GRADE 12 PHYSICAL SCIENCE
EXAMINER: PW
PAPER 2
MODERATOR: AS
JUNE 2015
150 marks/3 hours
BISHOPS
INSTRUCTIONS and NOTES:
 This question paper consists of FIVE questions. Answer ALL the questions on lined
paper.
 Write your name and your teacher’s initials on each page.
 Both sides of the paper may be used. Start each question on a new page.
 Graph paper will be supplied for Question 3.2.5
 Number the answers correctly according to the numbering system used in this question
paper.
 Leave ONE line between two sub questions, for example between 2.1 and 2.2.
 You may use a non-programmable calculator.
 You are advised to use the attached DATA SHEETS.
 Show formulae and substitutions in calculations.
 Round off your final numerical answers to a minimum of TWO decimal places
 Write neatly and legibly.
QUESTION 1
Four options are provided as possible answers to the following questions. Each question has only
ONE correct answer. Write only the letter (A–D) next to the question number (1.1–1.10) on your
lined paper.
1.1
The following molecules all have similar molecular masses. Which compound will have the
highest boiling point?
A. CH3CH2CH2CH2CH3
1.2
C. CH2CHCH2CH2CH3
D. CH3CH2CH2CH2CHO
Which of the following is NOT a characteristic of an activated complex?
A.
B.
C.
D.
1.3
B. Cl2
It is a mixture of reactants and products.
It is a high energy group of bonded atoms.
It can break down into reactants or products.
It is unstable and readily breaks down.
What is the oxidising agent in the following reaction?
2FeF2 + F2  2FeF3
A. FeF2
B. F2
C. FeF3
D. There is no oxidizing agent.
1
1.4
Which of the following actions would have a negative impact on the accuracy of an acidbase titration in which the acid was run out of the burette?
A.
B.
C.
D.
1.5
A 4 mol.dm-3 solution of a monoprotic acid had a pH of exactly 4. Which statement is true
about this acid?
A.
B.
C.
D.
1.6
It is a weak acid.
It has a high Ka value.
There are no hydroxide ions in the solution.
The concentration of oxonium ions in the solution is 4 mol.dm-3.
A heterogeneous catalyst can be described as:
A.
B.
C.
D.
1.7
Rinsing the burette with acid only.
Rinsing the conical flask with distilled water before adding the alkali.
Rinsing the pipette with distilled water before filling it with alkali.
Rinsing the funnel with acid before using it to fill the burette.
one which is in the same phase as the reactants and raises the activation energy.
one which is in the same phase as the reactants and lowers the activation energy.
one which is in a different phase to the reactants and raises the activation energy.
one which is in a different phase to the reactants and lowers the activation energy.
The graphs below represent the change in the rate of reaction versus time for the
reversible reaction that took place when an amount of hydrogen (H2) gas and iodine (I2) gas
was sealed off in a container. (The broken line represents the reverse reaction.)
H2 (g)
+ I2 (g)
2HI (g)
H < 0
The possible changes that occurred at 10 minutes and 15 minutes would be…
A
B
C
D
At 10 minutes
Catalyst added
P increased by decreasing V
T increased
P increased by decreasing V
At 15 minutes
P decreased by increasing V
T decreased
H2 extracted
T increased
2
1.8
When a chemical system is in equilibrium and a change in the conditions causes an
increase in the value of Kc then the following always happens:
A.
B.
C.
D.
1.9
Which ratio of elements below could be a saturated straight chain alcohol?
A.
1.10
The rate of the forward reaction increases only.
The rate of the reverse reaction increases only.
The rate of both forward and reverse reactions increases.
The yield of products increases.
C4H8O
B. C4H9O
C.
C4H10O
D. C4H11O2
Which of the following is an example of an elimination reaction?
A.
B.
C.
D.
The reaction of a carboxylic acid with an alcohol to form an ester.
The reaction between an alkene and water to form an alcohol.
The reaction decomposition of alcohol into water and an alkene.
The reaction of an alkane with a halogen to form a haloalkane.
{20 marks}
3
QUESTION 2
2.1
A chemist wanted to determine the metal (X) of a hydrated sulphate salt with the formula:
XSO4.5H2O. He carefully weighed out 8,55 g of the solid. He heated this gently and the mass
dropped to a steady 5,15 g as the water was driven off.
2.1.1
How many moles of water were driven off?
(4)
2.1.2
Calculate the atomic mass of element X.
(4)
2.1.3
Name the element X.
(1)
[9]
2.2
Calculate the percentage purity of a sample of iron(III) carbonate if 15,0 g of the impure
sample produced 5,71 x 10-2 mol of carbon dioxide when reacted with excess hydrochloric
acid.
Fe2(CO3)3 + 6HCl  2FeCl3 + 3H2O + 3CO2
(The molecular mass of Fe2(CO3)3 is 292.)
(5)
[5]
2.3
2.3.1
Define an acid according to Lowry-Brønsted.
(1)
2.3.2
What is the conjugate base of the HCO3- ion?
(1)
2.3.3
Is ammonia a weak base?
(1)
2.3.4
Name the two substances formed when calcium oxide reacts with nitric acid.
(2)
2.3.5
Will the pH of a solution of sodium ethanoate be MORE THAN, LESS THAN OR EQUAL TO
seven?
(1)
2.3.6
Calculate the pH of a 0,44 mol.dm-3 solution of sulphuric acid.
2.4
An acid-base titration is performed to find the concentration of a solution of oxalic acid
using a standard solution of sodium hydroxide. An indicator is used to determine the end
point.
2.4.1
Define a “standard solution”.
(2)
2.4.2
Name a suitable indicator for this titration.
(1)
2.4.3
What colour is this indicator in alkali?
(1)
2.4.4
What ion is the predominant ion in all alkali solutions?
4
(4)
[10]
(1)
[5]
{29}
QUESTION 3
3.1
White phosphorus burns in air to produce a mixture of two oxides. It is a spontaneous
reaction on a warm day.
Reaction 1:
Reaction 2:
P4 + 3O2  P4O6
P4 + 5O2  P4O10
3.1.1
What is the oxidation number of the phosphorus in P4O6?
(1)
3.1.2
What is the empirical formula of the second oxide?
(1)
3.1.3
What does “spontaneous” mean in this context?
(2)
3.1.4
Do these reactions have high or low activation energies?
(1)
3.1.5
Draw an energy diagram (potential energy versus course of reaction) for the first reaction,
using labelled single-headed arrows show the activation energy (EA) and enthalpy change
(∆H). Put the formulae of reactants and product into the diagram.
(5)
3.1.6
Red phosphorus does not ignite spontaneously. Therefore it has a ….(a)….. activation
energy and a …(b)…. P-P bond energy than white phosphorus.
(2)
Calculate ∆H for the second reaction using the information provided below.
(5)
3.1.7
P4
P4O10
Bond energy
kJ.mol-1
P-P
200
O-O
204
O=O
498
O-P
351
O=P
544
[17]
5
3.2
A chemist used the reaction between hexane and bromine to study the rate of a reaction
over a period of time. He made use of a spectrometer to record the ratio of the incident
light (Io) to transmitted light (I ) for a frequency of light which bromine (Br2) absorbs. This
ratio can be related to the concentration of bromine present as the reaction proceeds.
1,55 g of bromine was added to hexane and the mixture stirred vigorously to dissolve all
the bromine forming 100 cm3 of solution . The mixture was then placed in the
spectrometer and after an initial reading further readings were taken every 2 minutes. The
results are recorded below.
Time
(min)
𝑰
𝑰𝒐
0
2
4
6
8
10
12
14
16
0,10
0,58
0,71
0,84
0,89
0,92
0,93
0,94
0,94
3.2.1
What is the independent variable in this experiment?
(1)
3.2.2
Calculate the concentration of the bromine solution at the start of the reaction.
(4)
3.2.3
State one fixed variable for this experiment.
(1)
3.2.4
Why does the I/Io ratio increase as the reaction proceeds?
(2)
3.2.5
Use the graph paper provided to plot these results.
(5)
3.2.6
On the same piece of graph paper draw a curve which could represent the same reaction
done at a higher temperature. Label it “higher T”.
(2)
3.2.7
What characteristic of the curve at any point indicates the rate of reaction?
6
(1)
[16]
{33}
QUESTION 4
4.1
Some fluorine and hydrogen were placed in a closed 2,0 dm3 container to set up the
following chemical equilibrium at 600oC :
F2(g) + H2(g) ⇄ 2HF(g)
4.1.1
What does chemical equilibrium mean:
4.1.1.1 in terms of rates of reaction?
4.1.1.2 in terms of macroscopic properties?
(1)
(1)
Write the expression for Kc for the reaction.
(1)
4.1.2
It was found that when equilibrium was reached the number of moles of each chemical
present was:
chemical
F2
H2
HF
moles
0,84
0,14
4,10
4.1.3
Show that the value of Kc is 143
(4)
4.1.4
Some hydrogen was then pumped into the 2 dm3 container to increase the number of
moles of hydrogen to a total value Y. Once a new equilibrium had been reached it was
found that the amount of HF present was 4,18 mol. Using the value of Kc given in 4.1.3
calculate the number of moles of hydrogen added to the reaction mixture.
(7)
4.1.5
What single change would change the value of KC for this reaction?
4.2
The following chemical equilibrium was set up in a closed container by adding equal
quantities of carbon monoxide and nitrogen(II) oxide and leaving for several hours.
2CO + 2NO ⇄ 2CO2 + N2
(1)
[15]
∆H = - 200 kJ (all gases)
The conditions were then varied causing changes to the system. Complete the table below
using INCREASE, DECREASE or NO CHANGE.
Change imposed
pressure increase by
decreasing the volume
catalyst added
Immediate rate of
forward reaction
4.2.1
Final moles of N2
4.2.3
4.2.4
4.2.5
4.2.6
Carbon dioxide added at
constant volume.
4.2.7
4.2.8
4.2.9
State le Chatelier’s principle.
Explain your answer to 4.2.5 using the word “collisions”.
Explain your answer to 4.2.2 in terms of le Chatelier’s principle.
7
4.2.2
(6)
(2)
(2)
(3)
[13]
4.3
The Contact process is used to make sulphuric acid. It was named the Contact process
because the reacting gases in one of the steps came into “contact” with the catalyst and
then reacted. Sulphuric acid has a variety of uses and millions of tonnes are produced every
year. When dissolved in water it forms a strong acid.
4.3.1
Write a balanced chemical equation for the reversible reaction which happens on the
catalyst.
(2)
4.3.2
What is the name of the compound H2S2O7?
(1)
4.3.3
Name the salt formed when ammonia reacts with sulphuric acid.
(2)
Ammonia is formed in the Haber Process for which the chemical equation is:
N2 + 3H2 ⇄ 2NH3 ∆H < 0
4.3.4
Explain whether a high or low temperature would give the highest yield and why a
temperature of 450 oC is used in some industrial plants.
(3)
[8]
{36}
QUESTION 5
5.1
Alkanes, alkenes and alkynes are all hydrocarbons. The main sources of hydrocarbons are
natural gas and crude oil.
5.1.1
Name the type of intermolecular force that makes hexane a liquid at 20 oC.
(1)
5.1.2
Define an isomer.
(2)
5.1.3
Name the following compounds:
5.1.3.1
CH3CH(CH3)CH2CH2CH3
(2)
5.1.3.2
5.1.4
(3)
Draw the structural formula of another branched isomer of the compound in question
5.1.3.1.
(2)
Write a chemical equation for the complete combustion of ethyne using molecular
formulae.
(3)
Write a chemical equation, using structural formulae for organic molecules, for the
reaction between hydrogen chloride (HCl) and but-1-ene.
(2)
5.1.7
Name the type of reaction in 5.1.6.
(1)
5.1.8
The reaction conditions specifically mention a compound which must not be present when
hydrogen chloride reacts with but-1-ene. What is the compound?
(1)
[17]
5.1.5
5.1.6
8
5.2
Ethanol is naturally produced by the process of fermentation but it can also be produced
synthetically from an alkene. It has many uses apart from being used in alcoholic drinks
such as wine.
5.2.1
Write the structural formula of ethanol.
(2)
5.2.2
Ethanol boils at +78 oC whereas dimethyl ether (shown below) boils at -24 oC. Explain
clearly why there is this large difference by naming and contrasting the intermolecular
forces involved.
(3)
5.2.3
Ethanol is a primary alcohol. NAME a secondary alcohol with five carbons.
(2)
5.2.4
Name the reagents needed to convert ethanol to chloroethane.
(2)
[9]
5.3.1
Esters are useful compounds. Their volatility and fragrances mean that they are used in
glues and in some sweets and other food stuffs. They are usually made by reacting a
carboxylic acid with an alcohol in the presence of a catalyst. Draw the structure of the ester
formed when methanoic acid reacts with butan-1-ol.
(2)
5.3.2
Name the ester.
5.4
To which homologous series do the following compounds belong?
5.4.1
CH3CH2COCH2CH3
(1)
5.4.2
CH3CH2CCCH2CH3
(1)
[2]
(2)
[4]
{32}
TOTAL 150 MARKS
9
(blank)
10
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