 (1)
in one molecule of W =
0.0147
(e) (i) n(OH–) =
29.4 ×1.00
= 0.0294 (1)
1000
1.97 g W ≡ 0.0294 mol NaOH
0.0294 ×134
134 g W ≡
= 1.999 ≈ 2 mol NaOH (1)
1.97
no. of –CO2H groups present in 1 molecule of W = 2 (1)
or n(OH–) =
[3]
(ii)
H
H—O
 
C—C—C—C
O
 
H
CH3
H—O

C —C—C
O

O—H
OH

H—C—H
H—O

C—C—C
O

H
one correct structure (1)
correctly displayed (1)
allow any correct ether
O—H
O
or
O—H
O
or
O—H
O
[2]
[Total: 13]
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An Introduction to Organic
Chemistry
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
An Introduction to Organic Chemistry
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 2
Time Allowed:
80 minutes
Score:
/66
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The structural formulae of six different compounds, A – F, are given below.
Each compound contains four carbon atoms in its molecule.
CH3CH=CHCH3
CH3CH2COCH3
CH2=CHCH2CH3
A
B
C
CH3CH2CH(OH)CH3
HOCH2CH2CH2CH2OH
CH3CH2OCH2CH3
D
E
F
(a) (i)
What is the empirical formula of compound E? ………………
(ii)
Draw the skeletal formula of compound D.
(iii)
Structural formulae do not show all of the isomers that may exist for a given
molecular formula. Which two compounds each show different types of isomerism
and what type of isomerism does each compound show? Identify each compound
by its letter.
compound
type of isomerism
[4]
Compound D may be converted into compound C.
(b) (i)
What type of reaction is this?
………………………………………
(ii)
What reagent would you use for this reaction?
………………………………………
(iii)
What is formed when compound E undergoes the same reaction using an excess
of the same reagent?
………………………………………
[3]
Compound A may be converted into compound B in a two-stage reaction.
CH3CH=CHCH3
(c) (i)
(ii)
stage I
→
intermediate
stage II
→
CH3CH2COCH3
What is the structural formula of the intermediate compound formed in this
sequence?
Outline how stage I may be carried out to give this intermediate compound.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(iii)
What reagent would be used for stage II?
…………………………………………
[4]
(d) Compounds D and F are isomers.
What type of isomerism do they show?
…………………………………………
[1]
[Total: 12]
2
Organic chemistry is the chemistry of carbon compounds. The types of organic reactions
that you have studied are listed below.
addition
elimination
hydrolysis
oxidation
reduction
substitution
Addition and substitution reactions are further described as follows.
electrophilic
nucleophilic
free radical
Complete the table below.
Fill in the central column by using only the types of reaction given in the lists above. Use
both lists when appropriate.
In the right hand column give the name(s) or formula(e) of the reagent(s) you would use to
carry out the reaction given.
organic reaction
type of reaction
reagent(s)
CH3CHO →
CH3CH(OH)CN
CH3CH2CH2CH3 →
CH3CH2CHBrCH3
CH3CH(OH)CH3 →
CH3CH=CH2
CH3CH=CH2 →
CH3CH(OH)CH2OH
[Total: 10]
3
By using iron and its compounds as examples, outline the different modes of action of
homogeneous and heterogeneous catalysis.
Choose two examples, and for each example you should
•
state what the catalyst is, and whether it is acting as a homogeneous or a
heterogeneous catalyst,
•
write a balanced equation for the reaction.
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..............................................................................................................................................[8]
[Total: 8]
4
Ethanal reacts with hydrogen cyanide, in the presence of a small amount of NaCN, as shown.
CH3CHO + HCN → CH3CH(OH)CN
(a) Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction.
Include a sign with your answer.
enthalpy change = .................................... kJ mol–1 [3]
(b) The product of this reaction shows stereoisomerism as it contains a chiral centre. This reaction
produces an equimolar mixture of two optical isomers.
(i) Explain the meanings of the terms stereoisomerism and chiral centre.
stereoisomerism .................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
chiral centre ........................................................................................................................
.............................................................................................................................................
[2]
(ii) Suggest why the two optical isomers are produced in equal amounts by this reaction.
.............................................................................................................................................
....................................................................................................................................... [1]
(c) (i) Complete the diagram to show the mechanism of this reaction. Include all necessary
charges, partial charges, lone pairs and curly arrows and show the structure of the
intermediate.
N
C–
CN
H
H 3C
H 3C
C
C
H
+
OH
O
H
C
N
[5]
(ii) With reference to your mechanism in (i), explain the role of the NaCN in this reaction.
.............................................................................................................................................
....................................................................................................................................... [1]
[Total: 12]
5
There are seven structural isomers with the molecular formula C5H10O that are carbonyl
compounds. Four of these are aldehydes.
These four aldehydes, A, B, C and D, have the following properties.
●
Aldehyde A has a straight chain while B, C and D are branched.
●
Aldehyde B is the only one of the four isomers with a chiral centre and it exists as a pair of
optical isomers.
●
Aldehyde C has two methyl groups in its structure but D has three.
(a)
a)
Give the structure of each of the four isomers.
A
B
C
D
[4]
(ii) Draw the three-dimensional structures of the two optical isomers of B.
[2]
(b) (i) Describe a chemical test that would allow you to distinguish between any of the four
isomers A to D and any of the other three structural isomers of C5H10O, that are carbonyl
compounds.
In your answer you should describe any necessary reagents and conditions as well as
explaining what you would see in each case.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Describe a test that would give the same result with all seven carbonyl isomers of C5H10O.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
[Total: 11]
6
Isomerism occurs in many organic compounds. The two main forms of isomerism are
structural isomerism and stereoisomerism. Many organic compounds that occur naturally
have molecules that can show stereoisomerism, that is cis-trans or optical isomerism.
(a) (i)
Explain what is meant by structural isomerism.
..................................................................................................................................
..................................................................................................................................
(ii)
State two different features of molecules that can give rise to stereoisomerism.
..................................................................................................................................
..................................................................................................................................
[3]
Unripe fruit often contains polycarboxylic acids, that is acids with more than one carboxylic
acid group in their molecule.
One of these acids is commonly known as tartaric acid, HO2CCH(OH)CH(OH)CO2H.
(b) Give the structural formula of the organic compound produced when tartaric acid is
reacted with an excess of NaHCO3.
[1]
Another acid present in unripe fruit is citric acid,
OH
HO2CCH2CCH2CO2H
CO2H
(c) Does citric acid show optical isomerism? Explain your answer.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [1]
A third polycarboxylic acid present in unripe fruit is a colourless crystalline solid, W, which
has the following composition by mass: C, 35.8%; H, 4.5%; O, 59.7%.
(d) (i)
(ii)
Show by calculation that the empirical formula of W is C4H6O5.
The Mr of W is 134. Use this value to determine the molecular formula of W.
[3]
A sample of W of mass 1.97 g was dissolved in water and the resulting solution titrated with
1.00 mol dm–3 NaOH. 29.4 cm3 were required for complete neutralisation.
(e) (i)
(ii)
Use these data to deduce the number of carboxylic acid groups present in one
molecule of W.
Suggest the displayed formula of W.
[5]
[Total: 13]
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Alkanes
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkanes
Theory
Booklet
Mark Scheme 1
Time Allowed:
82 minutes
Score:
/68
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) heat with catalyst or heat with Al2O3 / SiO2
1
(ii) B is CH3CH2CH3
1
(iii) C is CH2=CHCH2CH2CH3
1
D and E are CH3CH=CHCH2CH3 (one shown as cis, the other as trans)
1
F is CH3CH2CH2CO2H
1
G is CH3CO2H
H is CH3CH2CO2H
(iv) geometrical or cis-trans or E–Z
1
(b) (i) No particular conditions or in the dark
1
(ii) electrophilic addition
(iii) CH3
1
CH3
CH
CH2
CH3
CH
CH
Br
δ+ Br
δ- Br
CH2
Br
Br
CH2
Br
1
1
[Total: 10]
Question
uestion
2
Mark
Total
physical: fractional distillation / fractionation
chemical: crack(ing) (allow: reforming, isomerisation, thermal decomposition,
desulfurisation)
1
1
2
Strong (C–C and C–H) bonds / high bond energies
Non-polar / C and H have similar electronegativities
1
1
2
(ii)
109.5° AND 120° (117º – 122º)
1
1
(iii)
ethane = tetrahedral
ethene = trigonal planar
1
1
4 × σ / single bonds on Cs in ethane AND
3 × σ and 1 × π on Cs in ethene OR
2 × single and 1 × double on Cs in ethene
allow from suitable labelled diagram
1
1
Cl 2 → 2Cl •
1
C2H6 + Cl • → •C2H5 + HCl
•C2H5 + Cl 2 → C2H5Cl + Cl •
1
1
•C2H5 + Cl • → C2H5Cl
1
(a)
(b) (i)
(iv)
(c) (i)
correct alternative terminations allowed
(ii)
initiation, propagation, termination (correctly assigned)
1
•C2H5 + •C2H5 → C4H10
1
5
13
Question
Mark Scheme – 9701 / 23
3
3
the amount of substance containing 6(.02) x 1023 (fundamental)
particles of that substance (or; the amount of substance
containing as many particles as there are atoms in 12 g of
carbon-12)
(1)
2NaOH + CO2 Na2CO3 + H2O
(1)
1)
(a)
(b) (i)
Ma
Total mark
[1]
allow ionic equations or formation of NaHCO3
(ii)
95 – 75 = 20 cm3
(1)
[1]
(iii)
excess oxygen = 75 cm3 so used = 25 cm3
(1)
[1]
(iv)
2CxHy + 5O2 4CO2 + zH2O
(2)
[2]
(v)
x = 2; y = 2; z = 2 (or z = 1 if CxHy + 2.5O2 2CO2 + zH2O)
(1+1+1)
[3]
(c) (i)
(ii)
W = (CH3)2C=CH2 = 2–methylpropene
(1)
X = (CH3)2CBrCH3 = 2–bromo–2–methylpropane
(1)
Y = (CH3)2CHCH2Br = 1–bromo–2–methylpropane
(1)
Z = (CH3)3COH = 2–methylpropan–2–ol
(1)
Markovnikov addition / H adds to C with most Hs
(1)
tertiary carbocation more stable than primary
(1)
inductive effect of three alkyl groups owtte
(1)
Total
ot
[4]
[Max 2]
4
(a
(i) alkanes or paraffins not hydrocarbons
(ii)
i
(b)
b) (
(ii)
i
C4H10 + 13O2 → 8CO2 + 10H2O
(1
carbon allow graphite
(1)
C4H10 + 5O2 → 8C + 10H2O
allow balanced equations which include CO and/or CO2
(1)
(c) enthalpy change when 1 mol of a substance
is burnt in an excess of oxygen/air under standard conditions
or is completely combusted under standard conditions
m=
(d)
d)
(1)
pVM r 1.01× 10 5 × 125 × 10 −6 × 44
=
g
RT
8.31× 293
(1)
(ii) heat released = m c δ T = 200 × 4.18 × 13.8 J
= 11536.8 J = 11.5 kJ
(1)
(1)
(iii) 0.23 g of propane produce 11.5 kJ
11.5 × 44
44 g of propane produce
kJ
0.23
= 2200 kJ mol–1
(1)
(ii) straight chain molecules can pack more closely
therefore stronger van der Waals’ forces
or reverse argument
[2]
(1
(1)
from methane to butane
there are more electrons in the molecule
therefore greater/stronger van der Waals’ forces
[2]
(1)
= 0.228147345 g
= 0.23 g
(e)
e) (
[2]
[5]
(1)
(1)
(1)
(1)
[4]
[Total: 15]
5
(a
(i) break large hydrocarbons into smaller hydrocarbons or
break down large hydrocarbons
smaller hydrocarbons are more useful or
smaller hydrocarbons are more in demand
(1)
(1)
(ii) using high temperatures/thermal cracking or
using catalysts/catalytic cracking
(1)
(iii) C14H30 → C7H16 + C7H14 or
C14H30 → C7H16 + C2H4 + C5H10 or
C14H30 → C7H16 + C3H6 + C4H8 or
C14H30 → C7H16 + 2C2H4 + C3H6
(1)
do not allow any equation with H2
(b) ethanol has hydrogen bonding, ethanethiol does not
(c)
c)
C2H5SH + 9/2 O2 → 2CO2 + SO2 + 3H2O or
2C2H5SH + 9O2 → 4CO2 + 2SO2 + 6H2O
correct products
correct equation which is balanced
(ii) for CO2
enhanced greenhouse effect
global warming
for SO2
formation of acid rain
damage to stonework of buildings/
dissolving of aluminium ions into rivers/
damage to watercourses or forests/
aquatic life destroyed/
corrosion of metals
[4]
(1)
[1]
(1)
(1)
(1)
(1)
(1)
(1)
[6]
(d) help detect leaks of gas
(1)
[1]
(e) temperature of 450°C
pressure of 1 – 2 atm
V2O5/vanadium(V) oxide/vanadium pentoxide catalyst
ata
(1)
(1)
[3]
[Total: 15]
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Alkanes
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkanes
Theory
Booklet
Question Paper 1
Time Allowed:
82 minutes
Score:
/68
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Long chain alkanes such as 4-methylheptane can be ‘cracked’ to produce shorter chain
hydrocarbons.
B
C 3H8
+
a mixture of C, D and E
(isomers of C5H10)
4-methylheptane
(i)
State the conditions necessary for this reaction to take place.
....................................................................................................................................... [1]
(ii)
Suggest the structure of B.
B
[1]
(iii)
Compounds C, D and E are isomers with the molecular formula C5H10.
On heating with concentrated acidified KMnO4,
●
compound C gives CO2 and compound F (C4H8O2),
●
D and E each give a 1 : 1 mixture of compounds G (C2H4O2) and H (C3H6O2).
Suggest structures for compounds C - H.
C
D
E
F
G
H
[3]
(iv)
Name the type of isomerism shown between D and E.
....................................................................................................................................... [1]
(b) Propene, CH3CH=CH2, reacts with bromine to give 1,2-dibromopropane.
(i)
How is this reaction usually carried out?
....................................................................................................................................... [1]
(ii)
State the type of reaction that is occurring here.
....................................................................................................................................... [1]
(iii)
Draw the mechanism of this reaction, including the structures of any intermediates, and
any dipoles, lone pairs and curly arrows to show the movements of electrons.
[2]
[Total: 10]
2
Crude oil is processed to give a wide variety of hydrocarbons.
(a) Give the names of one physical process and one chemical process carried out during the
processing of crude oil.
physical process ........................................................................................................................
chemical process .......................................................................................................................
[2]
(b) Alkanes and alkenes can both be obtained from crude oil.
(i) Explain why alkanes are unreactive.
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) State the bond angles in a molecule of
ethane, ................................................................................................................................
ethene. ................................................................................................................................
[1]
(iii) State the shape of each molecule in terms of the arrangement of the atoms bonded to
each carbon atom.
ethane ...................................................... ethene ...................................................... [1]
(iv) Explain why these molecules have different shapes in terms of the carbon-carbon bonds
present.
.............................................................................................................................................
....................................................................................................................................... [1]
(c)
c)
Use a series of equations to describe the mechanism of the reaction of ethane with chlorine
to form chloroethane. Name the steps in this reaction.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [5]
(ii) Write an equation to show how butane could be produced as a by-product of this reaction.
....................................................................................................................................... [1]
[Total: 13]
3
(a)Definetheterm
mole.
....................................................................................................................................................
.............................................................................................................................................. [1]
(b) 10 cm3 of a gaseous hydrocarbon, CxHy, was reacted with 100 cm3 of oxygen gas, an excess.
The final volume of the gaseous mixture was 95 cm3.
This gaseous mixture was treated with concentrated, aqueous sodium hydroxide to absorb the
carbon dioxide present. This reduced the gas volume to 75 cm3.
All gas volumes were measured at 298 K and 100 kPa.
(i) Write an equation for the reaction between sodium hydroxide and carbon dioxide.
....................................................................................................................................... [1]
(ii) Calculate the volume of carbon dioxide produced by the combustion of the hydrocarbon.
volume of CO2 produced = ................. cm3 [1]
(iii) Calculate the volume of oxygen used up in the reaction with the hydrocarbon.
volume of O2 used = ................. cm3 [1]
(iv) Use your answers to (b)(ii) and (b)(iii), together with the initial volume of hydrocarbon, to
balance the equation below.
............CxHy + ............O2  ............CO2 + zH2O
[2
(v) Deduce the values of x, y and z in the equation in (iv).
x = .............................
y = .............................
z = .............................
[3]
(c) Another hydrocarbon, W, with the formula C4H8, reacts with hydrogen bromide, HBr, to give
two products X and Y. X and Y are structural isomers of molecular formula C4H9Br.
Reaction of X with aqueous alkali produces an alcohol, Z, that has no reaction with acidified
dichromate(VI).
(i) Give the structures and names of the compounds W, X, Y, and Z
W
........................................................
........................................................
Y
........................................................
........................................................
[4]
(ii) When W reacts with hydrogen bromide, more X than Y is produced. Explain why.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
[Total: 15]
4
Propane, C3H8, and butane, C 4H10, are components of LiquefiedPetroleumGas(LPG)which
is widely used as a fuel for domestic cooking and heating.
(a) (i) To which class of compounds do these two hydrocarbons belong?
......................................................
(ii) Write a balanced equation for the complete combustion of butane.
....................................................................................................................................
[2]
(b) When propane or butane is used in cooking, the saucepan may become covered by a
solid black deposit.
(i) What is the chemical name for this black solid?
......................................................
(ii) Write a balanced equation for its formation from butane.
....................................................................................................................................
[2]
(c) Propane and butane have different values of standard enthalpy change of combustion.
Define the term standard enthalpy change of combustion.
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(d) A 125 cm3 sample of propane gas, measured at 20 °C and 101 kPa, was completely burnt
in air.
The heat produced raised the temperature of 200 g of water by 13.8 °C.
Assume no heat losses occurred during this experiment.
(i) Use the equation pV = nRT to calculate the mass of propane used.
(ii) Use relevant data from the Data Booklet to calculate the amount of heat released in
this experiment.
(iii) Use the data above and your answers to (i) and (ii) to calculate the energy produced
by the burning of 1 mol of propane.
[5]
(e) The boiling points of methane, ethane, propane, and butane are given below.
compound
CH4
CH3CH3
CH3CH2CH3
CH3(CH2)2CH3
boiling point / K
112
185
231
273
(i) Suggest an explanation for the increase in boiling points from methane to butane.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) The isomer of butane, 2-methylpropane, (CH3)3CH, has a boiling point of 261 K.
Suggest an explanation for the difference between this value and that for butane in
the table above.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
[Total: 15]
5
Crude oil contains a mixture of hydrocarbons together with other organic compounds which
may contain nitrogen, oxygen or sulfur in their molecules.
At an oil refinery, after the fractional distillation of crude oil, a number of other processes may
be used including ‘cracking’, ‘isomerisation’, and ‘reforming’.
(a) (i)
What is meant by the term ‘cracking ’ and why is it carried out?
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Outline briefly how the cracking of hydrocarbons would be carried out.
..................................................................................................................................
..................................................................................................................................
(iii)
Construct a balanced equation for the formation of heptane, C7H16, by cracking
tetradecane, C14H30.
..................................................................................................................................
[4]
One of the sulfur-containing compounds present in crude oil is ethanethiol, C2H5SH, the
sulfur-containing equivalent of ethanol. Ethanethiol is toxic and is regarded as one of the
smelliest compounds in existence.
(b) The boiling point of ethanol, C2H5OH, is higher than that of C2H5SH.
Suggest a reason for this difference.
..........................................................................................................................................
...................................................................................................................................... [1]
When ethanethiol is burned in an excess of air, three oxides of different elements are
formed.
(c) (i)
Construct a balanced equation for this reaction.
..................................................................................................................................
(ii)
Two of the oxides formed cause serious environmental damage.
For each of these oxides, identify the type of pollution caused and describe one
consequence of this pollution.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[6]
(d) A small amount of ethanethiol is added to liquefied gases such as butane that are widely
used in portable cooking stoves.
Suggest a reason for this.
...................................................................................................................................... [1]
Sulfur-containing compounds are removed from oil products at the refinery. The sulfur is
recovered and converted into SO2, which is then used in the Contact process.
(e) State the main operating details of the formation of SO3 in the Contact process.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [3]
[Total: 15]
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Alkanes
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkanes
Theory
Booklet
Mark Scheme 2
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
the actual number of atoms of each element present (1)
in one molecule of a compound (1)
y

(b) CХHУ +  x +  O2
4

xCO2 +
[2]
y
H2O
2
xCO2 (1)
y
H2O (1)
2
(c)
c) (
[2]
oxygen/O2 (1)
(ii) carbon dioxide/CO2 (1)
(iii) 10 cm3 (1)
(iv) 20 cm3 (1)
(d) CХHУ +
10 cm3
[4]
y

 x +  O2
4

20 cm3
xCO2 +
10 cm3
y
H2O
2
1 mol of CxHy gives 1 mol of CO2
whence x = 1 (1)
1 mol of CxHy reacts with 2 mol of O2
whence
and
y

x + 
4

= 2
y = 4 (1)
molecular formula is CH4 (1)
[3]
[Total: 11]
2
(a
(i) a compound which contains only carbon and hydrogen (1)
(ii) separation of compounds by their boiling points (1)
[2]
(b) (i) high temperature and high pressure (1)
high temperature and catalyst (1)
(ii) C11H24 → C5H12 + C6H12 or
C11H24 → C5H12 + 2C3H6 or
C11H24 → C5H12 + 3C2H4 (1)
[3]
(c)
c)
CH3
CH3CH2CH2CH2CH3
CH3CH2CHCH3
CH3CCH3
CH3
isomer B
(1)
isomer C
CH3
isomer D
(1)
(1)
(ii) the straight chain isomer (isomer B above) (1)
it has the greatest van der Waals’ forces (1)
because unbranched molecules have greater area of contact/
can pack more closely together (1)
[6]
(d) enthalpy change when 1 mol of a substance (1)
is burnt in an excess of oxygen/air under standard conditions
or is completely combusted under standard conditions (1)
[2]
(e) (i) heat released = m c δT = 200 x 4.18 x 27.5 (1)
= 22990 J = 23.0 kJ (1)
(ii) 23.0 kJ produced from 0.47 g of E
2059 kJ produced from
0.47 x 2059
g of E (1)
23.0
= 42.08 g of E (1)
allow ecf in (i) or (ii) on candidate’s expressions
[4]
(f) C3H6 = 42
E is C3H6
for ecf, E must be unsaturated and be no larger than C5 (1)
1)
[Total: 18]
3
(a
(i)
CH4
–75
reaction
(ii)
broken
reaction
+
Cl2
0
→
+
HCl
–92
= –82 + (–92) – (–75)
= –99 kJ mol–1
CH4
C–H
410
+
I2
I–I
151
→
made
initiation
nit
Cl2 + uvl → 2Cl
propagation
CH4 + Cl → CH3 + HCl
CH3 + Cl2 → CH3Cl + Cl
termination
(1)
(1)
CH3I
C–I
240
= –240 + (–299) + 410 + 151
= +22 kJ mol–1
(iii) activation energy is too great
(b)
b) (
CH3Cl
–82
+
HI
H–I
299
(1)
(1)
(1)
[5]
(1)
(1)
both needed (1)
(1)
CH3 + CH3 → C2H6 or
CH3 + Cl → CH3Cl or
Cl + Cl → Cl2
(1)
(ii) CH3/methyl radical
(1)
[7]
(c)
energy
I
Ea
CH4 + Cl2
∆H
CH3Cl + HCl
progress of reaction
correct placement of 16 kJJ
correct placement of –99 kJ (allow ecf on wrong calculation in (a) (i))
intermediate clearly shown at I
correct ‘double peak’ shape
second peak lower than first
(
(1
(1)
(1)
(1)
[5]
[Total: max 16]
4
(a
(i) CH2=CH–CH2CH2CH3 accept C3H7 on RHS
[1]
(ii) 8
[1]
(b)
b) (
e.g. C40H82 → C16H34 + 2 C12H24 OR C24H48
(ii) heat + catalysts/SiO2/Al2O3/Pt/ceramic/pumice/zeolite etc
if temp given >500 °C
=
1400 kJ mol–1
=
1220 kJ mol–1
∴∆H = +180 kJ mol–1
from eqn in (i) : +90 kJ mol –1 for each C=C formed (could be multiples of 90)
(iii) bonds broken: 4(C–C) =
bond formed: 2 (C=C) =
(iv) endothermic reactions ∆H > 0
[1]
[1]
4 × 350
2 × 610
[1]
[1]
[Total: 6]
5
(a) (i) stage I
Cl2/chlorine
uvl/sunlight
(1)
(1)
KCN
heat in ethanol
(1)
(1)
Br2
uvl/sunlight
(1)
(1)
H2SO4(aq)/HCl(aq) or
NaOH(aq) followed by H+
heat/reflux
(1)
(1)
NaOH(aq)
heat
(1)
(1)
(c) (i) a carbon atom in a molecule attached to
four different atoms or groups of atoms
(1)
stage II
(ii) stage III
(b)
stage IV
stage V
(ii)
Br

R  C  C:N

H
or
correct cpd correctly displayed
one correct isomer shown as 3D
both isomers shown in
mirror object/mirror image arrangement
[6]
[4]
Br/OH

RCC=O


H
OH
(1)
(1)
(1)
[4]
[Total: 13 max]
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Alkanes
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkanes
Theory
Booklet
Question Paper 2
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A,
from the ground near Florence in Italy.
They analysed A which they found to be a hydrocarbon. Further experiments were then
carried out to determine the molecular formula of A.
(a) What is meant by the term molecular formula?
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and
analysing the products of combustion.
(b) Complete and balance the following equation for the complete combustion of a
hydrocarbon with the formula CxHy .
(
CxHy + x +
)
y
O
4 2
................................ + ................................
[2]
(c) When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess)
and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperature
and pressure.
When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide,
KOH, 30 cm3 of gas still remained.
(i)
What is the identity of the 30 cm3 of gas that remained at the end of the
experiment?
...................................................
(ii)
The combustion of A produced a gas that reacted with the KOH(aq).
What is the identity of this gas?
...................................................
(iii)
What volume of the gas you have identified in (ii) was produced by the combustion
of A?
...............................cm3
(iv)
What volume of oxygen was used up in the combustion of A?
...............................cm3
[4]
(d) Use your equation in (b) and your results from (c)(iii) and (c)(iv) to calculate the
molecular formula of A.
Show all of your working.
[3]
[Total: 11]
2
Crude oil is a naturally occurring flammable liquid which consists of a complex mixture of
hydrocarbons. In order to separate the hydrocarbons the crude oil is subjected to fractional
distillation.
(a) Explain what is meant by the following terms.
(i)
hydrocarbon .............................................................................................................
..................................................................................................................................
(ii)
fractional distillation ..................................................................................................
.............................................................................................................................. [2]
(b) Undecane, C11H24, is a long chain hydrocarbon which is present in crude oil.
Such long chain hydrocarbons are ‘cracked’ to produce alkanes and alkenes which have
smaller molecules.
(i)
Give the conditions for two different processes by which long chain molecules
may be cracked.
process 1 ..................................................................................................................
..................................................................................................................................
process 2 ..................................................................................................................
..................................................................................................................................
(ii)
Undecane, C11H24, can be cracked to form pentane, C5H12, and an alkene.
Construct a balanced equation for this reaction.
.............................................................................................................................. [3]
Pentane, C5H12, exhibits structural isomerism.
(c) (i)
Draw the three structural isomers of pentane.
isomer B
isomer C
isomer D
(ii)
The three isomers of pentane have different boiling points.
Which of your isomers has the highest boiling point?
isomer .........
Suggest an explanation for your answer.
..................................................................................................................................
..................................................................................................................................
.............................................................................................................................. [6]
The unsaturated hydrocarbon, E, is obtained by cracking hexane and is important in the
chemical industry.
The standard enthalpy change of combustion of E is –2059 kJ mol–1.
(d) Define the term standard enthalpy change of combustion.
..........................................................................................................................................
...................................................................................................................................... [2]
When 0.47 g of E was completely burnt in air, the heat produced raised the temperature of
200 g of water by 27.5 °C. Assume no heat losses occurred during this experiment.
(e) (i)
Use relevant data from the Data Booklet to calculate the amount of heat released
in this experiment.
(ii)
Use the data above and your answer to (i) to calculate the relative molecular mass,
Mr, of E.
[4]
(f)
Deduce the molecular formula of E.
[1]
[Total: 18]
3
Alkanes such as methane, CH4, undergo few chemical reactions. Methane will, however,
react with chlorine but not with iodine.
Relevant standard enthalpy changes of formation for the reaction of methane with chlorine
to form chloromethane, CH3Cl, are given below.
∆H of / kJ mol–1
(a) (i)
CH4
–75
CH3Cl
–82
HCl
–92
Use the data to calculate ∆H reaction for the formation of CH3Cl.
CH4 +
(ii)
Cl 2 →
CH3Cl
+
HCl
The corresponding reaction with iodine does not take place.
Use bond energy data from the Data Booklet to calculate a ‘theoretical value’ for
∆Hreaction for the following equation.
CH4 + I2 → CH3I + HI
(iii)
Suggest why this reaction does not in fact occur.
..................................................................................................................................
..................................................................................................................................
[5]
(b) (i)
By using equations, describe the mechanism of the reaction between chlorine and
methane to form chloromethane, CH3Cl.
Identify, by name, the separate steps of the overall reaction.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
What is the intermediate organic species in this reaction?
..............................................
[7]
(c) The energy of activation for the formation of CH3Cl is 16 kJ mol–1.
Use this figure and your answer to (a)(i) to complete the reaction pathway diagram
below showing the formation of CH3Cl from CH4 and Cl2.
Show clearly the intermediate organic species and the final products.
Indicate on your sketch the relevant enthalpy changes and their values.
enthalpy
CH4 + Cl 2
progress of reaction
[4]
[Total: 16]
4
(a) The viscosity of engine oil can be improved by the addition of certain medium chainlength polymers.
A portion of the chain of one such polymer is shown below.
–CH2CH(CH2CH2CH3)CH2CH(CH2CH2CH3)CH2–
On average, the molecules of the medium-chain polymer contain 40 carbon atoms.
(i)
Suggest the structure of the monomer.
..................................................................................................................................
(ii)
How many monomer units are incorporated into the average molecule of the
polymer?
..................................................................................................................................
[2]
(b) Used car engine oil can be recycled for use as a fuel by the processes of distillation and
cracking.
(i)
Assuming a typical molecule of engine oil has the formula C40H82, suggest an
equation for a cracking reaction that could produce diesel fuel with the formula
C16H34 and other hydrocarbons only.
..................................................................................................................................
(ii)
What conditions are needed for this cracking reaction?
..................................................................................................................................
(iii)
Considering only the bonds broken and the bonds formed during the reaction, use
the Data Booklet to calculate the enthalpy change for the reaction you wrote in
(b)(i).
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(iv)
Comment on how the conditions you described in (b)(ii) relate to the enthalpy
change you calculated in (b)(iii).
..................................................................................................................................
..................................................................................................................................
[4]
[Total: 6]
5
Compound G, in which R– represents the rest of the molecule, was made for use as a tear
gas in World War 2.
H
R
C
CN
Br
compound G
Compound G was made by the following sequence of reactions.
R–CH3
(a)
stage I
R–CH2Cl
stage II
R–CH2CN
stage III
R–CHBrCN
(i) For stage I and for stage II, state the reagent(s) and condition(s) used to carry out
each change.
stage I
reagent(s) ..................................................................................................
condition(s) ................................................................................................
stage II reagent(s) ..................................................................................................
condition(s) ................................................................................................
(ii) Suggest the reagent(s) and condition(s) necessary to carry out stage III.
reagent(s) .................................................................................................................
condition(s) ...............................................................................................................
[6]
Compound G was not actually used in World War 2 and stocks of it had to be destroyed
safely. The following sequence of reactions was used in this process.
R–CHBrCN
stage IV
R–CHBrCO2H
stage V
R–CH(OH)CO2H
stage VI
R–CH2CO2H
(b) For stage IV and for stage V state the reagent(s) and condition(s) necessary to bring
about each reaction.
stage IV reagent(s) .........................................................................................................
condition(s) ......................................................................................................
stage V reagent(s) .........................................................................................................
condition(s) ................................................................................................ [4]
(c) The full sequence of stages I to VI involves some compounds which contain chiral
centres.
(i) Explain what is meant by the term chiral centre.
..................................................................................................................................
..................................................................................................................................
(ii) Draw displayed formulae for the isomers of one compound in the full sequence of
stages I to VI which you consider to be chiral.
[3]
[Total: 13]
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Alkanes
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkanes
Multiple Choice
Booklet
Question Paper
Time Allowed:
28 minutes
Score:
/23
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1 Four students, W, X, Y and Z, made the following statements about alkanes and alkenes.
W ‘Bromine reacts with alkanes by electrophilic substitution.’
X
‘Bromine reacts with alkenes by a free-radical addition mechanism.’
Y
‘Alkenes can be oxidised by acidified manganate(VII) ions.’
Z
‘Alkenes are formed from alkanes by cracking.’
Which two students are correct?
A
W and X
B
W and Z
C
X and Y
D
Y and Z
2 The hydrocarbon C17H36 can be cracked.
Which compound is the least likely to be produced in this reaction?
A
C3H8
B
C4H8
C
C8H16
D
C16H34
3 In the presence of ultraviolet light, ethane and chlorine react to give a mixture of products.
Which compound could be present in the mixture of products?
A
CH3Cl
B
CH3CH2CH2Cl
C
CH3CH2CH2CH3
D
CH3CH2CH2CH2CH3
4 Which molecule could not be obtained from the cracking of a molecule of nonane,
CH3(CH2)7CH3?
5
A
CH2=CHCH=CH2
B
CH3CH2CH2CH2CH3
C
CH3CH2CH2CH2CH2CH=CH2
D
(CH3CH2CH2)3CH
Aluminium carbide, Al 4C3, reacts readily with aqueous sodium hydroxide. The two products of the
reaction are NaAl O2 and a hydrocarbon. Water molecules are also involved as reactants.
What is the formula of the hydrocarbon?
A
CH4
B
C2H6
C
C3H8
D
C6H12
6 Which equation correctly represents the balanced equation for the complete combustion of a
hydrocarbon with the formula CxHy?
A
CxHy + (x +
y
y
)O2 → xCO2 +
H2O
2
2
B
CxHy + (x +
y
)O2 → xCO2 + yH2O
4
C
CxHy + (x +
y
y
)O2 → xCO2 +
H2O
4
4
D
CxHy + (x +
y
y
)O2 → xCO2 +
H2O
4
2
7 Which substance does not produce a poisonous gas, when burnt in a limited amount of air?
A
hydrogen
B
methane
C
propene
D
sulfur
8 Oct-1-ene, CH3(CH2)5CH=CH2, is subjected to thermal cracking.
Which combination of compounds W, X, Y and Z can be obtained?
CH2=CH2
CH3CH=CH2
CH3CH2CH3
CH2=CHCH=CH2
W
X
Y
Z
A
W, X, Y and Z
B
W, X and Y only
C
W, X and Z only
D
W and X only
9 A compound Y has the following properties.
• It is a liquid at room temperature and atmospheric pressure.
• It does not mix completely with water.
• It does not give steamy fumes with PCl5.
What could Y be?
A
ethane
B
ethanoic acid
C
ethanol
D
ethyl ethanoate
10 The cracking of a single hydrocarbon molecule, CnH2n+2, produces two hydrocarbon molecules
only. Each hydrocarbon product contains the same number of carbon atoms in one molecule.
Each hydrocarbon product has non-cyclic structural isomers.
What is the value of n?
A
4
B
6
C
8
D
9
11 The products obtained by cracking an alkane, X, are methane, ethene and propene.
The mole fraction of ethene in the products is 0.5.
What is the identity of X?
A
C6H14
B
C8H18
C
C9H20
D
C11H24
12 Which reagent could best be used to distinguish between cyclohexene and cyclohexanol?
A
Ag(NH3)2+ in H2O
B
Br2 in CCl 4
C
2,4-dinitrophenylhydrazine in CH3OH
D
NaBH4 in CH3OH
13 Compound X, molecular formula C4H8, undergoes the following reactions.
C 4H 8
Br2
X
C 4H 8
H2 / Ni
X
What is the formula of compound Z?
A
CH3CH2CH(OH)CH2OH
B
CH3CH(OH)CH(OH)CH3
C
CH3CH(CH2OH)CH2OH
D
(CH3)2C(OH)CH2OH
aq.NaOH / heat
C4H8Br2
C4H10O2
Y
Z
methylpropane
14 Which equation represents a valid propagation step in the free radical reaction between ethane
and chlorine?
A
C2H6 + Cl • → C2H5Cl + H•
B
C2H5Cl + Cl • → C2H4Cl • + HCl
C
C2H6 + H• → C2H •5 + HCl
D
C2H5• + Cl • → C2H5Cl
15 Samples of 10 cm3 of each of the first four members of the alkane series are separately mixed
with 70 cm3 of oxygen. Each is then burned and the total volume, V, of residual gas measured
again at room temperature and pressure.
Which graph represents the results that would be obtained?
A
B
3
V / cm
V / cm
3
X
80
80
60
60
X
X
40
X
40
X
X
X
20
20
X
0
0
CH4
C3H 8
C 2H 6
C 3H8
CH4
C4H10
C 2H 6
C
C4H10
D
V / cm3
V / cm3
80
80
60
60
X
X
X
40
X
X
40
X
X
X
20
0
20
0
C3H 8
CH4
C 2H 6
C 3H8
CH4
C4H10
C 2H 6
C4H10
16 Which compound could not be obtained from cracking a sample of nonane, CH3(CH2)7CH3?
A
CH3CH=CHCH=CHCH2CH2CH2CH3
B
CH3CH2CH2CH2CH3
C
CH3CH2CH2CH2CH2CH=CH2
D
(CH3CH2CH2)3CH
17 In which way are ethene and propane similar?
CH2=CH2
ethene
CH3CH2CH3
propane
A
They are both obtained by the dehydration of alcohols.
B
They are both neutral to an indicator solution.
C
They can both be hydrogenated using a suitable catalyst.
D
They can both undergo polymerisation under suitable conditions.
18 Which reaction occurs with saturated hydrocarbons?
A
catalytic hydrogenation
B
ready decolourisation of aqueous bromine
C
polymerisation
D
thermal cracking
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
D
1 only
is
correct
No other combination of statements is used as a correct response.
19 Which structural formulae represent 2,2-dimethylpentane?
1
(CH3)2CHCH2CH(CH3)2
2
(CH3)3CCH2CH2CH3
3
CH3CH2CH2C(CH3)3
20 A fraction of distilled crude oil contains molecules with between 15 and 19 carbon atoms. This
fraction is cracked by strong heating.
Why is this done?
1
To produce alkenes.
2
To produce smaller molecules which are in higher demand.
3
To insert oxygen atoms into the hydrocarbons.
21 The diagram shows an experiment.
silica, alumina
or baked clay
liquid X on
mineral wool
support
gentle
heat
gas collected
strong
heat
trough of
water
Which processes could be demonstrated by using the above apparatus?
1
the oxidation of ethanol (the liquid X)
2
the dehydration of ethanol (the liquid X)
3
the cracking of paraffin (the liquid X)
22 During the bromination of methane, the free radical CH•3 is generated and a possible terminating
step of this reaction is the formation of C2H6 by the combination of two free radicals.
What could be produced in a terminating step during the bromination of propane?
CH3
1
CH3CH2CH2CHCH3
CH3
CH3
2
CH3CHCHCH3
CH3
3
CH3CH2CHCH2CH3
23 Long-chain alkanes are converted on an industrial scale into alkylsulphates for use as detergents,
e.g. sodium lauryl sulphate.
O
CH3(CH2)10CH2O
S
ONa
O
sodium lauryl sulphate
What deductions about the properties of this substance can be made from this structure?
1
Part of the structure is polar and is water–attracting.
2
The alkyl chain is soluble in oil droplets.
3
All the C-C-C bond angles are tetrahedral.
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Alkenes
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkenes
Theory
Booklet
Mark Scheme 1
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
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1
(a
(i)
H3C
CH2OH
H3C C
C
HO
(ii)
CH3
[1]
OH
CH3
H3C
[1]
C
[1]
O
C OOH
O
C
[1]
[2]
[1]
[1]
[1]
[3]
[1]
[
CH3
(b) (i) H3C
CH2OH
C
C
H3C
H3C
CH2OH
H
CH2OH
H3C C
C CH3
+
H3C C
C CH3
Br
CH3
Br
Br
Br
Brδ+
Br δ−
M1 = 2 curly arrows
M2 = intermediate ion
M3 = Br with –ve charge, lone pair and curly arrow to C+
(ii) dipole is induced by proximity to C=C
(iii) Optical
pti
(iv)
[1]
H2C OH
H2C OH
C
C
Br
C
H3C
Br
CH3
CH3
H3C
Br
[2]
Br
C
CH3
[1+1]
H3C
[10]
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2
(a)
decolourisation with an alkene at room conditions / quickly / easily /
OR alkane needs higher temp / UV / is slow at room conditions
1
double / π / pi bond / C = C present in alkenes
1
2
UV light / sunlight / high temperature
1
1
(Free) radical
Substitution
1
1
2
(iii)
•C2H5 + •C2H5 C4H10
1
1
(iv)
C2H5Br + Br• •C2H4Br + HBr OR
•C2H4Br + Br2 C2H4Br2 + Br•
1
Electrophilic
Addition
1
1
(b) (i)
(ii)
(c) (i)
2
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Question
uesti
Scheme
Mark
ark
T
(ii)
H
H
H C
H
C H
H
C
H
+
C
H
H
H
H
C
C
H
Br Br
Br
δ+
Br
Br
Br δ−
M3:
M3: Correct
M3
correctintermediate
intermediat
-
M1:
M1:22correct
correctcurly
curly
arrows
arrows
M4: Curly arrow from
+
−
M4: curly
C+ lone pair on Br to C
lone
pair onarrow
Br− tofrom
M2: dipole
M2: correct dipole
(d)
H
4
H
H
H
H
H
H
C
C
C
C
C
C
H
Cl
H
Cl
H
Cl
H
2
2
minimum of three repeat units
(e) (i)
(ii)
NaOH/KOH
1
ethanolic / alcoholic AND heat / reflux
1
H
2
1
H
H OH
(iii)
N
C
H
H
C
C
H
H
1
H
Propanenitrile / propanonitrile / propionitrile / ethyl cyanide / cyanoethane
1
2
20
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Question
uestion
3
(a
(i)
Mark
decolourisation of bromine: P is an alkene / contains C=C / is unsaturated
1
hot conc. manganate(VII): breaks C=C OR single product implies P is symmetrical OR
single organic product implies terminal =CH2 as methanal is oxidised to CO2
1
2,4–DNPH confirms >C=O / carbonyl / ketone in Q
1
no reaction with Tollens’: Q is not an aldehyde / is a ketone
1
Total
4
(ii)
1
(2,3–)dimethylbut–2–ene, 2–ethylbut(–1–)ene, 2–methylpent–1–ene,
(2,3–)dimethylbut(–1–)ene
1
2
(iii)
O
O
O
O
propan(–2–)one / acetone, pentan–3–one, pentan–2–one, 3–methylbutan(–2–)one
ecf possible on (a)(ii)
(b)
1
1
2
1
1
1
1
max 3
any 3 of
CH3CH=C(CH3)C2H5
CH3CH=CHCH2CH2CH3
CH3CH=CHCH(CH3)2
C2H5CH=CHC2H5
11
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Questi
Question
4
(a)
Scheme
Marks
P: CH3CH2CH2CH=CH2
Q: CH3CH2CH=CHCH3
R: CH3CH2C(CH3)=CH2
S: CH3CH=C(CH3)2
T: CH3CH2COCH3
1
1
1
1
1
(b) (i) (Different molecules with the) same (molecular and) structural formula
different arrangements of atoms (in space)
H
(ii)
H
H
C
H
H
C
H
H
C
C
H
H
C
H
trans-pent-2-ene
(c)
butan-2-ol
H
[5]
1
1
[2]
H
C
H
T
H
HH
C
H
C
H
H
C
1
H
cis-pent-2-ene
1
[2]
1
[1
[10]
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5
(a)
amide group circled OR indicated as diagram
ester group circled OR indicated as diagram
1
1
[2]
[1
O
O
O
H3C
H3C
CH3
HN
CH3
H3C
O
(b)
lower doses of the drug required
OR improved activity of the drug
OR reduced side effects
1
(c)
decreases enzyme activity OR decreases rate at which product is formed
1
binds with the enzyme’s active site OR has a complementary shape to active site OR similar
shape to substrate
1
(d)
Total
(competitive inhibition can be overcome by)
increasing [substrate] OR increasing substrate concentration
1
[3]
energy source/carrier OR releases energy when hydrolysed
1
[1
7
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Alkenes
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Alkenes
Theory
Booklet
Question Paper 1
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The structure of H is shown.
CH3
C
CH2OH
C
CH3
CH3
H
(a) H reacts with both cold, dilute, acidified potassium manganate(VII) and with hot, concentrated,
acidified potassium manganate(VII).
(i) Give the structure of the organic product of the reaction of H with cold, dilute, acidified
potassium manganate(VII).
[1]
(ii) Give the structures of the organic products of the reaction of H with hot, concentrated,
acidified potassium manganate(VII).
[2]
(b) (i) Complete the reaction scheme to show the mechanism of the reaction of H with bromine
to form J.
Include all necessary curly arrows, lone pairs and charges.
CH3 CH2OH
CH2OH
CH3
C
C
CH3
CH3
CH3
Br
δ+
C
C
Br
Br
CH3
J
Br δ–
[3]
(ii) Explain the origin of the dipole on the bromine molecule.
.............................................................................................................................................
....................................................................................................................................... [1]
J is formed as an equimolar mixture of isomers.
(iii) State the type of isomerism shown by J.
....................................................................................................................................... [1]
(iv) Draw the structures of the two isomers of J.
[2]
[Total: 10]
2
Alkanes and alkenes both react with bromine.
(a) Explain how and why bromine can be used to distinguish between an alkene and an alkane.
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
(b) The reaction of ethane with bromine forms a mixture of products.
(i) State the essential conditions for this reaction to occur.
....................................................................................................................................... [1]
(ii) Give the full name of the mechanism of this reaction.
....................................................................................................................................... [2]
(iii) Give the equation for a termination step that could occur, producing a hydrocarbon.
....................................................................................................................................... [1]
(iv) Give the equation for one propagation step involved in the formation of dibromoethane
from bromoethane during this reaction.
....................................................................................................................................... [1]
(c) The reaction of ethene with bromine forms a single product.
(i) Give the full name of the mechanism of this reaction.
....................................................................................................................................... [2]
(ii) Complete the diagram below to illustrate this mechanism.
Include all relevant charges, partial charges, curly arrows and lone pairs.
H
H
H
C
C
H
H
H
H
C
C
Br
Br
H
Br
Br
[4]
(d) Chloroethene can be polymerised to form a polymer commonly known as PVC.
Draw a diagram of the structure of PVC including three repeat units.
[2]
(e) Chloroethane undergoes a series of reactions as shown in the diagram below.
H
H
H
H
reaction 1
product Q
NaCN
H
C
C
Cl
H
H
C
H
C
H
OH–(aq)
product P
(i) Give the reagent and conditions necessary for reaction 1.
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Give the skeletal formula of product P.
[1]
(iii) Give the displayed formula and the name of product Q.
....................................................................................................................................... [2]
[Total: 20]
3
A hydrocarbon, P, with the formula C6H12 readily decolourises bromine.
On reaction with hot, concentrated, acidified potassium manganate(VII) solution a single organic
product, Q, is obtained.
Q gives an orange precipitate when reacted with 2,4-dinitrophenylhydrazine, 2,4-DNPH reagent,
but has no reaction with Tollens’ reagent.
(a) (i) Explain these observations.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
(ii) Draw the skeletal formula of P and give its name.
name of P ...........................................................................................................................
[2]
(iii) Draw the skeletal formula of Q and give its name.
name of Q ...........................................................................................................................
[2]
(b) There are several structural isomers of P that also decolourise bromine, but only four of these
structural isomers exhibit geometrical (cis-trans) isomerism.
Give the structures of any three structural isomers of P that exhibit geometrical (cis-trans)
isomerism.
[3]
[Total: 11]
4
P, Q, R and S are structural isomers with the molecular formula C5H10.
All four compounds readily decolourise bromine in the dark.
P, R and S do not exhibit stereoisomerism but Q exists as a pair of geometrical (cis-trans) isomers.
All four compounds react with hot concentrated, acidified potassium manganate(VII) to produce a
variety of products as shown in the table.
compound
products
P
CO2 and CH3CH2CH2CO2H
Q
CH3CO2H and CH3CH2CO2H
R
CO2 and T (C4H8O)
S
CH3CO2H and (CH3)2CO
T reacts with 2,4-dinitrophenylhydrazine reagent, 2,4-DNPH, to form an orange crystalline product
but does not react with Fehling’s reagent.
(a) Give the structural formulae of P, Q, R, S and T.
P ..................................................................... Q ......................................................................
R ..................................................................... S ......................................................................
T .....................................................................
[5]
(b) (i) Explain what is meant by the term stereoisomerism.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Draw the displayed formulae of the geometrical isomers of Q and name them both.
name ......................................................... name ........................................................ [2]
(c) Name the organic product of the reaction of T with sodium borohydride, NaBH4.
.............................................................................................................................................. [1]
[Total: 10]
5 (a)
Oseltamivir is an antiviral drug that slows the spread of the influenza( flu)virus.
O
O
O
HN
O
NH2
oseltamivir
Circle two bonds, each in a different functional group, that could be easily hydrolysed in the
body.
[2]
(b) Oseltamivir is a chiral drug. This drug is usually taken as a single optical isomer rather than as
a mixture of isomers.
Suggest one benefit of taking a drug in this way.
....................................................................................................................................................
.............................................................................................................................................. [1]
(c) Oseltamivir is a competitive inhibitor of an enzyme produced by the flu virus.
Explain the meaning of the term competitive inhibitor and state how its action could be
overcome.
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [3]
(d) ATP plays an important role in metabolic reactions in living organisms.
NH2
N
N
N
O
O
N
H
H
HO
H
CH2O
P
H
O–
O
O
P
O–
O
O
P
O–
O–
OH
ATP
What is the function of ATP in living organisms?
....................................................................................................................................................
.............................................................................................................................................. [1]
[Total: 7]
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Hydrocarbons as
fuels
Mark Scheme
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Hydrocarbons as fuels
Theory
Booklet
Mark Scheme
Time Allowed:
74 minutes
Score:
/61
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) alkanes or paraffins not hydrocarbons
(ii)
i
(b)
b) (
C9H20 + 14O2 → 9CO2 + 10H2O
carbon
carbon monoxide
(names required)
(ii) CO is toxic or affects or combines with haemoglobin
or carbon causes respiratory problems
(iii)
i
(1)
(1
[2]
(1)
(1)
(1)
C14H30 + 15O2 → 28C + 30H2O or
2C14H30 + 29O2 → 28CO + 30H2O
or other balanced equations such as
C14H30 + 11O2 → 7C + 7CO + 15H20
C14H30 + 18O2 → 7CO + 7CO2 + 15H20
(c) enthalpy change when 1 mol of a substance
is burnt in an excess of oxygen/air under standard conditions
or is completely combusted under standard conditions
(1
[4]
(1)
(1)
[2]
(d) working must be shown
(i) heat released = m c δT = 250 × 4.18 × 34.6
= 36157 J = 36.2 kJ
(1)
(1)
(ii) Mr of C14H30 = 198
mass of C14H30 = 1.00 × 0.763 = 0.763 g
0.763 g of C14H30 produce 36.2 kJ
36.2 ×198
198 g of C14H30 produce
0.763
= 9394 kJ mol–1
(1)
(1)
(1)
[5]
[Total: 13]
2
In this question, numerical answers should be given to three significant figures.
(a) (i) C6H12O6 + 6O2 → 6CO2 + 6H2O
(1
(ii) Mr C6H12O6 = 180
180 g C6H12O6 → 6 mol CO2
(1)
1200 g C6H12O6 → 6 × 200 mol CO2
180
= 40.0 mol to 3 sf
allow ecf on wrong equation and/or wrong Mr
(1)
(iii) 6.82 × 109 people will produce 6.82 × 109 × 40.0 mol CO2
= 2.728 × 1011 mol CO2
(1)
2.728 × 1011 mol CO2 ≡ 2.728 × 1011 × 44 = 1.20032 × 1013 g
= 1.20 × 107 tonnes CO2 to 3 sff
(
[5]
allow ecf on answer from (ii)
(b) (i) 2C8H18 + 25O2 → 16CO2 + 18H2O or
C8H18 + 12½O2 → 8CO2 + 9H2O
(1
(ii) Mr C8H18 = (8 × 12) + (18 × 1) = 114
(1)
mass of 4.00 dm3 of octane = 4000 × 0.70 = 2800 g
(1)
n(C8H18) = 2800 = 24.56140351 mol in 4.00 dm3
114
= 24.6 mol to 3 sff
(
(iii) 2 mol C8H18 produce 16 × 44 g CO2
24.6 mol C8H18 produce 16 × 44 × 24.6 g CO2
2
= 8659.2 g CO2
= 8660 g CO2 to 3 sff
(
[5]
(c) 6.82 × 109 people produce 1.20 × 107 tonnes CO2 per day
8660 g CO2 produced when car travels 100 km
when travelling 1 km, car produces 8660 = 8.66 × 10–1 g
100
= 8.66 × 10–5 tonnes
(1)
to produce 1.20 × 107 tonnes CO2 car must travel
1.20 × 107
8.66 × 10–5
= 1.385681293 × 1011 = 1.39 × 1011 km to 3 sf
(1)
[2]
(d) possible pollutants and the damage they cause
CO
NOX
NO
O
toxic t
toxic
global
warming
photochemical
smog
compound
damage
SO2
N
toxic
respiratory
problems
toxic
respiratory
problems
acid rain
acid rain
H2O
unburned
C8H18
global
warming
respiratory respiratory
problems
problems
(1)
(1)
1)
[Total: 14]
3
(a
manufacture of ammonia/Haber process or hydrogenation of fats/oils or
making margarine or hydrocracking
(b)
b)
(1)
increasing the pressure
equilibrium will move to LHS
fewer moles/molecules on LHS or more moles/molecules on RHS
[1]
(1)
(1)
(ii) decreasing the temperature
equilibrium will move to LHS
forward reaction is endothermic
(1)
(1)
[4]
(c) rate will increase
collisions will occur more frequently
(1)
(1)
[2]
(d) (i) Kc = [CO2][H2]
[CO][H20]]
(
(ii)
CO(g)
initial moles
equil moles
equil concn./mol
dm–3
0.40
(0.40 – y)
(0.40 – y)
1
+ H2O (g)
0.40
(0.40 – y)
(0.40 – y)
1
Kc = (0.20 + y)2 = 6.40 × 10–1
(0.40 – y)2
(0.20 + y) =
(0.40 – y)
CO2(g)
0.20
(0.20 + y)
(0.20 + y)
1
+ H2(g)
0.20
(0.20 + y)
(0.20 + y)
1
(1)
6.40 × 10–1 = 0.8
(0.20 + y) = 0.8 × (0.40 – y)
0.20 + y = 0.32 – 0.8 y
1.8 y = 0.12
gives y = 0.067
(1)
at equilibrium
n(CO) = n(H2O) = (0.40 – 0.067) = 0.33 mol and
n(CO2) = n(H2) = (0.20 + 0.067) = 0.27 mol
ol
allow ecf as appropriate
[5]
[Total: 12]
4
(a
Ratio of the concentrations of a solute / distribution of solute [1] in two immiscible liquids
(b) Kc =
[pesticide in hexane]
[pesticide in hexane]
hence 8.0 =
[pesticide in water]
0.0050 - [pesticide in hexane]
[1]
Therefore [pesticide in hexane] x = 0.040 – 8x
Hence x = 0.0044(g)
(c)
c)
[1]
[2]
Ratio would be 3 : 1
[1]
(ii) Each chlorine at could be 35Cl or 37Cl
Only way of getting M+4 is for both chlorines to be 37Cl (1 in 9 chance)
Ratio of peaks M M+2 M+4
9
6
1
(d)
d)
[1]
[2]
[1]
[1]
[3]
Accept dioxins and furans (without specifying)
[1]
(ii) PCBs (but don’t penalise non-specified dioxins and furans)
[1]
(iii) Allow : pollution control / environmental legislation / removal of dioxins and furans /
mill closed down (owtte)
[1]
(iv) Five
[1]
[4]
[Total: 11]
5
(a
(i) substance that speeds up a chemical reaction (1)
by lowering Ea
or by providing an alternative reaction pathway
or without being used up in the process (1)
(ii) 2H2O2 → 2H2O + O2 (1)
(b)
b) (
alkanes or paraffins (1)
(ii) 2H2O2 : O2 and C15H32 : 23O2 (1)
whence C15H32 : 46H2O2 (1)
allow e.c.f. on (a)(ii)
(c)
c) (
[3]
[3]
C15H32 = 212 (1)
212 × 10 6
n(C15H32) =
= 1 × 106 mol
212
allow e.c.f. on wrong Mr of C15H32 (1)
(ii) n(H2O2) required = 46 × 106 mol (1)
mass of H2O2 = 34 × 46 × 106 g = 1564 tonnes
final answer must be in tonnes (1)
allow e.c.f. on (b)(ii) and (c)(i)
(d) they would dissolve (1)
[4]
[1]
[Total: 11]
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Hydrocarbons as
fuels
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydrocarbons
Sub-Topic
Paper Type
Hydrocarbons as fuels
Theory
Booklet
Question Paper
Time Allowed:
74 minutes
Score:
/61
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Petrol and diesel fuel are both used in internal combustion engines.
Petrol may be regarded as having the formula C9H20 and diesel fuel as having the formula
C14H30.
(a) (i) To which class of compounds do these two hydrocarbons belong?
......................................................
(ii) Write a balanced equation for the complete combustion of petrol.
....................................................................................................................................
[2]
(b) When petrol or diesel fuel are used in internal combustion engines, several different
products of the incomplete combustion of the fuel may be formed.
(i) Name two of these products that do not contain hydrogen.
.................................. and ..................................
(ii) Choose one of these and state a hazard it causes.
product .......................................................................................................................
hazard ........................................................................................................................
(iii) Write a balanced equation for the formation of one of the products in (i) from diesel
fuel.
....................................................................................................................................
[4]
(c) Define the term standard enthalpy change of combustion.
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(d) A 1.00 cm3 sample of C14H30 was completely burnt in air.
The heat produced raised the temperature of 250 g of water by 34.6 °C.
Assume no heat losses occurred during this experiment.
The density of C14H30 is 0.763 g cm–3.
(i) Use relevant data from the Data Booklet to calculate the amount of heat released in
this experiment.
(ii) Use the data above and your answer to (i) to calculate the energy produced by the
combustion of 1 mol of C14H30.
[5]
[Total: 13]
2
Carbon dioxide, CO2, makes up about 0.040 % of the Earth’s atmosphere. It is produced by
animal respiration and by the combustion of fossil fuels.
In animal respiration, oxygen reacts with a carbohydrate such as glucose to give water,
carbon dioxide and energy.
The typical daily food requirement of a human can be considered to be the equivalent of
1.20 kg of glucose, C6H12O6.
You should express all of your numerical answers in this question to three significant
figures.
(a)
a)
Construct a balanced equation for the complete oxidation of glucose.
....................................................................................................................................
(ii) Use your equation to calculate the amount, in moles, of CO2 produced by one person
in one day from 1.20 kg of glucose.
(iii) On the day on which this question was written, the World population was estimated
to be 6.82 × 109.
Calculate the total mass of CO2 produced by this number of people in one day. Give
your answer in tonnes. [1 tonne = 1.00 ×106 g]
[5]
(b) When fossil fuels are burned in order to give energy, carbon dioxide and water are also
produced.
The hydrocarbon octane, C8H18, can be used to represent the fuel burned in motor cars.
A typical fuel-efficient motor car uses about 4.00 dm3 of fuel to travel 100 km.
(i) Construct a balanced equation for the complete combustion of octane.
....................................................................................................................................
(ii) The density of octane is 0.700 g cm–3.
Calculate the amount, in moles, of octane present in 4.00 dm3 of octane.
(iii) Calculate the mass of CO2 produced when the fuel-efficient car is driven for a
distance of 100 km.
[5]
(c) Calculate how many kilometres the same fuel-efficient car would have to travel in order
to produce as much CO2 as is produced by the respiration of 6.82 × 109 people during
one day. Use your answer to (a)(iii).
[2]
(d) Carbon dioxide is one of a number of gases that are responsible for global warming.
When fossil fuels such as octane are burned in a car engine, other atmospheric pollutants
are also produced.
Give the formula of one atmospheric pollutant that may be produced in a car engine,
other than CO2, and state how this pollutant damages the environment.
pollutant .................................
damage caused ......................................................................
[2]
[Total: 14]
3
Hydrogen is the most abundant element in the Universe, although on Earth only very small
quantities of molecular hydrogen have been found to occur naturally.
Hydrogen is manufactured on a large scale for use in the chemical industry and is also
regarded as a possible fuel to replace fossil fuels in internal combustion engines.
(a) State one large scale use of hydrogen in the chemical industry.
..................................................................................................................................... [1]
One common way of producing hydrogen on a large scale for use in the chemical industry
is by the steam ‘reforming’ of methane (natural gas), in which steam and methane are
passed over a catalyst at 1000–1400 K to produce carbon monoxide and hydrogen.
CH4(g) + H2O(g)
CO(g) + 3H2(g)
∆H = +206 kJ mol–1
(b) Use the information above to state and explain the effect on the equilibrium position of
the following changes.
(i) increasing the pressure applied to the equilibrium
....................................................................................................................................
....................................................................................................................................
(ii) decreasing the temperature of the equilibrium
....................................................................................................................................
....................................................................................................................................
[4]
(c) What will be the effect on the rate of the reaction of increasing the pressure at which it is
carried out? Explain your answer.
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(d) Further hydrogen can be obtained by the ‘water-gas shift’ reaction in which the carbon
monoxide produced is reacted with steam.
CO(g) + H2O(g)
CO2(g) + H2(g)
Kc = 6.40 × 10–1 at 1100 K
A mixture containing 0.40 mol of CO, 0.40 mol of H2O, 0.20 mol of CO2 and 0.20 mol of H2
was placed in a 1 dm3 flask and allowed to come to equilibrium at 1100 K
(i) Give an expression for Kc for this reaction.
(ii) Calculate the amount, in moles, of each substance present in the equilibrium mixture
at 1100 K.
CO(g)
initial moles
0.40
.40
+
H2O(g)
CO2(g)
+
H2(g)
0.40
.40
[5]
[Total: 12]
4
The residues from organohalogen pesticides are known to be a major cause of the decline
in numbers of different birds of prey in many countries. These residues are concentrated in
birds at the top of food chains.
(a) Analysis of the bodies of birds of prey show that the pesticide residues accumulate in
the fatty tissues of the birds. This is because of the high partition coefficient between the
fat in the tissues and water found in blood.
Explain what is meant by the term partition coefficient.
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
(b) A particular pesticide has a partition coefficient of 8.0 between the solvent hexane and
water. If a 25 cm3 sample of water containing 0.0050 g of the pesticide is shaken with
a 25 cm3 sample of hexane, calculate the mass of pesticide that will dissolve in the
hexane layer.
[2]
(c) Compounds used as pesticides may contain bromine or chlorine.
(i)
What would be the difference in the ratio of the M: M+2 peaks if the pesticide
contained one chlorine rather than one bromine atom?
..................................................................................................................................
(ii)
If a given pesticide contains two chlorine atoms per molecule, deduce the relative
heights of the M, M+2 and M+4 peaks.
[3]
(d) The following graph shows the occurrence of pesticide residues in the eggs of fish-eating
birds of prey upstream and downstream of a paper mill at Castlegar on the Columbia
River in Canada.
Columbia River Basin
120
PCBs
80
Other Dioxins / Furans
60
Dioxin 2378TCDD
Furan 2378TCDF
40
upstream of Castlegar
1997
1996
1995
1994
1993
1997
1996
1995
1994
20
1993
TEQs parts per trillion
100
downstream of Castlegar
PCBs, the dioxin 2378TCDD, and the furan 2378TCDF all come from chemicals
containing chlorine.
(i)
Suggest which compounds are present directly as a result of the paper mill.
..................................................................................................................................
(ii)
By studying the data for 1994, suggest which chemical(s) come from sources other
than the paper mill.
..................................................................................................................................
(iii)
Compare the downstream data for 1994 with that for 1997. Suggest what might be
responsible for the change.
..................................................................................................................................
(iv)
A molecule of 2378TCDD contains four chlorine atoms. How many molecular ion
peaks would this compound show in its mass spectrum?
..................................................................................................................................
[4]
[Total:11]
5
Most submarines travel under water using electrical power from batteries. The German
engineer Helmut Walter designed a diesel engine that could be used to propel a submarine
beneath the surface of the sea. Instead of taking air from above the surface of the sea,
Walter’s engine used hydrogen peroxide, H2O2, to provide oxygen for a conventional diesel
engine.
Hydrogen peroxide may be catalytically decomposed to give water and oxygen.
(a) (i)
What is meant by the term catalyst?
..................................................................................................................................
..................................................................................................................................
(ii)
Construct a balanced equation for the decomposition of H2O2.
............................................................................................................................. [3]
Diesel fuel may be considered to consist of the hydrocarbon C15H32 which reacts completely
with oxygen according to the following equation.
C15H32 + 23O2 → 15CO2 + 16H2O
(b) (i)
To which homologous series does C15H32 belong?
................................................
(ii)
Use the equation above and your answer to (a)(ii) to calculate the amount, in moles,
of H2O2, that will provide sufficient oxygen for the complete oxidation of one mole
of C15H32.
amount of H2O2 = ................................. mol
[3]
A submarine equipped with a Walter engine used 212 tonnes of diesel fuel during an
underwater voyage. The submarine also carried concentrated aqueous H2O2.
[1 tonne = 106 g]
(c) (i)
Calculate the amount, in moles, of diesel fuel used during the underwater voyage.
amount of diesel fuel = ................................. mol
(ii)
Use your answers to (b)(ii) and (c)(i) to calculate the mass, in tonnes, of hydrogen
peroxide used during the underwater voyage.
mass of H2O2 = ................................. tonnes
[4]
(d) The exhaust products of the Walter engine were passed into the sea.
What would happen to them?
..................................................................................................................................... [1]
[Total: 11]
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Halogenoalkanes
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Halogen Derivatives
Sub-Topic
Paper Type
Halogenoalkanes
Theory
Booklet
Mark Scheme 1
Time Allowed:
75 minutes
Score:
/62
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
CH3CH2COCl > CH3CH2CH2Cl > C6H5Cl
1
any two of:
• C-Cl bond strength is weakest in CH3CH2COCl ora
•
In C6H5Cl (no hydrolysis) C-Cl bond is part of delocalised system OR p-orbital on Cl
overlaps with π system OR electrons from Cl overlap with π system
•
CH3CH2COCl carbon in C-Cl bond is more electron deficient since it is also attached to an
oxygen atom ora
[3]
1+1
(b)
ketone, amine, carboxylic acid
two correct 1 mark, all three 2
2
(c) (i)
dipole on C-Br
curly arrow breaking C-Br bond
curly arrow from lone pair on N to carbon in C-Br bond
1
1
1
O
H2N
[2
OH
O
H3C
CH2
δ+
δ-
Br
(ii)
nucleophilic substitution
1
(iii)
HBr or hydrogen bromide
1
[5
O
(d)
Y=
W = H N+
3
(Cl−)
X=
O
1
1
[2]
OH
O
OH
[3
OH
H2N
O
3
O
NH
H3C
OH
O
each structure 1 mark
(e)
O
O
C
CH2
CH2
C
O
CH2
N
H
correct displayed amide formula
correct polyamide with two repeat units
Total
C
O
H2
CH2
C
CH2
N
H
15
2
(a
(i) RBr + OH– → ROH+ Br–
[1]
(ii) nucleophilic substitution
[1]
[2]
(b)
b)
plotting of all points (plotted to within ½ small square) [1]
good line of best fit [1]
(ii) t ½ = 118 min or 79 min (± 5 min)
or
construction lines for two half-lives and mention that half-life is constant
or
calculate the ratio of two rates at two different concentrations
[1]
(iii) either ratio of initial rates (slopes)
or
ratio of t ½
or
ratio of times for [RBr] to fall to the same level: all should be = 1.5
[1]
therefore reaction is first order w.r.t. [OH–]
(iv) rate = k [RBr] [OH–]
[1]
[1
initial rate = 0.01 / 185 = 5.4 × 10–5 (mol dm–3 min–1)
[1
k = 5.4 x 10-5 / (0.01 × 0.1) = 0.054 (mol–1 dm3 min–1)
[1
[8 max 7]
energy/kJ moli1
(c)
+5.4
(2NO + Br2)
-23
2NOBr
extent of reaction
four marking points: one activation "hump"
2NOBr (not just NOBr)
∆H labelled correctly (arrow down, or double headed, or just a line)
Ea labelled correctly (arrow up, or double headed, or just a line)
all four points [2]
three or two points [1]
[2]
[Total: 11]
3
(a
117° to 120°
(b) (i) electrophilic addition
(1)
[1]
(1)
(ii)
1 mark for each correct structure
allow correctly drawn optical isomers of the first structure
(3 × 1)
[4]
[Total: 5]
4
(a
(the energy change) when 1 mol of bonds
is broken in the gas phase
[1]
[1]
[2]
(b) (i) (C-X bond energy) decreases/becomes weaker (from F to I)
[1
due to bond becoming longer/not such efficient orbital overlap
[1]
(ii) (as the bond energy of C-X decreases) the halogenalkanes become more reactive
(answer must imply that it is from F to I)
[1
[3]
(c) The C-Cl bond is weaker than the C-F and C-H bonds
or C-Cl bond (E = 340) and C-H (E = 410)
[1]
so is (easily) broken to form Cl •/Cl radicals/Cl atoms
tom
causing the breakdown of O3 into O2
[1]
[3]
(d) Cl-CH2CH2-CO2H
HO-CH2CH2CH2-Cl
[1]
[1]
OH
Br
[1]
[3]
light/UV/hν or 300°C
[1
(ii) (free) radical substitution
[1]
(iii) ∆H = E(C-H) – E(H-Cl) = 410 – 431 = –21 kJ mol-1
[1]
(e)
e) (
(iv) ∆H = E(C-H) – E(H-I) = 410 – 299 = +111 kJ mol-1
ecf
[1]
(v) The reaction with iodine is endothermic or ∆H is positive or requires energy
[1]
(vi) Cl2 → 2Cl •
CH3CH2• + Cl2 → CH3CH2Cl + Cl •
CH3CH2• + Cl • → CH3CH2Cl
[1]
[1]
[1]
[8]
[Total: 19]
5
(a
CH2=CH2 + HF
bonds
4 C-H
broken 1 C=C
/kJ mol-1 1 H-F
1640
610
562
2812
→
CH3CH2F
bonds
made
/kJ mol-1
5 C-H
2050
1 C-C
350
1 C-F
E
(2400 + E)
breaking reactant bonds requires
4 x 410 + 610 + 562 = 2812 kJ mol-1
(1)
making product bonds gives
5 x 410 + 350 + E = (2400 + E) kJ mol-1
∆H
o
reaction
(1)
-1
= - (2400 + E) + 2812 = – 73 kJ mol
(1)
-1
(2400 + E) = 2812 + 73 = 2885 kJ mol
E = 2885 - 2400 = 485 kJ mol-1
(1)
allow ecf on wrong bond energy values and/or incorrect arithmetic
(b) any two from
non-toxic
unreactive
volatile
non-flammable
easily liquefied
(c) in CCl2F2
C-Cl bond energy is 340 kJ mol-1 and is weaker than C-F or C-H bonds
C-Cl bond is broken by uvl or
Cl. free radicals are formed
[4]
(1 + 1)
[2]
(1)
(1)
[2]
(1)
[3]
(1)
[1]
(d) (i) the trapping of reflected heat from the Earth in the lower atmosphere
producing global warming
(ii) CO2/carbon dioxide
(e) octahedral
[Total: 12]
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Halogenoalkanes
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Halogen Derivatives
Sub-Topic
Paper Type
Halogenoalkanes
Theory
Booklet
Question Paper 1
Time Allowed:
75 minutes
Score:
/62
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Organohalogen compounds can undergo hydrolysis.
R–Cl + H2O → R–OH + HCl
State the relative rates of hydrolysis of the following compounds.
CH3CH2CH2Cl
CH3CH2COCl
C6H5Cl
Explain your answer.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [3]
(b) Aminolaevulinic acid is involved in the synthesis of haemoglobin and chlorophyll.
O
H2N
OH
O
aminolaevulinic acid
Name the three functional groups in aminolaevulinic acid.
............................................................................................................................................. [2]
(c) Aminolaevulinic acid reacts readily with bromoethane.
(i) Show the mechanism of the first step of this reaction on the diagram. Include all necessary
curly arrows, lone pairs and relevant dipoles.
O
O
intermediate
H 2N
H3C
O
H3 C
HN
OH
CH2
Br
OH
O
(ii) Name the mechanism in (c)(i).
.............................................................................................................................................
(iii) Identify the non-organic product formed in this reaction.
.............................................................................................................................................
[5]
(d) Three reactions of aminolaevulinic acid are shown. Draw the structures of the products W, X
and Y in the boxes below.
O
NaBH4
H 2N
OH
O
aminolaevulinic acid
CH3COCl
Y
HCl (aq), warm
X
W
[3]
(e) Aminolaevulinic acid can undergo polymerisation.
Draw the structure of the polymer showing two repeat units. The linkages between the
monomer units should be shown fully displayed.
[2]
[Total: 15]
2
A bromoalkane, R–Br, is hydrolysed by aqueous sodium hydroxide.
(a) (i) Write a balanced equation for this reaction.
....................................................................................................................................
(ii) What type of reaction is this?
....................................................................................................................................
[2]
(b) The concentration of bromoalkane was determined at regular time intervals as the
reaction progressed.
Two separate experiments were carried out, with different NaOH concentrations.
The graph below shows the results of an experiment using [NaOH] = 0.10 mol dm–3.
0.010
0.009
0.008
0.007
0.006
[R–Br]
0.005
/ mol dm–3
0.004
0.003
0.002
0.001
0
0
50
100
150
200
250
time / min
When the experiment was repeated using [NaOH] = 0.15 mol dm–3, the following results
were obtained.
time / min
[R–Br] / mol dm–3
0
40
80
120
160
200
240
0.0100
0.0070
0.0049
0.0034
0.0024
0.0017
0.0012
(i) Plot these data on the axes above, and draw a line of best fit.
(ii) Use one of the graphs to confirm that the reaction is first order with respect to R–Br.
Show all your working, and show clearly any construction lines you draw.
(iii) Use the graphs to calculate the order of reaction with respect to NaOH. Show all
your working, and show clearly any construction lines you draw on the graphs.
(iv) Write the rate equation for this reaction, and calculate the value of the rate constant.
rate =
[7]
(c) Nitric oxide, NO, and bromine vapour react together according to the following equation.
2NO(g) + Br2(g) → 2NOBr(g)
∆H = –23 kJ mol–1
The reaction has an activation energy of +5.4 kJ mol–1.
Use the following axes to sketch a fully-labelled reaction pathway diagram for this
reaction.
Include all numerical data on your diagram.
2NO + Br2
energy
/ kJ mol–1
extent of the reaction
[2]
[Total: 11]
3
The molecular formula C3H6 represents the compounds propene and cyclopropane.
H
H
CH3CH
CH2
C
H
propene
C
H
H
C
H
cyclopropane
(a) What is the H–C–H bond angle at the terminal =CH2 group in propene?
................
[1]
(b) Under suitable conditions, propene and cyclopropane each react with chlorine.
(i) With propene, 1,2-dichloropropane, CH3CHCl CH2Cl is formed.
State fully what type of reaction this is.
.............................................................................................................................. [1]
(ii) When cyclopropane reacts with chlorine, three different compounds with the
molecular formula C3H4Cl 2 can be formed.
Draw displayed structures of each of these three compounds.
[3]
[Total: 5]
4
(a) Explain what is meant by the term bond energy.
...........................................................................................................................................
...........................................................................................................................................
[2]
(b)
b)
Describe and explain the trend in bond energies of the C–X bond in halogenoalkanes,
where X = F, Cl, Br or I.
....................................................................................................................................
....................................................................................................................................
(ii) Describe the relationship between the reactivity of halogenoalkanes, RX, and the
bond energies of the C–X bond.
....................................................................................................................................
....................................................................................................................................
[3]
(c) Use the Data Booklet to suggest an explanation as to why CFCs such as CF2Cl 2 are
much more harmful to the ozone layer than fluorocarbons such as CF4 or hydrocarbons
such as butane, C4H10.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[3]
(d) Predict the products of the following reactions and draw their structures in the boxes
below. The molecular formula of each product is given, where X = Cl , Br or I.
H 2O
+
Cl
Cl
C3H5O2X
O
H 2O
+
I
Cl
C3H7OX
Br
H 2O
+
Br
C7H7OX
[3]
(e) Ethane reacts with chlorine according to the following equation.
C2H6 + Cl 2 → C2H5Cl + HCl
(i) State the conditions needed for this reaction.
....................................................................................................................................
(ii) State the type of reaction occurring here.
....................................................................................................................................
One of the steps during this reaction is the following process.
Cl ● + CH3CH3 → HCl + CH3CH2●
(iii) Use the Data Booklet to calculate the enthalpy change, ∆H, of this step.
∆H = ................................ kJ mol–1
(iv) Use the Data Booklet to calculate the enthalpy change, ∆H, of the similar reaction:
I● + CH3CH3 → HI + CH3CH2●
∆H = ................................ kJ mol–1
(v) Hence suggest why it is not possible to make iodoethane by reacting together iodine
and ethane.
....................................................................................................................................
(vi) Complete the following equations of some possible steps in the formation of
chloroethane.
Cl 2 → ..............
Cl ● + CH3CH3 → HCl + CH3CH2●
CH3CH2● + .............. → ........................ + ..............
.............. + .............. → CH3CH2Cl
[8]
[Total: 19]
5
Halogenoalkanes have been widely used as aerosol propellants, refrigerants and solvents
for many years.
Fluoroethane, CH3CH2F, has been used as a refrigerant. It may be made by reacting ethene
with hydrogen fluoride.
You are to calculate a value for the C–F bond energy in fluoroethane.
(a) Use relevant bond energies from the Data Booklet, and the equation below to calculate
a value for the bond energy of the C–F bond.
CH2 = CH2(g)
+
CH3CH2F(g)
ΔH o = – 73 kJ mol–1
C–F bond energy = .................................... kJ mol–1 [4]
(b) Another halogenoalkane which was used as a refrigerant, and also as an aerosol
propellant, is dichlorodifluoromethane, CCl2F2.
State two reasons why compounds such as CH3CH2F and CCl2F2 have been used as
aerosol propellants and refrigerants.
..........................................................................................................................................
..................................................................................................................................... [2]
CCl2F2 is one of many chlorofluorocarbon compounds responsible for damage to the ozone
layer in the stratosphere.
(c) By using relevant data from the Data Booklet, and your answer to (a) suggest why CCl2F2
is responsible for damage to the ozone layer in the stratosphere whereas CH3CH2F is
not.
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
Both CH3CH2F and CCl2F2 are greenhouse gases.
The ‘enhanced greenhouse effect’ is of great concern to the international community.
(d) (i)
What is meant by the term enhanced greenhouse effect?
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Water vapour is the most abundant greenhouse gas.
What is the second most abundant greenhouse gas?
........................................
[3]
A greenhouse gas which is present in very small amounts in the atmosphere is sulfur
hexafluoride, SF6, which is used in high voltage electrical switchgear.
(e) What shape is the SF6 molecule?
...................................................
[1]
[Total: 12]
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Alcohols
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydroxy Compounds
Sub-Topic
Paper Type
Alcohols
Theory
Booklet
Mark Scheme 1
Time Allowed:
72 minutes
Score:
/60
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Question
Mark Scheme
Mark
Total
1 (a)
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[7]
(b) (i)
(ii)
but-1-ene / 1-butene
but-2-ene / 2-butene
[1]
[1]
[2]
but-2-ene AND two different groups on each carbon (of C=C)
double bond means no free rotation
[1]
[1]
[2]
(iii)
[1+1]
and
(either way round)
[2]
[13]
Question
Questi
2
(a)
Scheme
Marks
Marks
reagent = conc H2SO4 or conc H3PO4
1
conditions = heat
1
OR
pas vapour over hot Al2O3
“reagent”
“conditions”
[2]
(b) (i) C3H7OH + 2[O] C2H5CO2H + H2O
1
(ii) reagent = sodium / potassium dichromate or correct formula
(c)
(d)
T
[1
1
conditions = H+ / acidified and (heat under) reflux
1
[2]
U = CH3CH(OH)CH3
V = CH3CHBrCH3
1
1
[2]
OR
U = CH3CH2CH2OH
V = CH3CH2CH2Br
reagent = KOH / NaOH
1
conditions = ethanol / alcohol AND Heat / reflux
1
[2]
[9]
3
(a)
any five of these seven points.
• σ-bonds are between C-C OR C-H
• carbons are sp2
• rings of charge above and below the ring must be in diagram
• presence of σ-bonds
• electrons/bonds are delocalised
• planar molecule/bond angles 120o
• all C-C are the same length/have intermediate bond length between C-C & C=C
5
[5]
(b)
Reagent X e.g. Br2, HNO3, Na, NaOH, benzenediazonium salt / ion; RCOCl ; Fe3+ ; H2+Ni
substituted product for L-DOPA & vanillin (examples given are for X = Br2 and NaOH)
Br
Br
HO
HO
NH2
O
H
H 3 CO
COOH
HO
or
1
-
O
NH2
O
HO
-
2
O
-
H 3 CO
O
H
O
Reagent Y e.g. HCl; Na2CO3, Mg, SOCl2, PCl5, ROH + c.H2SO4; HCl+NaNO2 / HNO2; CH3Cl
Correct substituted product for L-DOPA
HO
1
1
+
NH3
COOH
HO
Reagent Z e.g. acidified Cr2O72– ; 2,4-DNPH, hydrazine ; Fehling’s, Tollens’; HCN; HCN + NaCN;
NaBH4 ;
correct substituted product for vanillin
HO
OH
HO
O
1
1
[7]
4
(a)
A
Br2 in an inert organic
solvent
B
PCl5
C
2
D
NaB
E
K2Cr2O7/H+,
heat under reflux
CH3CHBrCHBrCH2OH
CH3CH=CHCH2Cl
and Ni catalyst
4
give one mark for each correct answer
CH3CH2CH2CH2OH
NO REACTION
CH3CH=CHCO2H
(5 × 1)
[5]
(b)
(1)
1)
(c)
correct C4 with C=C in position 2
accept cis form
correctly shown –CO2H
allow ecf on candidate’s answer to E in (a)
(1)
(1
[2]
(d) (i) reagent
observation
2,4-dinitrophenylhydrazine
,4-dinitrop
Tollens' reagent
ppt.
silver mirror or
grey ppt. or
black ppt.
brick red ppt.
Fehling’s reagent
correct reagent
observation
(1)
(1)
(ii) reduction or nucleophilic addiction
(e)
C : H : O =
(1)
[3]
73.7
12.3
14.0
:
:
12
1
16
= 6.14 : 12.3
= 7.01 : 14.1
gives C7H14O
formula must be given
: 0.875
: 1
(1)
(1)
[2]
[Total: 13]
5
(a
(i) CH2=CHCO2H
(1
(ii) BrCH2CHBrCH2OH
H
(
(iii) product is HOCH2CH(OH)CH2OH
correct addition across >C=C<
(1)
original –CH2OH remains
(1)
(iv) HO2CCO2H
(b) (i) nucleophilic substitution
(1
[5]
(1)
(ii) oxidation
xid
[2]
(c) (i) step I
H2
(1)
heat with Ni catalyst
(1)
step II
acidified K2Cr2O7
(1)
heat or distil off product
(1)
(ii) structural isomerism
or
functional group isomerism
(1)
[5]
(1)
[1]
(d) both oxidation and reduction have occurred or
disproportionation has taken place
[Total: 13]
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Alcohols
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydroxy Compounds
Sub-Topic
Paper Type
Alcohols
Theory
Booklet
Question Paper 1
Time Allowed:
72 minutes
Score:
/60
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula
C4H10O.
Alcohol A does not react with acidified potassium dichromate(VI) solution but B, C and D do.
All four alcohols react with hot, concentrated sulfuric acid to form products with the molecular
formula C4H8. A, C and D each give a single product in this reaction. B gives a mixture of two
structural isomers, one of which shows stereoisomerism.
(a) Give the skeletal formula for each of the four alcohols and complete the diagram with the
names of the types of structural isomerism shown by each linked pair of compounds.
A
B
..........................
isomerism
..........................
isomerism
C
D
..........................
isomerism
[7]
(b)
b)
Give the names of the two structural isomers produced by the reaction of B with hot,
concentrated sulfuric acid
...........................................................
.
............................................................. [2]
(ii) State which of these two isomers shows stereoisomerism. Explain why this molecule is
capable of showing stereoisomerism.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(iii) Draw displayed formulae to show the two stereoisomers.
stereoisomer 1
stereoisomer 2
[2]
[Total: 13]
2
A series of reactions based on propan-1-ol is shown.
CH3CH2CH2OH
reaction 1
steam
CH3CH=CH2
catalyst
reaction 2
U (C3H8O)
HBr
reaction 3
CH3CH2CO2H
V
(a) Suggest a suitable reagent and conditions for reaction 1.
.............................................................................................................................................. [2]
(b)
b)
Write an equation for reaction 2, using [O] to represent the oxidising agent.
....................................................................................................................................... [1]
(ii) Suggest a suitable reagent and conditions for reaction 2.
....................................................................................................................................... [2]
(c) Give the structural formulae of U and V.
U ................................................................................................................................................
V ................................................................................................................................................
[2]
(d) Suggest a suitable reagent and conditions for reaction 3.
....................................................................................................................................................
.............................................................................................................................................. [2]
[Total: 9]
3
L-DOPA is used in the treatment of Parkinson's disease. It can be prepared from vanillin.
HO
HO
NH2
CO2H
HO
H
CH3O
O
L-DOPA
vanillin
(a) L-DOPA and vanillin each contain an aromatic benzene ring.
Describe, with the aid of a diagram, the bonding and shape of a molecule of benzene, C6H6.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [5]
(b) A student carried out some reactions with samples of L-DOPA and vanillin using reagents X, Y
and Z.
●
●
●
Reagent X reacted with L-DOPA and with vanillin.
Reagent Y reacted with L-DOPA but not with vanillin.
Reagent Z reacted with vanillin but not with L-DOPA.
Assume that the CH3O– group in vanillin does not react.
Suggest possible identities of reagents X, Y and Z and give the structures of the organic
products that were formed.
Reagent X ..................................................................................................................................
product with L-DOPA
product with vanillin
Reagent Y ..................................................................................................................................
product with L-DOPA
Reagent Z ..................................................................................................................................
product with vanillin
[7]
[Total: 12]
4
Crotyl alcohol, CH3CH=CHCH2OH, is a colourless liquid which is used as a solvent.
(a) In the boxes below, write the structural formula of the organic compound formed when
crotyl alcohol is reacted separately with each reagent under suitable conditions.
If you think no reaction occurs, write 'NO REACTION' in the box.
A
Br2 in an inert organic
solvent
B
PCl 5
C
H2 and Ni catalyst
D
NaBH4
E
K2Cr2O7 / H+
heat under reflux
[5]
(b) Draw the displayed formula of the organic compound formed when crotyl alcohol is
reacted with cold, dilute acidified potassium manganate(VII).
[1]
(c) Draw the skeletal formula of the compound formed in reaction E.
[2]
(d) Crotyl alcohol is obtained from crotonaldehyde, CH3CH=CHCHO.
(i) Describe one test that would confirm the presence of a small amount of unreacted
crotonaldehyde in the crotyl alcohol.
Give the name of the reagent used and state what you would see.
reagent ......................................................................................................................
observation ................................................................................................................
(ii) What type of reaction is the conversion of crotonaldehyde into crotyl alcohol?
....................................................................................................................................
[3]
(e) Compound P, another unsaturated compound, is found in some blue cheeses.
The percentage composition by mass of compound P is C: 73.7%; H: 12.3%; O: 14.0%.
Calculate the empirical formula of compound P.
[2]
[Total: 13]
5
Compounds containing the allyl group, CH2=CHCH2–, have pungent smells and are found in
onions and garlic.
Allyl alcohol, CH2=CHCH2OH, is a colourless liquid which is soluble in water.
(a) Allyl alcohol behaves as a primary alcohol and as an alkene.
Give the structural formula of the organic compound formed when allyl alcohol is reacted
separately with each of the following reagents.
(i) acidified potassium dichromate(VI), heating under reflux
(ii) bromine in an inert organic solvent
(iii) cold, dilute, acidified potassium manganate(VII)
(iv) hot, concentrated, acidified potassium manganate(VII)
[5]
(b) Allyl alcohol undergoes the following reactions.
(i) When reacted with concentrated HCl at 100 °C, CH2=CHCH2Cl is formed.
State as fully as you can what type of reaction this is.
....................................................................................................................................
(ii) When reacted with MnO2 at room temperature, CH2=CHCHO is formed.
What type of reaction is this?
....................................................................................................................................
[2]
(c) Allyl alcohol can be converted into propanal in two steps.
step I
CH2=CHCH2OH
step II
CH3CH2CH2OH
CH3CH2CHO
(i) What reagents and conditions would be used for each step?
step I
reagent(s) ..................................................................................................................
condition(s) ................................................................................................................
step II
reagent(s) ..................................................................................................................
condition(s) ................................................................................................................
(ii) Allyl alcohol and propanal are isomers.
What form of isomerism do they display?
....................................................................................................................................
[5]
(d) Allyl alcohol may also be converted into propanal by using a ruthenium(IV) catalyst in
water.
ruthenium(IV) catalyst
CH2=CHCH2OH
CH3CH2CHO
Suggest what is unusual about this single step reaction.
...........................................................................................................................................
..................................................................................................................................... [1]
[Total: 13]
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Phenol
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydroxy Compounds
Sub-Topic
Paper Type
Phenol
Theory
Booklet
Mark Scheme 1
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) H2 + Pt or H2 + Ni / Pd + heat / warm or 50o < T < 500 oC
[1]
(ii)
OH
[1]
(iii) 22 = 4
[1]
(iv)
CH(CH3)2
H
H
H
CH(CH3)2
or
OH
OH
H
2 Hs have to be on the same side of the ring. Allow –C3H7 or –R for –CH(CH3)2
(b)
b)
[1]
[1]
C
or
N
N
N2
or
N
N
(ignore additional Cl or Cl-, but don't allow covalent -N=N-Cl)
(ii) step 1: conc HNO3 + H2SO4 (@ 25 oC < T < 60 oC – see below) ("aq" negates)
step 2: Sn / Fe + HCl
step 3: HNO2 or NaNO2 + HCl (@ T< 10 °C – see below)
both temperatures correct for steps 1 + 3 (temperature not required for step 2)
(inclusion of the word "heat" or "reflux" in step 3 negates the temperature mark)
(c)
[4]
[5]
HBr
Br
reaction
Br
Na
ONa
NaOH(aq)
ONa
no reaction
ONa
[Total: 14]
2
(a
(i)
(ii)
(b) (i)
(ii)
2H2SO4 + HNO3 → 2HSO4– + NO2+ + H3O+
OR H2SO4 + HNO3 →HSO4– + NO2+ + H2O
1
any three of
• curly arrow from inside the benzene ring to NO2+ group
• intermediate – penalise NO2 connectivity or missing methyl group (once)
• curly arrow from C-H bond into ring
• product + H+ (or as diagram –H+)
allow 2- and 3-substituted nitromethylbenzene)
3
acidity of ClCH2CO2H > CH3CO2H AND (ClCH2CO2H) as an electronegative/electron withdrawing
Cl
acidity of phenol > CH3CH2OH AND electrons on oxygen (on phenol) delocalised into ring
OR benzene ring withdraws electrons from oxygen
stronger acid linked to weakening O-H bond/anion being stabilised
1
[4
1
1
[3]
(c)
Na
redox/reduction
O
O
ONa
(or ionic)
Br2
O
Br
(electrophilic)
substitution
O
OH
Br
O
NaOH
hydrolysis/
acid-base/
OH
and
OH [1]
OH
or ionic
O
ONa
ONa
ONa
1 mark for each correct structure
for reaction types, 2 correct = 1 mark, 3 correct = 2 marks
4
2
[6]
3
(a
(i)
C15H21NO2
1
O
(ii)
OCH 3
1
∗
NHCH2CH3
(iii)
any two of ketone, amine or ether
2
[4
(b)
(i)
i) Li
(ii)
ii
OH
4
O
l (aq)
OCH3
reduction / nucleophilic
addition
NHCH2CH3
OCH3
acid-base / neutralisation
OCH3
acylation / condensation
+
NH2CH2CH3
(Cl-)
(iii)
ii
O
3COCl
allow addition +
elimination
allow nucleophilic
substitution
N
H3CH2C
COCH3
1 mark for each correct structure
1 mark for each correct reaction type
3
3
[6]
4
(a)
OH
CO2H
OH
H2
H2
H2
H2O
Na
a
2
KOH(aq)
O
X
Na2CO3(aq)
a
X
X
C
2
X
[5]
(b)
b) (
(CH3)3 C–Cl (any unambiguous structure or name)
[1]
(ii) reduction or hydrogenation
[1]
(iii) either CH3CO2H and heat with (conc) H2SO4
or
CH3COCl
[1]
(iv) reflux
[1]
dilute HCl
[1]
[5]
(c)
c)
reagent and conditions
product with A
Br
OH
product with B
Br
Br2(aq)
no reaction
C(CH3)3
Br
heat with HBr
no reaction
C(CH3)3
pass vapour over
heated Al2O3
no reaction
C(CH3)3
O
heat with acidified
K2Cr2O7
no reaction
C(CH3)3
[6]
(ii) either: Cr2O72–/H+: no observation with A and goes from orange to green with B.
or:
Br2(aq): white ppt. with A and no observation/ppt with B
[1]
[7]
[Total: 17]
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Phenol
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Hydroxy Compounds
Sub-Topic
Paper Type
Phenol
Theory
Booklet
Question Paper 1
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
Compound B is a component of several perfumes and flavourings. It can be obtained by the
hydrogenation of compound A.
During the reaction, the hydrogen atoms all add onto the same side of the benzene ring.
+ 6[H
OH
A
(i)
(ii)
(iii)
OH
B
Suggest reagents and conditions for this reaction.
.......................................................................................................................................
[1]
Circle
all the chiral atoms on the structure of B above.
How many possible optical isomers are there with the same structural formula as B?
[1]
....................................................................................................................................... [1]
(iv)
Complete the following part-structure to show the structure of one of the isomers of B that
would be formed during the above reaction.
[1]
(b) Compound A can be obtained from propan-2-ylbenzene by the following route.
step 1
propan-2-ylbenzene
step 2
NO2
NH2
step 3
step 4
heat in water
OH
A
(i)
C
Suggest the structure of the intermediate cation C and draw it in the box above.
[1]
(ii)
Suggest reagents and conditions for the following steps.
step 1 ..................................................................................................................................
step 2 ..................................................................................................................................
step 3 ..................................................................................................................................
[4]
(c)
Suggest the structures of the organic products of the reactions between each of the compounds
A and B and the following reagents. If no reaction occurs write ‘no reaction’ in the relevant box.
product with A,
product with B,
reagent
OH
OH
HBr
Na
NaOH(aq)
[5]
[Total: 14]
2
(a) Methylbenzene undergoes electrophilic substitution with nitronium ions, NO2+.
Nitronium ions are generated by the reaction between concentrated sulfuric acid and
concentrated nitric acid.
(i) Construct an equation for the formation of nitronium ions, NO2+, by this method.
.............................................................................................................................................
(ii) Complete the scheme to show the mechanism for this reaction. Use curly arrows to show
the movement of electron pairs.
CH3
NO2+
[4]
(b)
b)
Describe and explain the relative acidities of chloroethanoic acid and ethanoic acid.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
(ii) Describe and explain the relative acidities of phenol and ethanol.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[3]
(c) Phenyl 2-hydroxybenzoate is an antiseptic.
O
O
OH
phenyl 2-hydroxybenzoate
Complete the following table about the reactions of phenyl 2-hydroxybenzoate with the three
reagents.
reagent
structure of product(s)
type of reaction
Na
excess
Br2(aq)
excess hot
NaOH(aq)
[6]
[Total: 13]
3
Methoxetamine is a derivative of the pharmaceutical drug, ketamine.
O
OCH3
NHCH2CH3
methoxetamine
(a) (i) What is the molecular formula of methoxetamine?
.............................................................................................................................................
(ii) On the diagram above, circle any chiral centres that are present in methoxetamine.
(iii) Name two functional groups in methoxetamine, in addition to the aryl group.
.............................................................................................................................................
[4]
(b) In the table, complete the structure of each of the compounds formed when methoxetamine is
reacted with the following reagents.
State the type of reaction in each case.
reagent
structure of product
type of reaction
(i) LiAl H4
OCH3
(ii) HCl (aq)
OCH3
(iii) CH3COCl
OCH3
[6]
[Total: 10]
4
(a) A series of experiments is carried out in which the reagent shown at the top of the column
of the table is mixed, in turn, with each of the reagents at the side.
Complete the following table by writing in each box the formula of any gas produced.
Write x in the box if no gas is produced.
The first column has been completed as an illustration.
OH
CO2H
OH
H2O
Na
H2
KOH(aq)
x
Na2CO3(aq)
x
[5]
(b) Compound C is responsible for the pleasant aroma of apples. It can be prepared from
phenol by the following 3-step synthesis.
O
OH
OH
OH
step
1
O
step
2
C
C
CH3
H 3C
CH3
step
3
C
CH3
H 3C
CH3
H 3C
CH3
CH3
CH3
A
B
C
(i) The only by-product of step 1 is HCl. Suggest the reagent that was used to react
with phenol to produce compound A.
....................................................................................................................................
(ii) What type of reaction is occurring in step 2?
....................................................................................................................................
(iii) What reagents and conditions are required for step 3?
....................................................................................................................................
(iv) State the reagent and conditions needed to convert C back to B, the reverse of
step 3.
....................................................................................................................................
[5]
(c) (i) Either compound A or compound B, or both, react with the following reagents.
For each reagent draw the structure of the organic product formed with A, and with
B. If no reaction occurs, write ‘no reaction in the relevant box.
reagent and conditions
product with A
product with B
an excess of Br2(aq)
heat with HBr
pass vapour over
heated Al 2O3
heat with acidified K2Cr2O7
(ii) Choose one of the above reactions to enable you to distinguish between A and B.
State below the observations you would make with each compound.
reagent
observation with A
observation with B
[7]
[Total: 17]
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Carbonyl Compounds
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Carbonyl Compounds
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Question
1
(a)
Mark Scheme
Bond breaking =
Bond forming =
Enthalpy change =
(b) (i)
(ii)
3
(c
Mark
C=O
C–H
= 740
= 410
= 1150 kJ
[1]
C–C
C–O
O
O–H
= 350
= 360
= 460
= 1170 kJ
[1]
= –20 kJ mol–1
[1]
1150 – 1170
Total
[3]
Stereoisomerism = (molecules with the same molecular formula and)
same structural formula but different spatial
arrangements of atoms
[1]
Chiral centre =
[1]
[2]
(Planar) carbonyl so (equal chance of nucleophile) attacking either side
[1]
[1]
M1 = lone pair AND curly arrow from lone pair to carbonyl C
M2 = partial charges on C=O AND curly arrow from bond (=) to Oδ–
M3 = structure of intermediate including charge
M4 = lone pair AND two correct curly arrows (from lone pair to H AND from
H—C to C)
M5 = CN–
[1]
[1]
[1]
[1]
[1]
[5]
(CN– regenerated so) catalyst
[1]
[1]
atom with four different atoms/groups attached
(i)
(ii)
[12]
2
(a
(i)
(ii)
A = CH3CH2CH2CH2CHO
[1]
B = CH3CH2CH(CH3)CHO
[1]
C = (CH3)2CHCH2CHO
[1]
D = (CH3)3CCHO
[1]
CH3
CH3
HC
H3CCH2
(b) (i)
(ii)
CH
H2
CHO
[4]
H2
O HC
[1+1]
[1+1]
CH2CH3
Fehling’s / Benedict’s OR Tollens’ OR dichromate OR manganate
Warm / heat
Fehling’s / Benedict’s =(Brick)-red ppt
Tollens’ = silver / mirror OR grey/black precipitate
with the aldehyde / A-D
Dichromate = orange to green
Manganate = purple to colourless
[1]
[1]
(2,4-)DNP(H) / Brady’s reagent
[1]
Orange / yellow / red-orange / yellow-orange ppt
[1]
[1]
[3]
[2]
[11]
3
(a
[1]
(i) A/B =
[1]
O
O
O
C=
[1]
[3]
(ii) Chain
hai
[1]
(iii) Silver mirror/ppt/solid (black/grey)
[1]
[1]
(b) (i)
D
[1]
CH2=C(CH3)CH2OH
E
E
H
H3C
C
H3C
C
H
CH2OH
C
CH2 OH
trans OR E
H
[1+1]
C
H
[1]
cis OR Z
[1]
F
H2C=CHCH2CH2OH
[5]
(ii) Hydrogen
ydr
[1]
(c) (i) C3H6O + [O] C3H6O2
[1]
[1]
(ii) C3H6O +2[H] C3H8O
[1
[1]
[13]
4
(a)
(b) (i)
P; CH2 = C(CH3)2
Q; CH3CH2CH = CH2
R; CH3CH = CHCH3
S; (CH3)2CO
1
1
1
1
(Different molecules with) the same (molecular and) structural formula
1
different arrangements of atoms (in space) / different displayed formula
1
H
(ii)
H
C
H
H
C
C
H
H
H
C
H
H
trans-but-2-ene
(c)
H
C
HH
C
[4]
[2]
H
C
C
H
H
cis-but-2-ene
H
1
1
reagent; NaBH4 or LiA l H4 or names
1
product; propan-2-ol
1
[2]
[2]
[10]
5
(a)
reaction
eaction
product
A
Br2 in
solvent
B
PCl3
C
2
D
NaB
E
an
inert
CH3CHBrCHBrCHO
organic
NO REACTION
and Ni catalyst
CH3CH2CH2CH2OH
CH3CH=CHCH2OH
4
2Cr2O7/H
+
CH3CH=CHCO2H
one mark for each correct answer
[5]
(b)
trans or E
cis or Z
two correct structures
(1)
[1]
both correctly labelled
(1)
[1]
correctly displayed -CHO group
(1)
(c)
(1)
(d)
d) (
CH3CH(OH)CH(OH)CO2H
(ii) CH3CO2H
HO2CCO2H
(1)
[1]
(1)
(1)
[1]
allow ecf on candidate’s answer to E in (a)
[Total: 12]
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Carbonyl Compounds
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Carbonyl Compounds
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Ethanal reacts with hydrogen cyanide, in the presence of a small amount of NaCN, as shown.
CH3CHO + HCN → CH3CH(OH)CN
(a) Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction.
Include a sign with your answer.
enthalpy change = .................................... kJ mol–1 [3]
(b) The product of this reaction shows stereoisomerism as it contains a chiral centre. This reaction
produces an equimolar mixture of two optical isomers.
(i) Explain the meanings of the terms stereoisomerism and chiral centre.
stereoisomerism .................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
chiral centre ........................................................................................................................
.............................................................................................................................................
[2]
(ii) Suggest why the two optical isomers are produced in equal amounts by this reaction.
.............................................................................................................................................
....................................................................................................................................... [1]
(c) (i) Complete the diagram to show the mechanism of this reaction. Include all necessary
charges, partial charges, lone pairs and curly arrows and show the structure of the
intermediate.
N
C–
CN
H
H 3C
H 3C
C
C
H
+
OH
O
H
C
N
[5]
(ii) With reference to your mechanism in (i), explain the role of the NaCN in this reaction.
.............................................................................................................................................
....................................................................................................................................... [1]
[Total: 12]
2
There are seven structural isomers with the molecular formula C5H10O that are carbonyl
compounds. Four of these are aldehydes.
These four aldehydes, A, B, C and D, have the following properties.
●
Aldehyde A has a straight chain while B, C and D are branched.
●
Aldehyde B is the only one of the four isomers with a chiral centre and it exists as a pair of
optical isomers.
●
Aldehyde C has two methyl groups in its structure but D has three.
(a)
a)
Give the structure of each of the four isomers.
A
B
C
D
[4]
(ii) Draw the three-dimensional structures of the two optical isomers of B.
[2]
(b) (i) Describe a chemical test that would allow you to distinguish between any of the four
isomers A to D and any of the other three structural isomers of C5H10O, that are carbonyl
compounds.
In your answer you should describe any necessary reagents and conditions as well as
explaining what you would see in each case.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Describe a test that would give the same result with all seven carbonyl isomers of C5H10O.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
[Total: 11]
3
A, B, C, D, E and F are all structural isomers with the molecular formula C4H8O.
(a) A, B and C all give an orange precipitate when treated with 2,4-DNPH but only A and B give a
brick-red precipitate when warmed with Fehling’s solution.
(i) Draw the skeletal formulae of A, B and C.
A
B
C
[3]
(ii) Name the type of structural isomerism shown by A and B.
....................................................................................................................................... [1]
(iii) State what you would see when a sample of A is warmed with Tollens’ reagent.
....................................................................................................................................... [1]
(b) D, E and F all decolourise bromine and effervesce slowly with sodium metal.
E shows geometrical isomerism. Only D has a branched chain.
None of these isomers contains an oxygen atom bonded to a carbon atom involved in π bonding.
None of these isomers contains a chiral centre.
(i) Give the structures of D, E and F. Show the two stereoisomers of E and label the
stereoisomerism shown.
D
E
E
.......................................
.......................................
F
[5]
(ii) Identify the gas produced during the reaction of each of these isomers with sodium metal.
....................................................................................................................................... [1]
(c) Another compound, G, C3H6O, contains the same functional group as A.
Give equations for the reactions of G with each of acidified potassium dichromate(VI) and
sodium tetrahydridoborate, NaBH4, using [O] or [H] as appropriate.
(i) reaction with acidified potassium dichromate(VI)
C3H6O + ..................................... → .......................................................................... [1]
(ii) reaction with NaBH4
C3H6O + ..................................... → .......................................................................... [1]
[Total: 13]
4
P, Q and R are structural isomers with the molecular formula C4H8.
All three compounds readily decolourise bromine in the dark.
P and Q do not exhibit stereoisomerism but R exists as a pair of geometrical (cis-trans) isomers.
All three compounds react with hot concentrated, acidified potassium manganate(VII) to produce
a variety of products as shown in the table.
compound
products
P
CO2 and S (C3H6O)
Q
CO2 and CH3CH2CO2H
R
CH3CO2H only
S reacts with 2,4-dinitrophenylhydrazine reagent, 2,4-DNPH, to form an orange crystalline product
but does not react with Fehling’s reagent.
(a) Give the structural formulae of P, Q, R and S.
P .................................................................... Q .....................................................................
R .................................................................... S .....................................................................
[4]
(b) (i) Explain what is meant by the term stereoisomerism.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Draw the displayed formulae of the geometrical isomers of R and name them both.
name ........................................................ name ......................................................... [2]
(c) State a reagent that could be used for the reduction of S and name the organic product of this
reduction.
reagent ......................................................... product ......................................................... [2]
[Total: 10]
5
Crotonaldehyde, CH3CH=CHCHO, occurs in soybean oils.
(a) In the boxes below, write the structural formula of the organic compound formed when
crotonaldehyde is reacted separately with each reagent under suitable conditions.
If you think no reaction occurs, write 'NO REACTION' in the box.
reaction
reagent
A
Br2 in an inert organic
solvent
B
PCl 3
C
H2 and Ni catalyst
D
NaBH4
E
K2Cr2O7 / H+
product
[5]
(b) Crotonaldehyde exists in more than one stereoisomeric form.
Draw the displayed formulae of the stereoisomers of crotonaldehyde.
Label each isomer.
[3]
(c) Draw the skeletal formula of crotonaldehyde.
[1]
(d) The product of reaction E in the table opposite will react with a solution containing
acidified manganate(VII) ions.
Draw the structural formulae of the organic products when the reagent is
(i) cold, dilute;
(ii) hot, concentrated.
[3]
[Total: 12]
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Atoms, Molecules &
Stoichiometry
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
69 minutes
Score:
/57
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
p
protons
rotons
14
C2–
ele
neutrons
1
1
6
(b)
no reaction
CCl4:
GeCl4 and SnCl4: for each steamy fumes evolved or white solid produced
GeCl4 + 2H2O → GeO2 + 4HCl
SnCl4 + 2H2O → SnO2 + 4HCl
1
1
1
1
(c)
Ge / Sn use d–orbitals
or Ge / Sn have low lying d orbitals
or carbon cannot expand its octet
or carbon cannot accommodate more than 4 bonded pairs
1
(d)
Sn4+ / Sn2+ = +0.15V and Pb4+ / Pb2+ = +1.69 V and Cl2 / Cl – = + 1.36 V
1
Sn2+ is oxidised by Cl2 because its Eo is less positive / more negative
or Sn2+ is a good reducing agent due to its smaller E value than Cl2 ora
or Pb4+ is a stronger oxidising agent than Cl2 so Pb2+ with Cl2 reaction is not
feasible
or Sn4+ is a weaker oxidising agent than Cl2 so Sn2+ with Cl2 reaction is
feasible
1
SnCl2 + Cl2 → SnCl4
or Sn2+ + Cl2 → Sn4+ + 2Cl –
or SnCl2 + Cl2 + 2H2O → SnO2 + 4HCl
1
F = Le
1
moles of O2(g) = 130 / 24 000 = 5.417 x 10–3 mol
1
(e) (i)
(ii)
moles of electrons needed = 4 x 5.417 x 10–3 or 2.17 x 10–2 mol
no. of coulombs passed = 1.2 x 30 x 60 or 2160 C
1
no. of electrons passed = 2160 / 1.6 x 10–19 or 1.35 x 1022
1
no. of electrons per mole = 1.35 x 1022 / 2.17 x 10–2 = 6.2 x 1023 (mol–1)
1
[Total: 15]
2
(a
25.0 × 1.00
= 0.025 mol
1000
16.2 × 2.00
n(NaOH) =
= 0.0324 mol
1000
0.0324
= 0.0162 mol
n(H2SO4) reacting with NaOH =
2
n(H2SO4) reacting with NH3 = 0.025 - 0.0162 = 0.0088 mol
n(NH3) reacting with H2SO4 = 2 x 0.0088 = 0.0176 mol
n(NaNO3) reacting = n(NH3) produced = 0.0176 mol
mass of NaNO3 that reacted = 0.0176 x 85 = 1.496 g
1.496 ×100
% of NaNO3 =
= 91.2195122 = 91.2
1.64
give one mark for the correct expression
give one mark for answer given as 91.2 – i.e to 3 sig. fig.
allow ecf where appropriate
(i) n(H2SO4) =
(1)
(ii)
(1)
(iii)
(iv)
(v)
(vi)
(vii)
(viii)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
[9]
(b)
NaNO3 +5 and NH3 -3 both required
equ
[1]
[Total: 10]
3
(a
(i) mass of C = 12 × 1.32 = 0.36g
44
n(C) = 0.36 = 0.03
12
(ii) mass of H = 2 × 0.54 = 0.06 g
18
n(H) = 0.06 = 0.06
1
(iii) yes because 0.03 mol of C are combined with 0.06 mol of H or
C : H ratio is 1 : 2 or
empirical formula is CH2
(b) (i) C : H : O = 64.86 : 13.50 : 21.64
12
1
16
(1)
(1)
(1)
(1)
(1)
1)
(1)
= 5.41: 13.50 : 1.35
= 4 : 10 : 1
gives C4H10O
(1)
correct compound and correct chiral C*
correct mirror object/ mirror
image relationship in 3D
(1)
(ii)
(1)
(iii)
(1)
1)
[7]
[Total: 12]
Question
4
(a)
Mark Scheme
sub-atomic particle
relative mass
Mark
relative charge
neutron
e
electron
1/1836
proton
r
(b) (i)
(ii)
0
[1]
–
[1]
+
[1]
RAM = mean / average mass of the isotopes / an atom(s)
relative to 1/12 the mass of an atom of 12C / on a scale where an
atom of 12C is (exactly) 12 (units)
isotope =
atoms with the same number of protons / atomic number / proton
number with different mass numbers / numbers of
neutrons / nucleon number
(0.89 × 74) + (9.37 × 76) + (7.63 × 77) + (23.77 × 78) + (49.61× 80 ) + (8.73 × 82)
100
= 79.04 (2 d.p.) AND Se
(c) (i)
Te
Cl
47.4
128
52.6
35.5
0.370
0.370
1.48
0.370
1
4
(iii)
(d) (i)
[3]
[1]
[1]
[1]
[3]
[1]
[1]
[2]
[1]
so EF = TeCl4
Empirical Formula Mass = 270
(c) (ii)
Total
[1]
so MF = TeCl4
[1]
[3]
Covalent AND simple / molecular
[1]
low melting point / reaction with water
[1]
[2]
TeCl4 + 3H2O → H2TeO3 + 4HCl
OR TeCl4 + 2H2O → TeO2 + 4HCl
[1]
[1]
Yellow / orange flame
White fumes / solid
Yellow / green gas disappears
[1]
[1]
[1]
[max 2]
(ii)
NaCl giant / lattice AND ionic
SiCl4 simple / molecular AND covalent
[1]
[1]
For NaCl large difference in electronegativity
(of sodium / Na and chlorine / Cl / Cl2) (indicates electron transfer/ions)
[1]
For SiCl4 smaller difference (indicates sharing/covalency) with (weak)
van der Waals’ / IM forces (between molecules) ora
[1]
[4]
[20]
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Atoms, Molecules &
Stoichiometry
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
69 minutes
Score:
/57
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Atoms and ions of elements are made up from the three subatomic particles, protons, electrons
and neutrons, in varying amounts.
Complete the following table to show the number of each particle in 14C2–.
protons
14
electrons
neutrons
C2–
[2]
(b) Describe the observations you would make during the reactions, if any, of the following chlorides
with water.
Write equations for any reactions that occur.
CCl 4
observation ..................................................................................................................
......................................................................................................................................
equation .......................................................................................................................
GeCl 4 observation ..................................................................................................................
......................................................................................................................................
equation .......................................................................................................................
SnCl 4
observation ..................................................................................................................
......................................................................................................................................
equation .......................................................................................................................
[4]
(c) Suggest a reason for any difference in the reactivities of the chlorides given in (b).
....................................................................................................................................................
.............................................................................................................................................. [1]
(d) Use data from the Data Booklet to explain why an aqueous solution of SnCl 2 reacts with Cl 2(g)
but an aqueous solution of PbCl 2 does not.
Write an equation for the reaction.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [3]
(e)
e)
State the relationship between the Faraday constant and the Avogadro constant.
....................................................................................................................................... [1]
(ii)
When a current of 1.2 A was passed through dilute sulfuric acid for 30 minutes, it was
found that 130 cm3 of oxygen, measured at 25 °C and 1 atm, was collected at the anode.
The following reaction takes place.
2H2O(l) → 4H+(aq) + O2(g) + 4e–
Use these data and data from the Data Booklet to calculate a value for the Avogadro
constant, L, by calculating
•
•
•
•
•
the number of moles of oxygen produced,
the number of moles of electrons needed for this,
the number of coulombs passed,
the number of electrons passed,
the number of electrons in one mole of electrons (L).
L = ............................................... mol–1
[4]
[Total: 15]
2
Chile saltpetre is a mineral found in Chile and Peru, and which mainly consists of sodium
nitrate, NaNO3. The mineral is purified to concentrate the NaNO3 which is used as a fertiliser
and in some fireworks.
In order to find the purity of a sample of sodium nitrate, the compound is heated in NaOH(aq)
with Devarda's alloy which contains aluminium. This reduces the sodium nitrate to ammonia
which is boiled off and then dissolved in acid.
3NaNO3(aq) + 8Al (s) + 5NaOH(aq) + 18H2O(l) → 3NH3(g) + 8NaAl (OH)4(aq)
The ammonia gas produced is dissolved in an excess of H2SO4 of known concentration.
2NH3 + H2SO4 → (NH4)2SO4
The amount of unreacted H2SO4 is then determined by back-titration with NaOH of known
concentration.
H2SO4 + 2NaOH → Na2SO4 + 2H2O
(a) A 1.64 g sample of impure NaNO3 was reacted with an excess of Devarda's alloy.
The NH3 produced was dissolved in 25.0 cm3 of 1.00 mol dm–3 H2SO4.
When all of the NH3 had dissolved, the resulting solution was titrated with NaOH(aq).
For neutralisation, 16.2 cm3 of 2.00 mol dm–3 NaOH were required.
(i) Calculate the amount, in moles, of H2SO4 present in the 25.0 cm3 of 1.00 mol dm–3
H2SO4.
(ii) Calculate the amount, in moles, of NaOH present in 16.2 cm3 of 2.00 mol dm–3 NaOH.
(iii) Use your answer to (ii) to calculate the amount, in moles, of H2SO4 that reacted with
16.2 cm3 of 2.00 mol dm–3 NaOH.
(iv) Use your answers to (i) and (iii) to calculate the amount, in moles, of H2SO4 that
reacted with the NH3.
(v) Use your answer to (iv) to calculate the amount, in moles, of NH3 that reacted with
the H2SO4.
(vi) Use your answer to (v) to calculate the amount, in moles, of NaNO3 that reacted with
the Devarda's alloy.
(vii) Hence calculate the mass of NaNO3 that reacted.
(viii) Use your answer to (vii) to calculate the percentage by mass of NaNO3 present in
the impure sample.
Write your answer to a suitable number of significant figures.
[9]
(b) The above reaction is an example of a redox reaction.
What are the oxidation numbers of nitrogen in NaNO3 and in NH3?
NaNO3 .......................
NH3 .......................
[1]
[Total: 10]
3
When 0.42 g of a gaseous hydrocarbon A is slowly passed over a large quantity of heated
copper(II) oxide, CuO, A is completely oxidised.
The products are collected and it is found that 1.32 g of CO2 and 0.54 g of H2O are formed.
Copper is the only other product of the reaction.
(a) (i)
Calculate the mass of carbon present in 1.32 g of CO2.
Use this value to calculate the amount, in moles, of carbon atoms present in 0.42 g
of A.
(ii)
Calculate the mass of hydrogen present in 0.54 g of H2O.
Use this value to calculate the amount, in moles, of hydrogen atoms present in
0.42 g of A.
(iii)
It is thought that A is an alkene rather than an alkane.
Use your answers to (i) and (ii) to deduce whether this is correct.
Explain your answer.
..................................................................................................................................
............................................................................................................................. [5]
(b) Analysis of another organic compound, B, gave the following composition by mass:
C, 64.86%; H, 13.50%, O, 21.64%.
(i)
Use these values to calculate the empirical formula of B.
(ii)
The empirical and molecular formulae of B are the same.
B is found to be chiral.
Draw displayed formulae of the two optical isomers of this compound, indicating
with an asterisk (*) the chiral carbon atom.
(iii)
There are three other structural isomers of B which are not chiral but which contain
the same functional group as B.
In the boxes below, draw the structural formulae of these isomers.
[7]
[Total: 12]
4
(a) Chemists recognise that atoms are made of three types of particle.
Complete the following table with their names and properties.
name of particle
relative mass
relative charge
0
1/1836
[3]
(b) The relative atomic mass of an element can be determined using data from its mass spectrum.
The mass spectrum of element X is shown, with the percentage abundance of each isotope
labelled.
60
49.61
50
40
percentage
abundance
30
23.77
20
9.37
10
8.73
7.63
0.89
0
73
74
75
76
77
78
79
80
81
82
83
m/e
(i)
Define the terms relative atomic mass and isotope.
relative atomic mass ...........................................................................................................
.............................................................................................................................................
.............................................................................................................................................
isotope ................................................................................................................................
.............................................................................................................................................
[3]
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(ii)
Use the data in the mass spectrum to calculate the relative atomic mass, Ar, of X.
Give your answer to two decimal places and suggest the identity of X.
Ar of X ....................................
(c)
identity of X ....................................
The element tellurium, Te, reacts with chlorine to form a single solid product, with a relative
[2]
formula mass of 270. The product contains 52.6% chlorine by mass.
(i)
Calculate the molecular formula of this chloride.
molecular formula .................................... [3]
(ii)
This chloride melts at 224 °C and reacts vigorously with water.
State the type of bonding and structure present in this chloride and explain your reasoning.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(iii)
Suggest an equation for the reaction of this chloride with water.
....................................................................................................................................... [1]
(d) Sodium and silicon also react directly with chlorine to produce the chlorides shown.
point / °C
difference between the
electronegativities of the elements
NaCl
801
2.2
SiCl 4
–69
1.3
chloride
melting
(i) Describe what you would see during the reaction between sodium and chlorine.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Explain the differences between the melting points of these two chlorides in terms of their
structure and bonding. You should refer to the difference between the electronegativities
of the elements in your answer.
NaCl structure and bonding ...............................................................................................
.............................................................................................................................................
SiCl 4 structure and bonding ................................................................................................
.............................................................................................................................................
explanation .........................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
[Total: 20]
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Atoms, Molecules &
Stoichiometry
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 2
Time Allowed:
62 minutes
Score:
/51
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
(b) (i)
the amount of substance containing 6(.02) x 1023 (fundamental)
particles of that substance (or; the amount of substance
containing as many particles as there are atoms in 12 g of
carbon-12)
(1)
2NaOH + CO2 Na2CO3 + H2O
(1)
1)
[1]
allow ionic equations or formation of NaHCO3
(ii)
95 – 75 = 20 cm3
(1)
[1]
(iii)
excess oxygen = 75 cm3 so used = 25 cm3
(1)
[1]
(iv)
2CxHy + 5O2 4CO2 + zH2O
(2)
[2]
(v)
x = 2; y = 2; z = 2 (or z = 1 if CxHy + 2.5O2 2CO2 + zH2O)
(1+1+1)
[3]
(c) (i)
(ii)
W = (CH3)2C=CH2 = 2–methylpropene
(1)
X = (CH3)2CBrCH3 = 2–bromo–2–methylpropane
(1)
Y = (CH3)2CHCH2Br = 1–bromo–2–methylpropane
(1)
Z = (CH3)3COH = 2–methylpropan–2–ol
(1)
Markovnikov addition / H adds to C with most Hs
(1)
tertiary carbocation more stable than primary
(1)
inductive effect of three alkyl groups owtte
(1)
Total
ot
[4]
[Max 2]
Question
Questi
2
(a
Scheme
Marks
TPUBM
increasing distance of (outer) electron(s) from nucleus
OR increasing distance of outer / valence shell from nucleus
1
increased shielding / screening (from inner shells)
1
reduces attraction
1
(3rd electron for each in) inner / lower energy level / shell / closer to nucleus
(than first two) / less shielding
1
(large) increase in nuclear attraction
1
[2]
(1s2 2s2 2p6) 3s2 3p6 3d10 4s2 4p6 5s2
1
[1
(ii)
four isotopes owtte
1
[1
(iii)
(84 × 0.56) + (86 × 9.86) + (87 × 7) + (88 × 82.58)
100
= 87.7 (must be 3 sig figs)
1
1
[2]
(a species that) gains / takes electron(s)
1
[1
(i)
(ii)
(b) (i)
(c) (i)
[3]
Question
Questi
(ii)
Scheme
Marks
M
arks
Ba
Cl
O
45.1
137
23.4
35.5
31.5
16
0.329
0.329
0.659
0.329
1.969
0.329
1.00
2.00
5.98 / 6
emp form = BaCl2O6
Total
1
1
1
[3]
X = Mg(OH)2
Y = MgO
Z = Mg(NO3)2
1
1
1
[3]
reagent = nitric acid
1
MgO + 2HNO3 → Mg(NO3)2 + H2O
1
[2]
(iii)
Heat / thermal decomposition
1
[1
(iv)
Mg + 2H2O → Mg(OH)2 + H2
1
2Mg(NO3)2 → 2MgO + 4NO2 + O2
1
(d) (i)
(ii)
[2]
[21]
3
(a
(i) structural or functional group isomerism
(1)
(ii)
i
primary alcohol and carboxylic acid – not ‘acid’
S primary alcohol and ester
T primary alcohol and ester
(1)
(1)
(1)
(iii)
iii)
Na2CO3
carboxylic acid
(1)
(iv)
iv) w
Na
alcohol and carboxylic acid
(b)
b) (
n(CO2) =
24.0
= 0.001 mol
24000
(ii) 0.002 mol of Q → 0.001 mol of CO2
1 mol of Q → 0.5 mol of CO2
(c)
c) (
n(H2) =
48.0
= 0.002 mol
24000
(ii) 0.002 mol of Q → 0.002 mol of H2
1 mol of Q → 1 mol of H2
(d)
d)
is isomer R
(1)
[6]
(1)
(1)
[2]
(1)
(1)
[2]
(1)
with sodium carbonate
2HOCH2CH2CO2H + Na2CO3 → 2 HOCH2CH2CO2Na + H2O + CO2
correct products
balanced
(1)
(1)
with sodium metal
HOCH2CH2CO2H + 2Na → NaOCH2CH2CO2Na + H2
correct products
balanced
(1)
(1)
1)
[Total: 15]
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Atoms, Molecules &
Stoichiometry
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 2
Time Allowed:
62 minutes
Score:
/51
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Define the term mole.
....................................................................................................................................................
.............................................................................................................................................. [1]
(b) 10 cm3 of a gaseous hydrocarbon, CxHy, was reacted with 100 cm3 of oxygen gas, an excess.
The final volume of the gaseous mixture was 95 cm3.
This gaseous mixture was treated with concentrated, aqueous sodium hydroxide to absorb the
carbon dioxide present. This reduced the gas volume to 75 cm3.
All gas volumes were measured at 298 K and 100 kPa.
(i) Write an equation for the reaction between sodium hydroxide and carbon dioxide.
....................................................................................................................................... [1]
(ii) Calculate the volume of carbon dioxide produced by the combustion of the hydrocarbon.
volume of CO2 produced = ................. cm3 [1]
(iii) Calculate the volume of oxygen used up in the reaction with the hydrocarbon.
volume of O2 used = ................. cm3 [1]
(iv) Use your answers to (b)(ii) and (b)(iii), together with the initial volume of hydrocarbon, to
balance the equation below.
............CxHy + ............O2  ............CO2 + zH2O
[2
(v) Deduce the values of x, y and z in the equation in (iv).
x = .............................
y = .............................
z = .............................
[3]
(c) Another hydrocarbon, W, with the formula C4H8, reacts with hydrogen bromide, HBr, to give
two products X and Y. X and Y are structural isomers of molecular formula C4H9Br.
Reaction of X with aqueous alkali produces an alcohol, Z, that has no reaction with acidified
dichromate(VI).
(i) Give the structures and names of the compounds W, X, Y, and Z
W
........................................................
........................................................
Y
........................................................
........................................................
[4]
(ii) When W reacts with hydrogen bromide, more X than Y is produced. Explain why.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
[Total: 15]
2
(a) Successive ionisation energies for the elements magnesium to barium are given in the table.
element
1st ionisation
2nd ionisation
3rd ionisation
energy / kJ mol–1 energy / kJ mol–1 energy / kJ mol–1
Mg
736
1450
7740
Ca
590
1150
4940
Sr
548
1060
4120
Ba
502
966
3390
(i) Explain why the first ionisation energies decrease down the group.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Explain why, for each element, there is a large increase between the 2nd and 3rd ionisation
energies.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(b) A sample of strontium, atomic number 38, gave the mass spectrum shown. The percentage
abundances are given above each peak.
100
82.58
percentage
abundance
9.86 7.00
0.56
0
80
81
82
83
84
85
86
atomic mass units
87
88
89
90
(i) Complete the full electronic configuration of strontium.
1s2 2s2 2p6 ................................................................................................................... [1]
(ii) Explain why there are four different peaks in the mass spectrum of strontium.
.............................................................................................................................................
....................................................................................................................................... [1]
(iii) Calculate the atomic mass, Ar, of this sample of strontium.
Give your answer to three significant figures.
Ar = ............................. [2]
(c) A compound of barium, A, is used in fireworks as an oxidising agent and to produce a green
colour.
(i) Explain, in terms of electron transfer, what is meant by the term oxidising agent.
.............................................................................................................................................
....................................................................................................................................... [1]
(ii) A has the following percentage composition by mass: Ba, 45.1; Cl , 23.4; O, 31.5.
Calculate the empirical formula of A.
empirical formula of A ........................................... [3]
(d) Some reactions involving magnesium and its compounds are shown in the reaction scheme
below.
X(aq)
water
Mg(s)
HNO3(aq)
steam
reaction
1
Z(aq)
Y(s)
reaction
2
Z(s)
(i) Give the formulae of the compounds X, Y and Z.
X .........................................................................................................................................
Y .........................................................................................................................................
Z .........................................................................................................................................
[3]
(ii) Name the reagent needed to convert Y(s) into Z(aq) in reaction 1 and write an equation for
the reaction.
reagent ...............................................................................................................................
equation ..............................................................................................................................
[2]
(iii) How would you convert a sample of Z(s) into Y(s) in reaction 2?
....................................................................................................................................... [1]
(iv) Give equations for the conversions of Mg into X, and Z(s) into Y.
Mg to X ...............................................................................................................................
Z to Y ..................................................................................................................................
[2]
[Total: 21]
3
Compound Q is a viscous liquid which is very soluble in water.
The Mr of Q is 90.0.
Three possible structures for Q are shown below.
R
S
T
HOCH2CH2CO2H
HOCH2CO2CH3
HCO2CH2CH2OH
(a) (i) What type of isomerism do R, S and T show?
............................................................
(ii) What oxygen-containing functional groups are present in R, S and T?
Give their full names.
R ........................................................... and ...........................................................
S ........................................................... and ...........................................................
T ........................................................... and ...........................................................
(iii) Which functional group(s) in (ii) will react with sodium carbonate?
....................................................................................................................................
(iv) Which functional group(s) in (ii) will react with sodium metal?
....................................................................................................................................
[6]
(b) When 0.002 mol of Q is reacted with an excess of solid sodium carbonate, Na2CO3,
24 cm3 of carbon dioxide, measured at room temperature and pressure, is produced.
(i) Calculate the amount, in moles, of carbon dioxide produced in this reaction.
(ii) Hence calculate the amount, in moles, of carbon dioxide produced by 1 mol of Q.
[2]
When 0.002 mol of Q is reacted with an excess of metallic sodium, 48 cm3 of hydrogen,
measured at room temperature and pressure, is produced.
(c) (i) Calculate the amount, in moles, of hydrogen molecules produced in this reaction.
(ii) Hence calculate the amount, in moles, of hydrogen molecules produced by 1 mol of Q.
[2]
(d) Use your answers to (b) and (c) to deduce which structure, R, S or T, corresponds to the
structure of Q and write balanced equations for the reactions that occurred.
identity of Q is .........
equation for reaction with sodium carbonate
...........................................................................................................................................
equation for reaction with sodium metal
..................................................................................................................................... [5]
[Total: 15]
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Atoms, Molecules &
Stoichiometry
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 3
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) mass of C = 12 × 0.352 = 0.096g
44
n(C) = 0.096 = 0.008
12
(ii) mass of H = 2 × 0.144 = 0.016g
18
n(H) = 0.016 = 0.016
1
(iii) mass of oxygen = 0.240 – (0.096 + 0.016) = 0.128g
n(O) = 0.128 = 0.008
16
(1)
(1)
(1)
(1)
(1)
(1)
allow ecf at any stage
[6]
(b) C : H : O = 0.008: 0.016 : 0.008 = 1:2:1
allow C : H : O = 0.096 : 0.016 : 0.128 = 1:2:1
12
1
16
gives C H2O
(c) (i) Mr = mRT
pV
(1
=
0.148 x 8.31 x 333
1.01 x 105 x 67.7 x 10–6
[1]
(1)
= 59.89
allow 59.9 or 60
(ii) C2H4O2
(1)
(1)
(d) CH3CO2H
(1)
HCO2CH3
(1)
1)
(e) the only products of the reaction are the two oxides H2O and CO2 and copper
(1)
[3]
[1]
[Total: 13]
2
(a) Cr3+:
Mn2+:
1 22s22p6 3s2 3p6 3d3
1 22s22p6 3s2 3p6 3d5
[1]
[1]
[2]
(b) (i) Any two from
• H+ is on the oxidant/L.H. side of each of the ½-equations, or H+ is a reactant
• (increasing [H+]) will make Eo more positive
• (increasing [H+]) will drive the reaction over to the R.H./reductant side or forward
direction
[1] +
(ii) KMnO4:
K2Cr2O7
Purple/violet to colourless (allow very pale pink)
Orange to green
[1]
[1]
[4]
(c) (i) MnO2 + SO2 → MnSO4 (or Mn2+ + SO42–)
[1
manganese changes/is reduced from +4 to +2
sulfur changes/is oxidised from +4 to +6
[1]
[1]
(ii) No effect, because H+ does not appear in the overall equation or its effect on the
MnO2/Mn2+ change is cancelled out by its effect on the SO2/SO42– change
[1]
[4]
(d) (i) MnO2 + 4H+ + Sn2+ → Mn2+ + 2H2O + Sn4+
(ii) n(MnO4–) = 0.02 × 18.1/1000 = 3.62 × 10–4 mol
n(Sn2+) = 3.62 × 10–4 × 5/2 = 9.05 × 10–4 mol
n(Sn2+) that reacted with MnO2 = (20 – 9.05) × 10–4 = 1.095 × 10–3 mol
reaction is 1:1, so this is also n(MnO2)
mass of MnO2 = 1.095 × 10–3 × (54.9+16+16) = 0.0952 g
⇒ 95% – 96%; 2 or more s.f.
[1]
[1]
[1]
[1]
[1]
[1]
[6]
[Total: 16]
3
(a
the actual number of atoms of each element present (1)
in one molecule of a compound (1)
y

(b) CХHУ +  x +  O2
4

xCO2 +
[2]
y
H2O
2
xCO2 (1)
y
H2O (1)
2
(c)
c) (
[2]
oxygen/O2 (1)
(ii) carbon dioxide/CO2 (1)
(iii) 10 cm3 (1)
(iv) 20 cm3 (1)
(d) CХHУ +
10 cm3
[4]
y

 x +  O2
4

20 cm3
xCO2 +
10 cm3
y
H2O
2
1 mol of CxHy gives 1 mol of CO2
whence x = 1 (1)
1 mol of CxHy reacts with 2 mol of O2
whence
and
y

x + 
4

= 2
y = 4 (1)
molecular formula is CH4 (1)
[3]
[Total: 11]
4
(a
Al 1s2 2s22p6 3s23p1
Ti
(1)
1s2 2s22p6 3s2 3p6 3d2 4s2 or
1s2 2s22p6 3s2 3p6 4s23d2 penalise any error
(1)
(b) (i) pass chlorine gas
over heated aluminium
[2]
(1)
(1)
(ii) aluminium glows
white/yellow solid formed
chlorine colour disappears/fades
(1)
(1)
(1) (any 2)
(iii)
x x
x
x
x x
x
x
Cl
•
x
x x
x
x
Cl
x •
Al
• x
Cl
x
x
x x
x
x
x
x
Cl
x •
Al
• x
x x
x
x
Cl
x
x
x x
x
•
Cl
x
x x
x
x
x x
correct numbers of electrons, i.e.
3 • per Al atom and 7x per Cl atom
i.e. 6 • and 42 x in total
(1)
dative bond Cl to Al clearly shown by xx
(1)
[6]
(c) chlorine is a strong/powerful oxidising agent
(1)
[1]
(d) (i) n(Ti) = 0.72 = 0.015
47.9
(ii) n(Cl) = (2.85 – 0.72) = 0.06
35.5
(iii) 0.015 : 0.06 = 1:4
empirical formula of A is TiCl4
Allow ecf on answers to (i) and/or (ii).
(iv) Ti + 2Cl2 → TiCl4
Allow ecf on answers to (iii).
(e) covalent/not ionic
simple molecular or
mention of weak intermolecular forces or
weak van der Waals’s forces between molecules
(1)
(1)
(1)
(1)
[4]
(1)
(1)
[2]
[Total: 14 max]
5
(a
same proton no./atomic no./no. of protons
different mass no./nucleon no./no. of neutrons
(1)
(1)
[2]
(b)
isotope
sotope
56
Fe
59
Co
number of
neutrons
p
26
6
27
7
(1)
electrons
(1)
(1)
give one mark for each correct column
allow (1) if no column is correct but one row is correct
(c)
c)
weighted mean/average mass
of an atom (not element)
compared with 12C
one atom of 12C has a mass of exactly 12
[relative to 1/12th the mass of a 12C atom would get 2]
[3]
(1)
(1)
(1)
or
mass of 1 mol of atoms
compared with 12C
1 mol of 12C has a mass of 12 g
(ii) Ar = 54 x 5.84 + 56 x 91.68 + 57 x 2.17
100
= 5573.13 = 55.7 to 3 sf
100
allow 55.9 if Ar is calculated using 99.69 instead of 100
(1)
(1)
(1)
(1)
(1)
[5]
[Total: 10]
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Atoms, Molecules &
Stoichiometry
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 3
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Compound A is an organic compound which contains carbon, hydrogen and oxygen.
When 0.240 g of the vapour of A is slowly passed over a large quantity of heated copper(II)
oxide, CuO, the organic compound A is completely oxidised to carbon dioxide and water.
Copper is the only other product of the reaction.
The products are collected and it is found that 0.352 g of CO2 and 0.144 g of H2O are
formed.
(a) In this section, give your answers to three decimal places.
(i)
Calculate the mass of carbon present in 0.352 g of CO2.
Use this value to calculate the amount, in moles, of carbon atoms present in 0.240 g
of A.
(ii)
Calculate the mass of hydrogen present in 0.144 g of H2O.
Use this value to calculate the amount, in moles, of hydrogen atoms present in 0.240 g
of A.
(iii)
Use your answers to calculate the mass of oxygen present in 0.240 g of A.
Use this value to calculate the amount, in moles, of oxygen atoms present in 0.240 g
of A.
[6]
(b)
Use your answers to (a) to calculate the empirical formula of A.
[1]
(c) When a 0.148 g sample of A was vapourised at 60oC, the vapour occupied a volume of
67.7 cm3 at a pressure of 101 kPa.
(i)
Use the general gas equation pV = nRT to calculate Mr of A.
Mr =......................
(ii)
Hence calculate the molecular formula of A.
[3]
(d) Compound A is a liquid which does not react with 2,4-dinitrophenylhydrazine reagent or
with aqueous bromine.
Suggest two structural formulae for A.
[2]
(e) Compound A contains only carbon, hydrogen and oxygen.
Explain how the information on the opposite page about the reaction of A with CuO
confirms this statement.
..........................................................................................................................................
................................................................................................................................... [1]
[Total: 13]
2
(a) Complete the electronic configurations of the following ions.
Cr3+:
1s22s22p6..........................................
Mn2+:
1s22s22p6..........................................
[2]
(b) Both KMnO4 and K2Cr2O7 are used as oxidising agents, usually in acidic solution.
(i)
Use information from the Data Booklet to explain why their oxidising power increases
as the [H+(aq)] in the solution increases.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
What colour changes would you observe when each of these oxidising agents is
completely reduced?
•
•
KMnO4
K2Cr2O7
from .......................................
to ....................................
from........................................
to .....................................
[4]
(c) Manganese(IV) oxide, MnO2, is a dark brown solid, insoluble in water and dilute acids.
Passing a stream of SO2(g) through a suspension of MnO2 in water does, however,
cause it to dissolve, to give a colourless solution.
(i)
Use the Data Booklet to suggest an equation for this reaction, and explain what
happens to the oxidation states of manganese and of sulfur during the reaction.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
The pH of the suspension of MnO2 is reduced.
Explain what effect, if any, this would have on the extent of this reaction.
..................................................................................................................................
..................................................................................................................................
[4]
(d) The main ore of manganese, pyrolusite, is mainly MnO2. A solution of SnCl2 can be used
to estimate the percentage of MnO2 in a sample of pyrolusite, using the following method.
•
A known mass of pyrolusite is warmed with an acidified solution containing a known
amount of SnCl2.
•
The excess Sn2+(aq) ions are titrated with a standard solution of KMnO4.
In one such experiment, 0.100 g of pyrolusite was warmed with an acidified solution
containing 2.00 × 10–3 mol Sn2+. After the reaction was complete, the mixture was
titrated with 0.0200 mol dm–3 KMnO4, and required 18.1 cm3 of this solution to reach the
end point.
The equation for the reaction between Sn2+(aq) and MnO4–(aq) is as follows.
2MnO4– + 5Sn2+ + 16H+
(i)
2Mn2+ + 5Sn4+ + 8H2O
Use the Data Booklet to construct an equation for the reaction between MnO2 and
Sn2+ ions in acidic solution.
..................................................................................................................................
(ii)
Calculate the percentage of MnO2 in this sample of pyrolusite by the following steps.
•
number of moles of MnO4– used in the titration
•
number of moles of Sn2+ this MnO4– reacted with
•
number of moles of Sn2+ that reacted with the 0.100 g sample of pyrolusite
•
number of moles of MnO2 in 0.100 g pyrolusite. Use your equation in (i).
•
mass of MnO2 in 0.100 g pyrolusite
•
percentage of MnO2 in pyrolusite
percentage = ..................................................%
[6]
[Total: 16]
3
In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A,
from the ground near Florence in Italy.
They analysed A which they found to be a hydrocarbon. Further experiments were then
carried out to determine the molecular formula of A.
(a) What is meant by the term molecular formula?
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and
analysing the products of combustion.
(b) Complete and balance the following equation for the complete combustion of a
hydrocarbon with the formula CxHy .
(
CxHy + x +
)
y
O
4 2
................................ + ................................
[2]
(c) When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess)
and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperature
and pressure.
When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide,
KOH, 30 cm3 of gas still remained.
(i)
What is the identity of the 30 cm3 of gas that remained at the end of the
experiment?
...................................................
(ii)
The combustion of A produced a gas that reacted with the KOH(aq).
What is the identity of this gas?
...................................................
(iii)
What volume of the gas you have identified in (ii) was produced by the combustion
of A?
...............................cm3
(iv)
What volume of oxygen was used up in the combustion of A?
...............................cm3
[4]
(d) Use your equation in (b) and your results from (c)(iii) and (c)(iv) to calculate the
molecular formula of A.
Show all of your working.
[3]
[Total: 11]
4
Copper and titanium are each used with aluminium to make alloys which are light, strong
and resistant to corrosion.
Aluminium, Al, is in the third period of the Periodic Table; copper and titanium are both
transition elements.
(a) Complete the electronic configuration of aluminium and of titanium, proton number 22.
Al
1s2
Ti
1s2
[1]
Aluminium reacts with chlorine.
(b) (i)
Outline how, starting from aluminium powder, this reaction could be carried out
in a school or college laboratory to give a small sample of aluminium chloride. A
diagram is not necessary.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Describe what you would see during this reaction.
..................................................................................................................................
..................................................................................................................................
(iii)
At low temperatures, aluminium chloride vapour has the formula Al2Cl6.
Draw a ‘dot-and-cross’ diagram to show the bonding in Al2Cl6.
Show outer electrons only.
Represent the aluminium electrons by z.
Represent the chlorine electrons by x.
[6]
Copper forms two chlorides, CuCl and CuCl2.
(c) When copper is reacted directly with chlorine, only CuCl2 is formed.
Suggest an explanation for this observation.
..........................................................................................................................................
..................................................................................................................................... [1]
Titanium also reacts with chlorine.
(d) When an excess of chlorine was reacted with 0.72 g of titanium, 2.85 g of a chloride A
was formed.
(i)
Calculate the amount, in moles, of titanium used.
(ii)
Calculate the amount, in moles, of chlorine atoms that reacted.
(iii)
Hence, determine the empirical formula of A.
(iv)
Construct a balanced equation for the reaction between titanium and chlorine.
..................................................................................................................................
[4]
(e) At room temperature, the chloride of titanium, A, is a liquid which does not conduct
electricity.
What does this information suggest about the bonding and structure in A?
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
[Total: 14]
5
Iron and cobalt are adjacent elements in the Periodic Table. Iron has three
main occurring isotopes, cobalt has one.
naturally
(a) Explain the meaning of the term isotope.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(b) The most common isotope of iron is 56Fe; the only naturally occurring isotope of cobalt
is 59Co.
Use the Data Booklet to complete the table below to show the atomic structure of 56Fe
and of 59Co.
number of
isotope
protons
neutrons
electrons
56Fe
59Co
[3]
(c) A sample of iron has the following isotopic composition by mass.
isotope mass
54
56
57
% by mass
5.84
91.68
2.17
(i) Define the term relative atomic mass.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii) By using the data above, calculate the relative atomic mass of iron to three
significant figures.
[5]
[Total: 10]
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Atoms, Molecules &
Stoichiometry
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper
Time Allowed:
69 minutes
Score:
/57
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Use of the Data Booklet is relevant to this question.
1.00 g of carbon is combusted in a limited supply of pure oxygen. 0.50 g of the carbon combusts
to form CO2 and 0.50 g of the carbon combusts to form CO.
The resultant mixture of CO2 and CO is passed through excess NaOH(aq) and the remaining gas
is then dried and collected.
What is the volume of the remaining gas? (All gas volumes are measured at 25 °C and
1 atmosphere pressure.)
A
2
1 dm3
B
1.5 dm3
C
2 dm3
D
3 dm3
The shell of a chicken’s egg makes up 5% of the mass of an average egg. An average egg has a
mass of 50 g.
Assume the egg shell is pure calcium carbonate.
How many complete chicken’s egg shells would be needed to neutralise 50 cm3 of 2.0 mol dm–3
ethanoic acid?
A
1
B
2
C
3
D
4
3 Use of the Data Booklet is relevant to this question.
A chemist took 2.00 dm3 of nitrogen gas, measured under room conditions, and reacted it with a
large volume of hydrogen gas, in order to produce ammonia. Only 15.0% of the nitrogen gas
reacted to produce ammonia.
What mass of ammonia was formed?
A
0.213 g
B
0.425 g
C
1.42 g
D
2.83 g
4 Use of the Data Booklet is relevant to this question.
In an experiment, 0.125 mol of chlorine gas, Cl 2, is reacted with an excess of cold aqueous
sodium hydroxide. One of the products is a compound of sodium, oxygen, and chlorine.
Which mass of this product is formed?
A
9.31 g
B
13.3 g
C
18.6 g
D
26.6 g
D
C12H12N2
5 The diagram shows the skeletal formula of phenazine.
N
N
phenazine
What is the empirical formula of phenazine?
A
C6H4N
B
C6H6N
C
C12H8N2
6 Use of the Data Booklet is relevant to this question.
In an experiment, 0.6 mol of chlorine gas, Cl 2, is reacted with an excess of hot aqueous sodium
hydroxide. One of the products is a compound of sodium, oxygen and chlorine.
Which mass of this product is formed?
A
21.3 g
B
44.7 g
C
63.9 g
D
128 g
7 Use of the Data Booklet is relevant to this question.
A sample of potassium oxide, K2O, is dissolved in 250 cm3 of distilled water. 25.0 cm3 of this
solution is titrated against sulfuric acid of concentration 2.00 mol dm–3. 15.0 cm3 of this sulfuric
acid is needed for complete neutralisation.
Which mass of potassium oxide was originally dissolved in 250 cm3 of distilled water?
A
8
2.83 g
B
28.3 g
C
47.1 g
D
56.6 g
Use of the Data Booklet is relevant to this question.
Ferrochrome is an alloy of iron and chromium. Ferrochrome can be dissolved in dilute sulfuric
acid to produce a mixture of FeSO4 and Cr2(SO4)3. The FeSO4 reacts with K2Cr2O7 in acid
solution according to the following equation.
14H+ + 6Fe2+ + Cr2O72– → 2Cr3+ + 6Fe3+ + 7H2O
When 1.00 g of ferrochrome is dissolved in dilute sulfuric acid, and the resulting solution titrated,
13.1 cm3 of 0.100 mol dm–3 K2Cr2O7 is required for complete reaction.
What is the percentage by mass of Fe in the sample of ferrochrome?
A
9
1.22
B
4.39
C
12.2
D
43.9
A mixture of 10 cm3 of methane and 10 cm3 of ethane was sparked with an excess of oxygen.
After cooling to room temperature, the residual gas was passed through aqueous potassium
hydroxide.
All gas volumes were measured at the same temperature and pressure.
What volume of gas was absorbed by the alkali?
A
15 cm3
B
20 cm3
C
30 cm3
D
40 cm3
10 A solution of Sn2+ ions will reduce an acidified solution of MnO4– ions to Mn2+ ions. The Sn2+ ions
are oxidised to Sn4+ ions in this reaction.
How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is
added to an excess of acidified KMnO4 solution?
A
0.010
B
C
0.020
0.050
D
0.125
11 Use of the Data Booklet is relevant to this question.
Magnesium nitrate, Mg(NO3)2, will decompose when heated to give a white solid and a mixture of
gases. One of the gases released is an oxide of nitrogen, X.
7.4 g of anhydrous magnesium nitrate is heated until no further reaction takes place.
What mass of X is produced?
A
1.5 g
B
C
2.3 g
3.0 g
D
4.6 g
12 Use of the Data Booklet is relevant to this question.
A washing powder contains sodium hydrogencarbonate, NaHCO3, as one of the ingredients. In a
titration, a solution containing 1.00 g of washing powder requires 7.15 cm3 of 0.100 mol dm–3
sulfuric acid for complete reaction. The sodium hydrogencarbonate is the only ingredient that
reacts with the acid.
What is the percentage by mass of sodium hydrogencarbonate in the washing powder?
A
3.0
B
C
6.0
12.0
D
24.0
13 How many moles of hydrogen, H2, are evolved when an excess of sodium metal is added to one
mole of citric acid?
CO2H
HO
CH2CO2H
C
CH2CO2H
citric acid
A
1
B
2
C
3
D
4
14 Use of the Data Booklet is relevant to this question.
Which sodium compound contains 74.2 % by mass of sodium?
A
sodium carbonate
B
sodium chloride
C
sodium hydroxide
D
sodium oxide
15 Use of the Data Booklet is relevant to this question.
Which calcium compound contains 54.1 % by mass of calcium?
A
calcium hydroxide
B
calcium nitrate
C
calcium oxide
D
calcium sulfate
16 Use of the Data Booklet is relevant to this question.
The reaction between aluminium powder and anhydrous barium nitrate is used as the propellant
in some fireworks. The reaction produces the metal oxides and nitrogen.
10Al + 3Ba(NO3)2 → 5Al 2O3 + 3BaO + 3N2
Which mass of barium oxide is produced when 5.40 g of aluminium powder reacts with an excess
of anhydrous barium nitrate?
A
1.62 g
B
3.06 g
C
9.18 g
D
10.2 g
17 Use of the Data Booklet is relevant to this question.
The reaction between aluminium powder and anhydrous barium nitrate is used as the propellant
in some fireworks. The metal oxides and nitrogen are the only products.
Which volume of nitrogen, measured under room conditions, is produced when 0.783 g of
anhydrous barium nitrate reacts with an excess of aluminium?
A
46.8 cm3
B
72.0 cm3
C
93.6 cm3
D
144 cm3
18 Use of the Data Booklet is relevant to this question.
A sample of ethyl propanoate is hydrolysed by heating under reflux with aqueous sodium
hydroxide. The two organic products of the hydrolysis are separated, purified and weighed.
Out of the total mass of products obtained, what is the percentage by mass of each product?
A
32.4 % and 67.6 %
B
38.3 % and 61.7 %
C
42.3 % and 57.7 %
D
50.0 % and 50.0 %
19 Use of the Data Booklet is relevant to this question.
The volume of a sample of ammonia is measured at a temperature of 60 °C and a pressure of
103 kPa. The volume measured is 5.37 × 10–3 m3.
What is the mass of the sample of ammonia, given to two significant figures?
A
0.00019 g
B
0.0034 g
C
0.19 g
D
3.4 g
20 Use of the Data Booklet is relevant to this question.
The nitrates of beryllium, calcium, magnesium, and strontium all decompose in the same way
when heated. When 2.00 g of one of these anhydrous nitrates is decomposed, 1.32 g of gas is
produced.
What is the nitrate?
A
beryllium nitrate
B
calcium nitrate
C
magnesium nitrate
D
strontium nitrate
21 Use of the Data Booklet is relevant to this question.
1.15 g of a metallic element reacts with 300 cm3 of oxygen at 298 K and 1 atm pressure, to form
an oxide which contains O2– ions.
What could be the identity of the metal?
A
calcium
B
magnesium
C
potassium
D
sodium
22 0.02 mol of aluminium is burned in oxygen and the product is reacted with 2.00 mol dm–3
hydrochloric acid.
What minimum volume of acid will be required for complete reaction?
A
15 cm3
B
20 cm3
C
30 cm3
D
60 cm3
23 0.144 g of an aluminium compound X react with an excess of water, to produce a gas. This gas
burns completely in O2 to form H2O and 72 cm3 of CO2 only. The volume of CO2 was measured at
room temperature and pressure.
What could be the formula of X?
[C = 12.0, Al = 27.0; 1 mole of any gas occupies 24 dm3 at room temperature and pressure]
A
Al 2C3
B
Al 3C4
C
Al 4C3
D
Al 5C3
24 Use of the Data Booklet is relevant to this question.
Lead(IV) chloride will oxidise bromide ions to bromine. The Pb4+ ions are reduced to Pb2+ ions in
this reaction.
If 6.980 g of lead(IV) chloride is added to an excess of sodium bromide solution, what mass of
bromine would be produced?
A
0.799 g
B
1.598 g
C
3.196 g
D
6.392 g
25 Use of the Data Booklet is relevant to this question.
2.76 g of ethanol were mixed with an excess of aqueous acidified potassium dichromate(VI). The
reaction mixture was then boiled under reflux for one hour. The organic product was then
collected by distillation.
The yield of product was 75.0 %.
What mass of product was collected?
A
1.98 g
B
2.07 g
C
2.70 g
D
4.80 g
26 Which mass of gas would occupy a volume of 3 dm3 at 25 °C and 1 atmosphere pressure?
[1 mol of gas occupies 24 dm3 at 25 °C and 1 atmosphere pressure.]
A
3.2 g O2 gas
B
5.6 g N2 gas
C
8.0 g SO2 gas
D
11.0 g CO2 gas
27 Which element of the third period requires the least number of moles of oxygen for the complete
combustion of 1 mol of the element?
A
aluminium
B
magnesium
C
phosphorus
D
sodium
28 Use of the Data Booklet is relevant to this question.
Nickel makes up 20 % of the total mass of a coin. The coin has a mass of 10.0 g.
How many nickel atoms are in the coin?
A
2.05 × 1022
B
4.30 × 1022
C
1.03 × 1023
D
1.20 × 1024
29 Camphor is a white solid which was used to make the early plastic celluloid. Camphor contains
the same percentage by mass of hydrogen and oxygen.
What is the molecular formula of camphor?
A
C10H6O6
B
C10H8O
C
C10H16O
D
C10H10O2
30 Use of the Data Booklet is relevant to this question.
In leaded petrol there is an additive composed of lead, carbon and hydrogen only. This
compound contains 29.7 % carbon and 6.19 % hydrogen by mass.
What is the value of x in the empirical formula PbC8HX?
A
5
B
6
C
16
D
20
31 A household bleach contains sodium chlorate(I), NaClO, as its active ingredient. The
concentration of NaClO in the bleach can be determined by reacting a known amount with
aqueous hydrogen peroxide, H2O2.
NaClO(aq) + H2O2(aq) → NaCl(aq) + O2(g) + H2O(l)
When 25.0 cm3 of bleach is treated with an excess of aqueous H2O2, 0.0350 mol of oxygen gas is
given off.
What is the concentration of NaClO in the bleach?
A
8.75 × 10–4 mol dm–3
B
0.700 mol dm–3
C
0.875 mol dm–3
D
1.40 mol dm–3
32 0.200 mol of a hydrocarbon undergo complete combustion to give 35.2 g of carbon dioxide and
14.4 g of water as the only products.
What is the molecular formula of the hydrocarbon?
A
C2H4
B
C2H6
C
C4H4
D
C4H8
33 In the Basic Oxygen steel-making process the P4O10 impurity is removed by reacting it with
calcium oxide. The only product of this reaction is the salt calcium phosphate, Ca3(PO4)2.
In this reaction, how many moles of calcium oxide react with one mole of P4O10?
A
1
B
C
1.5
3
D
6
34 Use of the Data Booklet is relevant to this question.
A typical solid fertiliser for use with household plants and shrubs contains the elements N, P, and
K in the ratio of 15 g : 30 g :15 g per 100 g of fertiliser. The recommended usage of fertiliser is 14 g
of fertiliser per 5 dm3 of water.
What is the concentration of nitrogen atoms in this solution?
A
0.03 mol dm–3
B
0.05 mol dm–3
C
0.42 mol dm–3
D
0.75 mol dm–3
35 The density of ice is 1.00 g cm–3.
What is the volume of steam produced when 1.00 cm3 of ice is heated to 323 °C (596 K) at a
pressure of one atmosphere (101 kPa)?
[1 mol of a gas occupies 24.0 dm3 at 25 °C (298 K) and one atmosphere.]
A
0.267 dm3
B
1.33 dm3
C
2.67 dm3
D
48.0 dm3
36 Use of the Data Booklet is relevant to this question.
The combustion of fossil fuels is a major source of increasing atmospheric carbon dioxide, with a
consequential rise in global warming. Another significant contribution to carbon dioxide levels
comes from the thermal decomposition of limestone, in the manufacture of cement and of lime for
agricultural purposes.
Cement works roast 1000 million tonnes of limestone per year and a further 200 million tonnes is
roasted in kilns to make lime.
What is the total annual mass output of carbon dioxide (in million tonnes) from these two
processes?
A
440
B
527
C
660
D
880
37 Use of the Data Booklet is relevant to this question.
Titanium(IV) oxide, TiO2, is brilliantly white and much of the oxide produced is used in the
manufacture of paint.
What is the maximum amount of TiO2 obtainable from 19.0 tonnes of the ore ilmenite, FeTiO3?
A
10.0 tonnes
B
12.7 tonnes
C
14.0 tonnes
D
17.7 tonnes
38 John Dalton’s atomic theory, published in 1808, contained four predictions about atoms.
Which of his predictions is still considered to be correct?
A
Atoms are very small in size.
B
No atom can be split into simpler parts.
C
All the atoms of a particular element have the same mass.
D
All the atoms of one element are different in mass from all the atoms of other elements.
39 Use of the Data Booklet is relevant to this question.
When a sports medal with a total surface area of 150 cm2 was evenly coated with silver, using
electrolysis, its mass increased by 0.216 g.
How many atoms of silver were deposited per cm2 on the surface of the medal?
A
8.0 × 1018
B
1.8 × 1019
C
1.2 × 1021
D
4.1 × 1022
40 N2O4 is a poisonous gas. It can be disposed of safely by reaction with sodium hydroxide.
N2O4(g) + 2NaOH(aq) → NaNO3(aq) + NaNO2(aq) + H2O(l)
What is the minimum volume of 0.5 mol dm–3 NaOH(aq) needed to dispose of 0.02 mol of N2O4?
A
8 cm3
B
12.5 cm3
C
40 cm3
D
80 cm3
41 The amount of calcium ions in a sample of natural water can be determined by using an ionexchange column as shown in the diagram.
water sample
ion-exchange resin
A 50 cm3 sample of water containing dissolved calcium sulphate was passed through the ionexchange resin. Each calcium ion in the sample was exchanged for two hydrogen ions. The
resulting acidic solution collected in the flask required 25 cm3 of 1.0 × 10–2 mol dm–3 potassium
hydroxide for complete neutralisation.
What was the concentration of the calcium sulphate in the original sample?
A
2.5 × 10–3 mol dm–3
B
1.0 × 10–2 mol dm–3
C
2.0 × 10–2 mol dm–3
D
4.0 × 10–2 mol dm–3
42 On collision, airbags in cars inflate rapidly due to the production of nitrogen.
The nitrogen is formed according to the following equations.
2NaN3 → 2Na + 3N2
10Na + 2KNO3 → K2O + 5Na2O + N2
How many moles of nitrogen gas are produced from 1 mol of sodium azide, NaN3?
A
1.5
B
1.6
C
3.2
D
4.0
43 One mole of magnesium, aluminium and sulphur are each completely burned in an excess of
oxygen gas.
Which graph shows the moles of oxygen used in each case?
A
B
moles of
oxygen
used
moles of
oxygen
used
0
0
Mg
Al
S
Mg
Al
S
D
C
moles of
oxygen
used
moles of
oxygen
used
0
0
Mg
Al
Mg
S
Al
S
44 Use of the Data Booklet is relevant to this question.
What volume of oxygen, measured under room conditions, can be obtained from the thermal
decomposition of 8.2 g of calcium nitrate (Mr = 164)?
A
150 cm3
B
300 cm3
C
600 cm3
D
1200 cm3
45 Which of these samples of gas contains the same number of atoms as 1g of hydrogen
(Mr : H2, 2)?
A
22 g of carbon dioxide (Mr : CO2, 44)
B
8 g of methane (Mr : CH4, 16)
C
20 g of neon (Mr : Ne, 20)
D
8 g of ozone (Mr : O3, 48)
46 Self-igniting flares contain Mg3P2. With water this produces diphosphane, P2H4, which is
spontaneously flammable in air.
Which equation that includes the formation of diphosphane is balanced?
A
Mg3P2 + 6H2O ® 3Mg(OH)2 + P2H4
B
Mg3P2 + 6H2O ® 3Mg(OH)2 + P2H4 + H2
C
2Mg3P2 + 12H2O ® 6Mg(OH)2 + P2H4 + 2PH3
D
2Mg3P2 + 12H2O ® 6Mg(OH)2 + 3P2H4
47 Use of the Data Booklet is relevant to this question.
Most modern cars are fitted with airbags. These work by decomposing sodium azide to liberate
nitrogen gas, which inflates the bag.
2NaN3 ® 3N2 + 2Na
A typical driver’s airbag contains 50 g of sodium azide.
Calculate the volume of nitrogen this will produce at room temperature.
A
9.2 dm3
B
13.9 dm3
C
27.7 dm3
D
72.0 dm3
48 Which substance, in 1 mol dm–3 aqueous solution, would have the same hydrogen ion
concentration as 1 mol dm-3 of hydrochloric acid?
A
ethanoic acid
B
nitric acid
C
sodium hydroxide
D
sulphuric acid
49
The use of the Data Booklet is relevant to this question.
What is the number of molecules in 500 cm3 of oxygen under room conditions?
50
A
1.25
1.2
1.
22
B
1.3
1.
1.34
22
C
3.
3.0
22
D
3.0
3.0
.
26
In the preparation of soft margarine, glyceryl trieleostearate
CH3(CH2)3CH
CHCH
CHCH
CH(CH2)7CO2CH2
CH3(CH2)3CH
CHCH
CHCH
CH(CH2)7CO2CH
CH3(CH2)3CH
CHCH
CHCH
CH(CH2)7CO2CH2
is suitably hydrogenated so that, on average, one of its side-chains is converted into the
CH3(CH2)4CH=CHCH2CH=CH(CH2)7CO2 residue and two side-chains are converted into the
CH3(CH2)7CH=CH(CH2)7CO2 residue.
How many moles of hydrogen are required to convert one mole of glyceryl trieleostearate into the
soft margarine?
A
4
B
5
C
6
D
9
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
51 Use of the Data Booklet is relevant to this question.
In an organic synthesis, a 62% yield of product is achieved.
Which conversions are consistent with this information?
1
74.00 g of butan-2-ol → 44.64 g of butanone
2
74.00 g of butan-1-ol → 54.56 g of butanoic acid
3
74.00 g of 2-methylpropan-1-ol → 54.56 g of 2-methylpropanoic acid
52 An organic compound, Z, will react with calcium metal to produce a salt with the empirical formula
CaC4H6O4.
What could be the identity of Z?
1
ethanoic acid
2
butanedioic acid
3
methylpropanedioic acid
53 X is a particle with 18 electrons and 20 neutrons.
What could be the symbol of X?
1
38
18
2
40
2+
20 Ca
3
39 +
19 K
Ar
54 An element X and compound YZ react separately with acid as shown.
X(s) + 2H+(aq) → X2+(aq) + H2(g)
YZ(s) + 2H+(aq) → Y2+(aq) + H2Z(g)
When 1.0 g of either X or YZ is reacted with an excess of acid, the total volume of gas formed is
the same.
Which statements are correct?
1
Ar(X) = Mr(YZ)
2
X and Y are metals.
3
X and Y must both be in the same Group of the Periodic Table.
55 Use of the Data Booklet is relevant to this question.
Zinc reacts with hydrochloric acid according to the following equation.
Zn + 2HCl → ZnCl 2 + H2
Which statements are correct?
[All volumes are measured at room conditions.]
1
A 3.27 g sample of zinc reacts with an excess of hydrochloric acid to give 0.050 mol of zinc
chloride.
2
A 6.54 g sample of zinc reacts completely with exactly 100 cm3 of 1.00 mol dm–3 hydrochloric
acid.
3
A 13.08 g sample of zinc reacts with an excess of hydrochloric acid to give 9.60 dm3 of
hydrogen.
56 A compound has a relative molecular mass of 88 and its molecule contains only four carbon
atoms.
What could this compound be?
1
a saturated non-cyclic diol
2
a secondary alcohol containing an aldehyde group
3
a primary alcohol containing a ketone group
57 The number of moles of chlorine that react with 1 mol of X is twice the number of moles of
chlorine that react with 1 mol of Y.
Which of these pairs could be X and Y?
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Atoms, Molecules &
Stoichiometry
Mark Scheme
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atoms, Molecules & Stoichiometry
Sub-Topic
Paper Type
Multiple Choice
Booklet
Mark Scheme
Time Allowed:
69 minutes
Score:
/57
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
SECTION – A
1.
A
2.
B
3.
B
4.
A
5.
A
6.
A
7.
B
8.
D
9.
C
10.
B
11.
D
12.
C
13.
B
14.
D
15.
A
16.
C
17.
B
18.
A
19.
D
20.
B
21.
D
22.
C
23.
C
24.
C
25.
C
26.
C
27.
D
28.
A
29.
C
30.
D
31.
D
32.
D
33.
D
34.
A
35.
C
36.
B
37.
A
38.
A
39.
A
40.
D
41.
A
42.
B
43.
D
44.
C
45.
C
46.
B
47.
C
48.
B
49.
A
50.
B
SECTION – B
51. A
52. D
53. A
54. B
55. D
56. C
57. B
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Atomic Structure
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Multiple Choice
Booklet
Mark Scheme 1
Time Allowed:
54 minutes
Score:
/45
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
SECTION – A
1. B
2. C
3. B
4. D
5. D
6. D
7. D
8. D
9. C
10. B
11. C
12. A
13. C
14. A
15. C
16. B
17. B
18. C
19. A
20. A
21. A
22. B
23. A
24. B
25. C
26. C
27. B
28. D
29. D
30. A
SECTION – B
31. A
32. D
33. D
34. B
35. A
36. A
37. B
38. A
39. C
40. C
41. A
42. B
43. B
44. B
45. D
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Atomic Structure
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 1
Time Allowed:
54 minutes
Score:
/45
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Use of the Data Booklet is relevant to this question.
In which option do all three particles have the same electronic configuration and the same
number of neutrons?
2
3
A
15
N3–
16
19 –
B
18
19 –
20
C
19 –
20
23
D
22
23
24
O2–
F
Ne
O2–
F
Ne
Na
F
Ne
Na+
Mg2+
Which pair has species with different shapes?
A
BeCl 2 and CO2
B
CH4 and NH4+
C
NH3 and BF3
D
SCl 2 and H2O
Use of the Data Booklet is relevant to this question.
Atoms of element X have six unpaired electrons.
What could be element X?
A
carbon
B
chromium
C
iron
D
selenium
4
Use of the Data Booklet is relevant to this question.
The most common ion-molecule reaction in gas clouds of the Universe is as shown.
H2(g) + H2+(g) → H(g) + H3+(g)
What could be the composition of an H3+ ion?
5 The species Ne, Na+ and Mg2+ are isoelectronic. This means that they have the same number of
electrons.
In which order do their radii increase?
6
Use of the Data Booklet is relevant to this question.
In some types of spectroscopy, it is important to know if ions are isoelectronic. This means that
they contain equal numbers of electrons.
Which ion is not isoelectronic with K+?
A
Ca2+
B
Cl –
C
S2–
D
Ti3+
7
In which species are the numbers of protons, neutrons and electrons all different?
A
8
B
−
35
17 Cl
C
32 2 −
16 S
D
39 +
19 K
Which ion has more electrons than protons and more protons than neutrons?
[H = 11 H ; D = 12 H ; O = 168 O]
A
9
27
13 Al
D–
B
H3O+
C
OD–
D
OH–
Dicarbon monoxide, C2O, is found in dust clouds in space. Analysis of it shows that the sequence
of atoms in this molecule is C – C – O. All bonds are double bonds and there are no unpaired
electrons.
How many lone pairs of electrons are present in a molecule of C2O?
A
1
B
2
C
3
D
4
10 Use of the Data Booklet is relevant to this question.
In which species are the numbers of protons, neutrons and electrons all different?
A
19 −
9F
B
+
23
11 Na
C
31
15 P
D
32 2 −
16 S
11 The first six ionisation energies of four elements are given.
Which element is most likely to be in Group IV of the Periodic Table?
ionisation energy / kJ mol−1
1st
st
2nd
3rd
4th
5th
6th
A
494
4 560
6 940
9 540
13 400
16 600
B
736
1 450
7 740
10 500
13 600
18 000
C
1 090
2 350
4 610
6 220
37 800
47 000
D
1 400
2 860
4 590
7 480
9 400
53 200
12 Which formula represents the empirical formula of a compound?
A
B
CH4O
C2H4
C
C6H12
D
H2O2
13 Use of the Data Booklet is relevant to this question.
In which set do all species contain the same number of electrons?
A
Co2+, C
B
F–, Br –, Cl –
C
Na+, Mg2+, Al 3+
D
K2SO4, K2SeO4, K2TeO4
3+
,C
4+
14 In which species does the underlined atom have an incomplete outer shell?
A
BF3
B
CH3–
C
F2O
D
H3O+
15 In which species are the numbers of protons, neutrons and electrons all different?
A
11
5B
B
19 −
9F
C
+
23
11Na
D
24
2+
12 Mg
16 Which molecule has the largest overall dipole?
A
B
H
CH3
C
H
CH3
O
C
C
CH3
C
D
Cl
O
CH3
H 3C
Cl
C
C
Cl
Cl
C
CH3
17 The value of the second ionisation energy of calcium is 1150 kJ mol–1.
Which equation correctly represents this statement?
A
Ca(g) → Ca2+(g) + 2e− ;
∆H o = +1150 kJ mol–1
B
Ca+(g) → Ca2+(g) + e− ;
∆H o = +1150 kJ mol–1
C
Ca+(g) → Ca2+(g) + e− ;
∆H o = –1150 kJ mol–1
D
Ca(g) → Ca2+(g) + 2e− ;
∆H o = –1150 kJ mol–1
18 Use of the Data Booklet is relevant to this question.
The 68Ge isotope is medically useful because it undergoes a natural radioactive process to give a
gallium isotope, 68Ga, which can be used to detect tumours. This transformation of 68Ge occurs
when an electron enters the nucleus, changing a proton into a neutron.
Which statement about the composition of an atom of the 68Ga isotope is correct?
A
It has 4 electrons in its outer p subshell.
B
It has 13 electrons in its outer shell.
C
It has 37 neutrons.
D
Its proton number is 32.
19 John Dalton’s atomic theory, published in 1808, contained four predictions about atoms.
Which of his predictions is still considered to be correct?
A
All atoms are very small in size.
B
All the atoms of a particular element have the same mass.
C
All the atoms of one element are different in mass from all the atoms of other elements.
D
No atom can be split into simpler parts.
20 In a car engine, non-metallic element X forms a pollutant oxide Y. Y can be further oxidised to Z.
Two students made the following statements.
Student P
The molecule of Y contains lone pairs of electrons.
Student Q
The oxidation number of X increases by 1 from Y to Z.
X could be carbon or nitrogen or sulfur.
Which student could be correct if X were any of these elements?
A
P only
B
Q only
C
both P and Q
D
neither P nor Q
21 Which diagram shows the variation of the metallic radius r of the Group I elements, Li, Na, K and
Rb, with increasing proton (atomic) number?
A
r
B
r
proton number
C
r
proton number
D
r
proton number
proton number
22 Which diagram represents the overlap of two orbitals which will form a π bond?
A
B
C
D
23 Which molecule is planar?
A
C2Cl 4
B
C3H6
C
C3H8
D
NF3
24 Helium, He, is the second element in the Periodic Table.
Tritium is the isotope of hydrogen 3H.
What is the same in an atom of 4He and an atom of 3H?
A
the number of electrons
B
the number of neutrons
C
the number of protons
D
the relative atomic mass
25 Tanzanite is used as a gemstone for jewellery. It is a hydrated calcium aluminium silicate mineral
with a chemical formula Ca2Al xSiyO12(OH).6½H2O. Tanzanite has Mr of 571.5.
Its chemical composition is 14.04 % calcium, 14.17 % aluminium, 14.75 % silicon, 54.59 % oxygen
and 2.45 % hydrogen.
(Ar values: H = 1.0, O = 16.0, Al = 27.0, Si = 28.1, Ca = 40.1)
What are the values of x and y?
26 Which formulae show propanone and propanal as different compounds?
A
empirical, molecular, structural and displayed formulae
B
molecular, structural and displayed formulae only
C
structural and displayed formulae only
D
displayed formulae only
27 Which equation represents the second ionisation energy of an element X?
A
X(g) → X2+(g) + 2e–
B
X+(g) → X2+(g) + e–
C
X(g) + 2e– → X2–(g)
D
X–(g) + e– → X2–(g)
28 Use of the Data Booklet is relevant to this question.
From which particle is the removal of an electron the most difficult?
A
Cl –(g)
B
F–(g)
C
K+(g)
D
Na+(g)
29 Which element has an equal number of electron pairs and of unpaired electrons within orbitals of
principal quantum number 2?
A
beryllium
B
carbon
C
nitrogen
D
oxygen
30 In the general formula of which class of compound, is the ratio of hydrogen atoms to carbon
atoms the highest?
A
alcohols
B
aldehydes
C
carboxylic acids
D
halogenoalkanes
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
31 Use of the Data Booklet is relevant to this question.
The isotope 99Tc is radioactive and has been found in lobsters and seaweed adjacent to nuclear
fuel reprocessing plants.
Which statements are correct about an atom of 99Tc?
1
It has 13 more neutrons than protons.
2
It has 43 protons.
3
It has 99 nucleons.
32 Use of the Data Booklet is relevant to this question.
Which statements about the phosphide ion, 31P3–, and the chloride ion, 35Cl –, are correct?
1
They have the same number of electrons.
2
They have the same number of neutrons.
3
They have the same number of protons.
33 The technetium-99 isotope, 99Tc, is radioactive and has been found in lobsters and seaweed near
to nuclear fuel reprocessing plants.
Which statements about an atom of 99Tc are correct?
1
It has 13 fewer protons than neutrons.
2
It forms 99Tc2+ which has 45 electrons.
3
It has 56 nucleons.
34 Which elements have atoms which can form π bonds with atoms of other elements?
1
oxygen
2
nitrogen
3
fluorine
35 In 2011 an international group of scientists agreed to add two new elements to the Periodic
Table. Both elements had been made artificially and were called ununquadium (Uuq) and
ununhexium (Uuh).
Uuq
Uuh
proton number
114
116
nucleon number
289
292
Which statements about these elements are correct?
1
One atom of Uuh has one more neutron than one atom of Uuq.
2
One Uuq2– ion has the same number of electrons as one atom of Uuh.
3
One Uuh+ ion has the same number of electrons as one Uuq– ion.
36 Use of the Data Booklet is relevant to this question.
Which ions contain one or more unpaired electrons?
1
Cu2+
2
Mn3+
3
V3+
37 Which statements are correct when referring to the isotopes of a single element?
1
The isotopes have different masses.
2
The isotopes have different numbers of nucleons.
3
The isotopes have different chemical reactions.
38 Use of the Data Booklet is relevant to this question.
In which pairs do both species have the same number of unpaired p electrons?
1
Al 2– and O+
2
N and Cl 2+
3
C and Cl +
39 Which substances contain delocalised electrons?
1
cyclohexene
2
graphite
3
sodium
40 Use of the Data Booklet is relevant to this question.
Which statements are correct when referring to the atoms 23Na and 24Mg?
1
They have the same number of full electron orbitals.
2
They have the same number of neutrons.
3
They are both reducing agents.
41 X is a particle with 18 electrons and 20 neutrons.
What could be the symbol of X?
1
38
18
2
40
2+
20 Ca
3
39 +
19 K
Ar
42 The 1H3+ ion was first characterised by J. J. Thomson over a century ago. 6Li is a rare isotope of
lithium which forms the 6Li+ ion.
Which statements are correct?
1
Both ions contain the same number of protons.
2
Both ions contain the same number of electrons.
3
Both ions contain the same number of neutrons.
43 Use of the Data Booklet is relevant to this question.
In which pairs do both species have the same number of unpaired p electrons?
1
O and Cl +
2
F+ and Ga–
3
P and Ne+
44 The phosphide ion
particles?
1
neutrons
2
electrons
3
protons
31 3–
15 P
and sulfide ion
2–
32
16 S
have the same number of which sub-atomic
45 In the gas phase, aluminium chloride exists as the dimer, Al2Cl6.
By using this information, which of the following are structural features of the Al2Cl6 molecule?
1
Each aluminium atom is surrounded by four chlorine atoms.
2
There are twelve non-bonded electron pairs in the molecule.
3
Each aluminium atom contributes electrons to four covalent bonds.
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Atomic Structure
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Question
1
(a)
Mark Scheme
sub-atomic particle
relative mass
Mark
relative charge
neutron
e
electron
1/1836
proton
r
(b) (i)
(ii)
0
[1]
–
[1]
+
[1]
RAM = mean / average mass of the isotopes / an atom(s)
relative to 1/12 the mass of an atom of 12C / on a scale where an
atom of 12C is (exactly) 12 (units)
isotope =
atoms with the same number of protons / atomic number / proton
number with different mass numbers / numbers of
neutrons / nucleon number
(0.89 × 74) + (9.37 × 76) + (7.63 × 77) + (23.77 × 78) + (49.61× 80 ) + (8.73 × 82)
100
= 79.04 (2 d.p.) AND Se
(c) (i)
Te
Cl
47.4
128
52.6
35.5
0.370
0.370
1.48
0.370
1
4
(iii)
(d) (i)
[3]
[1]
[1]
[1]
[3]
[1]
[1]
[2]
[1]
so EF = TeCl4
Empirical Formula Mass = 270
(c) (ii)
Total
[1]
so MF = TeCl4
[1]
[3]
Covalent AND simple / molecular
[1]
low melting point / reaction with water
[1]
[2]
TeCl4 + 3H2O → H2TeO3 + 4HCl
OR TeCl4 + 2H2O → TeO2 + 4HCl
[1]
[1]
Yellow / orange flame
White fumes / solid
Yellow / green gas disappears
[1]
[1]
[1]
[max 2]
Question
(ii)
Mark Scheme
Mark
NaCl giant / lattice AND ionic
SiCl4 simple / molecular AND covalent
[1]
[1]
For NaCl large difference in electronegativity
(of sodium / Na and chlorine / Cl / Cl2) (indicates electron transfer/ions)
[1]
Total
For SiCl4 smaller difference (indicates sharing/covalency) with (weak)
van der Waals’ / IM forces (between molecules) ora
[1]
[4]
[20]
Question
uest
2
Scheme
name of particle
(a)
relative mass
Mark
relative charge
proton
r
electron
1/1836
neutron
e
(b) (i)
(ii)
Total
+
[1]
–
[1]
0
[1]
Mass of an atom(s)
[1]
relative to 1 / 12th (the mass) of (an atom of) carbon-12
OR
relative to carbon-12 which is (exactly) 12
[1]
% of third isotope = 10
[1]
(24 × 79) + (26 ×11.0) +10x
= 24.3
100
[1]
[3]
[2]
10x = 248
x = 24.8 (3s.f.)
(c) (i)
(ii)
(d) (i)
(ii)
anode
ano
cathode
cat
l – Cl2 + 2e–
2+
+ 2e– Mg
Mg
31.65
24.3
O
20.84
16
1.3
1.30
0
1.30
H
1.31
1
Cl
46.2
35.5
[1]
[3]
[1]
[1]
[2]
[1]
MgOHCl
[1]
[2]
Na2O basic / alkaline; Al2O3 amphoteric / acidic and basic; SO3 acidic
Na2O (giant) ionic AND SO3 (simple / molecular) covalent
[1]
[1]
[2]
Na2O + 2HCl 2NaCl + H2O
[1]
Al2O3 + 6HCl 2AlCl3 + 3H2O
[1]
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
+
+
+
+
+
+
2NaOH + 7H2O 2NaAl(OH)4(H2O)2 OR
2NaOH + 3H2O 2NaAl(OH)4 OR
2NaOH 2NaAlO2 + H2O OR
2OH‒ + 7H2O 2[Al(OH)4(H2O)2] ‒ OR
2OH‒ + 3H2O 2[Al(OH)4] ‒OR
2OH− 2AlO2− + H2O
SO3 + NaOH NaHSO4 OR
SO3 + 2NaOH Na2SO4 + H2O
[1]
[1]
[4]
Question
uest
3
Scheme
(1s2)2s22p6
(a)
(b) (i) The amount of energy required/energy change when one electron is
removed
from each atom in one mol
of gaseous atoms
(ii) Greater nuclear charge/number of protons
Same shielding/number of shells/energy level
(c) (i) mean/average mass of the isotopes/an atom(s)
relative to 1/12 of the mass of an atom of 12C/on a scale where an atom
of 12C is (exactly) 12
(ii)
20.2 =
(20 × 90.48) + (21× 0.27) + (9.25y )
100
Mark
Total
[1]
[1]
[1]
[1]
[1]
[3]
[1]
[1]
[2]
[1]
[1]
[2]
[1]
2020 − 1815.27
= 22.133
9.25
y = 22
(d) (i)
pV =
mRT
Mr
Mr =
mRT
0.275 × 8.31 × 298
=
pV
100 × 10 3 × 200 × 10 −6
Mr = 34.05/34.1
[1]
[2]
[1]
[1]
[2]
[1]
[1]
(i) Van der Waal’s/London/dispersion
Uneven electron distribution/temporary dipole
Induced dipole-dipole attraction
[1]
[1]
[1]
[3]
(ii) more electrons
more polarisable/greater attraction/stronger IMFs
[1]
[1]
[2]
(ii) (Let % Ne = x so % Ar = 100-x)
20.2x + 39.9(100 - x)
= 34.05
100
% Ne = 29.7
1
(e
[18]
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Atomic Structure
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
Chemists recognise that atoms are made of three types of particle.
Complete the following table with their names and properties.
name of particle
relative mass
relative charge
0
1/1836
[3]
(b) The relative atomic mass of an element can be determined using data from its mass spectrum.
The mass spectrum of element X is shown, with the percentage abundance of each isotope
labelled.
60
49.61
50
40
percentage
abundance
30
23.77
20
9.37
10
8.73
7.63
0.89
0
73
74
75
76
77
78
79
80
81
82
83
m/e
(i)
Define the terms relative atomic mass and isotope.
relative atomic mass ...........................................................................................................
.............................................................................................................................................
.............................................................................................................................................
isotope ................................................................................................................................
.............................................................................................................................................
[3]
(ii)
Use the data in the mass spectrum to calculate the relative atomic mass, Ar, of X.
Give your answer to two decimal places and suggest the identity of X.
Ar of X ....................................
(c)
identitysolid
of X product,
....................................
The element tellurium, Te, reacts with chlorine to form a single
with a relative
[2]
formula mass of 270. The product contains 52.6% chlorine by mass.
(i)
Calculate the molecular formula of this chloride.
molecular formula .................................... [3]
(ii)
This chloride melts at 224 °C and reacts vigorously with water.
State the type of bonding and structure present in this chloride and explain your reasoning.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(iii)
Suggest an equation for the reaction of this chloride with water.
....................................................................................................................................... [1]
(d) Sodium and silicon also react directly with chlorine to produce the chlorides shown.
point / °C
difference between the
electronegativities of the elements
NaCl
801
2.2
SiCl 4
–69
1.3
chloride
melting
(i) Describe what you would see during the reaction between sodium and chlorine.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Explain the differences between the melting points of these two chlorides in terms of their
structure and bonding. You should refer to the difference between the electronegativities
of the elements in your answer.
NaCl structure and bonding ...............................................................................................
.............................................................................................................................................
SiCl 4 structure and bonding ................................................................................................
.............................................................................................................................................
explanation .........................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
[Total: 20]
2
(a) Chemists recognise that atoms are made of three types of particle.
Complete the following table with their names and properties.
name of particle
relative mass
relative charge
+1
1/1836
[3]
(b) Most elements exist naturally as a mixture of isotopes, each with their own relative isotopic
mass. The mass spectrum of an element reveals the abundances of these isotopes, which can
be used to calculate the relative atomic mass of the element.
Magnesium has three stable isotopes. Information about two of these isotopes is given.
isotope
relative
isotopic mass
percentage
abundance
24
Mg
24.0
79.0
26
Mg
26.0
11.0
(i) Define the term relative isotopic mass.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) The relative atomic mass of magnesium is 24.3.
Calculate the percentage abundance and hence the relative isotopic mass of the third
isotope of magnesium. Give your answer to three significant figures
percentage abundance = .................................
isotopic mass = .................................
[3]
(c) Magnesium can be produced by electrolysis of magnesium chloride in a molten mixture of
salts.
(i) Give equations for the anode and cathode reactions during the electrolysis of molten
magnesium chloride, MgCl 2.
anode ..................................................................................................................................
cathode ...............................................................................................................................
[2]
The electrolysis is carried out under an atmosphere of hydrogen chloride gas to convert any
magnesium oxide impurity into magnesium chloride.
(ii) An investigation of the reaction between magnesium oxide and hydrogen chloride
gas showed that an intermediate product was formed with the composition by mass
Mg, 31.65%; O, 20.84%; H, 1.31% and Cl, 46.20%.
Calculate the empirical formula of this intermediate compound.
empirical formula .................................... [2]
(d) The acid/base behaviour of the oxides in the third period varies across the period.
(i) Describe this behaviour and explain it with reference to the structure and bonding of
sodium oxide, Na2O, aluminium oxide, Al 2O3, and sulfur trioxide, SO3.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Write equations for reactions of these three oxides with hydrochloric acid and/or sodium
hydroxide as appropriate.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
[Total: 18]
3
Neon is a noble gas.
(a) Complete the full electronic configuration of neon.
1s2 ........................................................................................................................................ [1]
(b) (i) Explain what is meant by the term first ionisation energy.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Explain why the first ionisation energy of neon is greater than that of fluorine.
.............................................................................................................................................
....................................................................................................................................... [2]
(c)
c Neon has three stable isotopes.
isotope
mass number
1
percentage abundance
9.25
2
20
90.48
3
21
0.27
(i) Define the term relative atomic mass.
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Use the relative atomic mass of neon, 20.2, to calculate the mass number of isotope 1.
mass number = ................................. [2]
(d) A mixture of neon and argon has a mass of 0.275 g. The mixture was placed in a gas syringe
at a temperature of 25 °C and a pressure of 100 kPa. Under these conditions the mixture was
found to occupy a volume of 200 cm3.
(i) Calculate the average Mr of the mixture.
average Mr = ................................. [2]
(ii) Use your answer to (i) to calculate the percentage of neon in the mixture.
Give your answer to three significant figures.
percentage of neon = ................................. % [1]
(e) Neon and argon can both be obtained by fractional distillation of liquid air as they have different
boiling points.
Neon has a boiling point of 27.3 K. The boiling point of argon is 87.4 K.
(i) Name the force that has to be overcome in order to boil neon or argon and explain what
causes it.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Explain why argon has a higher boiling point than neon.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
[Total: 18]
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Atomic Structure
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 2
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Explain what is meant by the term nucleon number.
....................................................................................................................................................
.............................................................................................................................................. [1]
(b) Bromine exists naturally as a mixture of two stable isotopes, 79Br and 81Br, with relative isotopic
masses of 78.92 and 80.92 respectively.
(i) Define the term relative isotopic mass.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Using the relative atomic mass of bromine, 79.90, calculate the relative isotopic abundances
of 79Br and 81Br.
[3]
(c) Bromine reacts with the element A to form a compound with empirical formula ABr3. The
percentage composition by mass of ABr3 is A, 4.31; Br, 95.69.
Calculate the relative atomic mass, Ar, of A.
Give your answer to three significant figures.
Ar of A = ....................... [3]
(d) The elements in Period 3 of the Periodic Table show different behaviours in their reactions with
oxygen.
(i) Describe what you would see when separate samples of magnesium and sulfur are
reacted with oxygen.
Write an equation for each reaction.
magnesium
.............................................................................................................................................
.............................................................................................................................................
sulfur
.............................................................................................................................................
.............................................................................................................................................
[4]
(ii) Write equations for the reactions of aluminium oxide, Al 2O3, with
sodium hydroxide,
.............................................................................................................................................
hydrochloric acid.
.............................................................................................................................................
[2]
(e) Phosphorus reacts with chlorine to form PCl 5.
State the shape of and two different bond angles in a molecule of PCl 5.
shape of PCl 5 ............................................................................................................................
...........
bond angles in PCl 5 ............................
[2]
[Total: 17]
2 (a) (i)On the diagrams below, show the outer electron arrangements of the atoms and ions
indicated. (Use the symbol ↓↑ to represent a pair of electrons in an orbital.)
4s
4s
4s
3d
3d
3d
Fe
Fe2+(aq)
Zn2+(aq)
(ii) Use the above diagrams to explain why Fe2+(aq) ions are coloured, whereas Zn2+(aq) ions
are colourless.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[4]
(b) When concentrated HCl is added to a solution of Cu2+(aq) ions, the solution turns yellow.
(i) State the formula of the species responsible for the yellow colour and name the type of
reaction that has occurred.
.............................................................................................................................................
.............................................................................................................................................
(ii) Ammonia can react as a base or as a ligand.
Describe the colour changes that occur when NH3(aq) is gradually added, with stirring, to
the yellow solution, until the NH3(aq) is in excess.
Identify the three ions or compounds responsible for the new colours.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[7]
(c) When aqueous solutions of KI and K2S2O8 are mixed almost no reaction occurs, but when a
few drops of Fe2+(aq) or Fe3+(aq) are added, iodine, I2(aq), is produced at a steady rate.
(i) Write an equation for the overall reaction.
.............................................................................................................................................
(ii) State the precise role of the iron ions during this reaction.
.............................................................................................................................................
(iii) By means of equations or otherwise, explain why the presence of either Fe2+ or Fe3+ is able
to speed up the reaction.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[3]
[Total: 14]
3
(a) Successive ionisation energies for the elements magnesium to barium are given in the table.
element
1st ionisation
2nd ionisation
3rd ionisation
–1
–1
energy / kJ mol energy / kJ mol energy / kJ mol–1
Mg
736
1450
7740
Ca
590
1150
4940
Sr
548
1060
4120
Ba
502
966
3390
(i) Explain why the first ionisation energies decrease down the group.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Explain why, for each element, there is a large increase between the 2nd and 3rd ionisation
energies.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(b) A sample of strontium, atomic number 38, gave the mass spectrum shown. The percentage
abundances are given above each peak.
100
82.58
percentage
abundance
9.86 7.00
0.56
0
80
81
82
83
84
85
86
atomic mass units
87
88
89
90
(i) Complete the full electronic configuration of strontium.
1s2 2s2 2p6 ................................................................................................................... [1]
(ii) Explain why there are four different peaks in the mass spectrum of strontium.
.............................................................................................................................................
....................................................................................................................................... [1]
(iii) Calculate the atomic mass, Ar, of this sample of strontium.
Give your answer to three significant figures.
Ar = ............................. [2]
(c) A compound of barium, A, is used in fireworks as an oxidising agent and to produce a green
colour.
(i) Explain, in terms of electron transfer, what is meant by the term oxidising agent.
.............................................................................................................................................
....................................................................................................................................... [1]
(ii) A has the following percentage composition by mass: Ba, 45.1; Cl , 23.4; O, 31.5.
Calculate the empirical formula of A.
empirical formula of A ........................................... [3]
(d) Some reactions involving magnesium and its compounds are shown in the reaction scheme
below.
X(aq)
water
Mg(s)
HNO3(aq)
steam
reaction
1
Z(aq)
Y(s)
reaction
2
Z(s)
(i) Give the formulae of the compounds X, Y and Z.
X .........................................................................................................................................
Y .........................................................................................................................................
Z .........................................................................................................................................
[3]
(ii) Name the reagent needed to convert Y(s) into Z(aq) in reaction 1 and write an equation for
the reaction.
reagent ...............................................................................................................................
equation ..............................................................................................................................
[2]
(iii) How would you convert a sample of Z(s) into Y(s) in reaction 2?
....................................................................................................................................... [1]
(iv) Give equations for the conversions of Mg into X, and Z(s) into Y.
Mg to X ...............................................................................................................................
Z to Y ..................................................................................................................................
[2]
[Total: 21]
4
Valence Shell Electron Pair Repulsion theory (VSEPR) is a model of electron-pair repulsion
(including lone pairs) that can be used to deduce the shapes of, and bond angles in, simple
molecules.
(a) Complete the table below by using simple hydrogen-containing compounds. One
example has been included.
number of
bond pairs
number of
lone pairs
shape of
molecule
formula of
a molecule
with this shape
3
0
trigonal planar
BH3
4
0
3
1
2
2
[3]
(b) Tellurium, Te, proton number 52, is used in photovoltaic cells.
When fluorine gas is passed over tellurium at 150 °C, the colourless gas TeF6 is formed.
(i) Draw a ‘dot-and-cross’ diagram of the TeF6 molecule, showing outer electrons only.
(ii) What will be the shape of the TeF6 molecule?
..........................................
(iii) What is the F–Te–F bond angle in TeF6?
..........................................
[3]
[Total: 6]
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Atomic Structure
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 3
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
same proton number/atomic number
different mass number/nucleon number
(1)
(1)
(b) Ar = (32 × 95.00) + (33 × 0.77) + (34 × 4.23)
100
(1)
[2]
= 3040 + 25.41 + 143.82 = 3209.23
100
100
which gives Ar = 32.09
(1)
[2]
(3 × 1)
[3]
(c)
number of
isotopes
sotopes
213
Po
232
Th
neutrons
84
4
1
90
0
1
allow one mark for each correct column
if there are no ‘column’ marks,
allow maximum one mark for a correct row
(d)
d) (
nucleon no. is 228
proton no. is 88
(ii) Ra not radium
electrons
(1)
(1)
(1)
[3]
[Total: 10]
2
(a
(i)
2px
2py
2pz
2s
1s
nucleus
correct 1s and 2s (1)
correct 2px, 2py and 2pz (1)
(ii)
spherical s orbital (1)
double lobed p orbital along one axis (1)
both orbitals correctly labelled (1)
(iii)
nitrogen
oxygen
both correct (1)
[6]
(b) (i) N 1400 kJ mol–1 O 1310 kJ mol–1 both (1)
(ii) N is all singly filled 2p orbitals or O has one filled/paired 2p orbital (1)
these paired 2p electrons in the O atom repel one another (1)
[3]
[Total: 9]
3
(a) Cr3+:
1s22s22p6... 3s23p63d3
2+
Mn : 1s22s22p6... 3s23p63d5
(allow (1) out of (2) for 3s23p64s23d1 and 3s23p64s23d3)
(1)
(1)
[2]
(b) (i) any three of the following points:
• initial (pale) green (solution)
• fades to (almost) colourless (allow yellow)
• then (permanent faint) pink
• finally (deep) purple
(3)
(ii) MnO4– + 8H+ + 5Fe2+ (+ 5e–) → Mn2+ + 4H2O + 5Fe3+ (+ 5e–)
(c) Eo values: O2 + 4H+/2H2O = +1.23V
–
O2 +
2O/4OH = +0.40V
(1)
Fe3+/Fe2+ = +0.77 V
Fe(OH)3/Fe(OH)2 = –0.56V
[4]
(2)
Eocell = +0.46V (allow –0.37) in acid, but +0.96V in alkali or Eo (OH–) > Eo (H+)
(1)
If Ecell is more positive it means a greater likelihood of reaction
(1)
[4]
(d)
O
([1
1])
CH3CO2H
and
HO2C
CO2H
([1
1)]
([1
1)]
(or CO2H)
O
O
CO2H
H3C
or
CHO
H3C
([1
1)]
([1
1])
[5]
(e) (i) (CH3)2C(OH)–CH2OH
(1)
(ii) reaction I: (cold dilute) KMnO4 (“cold” not needed, but “hot” or “warm” negates)
reaction II: Cr2O72– + H+ + distil
(1)
(1)
[3]
[Total: 18 max 17]
4
(a) atoms of the same element / with same proton (atomic) number / same number of protons (1)
different numbers of neutrons / nucleon number / mass number (1)
[2]
(b)
isotope
no. of protons
no. of neutrons
no. of electrons
24
12
12
26
14
12
Mg
g
Mg
g
each correct row (1)
(c) Ar =
=
[2]
24 × 78.60 + 25 ×10.11 + 26 × 11.29
(1)
100
1886.40 + 252.75 + 293.54
100
gives 24.33 to 4 sig fig (same as data in question)
do not credit wrong number of sig figs or incorrect rounding up/down (1)
(d) Mg + Cl2 → MgCl2 (1)
(e) (i) n(Sb) =
[2]
[1]
2.45
= 0.020 (1)
122
(ii) mass of Cl in A = 4.57 – 2.45 = 2.12 g (1)
n(Cl) =
4.57 − 2.45
35.5
=
2.12
= 0.06
35.5
allow ecf as appropriate (1)
(iii) Sb : Cl = 0.02 : 0.06 = 1:3
empirical formula of A is SbCl3 (1)
(iv) 2Sb + 3Cl2 → 2SbCl3 (1)
(f)
[5]
(i) ionic (1)
(ii) covalent (1)
not van der Waals’ forces
[2]
[Total: 14]
5
(a
Al 1s2 2s22p6 3s23p1
Ti
(1)
1s2 2s22p6 3s2 3p6 3d2 4s2 or
1s2 2s22p6 3s2 3p6 4s23d2 penalise any error
(1)
(b) (i) pass chlorine gas
over heated aluminium
[2]
(1)
(1)
(ii) aluminium glows
white/yellow solid formed
chlorine colour disappears/fades
(1)
(1)
(1) (any 2)
(iii)
x x
x
x
x x
x
x
Cl
•
x
x x
x
x
Cl
x •
Al
• x
Cl
x
x
x x
x
x
x
x
Cl
x •
Al
• x
x x
x
x
Cl
x
x
x x
x
•
Cl
x
x x
x
x
x x
correct numbers of electrons, i.e.
3 • per Al atom and 7x per Cl atom
i.e. 6 • and 42 x in total
(1)
dative bond Cl to Al clearly shown by xx
(1)
[6]
(c) chlorine is a strong/powerful oxidising agent
(1)
[1]
(d) (i) n(Ti) = 0.72 = 0.015
47.9
(ii) n(Cl) = (2.85 – 0.72) = 0.06
35.5
(iii) 0.015 : 0.06 = 1:4
empirical formula of A is TiCl4
Allow ecf on answers to (i) and/or (ii).
(iv) Ti + 2Cl2 → TiCl4
Allow ecf on answers to (iii).
(e) covalent/not ionic
simple molecular or
mention of weak intermolecular forces or
weak van der Waals’s forces between molecules
(1)
(1)
(1)
(1)
[4]
(1)
(1)
[2]
[Total: 14 max]
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Atomic Structure
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 3
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Sulfur, S, and polonium, Po, are both elements in Group VI of the Periodic Table.
Sulfur has three isotopes.
(a) Explain the meaning of the term isotope.
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
(b) A sample of sulfur has the following isotopic composition by mass.
isotope mass
32
33
34
% by mass
95.00
0.77
4.23
Calculate the relative atomic mass, Ar, of sulfur to two decimal places.
Ar = ...............
[2]
(c) Isotopes of polonium, proton number 84, are produced by the radioactive decay of
several elements including thorium, Th, proton number 90.
The isotope 213Po is produced from the thorium isotope 232Th.
Complete the table below to show the atomic structures of the isotopes 213Po and 232Th.
number of
isotope
protons
neutrons
electrons
213Po
232Th
[3]
Radiochemical reactions, such as nuclear fission and radioactive decay of isotopes, can be
represented by equations in which the nucleon (mass) numbers must balance and the proton
numbers must also balance.
For example, the nuclear fission of uranium-235, 235
92 U, by collision with a neutron,
produces strontium-90, xenon-143 and three neutrons.
235
92 U
+
1
0n
90
38Sr
+
143
54 Xe
1
0n,
1
+ 3 0n
In this equation, the nucleon (mass) numbers balance because: 235 + 1 = 90 + 143 + (3x1).
The proton numbers also balance because:
92 + 0 = 38 + 54 + (3x0).
(d) In the first stage of the radioactive decay of
element E and an alpha-particle, 42 He.
(i)
232
90 Th,
the products are an isotope of
By considering nucleon and proton numbers only, construct a balanced equation
for the formation of the isotope of E in this reaction.
232
90 Th
................. +
4
2
He
Show clearly the nucleon number and proton number of the isotope of E.
nucleon number of the isotope of E ...........
proton number of the isotope of E .............
(ii)
Hence state the symbol of the element E.
............ ................................................................................................................. [3]
[Total: 10]
In the 19th and 20th centuries, experimental results showed scientists that atoms consist of
a positive, heavy nucleus which is surrounded by electrons.
Then in the 20th century, theoretical scientists explained how electrons are arranged in
orbitals around atoms.
(a) The diagram below represents the energy levels of the orbitals present in atoms of the
second period (Li to Ne).
(i)
Label the energy levels to indicate the principal quantum number and the type of
orbital at each energy level.
(ii)
On the axes below, draw a sketch diagram of one of each different type (shape)
of orbital that is occupied by the electrons in a second-period element.
energy
2
Label each type.
z
z
y
y
x
x
Complete the electronic configurations of nitrogen atoms and oxygen atoms on the
energy level diagrams below.
Use arrows to represent electrons.
energy
(iii)
energy
nitrogen
oxygen
[6]
(b) (i)
Use the Data Booklet to state the value of the first ionisation energy of nitrogen and
of oxygen.
N ............................... kJ mol–1
(ii)
O ............................... kJ mol–1
Explain, with reference to your answer to (a)(iii), the relative values of these two
ionisation energies.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 9]
3
(a) Complete the electronic structures of the Cr3+ and Mn2+ ions.
Cr3+
1s22s22p6 .............
Mn2+
1s22s22p6 .............
[2]
(b) (i)
Describe what observations you would make when dilute KMnO4(aq) is added
slowly and with shaking to an acidified solution of FeSO4(aq) until the KMnO4 is in
a large excess.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Construct an ionic equation for the reaction that occurs.
..................................................................................................................................
[4]
(c) By selecting relevant E o data from the Data Booklet explain why acidified solutions of
Fe2+(aq) are relatively stable to oxidation by air, whereas a freshly prepared precipitate
of Fe(OH)2 is readily oxidised to Fe(OH)3 under alkaline conditions.
relevant E o values and half equations
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
explanation
..........................................................................................................................................
..........................................................................................................................................
[4]
(d) Predict the organic products of the following reactions and draw their structures in the
boxes below. You may use structural or skeletal formulae as you wish.
hot conc.
MnO4– + H+
hot conc.
MnO4– + H+
hot
Cr2O72– + H+
OH
OH
[4]
(e) KMnO4 and K2Cr2O7 are the reagents that can be used to carry out the following
transformation.
I
II
CHO
OH
E
(i)
Draw the structure of intermediate E in the box above.
(ii)
Suggest reagents and conditions for the following.
reaction I ...................................................................................................................
reaction II ..................................................................................................................
[3]
[Total: 17]
4
The element magnesium, Mg, proton number 12, is a metal which is used in many alloys
which are strong and light.
Magnesium has several naturally occurring isotopes.
(a) What is meant by the term isotope?
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
(b) Complete the table below for two of the isotopes of magnesium.
isotope
number of
protons
number of
neutrons
number of
electrons
24Mg
26Mg
[2]
A sample of magnesium had the following isotopic composition:
78.60%; 25Mg, 10.11%; 26Mg, 11.29%.
24Mg,
(c) Calculate the relative atomic mass, Ar, of magnesium in the sample.
Express your answer to an appropriate number of significant figures.
[2]
Antimony, Sb, proton number 51, is another element which is used in alloys.
Magnesium and antimony each react when heated separately in chlorine.
(d) Construct a balanced equation for the reaction between magnesium and chlorine.
...................................................................................................................................... [1]
When a 2.45 g sample of antimony was heated in chlorine under suitable conditions, 4.57 g
of a chloride A were formed.
(e) (i)
Calculate the amount, in moles, of antimony atoms that reacted.
(ii)
Calculate the amount, in moles, of chlorine atoms that reacted.
(iii)
Use your answers to (i) and (ii) to determine the empirical formula of A.
(iv)
The empirical and molecular formulae of A are the same.
Construct a balanced equation for the reaction between antimony and chlorine.
.............................................................................................................................. [5]
(f)
The chloride A melts at 73.4 °C while magnesium chloride melts at 714 °C.
(i)
What type of bonding is present in magnesium chloride?
..................................................................................................................................
(ii)
Suggest what type of bonding is present in A.
.............................................................................................................................. [2]
[Total: 14]
5
Copper and titanium are each used with aluminium to make alloys which are light, strong
and resistant to corrosion.
Aluminium, Al, is in the third period of the Periodic Table; copper and titanium are both
transition elements.
(a) Complete the electronic configuration of aluminium and of titanium, proton number 22.
Al
1s2
Ti
1s2
[1]
Aluminium reacts with chlorine.
(b) (i)
Outline how, starting from aluminium powder, this reaction could be carried out
in a school or college laboratory to give a small sample of aluminium chloride. A
diagram is not necessary.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Describe what you would see during this reaction.
..................................................................................................................................
..................................................................................................................................
(iii)
At low temperatures, aluminium chloride vapour has the formula Al2Cl6.
Draw a ‘dot-and-cross’ diagram to show the bonding in Al2Cl6.
Show outer electrons only.
Represent the aluminium electrons by z.
Represent the chlorine electrons by x.
[6]
Copper forms two chlorides, CuCl and CuCl2.
(c) When copper is reacted directly with chlorine, only CuCl2 is formed.
Suggest an explanation for this observation.
..........................................................................................................................................
..................................................................................................................................... [1]
Titanium also reacts with chlorine.
(d) When an excess of chlorine was reacted with 0.72 g of titanium, 2.85 g of a chloride A
was formed.
(i)
Calculate the amount, in moles, of titanium used.
(ii)
Calculate the amount, in moles, of chlorine atoms that reacted.
(iii)
Hence, determine the empirical formula of A.
(iv)
Construct a balanced equation for the reaction between titanium and chlorine.
..................................................................................................................................
[4]
(e) At room temperature, the chloride of titanium, A, is a liquid which does not conduct
electricity.
What does this information suggest about the bonding and structure in A?
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
[Total: 14]
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Atomic Structure
Mark Scheme 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 4
Time Allowed:
83 minutes
Score:
/69
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) 162
160
158
81
79
(81Br – 81Br+)
(81Br – 79Br+)
(79Br – 79Br+) ignore missing charges
(81Br+)
(79Br+)
for molecular species [1]
for atomic species [1]
for 5 masses [1]
(ii) 158:160:162 =1:2:1
79:81 =1:1
(b)
b)
[1]
[1]
either BrCH2CHBr-CHO or CH2=CH-CH2OH (double bond needed)
[1]
(ii) reaction I:
reaction II:
Br2(aq or in CCl4 etc.), light negates – solvent not needed
NaBH4 or H2/Ni etc. (but not if A is CH2=CH-CH2OH)
allow LiAlH4 or Na/ethanol
(reactions can be reversed)
(c)
c)
C3H6OBr2 = 216, 218 and 220
(ii) 31
106
108
185
187
189
is
is
is
is
is
is
[1]
[1]
(any one)
[1]
CH2OH+/CH3O+
C2H379Br+
C2H381Br+
ignore missing charges
C2H379Br2+
C2H379Br81Br+
6 correct [4]
81
+
C2H3 Br2
5 correct [3] etc
if no mass numbers given – [1] only
[4]
[Total: 13 max 12]
2
(a
(i) Ka = [H+][RCO2–]/[RCO2H]
[1]
(ii) pKa = –log10Ka or –logKa or log [H+]2/[RCO2H] NOT ln;;
[
[2]
acid strength increases from no. 1 to no. 3 or down the table or as Cls increase
due to the electron-withdrawing effect/electronegativity of chlorine (atoms)
stabilising the anion or weakening the O-H bond NOT H+ more available
(b)
b)
(ii) chlorine atom is further away (from O-H) in no. 4, so has less influence
(iii) either: pH = ½ (pKa – log10[acid]) or Ka = 10–pKa = 1.259 x 10–3
= ½ (4.9 + 2)
[H+] = √(Ka. c) = 3.55 x 10–4
= 3.4 (allow 3.5)
pH = 3.4
([1] for correct expression & values; [1] for correct working)
[1]
[1]
[1]
[1]
[1]
ecf [1]
[6]
(c) (i) catalyst
(d)
[1]
(ii) CH3CH2CO2H + Cl2 → CH2CHClCO2H + HCl
[1]
(iii) nucleophilic substitution NOT addition/elimination
[1]
(iv) Mr (CH3CH2CO2H) = 74 Mr(CH2CH(NH2)CO2H) = 89
∴ 10.0 g should give 10 x 89/74 = 12.03 g
∴ percentage yield = 100 x 9.5/12.03 = 79%
[1]
+
NH3-CH(CH3)-CO2–
Allow charges on H of H3N, and –COO but not –C-O-O
ecf [1]
([2] for correct answer)
[5]
correct atoms [1]
correct charges [1]
[2]
[Total: 15]
3
(a
same proton no./atomic no./no. of protons
different mass no./nucleon no./no. of neutrons
(1)
(1)
[2]
(b)
isotope
sotope
56
Fe
59
Co
number of
neutrons
p
26
6
27
7
(1)
electrons
(1)
(1)
give one mark for each correct column
allow (1) if no column is correct but one row is correct
(c)
c)
weighted mean/average mass
of an atom (not element)
compared with 12C
one atom of 12C has a mass of exactly 12
[relative to 1/12th the mass of a 12C atom would get 2]
[3]
(1)
(1)
(1)
or
mass of 1 mol of atoms
compared with 12C
1 mol of 12C has a mass of 12 g
(ii) Ar = 54 x 5.84 + 56 x 91.68 + 57 x 2.17
100
= 5573.13 = 55.7 to 3 sf
100
allow 55.9 if Ar is calculated using 99.69 instead of 100
(1)
(1)
(1)
(1)
(1)
[5]
[Total: 10]
4
Atoms which have the same number of protons (or same element) but
different numbers of neutrons (1)
(a)
(b)
(i)
(ii)
(c)
35
Cl (1)
H37Cl (1)
[2]
H Cl line at 36 has rel. abundance of 90
38
30
These show 35Cl and 37Cl in ratio 3:1 (1)
[or use of 35 and 37]
(d)
[1]
Mean of the two isotopes 3 x 35 + 1 x 37 = 35.5 (1)
4
[2]
[1]
[Total: 6]
Question
uestion
5
(a)
(b) (i)
point
Marks
oxygen: (1s2) 2s22p4
fluorine: (1s2) 2s22p5
1
F2O / OF2
1
(ii)
1
F
O
F
bent or non-linear
1
Eo values: F2 / F– = 2.87 V and Cl2 / Cl – = 1.36 V
1
fluorine (has the more positive Eo so) is more oxidising
1
(ii)
redox
1
(iii)
Cl F + 2KBr → KCl + KF + Br2
1
(iii)
(c) (i)
[Total: 8]
Question
uesti
6
(a)
(b) (i)
(ii)
(c) (i)
(ii)
Scheme
Mark
ark
The amount of energy required / energy change / enthalpy change when one electron is
removed
from each atom / (cat)ion in one mol
of gaseous atoms / (cat)ions
OR energy change when 1 mole of electrons is removed from one mole of gaseous
atoms / ions
X(g) → X+(g) + e– gains 2 marks
1
Group V / 5 / 15
1
Big difference between fifth and sixth ionisation energies
1
1s2 2s2 2p3
ecf from (b)(i) if period 2
1
(Weighted) mean / average mass of an atom(s) (of an element)
1
Relative to 1 / 12th of (the mass of an atom of) carbon-12 OR
relative to carbon-12 which is (exactly) 12 (units)
allow as an expression
1
Z
31.13
Ar
So
1
1
3
2
2
Cl
68.87
= 1: 2
35.5
68.87/35.5
=2
31.13/Ar
2 × 31.13 × 35.5
= 32.0923 = 32.1 to 3s.f.
68.87
Allow alternative correct methods
Ar =
T
1
1
2
Question
uesti
(d) (i)
Scheme
Mark
ark
NaCl (+ aq ) NaCl + H2O Na+ + Cl –
Na+ + Cl – + H2O
1
SiCl 4 + 2H2O SiCl 4 + 4H2O SiCl 4 + 4H2O SiO2 + 4HCl
Si(OH)4 + 4HCl
SiO2.2H2O + 4HCl
1
2
Allow correct equation with other molar amounts of water
(ii)
(e)
T
NaCl is ionic AND giant / lattice
NaCl dissolves / does not react
SiCl 4 is covalent AND molecular / simple
SiCl 4 is hydrolysed / reacts
1
1
1
1
4
shape of SF6 = Octahedral
bond angle = 90°
1
1
2
18
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Atomic Structure
Question Paper 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 4
Time Allowed:
83 minutes
Score:
/69
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
(a) Natural bromine consists of the two isotopes 79Br and 81Br in roughly equal proportions.
1
The mass spectrum of bromine consists of 5 peaks.
(i)
Suggest the mass numbers for the 5 peaks and the identities of the species
responsible for them.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Suggest the ratios of the relative abundances of
•
the three lines with the highest mass numbers,
..................................................................................................................................
•
the two lines with the lowest mass numbers.
..................................................................................................................................
[4]
Esters of 2,3-dibromopropan-1-ol with phosphoric acid are useful flame retardants used in
plastics and fibres.
2,3-dibromopropan-1-ol can be made from propenal by the following two-stage process.
H
C
CH2
CHO
I
II
propenal
CH2
Br
CH2OH
CH
Br
A
2,3-dibromopropan-1-oI
(b) (i)
(ii)
Draw the structure of the intermediate A in the box opposite.
Suggest reagents and conditions for
•
reactio I,
..................................................................................................................................
•
reaction II.
..................................................................................................................................
[3]
(c) The mass spectrum of 2,3-dibromopropan-1-ol includes the following peaks.
(i)
mass number
relative abundance
31
100
106
44
108
45
185
0.3
187
0.6
189
0.3
At what mass number would you expect the molecular ion to occur?
..................................................................................................................................
(ii)
Identify the molecular formula (including isotopic composition where relevant) of
these 6 peaks.
mass number
molecular formula
31
106
108
185
187
189
[5]
[Total: 12]
2
(a) Use the general formula of a carboxylic acid, RCO2H, to write equations to explain the
following terms.
(i)
Ka .............................................................................................................................
(ii)
pKa ...........................................................................................................................
[2]
(b) The pKa values of four carboxylic acids are listed in the table below.
acid
(i)
formula of acid
pKa
1
CH3CH2CO2H
4.9
2
CH3CHCl CO2H
2.8
3
CH3CCl2CO2H
1.4
4
CH2Cl CH2CO2H
4.1
Describe and explain the trend in acid strength shown by acids 1, 2 and 3.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Suggest an explanation for the difference in the pKa values for acids 2 and 4.
..................................................................................................................................
..................................................................................................................................
(iii)
Calculate the pH of a 0.010 mol dm–3 solution of propanoic acid (acid 1).
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[6]
(c) A good way of making synthetic amino acids uses chloro-acids as intermediates.
CH3CH2CO2H
(i)
Cl2 + trace of P
I
CH3CHCl CO2H
NH3(excess)
II
CH3CH(NH2)CO2H
alanine
Suggest the role that the trace of phosphorus plays in reaction I.
..................................................................................................................................
(ii)
Write a fully balanced equation for reaction I.
..................................................................................................................................
(iii)
State the type of mechanism of reaction II.
..................................................................................................................................
(iv)
When 10.0 g of propanoic acid was used in this 2-stage synthesis, a yield of 9.5 g of
alanine was obtained.
Calculate the overall percentage yield.
..................................................................................................................................
[5]
(d) In the solid state and in aqueous solutions, alanine exists as a zwitterion.
Draw the structural formula of this zwitterion.
[2]
[Total: 15]
3
Iron and cobalt are adjacent elements in the Periodic Table. Iron has three main naturally
occurring isotopes, cobalt has one.
(a) Explain the meaning of the term isotope.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(b) The most common isotope of iron is 56Fe; the only naturally occurring isotope of cobalt
is 59Co.
Use the Data Booklet to complete the table below to show the atomic structure of 56Fe
and of 59Co.
number of
isotope
protons
neutrons
electrons
56Fe
59Co
[3]
(c) A sample of iron has the following isotopic composition by mass.
isotope mass
54
56
57
% by mass
5.84
91.68
2.17
(i) Define the term relative atomic mass.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii) By using the data above, calculate the relative atomic mass of iron to three
significant figures.
[5]
[Total: 10]
4
(a) Define an isotope in terms of its sub-atomic particles.
..........................................................................................................................................
..........................................................................................................................................
[1]
(b) In a mass spectrometer some hydrogen chloride molecules will split into atoms. The
mass spectrum of HCl is given. Chlorine has two isotopes. The hydrogen involved here
is the isotope 11H only.
100
80
relative
abundance
60
40
20
0
35
40
m /e
(i)
What particle is responsible for the peak at mass 35? .............................................
(ii)
What particle is responsible for the peak at mass 38? .............................................
[2]
(c) Use the relative heights of the peaks to determine the proportions of the two isotopes of
chlorine. Explain simply how you obtained your answer.
[2]
(d) Use your answer to (c) to explain why chlorine has a relative atomic mass of 35.5.
[1]
[Total : 6]
5
(a)Complete the electronic configurationsofthefollowingatoms.
oxygen: 1s2..........................................
fluorine: 1s2..........................................
[1]
(b) A compound of fluorine and oxygen contains three atoms in each molecule.
(i)
Predict its formula.
....................................................................................................................................... [1]
(ii)
Draw a ‘dot-and-cross’ diagram to show its bonding.
[1]
(iii)
Suggest the shape of this molecule.
....................................................................................................................................... [1]
Use E o values from the Data Booklet to predict the relative oxidising abilities of fluorine
and chlorine.
(c)
c)
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii)
Predict the type of reaction that would occur between the interhalogen compound chlorine
fluoride, Cl F, and potassium bromide solution.
....................................................................................................................................... [1]
(iii)
Construct an equation for this reaction.
....................................................................................................................................... [1]
[Total: 8]
6
(a) Explain what is meant by the term ionisation energy.
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [3]
(b) The first seven ionisation energies of an element, A, in kJ mol–1, are
1012
1903
2912
4957
6274
21 269
25 398.
(i) State the group of the Periodic Table to which A is most likely to belong. Explain your
answer.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Complete the electronic configuration of the element in Period 2 that is in the same group
as A.
1s2 ................................................................................................................................. [1]
(c) Another element, Z, in the same period of the Periodic Table as A, reacts with chlorine to
form a compound with empirical formula ZCl 2. The percentage composition by mass of ZCl 2
is Z, 31.13; Cl , 68.87.
(i) Define the term relative atomic mass.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Calculate the relative atomic mass, Ar, of Z.
Give your answer to three significant figures.
Ar of Z = ....................... [2]
(d) The chlorides of elements in Period 3 of the Periodic Table show different behaviours on
addition to water, depending on their structure and bonding.
(i) Write equations to show the behaviour of sodium chloride, NaCl , and silicon chloride,
SiCl 4 , when separately added to an excess of water.
NaCl ...................................................................................................................................
SiCl 4 ...................................................................................................................................
[2]
(ii) State and explain the differences in behaviour of these two chlorides when added to water,
in terms of their structure and the bonding found in the compounds.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
(e) Sulfur reacts with fluorine to form SF6. State the shape and bond angle of SF6.
shape of SF6 ..............................................................................................................................
bond angle of SF6 ......................................................................................................................
[2]
[Total: 18]
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Atomic Structure
Mark Scheme 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 5
Time Allowed:
86 minutes
Score:
/71
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i)
melting
point/°C
halogen
colour
chlorine
-10
green, yellow or
greenish-yellow
bromine
-7
orang or red or brown
grey
iodine
114
accept black
chlorine and bromine both correct
orr
iodine correct for solid
(ii) down the Group
there are more electrons in the molecule
hence stronger van der Waals’ forces
(1)
(1)
(1)
[4]
(b)
b)
chl
chlorine
bro
bromine
or
2
2s22p63s23p5
2
2s22p63s23p63d104s24p5
1s22s22p63s23p64s23d104p5
both needed (1)
(ii)
(1)
1)
(c)
c) (
gas or low boiling liquid
BrCl has fewer electrons than Br2
hence weaker van der Waals’ forces
(ii) accept colours in the range yellow, orange, red, brown
(d)
d) (
initially solution begins to turn yellow/brown
after several minutes black/dark grey solid formed
(1)
(1)
(1)
(1)
[4]
(1)
(1)
(ii) Cl2 + 2KI → 2KCl + I2
(1)
(iii) BrCl + 2KI → KCl + KBr + I2
(1)
(iv) as oxidising agents
(1)
[5]
[Total: 15]
(a
(i)
high
electrical conductivity
high
medium
melting point
2
low
C
Si
Ge
Sn
Pb
medium
or
low
C
Si
Ge
Sn
Pb
[2]
2] +
(ii) m. pt. trend: (from) giant/macro molecular/covalent to metallic bonding
(or implied from at least two specific examples, e.g. diamond and tin)
(mention of simple covalent anywhere negates this mark)
[1]
conductivity trend: increasing delocalisation of electrons (down the group)
[1]
or e– are more free-moving
(or implied from at least two examples, e.g. Si is semiconductor, lead has delocalised e–)
[6]
(b) (i) heat PbO2, or T > 200°C or ∆ on arrow: PbO2 → PbO + ½O2 (N.B. ½O2 NOT [O])
[1]
(ii) (burning CO in air produces CO2):CO + ½O2 → CO2
blue flame (ignore ref to limewater test)
[1]
[1]
(iii) e.g. SnCl2(aq) will turn KMnO4 from purple to colourless
5Sn2+ + 2MnO4– + 16H+ → 5Sn4+ + 2Mn2+ + 8H2O
[1]
[1]
or SnCl2(aq) will turn K2Cr2O7 from orange to green
3Sn2+ + Cr2O72– + 14H+ → 3Sn4+ + 2Cr3+ + 7H2O
[1]
[1]
or SnCl2(aq) will turn Fe3+ from orange/brown/yellow to green/colourless
Sn2+ + 2Fe3+ → Sn4+ + 2Fe2+
[1]
[1]
or SnCl2(aq) will turn Cu2+(aq) from blue to colourless or give a pink/brown/coppercoloured ppt.
[1]
Sn2+ + Cu2+ → Sn4+ + Cu
[1]
Other possible oxidants (Eo must be > +0.2V) include: S2O82–, H2O2, Cl2, Br2, I2 and Ag+.
No observations with the first three of these, but this should be stated explicitly, e.g. “no
colour change”.
[5]
[Total: 11 max 10]
3
(a
(b)
b)
(c)
a (d-block) element forming stable ions/compounds/oxidation states with incomplete/
[1]
partially filled [NOT empty] d-orbitals
(1s2 2s2 2p6) 3s2 3p6 3d3 4s2
[1]
(ii) (1s2 2s2 2p6) 3s2 3p6 3d9
[1]
[2]
(+)2, (+)3, (+)4, (+)5 or II, III, IV, V
[1]
[1]
(d) (pale blue solution ⇒) blue/cyan solid/ppt.(or (s) in the formula)
(e)
[1]
[1]
(blue ppt. is) Cu(OH)2 or copper hydroxide
[1]
(then produces a) deep blue or purple solution
[1]
which contains [Cu(NH3)4]2+ or [Cu(NH3)4(H2O)2]2+
[1]
formed by ligand replacement
[1]
2VO3– + 8H+ + Cu → 2VO2+ + 4H2O + Cu2+
or 2VO2+ + 4H+ + Cu → 2VO2+ + 2H2O + Cu2+
correct species
balancing
(award only [1] for just the two half-equations)
[5]
[1]
[1]
[2]
[Total: 11]
4
(a
same proton number/atomic number
different mass number/nucleon number
(b) Ar
=
=
(1)
(1)
(24 × 78.60 ) + (25 ×10.11) + (26 ×11.29 )
(1)
100
1886.4 + 252.75 + 293.54
100
=
[2]
2432.69
100
which gives Ar = 24.33
penalise (–1) for misuse of significant figures
(1)
[2]
(c)
number of
isotopes
protons
226
Ra
a
238
U
9
ne
138
88
146
92
allow one mark for each correct column
if there are no correct columns,
allow maximum one mark for a correct row
(d)
d) (
Ra2+
(ii) less than (502 + 966)
allow answers in the range 1000–1400 kJ mol–1
ionisation energies decrease down the Group
or must be less than IE for Ba → Ba2+
or size of atom increases down Group/
electrons are further away from nucleus
or there is increased shielding down Group
allow ecf on answer to (i)
electrons
(3 × 1)
[3]
(1)
(1)
(1)
[3]
[Total: 10]
5
(a)
[1]
[1]
[2]
(b)
b)
more shells of electrons
[1]
(ii) outermost shell has been removed
[1]
(iii) outermost electrons are further from nucleus/there are more shells
increased shielding
[1]
[1] [4]
(c) (i) very slow reaction
formation of bubbles of gas
Mg + H2O → MgO + H2
allow Mg + 2H2O → Mg(OH)2 + H2
(ii) faster reaction than with Mg
[1]
[1]
[1]
[1]
white suspension formed
or evolution of gas
or calcium dissolves/disappears
[1]
Ca + 2H2O → Ca(OH)2 + H2
[1]
allow 1 mark in (i) or (ii) if gas is described as colourless
[1] [7]
(d) (i) gas evolved
gas is brown
(ii) 2Sr(NO3)2 → 2SrO + 4NO2 + O2
correct products
balanced equation
[1]
[1]
[1]
[1] [4]
[Total: 17 max. 16]
1s2
6 (a)
2s2 2p6
(b)
5 or V
(c)
c)
3NaOH + H3PO4
3s2 3p3
[1]
[1]
Na3PO4 + 3H2O
[1]
(ii) (50 x 0.5) / 1000 = 0.025 (moles)
[1]
(iii) conseq. on (i)
[1]
(d)
d) (
OR
3 x .025 = 0.075 (moles)
P4S3 + 8O2
P4O10 + 3SO2
(or 2P2O5)
balanced = 2 marks
+
P4O6 + 3SO2
(or 2P2O3)
unbalanced = 1 mark
2
[2]
(ii)
P4O10 + 6H2O
OR P4O6 + 6H2O
SO2 + H2O
(if SO3 then e.c.f.)
4
3PO4
[1]
4H3PO3
H2SO3
[1]
Total = [9]
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Atomic Structure
Question Paper 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Atomic Structure
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 5
Time Allowed:
86 minutes
Score:
/71
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The elements of Group VII of the Periodic Table show variation in their properties.
(a) (i) Complete the table below, stating the colour of each element in its normal state at
room temperature.
halogen
melting point / °C
chlorine
–101
bromine
–7
iodine
114
colour
(ii) Briefly explain why the melting points of the halogens increase from chlorine to
iodine.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
(b) The halogens form many interhalogen compounds in which two different halogens are
combined. One such compound is bromine monochloride, BrCl.
(i) Complete the electronic configurations of chlorine and bromine.
chlorine
1s22s22p6
bromine
1s22s22p6
(ii) Draw a 'dot-and-cross' diagram of the BrCl molecule.
Show outermost electrons only.
[2]
(c) Interhalogen compounds like BrCl have similar properties to the halogens.
(i) By considering your answers to (a) and (b), predict the physical state of BrCl at room
temperature. Explain your answer.
physical state ............................................
explanation ................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) Suggest the colour of BrCl.
............................................
[4]
(d) Cl 2 and BrCl each react with aqueous KI.
(i) Describe what would be seen when Cl 2 is bubbled through aqueous KI for several
minutes.
initially ........................................................................................................................
....................................................................................................................................
after several minutes .................................................................................................
....................................................................................................................................
(ii) Construct an equation for the reaction that occurs.
....................................................................................................................................
(iii) Suggest an equation for the reaction that occurs between BrCl and aqueous KI.
....................................................................................................................................
(iv) How do Cl 2 and BrCl behave in these reactions?
....................................................................................................................................
[5]
[Total: 15]
2
The technique of DNA fingerprinting has been one of the most important developments
in biochemical analysis in recent times. It has enabled enormous advances to be made in
forensic science, medicine and archaeology.
(a) The table shows different stages in the production of a genetic fingerprint. Use the
numbers 1 to 6 to put the stages in the correct sequence in the blank column.
stages
process
A
place samples on agarose gel
B
use polymerase chain reaction
C
label with radioactive isotope
D
extract DNA
E
use restriction enzyme
F
carry out electrophoresis
correct sequence
(numbers)
[3]
(b) One of the stages above uses a radioactive isotope.
(i) What isotope is used? ...........................................
(ii)
Why is this isotope chosen?
..................................................................................................................................
..................................................................................................................................
[2]
(c) The following DNA fingerprints were taken from a family of mother, father and four
children.
mother
child 4
child 2
father
child 1
child 3
(i)
Are all of the children related to the mother? State the evidence for your answer.
..................................................................................................................................
..................................................................................................................................
(ii)
Which child is unlikely to be related to the father? State the evidence for your
answer.
..................................................................................................................................
..................................................................................................................................
[2]
(d) DNA fingerprinting has been successfully used in archaeological investigations.
(i)
Ancient writings were often made on goatskins. Over the centuries these have
often become broken into fragments, making reconstruction of the writings almost
impossible.
Suggest how the use of DNA fingerprinting might be able to identify which fragments
came from a particular skin.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Apart from the examples of human remains and goatskins, state one other material
that could be investigated using this technique.
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 10]
3
(a) Explain what is meant by the term transition element.
..........................................................................................................................................
..................................................................................................................................... [1]
(b) Complete the electronic configuration of
(i)
the vanadium atom,
1s22s22p6 .......................................................................
(ii)
the Cu2+ ion.
1s22s22p6 .......................................................................
[2]
(c) List the four most likely oxidation states of vanadium.
..................................................................................................................................... [1]
(d) Describe what you would see, and explain what happens, when dilute aqueous ammonia
is added to a solution containing Cu2+ ions, until the ammonia is in an excess.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [5]
(e) Copper powder dissolves in an acidified solution of sodium vanadate(V), NaVO3, to
produce a blue solution containing VO2+ and Cu2+ ions.
By using suitable half-equations from the Data Booklet, construct a balanced equation
for this reaction.
..................................................................................................................................... [2]
[Total: 11]
4
Magnesium, Mg, and radium, Ra, are elements in Group II of the Periodic Table.
Magnesium has three isotopes.
(a) Explain the meaning of the term isotope.
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
A sample of magnesium has the following isotopic composition by mass.
isotope mass
24
25
26
% by mass
78.60
10.11
11.29
(b) Calculate the relative atomic mass, Ar, of magnesium to four significant figures.
Ar = ………………
[2]
Radium, proton number 88, and uranium, proton number 92, are radioactive elements.
The isotope 226Ra is produced by the radioactive decay of the uranium isotope 238U.
(c) Complete the table below to show the atomic structures of the isotopes
238U.
226Ra
and
number of
isotopes
protons
neutrons electrons
226Ra
238U
[3]
(d) Radium, like other Group II elements, forms a number of ionic compounds.
(i)
What is the formula of the radium cation?
………………
(ii)
Use the Data Booklet to suggest a value for the energy required to form one mole of
the gaseous radium cation you have given in (i) from one mole of gaseous radium
atoms. Explain your answer.
..................................................................................................................................
..................................................................................................................................
............................................................................................................................. [3]
[Total: 10]
5
This question is about the elements in Group II of the Periodic Table, magnesium to barium.
(a) Complete the table below to show the electronic configuration of calcium atoms
and of strontium ions, Sr2+.
1s
2s
2p
Ca
2
2
6
Sr2+
2
2
6
3s
3p
3d
4s
4p
4d
[2]
(b) Explain the following observations.
(i)
The atomic radii of Group II elements increase down the Group.
..................................................................................................................................
..................................................................................................................................
(ii)
The strontium ion is smaller than the strontium atom.
..................................................................................................................................
..................................................................................................................................
(iii)
The first ionisation energies of the elements of Group II decrease with increasing
proton number.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[4]
(c) Samples of magnesium and calcium are placed separately in cold water and left for
some time. In each case, describe what you would see and write a balanced equation
for each reaction.
(i)
magnesium
observation ...............................................................................................................
..................................................................................................................................
equation ...................................................................................................................
(ii)
calcium
observation ...............................................................................................................
..................................................................................................................................
equation ...................................................................................................................
[6]
(d) Strontium nitrate, Sr(NO3)2 undergoes thermal decomposition.
(i)
State one observation you would make during this reaction.
..................................................................................................................................
..................................................................................................................................
(ii)
Write a balanced equation for this reaction.
..................................................................................................................................
[4]
[Total: 16]
6
Compounds of phosphorus have many uses in everyday life, e.g. fertilisers, matches and in water
softeners.
(a) State the full electronic configuration of phosphorus.
...............................................................................................................................................[1]
(b) Phosphoric acid, H3PO4, is used in the manufacture of phosphate fertilisers.
Deduce the oxidation number of phosphorus in H3PO4.
...............................................................................................................................................[1]
(c) The salt sodium phosphate, Na3PO4, is a water-softening agent.
(i)
Write the equation for the complete neutralisation of phosphoric acid with aqueous
sodium hydroxide.
............................................................................................................................................
Sodium phosphate was prepared from 50.0 cm3 of 0.500 mol dm–3 H3PO4 and an excess of
aqueous sodium hydroxide.
(ii)
How many moles of H3PO4 were used?
(iii)
Use your equation in (c)(i) to calculate how many moles of sodium hydroxide are
required.
[3]
(d) Phosphorus sulphide, P4S3, is used in small amounts in the tip of a match. On striking a
match, this compound burns.
(i)
Construct an equation for this reaction.
............................................................................................................................................
(ii)
Both oxides formed in (i) dissolve in water to give acidic solutions. Construct an equation
for the reaction of each oxide with water.
............................................................................................................................................
........................................................................................................................................[4]
[Total : 9]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
74 minutes
Score:
/61
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Question
uestion
1
(a)
(b) (i)
point
Marks
oxygen: (1s2) 2s22p4
fluorine: (1s2) 2s22p5
1
F2O / OF2
1
(ii)
1
F
O
F
bent or non-linear
1
Eo values: F2 / F– = 2.87 V and Cl2 / Cl – = 1.36 V
1
fluorine (has the more positive Eo so) is more oxidising
1
(ii)
redox
1
(iii)
Cl F + 2KBr → KCl + KF + Br2
1
(iii)
(c) (i)
[Total: 8]
Question
uesti
2
(a)
(b) (i)
(ii)
(c) (i)
(ii)
Scheme
Mark
ark
The amount of energy required / energy change / enthalpy change when one electron is
removed
from each atom / (cat)ion in one mol
of gaseous atoms / (cat)ions
OR energy change when 1 mole of electrons is removed from one mole of gaseous
atoms / ions
X(g) → X+(g) + e– gains 2 marks
1
Group V / 5 / 15
1
Big difference between fifth and sixth ionisation energies
1
1s2 2s2 2p3
ecf from (b)(i) if period 2
1
(Weighted) mean / average mass of an atom(s) (of an element)
1
Relative to 1 / 12th of (the mass of an atom of) carbon-12 OR
relative to carbon-12 which is (exactly) 12 (units)
allow as an expression
1
Z
31.13
Ar
So
1
1
3
2
2
Cl
68.87
= 1: 2
35.5
68.87/35.5
=2
31.13/Ar
2 × 31.13 × 35.5
= 32.0923 = 32.1 to 3s.f.
68.87
Allow alternative correct methods
Ar =
T
1
1
2
Question
uesti
(d) (i)
Scheme
Mark
ark
NaCl (+ aq ) NaCl + H2O Na+ + Cl –
Na+ + Cl – + H2O
1
SiCl 4 + 2H2O SiCl 4 + 4H2O SiCl 4 + 4H2O SiO2 + 4HCl
Si(OH)4 + 4HCl
SiO2.2H2O + 4HCl
1
2
Allow correct equation with other molar amounts of water
(ii)
(e)
T
NaCl is ionic AND giant / lattice
NaCl dissolves / does not react
SiCl 4 is covalent AND molecular / simple
SiCl 4 is hydrolysed / reacts
1
1
1
1
4
shape of SF6 = Octahedral
bond angle = 90°
1
1
2
18
3
(a
(i)
S
C
S
S atom has 6 and C atom has 4 electrons
(1)
S=C double bonds (4 electrons) clearly shown
(1)
(ii) linear and 180°
(b)
b) (
(1)
1)
CS2 + 3O2 → CO2 + 2SO2
(1)
(ii) enthalpy change when 1 mol of a substance
(1)
is burnt in an excess of oxygen/air
or is completely combusted
under standard conditions
(1)
[3]
(c)
CS2 + 3O2 →
CO2
+
∆Hf⦵/kJ mol–1 x
–395
∆Hreaction = –395 + 2(–298) – x = –1110 kJ mol–1
gives x = –395 + (–596) + 1110 = +119 kJ mol–1
(d)
d) (
2SO2
2(–298)
(1)
(1)
(1) [3]
CS2 + 2NO → CO2 + 2S + N2
or
CS2 + 2NO → CO + 2S + N2O
correct products (1)
correct equation (1)
(ii) from –2 to 0
both required (1)
[3]
[Total: 12]
4
(a)
NH3
CH4
pyramidal
tetrahedral
both ‘dot-and-cross’ diagrams correct
NH3 is pyramidal or trigonal pyramidal
CH4 is tetrahedral
(b)
b) (
nitrogen and hydrogen have different electronegativities
N–H bond has a dipole or
Nδ–  Hδ+ or
bonding pair is unequally shared
(1)
(1)
(1)
[3]
(1)
(1)
(ii) molecule is not symmetrical or
dipoles do not cancel out
(1)
(iii) NH3 has higher boiling point than expected from Mr value or
has higher boiling point than methane
or NH3 is soluble in water
(1)
[4]
(1)
(1)
(1)
[3]
(c) three covalent N–H bonds
one co-ordinate (dative covalent) N–H bond
one ionic bond between NH4+ and Cl –
[Total: 10]
5
(a) fewer electrons in Cl 2 than in Br2 (1)
smaller van der Waals’ forces in Cl 2 or stronger van der Waals’ forces in Br2 (1)
[2]
(b) CO has a permanent dipole or N2 does not (1)
permanent dipole-permanent dipole interactions are stronger than those from induced
dipoles (1)
[2]
(c) (i) a co-ordinate bond (1)
(ii) a covalent bond (1)
or
(iii) a lone pair (1)
or
penalise any groups of 3 or 4 electrons that are circled
(d) CO and HCN both have a dipole or N2 does not have a dipole (1)
[3]
[1]
(e) (i)
H H
 
HCCOH
 
H C≡N
C≡N must be shown (1)
(ii) nucleophilic addition (1)
(iii)
δ+ δ–
CH3C=O

H CN–
H
|
CH3CO–
|
CN
HCN
H

CH3COH + CN–

CN
C=O dipole correctly shown or correct curly arrow on C=O (1)
attack on Cδ+ by C of CN– (1)
correct intermediate (1)
CN– regenerated (1)
[5 max]
[Total: 13]
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Covalent Bonding &
Shapes of Molecules
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
74 minutes
Score:
/61
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Complete the electronic configurations of the following atoms.
oxygen: 1s2..........................................
fluorine: 1s2..........................................
[1]
(b) A compound of fluorine and oxygen contains three atoms in each molecule.
(i)
Predict its formula.
....................................................................................................................................... [1]
(ii)
Draw a ‘dot-and-cross’ diagram to show its bonding.
[1]
(iii)
Suggest the shape of this molecule.
....................................................................................................................................... [1]
Use E o values from the Data Booklet to predict the relative oxidising abilities of fluorine
and chlorine.
(c)
c)
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii)
Predict the type of reaction that would occur between the interhalogen compound chlorine
fluoride, Cl F, and potassium bromide solution.
....................................................................................................................................... [1]
(iii)
Construct an equation for this reaction.
....................................................................................................................................... [1]
[Total: 8]
2
(a) Explain what is meant by the term ionisation energy.
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [3]
(b) The first seven ionisation energies of an element, A, in kJ mol–1, are
1012
1903
2912
4957
6274
21 269
25 398.
(i) State the group of the Periodic Table to which A is most likely to belong. Explain your
answer.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Complete the electronic configuration of the element in Period 2 that is in the same group
as A.
1s2 ................................................................................................................................. [1]
(c) Another element, Z, in the same period of the Periodic Table as A, reacts with chlorine to
form a compound with empirical formula ZCl 2. The percentage composition by mass of ZCl 2
is Z, 31.13; Cl , 68.87.
(i) Define the term relative atomic mass.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Calculate the relative atomic mass, Ar, of Z.
Give your answer to three significant figures.
Ar of Z = ....................... [2]
(d) The chlorides of elements in Period 3 of the Periodic Table show different behaviours on
addition to water, depending on their structure and bonding.
(i) Write equations to show the behaviour of sodium chloride, NaCl , and silicon chloride,
SiCl 4 , when separately added to an excess of water.
NaCl ...................................................................................................................................
SiCl 4 ...................................................................................................................................
[2]
(ii) State and explain the differences in behaviour of these two chlorides when added to water,
in terms of their structure and the bonding found in the compounds.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
(e) Sulfur reacts with fluorine to form SF6. State the shape and bond angle of SF6.
shape of SF6 ..............................................................................................................................
bond angle of SF6 ......................................................................................................................
[2]
[Total: 18]
3
Carbon disulfide,CS 2, is a volatile, flammableliquidwhichisproducedinsmall
quantities in
volcanoes.
(a) The sequence of atoms in the CS2 molecule is sulfur to carbon to sulfur.
(i) Draw a ‘dot-and-cross’ diagram of the carbon disulfide molecule.
Show outer electrons only.
(ii) Suggest the shape of the molecule and state the bond angle.
shape .........................................................................................................................
bond angle .................................................................................................................
[3]
(b) Carbon disulfide is readily combusted to give CO2 and SO2.
(i) Construct a balanced equation for the complete combustion of CS2.
....................................................................................................................................
(ii) Define the term standard enthalpy change of combustion,
.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[3]
(c) Calculate the standard enthalpy change of formation of CS2 from the following data.
Include a sign in your answer.
standard enthalpy change of combustion of CS2 = –1110 kJ mol–1
standard enthalpy change of formation of CO2
= –395 kJ mol–1
standard enthalpy change of formation of SO2
= –298 kJ mol–1
[3]
(d) Carbon disulfide reacts with nitrogen monoxide, NO, in a 1:2 molar ratio.
A yellow solid and two colourless gases are produced.
(i) Construct a balanced equation for the reaction.
....................................................................................................................................
(ii) What is the change in the oxidation number of sulfur in this reaction?
from ..................................................... to .....................................................
[3]
[Total: 12]
4
Ammonia, NH3, and methane, CH4, are the hydrides of elements which are next to one
another in the Periodic Table.
(a) In the boxes below, draw the ‘dot-and-cross’ diagram of a molecule of each of these
compounds. Show outer electrons only.
State the shape of each molecule.
NH3
CH4
shape
shape
[3]
(b) Ammonia is polar whereas methane is non-polar. The physical properties of the two
compounds are different.
(i) Explain, using ammonia as the example, the meaning of the term bond polarity.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) Explain why the ammonia molecule is polar.
....................................................................................................................................
....................................................................................................................................
(iii) State one physical property of ammonia which is caused by its polarity.
....................................................................................................................................
....................................................................................................................................
[4]
(c) When ammonia gas is mixed with hydrogen chloride, white, solid ammonium chloride is
formed.
State each type of bond that is present in one formula unit of ammonium chloride and
how many of each type are present.
You may draw diagrams.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
[Total: 10]
5
Elements and compounds which have small molecules usually exist as gases or liquids.
(a) Chlorine, Cl 2, is a gas at room temperature whereas bromine, Br 2, is a liquid under the
same conditions.
Explain these observations.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(b) The gases nitrogen, N2, and carbon monoxide, CO, are isoelectronic, that is they have
the same number of electrons in their molecules.
Suggest why N2 has a lower boiling point than CO.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(c) A ‘dot-and-cross’ diagram of a CO molecule is shown below. Only electrons from outer
shells are represented.
C
O
In the table below, there are three copies of this structure.
On the structures, draw a circle round a pair of electrons that is associated with each of
the following.
(i) a co-ordinate bond
C
O
(ii) a covalent bond
C
O
(iii) a lone pair
C
O
[3]
(d) Hydrogen cyanide, HCN, is a gas which is also isoelectronic with N2 and with CO.
Each molecule contains a strong triple bond with the following bond energies.
bond
bond energy / kJ mol–1
–C⬅N in HCN
890
N⬅N
994
C⬅O
1078
Although each compound contains the same number of electrons and a strong triple
bond in its molecule, CO and HCN are both very reactive whereas N2 is not.
Suggest a reason for this.
..........................................................................................................................................
.................................................................................................................................... [1]
(e) HCN reacts with ethanal, CH3CHO.
(i)
Give the displayed formula of the organic product formed.
(ii)
What type of reaction is this?
...................................................................
(iii)
Draw the mechanism of this reaction. You should show all full and partial charges
and represent the movement of electron pairs by curly arrows.
[5]
[Total: 13]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Mark Scheme 2
Time Allowed:
58 minutes
Score:
/48
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(b)
b)
PbO2 decomposed into PbO (and O2). (SnO2 is stable)
[1]
PbCl4 dissociates into Cl2 and PbCl2 (white solid)
or PbCl4 → PbCl2 + Cl2 or in words
(1)
(1)
Cl2 + 2KI → 2KCl + I2
(1)
Eo(Cl2/Cl–) is more positive than Eo(I2/I–)
(1)
cce
(ii) SnCl4 is more stable than PbCl4 / answers using Eo accepted
(5 max 4)
(c)
c)
..
Cl:C:Cl
+
–
or
..
Cl=C–Cl
bent or non-linear or angle = 100–140o
(ii) CCl2 + H2O → CO + 2HCl
[4]
(1)
(1)
(1)
[3]
[Total: 8]
2
(a
(i) diagram to show tetrahedral arrangement (3D or bond angle marked) (1)
(ii) 4 covalent bonds/bond pairs (with Cl) only or no lone pairs. (1)
[2]
(b) (i) steamy/white fumes/gas or heat evolved (1)
(fumes are) HCl (from hydrolysis of Sn-Cl bonds) or exothermic reaction/bond breaking (1)
(can award second mark for HCl (g) in eqn.)
(ii) SnCl4 + 2H2O → SnO2 + 4HCl etc. (allow partial hydrolysis and with OHs) (1)
[3]
[Total: 5]
3
(a)
a) (
Covalent / co-ordinate
(ii) Mechlorethamine – binds the two chains together
– prevents unravelling
Cis-platin – binds to two Gs / bases in one chain
– so they are not available for base pairin
(1)
(1)
(1)
(1)
(1)
[Total: 5]
4
(a)
sphericall (1)
double lobes along the x-axis (1)
(b) (i) attraction between bonding electrons and nuclei
attraction is electrostatic
(ii) H2
(1)
(1)
s-s overlap clearly shown
must not be normal dot/cross diagram
HCl
[3]
(1)
s-p overlap clearly shown
overlap must involve s and p orbitals
(1)
[4]
(c) (i) bonding electrons are unequally shared or
the molecule has a dipole/δ+ and δ- ends to molecule
(1)
(ii) the H and Cl atoms have different electronegativities
or chlorine is more electronegative than hydrogen
(1)
[2]
(d)
allow two ‘sausages’ above and below the C-C axis
or two p orbitals overlapping sideways
to form one (localised) π bond over two carbon atoms
(1)
[1]
(e) ∆Hfo = 2(–393.7) + 2(–285.9) – (–1411)
= + 51.8 kJ mol–1(units given in qu.)
penalise errors:
no 2 for –393.7
no 2 for –285.9
wrong sign for –(–1411)
(3)
[3]
[Total: 13]
Question
uestion
5
Mark
ark
(a)
The (total) number of protons and neutrons (in the nucleus of an atom)
1
(b) (i)
Mass of an atom(s) or isotope
1
relative to 1 (the mass) of (an atom of) carbon–12
12
1
T
1
OR
2
relative to carbon–12 which is (exactly) 12 (units)
allow a correct expression
(ii)
79
Br
78.92x
so
81
Br
80.92(100–x) where x = % abundance of 79Br
78.92x + 80.92(100 − x )
= 79.9
100
x = 51
hence
1
1
79
Br : 81Br = 51 : 49
1
3
Question
uestion
(c)
Mark
ark
A
4.31
Ar
T
B
95.69 = 1 : 3
79.9
So 95.69/79.9 = 3
4.31/ Ar
1
Ar = 3 × 4.31× 79.9 = 10.796 = 10.8 to 3 s.f.
95.69
1
3 sig figs
1
allow alternative correct methods
(d) (i)
Mg: bright / white light / flame OR white solid / smoke
Mg + 1 O2 → MgO
2
allow correct multiples
(ii)
1
1
S: blue flame OR white / steamy fumes OR yellow solid disappears
1
S + O2 → SO2
allow correct multiples
1
Al 2O3
Al 2O3
Al 2O3
Al 2O3
Al 2O3
Al 2O3
+
+
+
+
+
+
2NaOH + 7H2O → 2NaAl (OH)4(H2O)2 OR
2NaOH + 3H2O → 2NaAl (OH)4 OR
2NaOH → 2NaAl O2 + H2O OR
2OH‒ + 7H2O → 2[Al (OH)4(H2O)2]– OR
2OH‒ + 3H2O → 2[Al (OH)4]– OR
2OH− → 2Al O2− + H2O
Al 2O3 + 6HCl → 2Al Cl 3 + 3H2O
allow correct ionic equations
4
1
1
2
Question
uestion
(e)
Mark
ark
shape of PCl 5 =(trigonal) bipyramid(al)
1
bond angles in PCl 5 = 120° and 90°
1
T
2
17
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Covalent Bonding &
Shapes of Molecules
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Question Paper 2
Time Allowed:
58 minutes
Score:
/48
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Describe how the behaviour of the oxides of tin and lead in their +4 oxidation states
differ on heating.
..........................................................................................................................................
...................................................................................................................................... [1]
(b) Explain the following by using data from the Data Booklet where appropriate, and writing
equations for all reactions.
(i)
A sample of liquid PbCl4 is placed in a flask and the flask is gently warmed. A gas
is evolved and a white solid is produced. When the gas is bubbled through KI(aq),
purple fumes are produced.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Repeating the same experiment using liquid SnCl4 instead of PbCl4 results in no
evolution of gas, and no reaction with KI(aq).
..................................................................................................................................
..................................................................................................................................
[4]
(c) The molecule dichlorocarbene, CCl2, can be produced under certain conditions. It is
highly unstable, reacting with water to produce carbon monoxide and a strongly acidic
solution.
(i)
Suggest the electron arrangement in CCl2 and draw a dot-and-cross diagram
showing this. Predict the shape of the molecule.
(ii)
Construct an equation for the reaction of CCl2 with water.
..................................................................................................................................
[3]
[Total: 8]
2
(a) (i)
(ii)
By means of a clear, labelled diagram, describe the shape of the tin(IV) chloride
molecule.
Explain the shape of the tin(IV) chloride molecule in terms of its bonding.
..................................................................................................................................
..................................................................................................................................
[2]
(b) (i)
What would you expect to observe when tin(IV) chloride reacts with water?
Suggest an explanation for your answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Write an equation for the reaction between tin(IV) chloride and water.
..................................................................................................................................
[3]
[Total: 5]
3
In recent years a great deal of research has been carried out into finding different anti-cancer
drugs. Tumours, which are often symptoms of cancer, are produced when cells replicate
uncontrollably. This in turn is brought about by the replication of DNA in these cells.
Two anti-cancer agents are mechlorethamine and cis-platin. They work by binding to the
DNA and preventing replication.
DNA
Cl
DNA
G
CH3
CH3
N
N
G
NH3
Cl
(a) (i)
NH3
Pt
NH3
mechlorethamine
Cl
crosslinked DNA
G
C
G
C
Pt
Cl
NH3
cis-platin
What type of bonding attaches both anti-cancer agents to the DNA?
..................................................................................................................................
(ii)
Suggest how each of the anti-cancer agents prevents replication of the DNA.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[5]
[Total: 5]
4
This question is about the bonding of covalent compounds.
(a) On the axes below, sketch the shapes of a 1s, a 2s, and a 2px orbital.
z
z
y
z
y
x
y
x
1s
x
2s
2px
[3]
(b) Covalent bonding occurs when two atoms share a pair of electrons. Covalent bonding
may also be described in terms of orbital overlap with the formation of σ bonds.
(i)
How are the two atoms in a covalent bond held together? In your answer, state which
particles are attracted to one another and the nature of the force of attraction.
..................................................................................................................................
..................................................................................................................................
(ii)
Draw sketches to show orbital overlap that produces the σ bonding in the H2 and
HCl molecules.
H2
HCl
[4]
(c) The bond in the HCl molecule is said to be ‘polar’.
(i)
What is meant by the term bond polarity?
..................................................................................................................................
(ii)
Explain why the HCl molecule is polar.
..................................................................................................................................
..................................................................................................................................
[2]
(d) The bonding in ethene may be described as a mixture of σ and π bonding.
Each carbon atom in ethene forms three σ bonds as shown below.
H
H
C
C
H
H
On the diagram, sketch the π bond that is also present in ethene.
[1]
(e) Carbon, hydrogen and ethene each burn exothermically in an excess of air.
C(s) + O2(g) → CO2(g)
H2(g) + ½O2(g) → H2O(l)
C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l)
∆H oc = –393.7 kJ mol–1
∆H oc = –285.9 kJ mol–1
∆H oc = –1411.0 kJ mol–1
Use the data to calculate the standard enthalpy change of formation, ∆H of , in kJ mol–1,
of ethene at 298 K.
2C(s) + 2H2(g) → C2H4(g)
∆H of = ................................. kJ mol–1
[3]
[Total: 13]
5
(a) Explain what is meant by the term nucleon number.
....................................................................................................................................................
.............................................................................................................................................. [1]
(b) Bromine exists naturally as a mixture of two stable isotopes, 79Br and 81Br, with relative isotopic
masses of 78.92 and 80.92 respectively.
(i) Define the term relative isotopic mass.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Using the relative atomic mass of bromine, 79.90, calculate the relative isotopic abundances
of 79Br and 81Br.
[3]
(c) Bromine reacts with the element A to form a compound with empirical formula ABr3. The
percentage composition by mass of ABr3 is A, 4.31; Br, 95.69.
Calculate the relative atomic mass, Ar, of A.
Give your answer to three significant figures.
Ar of A = ....................... [3]
(d) The elements in Period 3 of the Periodic Table show different behaviours in their reactions with
oxygen.
(i) Describe what you would see when separate samples of magnesium and sulfur are
reacted with oxygen.
Write an equation for each reaction.
magnesium
.............................................................................................................................................
.............................................................................................................................................
sulfur
.............................................................................................................................................
.............................................................................................................................................
[4]
(ii) Write equations for the reactions of aluminium oxide, Al 2O3, with
sodium hydroxide,
.............................................................................................................................................
hydrochloric acid.
.............................................................................................................................................
[2]
(e) Phosphorus reacts with chlorine to form PCl 5.
State the shape of and two different bond angles in a molecule of PCl 5.
shape of PCl 5 ............................................................................................................................
...........
bond angles in PCl 5 ............................
[2]
[Total: 17]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Mark Scheme 3
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Question
Questi
1
(a)
(b) (i)
(ii)
Scheme
Marks
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
1
1
Very exothermic / gets very hot
OR creates (acid / H2SO4) spray / mist / fog / fumes
1
SO3 + H2SO4 → H2S2O7
1
H2S2O7 + H2O → 2H2SO4
1
(c) (i)
O
1
S
(ii)
[2]
O
O
1+1
O
M1 SO2 correct M2 SO3 correct
(d) (i)
[2]
O
S
(ii)
T
[2]
115–120° bent / non-linear
120° trigonal planar
1
1
Advantage = higher rate
Greater KE / energy / speed / collision frequency / proportion of successful collisions / more particles with E>Ea
1
1
Disadvantage – reduced yield / less product
1
(Forward reaction) exothermic AND (hence in accordance with LCP) equilibrium / reaction shifts left (to counteract
inc T) ora
1
Kp =
pSO3
2
[2]
[4]
2
pSO 2 × pO 2
1
[1]
Question
Questi
(iii)
Scheme
Marks
Marks
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
2
2
0
(–1.8) (–0.9)
0.2
1.1
1.1
1
xSO3 = 1.8 / 3.1 = 0.581
xSO2 = 0.2 / 3.1 = 0.065
xO2 = 1.1 / 3.1 = 0.355
1
Kp =
0.5812 × (2 × 105)2
= 1.13 × 10–3 Pa–1
0.0652 × (2 × 105)2 × 0.355 × 2 × 105
T
1
1+1
[5]
[19]
Question
Questi
2
(a
Scheme
Marks
Marks
(i) increasing distance of (outer/highest energy) electron(s) from nucleus
OR increasing distance of outer/valence shell from nucleus
(b)
(c) (i)
1
increased shielding / screening (from inner shells)
1
reduces attraction
1
(ii) increasing cation charge / effective nuclear charge
OR decreasing number of electrons compared with protons
1
(boiling point) increases (down the group)
1
increasing number of electrons (in molecules) down group
1
increasing strength of / more van der Waals’ forces (allow correct alternatives to van der Waals’ forces)
1
so more energy needed to overcome (the forces)
1
I
2.253
0.450
5
[3]
1
increase in attraction
F
42.8
19
T
[2]
[4]
1
0
0
1
/ IF5
EF = MF or IF5= 222
1
1
[3]
(ii)
xx
x
x
xCl
xx
1
I
1
[2]
1
1
1
1
[4]
(ii) 3Cl2 + 6NaOH 5NaCl + NaClO3 + 3H2O
M1: correct species
M2: balanced equation
1
1
[2]
(iii) 0 to –1
(0 to) +5
1
1
[2]
(Yes) as electronegativities are different
(d) (i) W = NaClO;
X = NaClO3;
Y = HCl;
Z = AgCl
(iv) Ag+(aq) + Cl –(aq) AgCl(s)
[1]
[23]
3
(a
(i)
101 = P35Cl35Cl
103 = P35Cl37Cl
105 = P37Cl37Cl
1
1
1
(ii)
9:6:1
1
PCl5 5 bonding pairs around P
1
(b) (i)
Cl
(ii)
P
Cl
+
Cl
1
1
Cl
Cl
(c) (i)
Cl
Cl
Cl
Cl
O
O O
P
-
[3]
1
P
P
Cl
P
[4
P
O
O
O
P4O6 structure where each P has three P-O bonds and each O has two P-O bonds e.g.
O
O
P
O
P
P
O
P
O
O
(ii)
(d) (i)
(molecule/ion/species) that donates a lone pair of electrons (to a central transition metal atom or
ion)
1
Ksp =[Ca2+]3[PO43–]2
1
[2
(ii)
(e) (i)
(ii)
Total
[Ca2+] = 3 × 2.50 × 10–6 = 7.50 × 10–6 mol dm–3
[PO43–] = 2 × 2.50 × 10–6 = 5.00 × 10–6 mol dm–3
1
= (7.50 × 10–6)3(5.00 × 10–6)2
= 1.05(1.1) × 10–26
mol5dm–15
1
1
(enthalpy change) when 1 mole of an ionic compound
is formed from its gaseous ions
1
1
Mg2+ has a smaller (ionic) radii than Ca2+
OR Mg2+ is smaller than Ca2+
1
[4]
[3
[16]
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Covalent Bonding &
Shapes of Molecules
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Question Paper 3
Time Allowed:
70 minutes
Score:
/58
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The Contact process for the manufacture of sulfuric acid was originally patented in the
19th century and is still in use today.
The key step in the overall process is the reversible conversion of sulfur dioxide to sulfur trioxide in
the presence of a vanadium(V) oxide catalyst.
2SO2(g) + O2(g)
2SO3(g)
∆H = –196 kJ mol–1
(a) One way in which the sulfur dioxide for this reaction is produced is by heating the sulfide ore
iron pyrites, FeS2, in air. Iron(III) oxide is also produced. Write an equation for this reaction.
.............................................................................................................................................. [2]
(b) The sulfur trioxide produced in the Contact process is reacted with 98% sulfuric acid. The
resulting compound is then reacted with water to produce sulfuric acid.
(i) Explain why the sulfur trioxide is not first mixed directly with water.
.............................................................................................................................................
....................................................................................................................................... [1]
(ii) Write equations for the two steps involved in the conversion of sulfur trioxide into sulfuric
acid.
.............................................................................................................................................
....................................................................................................................................... [2]
(c)
c)
Sulfur dioxide and sulfur trioxide both contain only S=O double bonds.
Draw labelled diagrams to show the shapes of these two molecules.
SO2
SO3
[2]
(ii) For your diagrams in (i), name the shapes and suggest the bond angles.
SO2 shape ................................................. SO3 shape ...................................................
SO2 bond angle ......................................... SO3 bond angle ...........................................
[2]
(d) The conversion of sulfur dioxide into sulfur trioxide is carried out at a temperature of 400 °C.
(i) With reference to Le Chatelier’s Principle and reaction kinetics, state and explain one
advantage and one disadvantage of using a higher temperature.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
(ii) State the expression for the equilibrium constant, Kp, for the formation of sulfur trioxide
from sulfur dioxide.
Kp =
[1]
(iii) 2.00 moles of sulfur dioxide and 2.00 moles of oxygen were put in a flask and left to reach
equilibrium.
At equilibrium, the pressure in the flask was 2.00 × 105 Pa and the mixture contained
1.80 moles of sulfur trioxide.
Calculate Kp. Include the units.
Kp = ..............................
units = ..............................
[5]
[Total: 19]
2 (a)
Successive ionisation energies for the elements fluorine, F, to bromine, Br, are shown on the
graph.
12 000
F
10 000
8000
Cl
ionisation
6000
energy / kJ mol–1
Br
4000
2000
0
1
2
4
5
electrons removed
(i) Explain why the first ionisation energies decrease down the group.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) Explain why there is an increase in the successive ionisation energies of fluorine.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(b) Group VII is the only group in the Periodic Table containing elements in all three states of
matter at room conditions.
State and explain, in terms of intermolecular forces, the trend in the boiling points of the
elements down Group VII.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [4]
(c) Compounds containing different halogen atoms covalently bonded together are called
interhalogen compounds.
(i) One interhalogen compound can be prepared by the reaction between iodine and fluorine.
This compound has Mr = 222 and the percentage composition by mass: F, 42.8; I, 57.2.
Calculate the molecular formula of this interhalogen compound.
molecular formula ................................. [3]
(ii) Another interhalogen compound has the formula ICl.
Draw a ‘dot-and-cross’ diagram of a molecule of this compound, showing outer shell
electrons only. Explain whether or not you would expect this molecule to be polar.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(d) Some reactions involving chlorine and its compounds are shown in the reaction scheme below.
NaCl (aq) +
W(aq)
cold NaOH(aq)
Cl 2(g)
H2(g)
UV
bubble
into water
hot NaOH(aq)
NaCl (aq) +
X(aq)
Y(g)
Z(s)
AgNO3(aq)
Y(aq)
(i) Give the formulae of W, X, Y and Z.
W ........................................................................................................................................
X .........................................................................................................................................
Y .........................................................................................................................................
Z .........................................................................................................................................
[4]
(ii) Write an equation for the reaction of chlorine with hot NaOH(aq).
....................................................................................................................................... [2]
(iii) State the oxidation numbers of chlorine at the start and at the end of the reaction in (ii).
....................................................................................................................................... [2]
(iv) Write an ionic equation for the reaction of Y with AgNO3(aq). Include state symbols.
....................................................................................................................................... [1]
[Total: 23]
3
(a) Natural phosphorus consists of one isotope, 31P. Chlorine exists naturally as two isotopes, 35Cl
and 37Cl, in the relative abundance ratio of 3 : 1.
(i) The mass spectrum of PCl 3 contains several peaks corresponding to a number of
molecular fragments.
Suggest the isotopic composition of the fragments with the following mass numbers.
mass number
isotopic composition
101
103
105
(ii) Predict the relative ratios of the peak heights of the three peaks corresponding to these
fragments.
.............................................................................................................................................
[4]
(b) Phosphorus reacts with chlorine to form a variety of chlorides.
PCl 5 is an example of a compound that exists as two structures depending on the conditions.
2PCl 5(g)
[PCl 4]+[PCl 6]–(s)
(i) Draw a ‘dot-and-cross’ diagram to show the bonding in PCl 5. Show the outer electrons
only.
(ii) Draw diagrams to suggest the shapes of [PCl 4]+ and [PCl 6]–.
[PCl 4]+
[PCl 6]–
[3]
(c)
c)
Phosphorus(III) oxide, P4O6, contains no P–P or O–O bonds.
In the P4O6 molecule, all oxygen atoms are divalent and all phosphorus atoms are trivalent.
Sketch a structure for P4O6.
(ii) P4O6 can act as a ligand.
What is meant by the term ligand ?
.............................................................................................................................................
.............................................................................................................................................
[2]
(d) Phosphate ions in water can be removed by adding a solution containing Ca2+(aq) ions, which
form a precipitate of calcium phosphate, Ca3(PO4)2.
(i) Write an expression for the Ksp of Ca3(PO4)2.
Ksp =
(ii) The solubility of Ca3(PO4)2 is 2.50 × 10–6 mol dm–3 at 298 K.
Calculate the solubility product, Ksp, of Ca3(PO4)2 at this temperature. Include the units.
Ksp = ..................................................................
units ....................................................
[4]
(e)
e)
What is meant by the term lattice energy?
.............................................................................................................................................
.............................................................................................................................................
(ii) Explain why the lattice energy of calcium phosphate is less exothermic than that of
magnesium phosphate.
.............................................................................................................................................
.............................................................................................................................................
[3]
[Total: 16]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Mark Scheme 4
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Que
estio
on
1
Ma
arking poin
nt
(a)) (i)
Ma
arks
m/e
ide
entiity
35
35
Cll
37
37
Cll
70
35
Cl 35Cl or 35Cl2
37
Cl 35Cl
72
74
37
Cl 37Cl or 37Cl2
35, 37,, 70, 72
2, 74
4
corrrectt forrmullae
at leas
st on
ne sttructure
e as
s a posittive ion
(ii)
Markks
tota
al
1
1
1
9:6
6:1
1
co
orrecct ch
harg
ges
co
orrecct ellectrronss
1
1
La
attice en
nerg
gy = ∆H
Hf(SrrCl2) – (∆Hatom(Sr) + ∆Hi1(Sr) + ∆H
Hi2(S
Sr) + ∆H
Hatom
Hea(C
Cl))
m(Cll) + 2∆H
830) – (+ 164 + 48 + 1060 + 42 + (2 × –349
– 9))
= +(–8
= –2146 (kJ mol–1)
1
1
1
SrrCO
O3 + 2H
HNO
O3 Srr(NO
O3)2 + CO2 + H2O
1
[4]
(b)) (i)
(ii)
(c)) (i)
[5]
(ii)
(d)
Sr(NO3)2 SrO + 2NO2 + 0.5 O2
1
[2
(down the group) nitrates become more stable / require a higher temperature to decompose
1
1
1
[3]
as size/radius of ion increases OR charge density of ion decreases
so polarisation/distortion of anion/nitrate ion/NO3– /NO bond decreases
2
(a)
number of
bond pairs
number of
lone pairs
shape of
molecule
formula of a
molecule with
this shape
3
0
trigonal planar
BH3
4
3
2
CH4
allow other
Group IV
hydrides
0
tetrahedral
1
pyramidal or
trigonal
pyramidal
NH3
allow other
Group V
hydrides
non-linear or
bent or
V-shap
V-
H2O
allow other
Group VI
hydrides
2
1 mark for each correct row
(3 × 1)
[3]
(b)
b)
(1)
(ii) octahedral or square-based bipyramid
(1)
(iii) 90°
(1)
1)
[Total: 6]
3
(a)
8 e- around chlorine
1 H–electron (+) on the Cl - ion
3 covalent (ox) and one dative (oo) around N
[1]
[1]
[1]
[3]
(b) (i) it would react (with H2SO4)
[1
(ii) CaO + H2O → Ca(OH)2
[1]
(iii) CaO absorbs more water or CaO has greater affinity for water
[1]
[3]
(c) (i) 2Ca(NO3)2 → 2CaO + 4NO2 + O2
[1]
(ii) (Down the group, the nitrates)
become more stable/stability increases
[1]
because the size/radius of ion (M2+) increases
[1]
thus causing less polarisation/distortion
of the anion/NO3-/N-O bond
[1]
[4]
[Total: 10]
4
(a)
O
N
O
O
dative bond to an oxygen using two N electrons
8 electrons around N in 1 double + 2 single bonds
a total of 24 electrons, including one, and only one " "
(the extra electron, " ", can be in a bond or a lone pair)
[1]
[1]
[1
[3]
(b)
b)
2Mg(NO3)2 → 2MgO + 4NO2 + O2
[1]
(ii) (down the group)
nitrates become more stable or are more difficult to decompose or need a higher
temperature to decompose
[1]
because there is less polarisation of the anion / nitrate ion / N–O bonds
[1]
as radius of M2+ / metal ion increases or charge density of the cation decreases
[1]
[4]
(c) Cu + 4H+ + 2NO3– → Cu2+ + 2NO2 + 2H2O
specie [1]
balancing [1]
[2]
[Total: 9]
5
(a
(i) silicon/Si or phosphorus/P
(1)
(ii) sodium or sulfur name required
(1)
(iii) white solid formed/white fumes seen
chlorine gas decolourised
aluminium glows or burns
any two (2)
(iv) 2Al(s) + 3Cl2(g) → Al2Cl6(s) or
2Al(s) + 3Cl2(g) → 2AlCl3(s)
equation
state symbols
(1)
(1)
(v) outer shell of electrons is full/has a complete octet or
valence shell of electrons is full/has a complete octet or
activation energy is too high or
ionisation energy is too high
(1)
[7]
(b) (i)
element
Na
a
Does the chloride
dissolve or react?
approximate pH of the
resulting solution
dissol
7
Al
react
1 to 4
Si
react
1 to 4
one mark for each correct answer
(ii) hydrolysis
(c) (i) around the N atom there is only one lone pair
around the S atom there are two lone pairs
(6 × 1)
(1)
[7]
both (1)
(ii) angle (a) or sulfur – no mark for this
because two lone pairs repel more than one lone pair or
lone pair-lone pair repulsions are stronger
than lone pair-bond pair repulsions
(1)
[2]
[Total: 16]
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Covalent Bonding &
Shapes of Molecules
Question Paper 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Question Paper 4
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Chlorine exists naturally as a mixture of two isotopes, 35Cl and 37Cl , in the abundance ratio of 3 : 1.
The mass spectrum of chlorine consists of five peaks.
(i) Suggest the mass numbers for these five peaks and the identities of the species
responsible.
mass number
formula of species
(ii) Predict the ratios of the abundances of the three species with the highest mass numbers.
ratio of abundances = ........................................
[4]
(b) Strontium chloride, SrCl 2, can be used to produce a red colour in fireworks.
(i) Draw the ‘dot-and-cross’ diagram for strontium chloride. Show outer shell electrons only.
(ii) Use the following data, together with relevant data from the Data Booklet, to calculate
a value for the lattice energy of strontium chloride. You may find it helpful to construct a
Born-Haber cycle.
electron affinity per mole of chlorine atoms
–349 kJ mol–1
standard enthalpy of atomisation of Sr(s)
+164 kJ mol–1
standard enthalpy of formation of SrCl 2(s)
–830 kJ mol–1
lattice energy = .................. kJ mol–1
[5]
(c) Strontium nitrate, Sr(NO3)2, can also be used to produce a red colour in fireworks.
(i) Strontium nitrate can easily be prepared from strontium carbonate, SrCO3.
Suggest an equation for this preparation of strontium nitrate.
.............................................................................................................................................
(ii) Write an equation for the reaction that occurs when strontium nitrate is heated.
.............................................................................................................................................
[2]
(d) Describe and explain the trend in the thermal stabilities of the nitrates of the Group II elements.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [3]
[Total: 14]
2
Valence Shell Electron Pair Repulsion theory (VSEPR) is a model of electron-pair repulsion
(including lone pairs) that can be used to deduce the shapes of, and bond angles in, simple
molecules.
(a) Complete the table below by using simple hydrogen-containing compounds. One
example has been included.
number of
bond pairs
number of
lone pairs
shape of
molecule
formula of
a molecule
with this shape
3
0
trigonal planar
BH3
4
0
3
1
2
2
[3]
(b) Tellurium, Te, proton number 52, is used in photovoltaic cells.
When fluorine gas is passed over tellurium at 150 °C, the colourless gas TeF6 is formed.
(i) Draw a ‘dot-and-cross’ diagram of the TeF6 molecule, showing outer electrons only.
(ii) What will be the shape of the TeF6 molecule?
..........................................
(iii) What is the F–Te–F bond angle in TeF6?
..........................................
[3]
[Total: 6]
3
(a) Gaseous ammonia reacts with gaseous hydrogen chloride to form solid ammonium
chloride.
NH3 + HCl → NH4Cl
The bonding in ammonium chloride includes ionic, covalent and co-ordinate (dative
covalent) bonds.
Complete the following ‘dot-and-cross’ diagram of the bonding in ammonium chloride.
For each of the six atoms show all the electrons in its outer shell. Three electrons have
already been included.
Use the following code for your electrons.
● electrons from chlorine
x electrons from hydrogen
o electrons from nitrogen
+
H
x
●
o
N
H
–
H
Cl
H
[3]
(b) When a sample of dry ammonia is needed in the laboratory, the gas is passed through a
tower containing lumps of solid calcium oxide, CaO.
(i) Suggest why the usual drying agent for gases, concentrated H2SO4, is not used for
ammonia.
....................................................................................................................................
(ii) Write an equation for the reaction between CaO and H2O.
....................................................................................................................................
(iii) Suggest why CaO rather than MgO is used to dry ammonia.
....................................................................................................................................
[3]
(c) (i) Write an equation showing the thermal decomposition of calcium nitrate, Ca(NO3)2.
....................................................................................................................................
(ii) State and explain how the thermal stabilities of the nitrates vary down Group II.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
[Total: 10]
4
(a) The nitrate ion, NO3–, contains a dative covalent bond.
Complete the following ‘dot-and-cross’ diagram of the bonding in the nitrate ion. For
each of the four atoms show all the electrons in its outer shell. Three electrons have
already been included.
Use the following code for your electrons.
● electrons from oxygen
x electrons from nitrogen
□ added electron(s) responsible for the overall negative charge
–
O
x●
N
O
O
●
[3]
(b)
b)
Write an equation showing the action of heat on magnesium nitrate, Mg(NO3)2.
....................................................................................................................................
(ii) Describe and explain the trend that is observed in the thermal stabilities of the
Group II nitrates.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
(c) When concentrated nitric acid, HNO3, is added to copper turnings, a brown gas is evolved.
Use data from the Data Booklet to construct an ionic equation for this reaction.
...........................................................................................................................................
...........................................................................................................................................
[2]
[Total: 9]
5
The elements of the third period of the Periodic Table, sodium to sulfur, all form chlorides by
direct combination.
(a) (i) Sulfur forms a number of chlorides which are liquid at room temperature.
Which other element of the third period forms a chloride which is liquid at room
temperature?
....................................................................................................................................
(ii) Name one element of the third period which burns in chlorine with a coloured flame.
........................
(iii) Aluminium chloride may be produced by passing a stream of chlorine over heated
aluminium powder in a long hard-glass tube.
State two observations you could make during this reaction.
............................................................ and ................................................................
(iv) Write a balanced equation, with state symbols, for this reaction of aluminium with
chlorine.
....................................................................................................................................
(v) No chloride of argon has ever been produced.
Suggest a reason for this.
....................................................................................................................................
....................................................................................................................................
[7]
(b) When chlorides of the elements of the third period are added to water, some simply
dissolve while others can be seen to react with the water.
(i) Complete the table below, stating how the chlorides of Na, Al, and Si behave when
mixed with water. In the first column use only the terms ‘dissolve’ or ‘react’.
element
Does the chloride
dissolve or react?
approximate pH of
the resulting solution
Na
Al
Si
(ii) What type of reaction takes place between a chloride and water?
...................................................
[7]
(c) Sulfur forms the compound S4N4 with nitrogen. The structure of S4N4 is shown below.
Assume all bonds shown are single bonds.
N
S
a
N
S
b
S
N
N
S
(i) Determine the number of lone pairs of electrons around a nitrogen atom and a sulfur
atom in S4N4.
nitrogen atom ................................
sulfur atom ................................
(ii) Which bond angle, a or b, in the S4N4 molecule will be smaller? Explain your answer.
....................................................................................................................................
....................................................................................................................................
[2]
[Total: 16]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Mark Scheme 5
Time Allowed:
76 minutes
Score:
/63
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) [H+] = √(0.05 × 5.6 × 10–4) = 5.29 × 10–3 mol dm–3
pH = –log10(5.29 × 10–3) = 2.3
(b) (i) (Brønsted-Lowry)
equilibrium
[1]
[1]
[2]
acid-base/proton transfer/neutralisation/exothermic/reversible/
[1]
(ii)
H
H
N
H
H
F
H
[1]
H
N
F
H
H
[1]
[1]
3 x [1]
(iii) (in NH4F):
covalent: between N & H
dative: between N & H
ionic: between NH4+ & F– or N+ & F– or ammonium and fluoride (i.e. in words)
or between (oppositely charge) ions
[1]
[1]
[1]
(iv) (reverse reaction, remember)
high temperature, because reverse reaction is endothermic
[1]
low pressure, because reverse reaction causes an increase in no. of gaseous molecules
or an increase in partial pressure/volume.
[1]
[9]
(c) (i) 4NH3 + CuS + 2O2 → [Cu(NH3)4]SO4
[1]
(ii) deep/dark/royal blue or purple [NOT violet]
[1]
(iii) deep blue colour would change to light blue [NOT intensity of colour decreases]
⇒ hexaquocopper(II) ion or [Cu(H2O)6]2+ or [Cu(H2O)n(NH3)a–n]2+, where a = 4 or 6
or ligand exchange (of NH3) by H2O
[1]
(d) ligand exchange/substitution/displacement/replacement [IN WORDS]
(use of named ligands are OK instead of ‘ligand’. e.g. “water is displaced by chloride”)
formula of anion (see below for possibilities)
balanced equation. e.g.[Cu(H2O)6]2+ + nCl– → [Cu(H2O)6–nCln]2–n + nH2O
[1
[4]
[1]
[1]
[1]
(Allow n=1 up to n=6. Also allow [CuCln]2–n as product. Examples from many possible are:
[Cu(H2O)6]2+ + 2Cl– → [Cu(H2O)4Cl2] + 2H2O
[Cu(H2O)6]2+ + 4Cl– → [CuCl4]2– + 6H2O
equation could include HCl on the LHS, for example:
[3]
[Cu(H2O)6]2+ + 4HCl → H2CuCl4 + 2H+ + 6H2O or → CuCl42– + 4H+ + 6H2O
[Total: 18 max 17]
2
(a
enthalpy change when 1 mol of a compound is formed (1)
from its elements (1)
in their standard states under standard conditions (1)
[3]
N2H4(l) + O2(g) → N2(g) + 2H2O(g)
∆Hfo/kJ mol-1 +50.6
–241.8
∆Horeaction = 2(–241.8) – (+50.6) (1)
= –534.2 kJ mol-1 (1)
(b)
b)
(ii) Ea is too high (1)
(iii) products are H2O and N2 which are harmless/non toxic
or are already present in the atmosphere (1)
(c)
c) (
[4]
‘dot-and-cross’ diagram (1)
(ii)
(1)
(iii) minimum is
allow bond angle around N atom between 109o and 104o (1)
(d) –2 (1)
[4]
[1]
[Total: 12]
3
(a
(i)
formula of chloride
oxidation number of element in the chloride
NaCl
MgCl2
AlCl3
SiCl4
PCl3
SCl2
+
+
+
+
+
+
correct oxidation nos. for NaCl to SCl2
(1)
(ii) Na to Al
loss of outer/valence electrons
to give configuration of Ne/to complete octet
Si to S
gain or sharing of outer electrons
to give configuration of Ar/to complete octet
(b)
b) (
(1)
(1)
(1)
(1)
giant lattice (may be in diagram)
with strong ionic bonding
[5]
(1)
(1)
(ii) ionic
oni
(iii) –1
(iv)
(1)
.. +
: Na :
..
x
.H
correct numbers of electrons
correct charges
(1)
(1)
(v)
compound
omp
2
oxidation number of element in the hydride
+
AlH3
PH3
H2S
+
–
–
correct oxidation nos. for MgH2 and AlH3
correct oxidation nos. for PH3 and H2S
(1)
(1
[8]
(c) (i)
chloride
hloride
magnesium
aluminium
pH
H
6.5–6.9
1–4
(1)
(1)
(no mark)
(ii) NaH + H2O → NaOH + H2
(iii) 10–14
0–1
(1)
[4]
(d)
d) (
covalent
ova
(ii) SiCl4 + 4H2O → Si(OH)4 + 4HCl or
SiCl4 + 4H2O → SiO2.2H2O + 4HCl or
SiCl4 + 2H2O → SiO2 + 4HCl
(1)
1)
[Total: 19]
4
(a
(i) ∆H = 4 × 278 – 244 – 2 × 496
= –124 (kJ mol–1)
(correct ans [2])
[1]
[1
(ii) shape is bent/V-shaped/non-linear (or diagram)
[1]
due to (one) lone pair and/or (1) odd/unpaired electron (or shown on diag)
[1]
(assume electrons are on chlorine unless explicitly stated otherwise, in which case
award no mark)
(iii) 3KClO3 + H2SO4 → K2SO4 + KClO4 + H2O + 2ClO2
(b)
b)
[1] [5]
coal-fired power stations; fuel in cars; car exhausts/gas emissions; other named use of a
fossil fuel; contact process; cement manufacture; brick manufacture; roasting of sulphide
ores; burning tyres
(any 2) [1]
(NOT volcanoes etc; NOT burning of natural gas)
(no marks for only 1 correct source)
(ii) causes acid rain
[1]
which lower pH of lakes; leaches aluminium from soils; kills fish/plants/rainforests;
dissolves/corrodes/damages buildings
(any 1) [1]
(NOT asthma etc – since this is not environmental)
[3]
(c)
c)
CO2: simple + molecular/covalent or weak intermolecular forces
SiO2: giant/macro + molecular/covalent
SnO2: ionic/electrovalent (ignore “giant”)
(2 correct = [1], 1 correct = [0])
(ii) SnO2 is stable, PbO2 is not or SnO2 is the more stable
PbO2 → PbO + ½ O2
(iii) H2O + CO2 (⇌) H+ + HCO3¯
Kc = [H+][HCO3¯]/[H2O][CO2] or = [H+][HCO3¯]/[CO2]
(iv) HCO3¯ + H+ → H2CO3 or H2O + CO2 (or equation with H3O+)
HCO3¯ + OH¯ → CO32- + H2O (NB NOT H2CO3 + OH¯ →)
(all 3 correct) [2]
[1]
[1]
[1
ec [1]
[1]
[1]
(words can substitute for one of the equations but not both. If two correct word
descriptions are given, in the absence of at least one correct equation, award [1] mark
only)
[8]
[Total: 16 max 15]
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Covalent Bonding &
Shapes of Molecules
Question Paper 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Question Paper 5
Time Allowed:
76 minutes
Score:
/63
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Hydrogen fluoride, HF, behaves as a weak acid in water, with Ka = 5.6 × 10–4 mol dm–
3.
Calculate the pH of a 0.050 mol dm–3 solution of HF.
pH = ....................................... [2]
(b) Gaseous ammonia and hydrogen fluoride react together to give solid ionic ammonium
fluoride.
NH3(g) + HF(g)
(i)
NH4F(s)
ΔH = –147 kJ mol–1
What type of reaction is this?
..................................................................................................................................
(ii)
Draw dot-and-cross diagrams (outer shells only) describing the bonding in the three
compounds involved in this reaction.
NH3
(iii)
HF
NH4F
There are three types of bonding in NH4F.
Give the names of each of the three types, and state where in the compound each
type occurs.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(iv)
The reaction between NH3 and HF is reversible. What conditions of temperature
and pressure would favour the reverse reaction, i.e. the dissociation of NH4F?
Explain your answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[9]
(c) Many commercial copper and brass polishes contain ammonia. The tarnish that forms
on the surface of copper is often copper sulfide, CuS. In the presence of O2 from the
air, NH3 can combine with this copper sulfide to produce the soluble cuprammonium
sulfate, [Cu(NH3)4]SO4.
(i)
Construct an equation for this reaction.
..................................................................................................................................
(ii)
State the colour of cuprammonium sulfate solution.
..................................................................................................................................
(iii)
Describe what you would see if a solution of cuprammonium sulfate was diluted
with water. Explain your answer.
..................................................................................................................................
..................................................................................................................................
[3]
(d) When sulfuric acid is added to Cu2+(aq), no colour change occurs, but when concentrated
hydrochloric acid is added to Cu2+(aq), the solution turns yellow-green. The solution
reverts to its original colour when it is diluted with water.
Suggest the type of reaction occurring with HCl(aq), suggest what is formed during the
reaction, and write an equation for the change.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [3]
[Total: 17]
2
Hydrazine, N2H4, can be used as a rocket fuel and is stored as a liquid. It reacts exothermically
with oxygen to give only gaseous products.
The enthalpy change of a reaction such as that between hydrazine and oxygen may be
calculated by using standard enthalpy changes of formation.
(a) Define the term standard enthalpy change of formation, ΔHf .
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [3]
(b) Hydrazine reacts with oxygen according to the following equation.
N2H4(l) + O2(g)
(i)
N2(g) + 2H2O(g)
Use the data in the table to calculate the standard enthalpy change of this
reaction.
compound
ΔHf /kJ mol–1
N2H4(l)
50.6
H2O(g)
–241.8
ΔH = ........................................ kJ mol–1
(ii)
Although the above reaction is highly exothermic, hydrazine does not burn
spontaneously in oxygen.
Suggest a reason for this.
..................................................................................................................................
..................................................................................................................................
(iii)
Suggest why using hydrazine as a rocket fuel could be regarded as being
‘environmentally friendly’.
..................................................................................................................................
..................................................................................................................................
[4]
(c) The bonding in hydrazine is similar to that in ammonia.
(i)
Showing outer-shell electrons only, draw a ‘dot-and-cross’ diagram of an ammonia
molecule.
(ii)
Draw a diagram to show the three-dimensional shape of an ammonia molecule.
(iii)
Draw a diagram to show the shape of a hydrazine molecule.
Show clearly which atom is joined to which and show clearly the value of one bond
angle.
[4]
(d) Deduce the oxidation state of nitrogen in hydrazine.
..........................................
[1]
[Total: 12]
3
The elements of the third period of the Periodic Table form chlorides of general formula ECl x
where E represents the element. These chlorides show a variation in oxidation number from
sodium to sulfur.
(a) (i)
Use the information given to complete the table below.
formula of chloride
NaCl
MgCl 2
Al Cl 3
SiCl 4
PCl 3
SCl 2
oxidation number of element in
the chloride
(ii)
By considering the electron configurations of the elements, explain the variation in
oxidation number in the chlorides from Na to Al and from Si to S.
Na to Al ....................................................................................................................
..................................................................................................................................
Si to S .......................................................................................................................
..................................................................................................................................
[5]
Sodium hydride, NaH, is a colourless crystalline solid which melts at 800 °C and has the
same crystal structure as sodium chloride which has a melting point of 808 °C. When molten
sodium chloride is electrolysed using graphite electrodes, a shiny deposit, D, forms on the
cathode and a greenish-yellow gas is evolved from the anode. When molten sodium hydride
is electrolysed, under suitable conditions using graphite electrodes, the same shiny deposit
D is formed on the cathode and a colourless gas, G, is evolved from the anode.
(b) (i)
(ii)
Describe with the aid of a diagram the bonding in a sodium chloride crystal.
Suggest the type of bonding that is present in sodium hydride.
..................................................................................................................................
(iii)
What is the oxidation number of hydrogen in sodium hydride?
.......................
(iv)
Draw a ‘dot-and-cross’ diagram for sodium hydride. Show outer electrons only.
(v)
The metals magnesium and aluminium form hydrides with formulae MgH2 and
Al H3. The non-metals phosphorus and sulfur form hydrides with formulae PH3 and
H2S.
By considering their positions in the Periodic Table, suggest oxidation numbers for
these four elements in their hydrides.
compound
MgH2
Al H3
PH3
H2S
oxidation number of element in
the hydride
[8]
At room temperature, the chlorides of sodium, magnesium and aluminium are all solids which
dissolve in water.
The hydrides of sodium, magnesium and aluminium are also solids which react with water
with the rapid evolution of the same colourless gas G in each case.
(c) (i)
What is the pH of the solutions formed when separate samples of sodium chloride,
magnesium chloride, and aluminium chloride are dissolved in water?
chloride
sodium
magnesium
aluminium
pH
(ii)
Suggest an equation for the reaction between sodium hydride and water.
..................................................................................................................................
(iii)
Suggest a value for the pH of the solution formed in (ii).
.......................
[4]
At room temperature, the chlorides of silicon, phosphorus and sulfur are all low melting point
solids or low boiling point liquids that can be seen to react with water.
(d) (i)
Suggest what type of bonding is present in sulfur dichloride, SCl 2.
...................................................................
(ii)
Write a balanced equation for the reaction between the chloride of silicon, SiCl 4,
and water.
............................................................................................................................ [2]
[Total: 19]
4
This question is about the properties and reactions of the oxides of some elements in their
+4 oxidation state.
(a) Chlorine dioxide, Cl O2, is an important industrial chemical, used to bleach wood pulp
for making paper, and to kill bacteria in water supplies.
However, it is unstable and decomposes into its elements as follows.
2Cl O2(g)
(i)
Cl 2(g) + 2O2(g)
The chlorine atom is in the middle of the Cl O2 molecule. Using the chlorine-oxygen
bond energy as 278 kJ mol–1, and other values from the Data Booklet, calculate DH
for the above reaction.
DH = ........................................ kJ mol–1
(ii)
Assuming the Cl -O bonds in chlorine dioxide are double bonds, predict the shape
of the Cl O2 molecule. Explain your answer.
..................................................................................................................................
..................................................................................................................................
(iii)
Cl O2 can be made in the laboratory by reacting KCl O3 with concentrated H2SO4.
Other products are K2SO4, KCl O4 and H2O.
Construct a balanced equation for this reaction. You may find the use of oxidation
numbers helpful.
..................................................................................................................................
[5]
(b) Sulphur dioxide is an atmospheric pollutant.
(i)
State two sources of atmospheric SO2 that arise from human activity.
..................................................................................................................................
..................................................................................................................................
(ii)
Explain why SO2 is a pollutant, and state an environmental consequence of this
pollution.
..................................................................................................................................
..................................................................................................................................
[3]
(c) All the oxides of the elements in Group IV in their +4 oxidation state are high melting
point solids except CO2.
(i)
Explain this observation by describing the bonding in CO2, SiO2 and SnO2.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
State the difference in the thermal stabilities of SnO2 and PbO2. Illustrate your
answer with an equation.
..................................................................................................................................
..................................................................................................................................
CO2 dissolves in water to form a weakly acidic solution containing the hydrogencarbonate
ion.
(iii)
Write an equation for the reaction of CO2 with water, and write an expression for
the equilibrium constant, Kc.
..................................................................................................................................
..................................................................................................................................
(iv)
Explain the role of the hydrogencarbonate ion in controlling the pH of blood,
illustrating your answer with relevant equations.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[7]
[Total: 15]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme 6
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Mark Scheme 6
Time Allowed:
75 minutes
Score:
/62
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
tetrahedral diagram (either dashed+wedge, or similar representation)
angles (all) 109° – 110°
(award [0] for part (a) if an angle of 90° or 180° is mentioned)
(b) volatility decreases or boiling points increase
(allow b.pt. CCl4 > SiCl4 but b.pt. increases thereafter)
due to greater van der Waals’/intermolecular forces or due to more electrons
(mention of “ions” negates this mark)
(c) (i) Pb4+/Pb2+: E o = +1.69V, Sn4+/Sn2+: E o = +0.15V,
a valid comment about relative redox power or stability, e.g.:
(hence) Sn2+ easily oxidised or Sn4+ is more stable than Sn2+ or
Pb4+ is easily reduced or Pb2+ is more stable than Pb4+ or
+2 oxidation state more stable down the grou
(ii) Sn2+ + I2 → Sn4+ + 2I ¯
Pb4+ + SO2 + 2H2O → 4H+ + SO42- + Pb2+
(N.B. no marks in (ii) for E o values)
(d)
d)
for Si: ∆H = 244 – 2(359) = –474 (kJ mol–1)
for Sn: ∆H = 244 – 2(315) = –386 (kJ mol–1)
(allow [1] out of [2] salvage mark for 474 & 386; 962 & 874; or –962 & –874)
(ii) Yes: the +4 state becomes decreasingly stable – the ∆H is less exothermic
(mark is for relating ∆Hs to stability: allow ecf from d(i) and also from c(i))
[1]
[1]
[2]
[1]
[1]
[2]
[both] [1]
[1]
[1
[1]
[4]
[1
[1
[1]
[3]
[Total: 11]
2
(a
(i) H–C–H 117 to 120o (1)
o
C=C=O
(1)
(ii) molecule contains both ketone and alkene (1)
(b)
b) (
[3]
C2H2O + 2O2 → 2CO2 + H2O (1)
42 g C2H2O → 48 dm3 of CO2 (1)
48 × 3.5
whence 3.5 g C2H2O →
dm3 of CO2 (1)
42
= 4.0 dm3 of CO2 (1)
42
= 0.0833 (1)
n(C2H2O) =
3.5
n(CO2) = 2 × 0.083 = 0.0166 (1)
vol. of CO2 = 0.0166 × 24 = 4.0 dm3 (1)
allow e.c.f. on wrong eqn. in (b)(i)
penalise significant figure error
(ii) from eqn.,
or
(c)
c) (
[4]
enthalpy change when
1 mol of a compound is formed (1)
from its elements (1)
in their standard states under standard conditions (1)
(ii) C + O2 → CO2
–395 kJ mol–1
H2 + ½O2 → H2O
–286 kJ mol–1
–1028 kJ mol–1
C2H2O + 2O2 → 2CO2 + H2O
2C + H2 + ½O2 → C2H2O ∆H = 2(–395) + (–286) –(–1028)
= –48 kJ mol–1
correct cycle (1) use of 2 for C/CO2 (1) answer (1)
(d) H2O/water/steam (1)
[6]
[1]
[Total: 14]
3
(a
(i) between 117° and 120°
[1]
(ii)
14 electrons must be shown
single N-N bond
lone pair on each N atom
(iii) between 107° and 109°
(b) ethene – van der Waals’ forces
hydrazine – hydrogen bonds
hydrogen bonds are stronger
or van der Waals’ forces are weaker
(c) correct dipole on OH and NH bonds
labelled hydrogen bond shown
between an O atom of H2O and a H atom of N2H4
or between an N atom of N2H4 and a H atom of H2O
[1]
[1]
[1] [4]
[1]
[1]
[1] [3]
[1]
[1]
lone pair on O atom or on N atom in the H bond
i.
or
[1] [3]
(d) (i) CH2 = CH2 +HCl → CH3CH2Cl
(ii)
electrophilic addition
(iii) there is no further unsaturation
or CH3CH2Cl molecule is saturated
or no possibility of addition
or no free radicals are present
(e) (i) acid – base/neutralization
[1]
[1]
[1] [3]
[1]
(ii) N atom has a lone pair of electrons
or N atom can behave as a base
or N atom can form dative bond
[1]
(iii) each N atom has a lone pair
or each nitrogen atom can behave as a base
or each nitrogen atom can form a dative bond
[1] [3]
[Total: 16]
4 (a)
(b)
molecules
(1)
I2
(1)
(i)
(ii)
(c)
c)
(ii)
cations held in ‘sea’ of delocalised electrons
(1)
by strong metallic bonds
(1)
van der Waals’ forces between molecules
(1)
van der Waals’ forces are weak
(1)
oxidising agent
(1)
iodine is a weaker oxidising agent than chlorine
(1)
[2]
[4]
[2]
[Total: 8]
5
(a)
(b)
(c)
(d)
sulphur atom has 6 /carbon atom has 4 electrons
(1)
S=C double bonds (4 electrons) clearly shown
(1)
linear
(1)
180o
(1)
the enthalpy change when 1 mol of a compound
(1)
is formed from its elements in their standard states
(1)
under standard conditions (may be quoted)
(1)
[3]
(1)
[3]
C + O2 → CO2
-395
S + O2 → SO2
-298
CS2 + 3O2 → CO2 + 2SO2
-1110
C + 2S → CS2
[2]
[2]
∆H = -395 + 2(-298) -(-1110)
= +119 kJ mol-1
cycle (1)
(e)
use of 2 for S/SO2 (1)
answer
CO2
(1)
N2
(1)
CS2 + 2NO → CO2 + 2S + N2
(1)
completely correct equation gets (3)
consequential errors to be decided at co-ordination
[3]
[Total: 13]
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Covalent Bonding &
Shapes of Molecules
Question Paper 6
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Theory
Booklet
Question Paper 6
Time Allowed:
75 minutes
Score:
/62
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The elements of Group IV all form tetrachlorides with the general formula M Cl 4.
(a) Draw a diagram of a molecule of SiCl 4 stating bond angles.
[2]
(b) Describe and explain how the volatilities of the Group IV chlorides vary down the group.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(c) The relative stabilities of the M 2+(aq) and M 4+(aq) ions also vary down Group IV.
(i)
Use the Data Booklet to illustrate this observation when M = Sn and M = Pb.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Use the Data Booklet to predict the products formed, and write equations for the
reactions occurring, when
•
an equimolar mixture of Sn2+(aq) and Sn4+(aq) is added to I2(aq),
..................................................................................................................................
..................................................................................................................................
•
an equimolar mixture of Pb2+(aq) and Pb4+(aq) is added to SO2(aq).
..................................................................................................................................
..................................................................................................................................
[4]
(d) (i)
The Sn–Cl bond energy is +315 kJ mol–1. Use this and other values from the Data
Booklet to calculate DH o for the reaction
M Cl 2(g) + Cl 2(g)
M Cl 4(g)
for the following cases.
•
M = Si
DH o = ........................................ kJ mol–1
•
M = Sn
DH o = ........................................ kJ mol–1
(ii)
Do your results agree with the trend in relative stabilities of the +2 and +4 oxidation
states in (c)? Explain your answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 11]
2
Ketene, C2H2O, is a member of a class of unsaturated organic compounds that is widely
used in pharmaceutical research for the synthesis of organic compounds.
CH2=C=O
ketene
(a) (i)
Suggest values for the H-C-H and C=C=O bond angles in ketene.
H-C-H ……………………………………
(ii)
C=C=O ……………………………………
By considering the structure of the molecule, suggest why the name ketene is
used.
..................................................................................................................................
............................................................................................................................. [3]
(b) Ketene burns completely in air to form carbon dioxide and water.
(i)
Write a balanced equation for this reaction.
..................................................................................................................................
(ii)
Use your equation to calculate the volume of CO2, in dm3, measured at room
temperature and pressure, which will be formed when 3.5 g of ketene are burned in
an excess of air.
Give your answer to two significant figures.
volume of CO2 = ................................. dm3 [4]
(c) (i)
Define the term standard enthalpy change of formation.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Use the data below to calculate the standard enthalpy change of formation of
ketene.
∆H o / kJ mol–1
standard enthalpy change of
formation of CO2
–395
standard enthalpy change of
combustion of H2
–286
standard enthalpy change of
combustion of CH2=C=O
–1028
[6]
(d) Ketene can be converted directly into ethanoic acid, CH3CO2H, by reaction with a
compound A.
Suggest the identity of A.
.................………………................
[1]
[Total: 14]
3
Ethene, C2H4, and hydrazine, N2H4, are hydrides of elements which are adjacent in the
Periodic Table. Data about ethene and hydrazine are given in the table below.
C2H4
N2H4
melting
point/°C
–169
+2
boiling
point/°C
–104
+114
solubility in
water
insoluble
high
solubility in
ethanol
high
high
(a) Ethene and hydrazine have a similar arrangement of atoms but differently shaped
molecules.
(i)
What is the H-C-H bond angle in ethene?
..................................................................................................................................
(ii)
Draw a ‘dot-and-cross’ diagram for hydrazine.
(iii)
What is the H-N-H bond angle in hydrazine?
..................................................................................................................................
[4]
(b) The melting and boiling points of hydrazine are much higher than those of ethene.
Suggest reasons for these differences in terms of the intermolecular forces each
compound possesses.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
......................................................................................................................................[3]
(c) Explain, with the aid of a diagram showing lone pairs of electrons and dipoles, why
hydrazine is very soluble in ethanol.
[3]
Ethene and hydrazine each react with HCl.
(d) When ethene is reacted with HCl, C2H5Cl is the only product.
(i)
Using structural formulae, give an equation for the reaction between ethene and
HCl.
(ii)
What type of reaction occurs between HCl and ethene?
..................................................................................................................................
(iii)
Explain why there is no further reaction between C2H5Cl and HCl.
..................................................................................................................................
[3]
(e) When aqueous hydrazine is reacted with HCl, a solid compound of formula N2H5Cl may
be isolated. When an excess of HCl is used, a second solid, N2H6Cl2, is formed.
(i)
Suggest what type of reaction occurs between hydrazine and HCl.
..................................................................................................................................
(ii)
What feature of the hydrazine molecule enables this reaction to occur?
..................................................................................................................................
(iii)
Suggest why one molecule of hydrazine is able to react with one or two molecules
of HCl.
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 16]
4
Copper and iodine are both solids which have different physical and chemical properties.
Each element has the same face-centred crystal structure which is shown below.
The particles present in such a crystal may be atoms, molecules, anions or cations. In the
diagram above, the particles present are represented by
.
(a) Which type of particles are present in the iodine crystal? Give their formula.
particle ....................................
formula ....................................
[2]
(b) When separate samples of copper or iodine are heated to 50 °C, the copper remains as
a solid while the iodine turns into a vapour.
(i)
Explain, in terms of the forces present in the solid structure, why copper remains a
solid at 50 °C.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Explain, in terms of the forces present in the solid structure, why iodine turns into a
vapour when heated to 50°C.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[4]
(c) (i)
Although copper is a relatively unreactive metal, when it is heated to a high
temperature in an excess of chlorine, copper(II) chloride is formed.
How does chlorine behave in this reaction?
..................................................................................................................................
(ii)
When a mixture of copper and iodine is heated to a high temperature, no reaction
occurs.
Suggest a reason for this difference.
..................................................................................................................................
..................................................................................................................................
[2]
[Total: 8]
5
Carbon disulphide, CS2, is a volatile, stinking liquid which is used to manufacture viscose
rayon and cellophane.
(a) The carbon atom is in the centre of the CS2 molecule.
Draw a ‘dot-and-cross’ diagram of the carbon disulphide molecule.
Show outer electrons only.
[2]
(b) Suggest the shape of the molecule and give its bond angle.
shape .........................................................
bond angle .................................................
[2]
(c) Explain the term standard enthalpy change of formation, H f .
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [3]
(d) Calculate the standard enthalpy change of formation of CS2 from the following data.
standard enthalpy change of formation of SO2
= –298 kJ mol–1
standard enthalpy change of formation of CO2
= –395 kJ mol–1
standard enthalpy change of combustion of CS2 = –1110 kJ mol–1
[3]
(e) Carbon disulphide reacts with nitrogen monoxide, NO, to form a yellow solid and two
colourless gases which are produced in a 1:1 molar ratio.
Deduce the identity of each gas and write a balanced equation for the reaction.
gases ........................................................ and ...............................................................
equation ..................................................................................................................... [3]
[Total: 13]
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Covalent Bonding &
Shapes of Molecules
Mark Scheme
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Multiple Choice
Booklet
Mark Scheme
Time Allowed:
52 minutes
Score:
/43
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
SECTION – A
1.
A
2.
A
3. D
4. C
5. C
6. D
7. D
8. C
9. D
10. D
11. C
12. B
13. D
14. C
15. C
16. A
17. C
18. C
19. D
20. C
21. C
22. A
23. D
24. C
25. D
26. A
27. C
28. B
29. A
30. B
31. B
32. D
SECTION – B
33. D
34. D
35. C
36. C
37. A
38. B
39. A
40. B
41. C
42. B
43. D
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Covalent Bonding &
Shapes of Molecules
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Covalent Bonding & Shapes of Molecules
Paper Type
Multiple Choice
Booklet
Question Paper
Time Allowed:
52 minutes
Score:
/43
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1 The double bond between the two carbon atoms in an ethene molecule consists of one σ bond
and one π bond.
Which orbitals overlap to form each of these bonds?
2
σ bond
π bond
A
sp2–sp2
p–p
B
sp2–sp2
sp2–sp2
C
sp3–sp3
p–p
D
sp3–sp3
sp2–sp2
Phosphorus forms a compound with hydrogen called phosphine, PH3. This compound can react
with a hydrogen ion, H+.
Which type of interaction occurs between PH3 and H+?
A
dative covalent bond
B
dipole-dipole forces
C
hydrogen bond
D
ionic bond
3 The compound (CH3)3NAl Cl 3 has a simple molecular structure.
Which statement about (CH3)3NAl Cl 3 is correct?
A
(CH3)3NAl Cl 3 molecules attract each other by hydrogen bonds.
B
The Al atom has an incomplete valance shell of electrons.
C
The bonds around the Al atom are planar.
D
The molecules contain coordinate and covalent bonding
4 The diagram shows a molecule that has σ bonds and π bonds.
O
CH2
CH
CH2
C
O
CH2
CH
CH2
How many σ bonds are present in this molecule?
A
5
15
B
17
C
18
D
21
Al Cl 3 vapour forms molecules with formula Al 2Cl 6 as it is cooled.
What happens to the bond angles during the change from Al Cl 3 to Al 2Cl 6?
6
A
Some decrease, some remain the same.
B
Some increase, some remain the same.
C
They all decrease.
D
They all increase.
Copper and iodine are both shiny crystalline solids.
Which forces exist between particles in solid copper and between neighbouring iodine molecules
in solid iodine?
copper
opper
Iodine
A
ionic bonds
covalent bonds
B
ionic bonds
van der Waals’ forces
C
metallic bonds
covalent bonds
D
metallic bonds
van der Waals’ forces
7
8
Which pair of elements has chemical bonds of the same type between their atoms in the solid
state?
A
aluminium and phosphorus
B
chlorine and argon
C
magnesium and silicon
D
sulfur and chlorine
Two conversions are outlined below.
NH4+ → NH3
C2H4 → C2H6
What similar feature do these two conversions have?
9
A
a lone pair of electrons in the product
B
change in oxidation state of an element
C
decrease in bond angle of the species involved
D
disappearance of a π bond
What is the most likely shape of a molecule of hydrazine, N2H4?
A
H
B
H
H
90°
H
H
120°
90°
N
N
H
H
H
N
D
C
N
N
H
H
107°
N
N
H
N
H
H
H
H
H
10 Sodium borohydride, NaBH4, and boron trifluoride, BF3, are compounds of boron.
What are the shapes around boron in the borohydride ion and in boron trifluoride?
11
Some car paints contain small flakes of silica,
SiO2. In the structure of solid SiO2
●
each silicon atom is bonded to x oxygen atoms,
●
each oxygen atom is bonded to y silicon atoms,
●
each bond is a z type bond.
What is the correct combination of x, y and z in this statement?
12 In which pair do the molecules have the same shape as each other?
A
H2O and CO2
B
H2O and SCl 2
C
NH3 and BH3
D
SCl 2 and BeCl 2
13 Carvone is found in spearmint.
CH3
O
H
C
C
C
H2C
CH2
C
C
H3C
H
CH2
carvone
How many σ and π bonds are present in this molecule?
14 Which diagram correctly shows the bonding in the ammonium ion, NH4+?
key
A
N electron
B
+
H
H electron
H
N
H
H
H
N
D
+
H
N
H
H
C
H
+
H
+
H
H
H
H
N
H
H
15 Acrylic acid is produced from propene, a gaseous product of oil refineries.
O
x
y
OH
acrylic acid
Which statement about acrylic acid is not correct?
A
Both bond angles x and y are approximately 120°.
B
It decolourises aqueous bromine.
C
It gives an orange precipitate with 2,4-dinitrophenylhydrazine reagent.
D
It reacts with an alcohol to give an ester.
16 Which element shows the greatest tendency to form some covalent compounds?
A
aluminium
B
magnesium
C
neon
D
potassium
17 Methyl isocyanate, CH3NCO, is a toxic liquid which is used in the manufacture of some
pesticides.
In the methyl isocyanate molecule, the sequence of atoms is H3C — N
C
O.
What is the approximate angle between the bonds formed by the N atom?
A
N
B
C
H3C
O
N
C
C
N
C
109°
O
H 3C
H 3C
H3C
104°
O
D
120°
N
180°
C
O
18 Organic nitrates in photochemical smog can cause breathing difficulties.
The diagram shows an example of an organic nitrate molecule.
H
H
1
3
C
C
2
H
O
O
O
NO2
What is the correct order of the bond angles shown in ascending order (smallest first)?
A1→2→3B2→1→3C3→1→2D3→2→1
19 In which reaction does the carbon-containing product have a smaller bond angle than the organic
reactant?
A
bromoethane refluxed with ethanolic sodium hydroxide
B
complete combustion of methane in air
C
methane and an excess of chlorine under ultraviolet light
D
polymerisation of ethene
20 Which statement correctly describes what happens when silicon tetrachloride is added to water?
A
The SiCl4 dissolves to give a neutral solution only.
B
The SiCl4 reacts to give an acidic solution only.
C
The SiCl4 reacts to give a precipitate and an acidic solution.
D
The SiCl4 reacts to give a precipitate and a neutral solution.
21 The antidote molecule shown can help to prevent liver damage if someone takes too many
paracetamol tablets.
x
H
S
H
H
H
C
N
y
C
represents a
lone pair
z
H
H
H
What is the order of decreasing size of the bond angles x, y and z?
22 PCl5 dissociates as follows.
PCl5(g) → PCl3(g) + Cl2(g)
The extent of dissociation is 13 % at 160 °C and 100 % at 300 °C.
Which pair of statements about this formation of PCl3 is correct?
shape of PCl3 molecule
the reaction is
A
pyramidal
endothermic
B
pyramidal
exothermic
C
trigonal
endothermic
D
trigonal
exothermic
23 When barium metal burns in oxygen, the ionic compound barium peroxide, BaO2, is formed.
Which dot-and-cross diagram represents the electronic structure of the peroxide anion in BaO2?
key
A
B
C
D
electron from
first oxygen atom
electron from
second oxygen atom
electron from
barium atom
24 In this question, the methyl group, CH3, is represented by Me.
Trimethylamine, Me3N, reacts with boron trifluoride, BF3, to form a compound of formula
Me3N.BF3.
How may this reaction be written in terms of the shapes of the reactants and products?
Me
Me
F
Me
A
Me
Me
+
F
N
B
N
F
Me
F
F
B
F
Me
Me
Me
B
Me
Me
B
+
N
F
F
N
B
F
F
F
Me
F
Me
Me
Me
C
Me
Me
+
F
N
F
B
B
N
Me
F
F
F
F
Me
Me
B
Me
D
Me
Me
N
+
F
F
Me
N
F
B
F
F
F
25 Which pair of elements have bonds of the same type between their atoms in the solid state?
A
aluminium and phosphorus
B
chlorine and argon
C
magnesium and silicon
D
sulphur and chlorine
26 Which element is expected to show the greatest tendency to form some covalent compounds?
A
aluminium
B
calcium
C
magnesium
D
sodium
27 The CN– ion is widely used in the synthesis of organic compounds.
What is the pattern of electron pairs in this ion?
28 Which diagram describes the formation of a π bond from the overlap of its orbitals?
A
B
C
D
29 In an historically famous experiment Wöhler heated “inorganic” ammonium cyanate in the
absence of air. The only product of the reaction was “organic” urea, CO(NH2)2. No other products
were formed in the reaction.
What is the formula of the cyanate ion present in ammonium cyanate?
A
CNO–
B
CNO2–
C
CO–
D
NO–
30 Which molecule is planar?
A
NF3
B
C2Cl 4
C
C3H6
D
C3H8
31 What are the bond angles in the PH3 molecule likely to be?
A
32
90 o
B
104 o
C
109 o
D
Which of the following solids has a simple molecular lattice?
A
magnesium oxide
B
sodium
C
silicon(IV) oxide
D
sulphur
120 o
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
33 Urea is a product of animal metabolism. It can also be used as a fertiliser.
H
N
x
O
H
C
H
N
H
urea
The diagram shows angle x in this molecule.
Which statements about the structure of urea are correct?
1
Angle x is approximately 120°.
2
The molecule has two π bonds.
3
The molecule has only three lone pairs of electrons.
34 Why does aluminium chloride, Al2Cl6, sublime at the relatively low temperature of 180 °C?
1
The intermolecular forces between the Al 2Cl 6 molecules are weak.
2
The co-ordinate bonds between aluminium and chlorine are weak.
3
The covalent bonds between aluminium and chlorine are weak.
35 Nitrogen exists in air as covalently bonded diatomic molecules, N2.
Which features are present in one N2 molecule?
1
three π bonds
2
three shared pairs of electrons
3
two lone pairs of electrons
36 Use of the Data Booklet is relevant to this question.
When the liquid N2F4 is heated, it decomposes into a single product, X.
Which statements are correct?
1
N – F bonds are broken during this decomposition.
2
The enthalpy change when N2F4 decomposes into X is approximately +160 kJ mol–1.
3
Molecules of X are non-linear.
37 Which types of bonding are present in ammonium carbonate, (NH4)2CO3?
1
ionic
2
covalent
3
co-ordinate (dative covalent)
38 What always
is
involved in a carbon-carbon π bond?
1
a shared pair of electrons
2
a sideways overlap of p orbitals
3
delocalised electrons
39 Which of the following molecules and ions have a regular trigonal planar shape?
1
BF3
2
CH3+
3
Al Cl 3
40 Which of these substances have a giant structure?
1
silicon(IV) oxide
2
baked clay found in crockery
3
phosphorus(V) oxide
41 Which statements about covalent bonds are correct?
1
A triple bond consists of one π bond and two σ bonds.
2
The electron density in a σ bond is highest along the axis between the two bonded atoms.
3
A π bond restricts rotation about the σ bond axis.
42 Which of the following molecules and ions have a regular trigonal planar shape?
1
Al Cl3
2
CH3
3
PH3
+
43 Which molecules are planar?
1
BCl3
2
NH3
3
PH3
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Intermolecular Forces,
Electronegativity & Bond
Properties
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Intermolecular forces, electronegativity &
bond properties
Paper Type
Multiple Choice
Booklet
Question Paper
Time Allowed:
41 minutes
Score:
/34
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Which statement can be explained by intermolecular hydrogen bonding?
A
Ethanol has a higher boiling point than propane.
B
Hydrogen chloride has a higher boiling point than silane, SiH4.
C
Hydrogen iodide forms an acidic solution when dissolved in water.
D
Propanone has a higher boiling point than propane.
2 Four drops of 1-chlorobutane, 1-bromobutane and 1-iodobutane were put separately into three
test-tubes containing 1.0 cm3 of aqueous silver nitrate at 60 °C.
In each case, a hydrolysis reaction occurred. R represents the butane chain C4H9 and X the
halogen atom.
H2O(l) + R–X(l) + Ag+(aq) → R–OH(aq) + AgX(s) + H+(aq)
The rate of formation of cloudiness in the test-tubes was in the order RCl < RBr < RI.
Why is this?
A
The bond energy of R–X decreases from RCl to RI.
B
The first ionisation energy of the halogen decreases from Cl to I.
C
The solubility of AgX(s) decreases from AgCl to AgI.
D
The R–X bond polarity decreases from RCl to RI.
3
Which molecular structure will have the smallest overall dipole?
H 3C
Cl
C
Cl H2C
H3 C
Cl
C
C
Cl
Cl
C
C
H3C
H
D
C
B
A
Cl
H3C
Cl
CH3
C
C
H3 C
CH3
C
Cl
4 Use of the Data Booklet is relevant to this question.
Which graph correctly shows relative electronegativity plotted against relative atomic radius for
the elements Na, Mg, Al and Si?
A
B
Si
Al
electronegativity
Al
Mg
electronegativity
Mg
Na
Na
Si
atomic radius
atomic radius
C
D
Si
Na
Mg
Al
electronegativity
Al
electronegativity
Mg
Na
Si
atomic radius
atomic radius
5 Which energy change corresponds to the enthalpy change of atomisation of hydrogen at 298 K?
6
A
the bond energy of a H – H bond
B
half the bond energy of a H – H bond
C
minus half the bond energy of a H – H bond
D
minus the bond energy of a H – H bond
Use of the Data Booklet is relevant to this question.
A reaction which causes the presence of oxides of nitrogen in car exhausts is the formation of
NO.
N2 + O2 → 2NO
∆H = +180 kJ mol–1
What is the bond energy in kJ mol–1 of the bond between the atoms in NO?
A
7
655
B
835
C
1310
D
1670
Which statement can be explained by intermolecular hydrogen bonding?
A
Butane has a higher boiling point than propane.
B
Hydrogen bromide forms an acidic solution when dissolved in water.
C
SiH4 has a higher boiling point than CH4.
D
Water has a higher boiling point than CH4.
8 In which change would only van der Waals’ forces have to be overcome?
A
evaporation of ethanol
C2H5OH(l) → C2H5OH(g)
B
melting of ice
H2O(s) → H2O(l)
C
melting of solid carbon dioxide
CO2(s) → CO2(l)
D
solidification of butane
C4H10(l) → C4H10(s)
9 Use of the Data Booklet is relevant to this question.
Which element is likely to have an electronegativity similar to that of aluminium?
A
barium
B
beryllium
C
magnesium
D
strontium
10 The presence of dipoles helps to explain why the element Br2 and the compound CHCl 3 exist as
liquids at room temperature.
Which types of dipole are involved?
Br2
CHCl 3
induced dipoles and permanent
dipoles
B
induced dipoles and permanent
dipoles
induced dipoles and permanent
dipoles
C
induced dipoles only
induced dipoles and permanent
dipoles
D
induced dipoles only
induced dipoles only
A
induced dipoles only
11 Use of the Data Booklet is relevant to this question.
Which bond in the structure below has the lowest bond energy?
H
F
A
H
C
H
C
B
C
H
D
Cl
12 The ability of an atom in a covalent bond to attract electrons to itself is called its electronegativity.
The greater the difference between the electronegativities of the two atoms in the bond, the more
polar is the bond.
Which pair will form the most polar covalent bond between the atoms?
A
chlorine and bromine
B
chlorine and iodine
C
fluorine and chlorine
D
fluorine and iodine
13 Which statement explains why the boiling point of methane is higher than that of neon?
[Ar: H, 1; C, 12; Ne, 20]
A
A molecule of methane has a greater mass than a molecule of neon.
B
Molecules of methane form hydrogen bonds, but those of neon do not.
C
Molecules of methane have stronger intermolecular forces than those of neon.
D
The molecule of methane is polar, but that of neon is not.
14 A crystal of iodine produces a purple vapour when gently heated.
Which pair of statements correctly describes this process?
type of bond broken
formula of purple species
A
covalent
I
B
covalent
I2
C
induced dipole-dipole
I2
D
permanent dipole-dipole
I2
15 Which molecule has the largest overall dipole?
B
A
Cl
Cl
H
Cl
C
O
C
C
Cl
C
D
Cl
O
H
C
O
Cl
16 Al Cl3 reacts with LiAl H4 and (CH3)3N to give (CH3)3NAl H3.
Which statement about (CH3)3NAl H3 is correct?
A
It contains hydrogen bonding.
B
It is dimeric.
C
The Al atom has an incomplete octet of electrons.
D
The bonds around the Al atom are tetrahedrally arranged.
C
O
17 Hydrogen bonding can occur between molecules of methanal, HCHO, and molecules of liquid Y.
What could liquid Y be?
A
CH3OH
B
CH3CHO
C
CH3COCH3
D
CH3CO2CH3
18 In which process are hydrogen bonds broken?
A
H2(l) → H2(g)
B
NH3(l) → NH3(g)
C
2HI(g) → H2(g) + I2(g)
D
CH4(g) → C(g) + 4H(g)
19 Three substances, R, S, T, have physical properties as shown.
electrical conductivity
substance
sub
/ oC
b / oC
of solid
of liquid
R
801
1413
poor
good
S
2852
3600
poor
good
T
3550
4827
good
not known
What could be the identities of R, S and T ?
20 Which compound has a boiling point that is influenced by hydrogen bonding?
A
CH3CHO
B
CH3OCH3
C
HCO2H
D
HCO2CH3
21 The gecko, a small lizard, can climb up a smooth glass window. The gecko has millions of
microscopic hairs on its toes and each hair has thousands of pads at its tip. The result is that the
molecules in the pads are extremely close to the glass surface on which the gecko is climbing.
What is the attraction between the gecko’s toe pads and the glass surface?
A
co-ordinate bonds
B
covalent bonds
C
ionic bonds
D
van der Waals’ forces
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
22 Which physical properties are due to hydrogen bonding between water molecules?
1
Water has a higher boiling point than H2S.
2
Ice floats on water.
3
The H−O−H bond angle in water is approximately 104°.
23 P and Q are two compounds with similar Mr values. Molecules of P attract each other by
hydrogen bonds. Molecules of Q attract each other by van der Waals’ forces only.
A sample of liquid P is compared to a sample of liquid Q.
How will their properties differ?
1
P is more soluble in water than Q.
2
P has a higher melting point than Q.
3
P is more viscous than Q.
24 On being heated, hydrogen iodide breaks down more quickly than hydrogen chloride.
Which statements explain this faster rate?
1
The HI bond is weaker than the HCl bond.
2
The reaction of the breakdown of HI has a smaller activation energy than that of HCl.
3
The breakdown of HI is more exothermic than that of HCl.
25 Which types of intermolecular forces can exist between adjacent urea molecules?
O
C
H 2N
NH2
urea
1
hydrogen bonding
2
permanent dipole-dipole forces
3
instantaneous dipole-induced dipole forces
26 Compared with the HI molecule, the bond ……P…… of the HBr molecule is ……Q……
Which pairs of words correctly complete the above sentence?
27 Compared with the HCl molecule, the bond ……X…… of the HBr molecule is ……Y……
Which pairs of words correctly complete the above sentence?
28 What is involved when a hydrogen bond is formed between two molecules?
1
a hydrogen atom bonded to an atom less electronegative than itself
2
a lone pair of electrons
3
an electrostatic attraction between opposite charges
29 The three statements that follow are all true.
Which of these can be explained, at least in part, by reference to hydrogen bonding?
1
At 0 °C ice floats on water.
2
The boiling point of propan-2-ol is 82 °C. The boiling point of propanone is 56 °C.
3
At 20 °C propanone and propanal mix completely.
30 Why does aluminium chloride, Al2Cl6, sublime at the relatively low temperature of 180 °C?
1
The intermolecular forces between the Al 2Cl 6 molecules are weak.
2
The co-ordinate bonds between aluminium and chlorine are weak.
3
The covalent bonds between aluminium and chlorine are weak.
31 Which physical properties are due to hydrogen bonding between water molecules?
1
Water has a higher boiling point than H2S.
2
Ice floats on water.
3
The H−O−H bond angle in water is approximately 104°.
32 Which of the following solids contain more than one type of chemical bond?
1
brass (an alloy of copper and zinc)
2
graphite
3
ice
33 Hydroxyapatite, a basic calcium phosphate, Ca(OH)2.3Ca3(PO4)2, is the mineral found in bone.
In older people, calcium ions can be lost from the hydroxyapatite, weakening the bone structure.
In such cases, strontium salts are administered to strengthen the bone. The strontium ions
replace the lost calcium ions in the hydroxyapatite.
Which statements are correct?
1
Strontium ions are nearly the same size as calcium ions and so may easily replace them in
the hydroxyapatite.
2
Strontium hydroxide is less soluble than calcium hydroxide and so will precipitate better in
the bone structure.
3
There is ionic, covalent and metallic bonding in hydroxyapatite which gives it strength.
34 Silicon tetrachloride, SiCl4, is a liquid of low boiling point. In the presence of water it decomposes
to form silicon(IV) oxide and hydrogen chloride.
What types of bonding occur in SiCl4(I)?
1
co–ordinate bonding
2
covalent bonding
3
van der Waals forces
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Intermolecular Forces,
Electronegativity & Bond
Properties
Mark Scheme
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Intermolecular forces, electronegativity &
bond properties
Paper Type
Theory
Booklet
Mark Scheme
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
fluorine: 1s22s22p5
[1]
sulfur: 1s22s22p63s23p4
(b) (i) 2HCl → H2 + Cl2
[1]
(ii) bond energies: HF (562) is stronger than HCl (431)
or F2 (158) is weaker than Cl2 (244)
[1]
(c) electronegativity:
The attraction by an atom / nucleus / element of the electrons in a bond or a shared
pair or a molecule
bond polarity:
..is due to atoms / elements of different electronegativities at each end of a bond
[2]
(d)
d)
F
F
S
F
F
(ii) Yes, it will have a dipole moment,
[3]
either because it has an uneven distribution of electrons or because it contains a lone
pair
or the S–F dipoles don't cancel or molecule is not symmetrical or diagram of see-saw
shape.
(allow an ecf for "no dipole" if their structure in (d)(i) has no lone pair)
(e) Sulfur can use its d-orbitals or has low-lying / accessible / available d-orbitals or can
expand its octet.
(allow reverse argument for oxygen; do NOT allow just "sulfur has d-orbitals")
[1]
(f) (i) Burning of fossil fuels or coal / oil / petrol / natural gas (NOT methane or hydrocarbons)
or volcanoes or roasting / burning sulfide ores
(ii) Acid rain
[2]
[Total: 11]
2
(a
(i) 2 (1)
(ii) between 104° and 105° (1)
(b) ethanal
th
3CHO
A (1)
ethanol
th
3CH2OH
C (1)
methoxymethane
et
3OCH3
A (1)
(CH3)2CHCH3
B (1)
2-methylpropa
2(c)
c)
[2]
[4]
hydrogen bonds (1)
(ii) correct dipole on an -OH bond (1)
hydrogen bond shown between the lone pair
of an O and a H atom in an –OH group (1)
lone pair on O atom of CH3OH or H2O
clearly shown in the hydrogen bond (1)
e.
CH3

: O : LLHOH

H
or
H

: O : LLHOCH3

H
[4]
(d) hydrogen bonds exist between H2O molecules (1)
hydrogen bonds cannot form
between C2H5OC2H5 molecules (1)
[2]
[Total: 12]
3
(a) volatility: Cl 2 > Br2 > I2 or boiling points: Cl 2 < Br2 < I2 or Cl 2 is (g); Br2 is (l); I2 is (s)
[1]
more electrons in X2 down the group or more shells/bigger cloud of electrons
[1]
so there’s greater van der Waals/dispersion/id-id/induced/temporary dipole force/attraction [1]
[3]
(b) (i) H2O > H2S (see * below for mark)
due to H-bonding in H2O (none in H2S))
diagram minimum is: H2Oδ–···δ+H-OH or H2O:·H-OH [allow (+) for δ+]
[
[1]
(ii) CH3-O-CH3 > CH3CH2CH3 (see * below for mark)
due to dipole in CH3-O-CH3 (O is δ– not needed, but O is δ+ negates) or CH3OCH3 is
polar
[1]
* correct comparison of boiling points for both
[1]
[4]
(c) SF6 has 6 bonding pairs/bonds and no lone pairs (bonds can be read into a diagram e.g. S-F,
but ‘no lone pairs’ can only be read into a diagram showing 6 bonded pairs of electrons. [1]
clear diagram or ‘shape is octahedral’
[1]
[2]
[Total: 9]
4
(a
there are no inter-molecular forces present between ideal gas molecules
ideal gas molecules have no volume
collisions between ideal gas molecules are perfectly elastic
ideal gas molecules behave as rigid spheres
(any 2)
[2]
(b) high temperature
low pressure
(1)
(1)
[2]
(c) mo ideal ..... neon..... nitrogen..... ammonia..... least ideal
nitrogen has stronger van der Waals’ forces than argon
ammonia has hydrogen bonding as well as van der Waals’ forces
(1)
(1)
(1)
[3]
(d) with increasing temperature,
average kinetic energy of molecules increases
intermolecular forces are more easily broken
(1)
(1)
[2]
(e) 18
(1)
1)
(f)
f)
(
both have very similar/same van der Waals’ forces
(ii) CH3F has permanent dipole
(1)
(1)
[2]
[Total: 12]
5 (a)
covalent (giant or macro) negates, as also does any reference to ionic bonding) [1]
(simple molecular is not enough – look for covalent)
tetrahedral
[1]
(b)
b) ( plotting (allow ±1°)
138 – 151°C (stated in numbers, or read from the graph)
[1]
[1]
(ii) (b. pt. increases due to) larger intermolecular / van der Waals / induced dipole
(NOT permanent dipole) / attractions
(c)
c) (
[1]
due to the larger no. of electrons or more shells of electrons (in MX4)
[1]
Si has empty low-lying orbitals or empty d-orbitals (C does not)
[1]
(ii) SiCl4 + 2H2O
Si
2
[or SiCl4 + 4H2O
+ 4HCl
[1]
Si(OH 4 + 4HCl etc.]
(iii) (yes), because Ge also has empty (low lying d-) orbitals
(d)
d) ( SiCl4 + 2Zn
Si +
l2
[1]
[NOT ionic equation]
[1]
(ii) mass = 250 x 2 x 65.4/28.1
= 1164 (g) (actually 1163.7 – but allow 1160)
[2]
allow e.c.f from the stoichiometry of the candidate’s equation e.g. allow 582g for
[2]
2] marks if the equation shows the stoichiometry to be 1:1. But if 582g is obtai
because the candidate forgot to apply the stoichiometry as given in the equation,
award only [1] mark.
correct answer = [2], with – [1] for one error. OR marks as follows:
use of 2:1 ration
[1]
correct use of Ar data for Si and Zn
[1]
Total = [12]
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Intermolecular Forces,
Electronegativity & Bond
Properties
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Bonding
Sub-Topic
Intermolecular forces, electronegativity &
bond properties
Paper Type
Theory
Booklet
Question Paper
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Complete the electronic configurations of the following atoms.
fluorine: 1s2..........................................
sulfur:
1s2..........................................
[1]
(b)
b)
Write an equation to show the thermal decomposition of HCl.
....................................................................................................................................... [1]
(ii)
Using all relevant bond energy values from the Data Booklet, explain why the thermal
stability of HF is much more than that of HCl.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [1]
(c) Explain what is meant by the term electronegativity, and how it relates to the concept of bond
polarity.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
(d) Sulfur and fluorinereacttogethertogivethecovalentcompoundSF
(i)
4
.
Draw a ‘dot-and-cross’ diagram to show the bonding in SF4. Include all outer shell electrons
in your diagram.
[2]
(ii)
State whether a molecule of SF4 has a dipole moment. Explain your answer.
.............................................................................................................................................
....................................................................................................................................... [1]
(e) Suggest a reason why sulfur can form both SF4 and SF6 whereas oxygen can only form OF2.
....................................................................................................................................................
.............................................................................................................................................. [1]
(f)
f)
State a major source of atmospheric sulfur dioxide.
....................................................................................................................................... [1]
(ii)
State one environmental consequence of atmospheric sulfur dioxide.
....................................................................................................................................... [1]
[Total: 11]
2
The structural formulae of water, methanol and methoxymethane, CH3OCH3, are given
below.
O
H
(a) (i)
O
H
H3C
O
H
H3C
CH3
How many lone pairs of electrons are there around the oxygen atom in
methoxymethane?
..................................................................................................................................
(ii)
Suggest the size of the C–O–C bond angle in methoxymethane.
..................................................................................................................................
[2]
The physical properties of a covalent compound, such as its melting point, boiling point,
vapour pressure, or solubility, are related to the strength of attractive forces between the
molecules of that compound.
These relatively weak attractive forces are called intermolecular forces. They differ in their
strength and include the following.
A
interactions involving permanent dipoles
B
interactions involving temporary or induced dipoles
C
hydrogen bonds
(b) By using the letters A, B, or C, state the strongest intermolecular force present in each
of the following compounds.
For each compound, write the answer on the dotted line.
ethanal
CH3CHO
..............
ethanol
CH3CH2OH
..............
methoxymethane
CH3OCH3
..............
2-methylpropane
lpr
3)2CHCH3
..............
[4]
(c) Methanol and water are completely soluble in each other.
(i)
Which intermolecular force exists between methanol molecules and water molecules
that makes these two liquids soluble in each other?
..................................................................................................................................
(ii)
Draw a diagram that clearly shows this intermolecular force. Your diagram should
show any lone pairs or dipoles present on either molecule that you consider to be
important.
[4]
(d) When equal volumes of ethoxyethane, C2H5OC2H5, and water are mixed, shaken, and
then allowed to stand, two layers are formed.
Suggest why ethoxyethane does not fully dissolve in water. Explain your answer.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
[Total: 12]
3
(a) Describe and explain the trend in the volatilities of the halogens Cl 2, Br2 and I2.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
(b) For each of the following pairs of compounds, predict which compound has the higher
boiling point, and explain the reasons behind your choice.
Use diagrams in your answers where appropriate.
(i) H2O and H2S
(ii) CH3 – CH2 – CH3 and CH3 – O – CH3
[4]
(c) Briefly explain the shape of the SF6 molecule, drawing a diagram to illustrate your answer.
[2]
[Total: 9]
4
The kinetic theory of gases is used to explain the large scale (macroscopic) properties of
gases by considering how individual molecules behave.
(a) State two basic assumptions of the kinetic theory as applied to an ideal gas.
(i)
..................................................................................................................................
..................................................................................................................................
(ii)
..................................................................................................................................
..................................................................................................................................
[2]
(b) State two conditions under which the behaviour of a real gas approaches that of an
ideal gas.
(i)
..................................................................................................................................
(ii)
..................................................................................................................................
[2]
(c) Place the following gases in decreasing order of ideal behaviour.
ammonia, neon, nitrogen
most ideal ..................................................................................................... least ideal
Explain your answer.
..........................................................................................................................................
..........................................................................................................................................
[3]
(d) By using the kinetic-molecular model, explain why a liquid eventually becomes a gas as
the temperature is increased.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
(e) Ethane, CH3CH3, and fluoromethane, CH3F are iso -electronic, that is they have the
same total number of electrons in their molecules.
Calculate the total number of electrons in one molecule of CH3F.
[1]
(f)
The boiling points of these two compounds are given below.
compound
bp / K
CH3CH3
184.5
CH3F
194.7
Suggest explanations for the following.
(i)
the close similarity of the boiling points of the two compounds
..................................................................................................................................
..................................................................................................................................
(ii)
the slightly higher boiling point of CH3F
..................................................................................................................................
..................................................................................................................................
[2]
[Total: 12]
5
All the Group IV elements form chlorides with the formula MCl4.
(a) Describe the bonding in, and the shape of, these chlorides.
(i)
bonding .....................................................................................................................
(ii)
shape ....................................................................................................................[2]
The boiling point of lead(IV) chloride cannot be measured directly because it decomposes
on heating. The following table lists the boiling points of three Group IV chlorides.
(b) (i)
chloride
b.p. / °C
SiCl4
58
GeCl4
83
SnCl4
114
Plot these data on the following axes and extrapolate your graph to predict what the
boiling point of PbCl4 would be if it did not decompose.
150°C
100°C
50°C
Si
(ii)
Ge
Sn
Pb
Suggest why the boiling points vary in this way.
...................................................................................................................................
...................................................................................................................................
...............................................................................................................................[4]
(c) SiCl4 reacts vigorously with water whereas CCl4 is inert.
(i)
Suggest a reason for this difference in reactivity.
...................................................................................................................................
(ii)
Write an equation for the reaction between SiCl4 and water.
...................................................................................................................................
(iii)
Suggest, with a reason, whether you would expect GeCl4 to react with water.
...................................................................................................................................
...................................................................................................................................
[3]
(d) SiCl4 is used to make high-purity silicon for the semiconductor industry. After it has
been purified by several fractional distillations, it is reduced to silicon by heating with
pure zinc.
(i)
Suggest an equation for the reduction of SiCl4 by zinc.
...................................................................................................................................
(ii)
Use your equation to calculate what mass of zinc is needed to produce 250 g of
pure silicon by this method.
mass of zinc = ....................... g [3]
[Total: 12]
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States of Matter
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 1
Time Allowed:
54 minutes
Score:
/45
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Use of the Data Booklet is relevant to this question.
The gas laws can be summarised in the ideal gas equation below.
pV = nRT
0.96 g of oxygen gas is contained in a glass vessel of volume 7.0 × 10–3 m3 at a temperature of
30 °C.
Assume the gas behaves as an ideal gas.
What is the pressure in the vessel?
A
B
1.1 kPa
2.1 kPa
C
10.8 kPa
D
21.6 kPa
2 Mohr’s salt is a pale green crystalline solid which is soluble in water. It contains two cations, one
of which is Fe2+, and one anion which is SO42–.
The identity of the second cation was determined by heating Mohr’s salt with aqueous sodium
hydroxide. A colourless gas was evolved which readily dissolved in water giving an alkaline
solution.
A green precipitate was also formed.
What are the identities of the gas and the precipitate?
3
gas
precipitate
A
NH3
Fe(OH)2
B
NH3
Na2SO4
C
SO2
Fe(OH)2
D
SO2
Na2SO4
Which solid has a simple molecular lattice?
A
calcium fluoride
B
nickel
C
silicon(IV) oxide
D
sulfur
4
Use of the Data Booklet is relevant to this question.
The gas laws can be summarised in the ideal gas equation below.
pV = nRT
The volume of a sample of methane is measured at a temperature of 60 °C and a pressure of
103 kPa. The volume measured is 5.37 × 10–3 m3.
Assume the gas behaves as an ideal gas.
What is the mass of the sample of methane, given to two significant figures?
A
5
0.00018 g
B
0.0032 g
C
0.18 g
D
3.2 g
Which diagram shows the correct graph of pV against n for an ideal gas at constant temperature?
A
pV
0
0
B
pV
n
0
0
C
pV
n
0
0
D
pV
n
0
0
n
6 Use of the Data Booklet is relevant to this question.
1.00 g of a metallic element reacts completely with 300 cm3 of oxygen at 298 K and 1 atm
pressure to form an oxide which contains O2– ions.
The volume of one mole of gas at this temperature and pressure is 24.0 dm3.
What could be the identity of the metal?
A
calcium
B
magnesium
C
potassium
D
sodium
7 Use of the Data Booklet is relevant to this question.
The gas laws can be summarised in the ideal gas equation below.
pV = nRT
When an evacuated tube of volume 400 cm3 is filled with gas at 300 K and 101 kPa, the mass of
the tube increases by 0.65 g.
Assume the gas behaves as an ideal gas.
What could be the identity of the gas?
A
argon
B
helium
C
krypton
D
neon
8
Use of the Data Booklet is relevant to this question.
Iodine is a black, shiny, non-metallic solid and a member of Group VII. It sublimes easily on
heating to give a purple vapour.
A sample of iodine vapour of mass 6.35 g has a volume of 1.247 dm3 when maintained at
constant temperature and a pressure of 1.00 × 105 Pa.
If iodine vapour acts as an ideal gas, what is the temperature of the iodine vapour?
A
9
300 K
B
600 K
C
300 000 K
The table shows the physical properties of four substances.
Which substance has a giant covalent structure?
D
600 000 K
10 Substances X, Y and Z are all solids. Some of their physical properties are given in the table.
11 Use of the Data Booklet is relevant to this question.
In an experiment, 12.0 dm3 of oxygen, measured under room conditions, is used to burn
completely 0.10 mol of propan-1-ol.
What is the final volume of gas, measured under room conditions?
A
7.20 dm3
B
8.40 dm3
C
16.8 dm3
D
18.00 dm3
12 A 10.0 cm3 bubble of an ideal gas is formed on the sea bed where it is at a pressure of 2020 kPa.
Just below the sea surface the pressure is 101 kPa and the temperature is the same as the sea
bed.
What is the volume of the bubble when it rises to just below the sea surface?
A
10.0 cm3
B
20.2 cm3
C
200 cm3
D
2 020 000 cm3
13 Two glass vessels M and N are connected by a closed valve.
M
N
M contains helium at 20 °C at a pressure of 1 × 105 Pa. N has been evacuated, and has three
times the volume of M. In an experiment, the valve is opened and the temperature of the whole
apparatus is raised to 100 °C.
What is the final pressure in the system?
A
3.18 × 104 Pa
B
4.24 × 104 Pa
C
1.25 × 105 Pa
D
5.09 × 105 Pa
14 Which solid-line curve most accurately represents the distribution of molecular energies in a gas
at 500 K if the dotted-line curve represents the corresponding distribution for the same gas at
300 K?
A
number of
molecules
B
number of
molecules
molecular energy
molecular energy
C
number of
molecules
D
number of
molecules
molecular energy
molecular energy
15 Use of the Data Booklet is relevant to this question.
When an evacuated glass tube of volume 200 cm3 is filled with a gas at 300 K and 101 kPa, the
mass of the tube increases by 1.06 g.
What is the identity of the gas?
A
argon
B
krypton
C
neon
D
xenon
16 Which would behave the least like an ideal gas at room temperature?
A
carbon dioxide
B
helium
C
hydrogen
D
nitrogen
17 The general gas equation can be used to calculate the Mr value of a gas.
For a sample of a gas of mass m g, which expression will give the value of Mr?
A
Mr =
mpV
RT
B
Mr =
pVRT
m
C
Mr =
mRT
pV
D
Mr =
pV
mRT
18 Ethanol has a boiling point of 78 °C. At 101 kPa and 79 °C ethanol vapour does not perfectly obey
the gas equation pV = nRT.
What is the reason for this?
A
Ethanol vapour is in equilibrium with ethanol liquid at 79 °C.
B
There are intermolecular forces between the molecules of ethanol vapour.
C
The vapourisation of ethanol liquid is an endothermic process.
D
Vapours will not obey the gas equation perfectly at such a low pressure.
19 Which least resembles an ideal gas at room temperature and pressure?
A
ammonia
B
helium
C
hydrogen
D
methane
20 Use of the Data Booklet is relevant to this question.
When 0.15 g of an organic compound is vaporised, it occupies a volume of 65.0 cm3 at 405 K and
1.00 × 105 Nm–2.
Using the expression pV = nRT, which of the following expressions should be used to calculate
the relative molecular mass, Mr, of the compound?
A
0.15 × 65 × 10 − 6 × 1× 105
8.31× 405
B
0.15 × 8.31× 405
1× 105 × 65 × 10 − 3
C
0.15 × 65 × 10 − 3 × 1× 105
8.31× 405
D
0.15 × 8.31× 405
1× 105 × 65 × 10 − 6
21 Which compound is the only gas at room temperature and pressure?
A
CH3CH2CH2NH2
Mr = 59.0
B
CH3CH2CH2OH
Mr = 60.0
C
CH2OHCH2OH
Mr = 62.0
D
CH3CH2Cl
Mr = 64.5
22 Use of the Data Booklet is relevant to this question.
The approximate percentage composition of the atmosphere on four different planets is given in
the table below.
The density of a gas may be defined as the mass of 1 dm3 of the gas measured at s.t.p.
Which mixture of gases has the greatest density?
planet
major gases /
% by number of molecules
A
Jupiter
H2 89.8, He 10.2
B
Neptune
H2 80.0, He 19.0, CH4 1.0
C
Saturn
H2 96.3, He 3.25, CH4 0.45
D
Uranus
H2 82.5, He 15.2, CH4 2.3
23 Measured values of the pressure, volume and temperature of a known mass of a gaseous
compound are to be substituted into the equation pV = nRT.
The measurements are used to calculate the relative molecular mass, Mr, of a compound.
Which conditions of pressure and temperature would give the most accurate value of Mr?
24 Which solid contains more than one kind of bonding?
A
copper
B
diamond
C
ice
D
magnesium oxide
25 Use of the Data Booklet is relevant to this question.
When an evacuated fluorescent light tube of volume 300 cm3 is filled with a gas at 300 K and
101 kPa, the mass of the tube increases by 1.02 g. The gas obeys the ideal gas equation
pV = nRT.
What is the identity of the gas?
A
argon
B
krypton
C
neon
D
nitrogen
26 Use of the Data Booklet is relevant to this question.
The gas laws can be summarised in the ideal gas equation.
pV = nRT
0.56 g of ethene gas is contained in a vessel at a pressure of 102 kPa and a temperature of 30 °C.
What is the volume of the vessel?
A
49 cm3
B
494 cm3
C
48 900 cm3
D
494 000 cm3
27 Under which set of conditions is a gas most likely to behave ideally?
28 Use of the Data Booklet is relevant to this question.
The gas laws can be summarised in the ideal gas equation.
pV = nRT
0.96 g of oxygen gas is contained in a glass vessel of volume 7000 cm3 at a temperature of 30 °C.
What is the pressure in the vessel?
A
1.1 kPa
B
2.1 kPa
C
10.8 kPa
D
21.6 kPa
29 Use of the Data Booklet is relevant to this question.
The volume of a sample of ammonia is measured at a temperature of 60 °C and a pressure of
103 kPa. The volume measured is 5.37 × 10–3 m3.
What is the mass of the sample of ammonia, given to two significant figures?
A
0.00019 g
B
0.0034 g
C
0.19 g
D
3.4 g
30 Use of the Data Booklet is relevant to this question.
1.15 g of a metallic element reacts with 300 cm3 of oxygen at 298 K and 1 atm pressure, to form
an oxide which contains O2– ions.
What could be the identity of the metal?
A
calcium
B
magnesium
C
potassium
D
sodium
31 Which diagram shows the correct graph of V against p for a fixed mass of an ideal gas at
constant temperature?
A
B
V
0
C
V
0
0
p
D
V
0
0
p
V
0
0
p
0
p
32 Use of the Data Booklet is relevant to this question.
The volume of a sample of ammonia was measured at a temperature of 40 °C and a pressure of
95 kPa. The volume measured was 4.32 × 10–5 m3.
What is the mass of the sample of ammonia?
A
2.7 × 10–5 g
B
2.1 × 10–4 g
C
2.7 × 10–2 g
D
2.1 × 10–1 g
33 Three substances, R, S and T, have physical properties as shown.
34 The Boltzmann distribution for a gas at constant temperature is shown below.
Y
Z
X
n = number of gas
molecules having a
given kinetic energy
0
0
kinetic energy
If the temperature of the gas is reduced by 10 °C the graph changes shape.
What happens to the values of n for the points marked X, Y and Z?
35 At room temperature and pressure chlorine does not behave as an ideal gas.
At which temperature and pressure would the behaviour of chlorine become more ideal?
pressure
/ kPa
temperature
/K
A
50
200
B
50
400
C
200
00
D
200
00
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
B
A
1, 2 and 3
are
correct
1 and 2
only are
correct
C
D
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
36 The stoichiometry of a catalysed reaction is shown by the equation below.
P (g) + Q (g)
R (g) + S (l)
Two experiments were carried out in which the rate of production of R was measured. The results
are shown in the diagram below.
experiment 1
amount
of R
0
experiment 2
0
time
Which changes in the conditions might explain the results shown?
1
A lower pressure was used in experiment 2.
2
A different catalyst was used in experiment 2.
3
Product S was continuously removed from the reaction vessel in experiment 2.
37 A student borrowed a friend’s chemistry notes and copied out the notes in the box below.
Which statements are correct?
A gas behaves less like an ideal gas when the gas
1
is at low pressure.
2
is at low temperature.
3
can be easily liquefied.
38 Which diagrams represent part of a giant molecular structure?
1
2
=C
39
3
=C
What are necessary properties of a dynamic equilibrium?
1
Equal amounts of reactants and products are present.
2
Concentrations of reactants and products remain constant.
3
The rate of the forward reaction is the same as the rate of the reverse reaction.
= Na
= Cl
40 If N2O4 gas is placed in a sealed vessel the following equilibrium is established.
N2O4(g)
2NO2(g)
The forward reaction is endothermic.
What happens when the temperature is increased?
1
The equilibrium constant increases.
2
The partial pressure of NO2 increases.
3
The activation energy is unchanged.
41 The gas laws can be summarised in the ideal gas equation.
pV = nRT
where each symbol has its usual meaning.
Which statements are correct?
1
One mole of an ideal gas occupies the same volume under the same conditions of
temperature and pressure.
2
The density of an ideal gas at constant pressure is inversely proportional to the temperature,
T.
3
The volume of a given mass of an ideal gas is doubled if its temperature is raised from 25 °C
to 50 °C at constant pressure.
42 Which of these substances have a giant structure?
1
silicon(IV) oxide
2
baked clay found in crockery
3
phosphorus(V) oxide
43 Which substances have a giant structure?
1
calcium oxide
2
calcium
3
baked clay found in crockery
44 When a sample of a gas is compressed at constant temperature from 1500 kPa to 6000 kPa, its
volume changes from 76.0 cm3 to 20.5 cm3.
Which statements are possible explanations for this behaviour?
1
The gas behaves non-ideally.
2
The gas partially liquefies.
3
Gas is adsorbed on to the vessel walls.
45 Which equations apply to an ideal gas?
[p = pressure, V = volume, M = molar mass, ρ = density, c = concentration, R = gas constant,
T = temperature]
1
p=
ρRT
M
2
pV = MRT
3
pV = cRT
M
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States of Matter
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i)
Straight line drawn horizontally from same intercept
[1]
[1]
(ii)
T1 because it shows greatest deviation/furthest from ideal
[1]
[1]
(iii)
reducing T (reduces KE of particles) so intermolecular forces of attraction
become more significant
[1]
[1]
(iv)
greatest deviation is at high pressure
increasing pressure decreases volume so volume of particles becomes
more significant ora
[1]
[1]
[2]
(b)
Mass of air
Mass of flask
Mass of Y
pV = nRT =
Mr =
= 100 × 0.00118
= 0.118 g
= 47.930 – 0.118 = 47.812 g
= 47.989 – 47.812 = 0.177 g
m
RT
Mr
mRT 0.177 × 8.31× 299
=
pV
1× 10 5 × 100 × 10 −6
= 44.0 (43.979 to 2 or more sf)
(c) (i)
[1]
[1]
[1]
[1]
strong triple bond
[1]
1]
(ii)
high temperature (needed for reaction between N2 and O2)
[1]
(iii)
2NO + 2CO → N2 + 2CO2
OR 2NO + C → N2 + CO2
[1]
(iv)
4NO2 + 2H2O + O2 → 4HNO3
[1]
(v)
NO + ½O2 → NO2
[1]
NO2 + SO2 → NO + SO3
OR NO2 + SO2 + H2O → NO + H2SO4
[1]
[4]
[1]
[1]
[1]
[2]
[15]
2
(a
(b)
b)
any two from: molecules have negligible volume
negligible intermolecular forces or particles are not attracted to each other
or to the walls of the container
random motion
no loss of kinetic energy during collisions or elastic collisions (NOT
elastic molecules)
2 × [1]
[2]
low temperature and high pressure
(ii) (at low T) forces between particles are more important,
(at high P) volume of molecules are significant
both required [1]
[1]
[1]
[3 max 2]
(c)
c)
endothermic; because the equilibrium moves to the right on heating or with
increasing temperature or because bonds are broken during the reaction
[1]
(ii) e.g. halogenation or Friedel-Crafts alkylation / acylation
other possibilities: Cl2, I2, R–Cl, RCOCl etc.
reactants [1]
products [1]
[3]
[Total: 7]
3
(a)
a)
diamond and graphite
[1]
(ii) any three from
colour
electrical conductivity
hardness
density
melting point
graphite
black
lack
good conductor
soft / slippery
lipp
less dense than
diamond
lower
ower
diamond
transp
/ colourless
non-conductor
/ non slippery
more dense than graphite
h
3 × [1]
[4]
(b) Because each carbon is only bonded to 3 others or is unsaturated / doubly-bonded / sp2
or has 3 bonding locations
(NOT forms only 3 bonds)
C60H60
(c)
c)
[1
[1]
[2]
Number of atoms carbon present = 0.001 × 6.02 × 1023 / 12 = 5.02 × 1019
[1]
(ii) Number of hexagons present = 5.02 × 1019 / 2 = 2.51 × 1019
Area of sheet = 690 × 2.51 × 1019 = 1.73 × 1022 nm2
[1]
(iii) Graphene: Yes, since it has free / delocalised / mobile electrons
[1]
Buckminsterfullerene: No, (although there is delocalisation within each sphere)
it consists of separate / simple / discrete molecules / spheres / particles,
(so no delocalisation from one sphere to the next)
or electrons are trapped within each molecule / sphere
phe
[4]
[Total: 10]
4
(a
alkanes/paraffins
not hydrocarbon
(1)
[1]
(1
[1]
(b) 2 C14H30 + 43 O2 → 28 CO2 + 30 H2O or
C14H30 + 43/2O2 → 14 CO2 + 15 H2O
(c) (i) mass of C14H30 burnt
8195 x 10.8 = 88.506 = 88.5 t
1000
(1)
(ii) mass of CO2 produced
Mr of C14H30 = (14 x 12 + 30 x 1) = 198
(1)
2 x 198 t of C14H30 → 28 x 44 t of CO2
88.5 t of C14H30 → 28 x 44 x 88.5
2 x 198
(1)
= 275.3 t of CO2
(1)
allow 275.4 t if candidate has used 88.506
allow ecf on wrong value for Mr of C14H30
(d) n = PV = 6 x 105 x 710 x 10-6
RT
8.31 x 293
= 0.175
(e) P = nRT = 0.175 x 8.31 x 278
V
710 x 10-6
= 569410.5634 Pa = 5.7 x 105
allow ecf on (d)
[4]
(1)
(1)
1)
(1)
(1)
[2]
[Total: 10]
5
(a
there are no inter-molecular forces present between ideal gas molecules
ideal gas molecules have no volume
collisions between ideal gas molecules are perfectly elastic
ideal gas molecules behave as rigid spheres
(any 2)
[2]
(b) high temperature
low pressure
(1)
(1)
[2]
(c) mo ideal ..... neon..... nitrogen..... ammonia..... least ideal
nitrogen has stronger van der Waals’ forces than argon
ammonia has hydrogen bonding as well as van der Waals’ forces
(1)
(1)
(1)
[3]
(d) with increasing temperature,
average kinetic energy of molecules increases
intermolecular forces are more easily broken
(1)
(1)
[2]
(e) 18
(1)
1)
(f)
f)
(
both have very similar/same van der Waals’ forces
(ii) CH3F has permanent dipole
(1)
(1)
[2]
[Total: 12]
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States of Matter
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The relationship pV = nRT can be derived from the laws of mechanics by assuming ideal behaviour
for gases.
(a) The graph represents the relationship between pV and p for a real gas at three different
temperatures, T1, T2 and T3.
T1
T2
T3
pV
(i)
Draw one line on the graph to show what the relationship should be for the same amount
of an ideal gas.
[1]
(ii)
p
State and explain, with reference to the graph,
which of T1, T2 or T3 is the lowest temperature.
.............................................................................................................................................
....................................................................................................................................... [1]
(iii)
Explain your answer to (ii) with reference to intermolecular forces.
.............................................................................................................................................
....................................................................................................................................... [1]
(iv)
State and explain the effect of pressure on the extent to which a gas deviates from ideal
behaviour.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(b) A flask with a volume of 100 cm3 was first weighed with air filling the flask, and then with
another gas, Y, filling the flask. The results, measured at 26 °C and 1.00 × 105 Pa, are shown.
Mass of
flask containing air = 47.930 g
Mass of
flask containing Y = 47.989 g
Density of air
= 0.00118 g cm–3
Calculate the relative molecular mass, Mr, of Y.
(c) Although nitrogen gas makes up about 79% of the atmosphere it does not easily form
compounds.
(i)
Explain why nitrogen is so unreactive.
Mr of Y = .................................... [4]
.............................................................................................................................................
....................................................................................................................................... [1]
(ii)
Explain why the conditions in a car engine lead to the production of oxides of nitrogen.
.............................................................................................................................................
....................................................................................................................................... [1]
(iii)
Give an equation for a reaction involved in the removal of nitrogen monoxide, NO, from a
car’s exhaust gases, in the catalytic converter.
....................................................................................................................................... [1]
One of the main reasons for reducing the amounts of oxides of nitrogen in the atmosphere is
their contribution to the formation of acid rain.
(iv) Write an equation for the formation of nitric acid from nitrogen dioxide, NO2, in the
atmosphere.
....................................................................................................................................... [1]
(v) Write equations showing the catalytic role of nitrogen monoxide, NO, in the oxidation of
atmospheric sulfur dioxide, SO2.
.............................................................................................................................................
....................................................................................................................................... [2]
[Total: 15]
2
(a) State two assumptions of the kinetic theory of gases, as applied to ideal gases.
...........................................................................................................................................
...........................................................................................................................................
[2]
(b)
b)
State the conditions of temperature and pressure under which real gases behave
least like an ideal gas.
....................................................................................................................................
(ii) Explain why real gases do not behave ideally under these conditions.
....................................................................................................................................
....................................................................................................................................
[2]
(c) Gaseous aluminium chloride is dimeric at low temperatures, but the dimer dissociates on
heating.
Al 2Cl 6(g)
2Al Cl 3(g)
(i) State whether this dissociation is endothermic or exothermic. Explain your answer.
....................................................................................................................................
....................................................................................................................................
(ii) Choose one reaction in organic chemistry that is catalysed by Al Cl 3, and write the
structural formulae of the reactants and products in the boxes below.
Al Cl 3
[3]
[Total: 7]
3
Until 1985, carbon was thought to exist in only two structural forms or allotropes. In 1985
another form, buckminsterfullerene, was discovered, in which the carbon exists as spherical
molecules.
(a) The other two forms of carbon have very different structures.
(i) Name these two forms.
.............................................................. and ..............................................................
(ii) Give three differences in physical properties between these two forms.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
(b) The diagram shows the structure of buckminsterfullerene.
buckminsterfullerene
The molecule of buckminsterfullerene contains 60 carbon atoms. Suggest a reason why
buckminsterfullerene reacts with hydrogen under suitable conditions and give a formula
for the product.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[2]
(c) In 2010, two scientists from the University of Manchester were awarded the Nobel Prize
for Physics for their work on graphene, a new structural form of carbon. Graphene
is one of the new ‘nano-materials’ being developed for commercial uses in the next
10 years.
graphene
(i) Graphene is in the form of sheets of carbon one atom thick. Calculate the number
of carbon atoms present in a sheet of graphene with a mass of one thousandth of a
gram (0.001 g).
The number of hexagons in a large sheet of graphene can be assumed to be one half of
the number of carbon atoms. Each hexagon has an area of 690 nm2.
(ii) Calculate the area of the sheet of graphene in (i).
area of sheet = .......................... nm2
(iii) Would you expect samples of graphene and buckminsterfullerene to be electrical
conductors? Explain your answers.
graphene ...................................................................................................................
....................................................................................................................................
buckminsterfullerene .................................................................................................
....................................................................................................................................
[4]
[Total: 10]
4
Some intercontinental jet airliners use kerosene as fuel. The formula of kerosene may be
taken as C14H30.
(a) To which homologous series of compounds does kerosene belong?
..........................................................
[1]
(b) When kerosene burns in an excess of air, carbon dioxide and water form.
Balance the following equation for the complete combustion of kerosene.
......C14H30(l) + ......O2(g)
......CO2(g) + ......H2O(g)
[1]
(c) In this section, give your answers to one decimal place.
The flight path from Beijing to Paris is approximately 8195 km.
A typical intercontinental jet airliner burns 10.8 kg of kerosene for each kilometre
covered.
(i)
Calculate the mass, in tonnes, of C14H30 burnt on a flight from Beijing to Paris.
[1 tonne = 1 000 kg]
(ii)
Use your equation in (b) to calculate the mass, in tonnes, of CO2 produced during
this flight.
[4]
Bicycles may be carried on commercial airliners. When carried on airliners, bicycles are
placed in the luggage hold. This is a part of the aircraft which, in flight, will have different
temperatures and air pressures from those at sea level.
This question concerns the change in pressure in an inflated bicycle tyre from when it is at
sea level to when it is in the hold of an airliner in flight.
(d) At sea level and a temperature of 20 °C an inflated bicycle tyre contains 710 cm3 of air at
an internal pressure of 6 × 105 Pa.
Use the general gas equation PV = nRT to calculate the amount, in moles, of air in the
tyre at sea level.
[2]
The same bicycle, with its tyres inflated at sea level as described in (d) above, is placed in
the luggage hold of an airliner. At a height of 10 000 m, the temperature in the luggage hold
is 5 °C and the air pressure is 2.8 × 104 Pa.
(e) Assuming the volume of the tyre does not change, use your answer to (d) to calculate
the pressure inside the tyre at a height of 10 000 m.
[2]
[Total: 10]
5
The kinetic theory of gases is used to explain the large scale (macroscopic) properties of
gases by considering how individual molecules behave.
(a) State two basic assumptions of the kinetic theory as applied to an ideal gas.
(i)
..................................................................................................................................
..................................................................................................................................
(ii)
..................................................................................................................................
..................................................................................................................................
[2]
(b) State two conditions under which the behaviour of a real gas approaches that of an
ideal gas.
(i)
..................................................................................................................................
(ii)
..................................................................................................................................
[2]
(c) Place the following gases in decreasing order of ideal behaviour.
ammonia, neon, nitrogen
most ideal ..................................................................................................... least ideal
Explain your answer.
..........................................................................................................................................
..........................................................................................................................................
[3]
(d) By using the kinetic-molecular model, explain why a liquid eventually becomes a gas as
the temperature is increased.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
(e) Ethane, CH3CH3, and fluoromethane, CH3F are iso -electronic, that is they have the
same total number of electrons in their molecules.
Calculate the total number of electrons in one molecule of CH3F.
[1]
(f)
The boiling points of these two compounds are given below.
compound
bp / K
CH3CH3
184.5
CH3F
194.7
Suggest explanations for the following.
(i)
the close similarity of the boiling points of the two compounds
..................................................................................................................................
..................................................................................................................................
(ii)
the slightly higher boiling point of CH3F
..................................................................................................................................
..................................................................................................................................
[2]
[Total: 12]
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States of Matter
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 2
Time Allowed:
30 minutes
Score:
/25
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
At room temperature and pressure chlorine does not behave as an ideal gas.
At which temperature and pressure would the behaviour of chlorine become more ideal?
2
3
Which gas closely approaches ideal behaviour at room temperature and pressure?
A
ammonia
B
carbon dioxide
C
helium
D
oxygen
Which mass of gas would occupy a volume of 3 dm3 at 25 °C and 1 atmosphere pressure?
[1 mol of gas occupies 24 dm3 at 25 °C and 1 atmosphere pressure.]
A
3.2 g O2 gas
B
5.6 g N2 gas
C
8.0 g SO2 gas
D
11.0 g CO2 gas
4 When gaseous chemicals are transported by road or by rail they are classified as follows.
flammable
non-flammable
poisonous
Which commonly transported gas is non-flammable?
A
butane
B
hydrogen
C
oxygen
D
propene
5 When magnesium nitrate, Mg(NO3)2.7H2O, is heated, which three gases are given off?
6
7
A
dinitrogen oxide, oxygen, water vapour
B
hydrogen, nitrogen, oxygen
C
hydrogen, nitrogen dioxide, oxygen
D
nitrogen dioxide, oxygen, water vapour
Which solid has a simple molecular lattice?
A
calcium fluoride
B
nickel
C
silicon(IV) oxide
D
sulfur
Flask X contains 5 dm3 of helium at 12 kPa pressure and flask Y contains 10 dm3 of neon at 6 kPa
pressure.
If the flasks are connected at constant temperature, what is the final pressure?
A
8 kPa
B
9 kPa
C
10 kPa
D
11 kPa
8
Which diagram correctly describes the behaviour of a fixed mass of an ideal gas? (T is measured
in K.)
A
B
C
D
constant T
constant T
constant T
constant p
pV
p
0
0
V
0
0
pV
p
0
V
V
0
T
9
Carbon disulphide vapour burns in oxygen according to the following equation.
CS2(g) + 3O2(g) → CO2(g) + 2SO2(g)
A sample of 10 cm3 of carbon disulphide was burned in 50 cm3 of oxygen. After measuring the
volume of gas remaining, the product was treated with an excess of aqueous sodium hydroxide
and the volume of gas measured again. All measurements were made at the same temperature
and pressure, under such conditions that carbon disulphide was gaseous.
What were the measured volumes?
10 Which of the following would behave most like an ideal gas at room temperature?
A
carbon dioxide
B
helium
C
hydrogen
D
nitrogen
11 What are the lattice structures of solid diamond, iodine and silicon(IV) oxide?
12 Which of the following least resembles an ideal gas?
A
ammonia
B
helium
C
hydrogen
D
trichloromethane
13 The diagram shows part of the lattice structures of solids X and Y. [In X,
particles of different elements.]
X
What are the types of bonding present in X and Y?
Y
represent
14 For an ideal gas, the plot of pV against p is a straight line. For a real gas, such a plot shows a
deviation from ideal behaviour. The plots of pV against p for three real gases are shown below.
The gases represented are ammonia, hydrogen and nitrogen.
X
Z
Y
pV
0
ideal gas
0
p
What are the identities of the gases X, Y and Z?
15 Which gas is likely to deviate most from ideal gas behaviour?
A
HCl
B
He
C
CH4
D
N2
16 The distribution of molecular kinetic energies within a gas at temperature T1 and T2 are shown in
the diagram.
T2 > T1
Ea = activation energy
fraction of
total molecules
T1
T2
Ea
0
0
kinetic energy
Which statement correctly explains why a small increase in temperature leads to a significant
increase in the rate of a gaseous reaction?
A
The frequency of collisions between molecules is greater at a higher temperature.
B
The activation energy of the reaction is less when the gases are at a higher temperature.
C
The frequency of collisions between molecules with kinetic energy greater than the activation
energy is greater at higher temperature.
D
The proportion of molecules with more kinetic energy than the activation energy is lower at a
higher temperature.
17 Which solid exhibits more than one kind of chemical bonding?
A
brass
B
copper
C
diamond
D
ice
18 Use of the Data Booklet is relevant to this question.
Which expression gives the pressure exerted by 1.6 x 10– 3 mol of N2 in a container of
volume
3.0 dm3 at 273 oC?
A
1.6 x10 −3 x 8.31 x 273
3.0 x 10 − 6
B
1.6 x 10 − 3 x 8.31 x (273 + 273)
3.0 x 10 − 6
C
1.6 x 10 − 3 x 8.31 x 273
3.0 x 10 −3
D
1.6 x 10 − 3 x 8.31 x (273 + 273)
3.0 x 10 − 3
Pa
Pa
Pa
Pa
19
Measured values of the pressure, volume and temperature of a known mass of a gaseous
compound are to be substituted into the equation
pV = nRT
in order to calculate the relative molecular mass, Mr, of the compound.
Which conditions of pressure and temperature would give the most accurate value of Mr?
pressure
temperature
A
high
high
B
high
low
C
low
high
D
low
low
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
20
Which are assumptions of the kinetic theory of gases and hence of the ideal gas equation,
PV = nRT ?
1
Molecules move without interacting with one another except for collisions.
2
Intermolecular forces are negligible.
3
Intermolecular distances are much greater than the molecular size.
21 An ideal gas obeys the gas laws under all conditions of temperature and pressure.
Which of the following are true for an ideal gas?
1
The molecules have negligible volume.
2
There are no forces of attraction between molecules.
3
The molecules have an average kinetic energy which is proportional to its absolute
temperature.
22 Why does a mixture of hydrogen gas and bromine gas react together faster at a temperature of
500 K than it does at a temperature of 400 K?
1
A higher proportion of effective collisions occurs at 500 K.
2
Hydrogen molecules and bromine molecules collide more frequently at 500 K.
3
The activation energy of the reaction is lower at 500 K.
23 What are assumptions of the kinetic theory of gases and hence of the ideal gas equation,
PV = nRT ?
1
Molecules move without interacting with one another except for collisions.
2
Intermolecular forces are negligible.
3
Intermolecular distances are much greater than the molecular size.
24 Boron is a non-metallic element which is placed above aluminium in Group III of the Periodic
Table. It forms a compound with nitrogen known as boron nitride which has a graphite structure.
Which of the following conclusions can be drawn from this information?
1
The empirical formula of boron nitride is BN.
2
The boron and nitride atoms are likely to be arranged alternately in a hexagonal pattern.
3
Boron nitride has a layer structure with van der Waals’ forces between the layers.
25 Which pairs of compounds contain one that is giant ionic and one that is simple molecular?
1 Al 2O3 and Al 2Cl 6
2 SiO2 and SiCl 4
3 P4O10 and PCl 3
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States of Matter
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 2
Time Allowed:
59 minutes
Score:
/49
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) mass of C = 12 × 0.352 = 0.096g
44
n(C) = 0.096 = 0.008
12
(ii) mass of H = 2 × 0.144 = 0.016g
18
n(H) = 0.016 = 0.016
1
(iii) mass of oxygen = 0.240 – (0.096 + 0.016) = 0.128g
n(O) = 0.128 = 0.008
16
(1)
(1)
(1)
(1)
(1)
(1)
allow ecf at any stage
[6]
(b) C : H : O = 0.008: 0.016 : 0.008 = 1:2:1
allow C : H : O = 0.096 : 0.016 : 0.128 = 1:2:1
12
1
16
gives C H2O
(c) (i) Mr = mRT
pV
(1
=
0.148 x 8.31 x 333
1.01 x 105 x 67.7 x 10–6
[1]
(1)
= 59.89
allow 59.9 or 60
(ii) C2H4O2
(1)
(1)
(d) CH3CO2H
(1)
HCO2CH3
(1)
1)
(e) the only products of the reaction are the two oxides H2O and CO2 and copper
(1)
[3]
[1]
[Total: 13]
2
(a)
element
particle
Cu2+
allow Cu+
copper
opper
argon
rgon
formula
or molecule
Ar
one mark for each correct row or column (2 × 1)
[2]
(b) Cu cations held in ‘sea’ of delocalised electrons (1)
by strong metallic bonds (1)
Ar van der Waals’ forces between molecules (1)
which are weak (1)
[4]
(c) (i) oxidising agent or electron acceptor (1)
Ar has very high first I.E
or Ea for reaction is very high
or Ar has full valency shell/complete octet (1)
[2]
(d) from Ne to Xe more electrons in atom (1)
hence more induced dipoles/van der Waals’ forces (1)
[2]
[Total: 10]
3
(a) C : H : O =
:
:
(1)
12
1
16
= 4.06 : 8.1 : 2.70
= 1.5 : 3 : 1
= 3:6:2
empirical formula is C3H6O2 (1)
(b) (i) Mr =
[2]
0.13 × 8.31× 400
mRT
=
(1)
pV
1.00 × 10 5 × 58.0 × 10 −6
= 74.5 (1)
(ii) C3H6O2 = 36 + 6 + 32 = 74 (1)
n(C3H6O2) = 74.5
hence molecular formula of E is C3H6O2 (1)
[4]
(c) structures of F are
HCO2CH(CH3)2
HCO2CH2CH2CH3
CH3CO2CH2CH3
CH3CH2CO2CH3
S
T
U
V
each correct structure is worth one mark (3 × 1)
[3]
(d) (i) H2SO4/HCl/mineral acid or NaOH/KOH (1)
(ii) carboxylic acid not ‘acid’ (1)
[2]
(e) (i) aldehyde (1)
(ii) must be a primary alcohol (1)
(iii) CH3OH or CH3CH2OH or CH3CH2CH2OH (1)
(f)
[3]
(i) S (1)
(ii) only S is not the ester of a primary alcohol
or only S is the ester of a secondary alcohol (1)
[2]
[Total: 16]
4
(a
(i) ammonia/NH3
(1)
(ii) NH4+
(1)
(iii) iron(II) hydroxide/Fe(OH)2
(1)
1)
(b) barium sulphate/BaSO4
(1)
(c) (i) FeSO4
(1)
(NH4)2SO4
(1)
(ii) FeSO4 = 151.9 (allow 151.8 to 152)
(1)
(NH4)2SO4 = 132.1 (allow 132)
(1)
(iii) xH2O = 392 – (132.1 + 151.9) = 108
(1)
x = 108 = 6
18
allow e.c.f. on candidate’s sulphate in (c)(i)
e.c.f. answer must be a whole numb
e.
[1]
(1)
[6]
[Total: 10]
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States of Matter
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 2
Time Allowed:
59 minutes
Score:
/49
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Compound A is an organic compound which contains carbon, hydrogen and oxygen.
When 0.240 g of the vapour of A is slowly passed over a large quantity of heated copper(II)
oxide, CuO, the organic compound A is completely oxidised to carbon dioxide and water.
Copper is the only other product of the reaction.
The products are collected and it is found that 0.352 g of CO2 and 0.144 g of H2O are
formed.
(a) In this section, give your answers to three decimal places.
(i)
Calculate the mass of carbon present in 0.352 g of CO2.
Use this value to calculate the amount, in moles, of carbon atoms present in 0.240 g
of A.
(ii)
Calculate the mass of hydrogen present in 0.144 g of H2O.
Use this value to calculate the amount, in moles, of hydrogen atoms present in 0.240 g
of A.
(iii)
Use your answers to calculate the mass of oxygen present in 0.240 g of A.
Use this value to calculate the amount, in moles, of oxygen atoms present in 0.240 g
of A.
[6]
(b)
Use your answers to (a) to calculate the empirical formula of A.
[1]
(c) When a 0.148 g sample of A was vapourised at 60oC, the vapour occupied a volume of
67.7 cm3 at a pressure of 101 kPa.
(i)
Use the general gas equation pV = nRT to calculate Mr of A.
Mr =......................
(ii)
Hence calculate the molecular formula of A.
[3]
(d) Compound A is a liquid which does not react with 2,4-dinitrophenylhydrazine reagent or
with aqueous bromine.
Suggest two structural formulae for A.
[2]
(e) Compound A contains only carbon, hydrogen and oxygen.
Explain how the information on the opposite page about the reaction of A with CuO
confirms this statement.
..........................................................................................................................................
................................................................................................................................... [1]
[Total: 13]
2
Copper, proton number 29, and argon, proton number 18, are elements which have different
physical and chemical properties.
In the solid state, each element has the same face-centred cubic crystal structure which is
shown below.
The particles present in such a crystal may be atoms, molecules, anions or cations. In the
diagram above, the particles present are represented by
.
(a) Which types of particle are present in the copper and argon crystals?
In each case, give their formula.
element
particle
i
ormula
copper
argon
[2]
At room temperature, copper is a solid while argon is a gas.
(b) Explain these observations in terms of the forces present in each solid structure.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [4]
Although copper is a relatively unreactive element, when it is heated to a high temperature in
an excess of chlorine, copper(II) chloride is formed.
When a mixture of argon and chlorine is heated to a high temperature, no reaction occurs.
(c) (i)
How does chlorine behave in its reaction with copper?
..................................................................................................................................
(ii)
Suggest a reason for the lack of a reaction between argon and chlorine.
..................................................................................................................................
..................................................................................................................................
[2]
The melting points of the noble gases neon to xenon are given below.
melting point /K
Ne
Ar
Kr
Xe
25
84
116
161
(d) Explain why there is an increase in melting point from neon to xenon.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
[Total: 10]
3
An organic compound, E, has the following composition by mass:
C, 48.7%; H, 8.1%; O, 43.2%.
(a) Calculate the empirical formula of E.
[2]
(b) When vaporised in a suitable apparatus, 0.130 g of E occupied a volume of 58.0 cm3 at
127 °C and 1.00 × 105 N m–2.
(i)
Use the expression pV =
mRT
to calculate Mr of E,
Mr
where m is the mass of E.
(ii)
Hence calculate the molecular formula of E.
[4]
(c) Compound F, is an ester with the molecular formula C4H8O2.
F is one of four isomers, S, T, U, and V, that are all esters.
In the boxes below, the structural formula of S is given.
Draw the structural formulae of the other three isomers of F that are esters.
HCO2CH(CH3)2
S
T
U
V
[3]
(d) When the ester F is hydrolysed, an alcohol G is produced.
(i)
What reagent can be used to hydrolyse an ester to an alcohol?
...................................
(ii)
What other type of organic compound is produced at the same time?
...................................
[2]
(e) On mild oxidation, the alcohol G gives a compound H which forms a silver mirror with
Tollens’ reagent.
(i)
What functional group does the reaction with Tollens’ reagent show to be present in
compound H? Give the name of this group.
...................................
(ii)
What type of alcohol is G?
.........................................
(iii)
What could be the structural formula of the alcohol G?
[3]
(f)
(i)
Which of the four isomers, S, T, U, or V, could not be F?
.........................................
(ii)
Explain your answer.
..................................................................................................................................
..................................................................................................................................
[2]
[Total: 16]
4
Mohr’s salt is a pale green crystalline solid which is soluble in water. Mohr’s salt is a ‘double
salt’ which contains
two cations, one of which is Fe2+,
one anion which is SO42–,
and water of crystallisation.
(a) The identity of the second cation was determined by the following test.
Solid Mohr’s salt was heated with solid sodium hydroxide and a colourless gas was
evolved. The gas readily dissolved in water giving an alkaline solution.
(i)
What is the gas?
..................................................................................................................................
(ii)
What is the formula of the second cation identified by this test?
..................................................................................................................................
(iii)
In this test, a grey/green solid residue was also formed.
Suggest a name or formula for this solid.
..................................................................................................................................
[3]
(b) The identity of the anion present in Mohr’s salt was confirmed by adding dilute
hydrochloric acid followed by aqueous barium chloride to an aqueous solution of Mohr’s
salt. A white precipitate was formed.
Suggest the identity of the white precipitate.
......................................................................................................................................[1]
(c) When a double salt such as Mohr’s salt is made, the two individual salts are mixed
together in a 1:1 molar ratio, dissolved in water and the solution crystallised.
(i)
Give the formula of each of the two salts that would be mixed to make the double
salt, Mohr’s salt.
salt 1 ...............................................
salt 2 ...............................................
(ii)
Calculate the relative formula mass of each of the salts present in Mohr’s salt.
salt 1
relative formula mass of salt 1 ..................................
salt 2
relative formula mass of salt 2 ..................................
(iii)
The crystals of the double salt contain water of crystallisation.
The relative formula mass of Mohr’s salt is 392. Use your answers to (ii) to calculate
the number of moles of water of crystallisation present in one mole of Mohr’s salt.
[6]
[Total: 10]
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States of Matter
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 3
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
x
o
x
H oCxoCoxH
x
o
(1)
(b) n = PV = (1515 x 103) x (76 x 10-3)
RT
8.31 x 298
(1)
= 46.5
(c)
c) (
[1]
(1)
CaC2 + 2H2O → Ca(OH)2 + C2H2
[2]
(1)
(ii) n(C2H2) = n(CaC2) =100 x 46.5
(1)
mass of CaC2 = 100 x 46.5 x 64 =
= 297 570 g
= 297.6 kg (accept 298 kg)
correct units necessary
(1)
allow e.c.f. on candidate’s answer in (b)
[3]
(d) C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(g)
bonds broken: 2(H-C)
2 x 410
C≡C
840
5
/2(O=O) 5/2 x 496
bonds made:
4(C=O)
2(O-H)
4x7
2 x 460
=
=
=
=
=
820
840
1240
2900 kJ mol-1
(1)
2960
920
3880 kJ mol-1
(1)
∆Hcomb = -3880 + 2900 = -980 kJ mol-1
allow e.c.f. on incorrect bonds made/broken
(e) (i) the enthalpy/energy change when one mole of a substance
is burned in an excess of air/oxygen
or completely combusted
under standard conditions
(ii) calculation in (d) includes H2O(g) whereas ∆Hcomb involves H2O(l)
or average bond energy terms are used in the Data Booklet
(1)
[3]
(1)
(1)
(1)
[3]
[Total: 12]
2 (a)
The volume of the gas molecules / atoms / particles is insignificant compared
with the volume of the vessel.
There are no forces of attraction between the gas molecules.
All collisions by the gas molecules are perfectly elastics. Any two.
[2]
(b)
b) (
The pressure of / exerted by the gas.
Pa / Nm -2
[1]
[1]
(ii) The volume of the containing vessel
m3 / dm3 / cm3
[1]
[1]
(iii) The absolute temperature
In K or 273 + °C
[1]
[1]
(c) (i)
pV ≈ w/m x RT
m = (0.103 x 8.31 x 297) / (99.5 x 103 x 63.8 x 10-6)
= 40.0
[1]
[1]
The gas is argon
[1]
(ii) The hydrogen bonds between ammonia molecules (1)
are stronger than the Van De Waals’ forces between N2 and Ar molecules (1)
Ammonia is polar / has a dipole (1)
(Any two)
[2]
Total = [13]
3
(a)
(i)
That the volume of the gas molecules is negligible compared to the
volume of gas (1)
(ii)
That there are no intermolecular forces
OR collisions of the molecules are perfectly elastic
Particles are in constant motion, losing no energy on collision (1) any two [2]
6.02 x 1023 (1)
(b)
(c)
(d)
(i)
[1]
3
r = 0.192 nm (1)
Assume most candidat
v = 4 x 3.14 x (1.92 x 10-9)3 = 2.96 x 10-26 dm3 (2.96 x 10-29 m3) (1)
3
(ii)
2.96 x 10-26 x 6.02 x 1023 (1) = 1.78 x 10-2 dm3 (1.78 x 10-5 m3) (1)
(iii)
24 dm3 (0.024 m3) (1)
(iv)
1.78 x 10-2 x 102 = 0.074% (1)
24
(v)
Some statement which connects with (a) (i) above (1)
max [5]
· hot metals will react with oxygen in air (or nitrogen)
· to form oxides/will burn out/to a powder
· argon will not react
· at high temperatures O2 and N2 in air will react to give NOx
NOT expansion of gases on heating
any two
[2]
[Total: 10]
Question
Questi
4
Scheme
Marks
(a)
CH4 + H2O CO + 3H2
1
(b)
Label on graph indicating catalysed and uncatalysed Ea
OR statement Ea catalysed is lower (than Ea uncatalysed) owtte
1
Reference to catalyst creating alternative mechanism / reaction pathway / route
1
Idea that more molecules have sufficient energy (to react)
1
so greater chance / frequency of successful collisions
1
(c)
N
[1
[4]
1
H
H
H
angle = 107o
shape = (trigonal) pyramid(al)
(d) (i) Advantage = higher rate
Greater Kinetic Energy / speed / collision frequency / proportion of successful collisions
(ii)
T
1
1
[3]
1
1
Disadvantage – reduced yield / less product / more reactants
1
(Forward reaction) exothermic AND (hence in accordance with Le Chatelier’s Principle) equilibrium / reaction
shifts left (to counteract increasing temp) ora
1
[4]
1
[1]
Kp =
2
pNH3
3
pN2 × pH2
(iii)
N2(g) +
2
(–0.8)
1.2
3H2(g) 3
(–1.6×3/2)
0.6
2NH3(g)
0
1.60
xNH3 = 1.6/3.4 (= 0.471)
xN2 = 1.2/3.4 (= 0.353)
xH2 = 0.6/3.4 (= 0.176)
Kp =
0.4712 × (2 × 107)2
= 2.88 × 10–13 Pa–2
7
3
7 3
0.353 × 2 × 10 × 0.176 × (2 × 10 )
1
1
1+1
[5]
[18]
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States of Matter
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 3
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The unsaturated hydrocarbon ethyne (acetylene), C2H2, is widely used in ‘oxy-acetylene
torches’ for cutting and welding metals. In the torch, ethyne is burned in oxygen to produce a
flame with a temperature of 3400 K.
(a) Ethyne is a linear molecule with a triple bond, C⬅C, between the two carbon atoms.
Draw a ‘dot-and-cross’ diagram of an ethyne molecule.
[1]
(b) When used for cutting or welding, ethyne is transported in cylinders which contain the
gas under pressure. A typical cylinder has a volume of 76 dm3 and contains ethyne gas
at 1515 kPa pressure at a temperature of 25 °C.
Use the general gas equation, pV = nRT, to calculate the amount, in moles, of ethyne in
this cylinder.
[2]
(c) In some countries, ethyne is manufactured from calcium carbide, CaC2, which is
produced by heating quicklime and coke together at 2300 K.
CaO + 3C
CaC2 + CO
When water is added to the CaC2, calcium hydroxide, Ca(OH)2, and ethyne, C2H2, are
produced.
(i)
Construct a balanced equation for the formation of ethyne from calcium carbide.
..................................................................................................................................
(ii)
Use this equation and your answer to part (b) to calculate the mass of CaC2 which
will react with an excess of water to produce enough ethyne to fill 100 cylinders of
the gas.
[3]
(d) The equation for the complete combustion of ethyne is given below.
Use appropriate bond energy data from the Data Booklet to calculate a value for the
enthalpy change of combustion of ethyne.
C2H2(g) + ⁵⁄₂O2(g)
2CO2(g) + H2O(g)
[3]
(e) The value for the standard enthalpy change of combustion of ethyne is –1300 kJ mol–1.
(i)
Define the term standard enthalpy change of combustion.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Explain why your answer to (d) does not have the same value as the standard
enthalpy change of combustion.
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 12]
2
(a) State two assumptions of ideal gas behaviour.
(i)
...................................................................................................................................
...................................................................................................................................
(ii)
...................................................................................................................................
...............................................................................................................................[2]
Use of the Data Booklet is relevant in (b) and (c).
(b) The ideal gas equation is pV = nRT. Explain as fully as you can the meaning of the
following terms, and give the units for each to correspond with the value of R given in
the Data Booklet.
(i)
p ................................................................................................................................
...................................................................................................................................
(ii)
V ...............................................................................................................................
...................................................................................................................................
(iii)
T ................................................................................................................................
...............................................................................................................................[6]
(c) (i)
When an evacuated glass bulb of volume 63.8 cm3 is filled with a gas at 24 °C and
99.5 kPa, the mass increases by 0.103 g. Deduce whether the gas is ammonia,
nitrogen or argon.
(ii)
Explain why ammonia is the most likely of these three gases to deviate from ideal
gas behaviour.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...............................................................................................................................[5]
[Total : 13]
3
This question is about the physical chemistry of gases, with particular emphasis on the inert
gas argon. Argon exists in the atmosphere as single atoms.
(a) State two of the assumptions of the kinetic theory as applied to an inert gas.
(i)
...................................................................................................................................
...................................................................................................................................
(ii) .....................................................................................................................................
......................................................................................................................................
[2]
(b) How many atoms of argon are present in one mole of the gas?
......................................................................................................................................[1]
(c) You are to calculate the percentage of the volume occupied by the atoms themselves in
one mole of argon at room temperature and pressure.
(i)
Use the Data Booklet to calculate the volume of one atom of argon.
[volume = ₃ πr 3 π = 3.14]
(ii)
Use your answer to (c)(i) to calculate the volume of one mole of argon atoms.
(iii)
State the volume occupied by one mole of argon (assume it to behave as an ideal
gas) at room temperature and pressure.
...................................................................................................................................
(iv)
What percentage of this volume is occupied by the atoms themselves?
(v)
Explain how your answer to (c)(iv) justifies one of your assumptions in (a).
...................................................................................................................................
...................................................................................................................................
[5]
(d) Argon is used to fill electric light bulbs. These have a fine filament of a metal wire,
usually tungsten, which glows white hot from its electrical resistance to the current.
Suggest why argon, rather than air, is used to fill electric light bulbs.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
......................................................................................................................................[2]
[Total : 10]
4
The Haber process for the manufacture of ammonia, NH3, was originally devised at the start of the
20th century and was developed into a full-scale industrial process by Carl Bosch in 1913.
The key step in the process is the reversible reaction of nitrogen and hydrogen in the presence of
an iron catalyst.
N2(g) + 3H2(g)
2NH3(g)
∆H = –92 kJ mol–1
(a) The hydrogen for this reaction can be formed by reacting methane with steam, during which
carbon monoxide is also produced. Write an equation for this reaction.
.............................................................................................................................................. [1]
(b) Use the Boltzmann distribution shown to explain why a catalyst increases the rate of this
reaction.
number of
molecules
kinetic energy
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [4]
(c) Draw a three-dimensional diagram to show the shape of an ammonia molecule. Name this
shape and state the bond angle.
shape ....................................................................................... bond angle ........................ [3]
(d) The Haber process is typically carried out at a temperature of 400 °C.
(i) With reference to Le Chatelier’s Principle and reaction kinetics, state and explain one
advantage and one disadvantage of using a higher temperature.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
(ii) State the expression for the equilibrium constant, Kp, for the formation of ammonia from
nitrogen and hydrogen in the Haber process.
Kp =
[1]
(iii) 2.00 moles of nitrogen and 3.00 moles of hydrogen were put in a vessel and left to reach
equilibrium.
At equilibrium, the pressure was 2.00 × 107 Pa and the mixture contained 1.60 moles of
ammonia.
Calculate Kp. Include the units.
Kp = ............................
units = ............................
[5]
[Total: 18]
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States of Matter
Mark Scheme 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 4
Time Allowed:
51 minutes
Score:
/42
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) alkanes or paraffins not hydrocarbons
(ii)
i
(b)
b) (
(ii)
i
C4H10 + 13O2 → 8CO2 + 10H2O
(1
carbon allow graphite
(1)
C4H10 + 5O2 → 8C + 10H2O
allow balanced equations which include CO and/or CO2
(1)
(c) enthalpy change when 1 mol of a substance
is burnt in an excess of oxygen/air under standard conditions
or is completely combusted under standard conditions
m=
(d)
d)
(1)
pVM r 1.01× 10 5 × 125 × 10 −6 × 44
=
g
RT
8.31× 293
(1)
(ii) heat released = m c δ T = 200 × 4.18 × 13.8 J
= 11536.8 J = 11.5 kJ
(1)
(1)
(iii) 0.23 g of propane produce 11.5 kJ
11.5 × 44
44 g of propane produce
kJ
0.23
= 2200 kJ mol–1
(1)
(ii) straight chain molecules can pack more closely
therefore stronger van der Waals’ forces
or reverse argument
[2]
(1
(1)
from methane to butane
there are more electrons in the molecule
therefore greater/stronger van der Waals’ forces
[2]
(1)
= 0.228147345 g
= 0.23 g
(e)
e) (
[2]
[5]
(1)
(1)
(1)
(1)
[4]
[Total: 15]
2
(a
C(s) + O2(g) → CO2(g)
the enthalpy change/energy change/heat change when
one mole of a compound/CO2
is formed from its elements in their standard states
(b) (i)
∆Hof/kJ mol–1
CO2(g) + 3H2(g)
–39
0
CH3OH(g)
–20
(1)
(1)
(1)
+
[3]
H2O(g)
–24
∆Horeaction = –201 + (–242) – (–394)
–49 kJ mol–1
correct sign
(ii) removal of CO2 from the atmosphere
CO2 is a greenhouse gas/causes global warming
(1)
(1)
(1)
(1)
(1)
[5]
(c) In this part, in each case, the ‘effect’ must be correctly stated
in order to gain the explanation mark.
higher temperature
yield is reduced/equilibrium goes to LHS
because forward reaction is exothermic/reverse reaction is endothermic
(1)
(1)
higher pressure
yield is increased or equilibrium goes to RHS
fewer moles/molecules on RHS or more moles/molecules on LHS
(1)
(1)
use of catalyst
yield does not change
forward and backward rates speeded up by same amount
(1)
(1)
[6]
[Total: 14]
3
(a
CO2 is simple molecular/simple covalent/has discrete molecules
CO2 has induced dipole – induced dipole interactions/
van der Waals’ forces/weak intermolecular forces
SiO2 is giant molecular/giant covalent/macromolecular
SiO2 has strong covalent bonds
(1)
(1)
(1)
(1)
[any 3]
(b) minimum is
44-valent Si
and at least one Si-O-Si
(1)
(1)
i.
O
Si
O
O
O
Si
(c) (i) for an ideal gas, any four from the following
the molecules behave as rigid spheres
there are no/negligible intermolecular forces
between the molecules
collisions between the molecules are perfectly elastic
the molecules have no/negligible volume
the molecules move in random motion
the molecules move in straight lines
the kinetic energy of the molecules is
directly proportional to the temperature
the pressure exerted by the gas is due to the collisions
between the gas molecules and the walls of the container
not an ideal gas obeys pV = nRT
[2]
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)
(max 4)
(ii) there are intermolecular forces between CO2 molecules/
CO2 molecules have volume
(d) graphite has delocalised electrons
(e)
e) (
SiO2 + 2C → SiC + CO2 or
SiO2 + 3C → SiC + 2CO
(ii) diamond because SiC is hard
(1)
[5]
(1)
[1]
(1)
(1)
[2]
[Total: 13]
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States of Matter
Question Paper 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
States of Matter
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 4
Time Allowed:
51 minutes
Score:
/42
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Propane, C3H8, and butane, C 4H10, are components of LiquefiedPetroleumGas(LPG)which
is widely used as a fuel for domestic cooking and heating.
(a) (i) To which class of compounds do these two hydrocarbons belong?
......................................................
(ii) Write a balanced equation for the complete combustion of butane.
....................................................................................................................................
[2]
(b) When propane or butane is used in cooking, the saucepan may become covered by a
solid black deposit.
(i) What is the chemical name for this black solid?
......................................................
(ii) Write a balanced equation for its formation from butane.
....................................................................................................................................
[2]
(c) Propane and butane have different values of standard enthalpy change of combustion.
Define the term standard enthalpy change of combustion.
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(d) A 125 cm3 sample of propane gas, measured at 20 °C and 101 kPa, was completely burnt
in air.
The heat produced raised the temperature of 200 g of water by 13.8 °C.
Assume no heat losses occurred during this experiment.
(i) Use the equation pV = nRT to calculate the mass of propane used.
(ii) Use relevant data from the Data Booklet to calculate the amount of heat released in
this experiment.
(iii) Use the data above and your answers to (i) and (ii) to calculate the energy produced
by the burning of 1 mol of propane.
[5]
(e) The boiling points of methane, ethane, propane, and butane are given below.
compound
CH4
CH3CH3
CH3CH2CH3
CH3(CH2)2CH3
boiling point / K
112
185
231
273
(i) Suggest an explanation for the increase in boiling points from methane to butane.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) The isomer of butane, 2-methylpropane, (CH3)3CH, has a boiling point of 261 K.
Suggest an explanation for the difference between this value and that for butane in
the table above.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
[Total: 15]
2
Methanol, CH3OH, is considered to be a possible alternative to fossil fuels, particularly for use
in vehicles.
Methanol can be produced from fossil fuels and from agricultural waste. It can also be
synthesised from carbon dioxide and hydrogen.
(a) Define, with the aid of an equation which includes state symbols, the standard enthalpy
change of formation of carbon dioxide.
equation ............................................................................................................................
definition ...........................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
(b) Relevant
values for the reaction that synthesises methanol are given in th
compound
CO2(g)
–394
CH3OH(g)
–201
H2O(g)
–242
(i) Use these values to calculate
fo
Include a sign in your answer.
CO2(g) + 3H2(g)
CH3OH(g) + H2O(g)
= .........................kJ mol–1
(ii) Suggest one possible environmental advantage of this reaction. Explain your
answer.
....................................................................................................................................
....................................................................................................................................
[5]
(c) The synthesis of methanol is carried out at about 500 K with a pressure of between 40 and
100 atmospheres (between 4 × 106 Pa and 10 × 107 Pa) and using a catalyst. The use of
such conditions will affect both the rate of reaction and the equilibrium yield.
In the spaces below, explain the effects of higher temperature, higher pressure, and the
use of a catalyst on the equilibrium yield of methanol.
higher temperature
effect .................................................................................................................................
explanation .......................................................................................................................
...........................................................................................................................................
higher pressure
effect .................................................................................................................................
explanation .......................................................................................................................
...........................................................................................................................................
use of catalyst
effect .................................................................................................................................
explanation .......................................................................................................................
...........................................................................................................................................
[6]
[Total: 14]
3
The elements carbon and silicon are both in Group IV of the Periodic Table.
Carbon is the second most abundant element by mass in the human body and silicon is the
second most common element in the Earth’s crust.
Carbon and silicon each form an oxide of general formula XO2.
At room temperature, CO2 is a gas while SiO2 is a solid with a high melting point.
(a) Briefly explain, in terms of the chemical bonds and intermolecular forces present in each
compound, why CO2 is a gas and SiO2 is a solid at room temperature.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [3]
(b) Draw a simple diagram to show the structure of SiO2. Your diagram should contain at
least two silicon atoms and show clearly how many bonds each atom forms.
[2]
CO2 does not behave as an ideal gas.
(c) (i)
State the basic assumptions of the kinetic theory as applied to an ideal gas.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Suggest one reason why CO2 does not behave as an ideal gas.
..................................................................................................................................
[5]
Carbon exists in a number of forms, one of which is a conductor of electricity and one of which
is a non-conductor of electricity. Silicon is the main component of most semi-conductors.
(d) Graphite is the form of carbon that is a conductor of electricity. Give a simple explanation
for this property.
..........................................................................................................................................
.................................................................................................................................... [1]
When carbon and silicon(IV) oxide are heated together at about 2000 °C, silicon carbide,
SiC, is formed. Silicon carbide is a hard material which is widely used as an abrasive and in
ceramics.
(e) (i)
Construct an equation for the reaction of carbon and silicon(IV) oxide.
..................................................................................................................................
(ii)
SiC has a similar structure to one of the common forms of carbon.
Which form is this? Give a reason for your answer.
form ...........................................................
reason ......................................................................................................................
[2]
[Total: 13]
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Enthalpy Change &
Hess's Law
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Multiple Choice
Paper Type
Booklet
Question Paper 1
Time Allowed:
51 minutes
Score:
/42
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
2
Which quantity gives the best indication of the relative strengths of the hydrogen bonds between
the molecules in liquid hydrogen halides?
A
bond dissociation energies
B
enthalpy changes of formation
C
enthalpy changes of solution
D
enthalpy changes of vaporisation
The standard enthalpy changes of combustion of glucose and ethanol are given as –2820 and
–1368 kJ mol–1 respectively.
Glucose, C6H12O6, can be converted into ethanol.
C6H12O6(s) → 2C2H5OH(l) + 2CO2(g)
What is the standard enthalpy change for this reaction?
A
–1452 kJ mol–1
B
–84 kJ mol–1
C
+84 kJ mol–1
D
+1452 kJ mol–1
3
Enthalpy changes that are difficult to measure directly can often be determined using Hess’ Law
to construct an enthalpy cycle.
Which enthalpy change is indicated by X in the enthalpy cycle shown?
C(s) + 2H2(g) + 2O2(g)
X
CH4(g) + 2O2(g)
4
A
– 4 × the enthalpy of combustion of hydrogen
B
+ 4 × the enthalpy of combustion of hydrogen
C
– 2 × the enthalpy of formation of water
D
+ 2 × the enthalpy of formation of water
CO2(g)
+
2H2O(l)
A student mixed 25.0 cm3 of 0.350 mol dm–3 sodium hydroxide solution with 25.0 cm3 of
0.350 mol dm–3 hydrochloric acid. The temperature rose by 2.50 °C. Assume that no heat was lost
to the surroundings.
The final mixture had a specific heat capacity of 4.20 J cm –3 K–1.
What is the molar enthalpy change for the reaction?
A
–150 kJ mol–1
B
–60.0 kJ mol–1
C
–30.0 kJ mol–1
D
–0.150 kJ mol–1
5 The diagram shows the skeletal formula of cyclopropane.
The enthalpy change of formation of cyclopropane is +53.3 kJ mol–1 and the enthalpy change of
atomisation of graphite is +717 kJ mol–1.
The bond enthalpy of H – H is 436 kJ mol–1 and of C – H is 410 kJ mol–1.
What value for the average bond enthalpy of the C – C bond in cyclopropane can be calculated
from this data?
A
6
187 kJ mol–1
B
315 kJ mol–1
C
351 kJ mol–1
D
946 kJ mol–1
Ethanol is increasingly being used as a fuel for cars.
The standard enthalpy change of formation of carbon dioxide is –393 kJ mol–1.
The standard enthalpy change of formation of water is –286 kJ mol–1.
The standard enthalpy change of formation of ethanol is –277 kJ mol–1.
What is the standard enthalpy change of combustion of ethanol?
7
A
–1921 kJ mol–1
B
–1367 kJ mol–1
C
–956 kJ mol–1
D
– 402 kJ mol–1
In an experiment to calculate the enthalpy change of combustion of a fuel, 1.5 g (0.0326 mol) of
the fuel was used to heat 200 g of water. The temperature of the water rose from 25 °C to 55 °C.
The specific heat capacity of water is 4.18 J g–1 K–1.
There is significant heat loss in this experiment. Therefore, the experimental value for the
enthalpy change of combustion, ∆Hc, of the fuel will be different from the theoretical value.
Using the information above, what is the experimental value for the enthalpy change of
combustion, ∆Hc, of the fuel?
A
–1410 kJ mol–1
B
–769 kJ mol–1
C
–30.7 kJ mol–1
D
–16.7 kJ mol–1
8 For which equation is the enthalpy change correctly described as an enthalpy change of
formation?
9
A
C(g) + O2(g) → CO2(g)
B
C(s) +
C
2N(g) + 4O(g) → N2O4(g)
D
2NO(g) + O2(g) → 2NO2(g)
1
2
O2(g) → CO(g)
The reaction pathway for a reversible reaction is shown below.
30
energy
/ kJ mol–1
50
extent of reaction
Which statement is correct?
A
The activation energy of the reverse reaction is +80 kJ mol–1.
B
The enthalpy change for the forward reaction is +30 kJ mol–1.
C
The enthalpy change for the forward reaction is +50 kJ mol–1.
D
The enthalpy change for the reverse reaction is +30 kJ mol–1.
10 Use of the Data Booklet is relevant to this question.
This question should be answered using bond enthalpy data. The equation for the complete
combustion of methane is given below.
CH4 + 2O2 → CO2 + 2H2O
What is the enthalpy change of combustion of methane?
A
–1530 kJ mol–1
B
–1184 kJ mol–1
C
–770 kJ mol–1
D
–688 kJ mol–1
11 Use of the Data Booklet is relevant to this question.
A student carried out an experiment to determine the enthalpy change for the combustion of
methanol.
The following results were obtained by the student.
start temperature of the water
20 °C
final temperature of the water
53 °C
mass of alcohol burner before burning
259.65 g
mass of alcohol burner after burning
259.15 g
mass of glass beaker plus water
150.00 g
50.00 g
mass of glass beaker
How much of the heat energy produced by the burning of methanol went into the water?
A
209 J
B
C
13 794 J
20 691 J
D
22 154 J
12 The equation for a reaction is shown.
H2(g) +
1
2
O2(g) → H2O(l) ; ∆H = x kJ mol–1
Which pair of descriptions is fully correct for this reaction?
type(s) of enthalpy change
value of x
A
formation only
positive
B
formation only
negative
C
combustion, formation
positive
D
combustion, formation
negative
13
Propanone has the molecular formula C3H6O.
The enthalpy change of combustion of hydrogen is –286 kJ mol–1.
The enthalpy change of combustion of carbon is –394 kJ mol–1.
The enthalpy change of combustion of propanone is –1786 kJ mol–1.
Using this information, what is the enthalpy change of formation of propanone?
A
–1106 kJ mol–1
B
–540 kJ mol–1
C
–254 kJ mol–1
D
+1106 kJ mol–1
14 Slaked lime, Ca(OH)2, may be made from limestone, CaCO3.
On heating in a lime kiln at 1000 °C, limestone decomposes as follows.
reaction 1
CaCO3(s) → CaO(s) + CO2(g)
Water is then reacted with calcium oxide, CaO, as follows.
reaction 2
CaO(s) + H2O(l) → Ca(OH)2(s)
What are the enthalpy changes of these reactions?
15 Use of the Data Booklet is relevant to this question.
A reaction which causes the presence of oxides of nitrogen in car exhausts is the formation of
NO.
N2 + O2 → 2NO
∆H = +180 kJ mol–1
What is the bond energy in kJ mol–1 of the bond between the atoms in NO?
A
B
655
C
835
1310
D
1670
16 In the table below,
• ‘+’ means that this type of standard enthalpy change can only have positive values,
• ‘–’ means that this type of standard enthalpy change can only have negative values,
• ‘+ / –’ means that either positive or negative values are possible.
Which row is correct?
atomisation
formation
solution
A
+
+
+/–
B
+
+/–
/–
C
–
+/–
–
D
–
–
+
17 A student calculated the standard enthalpy change of formation of ethane, C2H6, using a method
based on standard enthalpy changes of combustion.
He used correct values for the standard enthalpy change of combustion of ethane
(–1560 kJ mol–1) and hydrogen (–286 kJ mol–1) but he used an incorrect value for the standard
enthalpy change of combustion of carbon. He then performed his calculation correctly. His final
answer was –158 kJ mol–1.
What did he use for the standard enthalpy change of combustion of carbon?
A
–1432 kJ mol–1
B
–860 kJ mol–1
C
–430 kJ mol–1
D
–272 kJ mol–1
18 Which process could be used to calculate the bond energy for the covalent bond X-Y by dividing
its ∆H by n?
A
XYn(g) → X(g) + nY(g)
B
2XYn (g) → 2XYn-1(g) + Y2(g)
C
Y(g) + XYn-1(g) → XYn(g)
D
nXY(g) → nX(g) +
n
2
Y2(g)
19 Ethyne, C2H2, completely combusts, as shown in the equation.
H
C
H + 2 21 O
C
O → H2O + 2CO2
Using the average bond enthalpies in the table, what is the enthalpy change of combustion of
ethyne?
average bond
enthalpy / kJ mol–1
bond
A
–980 kJ mol–1
B
C
H
41
C
C
84
O
O
49
C
O
74
O
H
46
C
O
36
–540 kJ mol–1
C
+540 kJ mol–1
D
+980 kJ mol–1
20 The equation below represents the combination of gaseous atoms of non-metal X and of
hydrogen to form gaseous X2H6 molecules.
2X(g) + 6H(g) → X2H6(g)
∆H = –2775 kJ mol–1
The bond energy of an X–H bond is 395 kJ mol–1.
What is the bond energy of an X–X bond?
A
– 405.0 kJ mol–1
B
– 202.5 kJ mol–1
C
+202.5 kJ mol–1
D
+405.0 kJ mol–1
21 50 cm3 of 2.50 mol dm–3 hydrochloric acid was placed in a polystyrene beaker of negligible heat
capacity. Its temperature was recorded and then 50 cm3 of 2.50 mol dm–3 NaOH at the same
temperature was quickly added, with stirring. The temperature rose by 17 °C.
The resulting solution may be considered to have a specific heat capacity of 4.2 J g–1 K–1.
What is an approximate value for the molar enthalpy change of neutralisation of hydrochloric acid
and sodium hydroxide from this experiment?
A
−(50 x 4.2 x17)
1
J mol −
(0.050 x 2.5)
B
−(50 x 4.2 x17)
1
J mol −
(0.10 x 2.5)
C
−(100 x 4.2 x17)
1
J mol −
(0.050 x 2.5)
D
−(100 x 4.2 x17)
1
J mol −
(50 x 2.5)
22 In the conversion of compound X into compound Z, it was found that the reaction proceeded by
way of compound Y, which could be isolated. The following steps were involved.
X → Y ; ∆H, positive
Y → Z ; ∆H, negative
Which reaction profile fits these data?
Z
progress of
reaction
Z
progress of
reaction
Y
Z
X
progress of
reaction
energy
X
energy
X
energy
energy
Y
Y
D
C
B
A
X
Y
progress of
reaction
Z
23 The standard enthalpy change for the reaction
2NF3(g) → 2N(g) + 6F(g)
is ∆H o = +1668 kJ
What is the bond energy of the N–F bond?
A
–556 kJ mol–1
B
–278 kJ mol–1
C
+278 kJ mol–1
D
+556 kJ mol–1
24 Which reaction is endothermic?
A
2HBr → H2 + Br2
B
N2 + 3H2 → 2NH3
C
2SO2 + O2 → 2SO3
D
SO3 + H2O → H2SO4
25 Hess’s Law can be used to calculate the average C-H bond energy in methane.
= standard enthalpy change of atomisation
= standard enthalpy change of formation
= standard enthalpy change of combustion
Which data values are needed in order to perform the calculation?
A
(C),
(H),
B
(C),
(H2),
(
4)
C
(C),
(H2),
(
4)
D
(CH4) only, as
4)
(C), and
(H2), are defined as zero
26 Some bond energy values are listed below.
These bond energy values relate to the following four reactions.
P
B 2 → 2Br
Q
2 l → Cl2
R
C
3
+ Cl → CH3Cl
S
C
4
→ CH3 + H
What is the order of enthalpy changes of these reactions from most negative to most positive?
A
P→Q→R→S
B
Q→R→S→P
C
R→Q→P→S
D
S→P→Q→R
27 Given the following enthalpy changes,
I2(g) + 3Cl2(g) → 2ICl3(s)
I2(s) → I2(g)
∆Ho = –214 kJ mol–1
∆Ho = +38 kJ mol–1
What is the standard enthalpy change of formation of iodine trichloride, ICl3(s)?
A
+176 kJ mol–1
B
–88 kJ mol–1
C
–176 kJ mol–1
D
–214 kJ mol–1
28 Equations involving four enthalpy changes are shown.
Na(g) → Na+(g) + e–
∆H = W
Na(g) → Na2+(g) + 2e– ∆H = X
Na(s) → Na(g)
∆H = Y
Na(s) → Na2+(g) + 2e– ∆H = Z
What is the second ionisation energy of sodium?
A
B
2W
X–W
C
Y–W
D
Z–Y
29 Enthalpy changes of combustion can be used to determine enthalpy changes of formation. The
following equation represents the enthalpy change of formation of butane.
4C(s) + 5H2(g) → C4H10(g)
By using the following standard enthalpy of combustion data, what is the value of the standard
enthalpy change of formation,
, for this reaction?
A
–5883 kJ mol–1
B
–129 kJ mol–1
C
+129 kJ mol–1
D
+2197 kJ mol–1
30 Which equation represents the change corresponding to the enthalpy change of atomisation of
iodine?
A
B
C
D
1
I (g)
2 2
→ I(g)
I2(g) → 2I(g)
1
I (s)
2 2
→ I(g)
I2(s) → 2I(g)
31 In a calorimetric experiment 1.60 g of a fuel is burnt. 45 % of the energy released is absorbed by
200 g of water whose temperature rises from 18 °C to 66 °C. The specific heat capacity of water is
4.2 J g–1 K–1.
What is the total energy released per gram of fuel burnt?
A
25 2
J
B
56 000 J
C
89 600 J
D
143 360 J
32 Hydrogen peroxide slowly decomposes into water and oxygen. The enthalpy change of reaction
can be calculated using standard enthalpies of formation.
(hydrogen peroxide(l)) = –187.8 kJ mol–1
(water(l))
= –285.8 kJ mol–1
Using a Hess cycle, what is the enthalpy change of reaction for this decomposition?
2H2O2(l) → 2H2O(l) + O2(g)
A
+98 kJ mol–1
B
−98 kJ mol–1
C
−196 kJ mol–1
D
−947.2 kJ mol–1
33 The first stage in the industrial production of nitric acid from ammonia can be represented by the
following equation.
4NH3(g) + 5O2(g)
4NO(g) + 6H2O(g)
Using the following standard enthalpy change of formation data, what is the value of the standard
enthalpy change, ∆Ho, for this reaction?
A
+905.2 kJ mol–1
B
–105.4 kJ mol–1
C
–905.2 kJ mol–1
D
–1274.0 kJ mol–1
34 PCl5 dissociates as follows.
PCl5(g) → PCl3(g) + Cl2(g)
The extent of dissociation is 13 % at 160 °C and 100 % at 300 °C.
Which pair of statements about this formation of PCl3 is correct?
shape of PCl3 molecule
the reaction is
A
pyramidal
endothermic
B
pyramidal
exothermic
C
trigonal
endothermic
D
trigonal
exothermic
35 For which equation does the enthalpy change correspond to the enthalpy change of atomisation
of iodine?
A
½ I2(s) → I(s)
B
½ I2(s) → I(g)
C
I2(g) → 2I(g)
D
I2(s) → 2I(g)
36 Titanium occurs naturally as the mineral rutile, TiO2. One possible method of extraction of
titanium is to reduce the rutile by heating with carbon.
TiO2(s) + 2C(s) → Ti(s) + 2CO(g)
The standard enthalpy changes of formation of TiO2(s) and CO(g) are –940 kJ mol–1 and
–110 kJ mol–1 respectively.
What is the standard enthalpy change of this reaction?
A
–830 kJ mol–1
B
–720 kJ mol–1
C
+720 kJ mol–1
D
+830 kJ mol–1
37 Which quantity would best indicate the relative strengths of the hydrogen bonds between the
molecules in liquid hydrogen halides?
A
bond dissociation energies
B
enthalpy changes of solution
C
enthalpy changes of formation
D
enthalpy changes of vaporisation
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
38 Which statements are correct for all exothermic reactions?
1
∆H for the reaction is negative.
2
On a reaction pathway diagram the products are shown lower than the reactants.
3
The reaction will happen spontaneously.
39 Use of the Data Booklet is relevant to this question.
The bond energy of the Br – O bond is 235 kJ mol–1.
Which reactions are exothermic?
1
OH• + HBr → H2 + BrO•
2
OH• + HBr → H2O + Br•
3
H• + HBr → H2 + Br•
40 The reaction pathway for a reversible reaction is shown below.
50
energy
/ kJ mol–1
20
extent of reaction
Which statements are correct?
1
The enthalpy change for the backward reaction is –20 kJ mol–1.
2
The forward reaction is endothermic.
3
The activation energy for the forward reaction is +70 kJ mol–1.
41 The diagram represents the Boltzmann distribution of molecular energies at a given temperature.
number
of molecules
energy
Which of the factors that affect the rate of a reaction can be explained using such a Boltzmann
distribution?
1
increasing the concentration of reactants
2
increasing the temperature
3
the addition of a catalyst
42 For which reactions does the value of ∆Ho represent both a standard enthalpy change of
combustion and a standard enthalpy change of formation?
1
C(s) + O2(g) → CO2(g)
2
2C(s) + O2(g) → 2CO(g)
3
CO(g) +
1
2
O2(g) → CO2(g)
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Enthalpy Change &
Hess's Law
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Theory
Paper Type
Booklet
Mark Scheme 1
Time Allowed:
78 minutes
Score:
/65
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i)
Bond breaking = Cl-Cl = 242
C-H = 410 = 652 kJ
Bond forming =
[1]
C-Cl = 340
H-Cl = 431 = 771 kJ
[1]
Enthalpy change = 652 – 771 = –119
[1]
(ii)
UV / High T / sunlight
unl
(iii)
Initiation
Cl2 2Cl•
[1]
Propagation
C2H6 + Cl• •C2H5 + HCl
•C2H5 + Cl2 C2H5Cl + Cl•
[1]
[1]
Termination
•C2H5 + •C2H5 C4H10
[1]
All three names correctly assigned
[1]
ethene
[1]
1]
KOH / NaOH
[1]
ethanolic AND heat / reflux
[1]
H2 AND Pt or Ni (catalyst)
[1]
(b) (i)
(ii)
(iii)
[3]
[1]
[5]
[2]
[1]
[13]
2
(a
(i)
Ksp = [Ag+(aq)]2[SO42–(aq)] and units: mol3dm–9
1
(ii)
Ksp = (2 x 0.025)2 x (0.025) = 6.25 x 10–5
1
(b)
24
+
H
o
latt
Ag2SO4(s)
o
hyd
o
sol
2
+
(c) (i)
(ii)
4
or
2-
4
1
1
1
1
Eocell (= 0.80 – 0.77 =) (+)0.03V and Ag+ / Ag or Ag / silver or right
1
Ecell would be less positive / more negative
1
because the [Ag+(aq)] (in the Ag electrode) is less than 1.0 mol dm–3
(iii)
(iv)
(d)
•
no change
1
•
more negative / less positive
1
the [Ag+(aq)] will decrease
Eelectrode becomes less positive or due to the common ion effect
1
[Fe3+(aq)] = 0.2 mol dm–3
1
[H+] = √(c.Ka) = √(0.2 x 8.9 x 10–4) or 1.33 x 10–2 (mol dm–3)
pH = –log([H+]) = 1.9 (or 1.87–1.89)
1
[Total: 13]
3
(a
(i)
101 = P35Cl35Cl
103 = P35Cl37Cl
105 = P37Cl37Cl
1
1
1
(ii)
9:6:1
1
PCl5 5 bonding pairs around P
1
(b) (i)
Cl
(ii)
P
Cl
+
Cl
1
1
Cl
Cl
(c) (i)
Cl
-
Cl
Cl
[3]
Cl
1
P
O
O O
P
Cl
P
[4
P
O
P
O
O
P4O6 structure where each P has three P-O bonds and each O has two P-O bonds e.g.
O
O
P
O
P
P
O
P
O
O
(ii)
(d) (i)
(molecule/ion/species) that donates a lone pair of electrons (to a central transition metal atom or
ion)
1
Ksp =[Ca2+]3[PO43–]2
1
[2
(ii)
(e) (i)
(ii)
Total
[Ca2+] = 3 × 2.50 × 10–6 = 7.50 × 10–6 mol dm–3
[PO43–] = 2 × 2.50 × 10–6 = 5.00 × 10–6 mol dm–3
1
= (7.50 × 10–6)3(5.00 × 10–6)2
= 1.05(1.1) × 10–26
mol5dm–15
1
1
(enthalpy change) when 1 mole of an ionic compound
is formed from its gaseous ions
1
1
Mg2+ has a smaller (ionic) radii than Ca2+
OR Mg2+ is smaller than Ca2+
1
[4]
[3
[16]
4
(a
(i) the enthalpy change/released when 1 mole is formed
of ionic lattice from the gas phase ions
(ii) Mg2+ + O2– → MgO
(b) measurements needed:
volume/mass/weight of water (in calorimeter)
initial + final temperature/temperature change/temperature rise (of the water)
mass of Mg (used)/mass MgO
Not volume/moles/mass of oxygen used
[1]
[1]
[1]
[3]
[1]
[1]
[1]
[3]
(c) ∆H = 148 + 736 + 1450 + 496/2 - 141 + 798 – 3791
= –552 kJ mol–1
(d) Na2O(s) + H2O(aq/l) → 2NaOH(aq)
MgO(s) + H2O(aq/l) → Mg(OH)2(s) or Mg(OH)2(aq)
pH 12.5-14 [NaOH] AND 8-10.5 [Mg(OH)2] respectively
[3]
[3]
[1]
[1]
[1]
[3]
[Total: 12]
5
(a
the overall enthalpy change/energy change/∆H for a reaction
(1)
is independent of the route taken or
is independent of the number of steps involved
provided the initial and final conditions are the same
(1)
(b) (i) K2CO3 + 2HCl → 2KCl + H2O + CO2
(ii) heat produced = m × c × δT = 30.0 × 4.18 × 5.2
= 652.08 J per 0.0200 mol of K2CO3
[2]
(1)
(1)
(iii) 0.020 mol K2CO3 ≡ 652.08 J
1 mol K2CO3 ≡ 652.08 × 1 = 32604 J
0.0200
enthalpy change = –32.60 kJmol–1
(iv) to prevent the formation of KHCO3 or
to ensure complete neutralisation
(c) (i) KHCO3 + HCl → KCl + H2O + CO2
(ii) heat absorbed = m × c × δT = 30.0 × 4.18 × 3.7
= 463.98 J per 0.0200 mol of KHCO3
(1)
(1)
[4]
(1)
(1)
(iii) 0.020 mol KHCO3 ≡ 463.98 J
1 mol KHCO3 ≡ 463.98 × 1 = 23199 J
0.0200
enthalpy change = +23.20 kJmol–1
(1)
1)
(d) ∆H = 2 × (+23.20) – (–32.60) = +79.00 kJ mol–1
(2)
2)
[Total: 11]
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Enthalpy Change &
Hess's Law
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Theory
Paper Type
Booklet
Question Paper 1
Time Allowed:
78 minutes
Score:
/65
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Ethane reacts with chlorine to form chloroethane.
C2H6(g) + Cl 2(g) → C2H5Cl (g) + HCl (g)
(a)
a)
Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction.
Include a sign in your answer.
enthalpy change = ................................. kJ mol–1 [3]
(ii) State the conditions needed for this reaction to occur.
....................................................................................................................................... [1]
(iii) Use a series of equations to describe the mechanism of this reaction including the names
of each stage and an indication of how butane can be produced as a minor by-product.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [5]
(b) Chloroethane can be converted back into ethane by a two-stage process via an intermediate
compound, X.
C2H5Cl
reaction 1
X
reaction 2
C 2H 6
(i) Give the name of X.
....................................................................................................................................... [1]
(ii) Suggest the reagent and conditions needed for reaction 1.
....................................................................................................................................... [2]
(iii) Suggest the reagent and conditions needed for reaction 2.
....................................................................................................................................... [1]
[Total: 13]
2
(a) Silver sulfate, Ag2SO4, is sparingly soluble in water. The concentration of its saturated solution
is 2.5 × 10–2 mol dm–3 at 298 K.
(i)
Write an expression for the solubility product, Ksp, of Ag2SO4, and state its units.
Ksp =
(ii)
units: .............................. [1]
Calculate the value for Ksp(Ag2SO4) at 298 K.
Ksp = ............................................... [1]
(b) Using Ag2SO4 as an example, complete the following Hess' Law energy cycle relating the
●
lattice energy,
●
enthalpy change of solution,
●
enthalpy change of hydration,
,
, and
.
On your diagram:
●
include the relevant species in the two empty boxes,
●
label each enthalpy change with its appropriate symbol,
●
complete the remaining two arrows showing the correct direction of enthalpy change.
..............................
Ag2SO4(s)
..............................
..............................
[4]
(c) An electrochemical cell is set up as follows.
V
Pt
Ag
Ag2SO4(aq)
Fe2(SO4)3(aq)
+
FeSO4(aq)
(i)
Ag2SO4(s)
Use the Data Booklet to calculate the value of
which electrode is the positive one.
= ..............................
(ii)
under standard conditions, stating
positive electrode: .............................. [1]
How would the actual Ecell of the above cell compare to the
Explain your answer.
under standard conditions?
.............................................................................................................................................
....................................................................................................................................... [1]
(iii)
How would the Ecell of the above cell change, if at all, if a few cm3 of concentrated Na2SO4(aq)
were added to
•
the beaker containing Fe3+(aq) + Fe2+(aq),
.............................................................................................................................................
•
the beaker containing Ag2SO4(aq)?
.............................................................................................................................................
[2]
(iv)
Explain any changes in Ecell you have stated in (iii).
.............................................................................................................................................
....................................................................................................................................... [1]
(d) Solutions of iron(III) sulfate are acidic due to the following equilibrium.
[Fe(H2O)6]3+(aq)
[Fe(H2O)5(OH)]2+(aq) + H+(aq)
Ka = 8.9 × 10–4 mol dm–3
Calculate the pH of a 0.1 mol dm–3 solution of iron(III) sulfate, Fe2(SO4)3.
pH = .........................
[2]
[Total: 13]
3
(a) Natural phosphorus consists of one isotope, 31P. Chlorine exists naturally as two isotopes, 35Cl
and 37Cl, in the relative abundance ratio of 3 : 1.
(i) The mass spectrum of PCl 3 contains several peaks corresponding to a number of
molecular fragments.
Suggest the isotopic composition of the fragments with the following mass numbers.
mass number
isotopic composition
101
103
105
(ii) Predict the relative ratios of the peak heights of the three peaks corresponding to these
fragments.
.............................................................................................................................................
[4]
(b) Phosphorus reacts with chlorine to form a variety of chlorides.
PCl 5 is an example of a compound that exists as two structures depending on the conditions.
2PCl 5(g)
[PCl 4]+[PCl 6]–(s)
(i) Draw a ‘dot-and-cross’ diagram to show the bonding in PCl 5. Show the outer electrons
only.
(ii) Draw diagrams to suggest the shapes of [PCl 4]+ and [PCl 6]–.
[PCl 4]+
[PCl 6]–
[3]
(c)
c)
Phosphorus(III) oxide, P4O6, contains no P–P or O–O bonds.
In the P4O6 molecule, all oxygen atoms are divalent and all phosphorus atoms are trivalent.
Sketch a structure for P4O6.
(ii) P4O6 can act as a ligand.
What is meant by the term ligand ?
.............................................................................................................................................
.............................................................................................................................................
[2]
(d) Phosphate ions in water can be removed by adding a solution containing Ca2+(aq) ions, which
form a precipitate of calcium phosphate, Ca3(PO4)2.
(i) Write an expression for the Ksp of Ca3(PO4)2.
Ksp =
(ii) The solubility of Ca3(PO4)2 is 2.50 × 10–6 mol dm–3 at 298 K.
Calculate the solubility product, Ksp, of Ca3(PO4)2 at this temperature. Include the units.
Ksp = ..................................................................
units ....................................................
[4]
(e)
e)
What is meant by the term lattice energy?
.............................................................................................................................................
.............................................................................................................................................
(ii) Explain why the lattice energy of calcium phosphate is less exothermic than that of
magnesium phosphate.
.............................................................................................................................................
.............................................................................................................................................
[3]
[Total: 16]
4
(a) (i) What is meant by the term lattice energy?
....................................................................................................................................
....................................................................................................................................
(ii) Write an equation to represent the lattice energy of MgO.
....................................................................................................................................
[3]
(b) The apparatus shown in the diagram can be used to measure the enthalpy change of
formation of magnesium oxide,
(MgO).
to suction pump
stirrer
copper spiral
water
magnesium ribbon
oxygen gas
small electric heater
(to ignite magnesium)
List the measurements you would need to make using this apparatus in order to calculate
(MgO).
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
(c) Use the following data, together with appropriate data from the Data Booklet, to calculate
a value of
(MgO).
lattice energy of MgO(s)
=
–3791 kJ mol–1
enthalpy change of atomisation of Mg
=
+148 kJ mol–1
electron affinity of the oxygen atom
=
–141 kJ mol–1
electron affinity of the oxygen anion, O–
=
+798 kJ mol–1
(MgO) = .......................... kJ mol–1
[3]
(d) Write equations, including state symbols, for the reactions, if any, of the following two
oxides with water. Suggest values for the pH of the resulting solutions.
oxide
equation
pH of resulting
solution
Na2O
MgO
[3]
[Total: 12]
5
For some chemical reactions, such as the thermal decomposition of potassium
hydrogencarbonate, KHCO3, the enthalpy change of reaction cannot be measured directly.
In such cases, the use of Hess’ Law enables the enthalpy change of reaction to be calculated
from the enthalpy changes of other reactions.
(a) State Hess’ Law.
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
In order to determine the enthalpy change for the thermal decomposition of potassium
hydrogencarbonate, two separate experiments were carried out.
experiment 1
30.0 cm3 of 2.00 mol dm–3 hydrochloric acid (an excess) was placed in a conical flask and the
temperature recorded as 21.0 °C.
When 0.0200 mol of potassium carbonate, K2CO3, was added to the acid and the mixture
stirred with a thermometer, the maximum temperature recorded was 26.2 °C.
(b) (i)
Construct a balanced equation for this reaction.
..................................................................................................................................
(ii)
Calculate the quantity of heat produced in experiment 1, stating your units.
Use relevant data from the Data Booklet and assume that all solutions have the
same specific heat capacity as water.
(iii)
Use your answer to (ii) to calculate the enthalpy change per mole of K2CO3.
Give your answer in kJ mol–1 and include a sign in your answer.
(iv)
Explain why the hydrochloric acid must be in an excess.
..................................................................................................................................
............................................................................................................................. [4]
experiment 2
The experiment was repeated with 0.0200 mol of potassium hydrogencarbonate, KHCO3.
All other conditions were the same.
In the second experiment, the temperature fell from 21.0 °C to 17.3 °C.
(c) (i)
Construct a balanced equation for this reaction.
..................................................................................................................................
(ii)
Calculate the quantity of heat absorbed in experiment 2.
(iii)
Use your answer to (ii) to calculate the enthalpy change per mole of KHCO3.
Give your answer in kJ mol–1 and include a sign in your answer.
[3]
(d) When KHCO3 is heated, it decomposes into K2CO3, CO2 and H2O.
2KHCO3
K2CO3 + CO2 + H2O
Use Hess’ Law and your answers to (b)(iii) and (c)(iii) to calculate the enthalpy change
for this reaction.
Give your answer in kJ mol–1 and include a sign in your answer.
[2]
[Total: 11]
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Enthalpy Change &
Hess's Law
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Multiple Choice
Paper Type
Booklet
Question Paper 2
Time Allowed:
23 minutes
Score:
/19
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Red lead oxide, Pb3O4, is used in metal priming paints. It can be made by heating PbO in air.
6PbO(s) + O2(g) → 2Pb3O4(s)
Which two values are needed to calculate the enthalpy change for this reaction?
2
A
enthalpy change of combustion of lead and enthalpy change of formation of Pb3O4
B
enthalpy change of combustion of PbO and enthalpy change of formation of Pb3O4
C
enthalpy change of formation of PbO and enthalpy change of atomisation of O2
D
enthalpy change of formation of PbO and enthalpy change of formation of Pb3O4
An exothermic chemical reaction proceeds by two stages.
stage 1
reactants
stage 2
intermediate
products
The activation energy of stage 1 is 50 kJ mol–1. The overall enthalpy change of reaction is
–100 kJ mol–1.
Which diagram represents the reaction pathway for this reaction?
A
100
75
50
25
0
-25 reactants
-50
-75
-100
products
progress
of reaction
B
100
75
50
25
0
-25 reactants
-50
products
-75
-100
progress
of reaction
C
100
75
50
25
0
-25 reactants
-50
-75
products
-100
progress
of reaction
D
100
75
50
25
0
-25 reactants
-50
products
-75
-100
progress
of reaction
3
Skiers trapped by snowstorms use heat packs to keep warm. The heat may be generated by the
reaction below.
4Fe(s) + 3O2(g) → 2Fe2O3(s)
;
∆HO = –1648 kJ
What is the standard enthalpy change of formation of iron(III) oxide?
A
0 kJ mol–1
B
–824 kJ mol–1
C
–1648 kJ mol–1
D
–3296 kJ mol–1
4 Slaked lime, Ca(OH)2, may be made from limestone, CaCO3.
On heating in a lime kiln at 1000 °C, limestone decomposes as follows.
reaction 1
CaCO3(s) → CaO(s) + CO2(g)
Water is then reacted with calcium oxide, CaO, as follows.
reaction 2
CaO(s) + H2O(l) → Ca(OH)2(s)
What are the enthalpy changes of these reactions?
5 The standard enthalpy changes of formation of HCl and HI are –92 kJ mol–1 and +26 kJ mol–1
respectively.
Which statement is most important in explaining this difference?
6
A
Chlorine is more electronegative than iodine.
B
The activation energy for the H2 / Cl2 reaction is much less than that for the H2 / I2 reaction.
C
The bond energy of HI is smaller than the bond energy of HCl.
D
The bond energy of I2 is smaller than the bond energy of Cl2.
Which equation represents the standard enthalpy change of atomisation of bromine?
A
Br2(l) → 2Br(g)
B
Br2(g) → 2Br(g)
C
1
2
Br2(l) → Br(g)
D
1
2
Br2(g) → Br(g)
7 The gaseous oxides of nitrogen have positive enthalpy changes of formation.
Which factor is likely to make the most significant contribution to these enthalpy changes?
A
the high bond energy of the nitrogen molecule, N2
B
the high electron affinity of nitrogen atoms
C
the high electron affinity of oxygen atoms
D
the similarity of the electronegativities of oxygen and nitrogen
8
9
For which equation is the enthalpy change correctly described as an enthalpy change of
formation?
A
2NO(g) → N2(g) + O2(g)
B
2CO(g) + O2(g) → 2CO2(g)
C
H2O(l) + NaCl(s) → NaCl(aq)
D
K(s) + Mn(s) + 2O2(g) → KMnO4(s)
Given
1
2
CO(g) +
H2(g) +
1
2
O2(g)
O2(g)
H2O(g)
→
CO2(g)
∆Ho = –283 kJ mol–1
→
H2O(l)
∆Ho = –286 kJ mol–1
→
H2O(l)
∆Ho = –44 kJ mol–1
what is the change in enthalpy, ∆Ho, for the following reaction?
CO2(g) + H2(g) → CO(g) + H2O(g)
A
–525 kJ mol–1
10 Given
and
B
–41 kJ mol–1
S(s) + O2(g) → SO2(g),
S(s) + 121 O2(g) → SO3(g)
C
+41 kJ mol–1
D
+525 kJ mol–1
∆H of = –297 kJ mol –1
∆H of = –395 kJ mol –1
what is the enthalpy change of reaction, ∆H o, of 2SO2(g) + O2(g) → 2SO3(g)?
A
–196 kJ mol –1
B
–98 kJ mol –1
C
+98 kJ mol –1
D
+196 kJ mol –1
11 The table shows the enthalpy change of neutralisation per mole of water formed, ∆H, for various
acids and bases.
acid
cid
base
∆H / kJ mol–1
hydrochloric acid
sodium hydroxide
–57.
P
sodium hydroxide
–54.
hydrochloric acid
Q
–52.
nitric acid
R
–57.
What are P, Q and R?
P
Q
R
A
ethanoic acid
ammonia
potassium hydroxide
B
ethanoic acid
sodium hydroxide
ammonia
C
sulphuric acid
ammonia
potassium hydroxide
D
sulphuric acid
sodium hydroxide
ammonia
12 The standard enthalpy changes of formation of iron(II) oxide, FeO(s), and aluminium oxide,
Al2O3(s), are –266 kJ mol–1 and –1676 kJ mol–1 respectively.
What is the enthalpy change under standard conditions for the following reaction?
3FeO(s) + 2Al (s) ® 3Fe(s) + Al 2O3(s)
A
+ 878 kJ
B
C
– 878 kJ
D
–1942 kJ
–2474 kJ
13 Use of the Data Booklet is relevant to this question.
Which of the bonds in the structure below has the lowest bond energy?
H
A
H
C
H
F
B
C
C
H
D
Cl
14
Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and
chlorine by heating. The table below gives the bond energies.
bond
bond energy / kJ mol–1
P-Cl (in both chlorides)
330
Cl-Cl
240
What is the enthalpy change in the decomposition of PCl5 to PCl3 and Cl2?
A
–420 kJ mol–1
B
–90 kJ mol–1
C
+90 kJ mol–1
D
+420 kJ mol–1
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
1, 2 and 3
are
correct
B
C
1 and 2
only are
correct
2 and 3
only are
correct
D
1 only
is
correct
No other combination of statements is used as a correct response.
15 Nitrogen and oxygen react in a hot car engine to form nitrogen monoxide which is a serious
pollutant in our cities and in the countryside. However, nitrogen and oxygen do not react at room
temperature.
Which statements help to explain why nitrogen and oxygen do not react at room temperature?
1
The reaction is endothermic.
2
A high activation energy is required.
3
Nitrogen has a high bond energy.
16 Sodium ions can be formed from sodium atoms.
Na(s) → Na+(g)
Which quantities are required to calculate the enthalpy change of formation of gaseous sodium
ions?
1
enthalpy change of atomisation of sodium
2
first ionisation energy of sodium
3
enthalpy change of formation of sodium
17 Which of the enthalpy changes of the following reactions can only be obtained by application of
Hess’ Law?
1
The hydration of anhydrous copper sulphate to form crystals of CuSO4.5H2O.
2
The formation of methane from its elements.
3
The combustion of glucose, C6H12O6.
18 The diagram illustrates the energy changes of a set of reactions.
H = _134 kJ mol
_
R
1
S
H = +92 J mol
T
H = _75 kJ mol
_
1
1
U
Which of the following statements are correct?
1
The enthalpy change for the transformation U → R is + 42 kJ mol–1 .
2
The enthalpy change for the transformation T → S is endothermic.
3
The enthalpy change for the transformation R → T is – 33 kJ mol–1 .
19
The conversion of graphite into diamond is an endothermic reaction (∆H = +3 kJ mol–1).
C(graphite) → C(diamond)
Which statements are correct?
1
The enthalpy change of atomisation of diamond is smaller than that of graphite.
2
The bond energy of the C–C bonds in graphite is greater than that in diamond.
3
The enthalpy change of combustion of diamond is greater than that of graphite.
Enthalpy Change &
Hess's Law
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Theory
Paper Type
Booklet
Mark Scheme 2
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) homogeneous
[1]
(ii) ions in 2 and 3 are oppositely charged ions (thus attract each other) or
ions in 1 are similarly charged ions (thus repel each other)
[1]
(iii)
two contiguous activation humps
both less than the original
starting and finishing at the same points as before
(b)
b)
[1]
[1]
[1]
[5]
SO3 produces acid rain or SO3 + H2O → H2SO4 or a consequence of acid rain,
e.g. lower pH of lakes; leaches aluminium from soils; kills fish/plants/rainforests;
dissolves/corrodes/damages buildings (NOT global warming)
[1]
(NOT asthma etc – since this is not environmental)
(ii) the burning of fossil fuels/coal/oil/petrol/gas/diesel/fuel or car exhausts or roasting of
sulphide ores or cement manufacture or volcanoes
[1]
(iii) SO2 + NO2 → SO3 + NO
NO + ½O2 → NO2
[1]
[1]
[4]
[Total: 9]
2
(a
The energy required to break....
.....1 mole of bonds in the gas phase
(b) HCl: nothing happens AND HI: purple fumes (at a low temperature)
purple is iodine formed (or in an equation: 2HI → H2 + I2)
H-X
H- bond energy becomes smaller/weaker down the gro
[1]
[1]
[2]
[1]
[1]
[1]
[3]
(c) data needed: F-F = 158
Cl-Cl = 244
6 E(Cl-F) –328 = 3×158 + 244
E(Cl-F) = +174 (kJ mol–1)
[2
[2]
[Total: 7]
3
(a
tetrahedral diagram (either dashed+wedge, or similar representation)
angles (all) 109° – 110°
(award [0] for part (a) if an angle of 90° or 180° is mentioned)
(b) volatility decreases or boiling points increase
(allow b.pt. CCl4 > SiCl4 but b.pt. increases thereafter)
due to greater van der Waals’/intermolecular forces or due to more electrons
(mention of “ions” negates this mark)
(c) (i) Pb4+/Pb2+: E o = +1.69V, Sn4+/Sn2+: E o = +0.15V,
a valid comment about relative redox power or stability, e.g.:
(hence) Sn2+ easily oxidised or Sn4+ is more stable than Sn2+ or
Pb4+ is easily reduced or Pb2+ is more stable than Pb4+ or
+2 oxidation state more stable down the grou
(ii) Sn2+ + I2 → Sn4+ + 2I ¯
Pb4+ + SO2 + 2H2O → 4H+ + SO42- + Pb2+
(N.B. no marks in (ii) for E o values)
(d)
d)
for Si: ∆H = 244 – 2(359) = –474 (kJ mol–1)
for Sn: ∆H = 244 – 2(315) = –386 (kJ mol–1)
(allow [1] out of [2] salvage mark for 474 & 386; 962 & 874; or –962 & –874)
(ii) Yes: the +4 state becomes decreasingly stable – the ∆H is less exothermic
(mark is for relating ∆Hs to stability: allow ecf from d(i) and also from c(i))
[1]
[1]
[2]
[1]
[1]
[2]
[both] [1]
[1]
[1
[1]
[4]
[1
[1
[1]
[3]
[Total: 11]
4
(a
A: voltmeter or V or potentiometer
[1]
B: platinum or Pt
[1]
C: 1 mol dm–3 and H+ or HCl (or 0.5 M H2SO4)
[1]
D: lead (metal) or Pb
[1]
4
(b)
b)
a in the box next to –0.17 V
a comment that the [Pb2+] has decreased plus a description of the outcome,
e.g. as [Pb2+] decreases (from 1 mol dm–3), Pb2+(aq) + 2e– ⇌ Pb(s) goes
over to the left hand side, or as [Pb2+] decreases, Pb2+ is less likely to be
reduced
[1]
[1]
(ii) (Ksp =) [Pb2+][Cl –]2
(iii) if [PbCl2] = 3.5 × 10–2, [Pb2+] = 3.5 × 10–2 and [Cl –] = 7.0 × 10–2
so Ksp = (3.5 × 10–2) × (7.0 × 10–2)2 = 1.715 (1.7) × 10–4 mol3 dm–9 ([2sf)
[1]
[1]
5
(c) (i) the (M2+ / M) Eo for the two elements are very similar or are –0.13 and –0.14 V
[1
Eo (Sn4+ / Sn2+) = 0.15 V and Eo (Pb4+ / Pb2+) = 1.69 V
[1]
so Sn2+ is quite easily oxidised (to Sn4+) or is a stronger reductant or Pb2+ is
not easily oxidised (to Pb4+) or Pb4+ is a stronger oxidant or Pb4+ is easily
reduced
[1]
(ii) e.g. PbCl2 + Zn → Pb + ZnCl2 (or ionic)
(other acceptable reductants: Fe, Mg, Ca but not Na or K)
Sn2+ + Br2 → Sn4+ + 2Br(other acceptable oxidants: VO2+, Cr2O72–, Ag+, Cl2, Br2, F2, Fe3+, MnO4–)
[1]
[1]
5
(d)
d)
Pb2+(g) + 2Cl –(g) → PbCl2(s)
[1]
(ii) ∆Hf = ∆Hat + E(Cl – Cl) + 1st IE + 2nd IE + 2 × EA(Cl) + LE
–359 = 195 + 242 + 716 + 1450 – 2 × 349 + LE
LE = 2 × 349 – 359 – 195 – 242 – 716 – 1450
LE = –2264 (kJ mol–1)
[3
(iii) LE(PbCl2) > LE(PbBr2) or more exothermic or stronger lattice
[1]
because Cl – / chloride anion has smaller radius / size than Br – / bromide
[1]
6
[Total: 20]
5
(a
catalyst: any two from the following three bullets for [1] mark:
• speeds up/increases (NOT alters or changes) the rate of a reaction
• lowers energy barrier/Eact or offers a lower energy pathway
• is not used up or remains unchanged or does not alter its mass/concentration
or does not appear in stoichiometric equation or is regenerated
[1]
homogeneous: (catalyst and reactants) in the same phase/state
[1]
[Total: 2]
(b) (i) e.g. car exhausts/engines or aeroplanes or lightning or burning fuels or power stations
[1]
nitrogen reacts with oxygen or N2 + O2
[1]
(ii) NO2 + SO2 → NO + SO3
NO + ½ O2 → NO2
SO3 + H2O → H2SO4
4NO2 + 2H2O + O2 → 4HNO3 or 3NO2 + H2O → 2HNO3 + NO (any 3 equations) 3 × [1]
[Total: 5]
(c)
∆H shown as negative
both Ea labelled and correct – i.e. for the forward reaction
Ea(cat) < Ea(uncat)
[1]
[1]
[1]
[Total: 3]
[TOTAL: 10]
Enthalpy Change &
Hess's Law
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Theory
Paper Type
Booklet
Question Paper 2
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1(a) The reaction between iodide ions and persulfate ions, S2O 82−, is slow.
2I− + S2O 82−
I2 + 2SO 42−
1
The reaction can be speeded up by adding a small amount of Fe2+ or Fe3+ ions. The
following two reactions then take place.
2I− + 2Fe3+
2Fe2+ + S2O 82−
(i)
I2 + 2Fe2+
2Fe3+ + 2SO 42−
2
3
What type of catalysis is occurring here?
..................................................................................................................................
(ii)
The rates of reactions 2 and 3 are both faster than that of reaction 1. By considering
the species involved in these reactions, suggest a reason for this.
..................................................................................................................................
..................................................................................................................................
(iii)
The following reaction pathway diagram shows the enthalpy profile of reaction 1.
enthalpy
progress of reaction
Use the same axes to draw the enthalpy profiles of reaction 2 followed by reaction
3, starting reaction 2 at the same enthalpy level as reaction 1.
[4]
(b) The oxidation of SO2 to SO3 in the atmosphere is speeded up by the presence of
nitrogen oxides.
(i)
Describe the environmental significance of this reaction.
..................................................................................................................................
(ii)
Describe a major source of SO2 in the atmosphere.
..................................................................................................................................
(iii)
By means of suitable equations, show how nitrogen oxides speed up this reaction.
..................................................................................................................................
..................................................................................................................................
[4]
[Total: 8]
2
(a) What is meant by the term bond energy?
..........................................................................................................................................
...................................................................................................................................... [2]
(b) Describe and explain what is observed when a red-hot wire is plunged into separate
samples of the gaseous hydrogen halides HCl and H I.
How are bond energy values useful in interpreting these observations?
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [3]
(c) The following reaction occurs in the gas phase.
3F2(g) + Cl2(g)
2ClF3(g),
o = –328 kJ mol–1
∆H—
r
Use these and other data from the Data Booklet to calculate the average bond energy
[2]
of the Cl-F bond in Cl F3.
[Total: 7]
3
The elements of Group IV all form tetrachlorides with the general formula M Cl 4.
(a) Draw a diagram of a molecule of SiCl 4 stating bond angles.
[2]
(b) Describe and explain how the volatilities of the Group IV chlorides vary down the group.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(c) The relative stabilities of the M 2+(aq) and M 4+(aq) ions also vary down Group IV.
(i)
Use the Data Booklet to illustrate this observation when M = Sn and M = Pb.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Use the Data Booklet to predict the products formed, and write equations for the
reactions occurring, when
•
an equimolar mixture of Sn2+(aq) and Sn4+(aq) is added to I2(aq),
..................................................................................................................................
..................................................................................................................................
•
an equimolar mixture of Pb2+(aq) and Pb4+(aq) is added to SO2(aq).
..................................................................................................................................
..................................................................................................................................
[4]
(d) (i)
The Sn–Cl bond energy is +315 kJ mol–1. Use this and other values from the Data
Booklet to calculate DH o for the reaction
M Cl 2(g) + Cl 2(g)
M Cl 4(g)
for the following cases.
•
M = Si
DH o = ........................................ kJ mol–1
•
M = Sn
DH o = ........................................ kJ mol–1
(ii)
Do your results agree with the trend in relative stabilities of the +2 and +4 oxidation
states in (c)? Explain your answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 11]
4
Lead(II) chloride, PbCl 2, can be used in the manufacture of some types of coloured glass.
PbCl 2 is only sparingly soluble in water. The [Pb2+] in a saturated solution of PbCl 2 can be estimated
by measuring the cell potential, Ecell, of the following cell.
A
H2(g)
1 atm, 298 K
salt bridge
B
D
saturated solution
of PbCl 2
C
solid PbCl 2
(a) In the spaces below, identify what the four letters A-D in the above diagram represent.
A .................................................................
B ................................................................
C .................................................................
D ................................................................
[4]
(b) In a saturated solution of PbCl 2, [PbCl 2(aq)] = 3.5  10–2 mol dm–3.
(i) The E o for the Pb2+ / Pb electrode is – 0.13 V. Predict the potential of the right-hand electrode
in the diagram above. Indicate this by placing a tick in the appropriate box in the table
below.
electrode
potential / V
place one tick only
in this column
– 0.17
– 0.13
– 0.09
0.00
Explain your answer.
.............................................................................................................................................
.............................................................................................................................................
(ii) Write an expression for the solubility product, Ksp, of PbCl 2.
.............................................................................................................................................
(iii)
i
Calculate the value of Ksp, including units.
Ksp = .......................................
units .......................................
[5]
(c) The behaviours of PbCl 2 and SnCl 2 towards reducing agents are similar, but their behaviours
towards oxidising agents are very different.
(i) Illustrate this comparison by quoting and comparing relevant E o values for the two metals
and their ions. Explain what the relative E o values mean in terms of the ease of oxidation
or reduction of these compounds.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
(ii) Writing a balanced molecular or ionic equation in each case, suggest a reagent to carry
out each of the following reactions.
the reduction of PbCl 2
.............................................................................................................................................
the oxidation of SnCl 2
.............................................................................................................................................
[5]
(d)
d)
Write an equation to represent the lattice energy of PbCl 2. Show state symbols.
.............................................................................................................................................
(ii) Use the following data, together with appropriate data from the Data Booklet, to calculate
a value for the lattice energy of PbCl 2.
electron affinity of chlorine
enthalpy change of atomisation of lead
enthalpy change of formation of PbCl 2(s)
= –349 kJ mol–1
= +195 kJ mol–1
= –359 kJ mol–1
lattice energy = ............................. kJ mol–1
(iii) How might the lattice energy of PbCl 2 compare to that of PbBr2? Explain your answer.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[6]
[Total: 20]
5
Nitrogen oxides in the atmosphere are homogeneous catalysts in the formation of acid rain.
(a) What is meant by the following terms?
catalyst
...........................................................................................................................................
...........................................................................................................................................
homogeneous
...........................................................................................................................................
...........................................................................................................................................
[2]
(b) (i) State a major source of nitrogen oxides in the atmosphere, explaining how they are
formed.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) Use equations to describe the chemical role played by nitrogen oxides in the
formation of acid rain.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[5]
(c) Use the following axes to draw a fully labelled reaction pathway diagram showing the
effect of a catalyst on an exothermic reaction. Label the ∆H and Ea values.
energy
reactants
extent of reaction
[3]
[Total: 10]
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Enthalpy Change &
Hess's Law
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Theory
Paper Type
Booklet
Mark Scheme 3
Time Allowed:
81 minutes
Score:
/67
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
CH2=CH2 + HF
bonds
4 C-H
broken 1 C=C
/kJ mol-1 1 H-F
1640
610
562
2812
→
CH3CH2F
bonds
made
/kJ mol-1
5 C-H
2050
1 C-C
350
1 C-F
E
(2400 + E)
breaking reactant bonds requires
4 x 410 + 610 + 562 = 2812 kJ mol-1
(1)
making product bonds gives
5 x 410 + 350 + E = (2400 + E) kJ mol-1
(1)
∆Horeaction = - (2400 + E) + 2812 = – 73 kJ mol-1
(1)
(2400 + E) = 2812 + 73 = 2885 kJ mol-1
E = 2885 - 2400 = 485 kJ mol-1
(1)
allow ecf on wrong bond energy values and/or incorrect arithmetic
(b) any two from
non-toxic
unreactive
volatile
non-flammable
easily liquefied
(c) in CCl2F2
C-Cl bond energy is 340 kJ mol-1 and is weaker than C-F or C-H bonds
C-Cl bond is broken by uvl or
Cl. free radicals are formed
[4]
(1 + 1)
[2]
(1)
(1)
[2]
(1)
[3]
(1)
[1]
(d) (i) the trapping of reflected heat from the Earth in the lower atmosphere
producing global warming
(ii) CO2/carbon dioxide
(e) octahedral
[Total: 12]
2
(a) fewer electrons in Cl 2 than in Br2 (1)
smaller van der Waals’ forces in Cl 2 or stronger van der Waals’ forces in Br2 (1)
[2]
(b) CO has a permanent dipole or N2 does not (1)
permanent dipole-permanent dipole interactions are stronger than those from induced
dipoles (1)
[2]
(c) (i) a co-ordinate bond (1)
(ii) a covalent bond (1)
or
(iii) a lone pair (1)
or
penalise any groups of 3 or 4 electrons that are circled
(d) CO and HCN both have a dipole or N2 does not have a dipole (1)
[3]
[1]
(e) (i)
H H
 
HCCOH
 
H C≡N
C≡N must be shown (1)
(ii) nucleophilic addition (1)
(iii)
δ+ δ–
CH3C=O

H CN–
H
|
CH3CO–
|
CN
HCN
H

CH3COH + CN–

CN
C=O dipole correctly shown or correct curly arrow on C=O (1)
attack on Cδ+ by C of CN– (1)
correct intermediate (1)
CN– regenerated (1)
[5 max]
[Total: 13]
3
(a
CH3CH2CH2CH2CH2OH
A
all three (any order)
(2 only = [1])
3CH2CH2CH(OH)CH3
(b) B above (may be different letter)
(c)
c)
(
CH3CH2CH(OH)CH2CH3
C
[2]
[2]
([0] if more than one compound stated)
B above (may be different letter)
[1]
([0] if more than one compound stated)
[1]
[1]
(ii) (pale) yellow ppt.
[1]
(iii) CHI3 + CH3CH2CH2CO2Na or anion (no credit for the acid, RCO2H)
[1]
[4]
(d) A → CH3CH2CH2CH2CO2H
[1]
B → CH3CH2CH2COCH3
C → CH3CH2COCH2CH3
(e)
e)
[1]
(letters may differ)
[1]
[3]
(C6H10O5)n → 5n H2 + 5n CO + n C correct species and the 5:5:1 ratio [1]
(allow n5 instead of 5n) balancing, i.e. multiplying by n
[1]
(ii) ∆H = 7(1080) + 15(436) – 6(350) – 16(410) – 14(460)
= –1000 kJ mol–1
4 correct values from DB (in bold italics above)
correct multipliers
correct signs and arithmetic
(correct answer = [3])
[1]
[1]
[1]
Some ecf values for [2] marks (i.e. 1 error):
for [1] mark (i.e. 2 errors):
+1000 (signs reversed)
–1350 (7 x (C-C) instead of 6
+135
+2220 (7 x O-H instead of 14
–222
–1410 (17 C-H instead of 16)
+1410
The omission of a type of bond (C-C is the most common one that is omitted) forfeits
2 marks, in addition to any other errors there may be.
[5]
[Total: 15]
4
(a
(i) Ksp = [Ca2+][SO42-]
[1]
units are: mol2dm-6
ecf [1]
(ii) [CaSO4] = √Ksp = 5.5 x 10-3 (5.477 x 10-3)(mol dm-3)
(iii) n(CaSO4) in 100 dm3 = 5.5 x 10-3 x 100 = 0.55 moles
ecf [1]
ecf from (ii) [1]
Mr(CaSO4) = 136.1
Thus mass(CaSO4) = 0.55 x 136.1 = 74.8g (0.55 x Mr)
(if the accurate [CaSO4] is held throughout the calculation, ans = 74.5g)
[1]
[5]
(b)
b)
down the group: the ∆Hsolution becomes more endothermic;
both lattice energy and ∆Hhydration become less (exothermic);
due to ionic radius (of M2+) increasing;
but ∆Hhydration changes more than lattice energy any three points
(ii) Ksp = [Ba2+][SO42-] = (9 x 10-6)2 = 8.1 x 10-11
[3]
NO ecf [1]
[4]
(c)
c)
LE is the energy change when 1 mole of (ionic) solid
[1]
is formed from its gaseous ions
[1]
(ii) LE(BaSO4) < LE(MgSO4), due to larger radius of Ba2+
both points
[1]
[3]
[Total: 12]
5 (a)
Mg2+ + 2e-
Mg
[1]
(b)
chlorine/Cl2
[1]
(c)
smaller Ar
larger (atomic/ionic) radius/size
[1]
[1]
(d) (i) the energy change when 1 mol of solid compound
is formed from its gaseous ions
(ii) Mg2+ (g) + 2Cl- (g)
MgCl2 (s)
[1]
[1]
charges + balancing
state symbols
(e) (i) LE (MgCl2) is greater than LE (NaCl)
(because) Mg2+ has higher charge / smaller radius than Na+
(ii) LE (MgCl2) is greater than LE (CaCl2)
(because) Mg2+ is smaller than Ca2+
(f)
[1]
[1]
[1]
[1]
[1]
[1]
LE = 349 – 122 – 494 – 107 – 411
= -785 (kJ mol-1)
[3]
correct answer = [3], with – [1] for one error. OR mark as follows:
use of all 5 ∆H values, with x1 multipliers
[1]
correct signs for all ∆H values
[1]
negative sign in answer
[1]
Total = [15]
Enthalpy Change &
Hess's Law
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Enthalpy Change & Hess's Law
Theory
Paper Type
Booklet
Question Paper 3
Time Allowed:
81 minutes
Score:
/67
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Halogenoalkanes have been widely used as aerosol propellants, refrigerants and solvents
for many years.
Fluoroethane, CH3CH2F, has been used as a refrigerant. It may be made by reacting ethene
with hydrogen fluoride.
You are to calculate a value for the C–F bond energy in fluoroethane.
(a) Use relevant bond energies from the Data Booklet, and the equation below to calculate
a value for the bond energy of the C–F bond.
CH2 = CH2(g)
+
HF(g)
CH3CH2F(g)
ΔH o = – 73 kJ mol–1
C–F bond energy = .................................... kJ mol–1 [4]
(b) Another halogenoalkane which was used as a refrigerant, and also as an aerosol
propellant, is dichlorodifluoromethane, CCl2F2.
State two reasons why compounds such as CH3CH2F and CCl2F2 have been used as
aerosol propellants and refrigerants.
..........................................................................................................................................
..................................................................................................................................... [2]
CCl2F2 is one of many chlorofluorocarbon compounds responsible for damage to the ozone
layer in the stratosphere.
(c) By using relevant data from the Data Booklet, and your answer to (a) suggest why CCl2F2
is responsible for damage to the ozone layer in the stratosphere whereas CH3CH2F is
not.
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
Both CH3CH2F and CCl2F2 are greenhouse gases.
The ‘enhanced greenhouse effect’ is of great concern to the international community.
(d) (i)
What is meant by the term enhanced greenhouse effect?
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Water vapour is the most abundant greenhouse gas.
What is the second most abundant greenhouse gas?
........................................
[3]
A greenhouse gas which is present in very small amounts in the atmosphere is sulfur
hexafluoride, SF6, which is used in high voltage electrical switchgear.
(e) What shape is the SF6 molecule?
...................................................
[1]
[Total: 12]
2
Elements and compounds which have small molecules usually exist as gases or liquids.
(a) Chlorine, Cl 2, is a gas at room temperature whereas bromine, Br 2, is a liquid under the
same conditions.
Explain these observations.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(b) The gases nitrogen, N2, and carbon monoxide, CO, are isoelectronic, that is they have
the same number of electrons in their molecules.
Suggest why N2 has a lower boiling point than CO.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(c) A ‘dot-and-cross’ diagram of a CO molecule is shown below. Only electrons from outer
shells are represented.
C
O
In the table below, there are three copies of this structure.
On the structures, draw a circle round a pair of electrons that is associated with each of
the following.
(i) a co-ordinate bond
C
O
(ii) a covalent bond
C
O
(iii) a lone pair
C
O
[3]
(d) Hydrogen cyanide, HCN, is a gas which is also isoelectronic with N2 and with CO.
Each molecule contains a strong triple bond with the following bond energies.
bond
bond energy / kJ mol–1
–C⬅N in HCN
890
N⬅N
994
C⬅O
1078
Although each compound contains the same number of electrons and a strong triple
bond in its molecule, CO and HCN are both very reactive whereas N2 is not.
Suggest a reason for this.
..........................................................................................................................................
.................................................................................................................................... [1]
(e) HCN reacts with ethanal, CH3CHO.
(i)
Give the displayed formula of the organic product formed.
(ii)
What type of reaction is this?
...................................................................
(iii)
Draw the mechanism of this reaction. You should show all full and partial charges
and represent the movement of electron pairs by curly arrows.
[5]
[Total: 13]
3
(a) In the following boxes draw the structural formulae of three alcohols having straight
(i.e. unbranched) chains, with the molecular formula C5H12O.
A
B
C
[2]
Use the letters A, B or C as appropriate when answering the following questions. Each
letter may be used once, more than once or not at all.
(b) Which of the alcohols are chiral? .................................................................................. [1]
(c) (i)
(ii)
Which of these alcohols react with alkaline aqueous iodine? ...................................
Describe the observation you would make during this reaction.
..................................................................................................................................
(iii)
Draw the structural formulae of the products of this reaction.
[4]
(d) Draw the structural formula of the product obtained when each of the alcohols A, B and
C is heated with an excess of acidified K2Cr2O7(aq).
A
B
C
[3]
(e) One of the many suggestions for converting biomass into liquid fuel for motor transport
is the pyrolysis (i.e. heating in the absence of air) of cellulose waste, followed by the
synthesis of alkanes.
(i)
In the first reaction, cellulose, (C6H10O5)n, is converted into a mixture of carbon
monoxide and hydrogen. Some carbon is also produced.
Complete and balance the equation for this reaction.
(C6H10O5)n
(ii)
————————— + ————————— + —————————
The second reaction involves the combination of CO and H2 to produce alkanes
such as heptane.
7CO + 15H2
C7H16 + 7H2O
heptane
Using the value of 1080 kJ mol−1 as the value for the C⬅O bond energy in CO,
and other relevant bond energies from the Data Booklet, calculate the ∆H for this
reaction.
∆H = ......................................... kJ mol−1
[5]
[Total: 15]
4
Monuments made of marble or limestone, such as the Taj Mahal in India and the Mayan
temples in Mexico, are suffering erosion by acid rain. The carbonate stone is converted by
the acid rain into the relatively more soluble sulphate.
CaCO3(s) + H2SO4(aq) → CaSO4(s) + H2O(l) + CO2(g)
acid rain
(a) (i)
Write an expression for the solubility product, Ksp, of CaSO4, stating its units.
...................................................................................................................................
(ii)
The Ksp of CaSO4 has a numerical value of 3 x 10–5. Use your expression in (i) to
calculate [CaSO4] in a saturated solution.
...................................................................................................................................
(iii)
Hence calculate the maximum loss in mass of a small statue if 100 dm3 of acid rain
falls on it. Assume the statue is made of pure calcium carbonate, and that the acid
rain becomes saturated with CaSO4.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
[5]
(b) The life of such monuments is now being extended by treating them with a mixture of
urea and barium hydroxide solutions. After soaking into the pores of the carbonate rock,
the urea gradually decomposes to ammonia and carbon dioxide. The carbon dioxide
then reacts with the barium hydroxide to form barium carbonate.
(NH2)2CO(aq) + H2O(l) ⎯→ 2NH3(g) + CO2(g)
Ba(OH)2(aq) + CO2(g) ⎯→ BaCO3(s) + H2O(l)
Acid rain then converts the barium carbonate to its sulphate.
BaCO3(s) + H2SO4(aq) ⎯→ BaSO4(s) + H2O(l) + CO2(g)
Barium sulphate is much less soluble than calcium sulphate. A saturated solution
contains [Ba2+] = 9.0 x 10–6 mol dm–3.
(i)
Explain why barium sulphate is less soluble than calcium sulphate.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(ii)
Write an expression for the Ksp of barium sulphate and use the data to calculate its
value.
...................................................................................................................................
...................................................................................................................................
[4]
(c) (i)
Explain what is meant by the term lattice energy.
...................................................................................................................................
...................................................................................................................................
(ii)
Predict, with a reason, how the lattice energy of BaSO4 might compare with that of
MgSO4.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
[3]
[Total: 12]
5
Magnesium is used extensively in the form of alloys as a constructional material due to its
low density (1.7 g cm–3, compared to 7.8 g cm–3 for iron). It is usually prepared by the
electrolysis of magnesium chloride, MgCl2, at a temperature a little above its melting point of
715 °C.
(a) Suggest the half-equation that represents the production of magnesium at the cathode
during the electrolysis.
......................................................................................................................................[1]
(b) What will be the product at the other electrode?
......................................................................................................................................[1]
(c) Suggest two properties of its atoms that could explain why magnesium is less dense
than iron.
..........................................................................................................................................
......................................................................................................................................[2]
One of the reasons the melting point of magnesium chloride is quite high is because it has a
fairly high lattice energy.
(d) (i)
Explain the term lattice energy.
...................................................................................................................................
...................................................................................................................................
(ii)
Write a balanced equation including state symbols to represent the lattice energy
of magnesium chloride.
...................................................................................................................................
...............................................................................................................................[4]
(e) Suggest, with an explanation in each case, how the lattice energy of magnesium
chloride might compare with that of
(i)
sodium chloride, NaCl,
...................................................................................................................................
...................................................................................................................................
(ii)
calcium chloride, CaCl2.
...................................................................................................................................
...............................................................................................................................[4]
(f)
Use the following data to calculate a value for the lattice energy of sodium chloride.
∆Hf (NaCl)
∆Hat (Na)
∆Hat (Cl)
first ionisation energy of Na
electron affinity of Cl
=
=
=
=
=
– 411 kJ mol–1
107 kJ mol–1
122 kJ mol–1
494 kJ mol–1
– 349 kJ mol–1
lattice energy of NaCl = ........................................ kJ mol–1 [3]
[Total: 15]
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Born-Haber Cycles
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 1
Time Allowed:
63 minutes
Score:
/52
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) K P =
p (NO) p (H2O )
4
6
(1)
p(NH3 ) p(O 2 )
4
5
atmospheres or Pa or kPa
allow ecf on incorrect powers
(b)
b) (
[1]
(1)
[2]
increasing temperature
yield of NO is decreased or reaction moves to LHS
forward reaction is exothermic
(ii) decreasing the pressure
yield of NO is increased or reaction moves to RHS
more moles/molecules of gas on RHS or
fewer moles/molecules of gas on LHS
(1)
(1)
[1]
[1]
(1)
[1]
(1)
(c) let ∆Hfo for NO be y kJ mol–1
4NH3(g) + 5O2(g)
∆Hfo 4 × (–46.0)
∆Horeaction
4NO(g) + 6H2O(g)
4y
= 4y + [6 × (–242)] – [4 × (–46.0)]
= 4y – 1452 + 184
∆Horeaction is –906 kJmol–1 so
4y = –906 + 1452 – 184 = 362
whence y = ∆Hfo for NO = +90.5 kJ mol–1
+ sign is require
6 × (–242)
(1)
[1]
(1)
[1]
(1)
[1]
(1)
[Total: 10]
2
(a
C(s) + O2(g) → CO2(g)
the enthalpy change/energy change/heat change when
one mole of a compound/CO2
is formed from its elements in their standard states
(b) (i)
∆Hof/kJ mol–1
CO2(g) + 3H2(g)
–39
0
CH3OH(g)
–20
(1)
(1)
(1)
+
[3]
H2O(g)
–24
∆Horeaction = –201 + (–242) – (–394)
–49 kJ mol–1
correct sign
(ii) removal of CO2 from the atmosphere
CO2 is a greenhouse gas/causes global warming
(1)
(1)
(1)
(1)
(1)
[5]
(c) In this part, in each case, the ‘effect’ must be correctly stated
in order to gain the explanation mark.
higher temperature
yield is reduced/equilibrium goes to LHS
because forward reaction is exothermic/reverse reaction is endothermic
(1)
(1)
higher pressure
yield is increased or equilibrium goes to RHS
fewer moles/molecules on RHS or more moles/molecules on LHS
(1)
(1)
use of catalyst
yield does not change
forward and backward rates speeded up by same amount
(1)
(1)
[6]
[Total: 14]
3
(a) CH3OCH3(l) + 3O2(g) → 2CO2(g) + 3H2O(l)
(l)
the enthalpy change/heat change/heat evolved when
one mole of CH3OCH3/a compound
is completely burned or
burned in an excess of air/oxygen
(b)
2CH3OH(l)
→
CH3OCH3(g)
–1
–1
∆Hof /kJ mol–1 2(–239)
∆Horeaction
= –184 + (–286) – 2(–239)
= +8 kJ mol–1
correct sign
(1)
(1)
+
[3]
H2O(l)
(1)
(1)
(1)
1)
(c) (i)
DME
ethanol
both correct
(ii) structural isomerism or functional group isomerism
(d) (i) hydrogen bonds
(ii) lone pair on O atom of C2H5OH
H
correct dipole Oδ–Hδ+ on bond in one molecule of ethanol
(1)
(1)
[2]
(1)
(
(1)
hydrogen bond shown between lone pair of an O atom and a hydrogen atom,
i.
(1)
[4]
[Total: 12]
4
(a
(i) enthalpy/energy change/released when 1 mol of ions…
in the gas phase (are dissolved in) water
[1
[1]
(ii) Mg2+(g) + aq (or H2O) → Mg2+(aq) or [Mg(H2O)6]2+
[1]
(iii) Mg2+ has a smaller radius/size or greater charge density than Ca2+ (ions required)
[1]
(iv) O2– reacts with water to give OH– or equation: O2– + H2O → 2OH–
[1]
[5]
(b) (apparatus: “insulated” calorimeter, water and thermometer)
•
measure (known volume/mass of) water or stated volume of water (into calorimeter)
take the temperature (of the water – NOT the MgCl 2)
•
•
weigh out known mass of MgCl 2 or stated mass of MgCl 2
take final/highest/constant temperature or record temperature change/rise
4 × [1]
•
[4]
(c) (i) ∆Hosol = 641 – 801 = –160 kJ mol–1
(ii) ∆Hohyd = (1890 – 2526 – 160)/2 = –398 kJ mol–1
[1]
[2]
[3]
(d)
•
•
•
•
•
solubility: MgSO4 > BaSO4 or decreases down the group
because ∆Hsol is more endothermic for BaSO4 or more exothermic for MgSO4
due to larger rion or smaller charge density of Ba2+ (ion has to be mentioned)
leading to smaller LE and HE or LE and HE decrease
but difference in HE (between Mg2+ and Ba2+) is larger than the difference in LE
(between MgSO4 and BaSO4)
or HE is dominant or HE decreases more than LE
any 4 points [4]
[4]
[Total: 16]
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Born-Haber Cycles
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 1
Time Allowed:
63 minutes
Score:
/52
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Ammonium nitrate fertiliser is manufactured from ammonia. fiThe
rst reaction in the
manufacture of the fertiliser is the catalytic oxidation of ammonia to form nitrogen monoxide,
NO. This is carried out at about 1 × 103 kPa (10 atmospheres) pressure and a temperature of
700 to 850 °C.
4NH3(g) + 5O2(g)
4NO(g) + 6H2O(g)
∆H
= –906 kJ mol–1
(a) Write the expression for the equilibrium constant, Kp, stating the units.
Kp =
units ..................................
[2]
(b) What will be the effect on the yield of NO of each of the following?
In each case, explain your answer.
(i) increasing the temperature
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) decreasing the applied pressure
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[4]
(c) The standard enthalpy changes of formation of NH3(g) and H2O(g) are as follows.
NH3(g), ∆Hf = –46.0 kJ mol–1
H2O(g), ∆Hf = –242 kJ mol–1
Use these data and the value of
change of formation of NO(g).
Include a sign in your answer.
4NH3(g)
+
5O2(g)
4NO(g)
given below to calculate the standard enthalpy
+
6H2O(g)
∆H
= –906 kJ mol–1
[4]
[Total: 10]
2
Methanol, CH3OH, is considered to be a possible alternative to fossil fuels, particularly for use
in vehicles.
Methanol can be produced from fossil fuels and from agricultural waste. It can also be
synthesised from carbon dioxide and hydrogen.
(a) Define, with the aid of an equation which includes state symbols, the standard enthalpy
change of formation of carbon dioxide.
equation ............................................................................................................................
definition ...........................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
(b) Relevant
values for the reaction that synthesises methanol are given in th
compound
CO2(g)
–394
CH3OH(g)
–201
H2O(g)
–242
(i) Use these values to calculate
fo
Include a sign in your answer.
CO2(g) + 3H2(g)
CH3OH(g) + H2O(g)
= .........................kJ mol–1
(ii) Suggest one possible environmental advantage of this reaction. Explain your
answer.
....................................................................................................................................
....................................................................................................................................
[5]
(c) The synthesis of methanol is carried out at about 500 K with a pressure of between 40 and
100 atmospheres (between 4 × 106 Pa and 10 × 107 Pa) and using a catalyst. The use of
such conditions will affect both the rate of reaction and the equilibrium yield.
In the spaces below, explain the effects of higher temperature, higher pressure, and the
use of a catalyst on the equilibrium yield of methanol.
higher temperature
effect .................................................................................................................................
explanation .......................................................................................................................
...........................................................................................................................................
higher pressure
effect .................................................................................................................................
explanation .......................................................................................................................
...........................................................................................................................................
use of catalyst
effect .................................................................................................................................
explanation .......................................................................................................................
...........................................................................................................................................
[6]
[Total: 14]
3
With the prospect that fossil fuels will become increasingly scarce in the future, many
compounds are being considered for use in internal combustion engines. One of these is
DME or dimethyl ether, CH3OCH3. DME is a gas which can be synthesised from methanol.
Methanol can be obtained from biomass, such as plant waste from agriculture.
(a) Define, with the aid of an equation which includes state symbols, the standard enthalpy
change of combustion,
, for DME at 298 K.
equation ............................................................................................................................
definition ...........................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
(b) DME may be synthesised
s
from methanol. Relevant enthalpy changes of formation,
for this reaction are given in the table below.
compound
CH3OH(l)
–239
CH3OCH3(g)
–184
H2O(l)
–286
Use these values to calculate
for the synthesis of DME, using the following
equation. Include a sign in your answer.
2CH3OH(l) → CH3OCH3(g) + H2O(l)
= ..................... kJ mol–1
[3]
(c) DME and ethanol are isomers with the molecular formula C2H6O.
(i) Draw the displayed formula of DME and of ethanol.
DME
ethanol
(ii) What type of isomerism do DME and ethanol show?
....................................................................................................................................
[2]
(d) DME is a gas at room temperature while ethanol is a liquid.
(i) Which intermolecular force exists between ethanol molecules, which causes ethanol
to be a liquid at room temperature?
.................................................
(ii) Draw a diagram that clearly shows this intermolecular force.
Your diagram should show any lone pairs or dipoles present that you consider to be
important. You should represent at least two molecules in your diagram.
[4]
[Total: 12]
4
(a) (i) What is meant by the term enthalpy change of hydration,
?
....................................................................................................................................
....................................................................................................................................
(ii) Write an equation that represents the
of the Mg2+ ion.
....................................................................................................................................
(iii) Suggest a reason why
of the Mg2+ ion is greater than
of the Ca2+ ion.
....................................................................................................................................
....................................................................................................................................
(iv) Suggest why it is impossible to determine the enthalpy change of hydration of the
oxide ion, O2–.
....................................................................................................................................
....................................................................................................................................
[5]
(b) The enthalpy change of solution for MgCl 2,
following equation.
(MgCl 2(s)), is represented by the
MgCl 2(s) + aq → Mg2+(aq) + 2Cl –(aq)
Describe the simple apparatus you could use, and the measurements you would make,
in order to determine a value for
(MgCl 2(s)) in the laboratory.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
(c) The table below lists data relevant to the formation of MgCl 2(aq).
enthalpy change
value / kJ mol–1
(MgCl 2(s))
–641
(MgCl 2(aq))
–801
lattice energy of MgCl 2(s)
(Mg2+(g))
–2526
–1890
By constructing relevant thermochemical cycles, use the above data to calculate a value for
(i)
(MgCl 2(s)),
= ....................................... kJ mol–1
(ii)
(Cl –(g)).
= ....................................... kJ mol–1
[3]
(d) Describe and explain how the solubility of magnesium sulfate compares to that of barium
sulfate.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
[Total: 16]
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Born-Haber Cycles
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 2
Time Allowed:
60 minutes
Score:
/50
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) heterogeneous: different states AND homogeneous: same state
[1]
(ii) the correct allocation of the terms heterogeneous and homogeneous to common
catalysts
[1]
example of heterogeneous, e.g. Fe (in the Haber process) linked to correct system
equation, e.g. N2 + 3H2 → 2NH3
[1]
[1]
how catalyst works, adsorption (onto the surface)
ecf for non-iron catalyst
[1]
example of homogeneous, e.g. Fe3+ or Fe2+ (in S2O82– + I–) linked to correct system
[1]
equation, e.g. S2O82– + 2I– → 2SO42– + I2
[1]
how catalyst works, e.g. Fe3+ + I– → Fe2+ + ½I2
ecf for non-iron catalyst
[1]
[8]
(b)
[2]
[Total: 10]
2
(a
CaC2 + 2H2O → Ca(OH)2 + C2H2
(b) (i) step 1
electrophilic
addition
elimination or dehydrohalogenation
(1)
(1)
(1)
(ii) reagent
NaOH/KOH/OH–
in alcohol/ethanol
conditions
only allow conditions mark if reagent is correct
(1)
(1)
step 2
(c)
c)
(1)
Q is CH3CHO ( as minimum)
R is CH3CO2H (as minimum)
(ii) step 3 is addition
step 4 is oxidation/redox
[5]
(1)
(1)
(1)
(1)
(d) (i) combustion
C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(l) or
equation must be for the combustion of one mole of C2H2
H2O must be shown as liquid
correct state symbols in this equation
formation
2C(s) + H2(g) → C2H2(g)
no mark for state symbols here
[1]
[4]
(1)
(1)
(1)
(ii) let Z be ∆Hof of C2H2
C2H2 +
o
∆H
f
Z
5
/2O2 → 2CO2 + H2O
0
2(-394) -286
o
∆H c = -1300 = 2(-394) + (-286) – Z
(1)
whence Z = 2(-394) + (-286) – (-1300)
= +226 kJ mol-1
value
sign
allow ecf on wrong equation
(1)
(1)
[6]
[Total: 16]
3
(a) N≡N triple bond is (very) strong
or the N2 molecule has no polarity
(b) 3Mg(s) → 3Mg2+(g)
N2(g) → 2N3–(g)
[1]
∆H1 = 3 × 148 + 3 × 2186 = 7002
∆H2 = 994 + 2 × 2148 = 5290
LE = –∆H1 – ∆H2 – 461 = –12,753 (kJ mol–1)
(c) (i) Li3N + 3H2O → NH3 + 3LiOH (balanced equation)
(–[1] for each error) [3]
[1]
(ii) advantage:
no high pressure/temperature/catalyst needed/standard conditions used
[1]
disadvantage: Li is expensive
or Li would need to be recycled/removed
or LiOH by-product is corrosive/strongly basic
or this would be a batch, rather than continuous process
[1]
(d) (i) Li3N: 100 × 14/35 = 40% N
urea: 100 × 28/60 = 47% N
[1]
[1]
(ii) amide
[1]
(iii) NH2CONH2 + H2O → 2NH3 + CO2
or → NH2CO2H + NH3
or NH2CONH2 + 2H2O → 2NH3 + H2CO3
[1]
(iv) The LiOH would be strongly alkaline
or would increase the pH of the soil
or would ‘burn’ the crops/reduce plant growth/stunt plants
or would contaminate the environment
[1]
[Total: 12]
4
(a
enthalpy change when 1 mol of a compound is formed (1)
from its elements (1)
in their standard states under standard conditions (1)
[3]
N2H4(l) + O2(g) → N2(g) + 2H2O(g)
∆Hfo/kJ mol-1 +50.6
–241.8
o
∆H reaction = 2(–241.8) – (+50.6) (1)
= –534.2 kJ mol-1 (1)
(b)
b)
(ii) Ea is too high (1)
(iii) products are H2O and N2 which are harmless/non toxic
or are already present in the atmosphere (1)
(c)
c) (
[4]
‘dot-and-cross’ diagram (1)
(ii)
(1)
(iii) minimum is
allow bond angle around N atom between 109o and 104o (1)
(d) –2 (1)
[4]
[1]
[Total: 12]
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Born-Haber Cycles
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 2
Time Allowed:
60 minutes
Score:
/50
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Catalysts can be described as homogeneous or heterogeneous.
(i) What is meant by the terms homogeneous and heterogeneous?
....................................................................................................................................
....................................................................................................................................
(ii) By using iron and its compounds as examples, outline the different modes of action
of homogeneous and heterogeneous catalysis.
Choose one example of each type, and for each example you should
●
●
●
state what the catalyst is, and whether it is acting as a homogeneous or a
heterogeneous catalyst,
write a balanced equation for the reaction,
outline how the catalyst you have chosen works to decrease the activation
energy.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[8]
(b) The reaction between SO2, NO2 and O2 occurs in two steps.
NO2 + SO2 → NO + SO3
NO +
1
2 O2
→ NO2
∆H 1o = –88 kJ mol –1
∆H 2o = –57 kJ mol–1
The activation energy of the first reaction, Ea , is higher than that of the second reaction,
1
Ea .
2
Use the axes below to construct a fully-labelled reaction pathway diagram for this
reaction, labelling Ea , Ea , ∆H 1o and ∆H o2.
1
2
NO2 + SO2
energy
extent of reaction
[2]
[Total: 10]
2
The gas ethyne, C2H2, more commonly known as acetylene, is manufactured for use
in the synthesis of organic compounds. It is also used, in combination with oxygen, in
‘oxy-acetylene’ torches for the cutting and welding of metals.
Industrially, ethyne is made from calcium carbide, CaC2, or by cracking liquid hydrocarbons.
(a) When calcium carbide is reacted with water, ethyne and calcium hydroxide are formed.
Construct a balanced equation for this reaction.
...................................................................................................................................... [1]
Ethyne can also be obtained from ethene by using the following sequence of reactions.
step 1
CH2CH2
(b) (i)
step 2
ClCH2CH2Cl
HC⬅CH
What types of reaction are step 1 and step 2?
step 1 ............................................................
step 2 ............................................................
(ii)
Suggest what reagent and conditions would be used in a laboratory in step 2.
reagent ..........................................................
conditions ......................................................
[5]
When ethyne is passed into water at 60 °C, in the presence of a little H2SO4 and Hg2+ ions, a
pungent, colourless organic liquid, Q, with Mr of 44 is obtained. This is step 3.
When Q is warmed with Tollens’ reagent in a test-tube, a silver mirror is formed.
On acidification, the solution remaining in the test-tube is found to contain the organic
compound R which has Mr of 60. This is step 4.
(c) (i)
Give the structural formulae of Q and R.
step 4
step 3
HC⬅CH
Q
(ii)
R
What type of reaction is step 3 and step 4?
step 3 ............................................................
step 4 ............................................................
[4]
(d) The standard enthalpy change of combustion of C2H2, ΔH –oc–, is –1300 kJ mol–1 at 298 K.
Values of relevant standard enthalpy changes of formation, ΔH –of–, measured at 298 K,
are given in the table.
(i)
substance
ΔH –of– / kJ mol–1
CO2(g)
–394
H2O(l)
–286
Write balanced equations, with state symbols, that represent
the standard enthalpy change of combustion, ΔH –oc–, of C2H2, and
..................................................................................................................................
the standard enthalpy change of formation, ΔH –of–, of C2H2.
..................................................................................................................................
(ii)
Use the data above and your answer to (i) to calculate the standard enthalpy
change of formation, ΔH –of–, of C2H2.
Show clearly whether the standard enthalpy change of formation of C2H2 has a
positive or negative value.
[6]
[Total: 16]
3
Taken together, nitrogen and oxygen make up 99% of the air. Oxygen is by far the more
reactive of the two gases, and most of the substances that react with air combine with the
oxygen rather than with the nitrogen.
(a) State one reason why the molecule of nitrogen, N2, is so unreactive.
...................................................................................................................................... [1]
Despite the apparent lack of reactivity of N2, nitrogen atoms have been found to form bonds
with almost all of the elements in the Periodic Table. Lithium metal reacts with nitrogen gas
at room temperature to give lithium nitride, Li3N. Magnesium produces magnesium nitride,
Mg3N2, as well as magnesium oxide, when heated in air.
(b) Calculate the lattice energy of magnesium nitride using the following data, in addition to
relevant data from the Data Booklet.
value/kJ mol–1
enthalpy change
atomisation of Mg(s)
+148
total of electron affinities for
the change N(g)
N3–(g)
+2148
enthalpy of formation of
Mg3N2(s)
–461
lattice energy = ...........................kJ mol–1 [3]
(c) Lithium reacts readily with nitrogen, and because of this Li3N has been considered as a
possible intermediate in the ‘fixing’ of nitrogen to make ammonia-based fertilisers.
+L
N2(g)
(i)
+
Li3N
2O
NH3 + A
Construct an equation for the reaction between Li3N and H2O, and hence identify
compound A.
..................................................................................................................................
(ii)
Using your knowledge of the Haber process, consider one advantage and one
disadvantage of using lithium as a means of fixing nitrogen, rather than the Haber
process.
advantage of the lithium method
..................................................................................................................................
disadvantage of the lithium method
..................................................................................................................................
[3]
(d) Another possible advantage of Li3N is that it contains a large percentage by mass of
nitrogen. Another fertiliser that contains a large percentage by mass of nitrogen is urea,
NH2CONH2.
(i)
Calculate and compare the percentages by mass of nitrogen in Li3N and
NH2CONH2.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
What class of organic compound is urea?
..................................................................................................................................
(iii)
Write an equation for the production of ammonia by the reaction between urea and
water.
..................................................................................................................................
(iv)
Urea can be applied directly to the soil either before or during the growing of
crops.
What would be a major disadvantage of using lithium nitride in this way?
..................................................................................................................................
..................................................................................................................................
[5]
[Total: 12]
4
Hydrazine, N2H4, can be used as a rocket fuel and is stored as a liquid. It reacts exothermically
with oxygen to give only gaseous products.
The enthalpy change of a reaction such as that between hydrazine and oxygen may be
calculated by using standard enthalpy changes of formation.
(a) Define the term standard enthalpy change of formation, ΔHf .
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [3]
(b) Hydrazine reacts with oxygen according to the following equation.
N2H4(l) + O2(g)
(i)
N2(g) + 2H2O(g)
Use the data in the table to calculate the standard enthalpy change of this
reaction.
compound
ΔHf /kJ mol–1
N2H4(l)
50.6
H2O(g)
–241.8
ΔH = ........................................ kJ mol–1
(ii)
Although the above reaction is highly exothermic, hydrazine does not burn
spontaneously in oxygen.
Suggest a reason for this.
..................................................................................................................................
..................................................................................................................................
(iii)
Suggest why using hydrazine as a rocket fuel could be regarded as being
‘environmentally friendly’.
..................................................................................................................................
..................................................................................................................................
[4]
(c) The bonding in hydrazine is similar to that in ammonia.
(i)
Showing outer-shell electrons only, draw a ‘dot-and-cross’ diagram of an ammonia
molecule.
(ii)
Draw a diagram to show the three-dimensional shape of an ammonia molecule.
(iii)
Draw a diagram to show the shape of a hydrazine molecule.
Show clearly which atom is joined to which and show clearly the value of one bond
angle.
[4]
(d) Deduce the oxidation state of nitrogen in hydrazine.
..........................................
[1]
[Total: 12]
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Born-Haber Cycles
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 3
Time Allowed:
56 minutes
Score:
/46
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) Mg+(g) → Mg2+(g) + e–
(ii) 736 + 1450 = +2186 kJ mol–1
(b) (i) dissolves
iss
6–7
(c)
eqn.
eqn.
state symbols
(1)
(1)
1)
(1)
(ii) does not dissolve/slightly soluble
8 – 11
(1)
(1)
(i) Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3
(1)
(ii) Mg3N2 N is –3
NH3 N is –3
(1)
(1)
No because
there is no change in the oxidation no. of N
e.c.f on (c)(i) and values of oxidation numbers
(1)
[4]
[4]
[Total: 11]
2
(i) H–C–H 117 to 120o (1)
o
C=C=O
(1)
(a
(ii) molecule contains both ketone and alkene (1)
(b)
b) (
[3]
C2H2O + 2O2 → 2CO2 + H2O (1)
42 g C2H2O → 48 dm3 of CO2 (1)
48 × 3.5
whence 3.5 g C2H2O →
dm3 of CO2 (1)
42
= 4.0 dm3 of CO2 (1)
42
= 0.0833 (1)
n(C2H2O) =
3.5
n(CO2) = 2 × 0.083 = 0.0166 (1)
vol. of CO2 = 0.0166 × 24 = 4.0 dm3 (1)
allow e.c.f. on wrong eqn. in (b)(i)
penalise significant figure error
(ii) from eqn.,
or
(c)
c) (
[4]
enthalpy change when
1 mol of a compound is formed (1)
from its elements (1)
in their standard states under standard conditions (1)
(ii) C + O2 → CO2
–395 kJ mol–1
H2 + ½O2 → H2O
–286 kJ mol–1
–1028 kJ mol–1
C2H2O + 2O2 → 2CO2 + H2O
2C + H2 + ½O2 → C2H2O ∆H = 2(–395) + (–286) –(–1028)
= –48 kJ mol–1
correct cycle (1) use of 2 for C/CO2 (1) answer (1)
(d) H2O/water/steam (1)
[6]
[1]
[Total: 14]
3 (a)
(b)
molecules
(1)
I2
(1)
(i)
(ii)
(c)
c)
(ii)
cations held in ‘sea’ of delocalised electrons
(1)
by strong metallic bonds
(1)
van der Waals’ forces between molecules
(1)
van der Waals’ forces are weak
(1)
oxidising agent
(1)
iodine is a weaker oxidising agent than chlorine
(1)
[2]
[4]
[2]
[Total: 8]
4
(a)
(b)
(c)
(d)
sulphur atom has 6 /carbon atom has 4 electrons
(1)
S=C double bonds (4 electrons) clearly shown
(1)
linear
(1)
180o
(1)
the enthalpy change when 1 mol of a compound
(1)
is formed from its elements in their standard states
(1)
under standard conditions (may be quoted)
(1)
[3]
(1)
[3]
C + O2 → CO2
-395
S + O2 → SO2
-298
CS2 + 3O2 → CO2 + 2SO2
-1110
C + 2S → CS2
[2]
[2]
∆H = -395 + 2(-298) -(-1110)
= +119 kJ mol-1
cycle (1)
(e)
use of 2 for S/SO2 (1)
answer
CO2
(1)
N2
(1)
CS2 + 2NO → CO2 + 2S + N2
(1)
completely correct equation gets (3)
consequential errors to be decided at co-ordination
[3]
[Total: 13]
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Born-Haber Cycles
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 3
Time Allowed:
56 minutes
Score:
/46
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Magnesium will react on heating with chlorine, or oxygen, or nitrogen to give the chloride, or
oxide, or nitride respectively. Each of these compounds is ionic and in them magnesium has
the same +2 oxidation state.
(a) (i)
Write an equation, with state symbols, for the second ionisation energy of
magnesium.
..................................................................................................................................
(ii)
Use the Data Booklet to calculate the enthalpy change that occurs when one mole
of gaseous magnesium ions, Mg2+, is formed from one mole of gaseous magnesium
atoms.
Include a sign in your answer.
enthalpy change = ……………… kJ mol–1
[3]
(b) Separate samples of magnesium chloride and magnesium oxide are shaken with water.
In each case, describe what you would see when this is done, and state the approximate
pH of the water after the solid has been shaken with it.
(i)
magnesium chloride
observation ...............................................................................................................
approximate pH of the water …………………
(ii)
magnesium oxide
observation ...............................................................................................................
approximate pH of the water …………………
[4]
(c) Magnesium burns in nitrogen to give magnesium nitride, a yellow solid which has the
formula Mg3N2.
Magnesium nitride reacts with water to give ammonia and magnesium hydroxide.
(i)
Construct an equation for the reaction of magnesium nitride with water.
..................................................................................................................................
(ii)
Does a redox reaction occur when magnesium nitride reacts with water?
Use the oxidation numbers of nitrogen to explain your answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[4]
[Total: 11]
2
Ketene, C2H2O, is a member of a class of unsaturated organic compounds that is widely
used in pharmaceutical research for the synthesis of organic compounds.
CH2=C=O
ketene
(a) (i)
Suggest values for the H-C-H and C=C=O bond angles in ketene.
H-C-H ……………………………………
(ii)
C=C=O ……………………………………
By considering the structure of the molecule, suggest why the name ketene is
used.
..................................................................................................................................
............................................................................................................................. [3]
(b) Ketene burns completely in air to form carbon dioxide and water.
(i)
Write a balanced equation for this reaction.
..................................................................................................................................
(ii)
Use your equation to calculate the volume of CO2, in dm3, measured at room
temperature and pressure, which will be formed when 3.5 g of ketene are burned in
an excess of air.
Give your answer to two significant figures.
volume of CO2 = ................................. dm3 [4]
(c) (i)
Define the term standard enthalpy change of formation.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Use the data below to calculate the standard enthalpy change of formation of
ketene.
∆H o / kJ mol–1
standard enthalpy change of
formation of CO2
–395
standard enthalpy change of
combustion of H2
–286
standard enthalpy change of
combustion of CH2=C=O
–1028
[6]
(d) Ketene can be converted directly into ethanoic acid, CH3CO2H, by reaction with a
compound A.
Suggest the identity of A.
.................………………................
[1]
[Total: 14]
3
Copper and iodine are both solids which have different physical and chemical properties.
Each element has the same face-centred crystal structure which is shown below.
The particles present in such a crystal may be atoms, molecules, anions or cations. In the
diagram above, the particles present are represented by
.
(a) Which type of particles are present in the iodine crystal? Give their formula.
particle ....................................
formula ....................................
[2]
(b) When separate samples of copper or iodine are heated to 50 °C, the copper remains as
a solid while the iodine turns into a vapour.
(i)
Explain, in terms of the forces present in the solid structure, why copper remains a
solid at 50 °C.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Explain, in terms of the forces present in the solid structure, why iodine turns into a
vapour when heated to 50°C.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[4]
(c) (i)
Although copper is a relatively unreactive metal, when it is heated to a high
temperature in an excess of chlorine, copper(II) chloride is formed.
How does chlorine behave in this reaction?
..................................................................................................................................
(ii)
When a mixture of copper and iodine is heated to a high temperature, no reaction
occurs.
Suggest a reason for this difference.
..................................................................................................................................
..................................................................................................................................
[2]
[Total: 8]
4
Carbon disulphide, CS2, is a volatile, stinking liquid which is used to manufacture viscose
rayon and cellophane.
(a) The carbon atom is in the centre of the CS2 molecule.
Draw a ‘dot-and-cross’ diagram of the carbon disulphide molecule.
Show outer electrons only.
[2]
(b) Suggest the shape of the molecule and give its bond angle.
shape .........................................................
bond angle .................................................
[2]
(c) Explain the term standard enthalpy change of formation, H f .
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [3]
(d) Calculate the standard enthalpy change of formation of CS2 from the following data.
standard enthalpy change of formation of SO2
= –298 kJ mol–1
standard enthalpy change of formation of CO2
= –395 kJ mol–1
standard enthalpy change of combustion of CS2 = –1110 kJ mol–1
[3]
(e) Carbon disulphide reacts with nitrogen monoxide, NO, to form a yellow solid and two
colourless gases which are produced in a 1:1 molar ratio.
Deduce the identity of each gas and write a balanced equation for the reaction.
gases ........................................................ and ...............................................................
equation ..................................................................................................................... [3]
[Total: 13]
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Born-Haber Cycles
Mark Scheme 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 4
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i)
S
C
S
S atom has 6 and C atom has 4 electrons
(1)
S=C double bonds (4 electrons) clearly shown
(1)
(ii) linear and 180°
(b)
b) (
(1)
1)
CS2 + 3O2 → CO2 + 2SO2
(1)
(ii) enthalpy change when 1 mol of a substance
(1)
is burnt in an excess of oxygen/air
or is completely combusted
under standard conditions
(1)
[3]
(c)
CS2 + 3O2 →
CO2
+
∆Hf⦵/kJ mol–1 x
–395
∆Hreaction = –395 + 2(–298) – x = –1110 kJ mol–1
gives x = –395 + (–596) + 1110 = +119 kJ mol–1
(d)
d) (
2SO2
2(–298)
(1)
(1)
(1) [3]
CS2 + 2NO → CO2 + 2S + N2
or
CS2 + 2NO → CO + 2S + N2O
correct products (1)
correct equation (1)
(ii) from –2 to 0
both required (1)
[3]
[Total: 12]
2
(a
(i) RBr + OH– → ROH+ Br–
[1]
(ii) nucleophilic substitution
[1]
[2]
(b)
b)
plotting of all points (plotted to within ½ small square) [1]
good line of best fit [1]
(ii) t ½ = 118 min or 79 min (± 5 min)
or
construction lines for two half-lives and mention that half-life is constant
or
calculate the ratio of two rates at two different concentrations
[1]
(iii) either ratio of initial rates (slopes)
or
ratio of t ½
or
ratio of times for [RBr] to fall to the same level: all should be = 1.5
[1]
therefore reaction is first order w.r.t. [OH–]
(iv) rate = k [RBr] [OH–]
[1]
[1
initial rate = 0.01 / 185 = 5.4 × 10–5 (mol dm–3 min–1)
[1
k = 5.4 x 10-5 / (0.01 × 0.1) = 0.054 (mol–1 dm3 min–1)
[1
[8 max 7]
energy/kJ moli1
(c)
+5.4
(2NO + Br2)
-23
2NOBr
extent of reaction
four marking points: one activation "hump"
2NOBr (not just NOBr)
∆H labelled correctly (arrow down, or double headed, or just a line)
Ea labelled correctly (arrow up, or double headed, or just a line)
all four points [2]
three or two points [1]
[2]
[Total: 11]
3
(a
(i) alkanes or paraffins not hydrocarbons
(ii)
i
(b)
b) (
C9H20 + 14O2 → 9CO2 + 10H2O
carbon
carbon monoxide
(names required)
(ii) CO is toxic or affects or combines with haemoglobin
or carbon causes respiratory problems
(iii)
i
(1)
(1
[2]
(1)
(1)
(1)
C14H30 + 15O2 → 28C + 30H2O or
2C14H30 + 29O2 → 28CO + 30H2O
or other balanced equations such as
C14H30 + 11O2 → 7C + 7CO + 15H20
C14H30 + 18O2 → 7CO + 7CO2 + 15H20
(c) enthalpy change when 1 mol of a substance
is burnt in an excess of oxygen/air under standard conditions
or is completely combusted under standard conditions
(1
[4]
(1)
(1)
[2]
(d) working must be shown
(i) heat released = m c δT = 250 × 4.18 × 34.6
= 36157 J = 36.2 kJ
(1)
(1)
(ii) Mr of C14H30 = 198
mass of C14H30 = 1.00 × 0.763 = 0.763 g
0.763 g of C14H30 produce 36.2 kJ
36.2 ×198
198 g of C14H30 produce
0.763
= 9394 kJ mol–1
(1)
(1)
(1)
[5]
[Total: 13]
4
(a
(the energy change) when 1 mol of bonds
is broken in the gas phase
[1]
[1]
[2]
(b) (i) (C-X bond energy) decreases/becomes weaker (from F to I)
[1
due to bond becoming longer/not such efficient orbital overlap
[1]
(ii) (as the bond energy of C-X decreases) the halogenalkanes become more reactive
(answer must imply that it is from F to I)
[1
[3]
(c) The C-Cl bond is weaker than the C-F and C-H bonds
or C-Cl bond (E = 340) and C-H (E = 410)
[1]
so is (easily) broken to form Cl •/Cl radicals/Cl atoms
tom
causing the breakdown of O3 into O2
[1]
[3]
(d) Cl-CH2CH2-CO2H
HO-CH2CH2CH2-Cl
[1]
[1]
OH
Br
[1]
[3]
light/UV/hν or 300°C
[1
(ii) (free) radical substitution
[1]
(iii) ∆H = E(C-H) – E(H-Cl) = 410 – 431 = –21 kJ mol-1
[1]
(e)
e) (
(iv) ∆H = E(C-H) – E(H-I) = 410 – 299 = +111 kJ mol-1
ecf
[1]
(v) The reaction with iodine is endothermic or ∆H is positive or requires energy
[1]
(vi) Cl2 → 2Cl •
CH3CH2• + Cl2 → CH3CH2Cl + Cl •
CH3CH2• + Cl • → CH3CH2Cl
[1]
[1]
[1]
[8]
[Total: 19]
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Born-Haber Cycles
Question Paper 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 4
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Carbon disulfide,CS 2, is a volatile, flammableliquidwhichisproducedinsmall
quantities in volcanoes.
(a) The sequence of atoms in the CS2 molecule is sulfur to carbon to sulfur.
(i) Draw a ‘dot-and-cross’ diagram of the carbon disulfide molecule.
Show outer electrons only.
(ii) Suggest the shape of the molecule and state the bond angle.
shape .........................................................................................................................
bond angle .................................................................................................................
[3]
(b) Carbon disulfide is readily combusted to give CO2 and SO2.
(i) Construct a balanced equation for the complete combustion of CS2.
....................................................................................................................................
(ii) Define the term standard enthalpy change of combustion,
.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[3]
(c) Calculate the standard enthalpy change of formation of CS2 from the following data.
Include a sign in your answer.
standard enthalpy change of combustion of CS2 = –1110 kJ mol–1
standard enthalpy change of formation of CO2
= –395 kJ mol–1
standard enthalpy change of formation of SO2
= –298 kJ mol–1
[3]
(d) Carbon disulfide reacts with nitrogen monoxide, NO, in a 1:2 molar ratio.
A yellow solid and two colourless gases are produced.
(i) Construct a balanced equation for the reaction.
....................................................................................................................................
(ii) What is the change in the oxidation number of sulfur in this reaction?
from ..................................................... to .....................................................
[3]
[Total: 12]
2
A bromoalkane, R–Br, is hydrolysed by aqueous sodium hydroxide.
(a) (i) Write a balanced equation for this reaction.
....................................................................................................................................
(ii) What type of reaction is this?
....................................................................................................................................
[2]
(b) The concentration of bromoalkane was determined at regular time intervals as the
reaction progressed.
Two separate experiments were carried out, with different NaOH concentrations.
The graph below shows the results of an experiment using [NaOH] = 0.10 mol dm–3.
0.010
0.009
0.008
0.007
0.006
[R–Br]
0.005
/ mol dm–3
0.004
0.003
0.002
0.001
0
0
50
100
150
200
250
time / min
When the experiment was repeated using [NaOH] = 0.15 mol dm–3, the following results
were obtained.
time / min
[R–Br] / mol dm–3
0
40
80
120
160
200
240
0.0100
0.0070
0.0049
0.0034
0.0024
0.0017
0.0012
(i) Plot these data on the axes above, and draw a line of best fit.
(ii) Use one of the graphs to confirm that the reaction is first order with respect to R–Br.
Show all your working, and show clearly any construction lines you draw.
(iii) Use the graphs to calculate the order of reaction with respect to NaOH. Show all
your working, and show clearly any construction lines you draw on the graphs.
(iv) Write the rate equation for this reaction, and calculate the value of the rate constant.
rate =
[7]
(c) Nitric oxide, NO, and bromine vapour react together according to the following equation.
2NO(g) + Br2(g) → 2NOBr(g)
∆H = –23 kJ mol–1
The reaction has an activation energy of +5.4 kJ mol–1.
Use the following axes to sketch a fully-labelled reaction pathway diagram for this
reaction.
Include all numerical data on your diagram.
2NO + Br2
energy
/ kJ mol–1
extent of the reaction
[2]
[Total: 11]
3
Petrol and diesel fuel are both used in internal combustion engines.
Petrol may be regarded as having the formula C9H20 and diesel fuel as having the formula
C14H30.
(a) (i) To which class of compounds do these two hydrocarbons belong?
......................................................
(ii) Write a balanced equation for the complete combustion of petrol.
....................................................................................................................................
[2]
(b) When petrol or diesel fuel are used in internal combustion engines, several different
products of the incomplete combustion of the fuel may be formed.
(i) Name two of these products that do not contain hydrogen.
.................................. and ..................................
(ii) Choose one of these and state a hazard it causes.
product .......................................................................................................................
hazard ........................................................................................................................
(iii) Write a balanced equation for the formation of one of the products in (i) from diesel
fuel.
....................................................................................................................................
[4]
(c) Define the term standard enthalpy change of combustion.
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [2]
(d) A 1.00 cm3 sample of C14H30 was completely burnt in air.
The heat produced raised the temperature of 250 g of water by 34.6 °C.
Assume no heat losses occurred during this experiment.
The density of C14H30 is 0.763 g cm–3.
(i) Use relevant data from the Data Booklet to calculate the amount of heat released in
this experiment.
(ii) Use the data above and your answer to (i) to calculate the energy produced by the
combustion of 1 mol of C14H30.
[5]
[Total: 13]
4
(a) Explain what is meant by the term bond energy.
...........................................................................................................................................
...........................................................................................................................................
[2]
(b)
b)
Describe and explain the trend in bond energies of the C–X bond in halogenoalkanes,
where X = F, Cl, Br or I.
....................................................................................................................................
....................................................................................................................................
(ii) Describe the relationship between the reactivity of halogenoalkanes, RX, and the
bond energies of the C–X bond.
....................................................................................................................................
....................................................................................................................................
[3]
(c) Use the Data Booklet to suggest an explanation as to why CFCs such as CF2Cl 2 are
much more harmful to the ozone layer than fluorocarbons such as CF4 or hydrocarbons
such as butane, C4H10.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[3]
(d) Predict the products of the following reactions and draw their structures in the boxes
below. The molecular formula of each product is given, where X = Cl , Br or I.
H 2O
+
Cl
Cl
C3H5O2X
O
H2O
+
I
Cl
C3H7OX
Br
H2O
+
Br
C7H7OX
[3]
(e) Ethane reacts with chlorine according to the following equation.
C2H6 + Cl 2 → C2H5Cl + HCl
(i) State the conditions needed for this reaction.
....................................................................................................................................
(ii) State the type of reaction occurring here.
....................................................................................................................................
One of the steps during this reaction is the following process.
Cl ● + CH3CH3 → HCl + CH3CH2●
(iii) Use the Data Booklet to calculate the enthalpy change, ∆H, of this step.
∆H = ................................ kJ mol–1
(iv) Use the Data Booklet to calculate the enthalpy change, ∆H, of the similar reaction:
I● + CH3CH3 → HI + CH3CH2●
∆H = ................................ kJ mol–1
(v) Hence suggest why it is not possible to make iodoethane by reacting together iodine
and ethane.
....................................................................................................................................
(vi) Complete the following equations of some possible steps in the formation of
chloroethane.
Cl 2 → ..............
Cl ● + CH3CH3 → HCl + CH3CH2●
CH3CH2● + .............. → ........................ + ..............
.............. + .............. → CH3CH2Cl
[8]
[Total: 19]
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Born-Haber Cycles
Mark Scheme 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 5
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) CH3Br(g) → CH3(g) + Br(g)
(ii)
[1]
1
/3 AlCl3(g) → 1/3Al(g) + Cl(g)
or AlCl3(g) → AlCl2(g) + Cl(g)
(AlCl3(g) → Al(g) + 3Cl(g) for (1) mark)
[2]
[3]
(b)
b)
bond energies decrease from Cl2 to I2
due to increasing bond length or increase in number of electron shells
which causes less effective orbital overlap or less attraction for the shared pair
[1]
[1]
[1]
(ii) either because fluorine is electronegative, (hence each F wants to keep its electrons
to itself)
or because the bond length is so short there is repulsion between the lone pairs (on
F)
or repulsion between the nuclei (of F)
[1]
[4 max 3]
(c)
c)
for chlorine:
∆H = E(H – H) + E(Cl – Cl) – 2E(H – Cl) =
=
for iodine:
=
∆H = E(H – H) + E(I – I) – 2E(H – I)
=
436 + 242 – (2 × 431)
–184 kJ mol–1
[2]
436 + 151 – (2 × 299)
–11 kJ mol–1
[1]
(ii) Hydrides become less thermally stable down the group from Cl to I
as the H–X bond energy decreases (more than does the X–X bond energy)
[1]
[1]
[5]
(d)
d)
Na
15.2 / 23
⇒ 0.661
÷ 0.661⇒ 1.0
O
31.8 / 16
1.99
3.0
Br
53.0 / 79.9
0.663
1.0
[1]
thus NaBrO3
(ii) 3Br2 + 6NaOH →NaBrO3 + 5NaBr + 3H2O
or 3Br2 + 6OH– →BrO3– + 5Br– + 3H2O
[1]
specie [1]
balancing [1]
[4]
[Total: 15]
2
(a) CH3OH(l) + 3/2O2(g) → CO2(g) + 2H2O(l)
(l)
the enthalpy change/heat change/heat evolved when
one mole of CH3OH
is completely burned or
is burned in an excess of air/oxygen
(1)
(1)
[3]
(b) ∆Horeaction = –283 + 2(–286) – (–726)
= –129 kJ mol–1
correct sign
(1)
(1)
(1)
[3]
(c) pressure
increases rate
by increasing frequency of collisions or
by increasing concentration of reactants
(1)
(1)
temperature
increases rate
because more molecules have energy >Ea
(1)
(1)
catalyst
increases rate
by providing an alternative route of lower Ea
(1)
(1)
[6]
[Total: 12]
3
(a
(i)
C
O
or
C
O
[1]
(ii) incomplete combustion (of hydrocarbon fuels) or insufficient O2/air
air
(iii) NO + CO → ½N2 + CO2
or CO + ½O2 → CO2
equation needs to be balanced
[1]
[3]
(b) ∆H = 394 – 2 × 111 = (+)172 kJ mol–1
[2]
[2]
(c) (i) ligand exchange/displacement/replacement/substitution
[1]
(ii)
•
•
•
•
•
d-orbitals are split (by the ligand field) or orbitals near ligands are at higher energy
the splitting/energy gap depends on the ligands (surrounding the ion) or the metal
(ion)
when an electron moves from lower to higher orbital/energy level or is promoted/
excited
light/a photon is absorbed or colour seen/reflected/transmitted is complement of
colour absorbed (“emitted” contradicts this mark)
different energy gap means different frequency absorbed means different colour
5 × [1]
(iii) from rows 1 and 3: rate3/rate1 = 2.0 which also equals [[complex]3]/[[complex]1]
[1]
(or this working mark can be awarded for any valid calculation that shows that order
w.r.t. complex is
w.
Thus order w.r.t. [complex] = 1 and order w.r.t. [CO] is zero
[1]
rate equation: rate = k[complex]
[1]
(iv) mechanism 2
[1]
it’s the only one that does not involve CO in the rate determining step or rate depends
on [complex] only.
[1]
[11 max 10]
[Total: 15]
4
(a
the overall enthalpy change/energy change/∆H for a reaction
(1)
is independent of the route taken or
is independent of the number of steps involved
provided the initial and final conditions are the same
(1)
(b) (i) K2CO3 + 2HCl → 2KCl + H2O + CO2
(ii) heat produced = m × c × δT = 30.0 × 4.18 × 5.2
= 652.08 J per 0.0200 mol of K2CO3
[2]
(1)
(1)
(iii) 0.020 mol K2CO3 ≡ 652.08 J
1 mol K2CO3 ≡ 652.08 × 1 = 32604 J
0.0200
enthalpy change = –32.60 kJmol–1
(iv) to prevent the formation of KHCO3 or
to ensure complete neutralisation
(c) (i) KHCO3 + HCl → KCl + H2O + CO2
(ii) heat absorbed = m × c × δT = 30.0 × 4.18 × 3.7
= 463.98 J per 0.0200 mol of KHCO3
(1)
(1)
[4]
(1)
(1)
(iii) 0.020 mol KHCO3 ≡ 463.98 J
1 mol KHCO3 ≡ 463.98 × 1 = 23199 J
0.0200
enthalpy change = +23.20 kJmol–1
(1)
1)
(d) ∆H = 2 × (+23.20) – (–32.60) = +79.00 kJ mol–1
(2)
2)
[Total: 11]
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Born-Haber Cycles
Question Paper 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 5
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1 (a)
Write equations, with state symbols, to definethefollowing.
(i) the C–Br bond energy in CH3Br
....................................................................................................................................
(ii) the Al –Cl bond energy in Al Cl 3
....................................................................................................................................
[3]
(b)
b)
Describe and explain the trend in bond energies of the bonds in Cl 2, Br2 and I2.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(ii) Fluorine, F2, does not follow this trend.
Suggest a possible reason why.
....................................................................................................................................
....................................................................................................................................
[3]
(c)
c)
Use data from the Data Booklet to calculate the enthalpy change of the following
reaction.
H2(g) + X2(g) → 2HX(g)
when X = Cl
∆H = ........................ kJ mol–1
when X = I
∆H = ........................ kJ mol–1
(ii) Use these results to describe and explain the trend in the thermal stabilities of the
hydrides of Group VII.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[5]
(d) Bromine reacts with hot NaOH(aq) to give a solution which on cooling produces white
crystals of compound A.
A has the following percentage composition by mass: Na, 15.2; O, 31.8; Br, 53.0.
The remaining solution contains mostly NaBr, with a little of compound A.
(i) Calculate the empirical formula of A.
(ii) Construct an equation for the reaction between Br2 and hot NaOH(aq).
....................................................................................................................................
[4]
[Total: 15]
2
Alcohols such as methanol, CH3OH, are considered to be possible replacements for fossil
fuels because they can be used in car engines.
(a) Define, with the aid of an equation which includes state symbols, the standard enthalpy
change of combustion,
, for methanol at 298 K.
equation ............................................................................................................................
definition ...........................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [3]
Methanol may be synthesised from carbon monoxide and hydrogen. Relevant
for this reaction are given in the table below.
values
compound
CO(g)
–283
H2(g)
–286
CH3OH(g)
–726
(b) Use these values to calculate
for the synthesis of methanol, using the following
equation. Include a sign in your answer.
CO(g) + 2H2(g) → CH3OH(g)
= ................kJ mol–1
[3]
(c) The operating conditions for this reaction are as follows.
pressure
200 atmospheres (2 × 107 Pa)
temperature
600 K
catalyst
oxides of Cr, Cu, and Zn
In the spaces below, explain how each of these conditions affects the rate of formation
of methanol.
pressure
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
temperature
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
catalyst
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[6]
[Total: 12]
3
Carbon monoxide, CO, occurs in the exhaust gases of internal combustion engines.
(a)
a)
Suggest a dot-and-cross diagram for CO.
(ii) Suggest one reason why CO is produced in addition to CO2 in some internal
combustion engines.
....................................................................................................................................
....................................................................................................................................
(iii) Carbon monoxide can be removed from the exhaust gases by a catalytic converter.
Write an equation for a reaction that occurs in a catalytic converter that removes CO.
....................................................................................................................................
[3]
(b) The standard enthalpy change of formation,
, of CO is –111 kJ mol–1, and that of CO2 is
–1
–394 kJ mol .
Calculate the standard enthalpy change of the following reaction.
C(s) + CO2(g) → 2CO(g)
∆H o = ....................................... kJ mol–1
[2]
(c) Carbon monoxide reacts with a ruthenium(II) chloride complex according to the equation
[Ru(H2O)2Cl 4]2– + CO → [Ru(H2O)(CO)Cl 4]2– + H2O.
(i) Describe the type of reaction that is occurring here.
....................................................................................................................................
(ii) During the reaction, the colour of the solution changes from deep blue to green.
Explain the origin of colour in transition element complexes, and why different
complexes often have different colours.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
The following table shows how the initial rate of this reaction varies with different
concentrations of reactants.
[[Ru(H2O)2Cl 4]2–] / mol dm–3
[CO] / mol dm–3
rate / mol dm–3 s–1
1.1 × 10–2
1.7 × 10–3
1.6 × 10–7
1.6 × 10–2
3.6 × 10–3
2.3 × 10–7
2.2 × 10–2
2.7 × 10–3
3.2 × 10–7
(iii) Use these data to determine the order of reaction with respect to each reagent, and
write the rate equation for the reaction.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
There are three possible mechanisms for this reaction, which are described below.
mechanism 1
[Ru(H2O)2Cl 4]2– + CO
mechanism 2
[Ru(H2O)2Cl 4]2–
slow
[Ru(H2O)Cl 4]2– + CO
mechanism 3
[Ru(H2O)2Cl 4]2– + CO
[Ru(H2O)2(CO)Cl 4]2–
slow
[Ru(H2O)(CO)Cl 4]2– + H2O
[Ru(H2O)Cl 4]2– + H2O
fast
slow
fast
[Ru(H2O)(CO)Cl 4]2–
[Ru(H2O)2(CO)Cl 4]2–
[Ru(H2O)(CO)Cl 4]2– + H2O
(iv) Deduce which of these three mechanisms is consistent with the rate equation you
suggested in part (iii). Explain your answer.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
[10]
[Total: 15]
4
For some chemical reactions, such as the thermal decomposition of potassium
hydrogencarbonate, KHCO3, the enthalpy change of reaction cannot be measured directly.
In such cases, the use of Hess’ Law enables the enthalpy change of reaction to be calculated
from the enthalpy changes of other reactions.
(a) State Hess’ Law.
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
In order to determine the enthalpy change for the thermal decomposition of potassium
hydrogencarbonate, two separate experiments were carried out.
experiment 1
30.0 cm3 of 2.00 mol dm–3 hydrochloric acid (an excess) was placed in a conical flask and the
temperature recorded as 21.0 °C.
When 0.0200 mol of potassium carbonate, K2CO3, was added to the acid and the mixture
stirred with a thermometer, the maximum temperature recorded was 26.2 °C.
(b) (i)
Construct a balanced equation for this reaction.
..................................................................................................................................
(ii)
Calculate the quantity of heat produced in experiment 1, stating your units.
Use relevant data from the Data Booklet and assume that all solutions have the
same specific heat capacity as water.
(iii)
Use your answer to (ii) to calculate the enthalpy change per mole of K2CO3.
Give your answer in kJ mol–1 and include a sign in your answer.
(iv)
Explain why the hydrochloric acid must be in an excess.
..................................................................................................................................
............................................................................................................................. [4]
experiment 2
The experiment was repeated with 0.0200 mol of potassium hydrogencarbonate, KHCO3.
All other conditions were the same.
In the second experiment, the temperature fell from 21.0 °C to 17.3 °C.
(c) (i)
Construct a balanced equation for this reaction.
..................................................................................................................................
(ii)
Calculate the quantity of heat absorbed in experiment 2.
(iii)
Use your answer to (ii) to calculate the enthalpy change per mole of KHCO3.
Give your answer in kJ mol–1 and include a sign in your answer.
[3]
(d) When KHCO3 is heated, it decomposes into K2CO3, CO2 and H2O.
2KHCO3
K2CO3 + CO2 + H2O
Use Hess’ Law and your answers to (b)(iii) and (c)(iii) to calculate the enthalpy change
for this reaction.
Give your answer in kJ mol–1 and include a sign in your answer.
[2]
[Total: 11]
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Born-Haber Cycles
Mark Scheme 6
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 6
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) either burn or shine light/uv on mixture of H2 + Cl2 but NOT heat
[1]
(ii) red/orange/brown colour of bromine decolourises/disappears
steamy/misty/white fumes produced
container gets warm/hot
[2]
(iii) H-H = 436
Cl-Cl = 244
H-Cl = 431
= –182 kJ mol–1
∆H = 436 + 244 – 2(431)
Br-Br = 193
H-H = 4
H-
[2]
H-Br = 3
H-
= –103 kJ mol–1
∆H = 436 + 193 – 2(366)
[2]
(iv) H-Br bond is weaker than the H-Cl bond – allow converse.
[1]
[8]
(b) (i) light
[1]
(ii) bonds broken = C-H & I-I
bonds made = C-I & H-I
∆H
= 410 + 151 = 561
= 240 + 299 = 539
= 551 – 539 = +22 kJ mol–1
[2]
(iii) The overall reaction is endothermic or no strong bonds/only weak bonds are
formed or high Eact
(c) (i) homolytic fission is the breaking of a bond to form (two) radicals/neutral species/
odd-electron species
(ii) •CH2Cl
the C-Br bond is the weakest or needs least energy to break/breaks most easily
(d)
Cl
Cl
Cl
Cl
*
Cl
Cl
Cl
[1]
[4]
[1]
[1]
[1]
[3]
Cl
4 structures: [2]
2 or 3 structures: [1]
Correct chiral atom identified
[1]
[3]
[Total: 18]
2
(a
(i) a compound which contains only carbon and hydrogen (1)
(ii) separation of compounds by their boiling points (1)
[2]
(b) (i) high temperature and high pressure (1)
high temperature and catalyst (1)
(ii) C11H24 → C5H12 + C6H12 or
C11H24 → C5H12 + 2C3H6 or
C11H24 → C5H12 + 3C2H4 (1)
[3]
(c)
c)
CH3
CH3CH2CH2CH2CH3
CH3CH2CHCH3
CH3CCH3
CH3
isomer B
(1)
isomer C
CH3
isomer D
(1)
(1)
(ii) the straight chain isomer (isomer B above) (1)
it has the greatest van der Waals’ forces (1)
because unbranched molecules have greater area of contact/
can pack more closely together (1)
[6]
(d) enthalpy change when 1 mol of a substance (1)
is burnt in an excess of oxygen/air under standard conditions
or is completely combusted under standard conditions (1)
[2]
(e) (i) heat released = m c δT = 200 x 4.18 x 27.5 (1)
= 22990 J = 23.0 kJ (1)
(ii) 23.0 kJ produced from 0.47 g of E
2059 kJ produced from
0.47 x 2059
g of E (1)
23.0
= 42.08 g of E (1)
allow ecf in (i) or (ii) on candidate’s expressions
[4]
(f) C3H6 = 42
E is C3H6
for ecf, E must be unsaturated and be no larger than C5 (1)
1)
[Total: 18]
3
(a
(i) P2O5 + 3H2O → 2H3PO4 (or similar) or P4O10 + 6H2O → 4H3PO4 (1)
SO2 + H2O → H2SO3 (1)
(ii) 2NO2 + H2O → HNO2 + HNO3 (1)
(iii) 2ClO2 + 2NaOH → NaClO2 + NaClO3 + H2O or ionic eqn (1)
[4]
(b) (i) 2CH4 + C2H6 + H2S + 9O2 → 4CO2 + SO2 + 8H2O
Formulae (1), balanced (1)
(ii) (The SO2 produced) causes acid rain (1)
or consequence of acid rain – defoliation etc. – or respiratory problem
(iii) 1000 dm3 contains 50 dm3 of H2S
this is 50/24 (= 2.083 moles) (1)
Mr(ethanolamine) = 24 + 7 + 14 + 16 = 61
therefore mass = 2.083 × 61 = 127(.1)g (1) (or ecf)
(iv) acid-base (1)
(v) ∆H = ∆Hf(rhs) – ∆Hf(lhs)
= {(3 × 11 – 2 × 242)}{–}{(2 × –21 – 297)} –1 for each { } in which there is an error
= –451 + 339
= –112 (kJ mol–1) (2)
[8]
[Total: 12]
4
(a
(i)
CH4
–75
reaction
(ii)
broken
reaction
+
Cl2
0
→
+
HCl
–92
= –82 + (–92) – (–75)
= –99 kJ mol–1
CH4
C–H
410
+
I2
I–I
151
→
made
initiation
nit
Cl2 + uvl → 2Cl
propagation
CH4 + Cl → CH3 + HCl
CH3 + Cl2 → CH3Cl + Cl
termination
(1)
(1)
CH3I
C–I
240
= –240 + (–299) + 410 + 151
= +22 kJ mol–1
(iii) activation energy is too great
(b)
b) (
CH3Cl
–82
+
HI
H–I
299
(1)
(1)
(1)
[5]
(1)
(1)
both needed (1)
(1)
CH3 + CH3 → C2H6 or
CH3 + Cl → CH3Cl or
Cl + Cl → Cl2
(1)
(ii) CH3/methyl radical
(1)
[7]
(c)
energy
I
Ea
CH4 + Cl2
∆H
CH3Cl + HCl
progress of reaction
correct placement of 16 kJ
J
correct placement of –99 kJ (allow ecf on wrong calculation in (a) (i))
intermediate clearly shown at I
correct ‘double peak’ shape
second peak lower than first
(
(1
(1)
(1)
(1)
[5]
[Total: max 16]
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Born-Haber Cycles
Question Paper 6
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 6
Time Allowed:
77 minutes
Score:
/64
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) The halogens chlorine and bromine react readily with hydrogen.
X2(g) + H2(g)
(i)
2HX(g)
[X = Cl or Br]
Describe how you could carry out this reaction using chlorine.
..................................................................................................................................
(ii)
Describe two observations you would make if this reaction was carried out with
bromine.
..................................................................................................................................
..................................................................................................................................
(iii)
Use bond energy data from the Data Booklet to calculate the ΔH o for this reaction
when
X = Cl,
ΔH o = ........................................ kJ mol–1
X = Br.
ΔH o = ........................................ kJ mol–1
(iv)
What is the major reason for the difference in these two ΔH o values?
..................................................................................................................................
[8]
(b) Some halogens also react readily with methane.
CH4(g) + X2(g)
(i)
CH3X(g) + HX(g)
What conditions are needed to carry out this reaction when X is bromine, Br?
..................................................................................................................................
(ii)
Use bond energy data from the Data Booklet to calculate the ΔH o of this reaction
for the situation where X is iodine, I.
ΔH o = ........................................ kJ mol–1
(iii)
Hence suggest why it is not possible to make iodomethane, CH3I, by this reaction.
..................................................................................................................................
[4]
(c) Halogenoalkanes can undergo homolytic fission in the upper atmosphere.
(i)
Explain the term homolytic fission.
..................................................................................................................................
..................................................................................................................................
(ii)
Suggest the most likely organic radical that would be formed by the homolytic
fission of bromochloromethane, CH2BrCl. Explain your answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[3]
(d) The reaction between propane and chlorine produces a mixture of many compounds,
four of which are structural isomers with the molecular formula C3H6Cl2.
Draw the structural or skeletal formulae of these isomers, and indicate any chiral atoms
with an asterisk (*).
[3]
[Total: 18]
2
Crude oil is a naturally occurring flammable liquid which consists of a complex mixture of
hydrocarbons. In order to separate the hydrocarbons the crude oil is subjected to fractional
distillation.
(a) Explain what is meant by the following terms.
(i)
hydrocarbon .............................................................................................................
..................................................................................................................................
(ii)
fractional distillation ..................................................................................................
.............................................................................................................................. [2]
(b) Undecane, C11H24, is a long chain hydrocarbon which is present in crude oil.
Such long chain hydrocarbons are ‘cracked’ to produce alkanes and alkenes which have
smaller molecules.
(i)
Give the conditions for two different processes by which long chain molecules
may be cracked.
process 1 ..................................................................................................................
..................................................................................................................................
process 2 ..................................................................................................................
..................................................................................................................................
(ii)
Undecane, C11H24, can be cracked to form pentane, C5H12, and an alkene.
Construct a balanced equation for this reaction.
.............................................................................................................................. [3]
Pentane, C5H12, exhibits structural isomerism.
(c) (i)
Draw the three structural isomers of pentane.
isomer B
isomer C
isomer D
(ii)
The three isomers of pentane have different boiling points.
Which of your isomers has the highest boiling point?
isomer .........
Suggest an explanation for your answer.
..................................................................................................................................
..................................................................................................................................
.............................................................................................................................. [6]
The unsaturated hydrocarbon, E, is obtained by cracking hexane and is important in the
chemical industry.
The standard enthalpy change of combustion of E is –2059 kJ mol–1.
(d) Define the term standard enthalpy change of combustion.
..........................................................................................................................................
...................................................................................................................................... [2]
When 0.47 g of E was completely burnt in air, the heat produced raised the temperature of
200 g of water by 27.5 °C. Assume no heat losses occurred during this experiment.
(e) (i)
Use relevant data from the Data Booklet to calculate the amount of heat released
in this experiment.
(ii)
Use the data above and your answer to (i) to calculate the relative molecular mass,
Mr, of E.
[4]
(f)
Deduce the molecular formula of E.
[1]
[Total: 18]
3
(a) (i)
Write equations to illustrate the reactions of the following oxides with water.
phosphorus(V) oxide ................................................................................................
sulfur(IV) oxide .........................................................................................................
(ii)
When NO2 reacts with water, nitrogen undergoes a disproportionation reaction in
which one nitrogen atom decreases its oxidation number by 1 and another nitrogen
atom increases its oxidation number by 1. A mixture of two acids results.
Suggest an equation for the reaction between NO2 and water.
..................................................................................................................................
(iii)
In a similar disproportionation reaction, Cl O2 reacts with aqueous NaOH to produce
a solution containing two chlorine-containing sodium salts.
Suggest an equation for the reaction between Cl O2 and aqueous NaOH.
..................................................................................................................................
[4]
(b) The major source of sulfur for the manufacture of sulfuric acid by the Contact process
is the de-sulfurisation of ‘sour’ natural gas. Many natural gas wells produce a mixture
of volatile hydrocarbons (mainly CH4 and C2H6) together with up to 25% hydrogen
sulfide, H2S.
(i)
Complete and balance the following equation showing the complete combustion of
a gaseous mixture consisting of 2 mol of CH4, 1 mol of C2H6 and 1 mol of H2S.
2CH4 + C2H6 + H2S + ______
(ii)
SO2 + ______ + ______
Explain why it is important to remove the H2S before burning the natural gas
industrially.
..................................................................................................................................
..................................................................................................................................
The H2S is removed by passing the ‘sour’ natural gas through a solvent containing
ethanolamine. The following reaction takes place.
HOCH2CH2NH2 + H2S(g)
(iii)
HOCH2CH2NH3+ + SH–
If a sample of natural gas contains 5% by volume of H2S, calculate the mass of
ethanolamine required to remove all the H2S from a 1000 dm3 sample of gas,
measured under room conditions.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
The H2S can be recovered by warming the solution to 120 °C, when the above
reaction is reversed. The ethanolamine can then be recycled.
(iv)
What type of reaction is occurring here?
..................................................................................................................................
The recovered H2S is converted to sulfur by the following two reactions.
I
Part of the H2S is burned in air.
H2S + 1.5O2
II
The gas stream resulting from reaction I is then blended with the remaining H2S and
fed into an iron oxide catalyst bed, where sulfur and water are produced according
to the following equation.
2H2S(g) + SO2(g)
(v)
SO2 + H2O
3S(g) + 2H2O(g)
Use the following data to calculate ΔH –o– for the reaction between H2S and SO2.
compound
ΔH –o–f / kJ mol–1
H2S(g)
–21
SO2(g)
–297
H2O(g)
–242
S(g)
+11
ΔH –o– = ........................................ kJ mol–1
[8]
[Total: 12]
4
Alkanes such as methane, CH4, undergo few chemical reactions. Methane will, however,
react with chlorine but not with iodine.
Relevant standard enthalpy changes of formation for the reaction of methane with chlorine
to form chloromethane, CH3Cl, are given below.
∆H of / kJ mol–1
(a) (i)
CH4
–75
CH3Cl
–82
HCl
–92
Use the data to calculate ∆H reaction for the formation of CH3Cl.
CH4 +
(ii)
Cl 2 →
CH3Cl
+
HCl
The corresponding reaction with iodine does not take place.
Use bond energy data from the Data Booklet to calculate a ‘theoretical value’ for
∆Hreaction for the following equation.
CH4 + I2 → CH3I + HI
(iii)
Suggest why this reaction does not in fact occur.
..................................................................................................................................
..................................................................................................................................
[5]
(b) (i)
By using equations, describe the mechanism of the reaction between chlorine and
methane to form chloromethane, CH3Cl.
Identify, by name, the separate steps of the overall reaction.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
What is the intermediate organic species in this reaction?
..............................................
[7]
(c) The energy of activation for the formation of CH3Cl is 16 kJ mol–1.
Use this figure and your answer to (a)(i) to complete the reaction pathway diagram
below showing the formation of CH3Cl from CH4 and Cl2.
Show clearly the intermediate organic species and the final products.
Indicate on your sketch the relevant enthalpy changes and their values.
enthalpy
CH4 + Cl 2
progress of reaction
[4]
[Total: 16]
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Born-Haber Cycles
Mark Scheme 7
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 7
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
Ca2+(g) + 2Cl–(g) → CaCl2(s)
s)
[1]
(b) CaF2 and CaS both have larger lattice energies (than CaCl2)
(i) F– is smaller than Cl–
[1]
(ii) S2– is more highly charged than Cl–
[1]
[3]
(c) LE = –[178 + 590 + 1150] – [244 – 2 × 349] – 796
= –2260 (kJ mol–1)
(d)
d)
[1
Ca
C
H
O
=
=
=
=
28.2/40.1
25.2/12
1.4/1
45.1/16
=
=
=
=
0.703
2.10
1.4
2.82
⇒
⇒
⇒
⇒
1
3
2
4
formula is CaC3H2O4
(ii) malonic acid must be C2H4O4, i.e. CH3(CO2H)2
signs
[3
[3]
(1 mark for initial step of calc’n)
(1)
[2]
(must be structural)
[1]
[3]
[Total: 10]
2
(a
(i) A is Cl2/chlorine
chl
B is NaCl or HCl or Cl ¯ [or words], etc.
[1]
C is salt bridge or KCl/KNO3, etc.
[1]
D is platinum/Pt
[1]
E is Fe2+ + Fe3+ or mixture of Fe(II) + Fe(III) salts
[1]
mention of standard conditions ([Cl ¯] of 1 mol dm–3 or Cl2 at 1 atmos
or T = 25°C/298 K)
[1]
(ii) Eo = EoR – EoL= 0.77 – 1.36 = (–)0.59 (V) (ignore sign)
[1]
(since R.H. electrode is negative) electrons flow (from right) to left or to the chlorine
electrode or anticlockwise or from (beaker) E to (beaker) B
[1] [8]
(b)
b)
∆H = 3 ×(–167.2) + (–48.5) – (–399.5)
= –150.6 or 151 (kJ mol–1)
(correct ans [2])
(ii) 2Fe3+ + Cu → 2Fe2+ + Cu2+
(or molecular: 2FeCl3 + Cu → 2FeCl2 + CuCl2)
Eo = 0.77 – 0.34 = (+) 0.43 (V)
(no mark for –0.43V)
[1]
[1
[1]
[1]
[4]
[Total: 12 max 11]
3
(a)
salt bridge + voltmeter
zinc metal + Zn2+
H2 (in, not out) + H+
Pt electrode
all solutions at 1 mol dm–3
T = 298K or 25oC
[1]
[1]
[1]
[1]
[1]
[1] [6]
(b)
conditions
ZnCl2(l)
ZnCl2(conc aq)
ZnCl2(dil aq)
product at anode
(chlorine)
chlorine [1]
oxygen [1]
product at cathode
zinc [1]
(H2 or zinc) (ignore)
hydrogen [1]
[1]
1] for each product in correct place [
[4]
(c)
LE
=B–A
= –415 – (131 + 908 + 1730) – {244 + 2(–349)}
[1]
[1]
= –415 – 2315
= –2730 (kJ mol–1)
[1]
(correct answer = [3]: deduct [1] for each error) [3]
(d) (i)
• instrumental method (e.g. spectrophotometer/colorimeter/conductance meter)
• what is measured (e.g. absorbance/transmission at a stated wavelength
or by use of a “suitable” (green) filter or conductance/resistance)
• measurement of time
• relation of time to rate (e.g. gradient of absorbance/time graph, or rate ∝ 1/t)
• repeat with different [Zn2+], (but the same [PAR])
• relation of rate to [Zn2+] (either by a plot or by simple proportion)
(all 6 points are unconditional on each other) any 5 points [5]
(ii) e.g. add Br2(aq)
aq)
decolourises or produces a white ppt.
or add FeCl3(aq or “neutral”); purple colour produced
[1]
[1]
1] + [
[2]
[Total: 20]
4
(a)
sphericall (1)
double lobes along the x-axis (1)
(b) (i) attraction between bonding electrons and nuclei
attraction is electrostatic
(ii) H2
(1)
(1)
s-s overlap clearly shown
must not be normal dot/cross diagram
HCl
[3]
(1)
s-p overlap clearly shown
overlap must involve s and p orbitals
(1)
[4]
(c) (i) bonding electrons are unequally shared or
the molecule has a dipole/δ+ and δ- ends to molecule
(1)
(ii) the H and Cl atoms have different electronegativities
or chlorine is more electronegative than hydrogen
(1)
[2]
(d)
allow two ‘sausages’ above and below the C-C axis
or two p orbitals overlapping sideways
to form one (localised) π bond over two carbon atoms
(1)
[1]
(e) ∆Hfo = 2(–393.7) + 2(–285.9) – (–1411)
= + 51.8 kJ mol–1(units given in qu.)
penalise errors:
no 2 for –393.7
no 2 for –285.9
wrong sign for –(–1411)
(3)
[3]
[Total: 13]
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Born-Haber Cycles
Question Paper 7
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 7
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Calcium chloride, CaCl2, is an important industrial chemical used in refrigeration plants, for
de-icing roads and for giving greater strength to concrete.
(a) Show by means of an equation what is meant by the lattice energy of calcium chloride.
..................................................................................................................................... [1]
(b) Suggest, with an explanation, how the lattice energies of the following salts might
compare in magnitude with that of calcium chloride.
(i)
calcium fluoride, CaF2
..................................................................................................................................
..................................................................................................................................
(ii)
calcium sulfide, CaS
..................................................................................................................................
..................................................................................................................................
[3]
(c) Use the following data, together with additional data from the Data Booklet, to calculate
the lattice energy of CaCl2.
standard enthalpy change of formation of CaCl2
–796 kJ mol–1
standard enthalpy change of atomisation of Ca(s)
+178 kJ mol–1
electron affinity per mole of chlorine atoms
–349 kJ mol–1
enthalpy
Ca(s) + Cl 2(g)
lattice energy = ............................................ kJ mol–1 [3]
(d) When a solution of CaCl2 is added to a solution of the dicarboxylic acid, malonic acid,
the salt calcium malonate is precipitated as a white solid. The solid has the following
composition by mass: Ca, 28.2 %; C, 25.2 %; H, 1.4 %; O, 45.2 %.
(i)
Calculate the empirical formula of calcium malonate from these data.
(ii)
Suggest the structural formula of malonic acid.
[3]
[Total: 10]
2
Chlorine gas and iron(II) ions react together in aqueous solution as follows.
Cl 2 + 2Fe2+
2Cl – + 2Fe3+
(a) The following diagram shows the apparatus needed to measure the E ocell for the above
reaction.
S
V
A
E
C
D
B
(i)
In the spaces below, identify what the five letters A – E in the above diagram
represent.
A .........................................................
B .........................................................
C .........................................................
D .........................................................
E .........................................................
(ii)
Use the Data Booklet to calculate the E ocell for this reaction, and hence decide which
direction (left to right, or right to left) electrons would flow through the voltmeter V
when switch S is closed.
E ocell = .................................................. V
direction of electron flow ......................................................
[7]
(b) Iron(III) chloride readily dissolves in water.
FeCl 3(s)
(i)
Fe3+(aq) + 3Cl –(aq)
Use the following data to calculate the standard enthalpy change for this process.
species
DH of / kJ mol–1
FeCl 3(s)
–399.5
Fe3+(aq)
–48.5
Cl –(aq)
–167.2
DH o = .........................................kJ mol–1
(ii)
A solution of iron(III) chloride is used to dissolve unwanted copper from printed
circuit boards.
When a copper-coated printed circuit board is immersed in FeCl 3(aq), the solution
turns pale blue.
Suggest an equation for the reaction between copper and iron(III) chloride and use
the Data Booklet to calculate the E o for the reaction.
equation ...................................................................................................................
E o = .................................................. V
[4]
[Total: 11]
3
Zinc chloride is one of the most important compounds of zinc. It is used in dry cell batteries,
as a flux for soldering and tinning, as a corrosion inhibitor in cooling towers and in the
manufacture of rayon.
(a) Draw a fully labelled diagram to show how you could use a standard hydrogen electrode
to measure the standard electrode potential, E o, of zinc.
[6]
(b) The electrolysis of zinc chloride can give different electrode products, depending on the
conditions used.
Suggest the products formed at each electrode in the following cases. One space has
been filled in for you.
conditions
product at anode
product at cathode
chlorine
ZnCl2(l)
ZnCl2(concentrated aqueous)
ZnCl2(dilute aqueous)
[3]
(c) Use the following data, together with relevant data from the Data Booklet, to construct a
Born-Haber cycle and calculate a value for the lattice energy of zinc chloride.
standard enthalpy change of formation of ZnCl2
–415 kJ mol–1
standard enthalpy change of atomisation of Zn(s)
+131 kJ mol–1
electron affinity per mole of chlorine atoms
–349 kJ mol–1
lattice energy = ............................................... kJ mol–1 [3]
(d) Zinc is an essential element for plant and animal life. It is often administered in the form
of a chelate, which is a complex between a metal ion and a polydentate ligand.
The rate of the reaction between zinc ions and the ligand 4-(2-pyridylazo)resorcinol,
PAR, has been studied.
HO
Zn2+ + 2
N
HO
Zn2+
N
N
N
N
+ 2
N
–
O
HO
PAR
2
Zn-PAR
Both PAR and its zinc complex absorb radiation in the UV-visible region. The figure
below shows their absorption spectra.
1.4
absorbance
1.2
1.0
0.8
0.6
PAR
Zn-PAR
0.4
0.2
0.0
300
400
500
600
700
wavelength / nm
(i)
Devise a suitable experimental technique for studying how the rate of this reaction
varies with [Zn2+(aq)].
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Describe a reaction you could carry out to show that PAR is a phenol.
..................................................................................................................................
..................................................................................................................................
[7]
[Total: 19]
+
4
This question is about the bonding of covalent compounds.
(a) On the axes below, sketch the shapes of a 1s, a 2s, and a 2px orbital.
z
z
y
z
y
x
y
x
1s
x
2s
2px
[3]
(b) Covalent bonding occurs when two atoms share a pair of electrons. Covalent bonding
may also be described in terms of orbital overlap with the formation of σ bonds.
(i)
How are the two atoms in a covalent bond held together? In your answer, state which
particles are attracted to one another and the nature of the force of attraction.
..................................................................................................................................
..................................................................................................................................
(ii)
Draw sketches to show orbital overlap that produces the σ bonding in the H2 and
HCl molecules.
H2
HCl
[4]
(c) The bond in the HCl molecule is said to be ‘polar’.
(i)
What is meant by the term bond polarity?
..................................................................................................................................
(ii)
Explain why the HCl molecule is polar.
..................................................................................................................................
..................................................................................................................................
[2]
(d) The bonding in ethene may be described as a mixture of σ and π bonding.
Each carbon atom in ethene forms three σ bonds as shown below.
H
H
C
C
H
H
On the diagram, sketch the π bond that is also present in ethene.
[1]
(e) Carbon, hydrogen and ethene each burn exothermically in an excess of air.
C(s) + O2(g) → CO2(g)
H2(g) + ½O2(g) → H2O(l)
C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l)
∆H oc = –393.7 kJ mol–1
∆H oc = –285.9 kJ mol–1
∆H oc = –1411.0 kJ mol–1
Use the data to calculate the standard enthalpy change of formation, ∆H of , in kJ mol–1,
of ethene at 298 K.
2C(s) + 2H2(g) → C2H4(g)
∆H of = ................................. kJ mol–1
[3]
[Total: 13]
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Born-Haber Cycles
Mark Scheme 8
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Mark Scheme 8
Time Allowed:
22 minutes
Score:
/18
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(b)
b)
CCl4 is unreactive. (The rest react (with increasing vigour))
no d-orbitals or available/low-lying empty orbitals in carbon or unable to expand octet
e.g. SiCl4 + 2H2O → SiO2 + 4HCl
(or GeCl4 etc)
or Si(OH)2Cl2
or Si(OH)4
(allow balanced equations for partial hydrolysis)
E(Cl-Cl) = 244 kJ mol–1;
∴ ∆H = –436 (kJ mol–1)
[1]
[1]
[1]
[3]
2 E(C-Cl) = 2 x 340 = 680 kJ mol–1
(ii) ∆H = 359 – 329 = +30 (kJ mol–1)
(iii) since reaction (ii) is endothermic, the +4 oxidation state is less stable
or the +2 oxidation state is more stable (down the group)
[1
[1
[1]
[3]
[Total: 6]
2
(a)
x
o
x
H oCxoCoxH
x
o
(1)
(b) n = PV = (1515 x 103) x (76 x 10-3)
RT
8.31 x 298
(1)
= 46.5
(c)
c) (
[1]
(1)
CaC2 + 2H2O → Ca(OH)2 + C2H2
[2]
(1)
(ii) n(C2H2) = n(CaC2) =100 x 46.5
(1)
mass of CaC2 = 100 x 46.5 x 64 =
= 297 570 g
= 297.6 kg (accept 298 kg)
correct units necessary
(1)
allow e.c.f. on candidate’s answer in (b)
[3]
(d) C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(g)
bonds broken: 2(H-C)
2 x 410
C≡C
840
5
/2(O=O) 5/2 x 496
bonds made:
4(C=O)
2(O-H)
4x7
2 x 460
=
=
=
=
=
820
840
1240
2900 kJ mol-1
(1)
2960
920
3880 kJ mol-1
(1)
∆Hcomb = -3880 + 2900 = -980 kJ mol-1
allow e.c.f. on incorrect bonds made/broken
(e) (i) the enthalpy/energy change when one mole of a substance
is burned in an excess of air/oxygen
or completely combusted
under standard conditions
(ii) calculation in (d) includes H2O(g) whereas ∆Hcomb involves H2O(l)
or average bond energy terms are used in the Data Booklet
(1)
[3]
(1)
(1)
(1)
[3]
[Total: 12]
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Born-Haber Cycles
Question Paper 8
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Theory
Booklet
Question Paper 8
Time Allowed:
22 minutes
Score:
/18
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) By choosing the chlorides of two of the Group IV elements as examples, describe the
trend in the reactions of these chlorides with water. Suggest an explanation for any
differences, and write equations for any reactions that occur.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
......................................................................................................................................[3]
(b) The standard enthalpy changes of formation of lead(II) chloride and lead(IV) chloride
are given in the following table.
compound
∆H of / kJ mol–1
PbCl2(s)
–359
PbCl4(l)
–329
Use these data, and also bond energy data from the Data Booklet, to calculate the
enthalpy changes for the following two reactions.
(i)
CCl2(g) + Cl2(g)
CCl4(g)
∆H o = ........................... kJ mol–1
(ii)
PbCl2(s) + Cl2(g)
PbCl4(l)
∆H o = ........................... kJ mol–1
(iii)
Make use of your answers to parts (i) and (ii) to suggest how the relative stabilities
of the two oxidation states vary down the Group.
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 6]
2
The unsaturated hydrocarbon ethyne (acetylene), C2H2, is widely used in ‘oxy-acetylene
torches’ for cutting and welding metals. In the torch, ethyne is burned in oxygen to produce a
flame with a temperature of 3400 K.
(a) Ethyne is a linear molecule with a triple bond, C⬅C, between the two carbon atoms.
Draw a ‘dot-and-cross’ diagram of an ethyne molecule.
[1]
(b) When used for cutting or welding, ethyne is transported in cylinders which contain the
gas under pressure. A typical cylinder has a volume of 76 dm3 and contains ethyne gas
at 1515 kPa pressure at a temperature of 25 °C.
Use the general gas equation, pV = nRT, to calculate the amount, in moles, of ethyne in
this cylinder.
[2]
(c) In some countries, ethyne is manufactured from calcium carbide, CaC2, which is
produced by heating quicklime and coke together at 2300 K.
CaO + 3C
CaC2 + CO
When water is added to the CaC2, calcium hydroxide, Ca(OH)2, and ethyne, C2H2, are
produced.
(i)
Construct a balanced equation for the formation of ethyne from calcium carbide.
..................................................................................................................................
(ii)
Use this equation and your answer to part (b) to calculate the mass of CaC2 which
will react with an excess of water to produce enough ethyne to fill 100 cylinders of
the gas.
[3]
(d) The equation for the complete combustion of ethyne is given below.
Use appropriate bond energy data from the Data Booklet to calculate a value for the
enthalpy change of combustion of ethyne.
C2H2(g) + ⁵⁄₂O2(g)
2CO2(g) + H2O(g)
[3]
(e) The value for the standard enthalpy change of combustion of ethyne is –1300 kJ mol–1.
(i)
Define the term standard enthalpy change of combustion.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Explain why your answer to (d) does not have the same value as the standard
enthalpy change of combustion.
..................................................................................................................................
..................................................................................................................................
[3]
[Total: 12]
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Born-Haber Cycles
Question Paper
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Chemical Energetics
Sub-Topic
Paper Type
Born-Haber Cycles
Multiple Choice
Booklet
Question Paper
Time Allowed:
57 minutes
Score:
/47
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Metaldehyde, (CH3CHO)4, is used as a solid fuel for camping stoves. The equation for the
complete combustion of metaldehyde is shown.
(CH3CHO)4(s) + 10 O2(g) → 8CO2(g) + 8H2O(l)
= standard enthalpy change of combustion.
Which expression will give a correct value for the enthalpy change of formation of metaldehyde?
2
A
metaldehyde – (8
carbon + 8
B
metaldehyde – (8
carbon + 16
C
(8
carbon + 8
D
(8
carbon + 16
hydrogen) –
hydrogen) –
hydrogen)
hydrogen)
metaldehyde
metaldehyde
A student performed an experiment to measure the enthalpy change of combustion of ethane.
He used the following values for the standard enthalpy changes of combustion of carbon and
hydrogen.
carbon = –394 kJ mol–1
hydrogen = –286 kJ mol–1
He calculated the enthalpy change of formation of ethane to be –140 kJ mol–1.
What was his experimental value for the standard enthalpy change of combustion of ethane?
A
–2364 kJ mol–1
B
–1506 kJ mol–1
C
–1112 kJ mol–1
D
–540 kJ mol–1
3
Carbon monoxide and methanol can react together to form ethanoic acid.
CO(g) + CH3OH(l)
CH3CO2H(l)
Standard enthalpy changes of combustion are given in the table.
What is the value for
4
A
–1883.1 kJ mol–1
B
–134.9 kJ mol–1
C
+134.9 kJ mol–1
D
+1883.1 kJ mol–1
compound
standard enthalpy change
of combustion,
CO
–283.0 kJ mol–1
CH3OH
–726.0 kJ mol–1
CH3CO2H
–874.1 kJ mol–1
for the reaction between carbon monoxide and methanol?
The enthalpy change of formation of carbon dioxide is –394 kJ mol–1.
The enthalpy change of formation of water is –286 kJ mol–1.
The enthalpy change of formation of methane is –74 kJ mol–1.
What is the enthalpy change of combustion of methane?
A
–892 kJ mol–1
B
–606 kJ mol–1
C
+606 kJ mol–1
D
+892 kJ mol–1
5
6
Which equation represents the standard enthalpy change of formation of ethanol, C2H5OH?
A
2C(g) + 3H2(g) +
1
2
O2(g) → C2H5OH(l)
B
2C(s) + 3H2(g) +
1
2
O2(g) → C2H5OH(l)
C
2C(s) + 3H2(g) +
1
2
O2(g) → C2H5OH(g)
D
2C(g) + 6H(g) + O(g) → C2H5OH(l)
A reaction pathway diagram is shown.
enthalpy
reactants
products
progress of reaction
Which enthalpy change could the diagram not apply to?
A
enthalpy of atomisation
B
enthalpy of combustion
C
enthalpy of formation
D
enthalpy of neutralisation
7
The enthalpy change of formation of Mn(NO3)2(s) is –696 kJ mol–1.
The enthalpy change of formation of MnO2(s) is –520 kJ mol–1.
The enthalpy change of formation of NO2(g) is +33 kJ mol–1.
On heating, Mn(NO3)2 decomposes into MnO2 and NO2.
Mn(NO3)2(s) → MnO2(s) + 2NO2(g)
What is the value of the standard enthalpy change of this reaction?
A
–242 kJ mol–1
B
–209 kJ mol–1
C
+209 kJ mol–1
D
+242 kJ mol–1
8 Which reaction has an enthalpy change equal to the standard enthalpy change of formation of
propane?
9
A
3C(g) + 4H2(g) → C3H8(g)
B
3C(g) + 8H(g) → C3H8(g)
C
3C(s) + 4H2(g) → C3H8(g)
D
3C(s) + 4H2(g) → C3H8(l)
In an experiment to calculate the enthalpy change of combustion of a fuel, 1.5 g (0.0326 mol) of
the fuel was used to heat 200 g of water. The temperature of the water rose from 25 °C to 55 °C.
The specific heat capacity of water is 4.18 J g–1 K–1.
There is significant heat loss in this experiment. Therefore, the experimental value for the
enthalpy change of combustion, ∆Hc, of the fuel will be different from the theoretical value.
Using the information above, what is the experimental value for the enthalpy change of
combustion, ∆Hc, of the fuel?
A
–1410 kJ mol–1
B
–769 kJ mol–1
C
–30.7 kJ mol–1
D
–16.7 kJ mol–1
10 The reaction pathway diagram below illustrates the energies of the reactants, the products and
the transition state of a reaction.
transition state
E1
energy
E2
reactants
E3
products
extent of reaction
Which expression represents the activation energy of the forward reaction?
A
E1 – E 2
B
E2 – E 1
C
E2 – E 3
D
E3 – E 2
11 Under standard conditions, which statement is correct?
A
Cl –(aq) can oxidise Br2(aq).
B
Cl –(aq) can reduce Br2(aq).
C
Cl 2(aq) can oxidise Br –(aq).
D
Cl 2(aq) can reduce Br –(aq).
12 Hydrogen sulfide, H2S, is released from volcanoes. It reacts with oxygen in the air to form sulfur
dioxide.
2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
∆Hfo [H2S(g)] = –21 kJ mol–1
∆Hfo [H2O(l)] = –286 kJ mol–1
∆Hfo [SO2(g)] = –297 kJ mol–1
What is the standard enthalpy change of this reaction?
A
–1208 kJ mol–1
B
–1124 kJ mol–1
C
–562 kJ mol–1
D
–541 kJ mol–1
13 Nitrogen monoxide is an atmospheric pollutant that is formed inside car engines by an
endothermic reaction between nitrogen and oxygen.
N2(g) + O2(g) → 2NO(g)
∆H = +66 kJ mol–1
Which labelled diagram correctly represents the energy profile for this reaction?
A
Ea
energy
0
B
0
0
Ea
energy
∆H
extent of
reaction
0
extent of
reaction
C
energy
0
D
Ea
∆H
0
0
Ea
energy
extent of
reaction
∆H
0
extent of
reaction
14 Equations involving four enthalpy changes are shown.
Na(g) → Na+(g) + e–
∆H = W
Na(g) → Na2+(g) + 2e–
∆H = X
Na(s) → Na(g)
∆H = Y
Na(s) → Na2+(g) + 2e–
∆H = Z
What is the second ionisation energy of sodium?
A
X
B
X–W
C
Y–W
D
Z–Y
∆H
15 Which factor can affect the value of the activation energy of a reaction?
A
changes in concentration of the reactants
B
decrease in temperature
C
increase in temperature
D
the presence of a catalyst
16 Use of the Data Booklet is relevant to this question.
A student mixed 25 cm3 of 0.10 mol dm–3 sodium hydroxide solution with 25 cm3 of 0.10 mol dm–3
hydrochloric acid and noted a temperature rise of 2.5 °C.
What is the enthalpy change of the reaction per mole of NaOH?
A
–209 kJ mol–1
B
–104.5 kJ mol–1
C
–209 J mol–1
D
–522.5 J mol–1
17 Propanone has molecular formula C3H6O.
The enthalpy change of combustion of hydrogen is –286 kJ mol–1.
The enthalpy change of combustion of carbon is –394 kJ mol–1.
The enthalpy change of formation of propanone is –254 kJ mol–1.
Using this information, what is the enthalpy change of combustion of propanone?
A
–2644 kJ mol–1
B
–2294 kJ mol–1
C
–1786 kJ mol–1
D
–426 kJ mol–1
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18 Use of the Data Booklet is relevant to this question.
This question should be answered using bond enthalpy data. The equation for the complete
combustion of methanal is given below.
H2C=O + O2 → CO2 + H2O
What is the enthalpy change of combustion of methanal?
A
+416 kJ mol–1
B
+396 kJ mol–1
C
–344 kJ mol–1
D
–690 kJ mol–1
19 Which stage in the free radical substitution of methane by chlorine will have the lowest activation
energy?
A
CH3• + Cl 2 → CH3Cl + Cl •
B
Cl • + Cl • → Cl 2
C
Cl • + CH4 → CH3• + HCl
D
Cl 2 → Cl • + Cl •
20 Use of the Data Booklet is relevant to this question.
A student carried out an experiment to determine the enthalpy change for the combustion of
methanol.
The following results were obtained by the student.
start temperature of the water
20 °C
final temperature of the water
53 °C
mass of alcohol burner before burning
259.65 g
mass of alcohol burner after burning
259.15 g
mass of glass beaker plus water
150.00 g
50.00 g
mass of glass beaker
How much of the heat energy produced by the burning of methanol went into the water?
A
209 J
B
13 794 J
C
20 691 J
D
22 154 J
21 A metal, X, reacts with water to produce a colourless solution which gives a white precipitate
when mixed with aqueous sulfuric acid.
What is metal X?
A
barium
B
magnesium
C
potassium
D
sodium
22 Which stage in the free radical substitution of ethane by chlorine will have the lowest activation
energy?
A
Cl 2 → 2Cl ●
B
Cl ● + C2H6 → C2H5● + HCl
C
C2H5● + Cl 2 → C2H5Cl + Cl ●
D
Cl ● + C2H5● → C2H5Cl
–1
23 The value of the third ionisation energy of aluminium is 2740 kJ mol .
Which correctly represents this statement?
A
Al (g) → Al 3+(g) + 3e–
∆Ho = –2740 kJ mol–1
B
Al 2+(g) → Al 3+(g) + e–
∆Ho = –2740 kJ mol–1
C
Al (g) → Al 3+(g) + 3e–
∆Ho = +2740 kJ mol–1
D
Al 2+(g) → Al 3+(g) + e–
∆Ho = +2740 kJ mol–1
24 Red lead oxide, Pb3O4, is used in metal priming paints. It can be made by heating PbO in air.
6PbO(s) + O2(g) → 2Pb3O4(s)
Which two values are needed to calculate the enthalpy change for this reaction?
A
enthalpy change of atomisation of O2 and enthalpy change of formation of Pb3O4
B
enthalpy change of formation of O2 and enthalpy change of formation of Pb3O4
C
enthalpy change of formation of PbO and enthalpy change of atomisation of O2
D
enthalpy change of formation of PbO and enthalpy change of formation of Pb3O4
25 The equation for a reaction is shown.
H2(g) +
1
2
O2(g) → H2O(l) ; ∆H = x kJ mol–1
Which pair of descriptions is fully correct for this reaction?
type(s) of enthalpy change
value of x
A
formation only
positive
B
formation only
negative
C
combustion, formation
positive
D
combustion, formation
negative
26 Propanone has the molecular formula C3H6O.
The enthalpy change of combustion of hydrogen is –286 kJ mol–1.
The enthalpy change of combustion of carbon is –394 kJ mol–1.
The enthalpy change of combustion of propanone is –1786 kJ mol–1.
Using this information, what is the enthalpy change of formation of propanone?
27
A
–1106 kJ mol–1
B
–540 kJ mol–1
C
–254 kJ mol–1
D
+1106 kJ mol–1
In the table below,
• ‘+’ means that this type of standard enthalpy change can only have positive values,
• ‘–’ means that this type of standard enthalpy change can only have negative values,
• ‘+ / –’ means that either positive or negative values are possible.
Which row is correct?
atomisation
formation
solution
A
+
+
+/–
B
+
+/–
/–
C
–
+/–
–
D
–
–
+
28 A student calculated the standard enthalpy change of formation of ethane, C2H6, using a method
based on standard enthalpy changes of combustion.
He used correct values for the standard enthalpy change of combustion of ethane
(–1560 kJ mol–1) and hydrogen (–286 kJ mol–1) but he used an incorrect value for the standard
enthalpy change of combustion of carbon. He then performed his calculation correctly. His final
answer was –158 kJ mol–1.
What did he use for the standard enthalpy change of combustion of carbon?
A
–1432 kJ mol–1
B
–860 kJ mol–1
C
–430 kJ mol–1
D
–272 kJ mol–1
29 The enthalpy change of the neutralisation given below is –114 kJ mol–1.
2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)
By using this information, what is the most likely value for the enthalpy change of the following
neutralisation?
Ba(OH)2(aq) + 2HCl(aq) → BaCl2(aq) + 2H2O(l)
A
–57 kJ mol–1
B
–76 kJ mol–1
C
–114 kJ mol–1
D
–228 kJ mol–1
30 Titanium occurs naturally as the mineral rutile, TiO2. One possible method of extraction of
titanium is to reduce the rutile by heating with carbon.
TiO2(s) + 2C(s) → Ti(s) + 2CO(g)
The standard enthalpy changes of formation of TiO2(s) and CO(g) are –940 kJ mol–1 and
–110 kJ mol–1 respectively.
What is the standard enthalpy change of this reaction?
A
–830 kJ mol–1
B
–720 kJ mol–1
C
+720 kJ mol–1
D
+830 kJ mol–1
31 Which reaction has an enthalpy change equal to the standard enthalpy change of formation of
propane?
A
3C(g) + 4H2(g) → C3H8(g)
B
3C(g) + 8H(g) → C3H8(g)
C
3C(s) + 4H2(g) → C3H8(g)
D
3C(s) + 4H2(g) → C3H8(l)
32 50 cm3 of 2.50 mol dm–3 hydrochloric acid was placed in a polystyrene beaker of negligible heat
capacity. Its temperature was recorded and then 50 cm3 of 2.50 mol dm–3 NaOH at the same
temperature was quickly added, with stirring. The temperature rose by 17 °C.
The resulting solution may be considered to have a specific heat capacity of 4.2 J g–1 K–1.
What is an approximate value for the molar enthalpy change of neutralisation of hydrochloric acid
and sodium hydroxide from this experiment?
A
−(50 x 4.2 x17)
1
J mol −
(0.050 x 2.5)
B
−(50 x 4.2 x17)
1
J mol −
(0.10 x 2.5)
C
−(100 x 4.2 x17)
1
J mol −
(0.050 x 2.5)
D
−(100 x 4.2 x17)
1
J mol −
(50 x 2.5)
33 The standard enthalpy changes of formation of HCl and HI are –92 kJ mol–1 and +26 kJ mol–1
respectively.
Which statement is most important in explaining this difference?
A
Chlorine is more electronegative than iodine.
B
The activation energy for the H2 + Cl2 reaction is much less than that for the H2 + I2 reaction.
C
The bond energy of HI is smaller than the bond energy of HCl.
D
The bond energy of I2 is smaller than the bond energy of Cl2.
34 The standard enthalpy change for the reaction
2NF3(g) → 2N(g) + 6F(g)
is ∆H o = +1668 kJ
What is the bond energy of the N–F bond?
A
–556 kJ mol–1
B
–278 kJ mol–1
C
+278 kJ mol–1
D
+556 kJ mol–1
35 Butanedioate ions can be dehydrogenated to form trans-butenedioate ions. The enzyme
fumarase speeds up this reaction.
Why does fumarase speed up this reaction?
A
Fumarase is a protein.
B
Fumarase is effective at body temperature.
C
Fumarase lowers the activation energy of the dehydrogenation reaction.
D
The enzyme fumarase is specific for this dehydrogenation reaction.
36 Given the following enthalpy changes,
I2(g) + 3Cl2(g) → 2ICl3(s)
I2(s) → I2(g)
∆Ho = –214 kJ mol–1
∆Ho = +38 kJ mol–1
What is the standard enthalpy change of formation of iodine trichloride, ICl3(s)?
A
+176 kJ mol–1
B
–88 kJ mol–1
C
–176 kJ mol–1
D
–214 kJ mol–1
37 Methanol may be prepared by the reaction between carbon monoxide and hydrogen.
CO(g) + 2H2(g) → CH3OH(g)
The relevant average bond energies are given below.
E(C≡O) 1077 kJ mol–1
E(C–O)
360 kJ mol–1
E(C–H)
410 kJ mol–1
E(H–H)
436 kJ mol–1
E(O–H)
460 kJ mol–1
What is the enthalpy change of this reaction?
A
–537 kJ mol–1
B
–101 kJ mol–1
C
+101 kJ mol–1
D
+537 kJ mol–1
38 The reaction pathway diagram below illustrates the energies of reactants, products and the
transition state of a reaction.
transition state
E1
energy
E2
reactants
E3
products
reaction coordinate
Which expression represents the activation energy of the forward reaction?
A
E1 – E 2
B
E1 – E 3
C
E2 – E 3
D
(E1 – E2) – (E2 – E3)
39 Equations involving four enthalpy changes are shown.
Na(g) → Na+(g) + e–
∆H = W
Na(g) → Na2+(g) + 2e– ∆H = X
Na(s) → Na(g)
∆H = Y
Na(s) → Na2+(g) + 2e– ∆H = Z
What is the second ionisation energy of sodium?
A
B
2W
X–W
C
Y–W
D
Z–Y
40 Enthalpy changes of combustion can be used to determine enthalpy changes of formation. The
following equation represents the enthalpy change of formation of butane.
4C(s) + 5H2(g) → C4H10(g)
By using the following standard enthalpy of combustion data, what is the value of the standard
enthalpy change of formation,
, for this reaction?
A
–5883 kJ mol–1
B
–129 kJ mol–1
C
+129 kJ mol–1
D
+2197 kJ mol–1
41 Which equation represents the change corresponding to the enthalpy change of atomisation of
iodine?
A
B
C
D
1
I (g)
2 2
→ I(g)
I2(g) → 2I(g)
1
I (s)
2 2
→ I(g)
I2(s) → 2I(g)
42 The first stage in the industrial production of nitric acid from ammonia can be represented by the
following equation.
4NH3(g) + 5O2(g)
4NO(g) + 6H2O(g)
Using the following standard enthalpy change of formation data, what is the value of the standard
enthalpy change, ∆Ho, for this reaction?
A
+905.2 kJ mol–1
B
–105.4 kJ mol–1
C
–905.2 kJ mol–1
D
–1274.0 kJ mol–1
43 Four reactions of the type shown are studied at the same temperature.
X (g) + Y (g) → Z (g)
Which is the correct reaction pathway diagram for the reaction that would proceed most rapidly
and with the highest yield?
A
B
energy
energy
reactant
product
reactant
C
product
D
energy
energy
reactant
product
reactant
product
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
1, 2 and 3
are
correct
1 and 2
only are
correct
C
D
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
44 Which names can be applied to the enthalpy change of the reaction shown?
H2(g) +
1
enthalpy change of formation
2
enthalpy change of combustion
3
enthalpy change of hydration
1
O2(g)
2
→ H2O(l)
45 The diagram shows the reaction pathway for a reversible reaction.
energy
/ kJ mol–1
90
30
extent of reaction
Which statements are correct?
1
The enthalpy change for the backward reaction is +90 kJ mol–1.
2
The forward reaction is exothermic.
3
The enthalpy change for the forward reaction is –30 kJ mol–1.
46 An energy profile diagram is shown.
W
reactants
Y
enthalpy, H
Z
X
products
progress of reaction
What do the labels on the diagram represent?
1
W = ∆H of the forward reaction, Y = Ea of the backward reaction
2
Z = ∆H of the backward reaction, Y = Ea of the backward reaction
3
X = ∆H of the forward reaction, W = Ea of the forward reaction
47 A reaction pathway diagram is shown.
energy
reaction pathway
Which reactions would have such a profile?
1
(CH3)3CBr + NaOH → (CH3)3COH + NaBr
2
CH3CH2Br + NaOH → CH3CH2OH + NaBr
3
(CH3)3CCH2CH2Cl + 2NH3 → (CH3)3CCH2CH2NH2 + NH4Cl
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Redox
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Multiple Choice
Booklet
Question Paper 1
Time Allowed:
51 minutes
Score:
/42
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
In oxygen difluoride, OF2, fluorine has an oxidation number of –1. OF2 will react with sulfur
dioxide according to the following equation.
OF2 + SO2 → SO3 + F2
What is oxidised and what is reduced in this reaction?
2 Chlorate(V) ions, Cl O3–, are produced in the redox reaction between chlorine and hot aqueous
sodium hydroxide. Oxidation numbers can be used to help balance the equation for this reaction.
What will be the values of coefficients v, x and y in the balanced equation?
vCl 2(g) + wOH–(aq) → xCl –(aq) + yCl O3–(aq) + zH2O(l)
3
In which reaction does an element have the largest change in oxidation number?
A
Cr2O72– + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O
B
3OCl – → Cl O3– + 2Cl –
C
5Fe2+ + MnO4– + 8H+ → 5Fe3+ + Mn2+ + 4H2O
D
PbO2 + Sn2+ + 4H+ → Sn4+ + Pb2+ + 2H2O
4 Redox reactions occur very frequently in the chemistry of Group VII.
Which statement is correct?
5
A
Chlorine will oxidise bromide ions but not iodide ions.
B
Fluorine is the weakest oxidising agent out of F2, Cl 2, Br2 and I2.
C
Iodide ions are the weakest reducing agent out of F –, Cl –, Br – and I –.
D
When chlorine reacts with water, chlorine is both oxidised and reduced.
In which reaction is the species in bold acting as an oxidising agent?
A
2Ca + O2 → 2CaO
B
Cr2O72– + 8H+ + 3SO32– → 2Cr3+ + 4H2O + 3SO42–
C
Mg + Fe2+ → Mg2+ + Fe
D
SO2 + 2H2O + 2Cu2+ + 2Cl – → H2SO4 + 2H+ + 2CuCl
6 When solid sodium iodide reacts with concentrated sulfuric acid, the products include NaHSO4,
H2S, SO2 and S.
In the formation of which product has the oxidation state of sulfur changed by a value of 8?
A
H2S
B
NaHSO4
C
S
D
SO2
7
In which reaction does hydrogen behave as an oxidising agent?
A
H2 + Cl 2 → 2HCl
B
C2H4 + H2 → C2H6
C
N2 + 3H2 → 2NH3
D
2Na + H2 → 2NaH
8 Chlorine gas reacts with cold aqueous sodium hydroxide. It can also react with hot aqueous
sodium hydroxide.
What are the oxidation numbers of chlorine in the products of these reactions?
9
Aluminium carbide, Al 4C3, reacts readily with aqueous sodium hydroxide. The two products of the
reaction are NaAl O2 and a hydrocarbon. Water molecules are also involved as reactants.
What is the formula of the hydrocarbon?
A
CH4
B
C2H6
C
C3H8
D
C6H12
10 What is the ionic equation for the reaction between aqueous sodium carbonate and dilute nitric
acid?
A
2HNO3(aq) + CO32–(aq) → H2O(l) + CO2(g) + 2NO3–(aq)
B
2H+(aq) + CO32–(aq) → CO2(g) + H2O(l)
C
2HNO3(aq) + Na2CO3(aq) → 2NaNO3(aq) + CO2(g) + H2O(l)
D
2HNO2(aq) + CO32–(aq) → H2O(l) + CO2(g) + 2NO2–(aq)
11 Solutions containing chlorate(I) ions are used as household bleaches and disinfectants. These
solutions decompose on heating as shown.
3Cl O– → Cl O3– + 2Cl –
Which oxidation state is shown by chlorine in each of these three ions?
12 What happens when iodine solution is added to a solution of sodium bromide?
A
A reaction occurs without changes in oxidation state.
B
Bromide ions are oxidised, iodine atoms are reduced.
C
Bromide ions are reduced, iodine atoms are oxidised.
D
No reaction occurs.
13 What happens when bromine solution is added to a solution of sodium iodide?
A
A reaction occurs without changes in oxidation state.
B
Bromine atoms are oxidised, iodide ions are reduced.
C
Bromine atoms are reduced, iodide ions are oxidised.
D
No reaction occurs.
14 In the redox reaction shown, how do the oxidation states of vanadium and sulfur change?
VO2+ + SO2 → V3+ + SO42–
occur when potassium iodate(V), KIO3, in hydrochloric acid solution
15 The following half reactions
oxidises iodine to ICl 2–.
IO3– + 2Cl – + 6H+ + 4e– → ICl 2– + 3H2O
I2 + 4Cl – → 2ICl 2– + 2e–
What is the ratio of IO3– to I2 in the balanced chemical equation for the overall reaction?
A
1:1
B
1:2
C
1:4
D
2:1
16 In which reaction does a single nitrogen atom have the greatest change in oxidation number?
A
4NH3 + 5O2 → 4NO + 6H2O
B
3NO2 + H2O → 2HNO3 + NO
C
2NO + O2 → 2NO2
D
4NH3 + 6NO → 5N2 + 6H2O
17 Solid potassium halides react with concentrated sulfuric acid, according to the following
equations.
reaction 1
2KCl + H2SO4 → K2SO4 + 2HCl
reaction 2
2KBr + 2H2SO4 → K2SO4 + SO2 + Br2 + 2H2O
reaction 3
8KI + 5H2SO4 → 4K2SO4 + H2S + 4I2 + 4H2O
What is the largest change in the oxidation number of sulfur in each of these reactions?
18 Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this
reaction proceeds?
A
–2, –4
B
+2, +6
C
+4, –6
D
+4, –4
19 A 10 cm3 sample of 0.30 mol dm–3 Tl +NO3– required 20 cm3 of 0.10 mol dm–3 acidified NH4VO3 to
oxidise it to Tl 3+ in solution. Vanadium is the only element reduced in this reaction.
What is the oxidation number of the vanadium in the reduced form?
A
+1
B
+2
C
+3
D
+4
20 The oxide of titanium, TiO2, is used as a ‘whitener’ in toothpaste. It is obtained from the ore
iron(II) titanate, FeTiO3.
What is the change, if any, in the oxidation number (oxidation state) of titanium in the reaction
FeTiO3 → TiO2?
A
It is oxidised from +3 to +4.
B
It is reduced from +3 to +2.
C
It is reduced from +6 to +4.
D
There is no change in the oxidation number.
21 In the treatment of domestic water supplies, chlorine is added to the water to form HCl O.
Cl 2(aq) + H2O(I) → H+(aq) + Cl –(aq) + HCl O(aq)
The HCl O reacts further to give Cl O– ions.
HCl O(aq) + H2O(I) → H3O+(aq) + Cl O–(aq)
Both HCl O and Cl O– kill bacteria by oxidation.
What is the overall change in oxidation number of chlorine when forming the Cl O– ion from the
aqueous chlorine?
A
–1
B
0
C
+1
D
+2
22 In which substance does nitrogen exhibit the highest oxidation state?
A
NO
B
N2O
C
N2O4
D
NaNO2
23 Chlorine shows oxidation states ranging from –1 to +7 in its compounds.
What are the reagent(s) and conditions necessary for the oxidation of elemental chlorine into a
compound containing chlorine in the +5 oxidation state?
A
AgNO3(aq) followed by NH3(aq) at room temperature
B
concentrated H2SO4 at room temperature
C
cold dilute NaOH(aq)
D
hot concentrated NaOH(aq)
24 In which reaction does an element undergo the largest change in oxidation state?
A
Cl 2 + 2OH– → OCl – + Cl – + H2O
B
3Cl 2 + 6OH– → Cl O3– + 5Cl – + 3H2O
C
Cr2O72– + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O
D
3MnO42– + 4H+ → MnO2 + 2MnO4– + 2H2O
25 The reaction between KI and concentrated H2SO4 is a redox reaction.
5H2SO4 + 8KI → 4K2SO4 + 4I2 + H2S + 4H2O
What is the change in oxidation state of the element that is reduced?
A
1
B
C
4
D
6
8
26 In flooded soils, like those used for rice cultivation, the oxygen content is low. In such soils,
anaerobic bacteria cause the loss of nitrogen from the soil as shown in the following sequence.
In which step is the change in oxidation number (oxidation state) of nitrogen different to the
changes in the other steps?
A
NO3–(aq)
B
NO2–(aq)
C
NO(g)
D
N2O(g)
N2(g)
27 Which compound contains two different elements with identical oxidation states?
A
HCl O
B
Mg(OH)2
C
Na2SO4
D
NH4Cl
28 A student observed the reactions when sodium chloride and sodium iodide were each reacted
separately with concentrated sulfuric acid and with concentrated phosphoric acid. The
observations are recorded in the table.
sodium chloride
sodium iodide
conc. H2SO4
colourless acidic gas formed
purple vapour formed
conc. H3PO4
colourless acidic gas formed
colourless acidic gas formed
Which deduction can be made from these observations?
A
Concentrated phosphoric acid is a stronger oxidising agent than concentrated sulfuric acid.
B
Concentrated phosphoric acid is a stronger oxidising agent than iodine.
C
Concentrated sulfuric acid is a stronger oxidising agent than chlorine.
D
Concentrated sulfuric acid is a stronger oxidising agent than iodine.
29 When chlorine and aqueous sodium hydroxide are heated together the following overall reaction
occurs.
3Cl 2(aq) + 6NaOH(aq) → 5NaCl (aq) + NaCl O3(aq) + 3H2O(l)
What are the oxidation numbers for chlorine in each of the following species?
30 The following equations the letters W, X, Y and Z all represent whole numbers.
When correctly balanced, which equation requires one of letters W, X, Y or Z to be 5?
A
WC3H7COOH + XO2 → YCO2 + ZH2O
B
WC4H8 + XO2 → YCO2 + ZH2O
C
WH3PO4 + XNaOH → YNa2HPO4 + ZH2O
D
WNH3 + XO2 → YN2 + ZH2O
31 The amount of titanium dioxide in an ore can be determined by using the following reaction.
3TiO2 + 4BrF3 → 3TiF4 + 2Br2 + 3O2
Which element increases in oxidation number in this reaction?
A
bromine
B
fluorine
C
oxygen
D
titanium
32 Sodium iodide reacts with concentrated sulfuric acid. The equation which represents one of the
reactions that takes place is shown.
8NaI + 9H2SO4 → 8NaHSO4 + 4I2 + H2S + 4H2O
Which species has been oxidised in this reaction?
A
H+
B
I–
C
Na+
D
SO42–
33 Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this
reaction proceeds?
A
–2, –4
B
+2, +6
C
+4, –6
D
+4, –4
34 How does concentrated sulfuric acid behave when it reacts with sodium chloride?
A
as an acid only
B
as an acid and oxidising agent
C
as an oxidising agent only
D
as a reducing agent only
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
#
1, 2 and 3
are
correct
1 and 2
only are
correct
$
2 and 3
only are
correct
D
1 only
is
correct
35 Which of these reactions are redox reactions?
1
6NO(g) + 4NH3(g) → 5N2(g) + 6H2O(g)
2
2SO2(g) + O2(g) → 2SO3(g)
3
SO3(g) + H2O(g) → H2SO4(g)
36 When dilute acid is added to an aqueous solution containing nitrite ions, NO2–, a mixture of gases
is produced.
2H+(aq) + 2NO2–(aq) → H2O(l) + NO(g) + NO2(g)
Which statements correctly describe the process?
1
Some nitrogen atoms are oxidised and some nitrogen atoms are reduced.
2
The H+(aq) ion is oxidised by NO2–(aq).
3
The H+(aq) ion acts as a catalyst.
37 Which pairs of reagents will react together in a redox reaction?
1
CH3CHO + Fehling’s reagent
2
C2H4 + Br2(aq)
3
CH4 + Cl 2(g)
38 Which pairs of reagents will take part in a redox reaction?
1
CH3COCH3 + Tollens’ reagent
2
CH3CH2CHO + Fehling’s reagent
3
CH3CH=CH2 + Br2
39 Which pairs of reagents will take part in a redox reaction under suitable conditions?
1
CH3(CH2)4CHO + Tollens’ reagent
2
CH3(CH2)4CH3 + Br2
3
CH3CO(CH2)4CH3 + Fehling’s reagent
40 Many crude oils contain H2S. During refining, by the Claus process, the H2S is converted into
solid sulfur, which is then removed.
reaction I
2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
reaction II
2H2S(g) + SO2(g) → 2H2O(l) + 3S(s)
Which statements about the Claus process are correct?
1
H2S is oxidised in reaction I.
2
SO2 oxidises H2S in reaction II.
3
Hydrogen is oxidised in reaction II.
41 In a solution that contains both Br2 and Cl 2, a process takes place that produces BrO3– ions.
The process is represented by the following equations.
equation 1
Br2 + H2O → HBr + HBrO
equation 2
3HBrO + Cl 2 → 2Cl – + BrO3– + Br2 + 3H+
Which statements about these reactions are correct?
1
Chlorine is reduced in equation 2.
2
Bromine is oxidised in both equation 1 and equation 2.
3
Bromine is reduced in both equation 1 and equation 2.
42 Which pairs of reagents will react together in a redox reaction?
1
CH3CHO + Fehling’s reagent
2
CH4 + Cl 2
3
CH3COCH3 + Tollens’ reagent
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Redox
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Theory
Booklet
Mark Scheme 1
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) (+)1; (+)2; (+)3; (+)4
O.N. corresponds to the no. of electrons in outer/valence shell/lost
[1]
[1]
(b) PCl5 fizzes or white/misty fumes or heat evolved
PCl5 + 4H2O → H3PO4 + 5HCl or PCl5 + 3H2O → HPO3 + 5HCl
(allow partial hydrolysis: PCl5 + H2O → POCl3 + 2HCl)
[1]
[1
(c) (i) P = 30.4/31 = 0.98 Cl = 69.6/35.5 = 1.96
Thus E.F = PCl2
Mr(PCl2) = 102, so 2 × PCl2 = 204 ≈ 200, so M.F. = P2Cl4
[1]
[1]
[1]
(ii)
Cl
Cl
P
Cl
(ignore lone pairs on Cl)
P
[1]
Cl
(iii) O.N. = (+)2
(iv) (HO)2P-P(OH)2 or H(HO)P(=O)-P(=O)(OH)H
Allow HO-P-OH or HO-P=O
│
H
[1]
ecf from structure in (ii) [1]
[Total: 10]
2
(a) Cr3+:
Mn2+:
1 22s22p6 3s2 3p6 3d3
1 22s22p6 3s2 3p6 3d5
[1]
[1]
[2]
(b) (i) Any two from
• H+ is on the oxidant/L.H. side of each of the ½-equations, or H+ is a reactant
• (increasing [H+]) will make Eo more positive
• (increasing [H+]) will drive the reaction over to the R.H./reductant side or forward
direction
[1] +
(ii) KMnO4:
K2Cr2O7
Purple/violet to colourless (allow very pale pink)
Orange to green
[1]
[1]
[4]
(c) (i) MnO2 + SO2 → MnSO4 (or Mn2+ + SO42–)
[1
manganese changes/is reduced from +4 to +2
sulfur changes/is oxidised from +4 to +6
[1]
[1]
(ii) No effect, because H+ does not appear in the overall equation or its effect on the
MnO2/Mn2+ change is cancelled out by its effect on the SO2/SO42– change
[1]
[4]
(d) (i) MnO2 + 4H+ + Sn2+ → Mn2+ + 2H2O + Sn4+
(ii) n(MnO4–) = 0.02 × 18.1/1000 = 3.62 × 10–4 mol
n(Sn2+) = 3.62 × 10–4 × 5/2 = 9.05 × 10–4 mol
n(Sn2+) that reacted with MnO2 = (20 – 9.05) × 10–4 = 1.095 × 10–3 mol
reaction is 1:1, so this is also n(MnO2)
mass of MnO2 = 1.095 × 10–3 × (54.9+16+16) = 0.0952 g
⇒ 95% – 96%; 2 or more s.f.
[1]
[1]
[1]
[1]
[1]
[1]
[6]
[Total: 16]
3
(a
the energy required to remove one electron from each atom (1)
in one mole of gaseous atoms (1)
or
the enthalpy change in kJ mol-1 for (1)
M(g) → M+(g) + e– (1)
(b)
b) (
first ionisation energy decreases down Group 1 (1)
outermost electron is further from nucleus
or has greater shielding (1)
(ii) outermost electron experiences less attraction
or formation of M+ cation becomes easier down Group 1 (1)
(c)
c) (
[2]
n(Li) =
[3]
0.83
= 0.12 (1)
6.9
(ii) 2 mol Li → 1 mol H2
1× 0.12
0.12 mol Li →
= 0.06 mol H2 (1)
2
volume of H2 = 0.06 × 24.0 = 1.44dm3 (1)
(iii) 2 mol Li → 2 mol LiOH
0.12 mol Li → 0.12 mol LiOH in 0.50 dm3 (1)
0.12 × 1
[LiOH] =
= 0.24 mol dm-3 (1)
0.50
[5]
(d) sodium burns with a yellow flame
or white solid formed
or colour of chlorine disappears (1)
2Na + Cl2 → 2NaCl (1)
[2]
[Total: 12]
4
(a) 1
S + O2 → SO2 (1)
2
2SO2 + O2
3
SO3 + H2O → H2SO4 or
SO3 + H2SO4 → H2S2O7 (1)
(b) condition 1
condition 2
2SO3
equation (1)
equilibrium sign (1)
[4]
400 – 600 °C (650 – 900K) (1)
1–10 atm/just above atmospheric pressure
allow equivalent pressure units (1)
vanadium pentoxide/vanadium(V) oxide/V2O5 (1)
[3]
(c) fertilisers/phosphates/ammonium sulfate or
lead/acid batteries or paints/pigments or dyestuffs or
steel pickling or metal treatment or detergents or explosives (1)
[1]
condition 3
(d) (i) 2H2S + 3O2 → 2SO2 + 2H2O (1)
(ii) H2S –2 SO2 +4
S 0
all three (1)
SO2 because the oxidation number of S is reduced (1)
[3]
(e) (i) 2NO + O2 → 2NO2 (1)
SO2 + NO2 → SO3 + NO (1)
SO3 + H2O → H2SO4
final product must be H2SO4 (1)
(ii) corrosion of buildings or
dissolving of Al 3+ ions from soil or
pollution of rivers/killing aquatic life or
making soil acidic/killing trees/corrosion of metals (1)
(f) it is a reducing agent/inhibits oxidation (1)
[4]
[1]
[Total: 16]
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Redox
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Theory
Booklet
Question Paper 1
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) State and explain the variation in the oxidation numbers of the chlorides of the elements
Na, Mg, Al and Si.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
(b) Describe the reaction of phosphorus(V) chloride with water, and write an equation for
the reaction.
..........................................................................................................................................
...................................................................................................................................... [2]
(c) When microwave radiation is passed through phosphorus(III) chloride, PCl3, at low
pressure, a new chloride of phosphorus, B, is formed.
B contains 69.6% by mass of chlorine and 30.4% by mass of phosphorus, and its Mr is
approximately 200.
(i)
Calculate the empirical and molecular formulae of B.
..................................................................................................................................
(ii)
Assuming phosphorus and chlorine show their typical valencies, draw the displayed
formula of B, showing all bonds and lone pairs.
..................................................................................................................................
(iii)
Calculate the oxidation number of phosphorus in B.
..................................................................................................................................
(iv)
One mole of B reacts with four moles of water.
Suggest the structure of the phosphorus-containing product of this reaction.
..................................................................................................................................
[6]
[Total: 10]
2
(a) Complete the electronic configurations of the following ions.
Cr3+:
1s22s22p6..........................................
Mn2+:
1s22s22p6..........................................
[2]
(b) Both KMnO4 and K2Cr2O7 are used as oxidising agents, usually in acidic solution.
(i)
Use information from the Data Booklet to explain why their oxidising power increases
as the [H+(aq)] in the solution increases.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
What colour changes would you observe when each of these oxidising agents is
completely reduced?
•
•
KMnO4
K2Cr2O7
from .......................................
to ....................................
from........................................
to .....................................
[4]
(c) Manganese(IV) oxide, MnO2, is a dark brown solid, insoluble in water and dilute acids.
Passing a stream of SO2(g) through a suspension of MnO2 in water does, however,
cause it to dissolve, to give a colourless solution.
(i)
Use the Data Booklet to suggest an equation for this reaction, and explain what
happens to the oxidation states of manganese and of sulfur during the reaction.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
The pH of the suspension of MnO2 is reduced.
Explain what effect, if any, this would have on the extent of this reaction.
..................................................................................................................................
..................................................................................................................................
[4]
(d) The main ore of manganese, pyrolusite, is mainly MnO2. A solution of SnCl2 can be used
to estimate the percentage of MnO2 in a sample of pyrolusite, using the following method.
•
A known mass of pyrolusite is warmed with an acidified solution containing a known
amount of SnCl2.
•
The excess Sn2+(aq) ions are titrated with a standard solution of KMnO4.
In one such experiment, 0.100 g of pyrolusite was warmed with an acidified solution
containing 2.00 × 10–3 mol Sn2+. After the reaction was complete, the mixture was
titrated with 0.0200 mol dm–3 KMnO4, and required 18.1 cm3 of this solution to reach the
end point.
The equation for the reaction between Sn2+(aq) and MnO4–(aq) is as follows.
2MnO4– + 5Sn2+ + 16H+
(i)
2Mn2+ + 5Sn4+ + 8H2O
Use the Data Booklet to construct an equation for the reaction between MnO2 and
Sn2+ ions in acidic solution.
..................................................................................................................................
(ii)
Calculate the percentage of MnO2 in this sample of pyrolusite by the following steps.
•
number of moles of MnO4– used in the titration
•
number of moles of Sn2+ this MnO4– reacted with
•
number of moles of Sn2+ that reacted with the 0.100 g sample of pyrolusite
•
number of moles of MnO2 in 0.100 g pyrolusite. Use your equation in (i).
•
mass of MnO2 in 0.100 g pyrolusite
•
percentage of MnO2 in pyrolusite
percentage = ..................................................%
[6]
[Total: 16]
3
The alkali metals are a series of six elements in Group I of the Periodic Table. The
first ionisation energy of these elements shows a marked trend as the Group is descended.
(a) Define the term first ionisation energy.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(b) (i)
State and explain the trend in first ionisation energy as Group I is descended.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Suggest how this trend helps to explain the increase in the reactivity of the elements
as the Group is descended.
..................................................................................................................................
..................................................................................................................................
[3]
(c) In a redox reaction, 0.83 g of lithium reacted with water to form 0.50 dm3 of aqueous
lithium hydroxide.
2Li(s) + 2H2O(l)
(i)
2LiOH(aq) + H2(g)
Calculate the amount, in moles, of lithium that reacted.
(ii)
Calculate the volume of hydrogen produced at room temperature and pressure.
(iii)
Calculate the concentration, in mol dm–3, of the LiOH(aq) formed.
[5]
(d) When heated in chlorine, all of the alkali metals react to form the corresponding
chloride.
Describe what you see when sodium is heated in chlorine and write a balanced equation
for the reaction.
description
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
equation
..........................................................................................................................................
[2]
[Total: 12]
4
Sulfur and its compounds are found in volcanoes, in organic matter and in minerals.
Sulfuric acid, an important industrial chemical, is manufactured from sulfur by the Contact
process.
The Contact process may be considered to be a three-stage process in which sulfur is
converted into sulfuric acid. Each stage consists of a single chemical reaction.
(a) Write a balanced equation for each of these reactions in the correct sequence.
to indicate that the reaction is an equilibrium.
Where appropriate, use
first reaction .....................................................................................................................
second reaction ...............................................................................................................
third reaction ................................................................................................................ [4]
(b) Give three different operating conditions that are used in the second stage.
condition 1 .......................................................................................................................
condition 2 .......................................................................................................................
condition 3 ................................................................................................................... [3]
(c) State one large scale use of sulfuric acid.
...................................................................
[1]
(d) Most of the sulfur that is used in the Contact process is recovered from sulfur compounds
present in crude oil and natural gas by using the Claus process.
(i)
In this process, about one third of the hydrogen sulfide, H2S, present in the oil or
gas, is converted into sulfur dioxide, SO2.
Balance the equation for this reaction.
.....H2S
+ .....O2
.....SO2
+
2O
(ii)
The SO2 formed is then reacted catalytically with the remaining H2S, producing
sulfur and water.
2H2S + SO2
3S + 2H2O
What are the oxidation numbers of each of the sulfur-containing substances in this
reaction?
H2S.........
SO2 ..........
S .......
Which substance is reduced? Explain your answer.
substance .............
explanation ........................................................................................................... [3]
The sulfur present in crude oil is removed in order to prevent the formation of sulfur dioxide
when fuels such as petrol (gasoline) or diesel fuel are burned in internal combustion
engines.
Other substances that may be present in the exhaust gases of motor vehicles include CO,
CO2, NO/NO2, and unburnt hydrocarbons.
The emission of sulfur dioxide can produce ‘acid rain’.
(e) (i)
Outline, with the aid of equations, how acid rain is formed from the exhaust gases
of motor vehicles.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
State one environmental effect of acid rain.
.............................................................................................................................. [4]
(f)
Sulfur dioxide is used to preserve dried fruits and vegetables.
What chemical property of SO2 enables it to be used as a food preservative?
...................................................................................................................................... [1]
[Total: 16]
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Redox
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Multiple Choice
Booklet
Question Paper 2
Time Allowed:
29 minutes
Score:
/24
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this
reaction proceeds?
A
–2, –4
B
C
+2, +6
+4, –6
D
+4, –4
2 How does concentrated sulfuric acid behave when it reacts with sodium chloride?
A
as an acid only
B
as an acid and oxidising agent
C
as an oxidising agent only
D
as a reducing agent only
3 In aqueous solution, the acid HIO disproportionates according to the following equation where m,
n, p and q are simple whole numbers in their lowest ratios.
mHIO → nI2 + pHIO3 + qH2O
This equation can be balanced using oxidation numbers.
What are the values for n and p?
4 Which pair of reagents will take part in a redox reaction?
5
A
CH3CH2OH + concentrated H2SO4
B
CH3CHO + Tollens’ reagent
C
CH3CO2C2H5 + dilute H2SO4
D
CH3COCH3 + Fehling’s solution
Sulfur dioxide, SO2, is added to wines to prevent oxidation of ethanol by air. To determine the
amount of SO2, a sample of wine is titrated with iodine, I2. In this reaction, one mole of SO2 is
oxidised by one mole of I2.
What is the change in oxidation number of sulfur in this reaction?
A
+2 to +4
B
+2 to +6
C
+4 to +5
D
+4 to +6
6 In black and white photographic film, light converts silver chloride into metallic silver. After the film
has been developed, the unreacted silver chloride is removed by reaction with sodium thiosulfate
to produce a ‘fixed’ negative.
AgCl + 2Na2S2O3 → 4Na+ + Cl – + [Ag(S2O3)2]3–
What is the function of the thiosulfate ion?
A
to make the silver ions soluble
B
to oxidise the silver ions
C
to oxidise the silver metal
D
to reduce the silver ions
7 Deposits of ammonium compounds have been discovered in areas of high atmospheric pollution.
They are believed to arise from the following reaction.
SO3 + H2O + 2NH3 → (NH4)2SO4
What does not occur in this reaction?
A
acid / base neutralisation
B
dative bond formation
C
ionic bond formation
D
oxidation / reduction
8
Which conversion involves a reduction of chromium?
A
CrO 2−
4 → CrO3
B
2−
CrO2−
4 → Cr2O7
C
CrO2Cl2 → CrO2−
4
D
CrO2Cl2 → Cr2O3
9 In an historically famous experiment Wöhler heated ‘inorganic’ ammonium cyanate in the
absence of air. The only product of the reaction was ‘organic’ urea, CO(NH2)2. No other products
were formed in the reaction.
What is the formula of the cyanate ion present in ammonium cyanate?
A
CNO–
B
CNO2–
C
CO–
D
NO–
10 Photochromic glass, used for sunglasses, darkens when exposed to bright light and becomes
more transparent again when the light is less bright. The depth of colour of the glass is related to
the concentration of silver atoms.
The following reactions are involved.
reaction 1
Ag+ + Cl –
reaction 2
Cu+ + Cl → Cu2+ + Cl –
reaction 3
Cu2+ + Ag → Cu+ + Ag+
Ag + Cl
Which statement about these reactions is correct?
A
Cu+ and Cu2+ ions act as catalysts.
B
Cu+ ions act as an oxidising agent in reaction 2.
C
Reaction 2 is the one in which light is absorbed.
D
Ag+ ions are oxidised in reaction 1.
11 In the treatment of domestic water supplies, chlorine is added to the water to form chloric(I) acid,
HClO.
Cl2(aq) + H2O(I) → H+(aq) + Cl –(aq) + HClO(aq)
This reacts further to give the chlorate(I) ion.
HClO(aq) + H2O(I) → H3O+(aq) + ClO–(aq)
Both HClO and ClO– kill bacteria by oxidation.
What is the change in oxidation number of chlorine in forming the chlorate(I) ion from the
aqueous chlorine?
A
–1
B
0
C
+1
D
+2
12 In an experiment, 50.0 cm3 of a 0.10 mol dm–3 solution of a metallic salt reacted exactly with
25.0 cm3 of 0.10 mol dm–3 aqueous sodium sulphite.
The half-equation for oxidation of sulphite ion is shown below.
+
–
SO 32− (aq) + H2O(I) → SO 2−
4 (aq) + 2H (aq) + 2e
If the original oxidation number of the metal in the salt was +3, what would be the new oxidation
number of the metal?
A
+1
B
+2
C
+4
D
+5
13 The nickel-cadmium rechargeable battery is based upon the following overall reaction.
Cd + 2NiOOH + 4H2O → Cd(OH)2 + 2Ni(OH)2.H2O
What is the oxidation number of nickel at the beginning and at the end of the reaction?
14 In some early paintings, lead(II) carbonate was used as a white pigment. In the 19th century
hydrogen sulphide from burning coal reacted with this pigment to form black lead(II) sulphide,
PbS. The original colour of the painting may be restored by carefully treating the area with dilute
hydrogen peroxide, producing lead(II) sulphate which is also white.
What is the role of the hydrogen peroxide?
A
catalyst
B
oxidising agent
C
reducing agent
D
solvent
15 A cheap carbon monoxide detector for a gas heater consists of a patch containing palladium
chloride crystals. When carbon monoxide is present, the crystals turn from orange to black as the
following reaction takes place.
CO(g) + PdCl2(s) + H2O(l) → CO2(g) + Pd(s) + 2HCl(aq)
orange
black
Which is the element whose oxidation number decreases in this reaction?
A
carbon
B
chlorine
C
hydrogen
D
palladium
16 Chlorine dioxide is produced on a large scale as it is used for bleaching paper pulp. It is made by
the following reaction.
−
2Cl O3(aq) + SO2(g) → 2Cl O2(g) + SO 24 − (aq)
How do the oxidation numbers of chlorine and sulphur change in this reaction?
chlorine
sulphur
A
decreases by 1
increases by 1
B
decreases by 1
increases by 2
C
decreases by 3
increases by 1
D
decreases by 3
increases by 2
17 Which element has the same oxidation number in all of its known compounds?
A
beryllium
B
chlorine
C
nitrogen
D
sulphur
18 A weedkiller can be prepared by heating a bleach solution.
3NaCl O
bleach
heat
2NaCl + NaCl O3
weedkiller
What are the oxidation states of chlorine in these three compounds?
19
A
–1
–1
+5
B
+1
–1
+5
C
+1
–1
+7
D
+2
+1
+7
When ammonia is converted into nitric acid on a commercial scale, the following reactions can
occur.
In which reaction does the greatest change in oxidation number of the nitrogen occur?
reaction
A
4NH3 + 5O2 → 4NO + 6H2O
B
3NO2 + H2O → 2HNO3 + NO
C
2NO + O2 → 2NO2
D
4NH3 + 6NO → 5N2 + 6H2O
20 Chlorine compounds show oxidation states ranging from –1 to +7.
What are the reagent(s) and conditions necessary for the oxidation of elemental chlorine into a
compound containing chlorine in the +5 oxidation state?
A
AgNO3(aq) followed by NH3(aq) at room temperature
B
concentrated H2SO4 at room temperature
C
cold dilute NaOH(aq)
D
hot concentrated NaOH(aq)
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
1, 2 and 3
are
correct
1 and 2
only are
correct
C
2 and 3
only are
correct
D
1 only
is
correct
No other combination of statements is used as a correct response.
21 Which reactions are redox reactions?
1
CaBr2 + 2H2SO4 → CaSO4 + Br2 + SO2 + 2H2O
2
CaBr2 + 2H3PO4 → Ca(H2PO4)2 + 2HBr
3
CaBr2 + 2AgNO3 → Ca(NO3)2 + 2AgBr
22 Disproportionation is the term used to describe a reaction in which a reactant is simultaneously
both oxidised and reduced.
To which incomplete equations does the term disproportionation apply?
1
Cl2(g) + 2OH–(aq) → H2O(l) + Cl –(aq) + ……
2
3Cl2(g) + 6OH–(aq) → 3H2O(l) + ClO3–(aq) + ……
3
2NO2(g) + H2O(l) → HNO3(aq) + ……
23 Ammonia and chlorine react in the gas phase.
8NH3 + 3Cl2 → N2 + 6NH4Cl
Which statements are correct?
1
Ammonia behaves as a reducing agent.
2
Ammonia behaves as a base.
3
The oxidation number of the hydrogen changes.
24 Chlorine reacts with hot concentrated aqueous sodium hydroxide according to the equation
below.
3Cl2(g) + 6NaOH(aq) → NaCl O3(aq) + 5NaCl (aq) + 3H2O(l)
Which conclusions can be drawn from this information?
1
The oxidation state of the chlorine in one of the products is +5.
2
The chlorine undergoes disproportionation.
3
The sodium hydroxide acts as a reducing agent.
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Redox
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Theory
Booklet
Mark Scheme 2
Time Allowed:
80 minutes
Score:
/66
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) PCl5 + 4H2O → H3PO4 + 5HCl (1)
SiCl4 + 2H2O → SiO2 + 4HCl (or giving H2SiO3, Si(OH)4 etc.) (1)
(b) bond energies: S-S
Cl-Cl
S-Cl
[2]
= 264 kJ mol–1
= 244 kJ mol–1
= 250 kJ mol–1
∆H = 8 × 264 + 8 × 244 – 16 × 250 = +64 kJ mol–1 (2)
[2]
(c) (i) +2 (1)
(ii) (half) the sulfur goes up by +2, (1)
(the other half) goes down by –2 (1)
(iii) HCl (can be read into (iv)) (1)
(iv) 2SCl2 + 2H2O → S + SO2 + 4HCl (1)
(v) (+ AgNO3)
(+ K2Cr2O7)
white ppt. (1)
solution turns green (1)
[7]
[Total: 11]
2
(a
(i)
formula of chloride
oxidation number of element in the chloride
NaCl
MgCl2
AlCl3
SiCl4
PCl3
SCl2
+
+
+
+
+
+
correct oxidation nos. for NaCl to SCl2
(1)
(ii) Na to Al
loss of outer/valence electrons
to give configuration of Ne/to complete octet
Si to S
gain or sharing of outer electrons
to give configuration of Ar/to complete octet
(b)
b) (
(1)
(1)
(1)
(1)
giant lattice (may be in diagram)
with strong ionic bonding
[5]
(1)
(1)
(ii) ionic
oni
(iii) –1
(iv)
(1)
.. +
: Na :
..
x
.H
correct numbers of electrons
correct charges
(1)
(1)
(v)
compound
omp
2
oxidation number of element in the hydride
+
AlH3
PH3
H2S
+
–
–
correct oxidation nos. for MgH2 and AlH3
correct oxidation nos. for PH3 and H2S
(1)
(1
[8]
(c) (i)
chloride
hloride
magnesium
aluminium
pH
H
6.5–6.9
1–4
(1)
(1)
(no mark)
(ii) NaH + H2O → NaOH + H2
(iii) 10–14
0–1
(1)
[4]
(d)
d) (
covalent
ova
(ii) SiCl4 + 4H2O → Si(OH)4 + 4HCl or
SiCl4 + 4H2O → SiO2.2H2O + 4HCl or
SiCl4 + 2H2O → SiO2 + 4HCl
(1)
1)
[Total: 19]
3
(a
P4
(1)
S8
(1)
Cl 2
(1)
1)
(b) (i) highest S8 ........... P4............ Cl2 lowest
allow S ... P ... Cl or names
(1)
(ii) from S8 to P4 to Cl2
there are fewer electrons in each molecule
(1)
hence weaker van der Waals’ forces
(1)
[3]
(c) (i) S2Cl2 = (2 x 32.1) + (2 x 35.5) = 135.2
n(S2Cl2) =
2.7
= 0.0199 = 0.02
135.2
0.02 mol S2Cl2 →
1.0 mol S2Cl2 →
(1)
0.96
= 0.03 mol S
32.1
0.03 ×1.0
= 1.5 mol S
0.02
(1)
(iii) 2S2Cl2 + 3H2O → 3S + H2SO3 + 4HCl
correct products
(1)
balanced equation
(1)
(d) oxidation product is H2SO3
(1)
reduction product is S
(1)
[4]
[2]
[Total: 12]
4
(a
The EMF of a cell made up of the test electrode and a standard hydrogen electrode.
(or the EMF of the electrode compared to the S.H.E.)
[1]
EMF measured under standard conditions of T, (P) and concentration.
(or at 298K and 1 mol dm-3)
[1]
2
(b) The stronger the halogen is as an oxidising agent, the more positive is its Eo value.
[1]
Two examples of F2/F-, Cl2/Cl-; Br2/Br-, I2/I- quoted
[1]
(data: F2/F- = +2.87V
Cl2/Cl- = +1.36V
Br2/Br- = +1.07V
I2/I- = +0.54V)
2
(c)
c)
or
H2O2 + 2I- + 2H+ → I2 + 2H2O
H2O2 + 2KI + 2H+ → 2K+ + I2 + 2H2O
[1
Eo = 1.77 - 0.54 = 1.23 V
(ii)
or
[1
Cl2 + SO2 + 2H2O → 2Cl - + SO42- + 4H+
Cl2 + SO2 + 2H2O → 2HCl + H2SO4
[1]
Eo = 1.36 – 0.17 = 1.19 V
[1]
4
(d) since Eo(I2/I-) is +0.54V, tin will be oxidised to Sn4+
(Eo for Sn2+/Sn = -0.14V and Eo forSn4/Sn2 = +0.15V)
Thus:
Sn + 2I2 → SnI4
[1]
[1]
2
total: 10
5
(a
(b)
b)
SiCl4: white solid or white/steamy fumes
[1]
SiCl4 + 2H2O → SiO2 + 4HCl
[1]
PCl5: fizzes or white/steamy fumes
PCl5 + 4H2O → H3PO4 + 5HCl
[1]
[1]
[4]
MnO4– + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+
[1]
(ii) 5 : 1
(iii) n(MnO4–) = 0.02 × 15/1000 = 3 × 10–4 (mol)
[1]
(iv) n(Fe2+) = 5 × 3 × 10–4 = 1.5 × 10–3 (mol) ecf from (i) or (ii)
[1]
(v) [Fe2+] = 1.5 × 10–3 × 1000/2.5 = 0.6 (mol dm–3) ecf from (iv)
[1]
(vi) In the original solution, there was 0.15 mol of Fe3+ in 100 cm3.
In the partially-used solution, there is 0.06 mol of Fe2+ in 100 cm3.
So remaining Fe3+ = 0.15 – 0.06 = 0.09 mol. ecf from (v)
[1]
This can react with 0.045 mol of Cu, which = 0.045 × 63.5 = 2.86 g of copper. ecf
[1]
[6]
(c) bonds broken are Si-Si and Cl-Cl = 222 + 244 = 466 kJ mol–1
bonds formed are 2 × Si-Cl = 2 × 359 = 718 kJ mol–1
∆H = –252 kJ mol–1
[2]
[2]
(d) (i) Ca2Si + 6H2O → 2Ca(OH)2 + SiO2 + 4H2
(ii) silcon has been oxidised AND hydrogen has been reduced
[1]
[1]
[2]
[Total: 14]
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Redox
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Theory
Booklet
Question Paper 2
Time Allowed:
80 minutes
Score:
/66
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) Write a balanced equation for the reaction of each of the following chlorides with water.
phosphorus(V) chloride ....................................................................................................
silicon(IV) chloride ............................................................................................................
[2]
(b) When sulfur is heated under pressure with chlorine, the major product is SCl2 (Cl-S-Cl).
S8(g) + 8Cl 2(g)
8SCl 2(g)
Use data from the Data Booklet to calculate the enthalpy change, ∆H, for this reaction.
The eight sulfur atoms in the S8 molecule are all joined in a single ring by single bonds.
∆H = ..........................................kJ mol–1
[2]
(c) Under suitable conditions, SCl 2 reacts with water to produce a yellow precipitate of
sulfur and a solution A. Solution A contains a mixture of SO2(aq) and compound B.
(i)
What is the oxidation number of sulfur in SCl2? ........................................................
(ii)
Work out how the oxidation number of sulfur changes during the reaction of SCl2
with water.
..................................................................................................................................
..................................................................................................................................
(iii)
Suggest the identity of compound B.
...................................................................
(iv)
Construct an equation for the reaction between SCl2 and water.
..................................................................................................................................
(v)
What would you observe when each of the following reagents is added to separate
samples of solution A?
AgNO3(aq).................................................................................................................
K2Cr2O7(aq) ..............................................................................................................
[7]
[Total: 11]
2
The elements of the third period of the Periodic Table form chlorides of general formula ECl x
where E represents the element. These chlorides show a variation in oxidation number from
sodium to sulfur.
(a) (i)
Use the information given to complete the table below.
formula of chloride
NaCl
MgCl 2
Al Cl 3
SiCl 4
PCl 3
SCl 2
oxidation number of element in
the chloride
(ii)
By considering the electron configurations of the elements, explain the variation in
oxidation number in the chlorides from Na to Al and from Si to S.
Na to Al ....................................................................................................................
..................................................................................................................................
Si to S .......................................................................................................................
..................................................................................................................................
[5]
Sodium hydride, NaH, is a colourless crystalline solid which melts at 800 °C and has the
same crystal structure as sodium chloride which has a melting point of 808 °C. When molten
sodium chloride is electrolysed using graphite electrodes, a shiny deposit, D, forms on the
cathode and a greenish-yellow gas is evolved from the anode. When molten sodium hydride
is electrolysed, under suitable conditions using graphite electrodes, the same shiny deposit
D is formed on the cathode and a colourless gas, G, is evolved from the anode.
(b) (i)
(ii)
Describe with the aid of a diagram the bonding in a sodium chloride crystal.
Suggest the type of bonding that is present in sodium hydride.
..................................................................................................................................
(iii)
What is the oxidation number of hydrogen in sodium hydride?
.......................
(iv)
Draw a ‘dot-and-cross’ diagram for sodium hydride. Show outer electrons only.
(v)
The metals magnesium and aluminium form hydrides with formulae MgH2 and
Al H3. The non-metals phosphorus and sulfur form hydrides with formulae PH3 and
H2S.
By considering their positions in the Periodic Table, suggest oxidation numbers for
these four elements in their hydrides.
compound
MgH2
Al H3
PH3
H2S
oxidation number of element in
the hydride
[8]
At room temperature, the chlorides of sodium, magnesium and aluminium are all solids which
dissolve in water.
The hydrides of sodium, magnesium and aluminium are also solids which react with water
with the rapid evolution of the same colourless gas G in each case.
(c) (i)
What is the pH of the solutions formed when separate samples of sodium chloride,
magnesium chloride, and aluminium chloride are dissolved in water?
chloride
sodium
magnesium
aluminium
pH
(ii)
Suggest an equation for the reaction between sodium hydride and water.
..................................................................................................................................
(iii)
Suggest a value for the pH of the solution formed in (ii).
.......................
[4]
At room temperature, the chlorides of silicon, phosphorus and sulfur are all low melting point
solids or low boiling point liquids that can be seen to react with water.
(d) (i)
Suggest what type of bonding is present in sulfur dichloride, SCl 2.
...................................................................
(ii)
Write a balanced equation for the reaction between the chloride of silicon, SiCl 4,
and water.
............................................................................................................................ [2]
[Total: 19]
3
The elements phosphorus, sulphur, and chlorine are regarded as having simple molecular
structures.
(a)
What are the molecular formulae of each of these three elements?
phosphorus ........................................
sulphur ...............................................
chlorine ..............................................
(b) (i)
[3]
Place the three elements in order of their melting points with the highest first.
highest ........................................................................................................... lowest
(ii)
Suggest an explanation for the order you have given in (i).
..................................................................................................................................
..................................................................................................................................
..............................................................................................................................[3]
(c) Sulphur and chlorine can be reacted together to form disulphur dichloride, S2Cl2.
Disulphur dichloride, S2Cl2, is decomposed by water forming sulphur and a mixture of
hydrochloric acid and sulphurous acid.
When 2.7 g of S2Cl2 is reacted with an excess of water, 0.96 g of sulphur, S, is
produced.
(i)
What is the amount, in moles, of S2Cl2 present in 2.7 g?
(ii)
What is the amount, in moles, of S produced from 1.0 mol of S2Cl2?
(iii)
Construct a balanced equation for the reaction of S2Cl2 with water.
..................................................................................................................................
[4]
(d) The reaction between S2Cl2 and water is a redox reaction.
Which product has been formed by oxidation and which by reduction?
product formed by oxidation ........................................
product formed by reduction ........................................
[2]
[Total: 12]
4
(a) What do you understand by the term standard electrode potential?
..........................................................................................................................................
.................................................................................................................................... [2]
(b) By reference to relevant E data in the Data Booklet, explain how the halogen/halide
electrode potentials relate to the relative reactivity of the halogens as oxidising agents.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(c) Use data from the Data Booklet to construct redox equations, and calculate the
standard cell potentials, for the reactions between
(i) Acidified H2O2(aq) and KI(aq),
..................................................................................................................................
(ii) Cl 2(aq) + SO2(aq).
..................................................................................................................................
[4]
(d) Use data from the Data Booklet to predict the likely product of the reaction between
I2(aq) and tin metal, writing a balanced equation for the reaction.
.................................................................................................................................... [2]
[Total: 10]
5
(a) Write down what you would see, and write equations for the reactions that occur,
when silicon(IV) chloride and phosphorus(V) chloride are separately mixed with water.
silicon(IV) chloride
...........................................................................................................................................
...........................................................................................................................................
phosphorus(V) chloride
...........................................................................................................................................
...........................................................................................................................................
[4]
(b) Iron(III) chloride, FeCl 3, is used to dissolve unwanted copper from printed circuit boards
(PCBs) by the following reaction.
2FeCl 3(aq) + Cu(s) → 2FeCl 2(aq) + CuCl 2(aq)
A solution in which [Fe3+(aq)] was originally equal to 1.50 mol dm–3 was re-used several
times to dissolve copper from the PCBs, and was then titrated as follows.
A 2.50 cm3 sample of the partially-used-up solution was acidified and titrated with
0.0200 mol dm–3 KMnO4.
This oxidised any FeCl 2 in the solution back to FeCl 3.
It was found that 15.0 cm3 of KMnO4(aq) was required to reach the end point.
(i) Construct an ionic equation for the reaction between Fe2+ and MnO4– in acid solution.
....................................................................................................................................
(ii) State here the Fe2+ : MnO4– ratio from your equation in (i). .......................................
(iii) Calculate the number of moles of MnO4– used in the titration.
(iv) Calculate the number of moles of Fe2+ in 2.50 cm3 of the partially-used-up solution.
(v) Calculate the [Fe2+] in the partially-used-up solution.
(vi) Calculate the mass of copper that could still be dissolved by 100 cm3 of the
partially-used-up solution.
mass of copper = ........................... g
[6]
(c) When SiCl 4 vapour is passed over Si at red heat, Si2Cl 6 is formed. Si2Cl 6 contains a Si-Si
bond.
The reaction of Si2Cl 6 and Cl 2 re-forms SiCl 4.
Si2Cl 6(g) + Cl 2(g) → 2SiCl 4(g)
Use bond energy data from the Data Booklet to calculate ∆H o for this reaction.
∆H o = ........................... kJ mol–1
[2]
(d) Calcium forms three calcium silicides, Ca2Si, CaSi and CaSi2. The first of these reacts
with water as follows.
.........Ca2Si + ........H2O → .......Ca(OH)2 + ......SiO2 + .....H2
(i) Balance this equation. You may find the use of oxidation numbers helpful.
(ii) During this reaction, state
which element(s) have been oxidised, .....................................................................
which element(s) have been reduced. ......................................................................
[2]
[Total: 14]
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Redox
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Theory
Booklet
Mark Scheme 3
Time Allowed:
83 minutes
Score:
/69
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(b)
b)
C(g) → C+(g) + e–
correct equation
correct state symbols
(1)
(1)
Na and Mg
Mg has greater nuclear charge/more protons than Na
(1)
in both atoms, the 3s electrons are in the same orbital/
same energy level/same shell
(1)
(ii) Mg and Al
in Al outermost electron is in 3p rather than 3s
3p electron is at higher energy or
is further away/is more shielded from nucleus
(1)
(1)
[2]
(iii) He and Ne
both He and Ne have the highest nuclear charges in their Period
(1)
(iv) He, Ne, and Ar
going down the group,
valence/outer shell electrons are farther from the nucleus
(1)
there is greater shielding
(1)
attraction between valence electrons and nucleus is less or
effective nuclear charge is less
(1)
(c) (i) from Na to Cl
increased nuclear charge/nuclear attraction
(1)
(ii) cation has fewer electrons than atom or
cation has lost outer electrons or
cation has fewer shells
(1)
but cation has same nuclear charge as atom or
proton number is the same
(1)
[8]
[3]
(d) ignore any state symbols
MgO(s)
Mg
NaOH(aq)
→
NO REACTION
(1)
MgO(s)
Mg
2HCl(aq)
→
MgCl2 + H2O
(1)
Al2O3(s)
+
2NaOH(aq)
a
3H2O(l)
→
2NaAl(OH)4 or
Al2O3(s)
+
2NaOH(aq)
a
H2O(l)
→
2NaAlO2 + 2H2O or
Al2O3(s)
+
a
6NaOH(aq)
3H2O(l)
→
2Na3Al(OH)6
Al2O3(s)
+
6HCl(aq)
→
2AlCl3 + 3H2O or
Al2O3(s)
+
6HCl(aq)
→
Al2Cl6 + 3H2O
SO2(g)
+
NaOH(aq)
→
NaHSO3 or
SO2(g)
+
2NaOH(aq)
→
Na2SO3 + H2O
HCl(aq)
→
NO REACTION
SO2(g
(g)
(1)
(1)
(1)
(1)
[6]
[Total: 19]
2
(a
CO2 is a gas (at room temperature); SiO2 is a high melting solid
CO2: simple / discrete molecular / covalent
SiO2: giant covalent or macromolecular / giant molecular
(b) (a substance that is..) hard, high melting, electrical insulator
SiO2 has strong covalent bonds (can be in (a))
(c)
c)
[1]
[1]
[1]
[3]
any two
[1]
[1
[2]
amphoteric
[1]
(ii) 2NaOH + PbO → Na2PbO2 + H2O
(or NaOH + PbO + H2O → NaPb(OH)3 etc.)
[1
[2]
(d)
d)
Zn + Sn4+ → Zn2+ + Sn2+
[1]
(ii) Eθ = 0.15 – (–0.76) = 0.91 V
Eθ = 1.52 – 0.15
= 1.37 V
(iii) n(Sn2+) = 0.02 × 13.5/1000 × 5/2 = 6.75 × 10–4 mol
n(Sn2+) = 0.02 × 20.3/1000 × 5/2 = 1.02 × 10–3 mol
[1]
[1]
use of the 5/2 ratio
correct rest of working
(iv) n(Sn4+) = 1.02 × 10–3 – 6.75 × 10–4 = 3.45 × 10–4 mol
∴ ratio = 6.75/3.45 = 1.96:1 ≈ 2:1
∴ formula is 2SnO + SnO2 ⇒ Sn3O4
(condl on calculation, but allow ecf)
(e)
e)
volume = 1 × 1 × 1 × 10–5 = 1 × 10–5 m3 or 10 cm3
[1]
[1]
[1]
[1]
[1]
[8]
[1]
(ii) mass = vol × density = 10 × 7.3 = 73 g
moles = mass/Ar = 73/119 = 0.61 mol
ecf
ecf
[1]
[1]
(iii) Q = nFz = 0.61 × 9.65 × 104 × 2 = 1.18 (1.2) × 105 coulombs
ecf
[1]
[4]
[Total: 19]
3
(a
Any two from: high(-ish) density of metal
variable oxidation states
ability to form complexes
formation of coloured compounds
incomplete d subshell
high m.p. / b.p.
[1]
1] +
[2]
(b) equ: MnO4– + 8H+ + 5Fe2+ → Mn2+ + 5Fe3+ + 4H2O
[1]
method: Take a known volume of Fe2+(aq)/in a pipette and place in (conical) flask
Add an excess of (dil) H2SO4
Titrate until end point is reached and note volume used
End point is first permanent pink colour
Repeat titration & take average of consistent readings
any 3 points
(c)
c)
2 MnO4– + 5 SO2 + 2 H2O → 2 Mn2+ + 5 SO42– + 4 H+
oxidation numbers:
+7
+
[2]
+
[1]
(ii) 1 Cr2O72– + 6 NO2 + 2 H+ → 2 Cr3+ + 6 NO3– + 1 H2O
oxidation numbers:
+6
[3]
[4]
[2]
+3
[1]
([2] marks for each equation: [1] for balancing of redox species,
[1]
1] for total balancing: i.e 2O and H+)
[6]
(d) Fe3+ is a homogeneous (catalyst)
Fe3+ oxidised I– (and is reduced to Fe2+)
Fe2+ reduces S2O82– (and is oxidised to Fe3+)
or equations showing this
any two points
[2]
[2]
[Total: 14]
4
(a)
a)
2
3
S + O2 → SO2
2SO2 + O2 2SO3
SO3 + H2O → H2SO4
equil
(1)
equation
(1)
(1)
(1)
Allow sequences that start with SO2
and include H2S2O7 before H2SO4.
Equilibrium mark is only scored if only appears in
the SO2/SO3 equation.
(b)
vanadium pentoxide/vanadium(V) oxide/V2O5
(c) (i)
[4]
(1)
[1]
oo
HxoSoxH
(1)
(ii) non-linear/bent/V-shaped
(1)
(iii) H2O has hydrogen bonds/H2S does not or
H2S has van der Waals’ forces only
(1)
hydrogen bonds are stronger
than van der Waals’ forces or
H2S has weaker intermolecular bonds
than H2O
(1)
oo
(d) (i) 2H2S + 3O2 → 2H2O + 2SO2
from -2 (1)
to +4
allow e.c.f. on equation
(ii) 68.2g H2S react with 3 x 24 dm3 O2
8.65g H2S react with 3 x 24 x 8.65 = 9.13 dm3
68.2
allow 9.16 dm3 if H2S = 68 is used
allow e.c.f on (d)(i)
(e) (i) an acid that is partially dissociated into ions
[4]
(1)
(1)
(1)
(1)
[5]
(1)
(ii) H2S(g) + H2O(l) → H3O+(aq) + HS-(aq)
or
H2S(g) + aq → H+(aq) + HS-(aq)
or
H2S(aq) → H+(aq) + HS-(aq)
equation (1) state symbols (1)
[3]
[Total: 17]
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Redox
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Redox
Theory
Booklet
Question Paper 3
Time Allowed:
83 minutes
Score:
/69
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The Periodic Table we currently use is derived directly from that proposed in 1869 by
Mendeleev who had noticed patterns in the physical and chemical properties of the elements
he had studied.
The diagram below shows the first ionisation energies of the first 18 elements of the
Periodic Table.
2500
He
Ne
2000
first
ionisation
energy
/ kJ mol–1
1500
1000
500
0
Ar
H
Li
0 1 2 3
Na
10 11 12 13 14 15 16 17 18
proton number
(a) Give the equation, including state symbols, for the first ionisation energy of carbon.
............................................................................................................................. [2]
(b) (i)
Explain why sodium has a lower first ionisation energy than magnesium.
..................................................................................................................................
..................................................................................................................................
(ii)
Explain why magnesium has a higher first ionisation energy than aluminium.
..................................................................................................................................
..................................................................................................................................
(iii)
Explain why helium, He, and neon, Ne, occupy the two highest positions on the
diagram.
..................................................................................................................................
..................................................................................................................................
(iv)
Explain why the first ionisation energy of argon, Ar, is lower than that of neon,
which is lower than that of helium.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[8]
(c) (i)
The first ionisation energies of the elements Na to Ar show a variation. Some
physical properties show similar variations.
The atomic radius of the elements decreases from Na to Cl.
Give a brief explanation of this variation.
..................................................................................................................................
..................................................................................................................................
(ii)
The cations formed by the elements Na to Al are smaller than the corresponding
atoms.
Give a brief explanation of this change.
..................................................................................................................................
..................................................................................................................................
[3]
(d) The oxides of the elements of the third Period behave differently with NaOH(aq) and
HCl (aq). In some cases, no reaction occurs.
Complete the table below by writing a balanced equation for any reaction that occurs,
with heating if necessary. If you think no reaction takes place write ‘no reaction’.
You do not need to include state symbols in your answers.
.....MgO(s)
MgO
..... NaOH (aq)
.....MgO(s)
MgO
..... HCl (aq)
.....Al2O3(s)
s)
..... NaOH (aq)
.....Al2O3(s)
..... HCl (aq)
.....SO2(g)
+ ..... NaOH (aq)
.....SO2(g)
+ ..... HCl (aq)
+ .....H2O (l)
[6]
[Total: 19]
2
(a) The Group IV oxides CO2 and SiO2 differ widely in their physical properties. Describe
these differences and explain them in terms of their structure and bonding.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [3]
(b) What are the properties of a ceramic material? Why is silicon(IV) oxide very suitable as
a component of ceramics?
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [2]
(c) Lead(II) oxide reacts with both acids and bases.
(i)
What is the name given to oxides that have this property?
..................................................................................................................................
(ii)
Write a balanced equation for the reaction between PbO and NaOH.
..................................................................................................................................
[2]
(d) Tin forms an oxide, A, that contains the metal in both oxidation states II and IV. The
formula of A can be found by the following method.
•
A sample of A was dissolved in H2SO4(aq), producing solution B, which was a mixture
of tin(II) sulfate and tin(IV) sulfate.
•
A 25.0 cm3 sample of solution B was titrated with 0.0200 mol dm–3 KMnO4.
13.5 cm3 of KMnO4 was required to reach the end-point.
•
Another 25.0 cm3 sample of solution B was stirred with an excess of powdered
zinc. This converted all the tin into tin(II). The excess of zinc powder was filtered off
and the filtrate was titrated with 0.0200 mol dm-3 KMnO4, as before.
This time 20.3 cm3 of KMnO4 was required to reach the end-point.
The equation for the reaction occurring during the titration is as follows.
2MnO4– + 16H+ + 5Sn2+
(i)
2Mn2+ + 8H2O + 5Sn4+
Write a balanced equation for the reaction between Zn and Sn4+.
..................................................................................................................................
(ii)
(iii)
Use the Data Booklet to calculate the E o- values for the reactions between
•
Zn and Sn4+, ....................................................................................................
•
MnO4– and Sn2+.. ................................................................................................
Use the results of the two titrations to calculate
•
the number of moles of Sn2+ in the first titration sample,
..................................................................................................................................
..................................................................................................................................
•
the number of moles of Sn2+ in the second titration sample.
..................................................................................................................................
..................................................................................................................................
(iv)
Use the results of your calculation in (iii) to deduce the Sn2+/ Sn4+ ratio in the oxide
A, and hence suggest the formula of A.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[8]
(e) A major use of tin is to make ‘tin plate’, which is composed of thin sheets of mild steel
electroplated with tin, for use in the manufacture of food and drinks cans. A tin coating of
1.0 3 10–5 m thickness is often used.
(i)
Calculate the volume of tin needed to coat a sheet of steel 1.0 m 3 1.0 m to this
thickness, on one side only.
..................................................................................................................................
..................................................................................................................................
(ii)
Calculate the number of moles of tin that this volume represents.
[The density of tin is 7.3 g cm–3.]
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(iii)
The solution used for electroplating contains Sn2+ ions. Calculate the quantity of
electricity in coulombs needed to deposit the amount of tin you calculated in (ii).
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[4]
[Total: 19]
3
Iron metal and its compounds are useful catalysts in certain reactions.
(a) Apart from its catalytic activity, state two properties of iron or its compounds that
show that it is a transition element.
..........................................................................................................................................
...................................................................................................................................... [2]
(b) You are provided with a solution of KMnO4 of known concentration in a burette.
Outline how you could use this solution to find out the concentration of Fe2+(aq) in a
solution. You should include relevant equations for any reactions you describe.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [4]
(c) For each of the following equations, write the oxidation number of the element printed
in bold underneath its symbol, and balance the equation by adding appropriate numbers
before each species.
(i)
oxidation numbers:
(ii)
oxidation numbers:
........ MnO –4 + ........ SO2 + ........ H2O → ........ Mn2+ + ........ SO24– + ........ H+
........
........
........
........
........ Cr2O27– + ........ NO2 + ........ H+ → ........ Cr3+ + ........ NO–3 + ........ H2O
........
........
........
........
[6]
(d) Outline the role that Fe3+ ions play in catalysing the reaction between iodide ions and
peroxydisulfate(VI) ions.
2I– + S2O28–
I2 + 2SO24–
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
[Total: 14]
4
Sulphur and its compounds are found in volcanoes, in organic matter and in minerals.
Sulphuric acid, an important industrial chemical, is manufactured from sulphur by the
Contact process. There are three consecutive reactions in the Contact process which are
essential.
(a) Write a balanced equation (using
in the correct sequence.
where appropriate) for each of these reactions
1 .......................................................................................................................................
2 .......................................................................................................................................
3 ................................................................................................................................. [4]
(b) What catalyst is used?
.................................................................................................................................... [1]
Hydrogen sulphide, H2S, is a foul-smelling compound found in the gases from volcanoes.
Hydrogen sulphide is covalent, melting at –85 °C and boiling at –60 °C.
(c)
(i) Draw a ‘dot-and-cross’ diagram to show the structure of the H2S molecule.
(ii) Predict the shape of the H2S molecule.
.............................................................
(iii) Oxygen and sulphur are both in Group VI of the Periodic Table.
Suggest why the melting and boiling points of water, H2O, are much higher than
those of H2S.
..................................................................................................................................
..................................................................................................................................
............................................................................................................................ [4]
Hydrogen sulphide burns with a blue flame in an excess of oxygen to form sulphur dioxide
and water.
(d)
(i) Write a balanced equation for the complete combustion of H2S.
..................................................................................................................................
(ii) What is the change in the oxidation number of sulphur in this reaction?
from ....................................................... to .............................................................
(iii) What volume of oxygen, measured at room temperature and pressure, is required
for the complete combustion of 8.65 g of H2S? Give your answer to two decimal
places.
[5]
Hydrogen sulphide is a weak diprotic (dibasic) acid. Its solution in water contains HS – and a
few S2– ions.
(e)
(i) What is meant by the term weak acid?
..................................................................................................................................
..................................................................................................................................
(ii) Write an equation, with state symbols, for the first ionisation of H2S when it
dissolves in water.
............................................................................................................................ [3]
[Total: 17]
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 1
Time Allowed:
76 minutes
Score:
/63
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) m. pt. is high(er) / large(r) / greater (for iron)
density is high(er) / large(r) / greater (for iron)
[1]
[1]
(ii) (higher m. pt. due to)
strong attraction between cations and electrons or
more delocalised electrons
[1]
(higher density due to) greater Ar and smaller radius
(b) (i) components to be added: voltmeter or V
salt bridge [must be labelled]
(ii) M1:
M2:
M3
A and B
either C or D
C and D
copper (metal) or Cu and iron (metal) or Fe
as 1 mol dm–3 / 1 M
Cu2+ or CuSO4 or CuCl2 or Cu (NO3)2 etc. and
Fe2+ or FeSO4 etc.
(iii) Eocell = 0.34 + 0.44 = 0.78 (V)
[1]
[1]
[1]
[1]
[1]
[1]
[1]
(iv) if C is Fe2+; (as [C] increases), the E of the Fe2+ / Fe increases / becomes more positive /
less negative
[1]
so the overall cell potential / Ecell would decrease / become less positive / more
negative
[1]
or
if C is Cu2+; (as [C] increases), the E of the Cu2+/Cu increases / becomes more
positive / less negative
[1]
so the overall cell potential / Ecell would increase / become more positive / less negative
[1]
(c) (i) (colour change is) colourless to pink/pale purple
or (end point is the first) permanent (pale) pink/pale purple colour
(ii) {n(MnO4–) = 0.02 × 18.1/1000 = 3.62 × 10-4 mol}
n(Fe2+) = 5 × n(MnO4–) = 1.81 × 10–3 mol
mass of Fe = 55.8 x 1.81 × 10–3 = 0.101 g (M2 × 55.8) ecf
[1]
[1]
[1]
Mr = mass / moles = 0.500/1.81 × 10–3 = 276.2 ecf
cf
[Total: 16]
2
(a
A: voltmeter or V or potentiometer
[1]
B: platinum or Pt
[1]
C: 1 mol dm–3 and H+ or HCl (or 0.5 M H2SO4)
[1]
D: lead (metal) or Pb
[1]
4
(b)
b)
a in the box next to –0.17 V
a comment that the [Pb2+] has decreased plus a description of the outcome,
e.g. as [Pb2+] decreases (from 1 mol dm–3), Pb2+(aq) + 2e– ⇌ Pb(s) goes
over to the left hand side, or as [Pb2+] decreases, Pb2+ is less likely to be
reduced
[1]
[1]
(ii) (Ksp =) [Pb2+][Cl –]2
(iii) if [PbCl2] = 3.5 × 10–2, [Pb2+] = 3.5 × 10–2 and [Cl –] = 7.0 × 10–2
so Ksp = (3.5 × 10–2) × (7.0 × 10–2)2 = 1.715 (1.7) × 10–4 mol3 dm–9 ([2sf)
[1]
[1]
5
(c) (i) the (M2+ / M) Eo for the two elements are very similar or are –0.13 and –0.14 V
[1
Eo (Sn4+ / Sn2+) = 0.15 V and Eo (Pb4+ / Pb2+) = 1.69 V
[1]
so Sn2+ is quite easily oxidised (to Sn4+) or is a stronger reductant or Pb2+ is
not easily oxidised (to Pb4+) or Pb4+ is a stronger oxidant or Pb4+ is easily
reduced
[1]
(ii) e.g. PbCl2 + Zn → Pb + ZnCl2 (or ionic)
(other acceptable reductants: Fe, Mg, Ca but not Na or K)
Sn2+ + Br2 → Sn4+ + 2Br(other acceptable oxidants: VO2+, Cr2O72–, Ag+, Cl2, Br2, F2, Fe3+, MnO4–)
[1]
[1]
5
(d)
d)
Pb2+(g) + 2Cl –(g) → PbCl2(s)
[1]
(ii) ∆Hf = ∆Hat + E(Cl – Cl) + 1st IE + 2nd IE + 2 × EA(Cl) + LE
–359 = 195 + 242 + 716 + 1450 – 2 × 349 + LE
LE = 2 × 349 – 359 – 195 – 242 – 716 – 1450
LE = –2264 (kJ mol–1)
[3
(iii) LE(PbCl2) > LE(PbBr2) or more exothermic or stronger lattice
[1]
because Cl – / chloride anion has smaller radius / size than Br – / bromide
[1]
6
[Total: 20]
3
(a)
(b) (i)
(ii)
(c)
(HCl) stronger acid / more dissociated / ionised in solution
(HCl has) more ions / higher concentration of ions
1
1
A solution that resists changes in the pH / keeps pH fairly constant
when small quantities / amounts / vols of acid / H+ or base / OH– are added
1
1
add (ethanoic acid) to NaOH OR an equation
excess (ethanoic acid)
OR mix with sodium ethanoate
1
1
[4]
CH3CH(NH2)COOH + H+ CH3CH(NH3+)COOH
CH3CH(NH2)COOH + OH– CH3CH(NH2)COO– + H2O
1
1
[2]
pKa 2.99
pKa 4.40
HO
OH
OH
OH
O
O
HO
O
HO
H
H
HOOC
H
COOH
HOOC
OH
OH
(R,S)
(S,R)
H
HO
COOH
HOOC
(R,R)
any two of the above
H
OH
+
O
+ H+
1
OH
2
HO
COOH
O
O
-O
OH
1
+
OH
OH
O
O
O
OH
HO
O
(ii)
O
OH
(d) (i)
H
[2]
[4
4
(a
The potential of an electrode compared to that of a standard hydrogen electrode (SHE)
or
the EMF of a cell composed of the test electrode and the SHE
all measurement concentrations of 1 mol dm–3 and 298 K / 1 atm pressure
[1]
[1]
[2]
(b)
H2 and good delivery system [1]
Fe2+/Fe3+ solution labelled [1]
platinum electrodes (both) [1]
salt bridge and voltmeter [1]
H+ or HCl or H2SO4 [1]
(acid is not sufficient)
[5]
(c)
c) (
E⦵ = 0.77 – 0.54 = 0.23 (V)
[1]
(ii) Since E⦵ is positive/ E⦵ >0
So more products / the equilibrium will be over to the right / forward reaction is favoured
ecf from (c)(i)
[1]
(iii) Kc = [Fe2+]2[I2] / [Fe3+]2[I–]2
units are mol–1 dm3 ecf on expression
(iv) ([Fe2+] must always be twice [I2], so) [Fe2+] = 0.02 (mol dm–3)
([I–] must always be equal to [Fe3+], so) [I–] = 2 × 10–4 (mol dm–3)
(v) Kc = {(0.02)2 × 0.01} / {(2 x 10–4)2 × (2 × 10–4)2} correct expression
(allow ecf from incorrect expression in (c)(iii))
(allow ecf from (c)(iv))
= (4 × 10–6) / (1.6 × 10–1.5) = 2.5 × 109 (mol–1 dm3)
[1]
[1]
[1
[1
[1]
[1
[8]
[Total: 15]
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Electrolysis, Electrode
Potentials & Cells
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 1
Time Allowed:
76 minutes
Score:
/63
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) (i) State how the melting point and density of iron compare to those of calcium.
melting point of iron: ...........................................................................................................
density of iron: ....................................................................................................................
(ii) Explain why these differences occur.
melting point: ......................................................................................................................
.............................................................................................................................................
density: ...............................................................................................................................
.............................................................................................................................................
[4]
(b) The following diagram shows the apparatus used to measure the standard electrode potential,
E o, of a cell composed of a Cu(II) / Cu electrode and an Fe(II) / Fe electrode.
(i) Finish the diagram by adding components to show the complete circuit. Label the
components you add.
A
B
C
D
(ii) In the spaces below, identify or describe what the four letters A-D represent.
A .........................................................................................................................................
B .........................................................................................................................................
C .........................................................................................................................................
D .........................................................................................................................................
(iii) Use the Data Booklet to calculate the E o for this cell.
.............................................................................................................................................
(iv) Predict how the size of the overall cell potential would change, if at all, as the concentration
of solution C is increased.
Explain your reasoning.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[8]
(c) The iron(II) complex ferrous bisglycinate hydrochloride is sometimes prescribed, in capsule
form, to treat iron deficiency or anaemia.
A capsule containing 500 mg of this iron(II) complex was dissolved in dilute H2SO4 and titrated
with 0.0200 mol dm–3 KMnO4.
18.1 cm3 of KMnO4 solution were required to reach the end point.
The equation for the titration reaction is as follows.
5Fe2+ + MnO4– + 8H+  5Fe3+ + Mn2+ + 4H2O
(i) Describe how you would recognise the end point of this titration.
.............................................................................................................................................
(ii) Calculate
●
the number of moles of Fe2+ in the capsule,
●
the mass of iron in the capsule,
●
the molar mass of the iron(II) complex, assuming 1 mol of the complex contains 1 mol
of iron.
[4]
[Total: 16]
2
Lead(II) chloride, PbCl 2, can be used in the manufacture of some types of coloured glass.
PbCl 2 is only sparingly soluble in water. The [Pb2+] in a saturated solution of PbCl 2 can be estimated
by measuring the cell potential, Ecell, of the following cell.
A
H2(g)
1 atm, 298 K
salt bridge
B
D
saturated solution
of PbCl 2
C
solid PbCl 2
(a) In the spaces below, identify what the four letters A-D in the above diagram represent.
A .................................................................
B ................................................................
C .................................................................
D ................................................................
[4]
(b) In a saturated solution of PbCl 2, [PbCl 2(aq)] = 3.5  10–2 mol dm–3.
(i) The E o for the Pb2+ / Pb electrode is – 0.13 V. Predict the potential of the right-hand electrode
in the diagram above. Indicate this by placing a tick in the appropriate box in the table
below.
electrode
potential / V
place one tick only
in this column
– 0.17
– 0.13
– 0.09
0.00
Explain your answer.
.............................................................................................................................................
.............................................................................................................................................
(ii) Write an expression for the solubility product, Ksp, of PbCl 2.
.............................................................................................................................................
(iii)
i
Calculate the value of Ksp, including units.
Ksp = .......................................
units .......................................
[5]
(c) The behaviours of PbCl 2 and SnCl 2 towards reducing agents are similar, but their behaviours
towards oxidising agents are very different.
(i) Illustrate this comparison by quoting and comparing relevant E o values for the two metals
and their ions. Explain what the relative E o values mean in terms of the ease of oxidation
or reduction of these compounds.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
(ii) Writing a balanced molecular or ionic equation in each case, suggest a reagent to carry
out each of the following reactions.
the reduction of PbCl 2
.............................................................................................................................................
the oxidation of SnCl 2
.............................................................................................................................................
[5]
(d)
d)
Write an equation to represent the lattice energy of PbCl 2. Show state symbols.
.............................................................................................................................................
(ii) Use the following data, together with appropriate data from the Data Booklet, to calculate
a value for the lattice energy of PbCl 2.
electron affinity of chlorine
enthalpy change of atomisation of lead
enthalpy change of formation of PbCl 2(s)
= –349 kJ mol–1
= +195 kJ mol–1
= –359 kJ mol–1
lattice energy = ............................. kJ mol–1
(iii) How might the lattice energy of PbCl 2 compare to that of PbBr2? Explain your answer.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[6]
[Total: 20]
3
(a) The following circuits were set up using aqueous hydrochloric and aqueous ethanoic acids as
electrolytes. Assume that the two circuits were identical apart from the electrolyte.
bulb
1
graphite
electrodes
bulb
2
switch
1 mol dm–3
HCl (aq)
graphite
electrodes
switch
1 mol dm–3
CH3CO2H(aq)
When the switches were closed, bulb 1 was brighter than bulb 2. Explain why.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
(b)
b)
State what is meant by a buffer solution.
.............................................................................................................................................
.............................................................................................................................................
(ii) Outline how a buffer solution can be prepared from ethanoic acid and a named base.
.............................................................................................................................................
.............................................................................................................................................
[4]
(c) Amino acids such as alanine, CH3CH(NH2)CO2H, can act as a buffer solution.
Construct two equations to illustrate this.
equation 1
equation 2
[2]
(d) Tartaric acid is present in many plants.
OH
O
HO
OH
O
OH
tartaric acid
(i) Tartaric acid has two dissociation constants, K1 and K2, for which the pKa values are 2.99
and 4.40.
Suggest equations showing the two dissociations that give rise to these pKa values.
pKa 2.99
pKa 4.40
(ii) One stereoisomer of tartaric acid is shown.
HO
H
CO2H
HO2C
H
OH
Complete the diagrams showing two other stereoisomers of tartaric acid.
CO2H
CO2H
[4]
[Total: 12]
4
(a) What is meant by the term standard electrode potential, SEP?
...........................................................................................................................................
...........................................................................................................................................
[2]
(b) Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the
Fe3+ / Fe2+ electrode.
[5]
(c) The reaction between Fe3+ ions and I– ions is an equilibrium reaction.
2Fe3+(aq) + 2I–(aq)
(i) Use the Data Booklet to calculate the
2Fe2+(aq) + I2(aq)
f
....................................................................................................................................
(ii) Hence state, with a reason, whether there will be more products or more reactants
at equilibrium.
....................................................................................................................................
....................................................................................................................................
(iii) Write the expression for Kc for this reaction, and state its units.
Kc =
units .................................................
An experiment was carried out using solutions of Fe3+(aq) and I–(aq) of equal
concentrations. 100 cm3 of each solution were mixed together, and allowed to reach
equilibrium.
The concentrations at equilibrium of Fe3+(aq) and I2(aq) were as follows.
[Fe3+(aq)] = 2.0 × 10–4 mol dm–3
[I2(aq)]
= 1.0 × 10–2 mol dm–3
(iv) Use these data, together with the equation given in (c), to calculate the concentrations
of Fe2+(aq) and I–(aq) at equilibrium.
[Fe2+(aq)] = ............................... mol dm–3
[I–(aq)] = ............................... mol dm–3
(v) Calculate the Kc for this reaction.
Kc = ......................................................
[8]
[Total: 15]
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 2
Time Allowed:
80 minutes
Score:
/66
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a)
a)
hydrogen
gas at 1 atm
Pt
H+/HCl at 1 mol dm-3 and 298K
H2(g) going in (i.e. not being produced) [1]
platinum electrode in contact with solution, with H2 bubbling over it [1]
H+ or HCl or H2SO4 [1]
–3
solution at 1 mol dm (or 0.5 M if H2SO4) and T=298 K, p=1 atm [1]
(ii) Eo = 1.33 – (-0.41) = 1.74 V
[1]
Cr2O72- + 14H+ + 6Cr2+ → 8Cr3+ + 7H2O
[1
(iii) Colour would change from orange
[1]
to green
[1]
[8]
(b) there are two ways of calculating the ratio:
pKa = –log10(Ka) = –log10(1.79 x 10–5) = 4.747 (4.75) or [H+] = 10-5.5 = 3.16 x 10-6
log10([B] / [A]) = pH – pKa = 0.753 (0.75) or [salt] / [acid] = Ka / [H+]
∴ [B] / [A] = 100.753 = 5.66
or = 1.79 x 10–5 / 3.16 x 10–6 = 5.66
(or [A] / [B] = 0.177)
since B + A = 100,∴ (100–A) / A = 5.66 ⇒
[1]
[1
[1]
(correct ratio = [3] marks)
vol of acid = 15 cm3
vol of salt = 85 cm3
[1]
[4]
CH3CO2Na + HCl → CH3CO2H + NaCl
[1]
(ii) CH3CO2H + NaOH → CH3CO2Na + H2O
[1]
[2]
(c)
c) (
(d) e.g. hydrolysis of esters RCO2R' (+ H2O) → RCO2H + R'OH or its reverse
or
hydrolysis of amides: RCONH2 (+ H3O+) → RCO2H + NH4+
hydrolysis of nitriles: RCN (+ H3O+ + H2O) → RCO2H + NH4+
nitration of benzene (or any arene): C6H6 + HNO3 → C6H5NO2 (+ H2O)
dehydration of alcohols, e.g. : CH3CH(OH)CH3 → CH3CH=CH2 + H2O
(or the reverse)
halogenation of ketones, e.g. : CH3COCH3 + X2 → CH3COCH2X (+ HX)
[3]
[Total: 17]
2
(a
The potential of an electrode compared to that of a standard hydrogen electrode (SHE)
or
the EMF of a cell composed of the test electrode and the SHE
all measurement concentrations of 1 mol dm–3 and 298 K / 1 atm pressure
[1]
[1]
[2]
(b)
H2 and good delivery system [1]
Fe2+/Fe3+ solution labelled [1]
platinum electrodes (both) [1]
salt bridge and voltmeter [1]
H+ or HCl or H2SO4 [1]
(acid is not sufficient)
[5]
(c)
c) (
E⦵ = 0.77 – 0.54 = 0.23 (V)
[1]
(ii) Since E⦵ is positive/ E⦵ >0
So more products / the equilibrium will be over to the right / forward reaction is favoured
ecf from (c)(i)
[1]
(iii) Kc = [Fe2+]2[I2] / [Fe3+]2[I–]2
units are mol–1 dm3 ecf on expression
(iv) ([Fe2+] must always be twice [I2], so) [Fe2+] = 0.02 (mol dm–3)
([I–] must always be equal to [Fe3+], so) [I–] = 2 × 10–4 (mol dm–3)
(v) Kc = {(0.02)2 × 0.01} / {(2 x 10–4)2 × (2 × 10–4)2} correct expression
(allow ecf from incorrect expression in (c)(iii))
(allow ecf from (c)(iv))
= (4 × 10–6) / (1.6 × 10–1.5) = 2.5 × 109 (mol–1 dm3)
[1]
[1]
[1
[1
[1]
[1
[8]
[Total: 15]
3
(a
(i) anode
cathode
Cl –(aq) → ½ Cl2(g) + e–
(1)
H+(aq) + e– → ½H2(g) or
2H2O(l) + 2e– → H2(g) + 2OH–(aq)
(1)
(ii) because iron in steel will react with chlorine
(b)
b) sod
burns with a yellow or orange flame or
forms a white solid
allow – once only – colour of chlorine disappears
2Na + Cl2 → 2NaCl
(1)
[3]
(1)
(1)
phosphorus
burns with a white or yellow flame or
colour of chlorine disappears – if not given for Na – or
for PCl5
forms a white or pale yellow solid
for PCl3
forms a colourless liquid
P + 2½Cl2 → PCl5
(1)
or P4 + 10Cl2 → 4PCl5
or
P + 1½Cl2 → PCl3
or P4 + 6Cl2 → 4PCl3
equation must refer to compound described
(1)
[4]
(c) cold dilute aqueous NaOH
NaOCl
+
(1)
(1)
hot concentrated aqueous NaOH
NaClO3
+
(1)
(1)
1)
(d) MgCl2 6.5 to 6.9
SiCl4
0 to 3
(1)
(1)
MgCl2 dissolves without reaction or
slight or partial hydrolysis occurs
(1)
SiCl4 reacts with water or
hydrolysis occurs
(1)
SiCl4 + 2H2O → SiO2 + 4HCl or
SiCl4 + 4H2O → Si(OH)4 + 4HCl or
SiCl4 + 4H2O → SiO2.2H2O + 4HCl
(1)
[5]
[Total: 16]
4
(a
(i) A = CuSO4
B = silver
[1]
[1]
(ii) salt bridge
voltmeter
[1]
[1]
[4]
(b) (i) 0.80 – 0.34 = (+) 0.46 V
[1]
(ii) If Ecell = 0.17, this is 0.29 V less than the standard Eo,
so EAg electrode must = 0.80 – 0.29 = 0.51 V
[1]
(iii) 0.51 = 0.80 + 0.06log [Ag+], so [Ag+] = 10(–0.29/0.06) = 1.47 x 10–5 mol dm–3 ecf from (ii)
[1]
[3]
(c)
c)
Ksp = [Ag+]2[SO42–]
units = mol3 dm–9 ecf on Ksp
(ii) [SO42–] = [Ag+]/2 Ksp = (1.6 × 10–2)2 × 0.8 × 10–2 = 2.05 × 10–6 (mol3 dm–9)
[1]
[1]
[1]
[3]
(d) AgCl
AgBr
AgI
white
cream
yellow
Solubility decreases down the group
[1]
[1]
[1]
[1]
[4]
(e) solubility decreases down the group
as M2+/ionic radius increases
both lattice energy and hydration(solvation) energy to decrease
enthalpy change of solution becomes more endothermic
[1]
[1]
[1]
[1]
[4]
[Total: 18]
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Electrolysis, Electrode
Potentials & Cells
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 2
Time Allowed:
80 minutes
Score:
/66
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) (i) With the aid of a fully-labelled diagram, describe the standard hydrogen electrode.
(ii) Use the Data Booklet to calculate the standard cell potential for the reaction between
Cr2+ ions and Cr2O72– ions in acid solution, and construct a balanced equation for the
reaction.
= ......................... V
equation .....................................................................................................................
(iii) Describe what you would see if a blue solution of Cr2+ ions was added to an acidified
solution of Cr2O72– ions until reaction was complete.
....................................................................................................................................
....................................................................................................................................
[8]
(b) A buffer solution is to be made using 1.00 mol dm–3 ethanoic acid, CH3CO2H, and
1.00 mol dm–3 sodium ethanoate, CH3CO2Na.
Calculate to the nearest 1 cm3 the volumes of each solution that would be required to
make 100 cm3 of a buffer solution with pH 5.50.
Clearly show all steps in your working.
Ka (CH3CO2H) = 1.79 × 10–5 mol dm–3
volume of 1.00 mol dm–3 CH3CO2H = ......................... cm3
volume of 1.00 mol dm–3 CH3CO2Na = ......................... cm3
[4]
(c) Write an equation to show the reaction of this buffer solution with each of the following.
(i) added HCl .................................................................................................................
(ii) added NaOH ..............................................................................................................
[2]
(d) Choose one reaction in organic chemistry that is catalysed by an acid, and write the
structural formulae of the reactants and products in the boxes below.
H+
[3]
[Total: 17]
2
(a) What is meant by the term standard electrode potential, SEP?
...........................................................................................................................................
...........................................................................................................................................
[2]
(b) Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the
Fe3+ / Fe2+ electrode.
[5]
(c) The reaction between Fe3+ ions and I– ions is an equilibrium reaction.
2Fe3+(aq) + 2I–(aq)
(i) Use the Data Booklet to calculate the
2Fe2+(aq) + I2(aq)
f
....................................................................................................................................
(ii) Hence state, with a reason, whether there will be more products or more reactants
at equilibrium.
....................................................................................................................................
....................................................................................................................................
(iii) Write the expression for Kc for this reaction, and state its units.
Kc =
units .................................................
An experiment was carried out using solutions of Fe3+(aq) and I–(aq) of equal
concentrations. 100 cm3 of each solution were mixed together, and allowed to reach
equilibrium.
The concentrations at equilibrium of Fe3+(aq) and I2(aq) were as follows.
[Fe3+(aq)] = 2.0 × 10–4 mol dm–3
[I2(aq)]
= 1.0 × 10–2 mol dm–3
(iv) Use these data, together with the equation given in (c), to calculate the concentrations
of Fe2+(aq) and I–(aq) at equilibrium.
[Fe2+(aq)] = ............................... mol dm–3
[I–(aq)] = ............................... mol dm–3
(v) Calculate the Kc for this reaction.
Kc = ......................................................
[8]
[Total: 15]
3
Chlorine gas is manufactured by the electrolysis of brine using a diaphragm cell.
(a) (i) Write half-equations, including state symbols, for the reactions occurring at each of
the electrodes of a diaphragm cell.
anode .........................................................................................................................
cathode ......................................................................................................................
(ii) In the diaphragm cell, the anode is made of titanium and the cathode is made of
steel.
Suggest why steel is never used for the anode.
....................................................................................................................................
....................................................................................................................................
[3]
(b) Chlorine is very reactive and will form compounds by direct combination with many
elements.
Describe what you would see when chlorine is passed over separate heated samples of
sodium and phosphorus.
In each case write an equation for the reaction.
sodium
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
phosphorus
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
(c) Chlorine reacts with aqueous sodium hydroxide in two different ways, depending on the
conditions used. In each case, water, sodium chloride and one other chlorine-containing
compound are formed.
For each condition below, give the formula of the other chlorine-containing compound
and state the oxidation number of chlorine in it.
condition
formula of other
chlorine-containing compound
oxidation number of
chlorine in this compound
cold dilute NaOH(aq)
hot concentrated NaOH(aq)
[4]
(d) Magnesium chloride, MgCl 2, and silicon tetrachloride, SiCl 4, each dissolve in or react
with water.
Suggest the approximate pH of the solution formed in each case.
MgCl 2 .................................
SiCl 4 .................................
Explain, with the aid of an equation, the difference between the two values.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [5]
[Total: 16]
4
(a) The diagram below shows an incomplete experimental set-up needed to measure the
Ecell of a cell composed of the standard Cu2+/Cu electrode and an Ag+/Ag electrode.
copper
electrode
electrode B
solution A
saturated
solution
of AgCl
solid AgCl
(i) State the chemical composition of
solution A, ..................................................................................................................
electrode B. ...............................................................................................................
(ii) Complete the diagram to show the whole experimental set-up.
[4]
(b) The above cell is not under standard conditions, because the [Ag+] in a saturated solution
of AgCl is much less than 1.0 mol dm–3. The Eelectrode is related to [Ag+] by the following
equation.
equation 1
Eelectrode = E oelectrode + 0.06 log[Ag+]
(i) Use the Data Booklet to calculate the E ocell if the cell was operating under standard
conditions.
E ocell = .......................... V
In the above experiment, the Ecell was measured at +0.17V.
(ii) Calculate the value of Eelectrode for the Ag+/Ag electrode in this experiment.
....................................................................................................................................
(iii) Use equation 1 to calculate [Ag+] in the saturated solution.
[Ag+] = .......................... mol dm–3
[3]
(c)
c)
Write an expression for Ksp of silver sulfate, Ag2SO4, including units.
Ksp = ..................................................
units ..................................................
Using a similar experimental set-up to that illustrated opposite, it is found that [Ag+] in a
saturated solution of Ag2SO4 is 1.6 × 10–2 mol dm–3.
(ii) Calculate the value of Ksp of silver sulfate.
Ksp = ...................................
[3]
(d) Describe how the colours of the silver halides, and their relative solubilities in NH3(aq),
can be used to distinguish between solutions of the halide ions Cl –, Br – and I –.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
(e) Describe and explain the trend in the solubilities of the sulfates of the elements in Group II.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
..................................................................................................................................... [4]
[Total: 18]
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 3
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) (i)
Cl2(g)
brine
H2(g)
NaCl(aq)
diaphragm
steel cathode
titanium/graphite
anode
NaOH(aq)
+
titanium/graphite anode identified correctly
steel cathode identified correctly
diaphragm identified correctly
all three outlets correctly shown
(ii) anode
2Cl–(aq) → Cl2(g) + 2e–
+
–
(1)
(1)
(1)
(1)
[4]
(1)
–
cathode 2H (aq) + 2e → H2(g)
or
2H2O(l) + 2e– → H2(g) + 2OH–(aq)
(iii) sodium hydroxide
(1)
[2]
(1)
[1]
[Total: 7]
2
(a) L = F/e or F = Le
[1]
[1]
(b) (i)
+
P .S .
A
a no d e
c a tho d e
C uS O 4 (a q )
allow the conventional symbol
to represent
(the "P.S." is not required)
correct cell (2 electrodes + PS circuit)
ammeter in series
anode and cathode of the right polarity [IN WORDS]
CuSO4(aq) or CuCl2(aq) or Cu2+(aq) or soln or 1 mol dm–3
(ii) n(Cu) = (52.542–52.243)/63.5 = 4.71 × 10–3 mol (4.67 × 10–3)
n(e–) required = 4.71 × 10–3 × 2 = 9.42 × 10–3 mol (9.34 × 10–3)
amount of electricity passed = 0.5 × 30 × 60 = 900 C
no. of electrons passed = 900/1.6 × 10–19 = 5.625 × 1021
[1]
[1]
[1]
[1]
[1]
ecf [1]
[1]
ecf [1]
no of electrons/n(e–) = L = 5.625 × 1021/9.42 × 10–3 = 5.97 × 1023 mol–1 (6.02 × 1023)
ecf [1]
(values in italics are if candidate has used Ar = 64, not 63.5. No last mark if not 3 s.f.:
correct ans = [5])
[9]
(c)
compound
AgF
g
product at anode
product at cathode
2
Ag
FeSO4
O2
H2
MgBr2
Br2
H2
6 correct ⇒ [5]
5 correct⇒ [4] etc.
Names can be used instead of symbols. If the atomic symbol (e.g. Br or H or O) is used
instead of the molecular formula (e.g. Br2 etc.) then deduct [1] mark only for the whole table.
[5]
[Total: 15]
3
(a
(b)
(i) Eo = 0.40 – (–0.83) = 1.23V
(1)
(ii) 2H2 + O2 → 2H2O
(1
(iii) LH electrode will become more negative
RH electrode will also become more negative / less positive
(1)
(1)
(iv) no change
(1)
ecf from (iii)
(v) increased conductance or lower cell resistance or increased rate of reaction
(1)
(i) Eo = 1.47 – (–0.13) = 1.60V
(ii) PbO2 + Pb + 4H+ → 2Pb2+ + 2H2O
(1)
(1
(iii) PbO2 + Pb + 4H+ + 2SO42– → 2PbSO4(s) + 2H2O
(1
(iv) Eocell will increase
(1)
as [Pb2+] decreases, Eelectrode(PbO2) will become more positive, but Eelectrode(Pb)
will become more negative
(1)
[6]
[5]
[Total: 11]
4
(a) Reaction II – since electrons are used up / required / gained / received (from
external circuit)
(b) (Pb2+ + 2e– → Pb)
(PbO2 + 4H+ + 2e– → Pb2+ + 2H2O)
Eo = –0.13V
Eo = +1.47V
two correct Eo values
Cell voltage is 1.6(0) (V)
(c) (i) 3(+)
(d) (i) Platinum or graphite / carbon
(ii) They need large quantities of compressed gases which take up space or the
hydrogen would need to be liquefied or the reactant is (highly) flammable /
explosive / combustible
Steel:
[1]
(1)
(1)
[2]
(1)
(ii) They are less heavy / poisonous / toxic / polluting or are safer due to no
(conc) H2SO4 within them
(e) Glass:
(1)
saves energy – the raw materials are easily accessible / cheap
or making glass is energy-intensive
(1)
[2]
(1)
(1)
[2]
(1)
saves energy – extracting iron from the ore
or mining the ore is energy intensive
or saves a resource – iron ore (NOT just “iron”) is becoming scarce
either one (1)
Plastics: saves a valuable / scarce resource: (crude) oil / petroleum
(1)
[3]
[Total: 10]
5
(a
(i) Cu(s) – 2e– → Cu2+(aq) allow electrons on RHS (1)
(ii) Eo for Ag+/Ag is +0.80V which is more positive than +0.34V for Cu2+/Cu, (1)
so it’s less easily oxidised (owtte) (1)
(iii) Eo for Ni2+ is –0.25V, (1)
Ni is readily oxidised and goes into solution as Ni2+(aq) (1)
[Mark (ii) and (iii) to max 3]
(iv) Cu2+(aq) + 2e– → Cu(s) (1)
(v) Eo for Zn2+/Zn is negative / = –0.76V, so Zn2+ is not easily reduced. (1)
(vi) The blue colour fades because Cu2+(aq) is being replaced by Zn2+(aq) or Ni2+(aq) or
[Cu2+] decreases (1)
[7]
(b) amount of copper = 225/63.5 = 3.54(3) mol (1)
amount of electrons needed = 2 × 3.54 = 7.08/9 (7.087) mol (1)
no. of coulombs = 20 × 10 × 60 × 60 = 7.2 × 105 C
no. of moles of electrons = 7.2 × 105/9.65 × 104 = 7.46 mol (1)
percentage “wasted” = 100 × (7.461 – 7.087)/7.461 = 5.01 (5.0)% (accept 4.98–5.10) (1)
[4]
(c) Eo data: Ni2+/Ni = –0.25V
Fe2+/Fe = –0.44V (1)
Because the Fe potential is more negative than the Ni potential, the iron will dissolve (1)
[2]
[Total: 13]
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Electrolysis, Electrode
Potentials & Cells
Question Paper 3
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 3
Time Allowed:
68 minutes
Score:
/56
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Chlorine is manufactured by electrolysis from brine, concentrated aqueous sodium chloride.
(a) (i)
(ii)
Describe, with the aid of a fully labelled diagram, the industrial electrolysis of brine
in a diaphragm cell. State what each electrode is made of and show clearly the inlet
for the brine and the outlets for the products.
Write a half-equation, with state symbols, for the reaction at each electrode.
anode .......................................................................................................................
cathode ....................................................................................................................
(iii)
Name the chemical that is produced in solution in this electrolytic process.
.................................................
[7]
[Total: 7]
2
(a) State the relationship between the Faraday constant, F, the charge on the electron, e,
and the Avogadro number, L.
...................................................................................................................................... [1]
(b) If the charge on the electron, the Ar and the valency of copper are known, the value
of the Avogadro number can be determined experimentally. This is done by passing
a known current for a known time through a copper electrolysis cell, and weighing the
mass of copper deposited onto the cathode.
(i)
Draw a diagram of suitable apparatus for carrying out this experiment.
Label the following: power supply (with + and – terminals); anode; cathode; and
ammeter.
State the composition of the electrolyte.
The following are the results obtained from one such experiment.
current passed through the cell
= 0.500 A
time current was passed through cell = 30.0 min
initial mass of copper cathode
= 52.243 g
final mass of copper cathode
= 52.542 g
(ii)
Use these data and relevant information from the Data Booklet to calculate a value
of L to 3 significant figures.
L = ..............................................
[9]
(c) Use relevant information from the Data Booklet to identify the substances formed at
the anode and at the cathode when aqueous solutions of the following compounds are
electrolysed.
compound
product at anode
product at cathode
AgF
FeSO4
MgBr2
[5]
[Total: 15]
3
Although standard electrode potentials are measured for solutions where the concentrations
of ions are 1.0 mol dm–3, cells used as sources of battery power tend to operate with more
concentrated solutions. This question concerns the electrode reactions involved in the
hydrogen-oxygen fuel cell and the lead-acid car battery.
(a) In the hydrogen-oxygen fuel cell, H2(g) and O2(g) are fed onto two inert electrodes
dipping into NaOH(aq).
V
oxygen
hydrogen
NaOH(aq)
The following reactions take place.
(i)
left hand electrode (cathode):
H2(g) + 2OH–(aq)
right hand electrode (anode):
O2(g) + 2H2O(l) + 4e–
2H2O(l) + 2e–
4OH–(aq)
o–
for this reaction.
Use the Data Booklet to calculate E –cell
..................................................................................................................................
(ii)
Construct an equation for the overall reaction.
..................................................................................................................................
(iii)
(iv)
By using one of the phrases more positive, more negative or no change, deduce
the effect of increasing [OH–(aq)] on the electrode potential of
•
the left hand electrode
.......................................................................
•
the right hand electrode .......................................................................
Hence deduce whether the overall Ecell is likely to increase, decrease or remain the
same, when [OH–(aq)] increases. Explain your answer.
..................................................................................................................................
..................................................................................................................................
(v)
Suggest one other reason why a high [NaOH(aq)] is used in the fuel cell.
..................................................................................................................................
[6]
(b) In the cells of a lead-acid car battery the following reactions take place.
(i)
Pb2+(aq) + 2e–
cathode:
Pb(s)
anode:
PbO2(s) + 4H+(aq) + 2e–
Pb2+(aq) + 2H2O(l)
o–
Use the Data Booklet to calculate E –cell
for this reaction.
..................................................................................................................................
(ii)
Construct an equation for the overall reaction.
..................................................................................................................................
The electrolyte in a lead-acid cell is H2SO4(aq). Most of the Pb2+(aq) ions that are
produced at the electrodes are precipitated as the highly insoluble PbSO4(s).
(iii)
Construct an equation for the overall cell reaction in the presence of H2SO4.
..................................................................................................................................
(iv)
By considering the effect of decreasing [Pb2+(aq)] on the electrode potentials of
the cathode and the anode, deduce the effect of the presence of H2SO4(aq) in the
electrolyte on the overall Ecell.
State whether the Ecell will increase, decrease or remain the same.
Overall Ecell will ................................................ .
Explain your answer.
..................................................................................................................................
..................................................................................................................................
[5]
[Total: 11]
4
The design and development of batteries has been a major research area in recent years.
(a) Lead-acid batteries, used in cars, are made up of a number of rechargeable cells in
series, and were first developed in 1860. They have the disadvantage of a relatively high
mass compared to the energy stored. During discharge, the electrode reactions in the
cells of these batteries are as follows.
I
Pb + SO42– J PbSO4 + 2e–
II
PbO2 + 4H+ + SO42– + 2e– J PbSO4 + 2H2O
State which of these reactions occurs at the positive electrode in a lead-acid cell during
discharge, explaining your answer.
..........................................................................................................................................
...................................................................................................................................... [1]
(b) Use the Data Booklet and the equations I and II above to calculate the voltage produced
by a lead-acid cell under standard conditions.
[2]
(c) Nickel-metal hydride batteries were developed in the 1980s and have become
increasingly common particularly for small devices such as mobile phones and digital
cameras that need near-constant sources of electrical energy. These cells use nickel
oxohydroxide (NiO(OH)) as one electrode and a hydrogen-absorbing alloy such as LiNi5
as the other electrode.
One reaction that takes place in these batteries is
NiO(OH) + H2O + e–
Ni(OH)2 + OH–
(i)
State the oxidation state of nickel in NiO(OH). .....................
(ii)
Suggest a likely advantage of these batteries compared with lead-acid batteries.
..................................................................................................................................
..................................................................................................................................
[2]
(d) Hydrogen fuel cells have been suggested as the next major advance in electrically
powered vehicles. In these fuel cells hydrogen is oxidized to produce water, using a
catalyst and inert electrodes.
(i)
Suggest a material for the electrodes.
..........................................................................
(ii)
Use your knowledge of hydrogen to suggest a disadvantage of these fuel cells in
powering vehicles.
..................................................................................................................................
..................................................................................................................................
[2]
(e) Many of the world’s countries are developing ways of recycling materials which are
valuable or which require large amounts of energy to produce.
For each of the following recyclable materials, state whether recycling of this material is
important in saving energy or in saving resources. Use your knowledge of chemistry to
explain each choice.
glass ................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
steel .................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
plastics .............................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
[3]
[Total: 10]
5
The electrolytic purification of copper can be carried out in an apparatus similar to the one
shown below.
impure copper anode
anode ‘sludge’
pure copper cathode
CuSO4 (aq)
The impure copper anode contains small quantities of metallic nickel, zinc and silver, together
with inert oxides and carbon resulting from the initial reduction of the copper ore with coke.
The copper goes into solution at the anode, but the silver remains as the metal and falls to
the bottom as part of the anode ‘sludge’. The zinc also dissolves.
(a) (i)
Write a half equation including state symbols for the reaction of copper at the
anode.
..................................................................................................................................
(ii)
Use data from the Data Booklet to explain why silver remains as the metal.
..................................................................................................................................
(iii)
Use data from the Data Booklet to predict what happens to the nickel at the anode.
..................................................................................................................................
..................................................................................................................................
(iv)
Write a half equation including state symbols for the main reaction at the cathode.
..................................................................................................................................
(v)
Use data from the Data Booklet to explain why zinc is not deposited on the
cathode.
..................................................................................................................................
..................................................................................................................................
(vi)
Suggest why the blue colour of the electrolyte slowly fades as the electrolysis
proceeds.
..................................................................................................................................
..................................................................................................................................
[7]
(b) Most of the current passed through the cell is used to dissolve the copper at the anode
and precipitate pure copper onto the cathode. However, a small proportion of it is
‘wasted’ in dissolving the impurities at the anode which then remain in solution.
When a current of 20.0 A was passed through the cell for 10.0 hours, it was found that
225 g of pure copper was deposited on the cathode.
(i)
(ii)
Calculate the following, using appropriate data from the Data Booklet.
•
number of moles of copper produced at the cathode
•
number of moles of electrons needed to produce this copper
•
number of moles of electrons that passed through the cell
Hence calculate the percentage of the current through the cell that has been
‘wasted’ in dissolving the impurities at the anode.
[4]
(c) Nickel often occurs in ores along with iron. After the initial reduction of the ore with coke,
a nickel-iron alloy is formed.
Use data from the Data Booklet to explain why nickel can be purified by a similar
electrolysis technique to that used for copper, using an impure nickel anode, a pure
nickel cathode, and nickel sulfate as the electrolyte. Explain what would happen to the
iron during this process.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
...................................................................................................................................... [2]
[Total: 13]
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 4
Time Allowed:
72 minutes
Score:
/60
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i) 2H2O – 4e → 4H+ + O2 (1)
(ii) 2Cl – – 2e → Cl2 (1)
[2]
(b) (i) Eo = (1.23 – (–0.83)) = 2.06V (1)
(ii) Eo = (1.36 – (–0.83)) = 2.19V (1)
(in (i) if (a)(i) as 4(OH–) – 4e → 2H2O + O2 ecf is 0.4 – (–0.83) = 1.23 (1) – needs
working shown)
[2]
(c)
c) (
no change (because [H2O] does not change) (1)
smaller/less positive (1)
(ii) The (overall) Eo for Cl2 production will decrease, (whereas that) for O2 production will
stay the same. (answer could be in terms of 1st Eo decreasing and becoming lower than
2nd)(or Eo for Cl2 becomes less than for O2) (1)
[3]
(d) (i) Cl – + 3H2O → ClO3– + 3H2 (1)
(ii) n(C) = 250 × 60 × 60 = (9 × 105 C) (1)
n(e–) = 9 × 105/96500 = 9.33 mol
n(NaClO3) = 9.33/6 = (1.55 mol) – allow ecf (1)
Mr(NaClO3) = 106.5
mass (NaClO3) = 1.55 × 106.5 = 165.5 g (1) (165 – 166 gets 3 marks, 993 gets 2 marks
as ecf)
[4]
[Total: 11]
2
(a
Graphite / graphene
(1)
(b) They do not exist as sheets / layers of carbon atoms
(1)
(c) The lengths of nanotubes are much shorter than the curvature of the paper /
they are so small that they are not effected by rolling
(1)
(d) Any molten ionic salt (or plausible organic ionic compounds)
(1)
[Total: 4]
3
(a
(i) A is Cl2/chlorine
chl
B is NaCl or HCl or Cl ¯ [or words], etc.
[1]
C is salt bridge or KCl/KNO3, etc.
[1]
D is platinum/Pt
[1]
E is Fe2+ + Fe3+ or mixture of Fe(II) + Fe(III) salts
[1]
mention of standard conditions ([Cl ¯] of 1 mol dm–3 or Cl2 at 1 atmos
or T = 25°C/298 K)
[1]
(ii) Eo = EoR – EoL= 0.77 – 1.36 = (–)0.59 (V) (ignore sign)
[1]
(since R.H. electrode is negative) electrons flow (from right) to left or to the chlorine
electrode or anticlockwise or from (beaker) E to (beaker) B
[1] [8]
(b)
b)
∆H = 3 ×(–167.2) + (–48.5) – (–399.5)
= –150.6 or 151 (kJ mol–1)
(correct ans [2])
(ii) 2Fe3+ + Cu → 2Fe2+ + Cu2+
(or molecular: 2FeCl3 + Cu → 2FeCl2 + CuCl2)
Eo = 0.77 – 0.34 = (+) 0.43 (V)
(no mark for –0.43V)
[1]
[1
[1]
[1]
[4]
[Total: 12 max 11]
4
(a
anode
Cl – (aq) → ½ Cl2(g) + e– (1)
cathode H+(aq) + e– → ½H2(g)
or
2H2O(l) + 2e– → H2(g) + 2OH–(aq) (1)
correct state symbols (1)
[2]
(b) because the iron in steel will react with chlorine (1)
[1]
(c) (i) sodium hydroxide/NaOH (1)
2H2O + 2e– → H2 + 2OH–
or 2H+ + 2e– → H2 (1)
leaving OH– in solution as NaOH (1)
[3]
(d) Na burns with a yellow flame/forms a white solid (1)
2Na + Cl2 → 2NaCl (1)
P burns with a white flame/forms a colourless liquid (PCl3) or a white solid (PCl5) (1)
P + 1½Cl2 → PCl3 or P4 + 6Cl2 → 4PCl3
or P + 2½Cl2 → PCl5 or P4 + 10Cl2 → 4PCl5 (1)
[4]
(e) MgCl2 6 to 7 (1)
SiCl4 0 to 3 (1)
MgCl2 dissolves without reaction (1)
SiCl4 reacts with water/hydrolyses (1)
SiCl4 + 2H2O → SiO2 + 4HCl or
SiCl4 + 4H2O → Si(OH)4 + 4HCl or
SiCl4 + 4H2O → SiO2.2H2O + 4HCl (1)
[5]
[Total: 15 max]
5
(a)
salt bridge + voltmeter
zinc metal + Zn2+
H2 (in, not out) + H+
Pt electrode
all solutions at 1 mol dm–3
T = 298K or 25oC
[1]
[1]
[1]
[1]
[1]
[1] [6]
(b)
conditions
ZnCl2(l)
ZnCl2(conc aq)
ZnCl2(dil aq)
product at anode
(chlorine)
chlorine [1]
oxygen [1]
product at cathode
zinc [1]
(H2 or zinc) (ignore)
hydrogen [1]
[1]
1] for each product in correct place [
[4]
(c)
LE
=B–A
= –415 – (131 + 908 + 1730) – {244 + 2(–349)}
[1]
[1]
= –415 – 2315
= –2730 (kJ mol–1)
[1]
(correct answer = [3]: deduct [1] for each error) [3]
(d) (i)
• instrumental method (e.g. spectrophotometer/colorimeter/conductance meter)
• what is measured (e.g. absorbance/transmission at a stated wavelength
or by use of a “suitable” (green) filter or conductance/resistance)
• measurement of time
• relation of time to rate (e.g. gradient of absorbance/time graph, or rate ∝ 1/t)
• repeat with different [Zn2+], (but the same [PAR])
• relation of rate to [Zn2+] (either by a plot or by simple proportion)
(all 6 points are unconditional on each other) any 5 points [5]
(ii) e.g. add Br2(aq)
aq)
decolourises or produces a white ppt.
or add FeCl3(aq or “neutral”); purple colour produced
[1]
[1]
1] + [
[2]
[Total: 20]
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Electrolysis, Electrode
Potentials & Cells
Question Paper 4
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 4
Time Allowed:
72 minutes
Score:
/60
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Chlorine is manufactured by the electrolysis of brine, NaCl(aq). At the cathode, H2(g) and
OH–(aq) are produced, but the product at the anode depends on the [NaCl(aq)] in the
solution. Either O2(g) or Cl2(g) is produced.
(a) The equation for the cathode reaction is 2H2O(l) + 2e–
H2(g) + 2OH–(aq).
Starting from neutral NaCl(aq), write equations for the production at the anode of
(i)
O2(g), .......................................................................................................................
(ii)
Cl2(g). ......................................................................................................................
[2]
(b) For electrolysis to occur, the voltage applied to the cell must be at least as large as the
–
, as calculated from standard electrode potentials.
E –ocell
–
for the production at the anode of
Use the Data Booklet to calculate E –ocell
(i)
O2(g), .......................................................................................................................
(ii)
Cl2(g). ......................................................................................................................
[2]
(c) (i)
By using one of the phrases more positive, less positive or no change, use the
equations you wrote in (a) to deduce the effect of increasing [Cl –(aq)] on
(ii)
•
the Eanode for the production of O2(g), .............................................................
•
the Eanode for the production of Cl2(g). .............................................................
g atio increases as [NaCl(aq)] increases.
Hence explain why the Cl2(g) : O2(g)
..................................................................................................................................
.............................................................................................................................. [3]
(d) Sodium chlorate(V) is prepared commercially by electrolysing NaCl(aq) in a cell which
allows the cathode and anode electrolytes to mix.
The cathode reaction is the same as that described in (a).
The equation for the anode reaction is
Cl –(aq) + 6OH–(aq) – 6e–
(i)
ClO3–(aq) + 3H2O(l)
Construct an ionic equation for the overall reaction.
..................................................................................................................................
(ii)
Calculate the mass of NaClO3 that is produced when a current of 250 A is passed
through the cell for 60 minutes.
mass of NaCl O3 = ............................................... g [4]
[Total: 11]
2
A new method of making very light, flexible batteries using nanotechnology was announced
in August 2007. Read the passage and answer the questions related to it.
Researchers have developed a new energy-storage device that could easily be mistaken
for a simple sheet of black paper. The nano-engineered battery is lightweight, ultra-thin and
completely flexible. It is geared towards meeting the difficult design and energy requirements
of tomorrow’s gadgets, such as implantable medical devices and even vehicles.
Researchers soaked ‘paper’ in an ionic liquid electrolyte which carries the charge. They then
treated it with aligned carbon nanotubes, which give the device its black colour.
The nanotubes act as electrodes and allow the storage devices to conduct electricity. The
device, engineered to function as both a battery and a supercapacitor, can provide the long,
steady power output comparable to a conventional battery, as well as a supercapacitor’s
quick burst of high energy. The device can be rolled, twisted, folded, or cut into shapes with
no loss of strength or efficiency. The ‘paper’ batteries can also be stacked, like a pile of
printer paper, to boost the total power output.
1.
Conventional batteries produce electrons through a chemical reaction between electrolyte
and metal.
2.
Chemical reaction in the ‘paper’ battery is between electrolyte and carbon nanotubes.
3.
Electrons collect on the negative terminal of a battery.
4.
Electrons must flow from the negative terminal, through the external circuit to the positive
terminal for the chemical reaction to continue.
nanotube
(a) From your knowledge of the different structures of carbon, suggest which of these is
used to make nanotubes.
..................................................................................................................................... [1]
(b) Suggest a property of this structure that makes it suitable for making nanotubes.
..........................................................................................................................................
..................................................................................................................................... [1]
(c) Carbon in its bulk form is brittle like most non-metallic solids. Suggest why the energy
storage device described can be rolled into a cylinder.
..........................................................................................................................................
..................................................................................................................................... [1]
(d) Name an example of an ‘ionic liquid electrolyte’ (not a solution).
..................................................................................................................................... [1]
[Total: 4]
3
Chlorine gas and iron(II) ions react together in aqueous solution as follows.
Cl 2 + 2Fe2+
2Cl – + 2Fe3+
(a) The following diagram shows the apparatus needed to measure the E ocell for the above
reaction.
S
V
A
E
C
D
B
(i)
In the spaces below, identify what the five letters A – E in the above diagram
represent.
A .........................................................
B .........................................................
C .........................................................
D .........................................................
E .........................................................
(ii)
Use the Data Booklet to calculate the E ocell for this reaction, and hence decide which
direction (left to right, or right to left) electrons would flow through the voltmeter V
when switch S is closed.
E ocell = .................................................. V
direction of electron flow ......................................................
[7]
(b) Iron(III) chloride readily dissolves in water.
FeCl 3(s)
(i)
Fe3+(aq) + 3Cl –(aq)
Use the following data to calculate the standard enthalpy change for this process.
species
DH of / kJ mol–1
FeCl 3(s)
–399.5
Fe3+(aq)
–48.5
Cl –(aq)
–167.2
DH o = .........................................kJ mol–1
(ii)
A solution of iron(III) chloride is used to dissolve unwanted copper from printed
circuit boards.
When a copper-coated printed circuit board is immersed in FeCl 3(aq), the solution
turns pale blue.
Suggest an equation for the reaction between copper and iron(III) chloride and use
the Data Booklet to calculate the E o for the reaction.
equation ...................................................................................................................
E o = .................................................. V
[4]
[Total: 11]
4
Chlorine gas is manufactured by the electrolysis of brine using a diaphragm cell.
(a) Write half-equations, including state symbols, for the reactions occurring at each of the
electrodes of a diaphragm cell.
anode ...............................................................................................................................
cathode ....................................................................................................................... [2]
(b) In the diaphragm cell, the anode is made of titanium and the cathode is made of steel.
Suggest why steel is never used for the anode.
..........................................................................................................................................
..................................................................................................................................... [1]
(c) One important product made in the diaphragm cell is formed in aqueous solution.
(i)
What substance is produced in aqueous solution in the diaphragm cell?
..................................................................................................................................
(ii)
Explain, with the aid of appropriate half-equation(s), how this compound is formed
by electrolysis.
..................................................................................................................................
..................................................................................................................................
............................................................................................................................. [3]
(d) Chlorine is very reactive and will form compounds by direct combination with many
elements.
Describe what you would see when chlorine is passed over separate heated samples of
sodium and phosphorus. In each case write an equation for the reaction.
sodium .............................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
phosphorus ......................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [4]
(e) Magnesium chloride, MgCl 2, and silicon tetrachloride, SiCl 4, each dissolve in or react
with water.
Suggest the approximate pH of the solution formed in each case.
MgCl 2 …………………………………
SiCl 4 …………………………………
Explain, with the aid of an equation, the difference between the two values.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [5]
[Total: 15]
5
Zinc chloride is one of the most important compounds of zinc. It is used in dry cell batteries,
as a flux for soldering and tinning, as a corrosion inhibitor in cooling towers and in the
manufacture of rayon.
(a) Draw a fully labelled diagram to show how you could use a standard hydrogen electrode
to measure the standard electrode potential, E o, of zinc.
[6]
(b) The electrolysis of zinc chloride can give different electrode products, depending on the
conditions used.
Suggest the products formed at each electrode in the following cases. One space has
been filled in for you.
conditions
product at anode
product at cathode
chlorine
ZnCl2(l)
ZnCl2(concentrated aqueous)
ZnCl2(dilute aqueous)
[3]
(c) Use the following data, together with relevant data from the Data Booklet, to construct a
Born-Haber cycle and calculate a value for the lattice energy of zinc chloride.
standard enthalpy change of formation of ZnCl2
–415 kJ mol–1
standard enthalpy change of atomisation of Zn(s)
+131 kJ mol–1
electron affinity per mole of chlorine atoms
–349 kJ mol–1
lattice energy = ............................................... kJ mol–1 [3]
(d) Zinc is an essential element for plant and animal life. It is often administered in the form
of a chelate, which is a complex between a metal ion and a polydentate ligand.
The rate of the reaction between zinc ions and the ligand 4-(2-pyridylazo)resorcinol,
PAR, has been studied.
HO
Zn2+ + 2
N
HO
Zn2+
N
N
N
N
+ 2
N
–
O
HO
PAR
2
Zn-PAR
Both PAR and its zinc complex absorb radiation in the UV-visible region. The figure
below shows their absorption spectra.
1.4
absorbance
1.2
1.0
0.8
0.6
PAR
Zn-PAR
0.4
0.2
0.0
300
400
500
600
700
wavelength / nm
(i)
Devise a suitable experimental technique for studying how the rate of this reaction
varies with [Zn2+(aq)].
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
(ii)
Describe a reaction you could carry out to show that PAR is a phenol.
..................................................................................................................................
..................................................................................................................................
[7]
[Total: 19]
+
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 5
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
(i)
(ii)
(iii)
Ammeter/galvanometer
[1]
Clock/watch/timer (or rheostat)
(For items above 2 in number, e.g. voltmeter, penalise [1])
[1]
Diagram to show ammeter (allow symbol) in circuit, and
complete circuit with terminal of power pack connected to LH
electrode
[1]
Volume/amount of hydrogen/gas
[1]
Time
[1]
Current/amps/ammeter reading
(ignore extra measurements)
[1]
[1]
Part (a): [7]
(b)
b)
(ii)
F=Lxe
[1]
L = 9.63 x 104/1.6 x 10-19 = 6.02 x 1023 (must show working)
[1]
Allow 6.0 but not 6 or 6.01
Part (b): [2]
Total: [9]
2
(a
Mr(AgBr) = 108 + 79.9 = 187.9
[1]
moles = 2.5 x 10-12/187.9 = 1.33 x 10-14
no. of ions = 1.33 x 10-14 x 6 x 1023 = 8.0 x 109 ions
(correct ans = [2])
[1]
2
(b)
b)
A: platinum
B: H+(aq) or HCl(aq) or H2SO4(aq)
(ignore concentration)
C: voltmeter
D: silver (wire)
4 x [1]
(ii) (As [Ag+] decreases), the potential will decrease/become more negative
[1]
(iii) Ksp = [Ag+][Br-]
[1]
= (7.1 x 10-7)2 = 5.0(41) x 10-13 mol2dm-6
units [1]
7
(c)
c)
Ag+(g) + Br-(g) → AgBr(s)
(ii) LE
[1]
=
∆Hf - (all the rest)
=
-100 – (731 + 285 + 112 – 325
(=
-100 - 731 - 285 - 112 + 325
=
-903 kJ mol-1
(-[1] for each error of sign or maths)
(iii) LE(AgCl) should be higher/more negative,
due to size/radius of Cl- being less than that of Br- (both)
[2]
[1]
4
(d) more energy needed, since rCl - < rBr- or ionised electron nearer to nucleus
or less shielding etc. or in terms of I.E.(Cl) > I.E.(Br)
1
total: 14
3 (a)
Mg2+ + 2e-
Mg
[1]
(b)
chlorine/Cl2
[1]
(c)
smaller Ar
larger (atomic/ionic) radius/size
[1]
[1]
(d) (i) the energy change when 1 mol of solid compound
is formed from its gaseous ions
(ii) Mg2+ (g) + 2Cl- (g)
MgCl2 (s)
[1]
[1]
charges + balancing
state symbols
(e) (i) LE (MgCl2) is greater than LE (NaCl)
(because) Mg2+ has higher charge / smaller radius than Na+
(ii) LE (MgCl2) is greater than LE (CaCl2)
(because) Mg2+ is smaller than Ca2+
(f)
[1]
[1]
[1]
[1]
[1]
[1]
LE = 349 – 122 – 494 – 107 – 411
= -785 (kJ mol-1)
[3]
correct answer = [3], with – [1] for one error. OR mark as follows:
use of all 5 ∆H values, with x1 multipliers
[1]
correct signs for all ∆H values
[1]
negative sign in answer
[1]
Total = [15]
4
(a) (i)
[4]
(ii) anode 2Cl - (aq) → Cl2(g) + 2ecathode 2H+(aq) + 2e- → H2(g) (1)
or 2H2O(l) + 2e- → H2(g) + 2OH-(aq) (1)
[2]
(iii) anode Cl goes from -1 to 0 (1)
cathode H goes from -1 to 0 (1)
(iv) sodium hydroxide (answer may be on diagram) (1)
[2]
[1]
(v) manufacture of
soap
detergents
paper
degreasing fluids
rayon
aluminium
glass
dyes
bleach/NaClO/Javel/Jik/Jenola
(b)
b) (
any 2 [1]
H2 + Cl2 → 2HCl (1)
(ii) HCl + H2O → H3O+ + Cl - (1)
thus bonding goes form covalent to ionic
(c)
c) (
[2]
AgNO3(aq) + HCl(aq) → AgCl(s) + HNO3(aq)
or Ag+(aq) + Cl - (aq) → AgCl(s) (1)
white ppt. forms (1)
(ii) ppt. dissolves to give colourless solution (1)
AgCl(s) + 2NH3(aq) → [Ag(NH3)2] Cl(aq)
or Ag+(s) + 2NH3(aq) → [Ag(NH3)2]+(aq) (1)
Correct state symbols in either (i) or (ii) (1)
[5]
[Total 17]
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Electrolysis, Electrode
Potentials & Cells
Question Paper 5
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 5
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
A student decided to determine the value of the Faraday constant by an electrolysis
experiment. The following incomplete diagram shows the apparatus that was used.
hydrogen
being
collected
+
power pack
dilute H2SO4
–
inert electrodes
(a)
(i) Apart from connecting wires, what two additional pieces of equipment are needed
for this experiment?
..................................................................................................................................
..................................................................................................................................
(ii) Complete the diagram, showing additional equipment connected in the circuit, and
showing the powerpack connected to the correct electrodes.
(iii) List the measurements the student would need to make in order to use the results
to calculate a value for the Faraday constant.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[7]
(b)
(i) Using an equation, state the relationship between the Faraday constant, F, the
Avogadro constant, L, and the charge on the electron, e.
..................................................................................................................................
(ii) The value the student obtained was:
1 Faraday = 9.63 × 104 Coulombs
Use this value and your equation in (b)(i) to calculate the Avogadro constant (take
the charge on the electron to be 1.60 × 10–19 Coulombs)
..................................................................................................................................
..................................................................................................................................
[2]
[Total: 9]
2
Silver bromide, AgBr, is widely used in photography. In a photographic film, AgBr crystals
are precipitated into a gelatine base as ‘grains’ of diameter about 1 × 10–6 m.
(a) Calculate the approximate number of silver ions contained in a grain of AgBr of mass
2.5 × 10–12 g.
..........................................................................................................................................
.................................................................................................................................... [2]
(b) AgBr is only sparingly soluble in water. The [Ag+] in a saturated solution of AgBr can
be estimated by measuring the Ecell of the following cell.
C
H2(g), 1 atm, 298 K
salt bridge
D
A
B
[Ag+(aq)] = x mol dm–3
(i) In the spaces below, identify what the four letters A – D in the above diagram
represent.
A ....................................................
C ....................................................
B ....................................................
D ....................................................
(ii) Predict how the potential of the right hand electrode might vary as [Ag+] is
decreased.
..................................................................................................................................
In its saturated solution, [AgBr(aq)] = 7.1 × 10–7 mol dm–3.
(iii) Write an expression for the solubility product of AgBr, and calculate its value,
including units.
..................................................................................................................................
..................................................................................................................................
[7]
(c)
(i) Write a chemical equation representing the lattice energy of AgBr.
..................................................................................................................................
(ii) Use the following data to calculate a value for the lattice energy of AgBr(s).
first ionisation energy of silver
electron affinity of bromine
enthalpy change of atomisation of silver
enthalpy change of atomisation of bromine
enthalpy change of formation of AgBr(s)
=
=
=
=
=
+731 kJ mol–1
–325 kJ mol–1
+285 kJ mol–1
+112 kJ mol–1
–100 kJ mol–1
..................................................................................................................................
(iii) How might the lattice energy of AgCl compare to that of AgBr? Explain your
answer.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[4]
In photography a bromide ion absorbs a photon and releases an electron which reduces a
silver ion to a silver atom.
Br –
→
Br + e–
Ag+ + e–
→
Ag
(d) Predict whether it would require more energy or less energy to initiate this process in
a AgCl emulsion, compared to a AgBr emulsion. Explain your answer.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [1]
[Total: 14]
3
Magnesium is used extensively in the form of alloys as a constructional material due to its
low density (1.7 g cm–3, compared to 7.8 g cm–3 for iron). It is usually prepared by the
electrolysis of magnesium chloride, MgCl2, at a temperature a little above its melting point of
715 °C.
(a) Suggest the half-equation that represents the production of magnesium at the cathode
during the electrolysis.
......................................................................................................................................[1]
(b) What will be the product at the other electrode?
......................................................................................................................................[1]
(c) Suggest two properties of its atoms that could explain why magnesium is less dense
than iron.
..........................................................................................................................................
......................................................................................................................................[2]
One of the reasons the melting point of magnesium chloride is quite high is because it has a
fairly high lattice energy.
(d) (i)
Explain the term lattice energy.
...................................................................................................................................
...................................................................................................................................
(ii)
Write a balanced equation including state symbols to represent the lattice energy
of magnesium chloride.
...................................................................................................................................
...............................................................................................................................[4]
(e) Suggest, with an explanation in each case, how the lattice energy of magnesium
chloride might compare with that of
(i)
sodium chloride, NaCl,
...................................................................................................................................
...................................................................................................................................
(ii)
calcium chloride, CaCl2.
...................................................................................................................................
...............................................................................................................................[4]
(f)
Use the following data to calculate a value for the lattice energy of sodium chloride.
∆Hf (NaCl)
∆Hat (Na)
∆Hat (Cl)
first ionisation energy of Na
electron affinity of Cl
=
=
=
=
=
– 411 kJ mol–1
107 kJ mol–1
122 kJ mol–1
494 kJ mol–1
– 349 kJ mol–1
lattice energy of NaCl = ........................................ kJ mol–1 [3]
[Total: 15]
4
(a) (i)
(ii)
Describe, with the aid of a fully labelled diagram, the industrial electrolysis of brine
(aqueous NaCl). State what the electrodes are made of and show clearly the inlet
and the outlets.
Write equations for the reactions at each electrode, giving state symbols.
anode ........................................................................................................................
cathode .....................................................................................................................
(iii)
Explain in terms of changes in oxidation number why redox processes take place at
the electrodes.
anode ........................................................................................................................
cathode .....................................................................................................................
(iv)
Name the chemical which is produced in solution by this electrolysis.
...................................................................................................................................
(v)
Suggest two large scale uses of this chemical.
...................................................................................................................................
...................................................................................................................................
[10]
(b) Hydrochloric acid is manufactured by burning the hydrogen formed in this electrolysis in
chlorine and dissolving the product in water.
(i)
Construct an equation for the burning of hydrogen in chlorine.
...................................................................................................................................
(ii)
When the product of (i) dissolves in water there is a change in bonding. Explain
with the aid of an equation what change in bonding has occurred.
[2]
(c) Describe, with the aid of equations including state symbols, what happens when
(i)
hydrochloric acid is added to aqueous silver nitrate,
...................................................................................................................................
...................................................................................................................................
(ii)
an excess of aqueous ammonia is added to the resulting mixture.
...................................................................................................................................
...................................................................................................................................
...............................................................................................................................[5]
[Total : 17]
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 6
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 6
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) O2 + 4H+ + 4e-
2H2O (or equation ÷ 2)
[1]
1
(b) ⊕
[1]
1
(c) 1.23 (V) (ignore sign)
[1]
1
(d) a better/larger salt bridge or a diaphragm or larger (area of) electrodes
or increase concentrations/pressure
[1]
(e) time = 400 x 24 x 60 x 60 = 34 560 000 seconds
[1]
charge = current x time = 0.01 x 34 560 000 = 345 600 C
moles of H = 345 600/96 500 = 3.6 mol
(f) advantages:
∴ mass of H = 3.6 g
ecf [1]
ecf [1]
3
less pollution/CO2/NOx etc. or cleaner by-products
less dependence on fossil fuels/finite resources
disadvantages:
1
any one [1]
more expensive (to develop or to run)
takes up more space
poor power-to-volume ratio
hydrogen is difficult to store or to transport
NOT hydrogen is explosive/flammable
any one [1]
2
Total 9
2
(a)
The EMF of a cell made up of the test electrode and a
standard hydrogen electrode.
[1]
EMF measured under standard conditions of T, P and concentration
[1]
2
(b)
(i) Eleft = Eright – Ecell
(ii)
= 0.34 - 0.76
= -0.42 (V)
[1]
(arrow from left to right)
(iii) I
II
[1]
pink/red solid/ppt or copper will be formed or blue solution
fades or M dissolves/corrodes
[1]
Cu2+ + M → Cu + M2+
[1]
hydrogen/gas evolved or M dissolves
(do not allow "M dissolves" for [2] marks in both I and II)
[1]
M + 2H+ → M2+ + H2
[1]
6
(c)
(i) polarity of d. c. source:
“* is on the left, % is on the right
electrolyte is Cu2+(aq)/CuSO4/CuCl2/Cu(NO3)2 etc. or name
(ii) moles of Cu = 0.5/63.5
moles of e- = 2 x 7.87 x 10-3
= 7.87 x 10-3
=
[1]
[1]
= 1.57 x 10-2
no. of coulombs = 96500 x 1.57 x 10-2 = 1517 (C)
time = 1520/0.5
[1]
[1]
ecf in n(e-)
[1]
ecf in coulombs
5
Total 13
Question
uest
3
Scheme
name of particle
(a)
relative mass
Mark
relative charge
proton
r
electron
1/1836
neutron
e
(b) (i)
(ii)
Total
+
[1]
–
[1]
0
[1]
Mass of an atom(s)
[1]
relative to 1 / 12th (the mass) of (an atom of) carbon-12
OR
relative to carbon-12 which is (exactly) 12
[1]
% of third isotope = 10
[1]
(24 × 79) + (26 ×11.0) +10x
= 24.3
100
[1]
[3]
[2]
10x = 248
x = 24.8 (3s.f.)
(c) (i)
(ii)
(d) (i)
(ii)
anode
ano
cathode
cat
l – Cl2 + 2e–
2+
+ 2e– Mg
Mg
31.65
24.3
O
20.84
16
1.3
1.30
0
1.30
H
1.31
1
Cl
46.2
35.5
[1]
[3]
[1]
[1]
[2]
[1]
MgOHCl
[1]
[2]
Na2O basic / alkaline; Al2O3 amphoteric / acidic and basic; SO3 acidic
Na2O (giant) ionic AND SO3 (simple / molecular) covalent
[1]
[1]
[2]
Na2O + 2HCl 2NaCl + H2O
[1]
Al2O3 + 6HCl 2AlCl3 + 3H2O
[1]
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
Al2O3
+
+
+
+
+
+
2NaOH + 7H2O 2NaAl(OH)4(H2O)2 OR
2NaOH + 3H2O 2NaAl(OH)4 OR
2NaOH 2NaAlO2 + H2O OR
2OH‒ + 7H2O 2[Al(OH)4(H2O)2] ‒ OR
2OH‒ + 3H2O 2[Al(OH)4] ‒OR
2OH− 2AlO2− + H2O
SO3 + NaOH NaHSO4 OR
SO3 + 2NaOH Na2SO4 + H2O
[1]
[1]
[4]
[18]
4
(a
(i)
Ksp = [Ag+(aq)]2[SO42–(aq)] and units: mol3dm–9
1
(ii)
Ksp = (2 x 0.025)2 x (0.025) = 6.25 x 10–5
1
(b)
+
H
2-
4
o
latt
Ag2SO4(s)
o
hyd
o
sol
2
+
(c) (i)
(ii)
4
or
24
1
1
1
1
Eocell (= 0.80 – 0.77 =) (+)0.03V and Ag+ / Ag or Ag / silver or right
1
Ecell would be less positive / more negative
1
because the [Ag+(aq)] (in the Ag electrode) is less than 1.0 mol dm–3
(iii)
(iv)
(d)
•
no change
1
•
more negative / less positive
1
the [Ag+(aq)] will decrease
Eelectrode becomes less positive or due to the common ion effect
1
[Fe3+(aq)] = 0.2 mol dm–3
1
[H+] = √(c.Ka) = √(0.2 x 8.9 x 10–4) or 1.33 x 10–2 (mol dm–3)
pH = –log([H+]) = 1.9 (or 1.87–1.89)
1
[Total: 13]
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Electrolysis, Electrode
Potentials & Cells
Question Paper 6
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 6
Time Allowed:
64 minutes
Score:
/53
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The diagram shows a laboratory illustration of a simple hydrogen-oxygen fuel cell.
V
oxygen gas at
1 atmosphere
hydrogen gas at
1 atmosphere
salt bridge
solution of
hydrochloric acid:
[H3O+] = 1 mol dm-3
inert electrodes
solution of
hydrochloric acid:
[H3O+] = 1 mol dm-3
(a) Write the half equation for the reaction occurring at the left hand (oxygen) electrode
when the cell operates.
..........................................................................................................................................
..................................................................................................................................... [1]
(b) State the polarity (+ or –) of the left hand (oxygen) electrode. ..................................... [1]
(c) Use the Data Booklet to calculate the voltage produced by this cell.
..................................................................................................................................... [1]
(d) Only a very small current can be drawn from this laboratory cell. Suggest one way in
which it could be modified to enable a larger current to be drawn from it.
..........................................................................................................................................
..................................................................................................................................... [1]
(e) A fuel cell in an orbiting satellite is required to produce a current of 0.010 A for 400 days.
Calculate the mass of hydrogen that will be needed.
..........................................................................................................................................
..........................................................................................................................................
..................................................................................................................................... [3]
(f)
State one advantage, and one disadvantage of using fuel cells to power road vehicles
compared to hydrocarbon fuels such as petrol.
advantage: .......................................................................................................................
..........................................................................................................................................
disadvantage: ...................................................................................................................
..................................................................................................................................... [2]
[Total: 9]
2
(a) What do you understand by the term standard electrode potential?
..........................................................................................................................................
......................................................................................................................................[2]
(b) The following cell was set up between a copper electrode and an unknown metal
electrode M 2+(aq) / M(s). The standard cell potential was found to be 0.76 V, and the
copper foil was the positive electrode.
direction of electron flow
V
unknown metal
wire, M
M 2+(1 mol dm–3)
(i)
copper foil
CuSO4(1 mol dm–3)
Use the Data Booklet to calculate the standard electrode potential of the
M 2+(aq) / M(s) system.
...................................................................................................................................
(ii)
Draw an arrow over the voltmeter symbol in the above diagram to show the
direction of electron flow through the voltmeter.
(iii)
Predict the outcomes of the following situations. Describe what you might see and
write ionic equations for any reactions that occur.
I
A rod of metal M is dipped into a solution of 1 mol dm–3 CuSO4.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
II
Dilute sulphuric acid is added to a beaker containing a powdered sample of metal
M.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
[6]
(c) Because of its increased scarcity, cheaper copper ornaments are no longer made from
the solid metal, but from iron that has been copper plated.
(i)
Complete the following diagram showing the set-up for a copper electroplating
process. Show clearly the polarity (+/–) of the power source, and suggest a suitable
electrolyte.
d.c. source
A
object to be plated
electrolyte:
(ii)
A current of 0.500 A is passed through the electroplating cell. Calculate the time
required to deposit a mass of 0.500 g of copper on to the ornament.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
[5]
[Total : 13]
3
(a) Chemists recognise that atoms are made of three types of particle.
Complete the following table with their names and properties.
name of particle
relative mass
relative charge
+1
1/1836
[3]
(b) Most elements exist naturally as a mixture of isotopes, each with their own relative isotopic
mass. The mass spectrum of an element reveals the abundances of these isotopes, which can
be used to calculate the relative atomic mass of the element.
Magnesium has three stable isotopes. Information about two of these isotopes is given.
isotope
relative
isotopic mass
percentage
abundance
24
Mg
24.0
79.0
26
Mg
26.0
11.0
(i) Define the term relative isotopic mass.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) The relative atomic mass of magnesium is 24.3.
Calculate the percentage abundance and hence the relative isotopic mass of the third
isotope of magnesium. Give your answer to three significant figures
percentage abundance = .................................
isotopic mass = .................................
[3]
(c) Magnesium can be produced by electrolysis of magnesium chloride in a molten mixture of
salts.
(i) Give equations for the anode and cathode reactions during the electrolysis of molten
magnesium chloride, MgCl 2.
anode ..................................................................................................................................
cathode ...............................................................................................................................
[2]
The electrolysis is carried out under an atmosphere of hydrogen chloride gas to convert any
magnesium oxide impurity into magnesium chloride.
(ii) An investigation of the reaction between magnesium oxide and hydrogen chloride
gas showed that an intermediate product was formed with the composition by mass
Mg, 31.65%; O, 20.84%; H, 1.31% and Cl, 46.20%.
Calculate the empirical formula of this intermediate compound.
empirical formula .................................... [2]
(d) The acid/base behaviour of the oxides in the third period varies across the period.
(i) Describe this behaviour and explain it with reference to the structure and bonding of
sodium oxide, Na2O, aluminium oxide, Al 2O3, and sulfur trioxide, SO3.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Write equations for reactions of these three oxides with hydrochloric acid and/or sodium
hydroxide as appropriate.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
[Total: 18]
4
(a) Silver sulfate, Ag2SO4, is sparingly soluble in water. The concentration of its saturated solution
is 2.5 × 10–2 mol dm–3 at 298 K.
(i)
Write an expression for the solubility product, Ksp, of Ag2SO4, and state its units.
Ksp =
(ii)
units: .............................. [1]
Calculate the value for Ksp(Ag2SO4) at 298 K.
Ksp = ............................................... [1]
(b) Using Ag2SO4 as an example, complete the following Hess' Law energy cycle relating the
●
lattice energy,
●
enthalpy change of solution,
●
enthalpy change of hydration,
,
, and
.
On your diagram:
●
include the relevant species in the two empty boxes,
●
label each enthalpy change with its appropriate symbol,
●
complete the remaining two arrows showing the correct direction of enthalpy change.
..............................
Ag2SO4(s)
..............................
..............................
[4]
(c) An electrochemical cell is set up as follows.
V
Pt
Ag
Ag2SO4(aq)
Fe2(SO4)3(aq)
+
FeSO4(aq)
(i)
Ag2SO4(s)
Use the Data Booklet to calculate the value of
which electrode is the positive one.
= ..............................
(ii)
under standard conditions, stating
positive electrode: .............................. [1]
How would the actual Ecell of the above cell compare to the
Explain your answer.
under standard conditions?
.............................................................................................................................................
....................................................................................................................................... [1]
(iii)
How would the Ecell of the above cell change, if at all, if a few cm3 of concentrated Na2SO4(aq)
were added to
•
the beaker containing Fe3+(aq) + Fe2+(aq),
.............................................................................................................................................
•
the beaker containing Ag2SO4(aq)?
.............................................................................................................................................
[2]
(iv)
Explain any changes in Ecell you have stated in (iii).
.............................................................................................................................................
....................................................................................................................................... [1]
(d) Solutions of iron(III) sulfate are acidic due to the following equilibrium.
[Fe(H2O)6]3+(aq)
[Fe(H2O)5(OH)]2+(aq) + H+(aq)
Ka = 8.9 × 10–4 mol dm–3
Calculate the pH of a 0.1 mol dm–3 solution of iron(III) sulfate, Fe2(SO4)3.
pH = .........................
[2]
[Total: 13]
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Electrolysis, Electrode
Potentials & Cells
Mark Scheme 7
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Mark Scheme 7
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) (i) a solution that resists / minimises a change in its pH or helps maintain its pH.....
(NOT any of: "maintains pH"; "keeps pH constant"; "no change in pH")
.....when small amounts of acid / H+ or base / OH– are added (both acid and
base are needed)
(ii) HCO3– reacts with H+ ions as follows:
HCO3– + H+ → H2CO3 (or H2O + CO2)
–
and with OH ions thus:
HCO3– + OH– → CO32– + H2O
[2]
[2]
(the equation arrows can be equilibrium arrows, as long as HCO3– is on the left)
(iii) (pKa = –log(Ka) = 7.21)
[2]
pH = pKa + log([base] / [acid]
(b) (i) Ksp = [Ag+]3[PO43–]
and
= 7.21 + log(0.5 / 0.3)
= 7.43 (7.4)
units: mol4dm–12
(ii) call [PO43–] = x, then [Ag+] = 3x, and Ksp = 27x4
x = (Ksp / 27)1/4
= (1.25 × 10–20 / 27)1/4
[Ag+] = 3x = 1.39 × 10–5 (mol dm–3)
(c)
H3PO3 + 2Fe3+ + H2O
[1]
[3]
= 4.64 × 10–6 mol dm–3
(allow 1.4 × 10–5)
→ H3PO4 + 2Fe2+ + 2H+
[2]
Eocell = 0.77 –(–0.28) = (+)1.05 V
or 3H3PO3 + 3H2O + 2Fe3+
→ 3H3PO4 + 6H+ + 2Fe
Eocell = –0.04 –(–0.28) = (+)0.24 V
[Total: 12]
2
(a
(i)
(ii)
K = Cl– / chloride / F– / fluoride
1
H2SO4 + 2NaCl Na2SO4 + 2HCl (or equation with F or K for Cl) OR
H2SO4 + NaCl NaHSO4 + HCl (or equation with F or K for Cl )
1
ecf from identity of K so long as halide
HK is acidic / HK is a gas / an acidic gas is produced
1
L = I– / iodide
1
colour = yellow
ecf from identity of L i.e. Cl – (white) or Br– (cream)
1
Ag+ + I‒ AgI (or equation with L)
AgNO3 + NaI → AgI + NaNO3 (or equation with L)
ecf from identity of L so long as halide
(iii)
(b) (i)
3
3
1
Br2 / bromine has fewer electrons than iodine / more electrons than chlorine
intermolecular / van der Waals’ forces (in Br2 / M2) weaker than in iodine / stronger than
in chlorine
1
1
2
B = chlorine / Cl 2
C = hydrogen / H2
D = sodium hydroxide / NaOH
1
1
1
3
(ii)
anode: 2Cl – Cl 2 + 2e–
1
cathode: 2H+ + 2e– H2 OR
2H2O + 2e– 2OH– + H2
1
2
13
3
(a
(1s22s22p6)3s23p63d9
[1]
[Total: 1]
(b)
b)
electron / orbitals near ligands are at a higher energy
due to repulsion from ligand lone pairs
[1]
[1]
(ii) when an electron moves to higher orbital / energy level or is promoted
it absorbs a photon or light (mention of light being emitted negates this mark)
[1]
[1]
(iii) (different ligands produce) different (sizes of) energy gap or ∆E
[1]
[Total: 5]
(c)
V
salt
bridge
Pt
Cu
Fe3+ + Fe2+
Cu2+
solutions at 1 mol dm–3 (1 M) and 298(K)/25°C
salt bridge and voltmeter
platinum/carbon/graphite electrode
(this mark is negated by inclusion of H2 around the electrode)
copper electrode
Fe3+/Fe2+ mixture and Cu2+ or CuSO4 etc
[1]
[1]
[1]
[1]
[1]
[Total: 5]
(d) Parts (i) – (iii) have to correspond to each other.
either
or
(i)
ligand
exchange/substitution/displacement/replacement
precipitation/acid-base/deprotonation
(ii)
[Cu(H2O)6]2+ + 4NH3 → [Cu(H2O)2(NH3)4]2+ + 4H2O
or [Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4]2+ + 6H2O
or [Cu(H2O)6]2+ + nNH3 → [Cu(H2O)6–n(NH3)n]2+ +
nH2O
Cu2+ + 2NH3 + 2H2O → Cu(OH)2 + 2NH4+
or Cu2+ + 2NH4OH → Cu(OH)2 + 2NH4+
or [Cu(H2O)6]2+ + 2NH3 → [Cu(H2O)4(OH)2]
+ 2N 4+
(iii)
turns purple or deep/dark/royal blue
forms a pale blue ppt
[1]
1] + [1] +
(iv) Eo will decrease/ be less positive/more negative...
...because [Cu2+] decreases or Cu2+ + 2e– Cu shifts to the LHS or
Eo [Cu(NH3)4]2+ = –0.05V or [Cu(NH3)4]2+ is more stable.
[1]
[Total: 4]
(e) (i) aldehyde
(ii) red ppt./solid
(iii)
2Cu2+ + CH3CHO + 5OH– → Cu2O + CH3CO2– + 3H2O
[1]
[1]
[1]
[Total: 3]
(f) pH = pKa + log [salt]/[acid] = –log(9.3 × 10–4) + log (0.8/0.5)
= 3.032 + 0.204 = 3.23/3.24 (3 or more sig. figs.)
[2]
[Total: 2]
[TOTAL: 20]
4
(a
The EMF of a cell made up of the test electrode and a standard hydrogen electrode.
(or the EMF of the electrode compared to the S.H.E.)
[1]
EMF measured under standard conditions of T, (P) and concentration.
(or at 298K and 1 mol dm-3)
[1]
2
(b) The stronger the halogen is as an oxidising agent, the more positive is its Eo value.
[1]
Two examples of F2/F-, Cl2/Cl-; Br2/Br-, I2/I- quoted
[1]
(data: F2/F- = +2.87V
Cl2/Cl- = +1.36V
Br2/Br- = +1.07V
I2/I- = +0.54V)
2
(c)
c)
or
H2O2 + 2I- + 2H+ → I2 + 2H2O
H2O2 + 2KI + 2H+ → 2K+ + I2 + 2H2O
[1
Eo = 1.77 - 0.54 = 1.23 V
(ii)
or
[1
Cl2 + SO2 + 2H2O → 2Cl - + SO42- + 4H+
Cl2 + SO2 + 2H2O → 2HCl + H2SO4
[1]
Eo = 1.36 – 0.17 = 1.19 V
[1]
4
(d) since Eo(I2/I-) is +0.54V, tin will be oxidised to Sn4+
(Eo for Sn2+/Sn = -0.14V and Eo forSn4/Sn2 = +0.15V)
Thus:
Sn + 2I2 → SnI4
[1]
[1]
2
total: 10
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Electrolysis, Electrode
Potentials & Cells
Question Paper 7
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Electrochemistry
Sub-Topic
Paper Type
Electrolysis, Electrode Potentials & Cells
Theory
Booklet
Question Paper 7
Time Allowed:
66 minutes
Score:
/55
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a) (i) What is meant by the term buffer solution?
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii)
Write equations to show how the hydrogencarbonate ion, HCO3–, controls the pH of blood.
.............................................................................................................................................
....................................................................................................................................... [2]
(iii)
A solution containing both Na2HPO4 and NaH2PO4 is commonly used as a buffer solution.
The following equilibrium is present in the solution.
H2PO4–(aq)
HPO42–(aq) + H+(aq)
Ka = 6.2 × 10–8 mol dm–3
Calculate the pH of a buffer solution made by mixing 100 cm3 of 0.5 mol dm–3 Na2HPO4 and
100 cm3 of 0.3 mol dm–3 NaH2PO4.
(b) Silver phosphate, Ag3PO4, is sparingly soluble in water.
(i)
Write an expression for the solubility product, Ksp, of Ag3PO4, and state its units.
pH = ........................ [2]
Ksp =
(ii)
units: .............................. [1]
The numerical value of Ksp is 1.25 × 10–20 at 298 K. Use this value to calculate [Ag+(aq)] in
a saturated solution of Ag3PO4.
[Ag+(aq)] = ............................................... mol dm–3 [3]
(c) The half-equation for the redox reaction between phosphoric(III) acid and phosphoric(V) acid is
shown.
H3PO4(aq) + 2H+(aq) + 2e–
H3PO3(aq) + H2O(l)
E o = –0.28 V
Find suitable data from the Data Booklet to write an equation for the reaction between H3PO3
and Fe3+(aq) ions, and calculate the
for the reaction.
equation: ....................................................................................................................................
= ..................... V [2]
[Total: 12]
2
(a) In this question, K, L and M refer to a halogen atom or halide ion.
For each part question, read the information and complete the answer lines below.
(i) When concentrated sulfuric acid is added to solid NaK, white fumes are produced that turn
damp blue litmus paper red. No other colour changes are observed.
identity of K = ...................................
equation for reaction ...........................................................................................................
explanation of observation ..................................................................................................
....................................................................................................................................... [3]
(ii) When silver nitrate solution is added to an aqueous solution of NaL, a precipitate forms
that remains after the addition of concentrated ammonia solution.
identity of L = ...................................
colour of precipitate ............................................................................................................
equation for reaction ..................................................................................................... [3]
(iii) M2 is a liquid at room temperature with a boiling point higher than that of chlorine but lower
than that of iodine.
identity of M = ...................................
explanation .........................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(b) The diagram below is a simplified representation of a diaphragm cell.
product C
product B
–
+
concentrated
brine
product D
titanium
anode
diaphragm
steel
cathode
(i) Identify each of the products.
B .........................................................................................................................................
C .........................................................................................................................................
D .........................................................................................................................................
[3]
(ii) Give the equations for the two electrode reactions.
anode ..................................................................................................................................
cathode ...............................................................................................................................
[2]
[Total: 13]
3
(a) Complete the following electronic configuration of the Cu2+ ion.
1s2 2s2 2p6 ........................................
[1]
(b) In a free, gas-phase transition metal ion, the d-orbitals all have the same energy, but
when the ion is in a complex the orbitals are split into two energy levels.
(i) Explain why this happens.
....................................................................................................................................
....................................................................................................................................
(ii) How does this splitting help to explain why transition metal complexes are often
coloured?
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(iii) Why does the colour of a transition metal complex depend on the nature of the
ligands surrounding the transition metal ion?
....................................................................................................................................
....................................................................................................................................
[5]
(c) Draw a fully-labelled diagram of the apparatus you could use to measure the E o of a cell
composed of the Fe3+/Fe2+ electrode and the Cu2+/Cu electrode.
(d) The E o for Cu2+/Cu is +0.34 V. When NH3(aq) is added to the electrode solution, the
Eelectrode changes.
(i) Describe the type of reaction taking place between Cu2+(aq) and NH3(aq).
....................................................................................................................................
(ii) Write an equation for the reaction.
....................................................................................................................................
(iii) Describe the change in the colour of the solution.
....................................................................................................................................
(iv) Predict and explain how the Eelectrode might change on the addition of NH3(aq).
....................................................................................................................................
....................................................................................................................................
[4]
(e) Fehling’s reagent is an alkaline solution of Cu2+ ions complexed with tartrate ions. It is
used in organic chemistry to test for a particular functional group.
(i) Name the functional group involved.
....................................................................................................................................
(ii) Describe the appearance of a positive result in this test.
....................................................................................................................................
(iii) Write an equation for the reaction between Cu2+ and OH– ions and a two-carbon
compound containing the functional group you named in (i).
....................................................................................................................................
[3]
(f) A solution containing a mixture of tartaric acid and its sodium salt is used as a buffer in
some pre-prepared food dishes.
Calculate the pH of a solution containing 0.50 mol dm–3 of tartaric acid and 0.80 mol dm–3
sodium tartrate.
[Ka(tartaric acid) = 9.3 × 10–4 mol dm–3]
pH = ...............................
[2]
[Total: 20]
4
(a) What do you understand by the term standard electrode potential?
..........................................................................................................................................
.................................................................................................................................... [2]
(b) By reference to relevant E data in the Data Booklet, explain how the halogen/halide
electrode potentials relate to the relative reactivity of the halogens as oxidising agents.
..........................................................................................................................................
..........................................................................................................................................
.................................................................................................................................... [2]
(c) Use data from the Data Booklet to construct redox equations, and calculate the
standard cell potentials, for the reactions between
(i) Acidified H2O2(aq) and KI(aq),
..................................................................................................................................
(ii) Cl 2(aq) + SO2(aq).
..................................................................................................................................
[4]
(d) Use data from the Data Booklet to predict the likely product of the reaction between
I2(aq) and tin metal, writing a balanced equation for the reaction.
.................................................................................................................................... [2]
[Total: 10]
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Equilibria
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Equilibria
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 1
Time Allowed:
52 minutes
Score:
/43
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1
One mole of phosphorus(V) chloride, PCl 5, is heated to 600 K in a sealed flask of volume 1 dm3.
Equilibrium is established and measurements are taken.
PCl 5(g)
PCl 3(g) + Cl 2(g)
The experiment is repeated with one mole of phosphorus(V) chloride heated to 600 K in a sealed
flask of volume 2 dm3.
How will the measurements vary?
2
3
A
The equilibrium concentrations of PCl 3(g) and Cl 2(g) are higher in the second experiment.
B
The equilibrium concentration of PCl 5(g) is lower in the second experiment.
C
The equilibrium concentrations of all three gases are the same in both experiments.
D
The value of the equilibrium constant is higher in the second experiment.
In which reaction is the underlined substance acting as a base?
A
HNO3 + H2SO4 → H2NO3+ + HSO4–
B
HSiO3– + HCN → CN– + H2O + SiO2
C
HNO2 + HCO3– → H2O + CO2 + NO2–
D
C6H5O– + CH2Cl CO2H → C6H5OH + CH2Cl CO2–
One molecule of haemoglobin, Hb, can bind with four molecules of oxygen according to the
following equation.
Hb(aq) + 4O2(aq)
Hb(O2)4(aq)
When the equilibrium concentration of O2 is 7.6 × 10–6 mol dm–3, the equilibrium concentrations of
Hb and Hb(O2)4 are equal.
What is the value of Kc for this equilibrium?
A
3.0 × 1020
B
1.3 × 105
C
7.6 × 10–6
D
3.3 × 10–21
4
Nitrogen dioxide, NO2, exists in equilibrium with dinitrogen tetroxide, N2O4.
2NO2(g)
∆H = –57 kJ mol–1
N2O4(g)
Which conditions give the greatest percentage of N2O4(g) at equilibrium?
5
pressure
temperature
A
high
high
B
high
low
C
low
high
D
low
low
When a sample of HI is warmed to a particular temperature the equilibrium below is established.
H2(g) + I2(g)
2HI(g)
At this temperature, it is found that the partial pressure of HI(g) is 28 times the partial pressure of
H2(g).
What is the value of Kp at this temperature?
A
1.28 × 10–3
B
0.035
C
28
D
784
6
The diagram shows the Boltzmann energy distribution curve for molecules of a mixture of two
gases at a given temperature. For a reaction to occur the molecules must collide together with
sufficient energy.
number of
molecules
0
0
Ea1
Ea2
molecular energy
Ea is used to represent the activation energy for the reaction between the gases. Of the two
values shown, one is the activation energy for a catalysed reaction, the other for an uncatalysed
reaction.
Which statement about Ea1 is correct?
A
Ea1 corresponds to a catalysed reaction with fewer effective collisions than the uncatalysed
reaction.
B
Ea1 corresponds to an uncatalysed reaction with fewer effective collisions than the catalysed
reaction.
C
Ea1 corresponds to a catalysed reaction with a greater number of effective collisions than the
uncatalysed reaction.
D
Ea1 corresponds to an uncatalysed reaction with a greater number of effective collisions than
the catalysed reaction.
7 Transition elements and their compounds are widely used as catalysts.
What is the identity and what is the oxidation number of the element present in the catalyst used
in the Contact process?
8
The Contact process is used in the manufacture of sulfuric acid. The equation for the main
reaction is shown below.
2SO2(g) + O2(g)
∆H = –196 kJ mol–1
2SO3(g)
Which statement about this reaction is incorrect?
A
Increased pressure gives a higher yield of SO3.
B
Increased temperature gives a higher yield of SO3.
C
In the forward reaction the oxidation state of sulfur changes from +4 to +6.
D
Vanadium(V) oxide is used as a catalyst.
2HI(g), is 60 at 450 °C.
9 The equilibrium constant, Kc, for the reaction H2(g) + I2(g)
What is the number of moles of hydrogen iodide in equilibrium with 2 mol of hydrogen and 0.3 mol
of iodine at 450 °C?
A
1
100
1
10
B
C
D
6
36
10 Hydrogen and carbon dioxide gases are mixed in equal molar amounts at 800 K. A reversible
reaction takes place.
H2(g) + CO2(g)
H2O(g) + CO(g)
At equilibrium, the partial pressures of H2 and CO2 are both 10.0 kPa. Kp is 0.288 at 800 K.
What is the partial pressure of CO in the equilibrium mixture?
A
5.37 kPa
B
18.6 kPa
C
28.8 kPa
D
347 kPa
11 The formation of hydrogen and ethyne, C2H2, from methane reaches dynamic equilibrium.
2CH4(g)
3H2(g) + C2H2(g)
What are the units of Kc?
A
mol dm–3
B
mol2 dm–6
C
mol3 dm–9
D
mol4 dm–12
12 The Boltzmann distribution for a gas at constant temperature is shown below.
n = number
of molecules
0
0
X
Y
Z
molecular energy
If the temperature of the gas is reduced by 10 °C the graph changes shape.
What happens to the values of n for the molecular energies X, Y and Z ?
13 Use of the Data Booklet is relevant to this question.
A sample of potassium oxide, K2O, is dissolved in 250 cm3 of distilled water. 25.0 cm3 of this
solution is titrated against sulfuric acid of concentration 2.00 mol dm–3. 15.0 cm3 of this sulfuric
acid is needed for complete neutralisation.
Which mass of potassium oxide was originally dissolved in 250 cm3 of distilled water?
A
2.83 g
B
28.3 g
C
47.1 g
D
56.6 g
14 Two glass vessels M and N are connected by a closed valve.
M
N
M contains helium at 20 °C at a pressure of 1 × 105 Pa. N has been evacuated, and has three
times the volume of M. In an experiment, the valve is opened and the temperature of the whole
apparatus is raised to 100 °C.
What is the final pressure in the system?
A
3.18 × 104 Pa
B
4.24 × 104 Pa
C
1.25 × 105 Pa
D
5.09 × 105 Pa
15 Sulfur trioxide is manufactured from sulfur dioxide and oxygen, using the Contact process.
Which condition affects the value of the equilibrium constant, Kc?
A
adjusting the temperature
B
increasing the pressure
C
removing SO3 from the equilibrium mixture
D
using a catalyst
16 The reaction between sulfur dioxide and oxygen is a dynamic equilibrium.
2SO2(g) + O2(g)
2SO3(g)
What happens when the pressure of the system is increased?
A
The rate of reaction will decrease and the position of the equilibrium will move to the left.
B
The rate of reaction will decrease and the position of the equilibrium will move to the right.
C
The rate of reaction will increase and the position of the equilibrium will move to the left.
D
The rate of reaction will increase and the position of the equilibrium will move to the right.
17 The diagram represents, for a given temperature, the Boltzmann distribution of the kinetic
energies of the molecules in a mixture of two gases that will react together. The activation energy
for the reaction, Ea , is marked.
number of
molecules
Ea
energy
The dotted curves below show the Boltzmann distribution for the same reaction at a higher
temperature. On these diagrams, H represents the activation energy at the higher temperature.
Which diagram is correct?
B
A
number of
molecules
number of
molecules
Ea
energy
Ea
energy
Ea
energy
H
H
C
D
number of
molecules
number of
molecules
Ea
H
energy
H
18 Nitrogen reacts with hydrogen to produce ammonia.
N2(g) + 3H2(g)
2NH3(g)
A mixture of 2.00 mol of nitrogen, 6.00 mol of hydrogen, and 2.40 mol of ammonia is allowed to
reach equilibrium in a sealed vessel of volume 1 dm3 under certain conditions. It was found that
2.32 mol of nitrogen were present in the equilibrium mixture.
What is the value of Kc under these conditions?
A
(1.76)2
(2.32)(6.96)3
B
(1.76)2
(2.32)(6.32)3
C
(2.08)2
(2.32)(6.32)3
D
(2.40)2
(2.32)(6.00)3
19 Nitrogen reacts with hydrogen to produce ammonia.
N2(g) + 3H2(g)
2NH3(g)
A mixture of 1.00 mol of nitrogen, 3.00 mol of hydrogen and 1.98 mol of ammonia is allowed to
reach equilibrium in a sealed vessel under certain conditions. It was found that 1.64 mol of
nitrogen were present in the equilibrium mixture.
What is the value of Kc under these conditions?
A
(0.70)2
(1.64)(4.92)3
B
(1.34)2
(1.64)(3.64)3
C
(1.64)(4.92)3
(0.70)2
D
(1.64)(3.64)3
(1.34)2
20
IAmmonia is manufactured by the Haber Process, in an exothermic reaction.
Assuming that the amount of catalyst remains constant, which change will not bring about an
increase in the rate of the forward reaction?
A
decreasing the size of the catalyst pieces
B
increasing the pressure
C
increasing the temperature
D
removing the ammonia as it is formed
21 Two moles of compound P were placed in a vessel. The compound P was partly decomposed by
heating. A dynamic equilibrium between chemicals P, Q and R was established.
At equilibrium, x mol of R were present and the total number of moles present was (2 + x).
What is the equation for this equilibrium?
A
P
B
2P
2Q + R
C
2P
Q+R
D
2P
Q + 2R
2Q + R
22 Methanol is manufactured by reacting carbon dioxide and hydrogen.
CO2(g) + 3H2(g)
CH3OH(g) + H2O(g)
∆H = –49 kJ mol–1
What would increase the equilibrium yield of methanol in this process?
A
adding a catalyst
B
adding an excess of steam
C
increasing the pressure
D
increasing the temperature
23 Elements X and Y are both in period three.
When the chloride of X is added to water, it reacts and a solution of pH 2 is produced.
When the chloride of Y is added to water, it dissolves and a solution of pH 7 is produced.
Which statement explains these observations?
A
Both chlorides hydrolyse in water.
B
X is phosphorus and Y is aluminium.
C
X is silicon and Y is sodium.
D
X is sodium and Y is phosphorus.
24 In the Haber process, the reaction between the two gaseous reactants requires the use of a
catalyst that contains a transition element.
What is the metal and in what mole ratio do the gases react?
25 In the last century the Haber process was sometimes run at pressures of 1000 atm and higher.
Now it is commonly run at pressures below 100 atm.
What is the reason for this change?
A
An iron catalyst is used.
B
Maintaining the higher pressures is more expensive.
C
The equilibrium yield of ammonia is increased at lower pressures.
D
The rate of the reaction is increased at lower pressures.
26 The esterification reaction
ethanol + ethanoic acid
ethyl ethanoate + water
is an equilibrium. The forward reaction is exothermic.
How can the value of the equilibrium constant KC be increased?
A
by adding a little concentrated sulfuric acid as a catalyst
B
by increasing the initial concentration of ethanol
C
by lowering the temperature
D
by raising the temperature
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
B
C
D
1, 2 and 3
are
correct
1 and 2
only are
correct
2 and 3
only are
correct
1 only
is
correct
No other combination of statements is used as a correct response.
27 When added to water, which oxides will cause a change in the pH of the water?
1
SiO2
2
CaO
3
SO2
28 R and S react together.
R + S
T
Which factors affect the rate of the forward reaction?
1
the activation energy of the reaction
2
the enthalpy change of the reaction
3
the equilibrium constant of the reaction
29 The Brønsted-Lowry theory describes acid and base character.
When concentrated sulfuric acid and concentrated nitric acid are mixed, the following reactions
occur.
HSO4– + H2NO3+
H2SO4 + HNO3
H2NO3+
H2O + NO2+
H2O + H2SO4
HSO4– + H3O+
Which species are bases in these reactions?
1
HSO4–
2
HNO3
3
NO2+
30 Sulfuric acid is a Brønsted-Lowry acid.
In which reactions is sulfuric acid behaving as an acid?
1
H2SO4 + HNO3 → H2NO3+ + HSO4–
2
H2SO4 + CO32– → CO2 + H2O + SO42–
3
H2SO4 + MgO → MgSO4 + H2O
31 A reversible reaction is catalysed.
Which statements about the effects of the catalyst on this system are correct?
1
The catalyst alters the mechanism of the reaction.
2
The catalyst reduces the activation energy for both the forward and the backward reaction.
3
The catalyst alters the composition of the equilibrium mixture.
32 What are necessary properties of a dynamic equilibrium?
1
Equal amounts of reactants and products are present.
2
Concentrations of reactants and products remain constant.
3
The rate of the forward reaction is the same as the rate of the reverse reaction.
33 If N2O4 gas is placed in a sealed vessel the following equilibrium is established.
N2O4(g)
2NO2(g)
The forward reaction is endothermic.
What happens when the temperature is increased?
1
The equilibrium constant increases.
2
The partial pressure of NO2 increases.
3
The activation energy is unchanged.
34 Methanoic acid molecules, HCO2H, and hydrogen carbonate ions, HCO3–, can both behave as
acids.
Why does a solution of methanoic acid have a lower pH than a solution of sodium hydrogen
carbonate of the same concentration?
1
HCO2H molecules dissociate more fully than HCO3– ions do.
2
Each HCO2H molecule has two hydrogen atoms; each HCO3– ion only has one.
3
Methanoic acid is a weaker acid than sodium hydrogen carbonate.
35 The following equilibrium is an exothermic reaction in the forward direction.
2CrO42–(aq) + 2H+(aq)
Cr2O72–(aq) + H2O(l)
What happens when the concentration of CrO42– ions increases and the temperature
decreases?
1
The concentration of Cr2O72– ions increases.
2
The equilibrium constant increases.
3
The activation energy decreases.
36 Which processes involve the conversion of sulfur dioxide into sulfur trioxide?
1
the combustion of sulfur contaminated fossil fuels
2
the Contact process for manufacturing sulfuric acid
3
the catalytic oxidation of sulfur dioxide by oxides of nitrogen
37 In the manufacture of sulfuric acid the reaction 2SO2(g) + O2(g)
2SO3(g) usually takes place
at 400 °C and 1 atm pressure. In one industrial plant, it is decided to change the pressure to
20 atm.
What will be the consequences of this change?
1
increased running costs
2
an increased percentage of sulfur trioxide in the equilibrium mixture
3
the rate of the backward reaction increases
38 Concentrated sulfuric acid behaves as a strong acid when it reacts with water.
H2SO4(l) + aq → H+(aq) + HSO4–(aq)
The HSO4– ion formed behaves as a weak acid.
HSO4–(aq)
H+(aq) + SO42–(aq)
Which statements are true for 1.0 mol dm–3 sulfuric acid?
1
[H+(aq)] is high
2
[SO42–(aq)] is high
3
[HSO4–(aq)] = [SO42–(aq)]
39 Which statements are true about the Haber process for the manufacture of ammonia?
1
At higher temperatures, the yield goes down but the rate of production of ammonia is faster.
2
At higher pressures, the yield goes down but the rate of production of ammonia is faster.
3
In the presence of a catalyst, the yield goes down but the rate of production of ammonia is
faster.
40 Which equations represent stages in the Contact process for manufacturing sulfuric acid?
1
2
O2 → SO3
1
SO2 +
2
SO2 + H2O → H2SO3
3
H2SO3 +
1
2
O2 → H2SO4
41 When added to water, which oxides will not cause a change in pH?
1
Al 2O3
2
SiO2
3
P4O10
42 The table describes some of the chemistry and thermodynamic properties of the halogens.
name and
symbol of quantity
process
2HX(g) → H2(g) + X2(g)
H2(g) + X2(g)
2HX(g)
X(g) → X+(g) + e–
enthalpy change of reaction,
equilibrium constant, Kp
ionisation energy,
Which statements about the relative values of these quantities are correct?
1
2
3
for HCl >
for HBr
Kp for HBr > Kp for HI
for I >
for Cl
43 Which statements are correct in terms of the Brønsted-Lowry theory of acids and bases?
1
Water can act as either an acid or a base.
2
Sulfuric acid, H2SO4, does not behave as an acid when dissolved in ethanol, C2H5OH.
3
The ammonium ion acts as a base when dissolved in liquid ammonia.
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Equilibria
Mark Scheme 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Equilibria
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 1
Time Allowed:
75 minutes
Score:
/62
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
(a
2PbS + 3O2 2PbO + 2SO2
reagents and formulae
balancing
[1]
[1]
[2]
S (is oxidised) –2 to (+)4
O (is reduced) 0 to –2
[1]
[1]
[2]
T = 400 – 600 °C (chosen as a compromise because)
High T increases rate ora
High T decreases yield / moves eqm left / makes less SO3 as forward
reaction exothermic ora
[1]
[1]
[1]
[3]
High pressure increases rate as collision frequency increases ora
[1]
High pressure moves eqm right / favours forward reaction as more moles on
left ora
Uneconomic to use high pressures / high yield at low pressure
[1]
[1]
[3]
Reaction (too) exothermic / acid spray produced
[1]
[1]
SO3 + H2SO4 H2S2O7
H2S2O7 + H2O 2H2SO4
[1]
[1]
[2]
Preservative owtte
antimicrobial / antioxidant / reducing agent
[1]
[1]
[2]
12.35 × 0.01 / 1000 = 1.235 × 10–4
[1]
[1]
(ii)
1.235 × 10–4 × 1000 / 50 = 2.47 × 10–3
[1]
[1]
(iii)
2.47 × 10–3 × 64.1 = 0.158327 g = 158 (3 sf only)
[1]
[1]
(i)
(ii)
(b) (i)
(ii)
(c) (i)
(ii)
(d)
(e) (i)
[18]
2
(a) (i) a solution that resists / minimises a change in its pH or helps maintain its pH.....
(NOT any of: "maintains pH"; "keeps pH constant"; "no change in pH")
.....when small amounts of acid / H+ or base / OH– are added (both acid and
base are needed)
(ii) HCO3– reacts with H+ ions as follows:
HCO3– + H+ → H2CO3 (or H2O + CO2)
–
and with OH ions thus:
HCO3– + OH– → CO32– + H2O
[2]
[2]
(the equation arrows can be equilibrium arrows, as long as HCO3– is on the left)
(iii) (pKa = –log(Ka) = 7.21)
[2]
pH = pKa + log([base] / [acid]
(b) (i) Ksp = [Ag+]3[PO43–]
and
= 7.21 + log(0.5 / 0.3)
= 7.43 (7.4)
units: mol4dm–12
(ii) call [PO43–] = x, then [Ag+] = 3x, and Ksp = 27x4
x = (Ksp / 27)1/4
= (1.25 × 10–20 / 27)1/4
[Ag+] = 3x = 1.39 × 10–5 (mol dm–3)
(c)
H3PO3 + 2Fe3+ + H2O
[1]
[3]
= 4.64 × 10–6 mol dm–3
(allow 1.4 × 10–5)
→ H3PO4 + 2Fe2+ + 2H+
[2]
Eocell = 0.77 –(–0.28) = (+)1.05 V
or 3H3PO3 + 3H2O + 2Fe3+
→ 3H3PO4 + 6H+ + 2Fe
Eocell = –0.04 –(–0.28) = (+)0.24 V
[Total: 12]
3
(a
(i)
(reaction between atmospheric N2 and O2) due to
lightning / biological processes or bacteria in soil
AND in car engines / power stations / metal refining / furnaces
(1)
2NO2 + H2O HNO2 + HNO3 OR
2NO2 + H2O + 1 / 2O2 2HNO3 OR
3NO2 + H2O 2HNO3 + NO
(1)
SO2 + NO2 SO3 + NO
(1)
NO + 1 / 2O2 NO2
(1)
SO3 + H2O H2SO4
(1)
[3]
Kp = pN2O4 / (pNO2)2
(1)
[1]
(ii)
moles of NO2 = 0.32
(1)
[1]
(iii)
x(N2O4) = 1.84 / 2.16 = 0.85
(1)
x(NO2) = 0.32 / 2.16 = 0.15
ecf from (b)(ii)
(1)
pN2O4 = 0.85 × 140 = 119 (kPa)
(1)
pNO2 = 0.15 × 140 = 21 (kPa)
ecf from (b)(iii)
(1)
Kp = 119 / 212 = 0.270 kPa–1
ecf from (b)(i) and (b)(iv)
(2)
2)
(ii)
(iii)
(b) (i)
(iv)
(v)
[1]
[1]
Total
ot
[2]
[2]
13
Question
Questi
4
(a)
(b) (i)
(ii)
Scheme
Marks
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
1
1
Very exothermic / gets very hot
OR creates (acid / H2SO4) spray / mist / fog / fumes
1
SO3 + H2SO4 → H2S2O7
1
H2S2O7 + H2O → 2H2SO4
1
(c) (i)
1
O
S
(ii)
[2]
O
O
1+1
O
M1 SO2 correct M2 SO3 correct
(d) (i)
[2]
O
S
(ii)
T
[2]
115–120° bent / non-linear
120° trigonal planar
1
1
Advantage = higher rate
Greater KE / energy / speed / collision frequency / proportion of successful collisions / more particles with E>Ea
1
1
Disadvantage – reduced yield / less product
1
(Forward reaction) exothermic AND (hence in accordance with LCP) equilibrium / reaction shifts left (to counteract
inc T) ora
1
Kp =
pSO3
2
[2]
[4]
2
pSO 2 × pO 2
1
[1]
Question
Questi
(iii)
Scheme
Marks
Marks
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
2
2
0
(–1.8) (–0.9)
0.2
1.1
1.1
1
xSO3 = 1.8 / 3.1 = 0.581
xSO2 = 0.2 / 3.1 = 0.065
xO2 = 1.1 / 3.1 = 0.355
1
Kp =
0.5812 × (2 × 105)2
= 1.13 × 10–3 Pa–1
5 2
5
0.065 × (2 × 10 ) × 0.355 × 2 × 10
2
T
1
1+1
[5]
[19]
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Equilibria
Question Paper 1
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Equilibria
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 1
Time Allowed:
75 minutes
Score:
/62
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
Sulfuric acid is an important chemical with a variety of uses.
It is manufactured by the Contact process, the first stage of which involves the conversion of sulfur
or a sulfide ore, such as galena, PbS, into sulfur dioxide, SO2.
(a) (i) Write an equation for the reaction between galena and oxygen to form sulfur dioxide and
lead(II) oxide.
....................................................................................................................................... [2]
(ii) Identify the oxidation number changes that take place during this reaction.
.............................................................................................................................................
....................................................................................................................................... [2]
(b) The second stage of the Contact process involves the production of sulfur trioxide, SO3, from
sulfur dioxide.
2SO2(g) + O2(g)
2SO3(g)
∆H = –197 kJ mol–1
(i) State the temperature usually chosen for this conversion and explain this in terms of
reaction rates and Le Chatelier’s principle.
temperature ........................................................................................................................
explanation .........................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(ii) State and explain the pressure conditions that would give the best rate and best yield of
sulfur trioxide. Explain why these conditions are not actually used.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(c) In the third stage of the process the sulfur trioxide is dissolved in 98% sulfuric acid followed by
carefully controlled addition of water.
(i) Explain why the sulfur trioxide is not dissolved directly in water to produce sulfuric acid.
.............................................................................................................................................
....................................................................................................................................... [1]
(ii) Write equations for the reaction of sulfur trioxide with sulfuric acid and for the subsequent
reaction with water.
.............................................................................................................................................
....................................................................................................................................... [2]
(d) Explain why sulfur dioxide is used as an additive in some foods and wines.
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
(e) The sulfur dioxide content of wine is most commonly measured by the Ripper Method which
involves titration with iodine in the presence of starch as an indicator.
SO2(aq) + I2(aq) + 2H2O(l) → 2I –(aq) + SO42–(aq) + 4H+(aq)
A 50.0 cm3 sample of wine required 12.35 cm3 of 0.010 mol dm–3 I2(aq) for complete reaction
with the SO2.
(i) How many moles of SO2 are present in 50.0 cm3 of wine?
moles of SO2 in 50.0 cm3 = ................................. [1]
(ii) How many moles of SO2 are present in 1 dm3 of wine?
moles of SO2 in 1 dm3 = ................................. [1]
(iii) How many milligrams, mg, of SO2 are present in 1 dm3 of wine? Give your answer to three
significant figures. (1 g = 1000 mg)
mass of SO2 in 1 dm3 = ................................. mg [1]
[Total: 18]
2
(a) (i) What is meant by the term buffer solution?
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii)
Write equations to show how the hydrogencarbonate ion, HCO3–, controls the pH of blood.
.............................................................................................................................................
....................................................................................................................................... [2]
(iii)
A solution containing both Na2HPO4 and NaH2PO4 is commonly used as a buffer solution.
The following equilibrium is present in the solution.
H2PO4–(aq)
HPO42–(aq) + H+(aq)
Ka = 6.2 × 10–8 mol dm–3
Calculate the pH of a buffer solution made by mixing 100 cm3 of 0.5 mol dm–3 Na2HPO4 and
100 cm3 of 0.3 mol dm–3 NaH2PO4.
(b) Silver phosphate, Ag3PO4, is sparingly soluble in water.
(i)
Write an expression for the solubility product, Ksp, of Ag3PO4, and state its units.
pH = ........................ [2]
Ksp =
(ii)
units: .............................. [1]
The numerical value of Ksp is 1.25 × 10–20 at 298 K. Use this value to calculate [Ag+(aq)] in
a saturated solution of Ag3PO4.
[Ag+(aq)] = ............................................... mol dm–3 [3]
(c) The half-equation for the redox reaction between phosphoric(III) acid and phosphoric(V) acid is
shown.
H3PO4(aq) + 2H+(aq) + 2e–
H3PO3(aq) + H2O(l)
E o = –0.28 V
Find suitable data from the Data Booklet to write an equation for the reaction between H3PO3
and Fe3+(aq) ions, and calculate the
for the reaction.
equation: ....................................................................................................................................
= ..................... V [2]
[Total: 12]
3
Nitrogen dioxide, NO2, can enter the atmosphere in a variety of ways.
(a) (i) State one natural and one man-made source of atmospheric NO2.
natural .................................................................................................................................
man-made ..........................................................................................................................
[1]
(ii) Write an equation to show how NO2 leads to the formation of nitric acid in acid rain.
....................................................................................................................................... [1]
(iii) Use equations to illustrate the catalytic role of NO2 in the formation of sulfuric acid in acid
rain.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [3]
(b) Nitrogen dioxide exists in equilibrium with dinitrogen tetroxide, N2O4.
2NO2(g)
N2O4(g)
2.00 mol of dinitrogen tetroxide was sealed in a container at 350 K. After equilibrium had been
established the total pressure was 140 kPa and the mixture of gases contained 1.84 mol of
dinitrogen tetroxide.
(i) Give the expression for the equilibrium constant, Kp, for this equilibrium.
Kp =
[1]
(ii) Calculate the number of moles of NO2 present at equilibrium.
[1]
(iii) Calculate the total number of moles of gas present at equilibrium and hence the mole
fraction of each gas present at equilibrium.
[2]
(iv) Calculate the partial pressure of each gas present at equilibrium.
[2]
(v) Calculate the value of the equilibrium constant, Kp, at 350 K.
Give your answer to three significant figures and include the units.
Kp = .................................
units = .................................
[2]
[Total: 13]
4
The Contact process for the manufacture of sulfuric acid was originally patented in the
19th century and is still in use today.
The key step in the overall process is the reversible conversion of sulfur dioxide to sulfur trioxide in
the presence of a vanadium(V) oxide catalyst.
2SO2(g) + O2(g)
2SO3(g)
∆H = –196 kJ mol–1
(a) One way in which the sulfur dioxide for this reaction is produced is by heating the sulfide ore
iron pyrites, FeS2, in air. Iron(III) oxide is also produced. Write an equation for this reaction.
.............................................................................................................................................. [2]
(b) The sulfur trioxide produced in the Contact process is reacted with 98% sulfuric acid. The
resulting compound is then reacted with water to produce sulfuric acid.
(i) Explain why the sulfur trioxide is not first mixed directly with water.
.............................................................................................................................................
....................................................................................................................................... [1]
(ii) Write equations for the two steps involved in the conversion of sulfur trioxide into sulfuric
acid.
.............................................................................................................................................
....................................................................................................................................... [2]
(c)
c)
Sulfur dioxide and sulfur trioxide both contain only S=O double bonds.
Draw labelled diagrams to show the shapes of these two molecules.
SO2
SO3
[2]
(ii) For your diagrams in (i), name the shapes and suggest the bond angles.
SO2 shape ................................................. SO3 shape ...................................................
SO2 bond angle ......................................... SO3 bond angle ...........................................
[2]
(d) The conversion of sulfur dioxide into sulfur trioxide is carried out at a temperature of 400 °C.
(i) With reference to Le Chatelier’s Principle and reaction kinetics, state and explain one
advantage and one disadvantage of using a higher temperature.
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [4]
(ii) State the expression for the equilibrium constant, Kp, for the formation of sulfur trioxide
from sulfur dioxide.
Kp =
[1]
(iii) 2.00 moles of sulfur dioxide and 2.00 moles of oxygen were put in a flask and left to reach
equilibrium.
At equilibrium, the pressure in the flask was 2.00 × 105 Pa and the mixture contained
1.80 moles of sulfur trioxide.
Calculate Kp. Include the units.
Kp = ..............................
units = ..............................
[5]
[Total: 19]
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Equilibria
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Equilibria
Sub-Topic
Paper Type
Multiple Choice
Booklet
Question Paper 2
Time Allowed:
47 minutes
Score:
/39
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Section A
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct.
1 The highest oxides of the elements sodium to chlorine are separately added to water.
Which diagram best represents the pH of the resulting mixtures?
A
B
Na2O
Al 2O3
P4O10
Cl 2O7
MgO
SO3
SiO2
Na2O
Al 2O3
P4O10
Cl 2O7
MgO
SO3
SiO2
C
D
pH
H
pH
Na2O
Al 2O3
P4O10
Cl 2O7
MgO
SO3
SiO2
pH
Na2O
Al 2O3
P4O10
Cl 2O7
MgO
SO3
SiO2
2 In the Contact process, what is the nature of the gaseous product and what is the identity of the
catalyst?
3
In the last century the Haber process was sometimes run at pressures of 1000 atm and higher.
Now it is commonly run at pressures below 100 atm.
What is the reason for this change?
4
A
An iron catalyst is used.
B
Maintaining the higher pressures is more expensive.
C
The equilibrium yield of ammonia is increased at lower pressures.
D
The rate of the reaction is increased at lower pressures.
An aqueous solution was prepared containing 1.0 mol of AgNO3 and 1.0 mol of FeSO4 in 1.00 dm3
of water. When equilibrium was established, there was 0.44 mol of Ag+(aq) in the mixture.
Ag+(aq) + Fe2+(aq)
Ag(s) + Fe3+(aq)
What is the numerical value of Kc?
A
0.35
B
0.62
C
1.62
D
2.89
5 When gaseous iodine is heated with hydrogen at 450 °C, an equilibrium is established.
H2(g)
colourless
I2(g)
purple
2HI(g)
colourless
∆H = +53 kJ mol–1
Which change of conditions will cause the purple colour of the equilibrium mixture to become
paler?
6
7
A
decrease in pressure
B
decrease in temperature
C
increase in pressure
D
increase in temperature
In the Haber process for the manufacture of ammonia, why is the heterogeneous catalyst iron in
a finely divided state?
A
to increase its surface area
B
to produce the maximum reduction in the activation energy
C
to reduce its loss during the reaction
D
to reduce its surface area
Use of the Data Booklet is relevant to this question.
560 kg of nitrogen and 120 kg of hydrogen are pressurised, heated and passed over an iron
catalyst. When the mixture of gases reaches equilibrium, it contains 96 kg of hydrogen.
Which mass of ammonia does it contain?
A
8
24 kg
B
68 kg
For the equilibrium 2SO2(g) + O2(g)
A
adding a catalyst
B
adding more O2
C
increasing the pressure
D
increasing the temperature
C
136 kg
D
680 kg
2SO3(g), what will change the value of Kp?
9 For the reaction
2Y(aq) + 3Z(aq)
W(aq) + 2X(aq)
what are the correct units for the equilibrium constant Kc?
A
B
mol dm–3
C
mol2 dm–6
mol–1 dm3
D
mol–2 dm6
10 The Haber process for the manufacture of ammonia is represented by the following equation.
N2(g) + 3H2(g)
2NH3(g)
∆H = –92 kJ mol–1
Which statement is correct about this reaction when the temperature is increased?
A
Both forward and backward rates increase.
B
The backward rate only increases.
C
The forward rate only increases.
D
There is no effect on the backward or forward rate.
11 The table gives the concentrations and pH values of the aqueous solutions of two compounds, X
and Y. Either compound could be an acid or a base.
Student P concluded that X is a strong acid.
Student Q concluded that the extent of dissociation is lower in X(aq) than in Y(aq).
Which of the students are correct?
A
both P and Q
B
neither P nor Q
C
P only
D
Q only
12 Swimming pool water can be kept free of harmful bacteria by adding aqueous sodium chlorate(I),
NaOCl. This reacts with water to produce HOCl molecules which kill bacteria.
OCl –(aq) + H2O
OH–(aq) + HOCl (aq)
In bright sunshine, the OCl – ion is broken down by ultra-violet light.
OCl –(aq) + uv light → Cl –(aq) + ½O2(g)
Which method would maintain the highest concentration of HOCl (aq)?
A
acidify the pool water
B
add a solution of chloride ions
C
add a solution of hydroxide ions
D
bubble air through the water
13 The percentage of ammonia obtainable, if equilibrium were established during the Haber process,
is plotted against the operating pressure for two temperatures, 400 °C and 500 °C.
Which diagram correctly represents the two graphs?
A
40
% NH3 at
20
equilibrium
400 °C
500 °C
B
40
% NH3 at
20
equilibrium
500 °C
400 °C
0
0
10
10
2
pressure / 103 kPa
0
0
10
10
2
pressure / 103 kPa
C
D
40
400 °C
% NH3 at
20
equilibrium
500 °C
0
0
10
10
2
pressure / 103 kPa
40
500 °C
% NH3 at
20
equilibrium
400 °C
0
0
10
pressure / 103 kPa
14 The value of the equilibrium constant, Kc, for the reaction to form ethyl ethanoate from ethanol
and ethanoic acid is 4.0 at 60 °C.
C2H5OH + CH3CO2H
CH3CO2C2H5 + H2O
When 1.0 mol of ethanol and 1.0 mol of ethanoic acid are allowed to reach equilibrium at 60 °C,
what is the number of moles of ethyl ethanoate formed?
A
15
1
3
B
2
3
C
1
4
D
3
4
Use of the Data Booklet is relevant to this question.
The enthalpy change of formation, ∆Hf, of hydrated calcium ions is the enthalpy change of the
following reaction.
Ca(s) + aq – 2e– → Ca2+(aq)
The following enthalpy changes are not quoted in the Data Booklet.
Ca(s) → Ca(g)
Ca2+(g) + aq → Ca2+(aq)
∆Ha = 177 kJ mol–1
∆Hhyd = –1565 kJ mol–1
What is the enthalpy change of formation of hydrated calcium ions?
A
–1388 kJ mol–1
B
–798 kJ mol–1
C
–238 kJ mol–1
D
+352 kJ mol–1
16 The following equilibrium is set up in a mixture of concentrated nitric and sulfuric acids.
HNO3 + H2SO4
H2NO3+ + HSO4–
Which row correctly describes the behaviour of each substance in the equilibrium mixture?
17 Which molecule or structure does not contain three atoms bonded at an angle between
109° and 110°?
A
ethanoic acid
B
graphite
C
propane
D
silicon(IV) oxide
18 Equimolar quantities of magnesium carbonate and strontium carbonate are separately heated
to bring about complete thermal decomposition. The minimum temperature for this to occur is
called Td.
The cold residues are separately added to equal volumes of water and the change in pH is
measured. The change in pH is called ∆pH.
Which metal has the higher value of Td, and the greater value of ∆pH?
19 The equilibrium
N2(g) + O2(g)
2NO(g)
∆H = +180 kJ mol–1
contributes to a series of reactions producing photochemical smog.
Which factors would affect the value of Kp of the above equilibrium?
change in
pressure
change in
temperature
presence or absence
of a catalyst
A
B
C
D
20 When sulfur trioxide is manufactured from sulfur dioxide and oxygen, using the Contact process,
which condition affects the value of the equilibrium constant, Kc?
A
adjusting the temperature
B
adjusting the pressure
C
using a catalyst
D
removing SO3 from the equilibrium mixture
21 For the reaction
W(aq) + 2X(aq)
2Y(aq) + 3Z(aq)
what are the correct units for the equilibrium constant Kc?
A
mol dm–3
B
mol2 dm–6
C
mol–1 dm3
D
mol–2 dm6
22 The diagram represents the Haber process for the manufacture of ammonia from nitrogen and
hydrogen.
heat exchanger
N2 + H2
catalytic
converter
condenser
NH3
What is the purpose of the heat exchanger?
A
to cool the incoming gas mixture to avoid overheating the catalyst
B
to cool the reaction products and separate the NH3 from unused N2 and H2
C
to warm the incoming gas mixture and shift the equilibrium to give more NH3
D
to warm the incoming gas mixture and speed up the reaction
23 For the equilibrium 2SO2(g) + O2(g)
A
adding a catalyst
B
adding more O2
C
increasing the pressure
D
increasing the temperature
2SO3(g), what will change the value of Kp?
24 Dinitrogen tetroxide dissociates into nitrogen dioxide on heating.
N2O4(g)
2NO2(g)
In an experiment the partial pressures of the gases at equilibrium were found to be NO2, 0.33 atm;
N2O4, 0.67 atm.
What is the numerical value of Kp at the temperature of the experiment?
A
0.16
B
0.49
C
0.65
D
2.03
25 Two equilibria are shown below.
reaction I
2X2(g) + Y2(g)
reaction II
X2Y(g)
2X2Y(g)
X2(g) + 21Y 2(g)
The numerical value of Kc for reaction I is 2.
Under the same conditions, what is the numerical value of Kc for reaction II?
A
1
2
B
1
2
C
1
4
D
–2
26 Nitrogen dioxide decomposes on heating according to the following equation.
2NO2(g)
2NO(g) + O2(g)
When 4 mol of nitrogen dioxide were put into a 1 dm3 container and heated to a constant
temperature, the equilibrium mixture contained 0.8 mol of oxygen.
What is the value of the equilibrium constant, Kc, at the temperature of the experiment?
A
0.82 × 0.8
42
B
1.6 × 0.8
2.42
C
1.62 × 0.8
42
D
1.62 × 0.8
2.42
27 There are three stages in the Contact process for the production of sulphuric acid.
1
S + O2 → SO2
2
S
2
+
3
S
3
+ H2O → H2SO4
1
2
O2 → SO3
Which statement about this process is correct?
A
In the first stage a large excess of air under high pressure is used to improve the yield.
B
Two of the three stages are equilibria.
C
All three stages are exothermic.
D
In the final stage SO3 is absorbed by water droplets.
Section B
For each of the questions in this section, one or more of the three numbered statements 1 to 3 may
be correct.
Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against
the statements that you consider to be correct).
The responses A to D should be selected on the basis of
A
1, 2 and 3
are
correct
B
1 and 2
only are
correct
C
2 and 3
only are
correct
D
1 only
is
correct
No other combination of statements is used as a correct response.
28 Which statements are correct in terms of the Brønsted-Lowry theory of acids and bases?
1
Water can act as either an acid or a base.
2
Sulfuric acid, H2SO4, does not behave as an acid when dissolved in ethanol, C2H5OH.
3
The ammonium ion acts as a base when dissolved in liquid ammonia.
29 A student puts 10 cm3 of 0.100 mol dm–3 sulfuric acid into one test-tube and 10 cm3 of
0.100 mol dm–3 ethanoic acid into another test-tube. He then adds 1.0 g (an excess) of
magnesium ribbon to each test-tube and takes suitable measurements. Both acids have the
same starting temperature.
Neither reaction is complete after 2 minutes, but both are complete after 20 minutes.
Which statements are correct?
1
After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.
2
After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
3
After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
30 In which ways are the main reactions in the Haber and Contact processes similar?
1
A higher yield is favoured by higher pressures.
2
The reaction is a redox process.
3
The forward reaction is exothermic.
31 Ethanol is manufactured by reacting ethene gas and steam in the presence of phosphoric(V)
acid.
C2H4(g) + H2O(g)
∆H = –45 kJ mol–1
C2H5OH(g)
The reaction is carried out at 570 K and 60 atm.
What would be the consequences of carrying out the reaction at the same temperature but at a
pressure of 200 atm?
1
The manufacturing costs would increase.
2
The maximum yield at equilibrium would be higher.
3
The reaction would proceed at a faster rate.
32 The diagram represents the Boltzmann distribution of molecular energies at a given temperature.
proportion
of molecules
energy
Which of the factors that affect the rate of a reaction can be explained using such a Boltzmann
distribution?
1
increasing the concentration of reactants
2
increasing the temperature
3
the addition of a catalyst
33 The following reaction takes place using liquid ammonia as a solvent.
Na+ NH2− + NH4+ Cl − → Na+ Cl − + 2NH3
Which statements best explain why this reaction should be classified as a Brønsted-Lowry acidbase reaction?
1
The ammonium ion acts as a proton donor.
2
Na+ Cl − is a salt.
3
Ammonia is always basic.
34 Which equilibria, in which all species are gaseous, would have equilibrium constants, Kp, with no
units?
1
sulfur dioxide and oxygen in equilibrium with sulfur trioxide
2
hydrogen and iodine in equilibrium with hydrogen iodide
3
carbon monoxide and steam in equilibrium with carbon dioxide and hydrogen
35 Catalysts are used in many reversible reactions in the chemical industry. Vanadium(V) oxide is
used in this way in the Contact process for the formation of SO3.
2SO2(g) + O2(g)
2SO3(g)
What effect does vanadium(V) oxide have on this equilibrium?
1
It speeds up the forward reaction.
2
It increases the value of Kp.
3
It increases the value of Ea for the reverse reaction.
36 Which of the following can act as a Bronsted-Lowry acid?
1
H3O+
2
NH 4
3
H2O
+
37 Under given conditions, what governs the rate of a forward reaction?
1
the activation energy of the reaction
2
the enthalpy change of the reaction
3
the equilibrium constant of the reaction
38 Which statements about the Haber process for the industrial production of ammonia are correct?
1
The equilibrium constant Kp increases with pressure.
2
As the temperature increases, the equilibrium constant for the forward reaction becomes
smaller.
3
The process is usually carried out at between 450 °C and 550 °C at a pressure of at least
150 atm.
39 Two bulbs R and S, connected by a mercury manometer, are held in a thermostat, as shown. The
volume of R is twice that of S. R contains gas, X, at the same pressure as the nitrogen in S.
R
X
S
nitrogen
thermostat
manometer
mercury
When the temperature is increased, which gases in bulb R would cause the mercury level in the
right-hand limb of the manometer to rise?
1
an equilibrium mixture N2F4(g)
2
an equilibrium mixture CH3NC(g)
3
nitrogen
2NF2(g); ∆H positive
CH3CN(g); ∆H negative
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Equilibria
Mark Scheme 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Equilibria
Sub-Topic
Paper Type
Theory
Booklet
Mark Scheme 2
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
Question
Questi
1
Scheme
Marks
(a)
CH4 + H2O CO + 3H2
1
(b)
Label on graph indicating catalysed and uncatalysed Ea
OR statement Ea catalysed is lower (than Ea uncatalysed) owtte
1
Reference to catalyst creating alternative mechanism / reaction pathway / route
1
Idea that more molecules have sufficient energy (to react)
1
so greater chance / frequency of successful collisions
1
(c)
N
[1
[4]
1
H
H
H
angle = 107o
shape = (trigonal) pyramid(al)
(d) (i) Advantage = higher rate
Greater Kinetic Energy / speed / collision frequency / proportion of successful collisions
(ii)
T
1
1
[3]
1
1
Disadvantage – reduced yield / less product / more reactants
1
(Forward reaction) exothermic AND (hence in accordance with Le Chatelier’s Principle) equilibrium / reaction
shifts left (to counteract increasing temp) ora
1
[4]
1
[1]
Kp =
2
pNH3
3
pN2 × pH2
(iii)
N2(g) +
2
(–0.8)
1.2
3H2(g) 3
(–1.6×3/2)
0.6
2NH3(g)
0
1.60
xNH3 = 1.6/3.4 (= 0.471)
xN2 = 1.2/3.4 (= 0.353)
xH2 = 0.6/3.4 (= 0.176)
Kp =
0.4712 × (2 × 107)2
= 2.88 × 10–13 Pa–2
0.353 × 2 × 107 × 0.1763 × (2 × 107)3
1
1
1+1
[5]
[18]
2
(a
a base is a proton acceptor or
a lone pair donor
a weak base is not fully ionised
e.g. NH3 + H2O NH4+ + OH– or
(b)
b) (
(1)
(1)
B + H+ BH+ or equivalent
⇌ is necessary
(1)
stated pressure
stated temperature
named catalyst
(1)
(1
(1)
greater than 1 atm up to 5 atm
400 to 500 oC
V2O5/vanadium(V) oxide
(ii) SO3 is dissolved in concentrated H2SO4
and then diluted with water
not 'SO3 dissolved in water' as the only statement
(1)
(c) (i) with concentrated sulfuric acid
ClCH2CH=CHCl
(1)
with ammonia
H2NCH2CH(OH)CH2NH2
(1)
(ii) nucleophilic
substitution
(1)
(1)
[3]
[4]
[4]
[Total: 11]
3
(a
(i) if the conditions of a system in equilibrium are changed
(1)
the position of equilibrium moves so as to reduce that change
(1)
(ii) lower temperature
(1)
because the forward reaction is exothermic
(1)
higher pressure
(1)
because the forward reaction shows a reduction in volume
or
there are fewer molecules/moles on RHS of equilibrium
(1)
(b)
CO2
[2]
+
2
⇌
CO
+
[4]
2O
initial moles
0.70
0.70
0.30
0.30
equil. moles
(0.70–x)
(0.70–x)
(0.30+x)
(0.30+x)
equil. concn.
(0.70–x)
1
(0.70–x)
1
(0.30+x)
1
(0.30+x)
1
(1)
Kc = (0.30+x)2 = 1.44
(0.70-x)2
(1)
gives x = 0.25
at equilibrium,
n(CO2) = n(H2) = 0.70 – 0.25 = 0.45 moles
and
n(CO) = n(H2O) = 0.3 + 0.25 = 0.55 moles
(1)
(1)
[4]
[Total: 10]
4
(a
(due to the) strong N≡N bond
(b)
b) (
Any balanced equation forming a stable nitrogen oxide
e.g. N2 + O2 → 2NO
or
N2 + 2O2 → 2NO2
[1]
[1]
[1]
[1]
(ii) in lightning
in an engine/combustion of fuels (or a specific example)
(iii) (NOx produces) acid rain or forms (photochemical) smog
(c) (base is a) proton acceptor
[1]
[1]
[4]
[1]
basicities: ethylamine > NH3 > phenylamine
[1]
ethylamine (more basic) due to electron donating ethyl group
[1]
phenylamine (less basic) due to lone pair being delocalised into the ring
[1]
[4]
(d)
d) (
step 1: nucleophilic substitution
[1]
step 2: hydrolysis
[1]
(ii) step 1: KCN (in ethanol) and reflux
step 2: H3O+ / aqueous acid and reflux
(iii) T is
[1]
[1]
NH2
[1]
W is
Cl
O
[1]
[6]
[Total: 15]
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Equilibria
Question Paper 2
Level
International A Level
Subject
Chemistry
Exam Board
CIE
Topic
Equilibria
Sub-Topic
Paper Type
Theory
Booklet
Question Paper 2
Time Allowed:
65 minutes
Score:
/54
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
1
The Haber process for the manufacture of ammonia, NH3, was originally devised at the start of the
20th century and was developed into a full-scale industrial process by Carl Bosch in 1913.
The key step in the process is the reversible reaction of nitrogen and hydrogen in the presence of
an iron catalyst.
N2(g) + 3H2(g)
2NH3(g)
∆H = –92 kJ mol–1
(a) The hydrogen for this reaction can be formed by reacting methane with steam, during which
carbon monoxide is also produced. Write an equation for this reaction.
.............................................................................................................................................. [1]
(b) Use the Boltzmann distribution shown to explain why a catalyst increases the rate of this
reaction.
number of
molecules
kinetic energy
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [4]
(c) Draw a three-dimensional diagram to show the shape of an ammonia molecule. Name this
shape and state the bond angle.
shape ....................................................................................... bond angle ........................