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2nd Edition
2nd Edition
Chemistry Matters for GCE 'O' Level Workbook (2nd Edition)
is the companion workbook to the revised best-selling Chemistry Matters for
GCE ‘O’ Level textbook. It is written in line with the 2013 GCE Ordinary Level
Chemistry syllabus from the Ministry of Education, Singapore. This workbook
is designed to promote learning with understanding. Its comprehensive range
of exercises builds foundational knowledge and develops critical higher-order
thinking skills. Coupled with tips on answering techniques and diagnostic selftests, this workbook will help students tackle questions with success and achieve
excellence in Chemistry.
Workbook (Teacher’s Edition)
Strengthens conceptual understanding
• Graded multiple-choice, structured and free-response questions reinforce learning
while building confidence and competency.
2nd Edition
Develops independent learning and critical thinking skills
• Every worksheet ends with a diagnostic checklist that encourages students to
evaluate their learning and take steps to secure their understanding.
• A variety of context-based and data-based questions challenge students to train
up their higher-order thinking skills.
Sharpens interpretive and answering skills
• Tips to guide students’ understanding of the questions they might be asked help
them to hit the mark with their answers.
• Accompanying worked examples of sample questions ensure students articulate
their answers effectively.
Tan Yin Toon • Chen Ling Kwong
John Sadler • Emily Sadler
Builds exam confidence
• A Trial Examination gives further practice and boosts exam confidence by helping
students familiarise themselves with the exam format.
Other components
• Practical Book
• Textbook
Tan Yin Toon • Chen Ling Kwong
John Sadler • Emily Sadler
ISBN 978-981-01-1702-3
Workbook
Teacher's Edition
(S)CMWB(TE)_Cover.indd 1
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welcome any information which would enable us to contact the copyright holders/owners involved.
(S)CMWB_IFC&IBC(TE).indd 1
7
6
5
21
45
Sc
b
23
51
V
24
52
Cr
55
Mn
26
56
Fe
27
59
Co
88
Radium
Ra
227
89
Actinium
Ac
57
226
56
Lanthanum
139
La
Yttrium
39
Barium
137
Ba
Strontium
38
89
Y
88
Sr
Scandium
Calcium
20
a
X
72
b = proton (atomic) number
X = atomic symbol
a = relative atomic mass
†
Hafnium
178
Hf
Zirconium
40
91
Zr
Titanium
73
90
Thorium
Th
232
Cerium
58
140
Ce
Tantalum
181
Ta
Niobium
41
93
Nb
Vanadium
184
W
59
91
Protactinium
Pa
Preseodymium
141
Pr
Tungsten
74
42
Molybdenum
96
Mo
Chromium
75
92
U
Uranium
238
Neodymium
60
144
Nd
Rhenium
185
Re
Technetium
43
99
Tc
Manganese
25
76
93
Neptunium
Np
Promethium
61
Pm
Osmium
190
Os
Ruthenium
44
101
Ru
Iron
77
94
Pu
Plutonium
62
Samarium
Sm
150
Iridium
Ir
192
Rhodium
45
103
Rh
Cobalt
28
59
Ni
106
Pd
Nickel
78
95
Am
Americium
Europium
63
152
Eu
Platinum
195
Pt
Palladium
46
The volume of one mole of any gas is 24 dm3 at room temperature and pressure.
Key
*
22
48
Ti
29
64
Cu
30
65
Zn
157
Gd
Gold
197
Au
Silver
96
Curium
Cm
Gadolinium
64
79
47
108
Ag
Copper
80
97
Bk
Berkelium
Terbium
65
159
Tb
Mercury
201
Hg
Cadmium
48
112
Cd
Zinc
81
98
Cf
Californium
Dysprosium
66
162
Dy
Thallium
Tl
204
Indium
49
In
115
Gallium
31
Ga
70
Ca
40
27
Al
Boron
Aluminium
13
5
Magnesium
12
*58-71 Lanthanoid series
†90-103 Actinoid series
87
Fr
Francium
55
Caesium
Cs
133
Rubidium
37
Rb
85
Potassium
19
K
39
Sodium
24
Mg
Beryllium
Second edition 2013
11
23
Na
4
11
B
165
Ho
Lead
207
Pb
Tin
99
Es
Einsteinium
Holmium
67
82
50
119
Sn
Germanium
32
73
Ge
Silicon
28
Si
Carbon
14
6
12
C
83
Bi
100
Fm
Fermium
Erbium
68
167
Er
Bismuth
209
Antimony
51
122
Sb
Arsenic
33
75
As
Phosphorus
31
P
Nitrogen
15
7
14
N
169
101
Md
Mendelevium
69
Thulium
Tm
84
Polonium
Po
Tellurium
52
128
Te
Selenium
34
79
Se
Sulfur
32
S
Oxygen
16
8
16
O
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Level Theory Workbook by Oxford University Press Pte Ltd
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Acknowledgements
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Printed in Malaysia
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Marshall Cavendish is a registered trademark of Times Publishing Limited.
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E-mail: tmesales@mceducation.com
7
addressed to the Publisher.
1
Original edition first published in 2001 as Chemistry Matters for GCE ‘O’
V
173
Yb
102
No
Nobelium
Ytterbium
70
85
At
Iodine
Astatine
53
175
Lu
Rn
Radon
Xenon
103
Lr
Lawrencium
Lutetium
71
86
54
Xe
131
I
127
84
Kr
Argon
Krypton
36
18
40
Ar
Neon
20
Ne
Helium
10
2
4
He
0
Bromine
35
Br
80
Chlorine
Cl
35.5
Fluorine
17
9
19
F
VII
Times Centre, 1 New Industrial Road, Singapore 536196
Li
of the copyright owner. Any requests for permission should be
H
First published 2007
IV
Published by Marshall Cavendish Education
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photocopying, recording or otherwise, without the prior permission
III
Private Limited
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or transmitted, in any form or by any means, electronic, mechanical,
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© 2014 Marshall Cavendish Education Pte Ltd
I
No part of this publication may be reproduced, stored in a retrieval system
Group →
All rights reserved.
Period
↓
Reprinted 2017
The Periodic Table of Elements
© 2001 Oxford University Press Pte Ltd
© 2002 Times Media Private Limited
© 2003, 2007, 2013 Marshall Cavendish International (Singapore)
3/10/16 9:23 AM
2nd Edition
Workbook
Teacher's Edition
Tan Yin Toon • Chen Ling Kwong
John Sadler • Emily Sadler
(S)CMWB_TP(TE).indd 1
8/30/12 2:17 PM
Preface
Chemistry Matters for GCE ‘O’ Level Workbook (2nd Edition) is designed to meet the
aims and objectives of the latest GCE ‘O’ Level Chemistry syllabus requirements set by
the Ministry of Education (MOE). All aspects of this new edition have been re-designed
to strengthen understanding of concepts, provide ample practice and equip you with the
edge and confidence to excel in Chemistry.
(e) The distil
late containin
g only bromoben
layers were obse
zene was cont
rved in the conic
aminated with
al flask.
an unknown liquid
, E. Two
How can the liquid
s be separated
? Explain your
answer.
WORK ON
IT!
In the table
below, circle
the question
relevant sect
(s) that you
ion(s) in the
have answered
textbook to stre
incorrectly. Revi
ngthen your unde
sit the
rstanding of
the key conc
ept(s).
Self-directed learning
Work On It! is an enhanced selfdiagnostic tool at the end of each
worksheet, that will help you identity
concepts that still need working on.
As you revise the relevant Textbook
sections, your understanding will be
strengthened.
Learning outco
mes
(a)
(b)
(c)
(d)
Question numb
er(s)
Multiplechoice
Name apparatus
time, temperatu for measuring mass,
liquids and gasere and volumes of
s.
Structured
1
Select suitable
a sample of gas.apparatus for collecting
–
3
2.1
–
2(c)(i)
6
4
–
–
–
3.4
2
3.5
–
1(a)
3.6
–
2(c)(ii)
3.6
–
2(a), 2(b),
2(c)(i)
3
3.3
–
1(b), 1(c),
1(d)
5
3.2
1
–
–
3.1
–
–
7, 8, 9
2.2
–
–
(e)
16
–
2
Understand the
pure substance difference between
s and mixtures.
Describe meth
purifying mixtu ods of separating and
res of a solid
liquid.
and a
Describe meth
purifying mixtu ods of separating and
res of solids.
(f) Describe
a method to sepa
rate and
purify a solve
nt from a solut
ion.
(g) Describe
meth
purifying mixtu ods of separating and
res of liquids.
(h) Describe
chrom
chromatograms.atography and interpret
(i) Explain
the use of a locat
ing agen
in the chromatogr
aphy of colou t
compounds.
rless
(j) Explain
the impo
the purity of subsrtance of deter mining
tances in daily
life.
(k) Identify
substance
given their melti s and their purity,
ng and boiling
points.
Textbook
section(s)
to revise
Freeresponse
–
3.7
–
3.7
Worksheet 2
© 2013 Marsh
all Cavendish
International (Singa
pore) Private Limite
d
Answer It Right!
Answer It Right! guides you on how to interpret questions, so you understand exactly
what a question is asking for. As you go through the pointers and accompanying
worked examples, you will pick up the secrets to answering questions well.
Worksheet 11
)
Date:
Class:
Atomic Structure
ANSWER IT RIGHT!
Go through the worked example.
Use the tips to guide you in understan
ding and answering
the questions.
The figure below shows the electronic
iʜvʈ˜vœÀ“
Ê܏Ṏœ˜½Ê
ÊޜÕÊ̜ʓ>ŽiÊÕà œ˜Ê¼`ˆÕÌiÊ Ãœ`ˆÕ“ÊV œÀˆ`i
ÃÌÀÕV̽ÊÀiµÕˆÀiÃ
À“>̈
UÊ / iÊÌiÀ“ʼVœ˜ œÕÊ܈Ê˜ii`Ê̜ÊÕÃiÊ Ì iʈ˜vœ
UÊ Ê˜ÊÌ ˆÃÊV>Ãi]ÊÞ
half-equations.
nt.
this experime
used for
apparatus
am to show the
diagr
–
+
–
Ê" .
+
Na ]Ê l ]Ê Ê>˜`
r.
gas and wate
ide solution are
ess
to form oxygen
Thought Proc
e sodium chlor
gas.
losing electrons
present –in dilut
form hydrogen
to
discharged by
(i) z The ions
are
rons
ions
elect
Ê"
gaining
z ÌÊÌ iÊ>˜œ`i]
+
discharged by
are
ions
Ê
z ÌÊÌ iÊV>Ì œ`i]
led
(ii) Draw a label
+ 4e
–
O2­}®Ê³ÊÓ2O(l)
Answer
œ`i\Ê{" +(aq)
–
Ê2(g)
(i) ÌÊÌ iÊ>˜
dilute NaCl]Ê
ÊÓ (aq) + 2e
electrolysis of
ÌÊÌ iÊV>Ì œ`i\
the products of
Ê
electrolysed —
ion that is being
i˜Ê}>ÃÊ܈ÊLiÊ
ˆ˜ÃÌi>`ʜvʜÝÞ}
the type of solut NaCl are different.
n
`]ÊV œÀˆ˜iÊ}>ÃÊ
z Take note of
NaCl and molte
> lÊ>ÀiÊiiVÌÀœÞÃi
concentrated
`ʜÀʓœÌi˜Ê
i]ʈvÊVœ˜Vi˜ÌÀ>Ìi
zÊ ÊœÀÊiÝ>“«
anode.
the
at
ct
the produ
2p
2n
14p
14n
9p
10n
10p
10n
14p
16n
P
Q
R
S
T
1
2
3
is correct?
P and S are Group 0 elements in
the Periodic Table.
Q and T are isotopes.
R and T have the same nucleon number.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
Not all Group 0 elements have eight
hydrogen gas
e
carbon cathod
carbon anode
S and T.
electrons in their outer shell. Helium
has only two outer electrons.
Thought Process
UÊ Ê iVŽÊÌ iʘՓLiÀʜvʜÕÌiÀÊiiV
ÌÀœ˜Ãʈ˜Êi>V Ê>̜“°Ê˜Ê}i˜iÀ>]Êii“
i˜ÌÃʈ˜ÊÌ iÊÃ>“iÊ}ÀœÕ«Ê >ÛiÊÌ iÊ
same number of outer electrons.
Helium in Group 0 is an exception.
UÊ ÃœÌœ«iÃÊ>ÀiÊ>̜“ÃÊÜˆÌ ÊÌ iÊÃ>“iʘՓ
LiÀʜvÊ«ÀœÌœ˜ÃÊLÕÌÊ`ˆvviÀi˜ÌʘՓLi
ÀÃʜvʘiÕÌÀœ˜Ã°
UÊ / iʘÕViœ˜Ê˜Õ“LiÀʈÃÊÌ iÊÃՓʜvÊÌ
iʘՓLiÀʜvÊ«ÀœÌœ˜ÃÊ>˜`ʘiÕÌÀœ˜
Ãʈ˜Ê>˜Ê>̜“°
Answer
A
oxygen gas
(ii)
structures of five atoms, P, Q, R,
Which of the following statements
–
Ê
)
Date:
for Chapter 5
ering the
ding and answ
you in understan
tips to guide
ple. Use the
worked exam
Go through the
The gases
s.
inert electrode
questions.
carried out with
ide solution was
e sodium chlor
rolysis of dilut
s.
(a) The elect
.
the electrode
at
cted
colle
place
produced were
tions that take
ions for the reac
À°
ionic half-equat
ÀˆÌiÊޜÕÀÊ>˜ÃÜi ˆÌiÊÌ iʈœ˜ˆVÊ
(i) Construct
>̈œ˜Ê}ˆÛi˜Ê̜ÊÜ
̜ÊÜÀ
RIGHT!
ANSWER IT
(
for Chapter 15
Electrolysis
Name:
Class:
Worksheet 4
(
Name:
dilute sodium
n
chloride solutio
batter y
Worksheet 11
all Cavendish
© 2013 Marsh
d
pore) Private Limite
International (Singa
85
© 2013 Marshall Cavendish International
(Singapore) Private Limited
Worksheet 4
23
ii
(S)CMWB_Frontmatter.indd ii
8/16/12 9:48 AM
Comprehensive exercises
Each worksheet comprises a complete range of exercises — multiple-choice,
structured and free-response — to give you all the practice you need. The
questions are designed to support learning with understanding and give you a firm
grounding in conceptual understanding. Challenging questions are indicated with an
asterisk(*). A Trial Examination at the end will further build your exam confidence.
TEST IT!
ns
ctured Questio
Stru
es provided.
Section B:
s in the spac
below
wing question
tes. The table
rent metal nitra
Answer the follo
reaction.
solutions of diffe
() indicates no
Section A: Multiple-C
hoice Questions
Choose the correct answe
r and write its letter
in the brackets provide
d.
1.
Which of the following
A
B
C
D
2.
1.
processes is exother mic?
Decomposition by heat
of zinc carbonate into
zinc oxide and carbon
Formation of glucose and
dioxide
oxygen during photosy
nthesis
Conversion of glucose
to carbon dioxide and
water during respiration
Sublimation of dry ice
(
Which of the following
A
B
C
D
does not involve an endothe
rmic change?
An iron nail rusting in
air
A few drops of ethanol
drying up
A potted plant making
food in sunlight
A candle melting
)
(
)
A thermometer is placed
in water and the tempera
(Figure 1). A liquid, X,
ture is measured at
room temperature
is then added to the
water and the tempera
(Figure 2).
ture is measured again
3.
A cross
ss to aqueous
ates a reaction.
added in exce
A tick () indic
Metals were
rvations obtained.
records the obse
Zinc nitrate
Nickel(II)
Silver nitrate
esium
Magn
l
(colourless)
Copper(II)
nitrate
Aqueous meta
(colourless)
nitrate
nitrate
nitrate
(green)
s)
urles
(colo
(blue)
Metal
Copper
Magnesium
Nickel
Silver
tive metal.
reac
Zinc
t
mos
with the
tivity, starting
r of their reac
metals in orde
(a) Place the
react to give the
l nitrate would
34
32
30
28
26
24
Figure 1
What conclusion can be
A
B
C
D
meta
l and aqueous
(b) Which meta
n:
(i) Blue to gree
28
26
24
22
20
18
ical
s to blue:
ate that a chem
(ii) Colourles
that would indic
r observations
state two othe
colour changes,
(c) Apar t from
.
place
n
reaction has take
Figure 2
drawn from Figures 1 and
r changes?
following colou
2?
The process of mixing
liquid X and water is exother
mic.
The temperature increas
ed by 3.5°C.
The temperature decreas
ed by 4.0°C.
The graph that shows
the temperature change
s after X is added
to water should be:
2.
Temperature/°C
the
(a) What are
to rust?
can cause iron
conditions that
room
temperature
(
)
Trial Examination
Name:
tion.
example of oxida
rusting is an
(b) Explain why
Class:
Date:
Time/min
104
(
)
Trial Examination
PAPER 1
Workshee
orksheett 13
© 2013 Marshall Cavendish
78
1.
The diagram below
1.
shows the Haber
stion
An isotope of element
A
B
C
D
facturing ammonia.
process for manu
2.
nitrogen
process X
N2 : H2 = 1 : 3
converter
condenser
liquid
ammonia
(a) (i)
Z forms an ion, Z3–. The
Z3– ion has 18 electron
(
)
Benzoic acid occurs naturall
y in some plants. It is
widely used in the food
preservative. The melting
industry as a food
and boiling points of benzoic
acid are shown below.
z Melting point: 122°C
z Boiling point: 249°C
occurs when benzoic acid
at 2000°C is cooled to
100°C?
Distance between particle
s
Energy of particles
increases
increases
increases
decreases
decreases
decreases
decreases
increases
3. A student is asked
to confirm the presenc
e of Ca2+ and I– ions in
a salt solution.
Which of the following
observations is incorrec
t?
Test
A
Observation
add ammonia solution
B add sodium hydroxid
no precipitate
e solution
white precipitate, insolub
C
add barium chloride solution
le in excess
D
yellow precipitate
add dilute sulfuric acid
white precipitate
4. A substance, X, has
the following properties:
z Melting point: 3550°C
z Does not conduct electric
ity
Which of the following
substances is likely to
be X?
A
Diamond
B Graphite
C Copper
D Poly(ethene)
ing nitrogen and
X and Y for obtain
hydrogen.
into
gases is converted
g
hydro
hy gen
re of nitrogen and
ibe how the mixtu
(ii) Briefly descr
rter.
ammonia in the conve
(a) In an experiment, 25.0 cm3 of hydrochloric acid was placed in an insulated container. Aqueous
sodium hydroxide of concentration 1.0 mol/dm3 was then added to the acid, 2.0 cm3 at a
time. The mixture was then stirred and the highest temperature reached was recorded after
rea on.
in the reacti
en and hydrogen
each addition. The graph below shows the results of the experiment.
ing unreacted nitrog
advantage of recycl
(iii) Suggest one
Temperature/°C
35
(b) (i)
30
s and 17 neutrons.
Argon
Nitrogen
Oxygen
Phosphorus
Which of the following
and
unreacted nitrogened
hydrogen recycl
Name the processes
d
pore) Private Limite
International (Singa
A
B
C
D
hydrogen
process Y
*2.
Worksheet 10
What is element Z?
ing question.
Answer the follow
© 2013 Marsh
) Private Limited
(S)CMWB_13.indd 104
-Response Que
Section C: Free
all Cavendish
Answer all questions.
International (Singapore
(
(
(
© 2013 Marshall Cavendish
3
of nitrogen
ced when 36 dm
at room
ted to be produ
es are measured
ammonia is expec
reaction? (All volum
What volume of 3
of hydrogen in the
reacts with 72 dm
pressure.)
temperature and
)
)
)
International (Singapore
) Private Limited
Paper 1
171
25
20
15
10
Worksheet 15
5
© 2013 Marshall
0
2
4
(i)
ional (Singapore)
Cavendish Internat
6
8
10
127
Private Limited
12
14
16
18
Volume of NaOH added/cm3
7/22/12 7:18 PM
State why the reaction is exothermic.
(ii) From the graph, what was the maximum temperature reached and volume of sodium
hydroxide added?
Handling information
and solving problems
(iii) Calculate the concentration, in mol/dm3, of hydrochloric acid used in the experiment.
© 2013 Marshall Cavendish International (Singapore) Private Limited
Worksheet 13
109
Data-based questions in the worksheets present
information and problems in real-life contexts.
You will evaluate, interpret data and solve
interesting problems applicable to everyday life.
iii
(S)CMWB_Frontmatter.indd iii
8/16/12 9:48 AM
Contents
Preface
ii
Worksheet 1
Kinetic Particle Theory
1
Worksheet 2
Experimental Techniques
9
Worksheet 3
Elements, Compounds and Mixtures
17
Worksheet 4
Atomic Structure
23
Worksheet 5
Chemical Bonding
31
Worksheet 6
Chemical Calculations
41
Worksheet 7
Acids and Bases
51
Worksheet 8
Salts
59
Worksheet 9
Oxidation and Reduction
67
Worksheet 10
Metals
75
Worksheet 11
Electrolysis
85
Worksheet 12
The Periodic Table
93
Worksheet 13
Energy Changes
103
Worksheet 14
Speed of Reaction
111
Worksheet 15
Ammonia
123
Worksheet 16
The Atmosphere and Environment
129
Worksheet 17
An Introduction to Organic Chemistry
135
Worksheet 18
Alkanes and Alkenes
141
Worksheet 19
Alcohols and Carboxylic Acids
153
Worksheet 20
Macromolecules
163
Trial Examination
171
The Periodic Table of Elements
iv
(S)CMWB_Frontmatter.indd iv
8/16/12 9:48 AM
Class:
)
Worksheet 1
(
Name:
Date:
Kinetic Particle Theory
for Chapter 1
ANSWER IT RIGHT!
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
The diagram below shows four balloons containing the gases, methane (CH4), oxygen (O2), nitrogen (N2)
and carbon dioxide (CO2) at a constant temperature of 25°C. Each balloon contains the same volume
of gas. When left in the air for some time, the balloons deflate and become smaller.
CH4
O2
N2
CO2
(a) Explain why the balloons deflate over a period of time.
• You need to familiarise yourself with the glossary of terms used in Chemistry papers.
• The term ‘explain’ implies that you will need to give reasons or refer to a particular theory to support
your answer.
• In this case, refer to the kinetic particle theory to explain why the balloons deflate.
Thought Process
Using the kinetic particle theory, consider the movement of gas particles.
Answer
According to the kinetic particle theory, gas particles are in constant motion. The rubber that is
used to make balloons contains millions of small pores. The gas particles can move through these
small pores. Hence, the balloons deflate over a period of time.
(b) State which balloon will deflate at the (i) fastest rate; (ii) slowest rate. Give a reason for your
answer.
‘State’ requires a concise answer. There is no need to give supporting reasons. However, if an explanation
is required, the question will ask for it.
Thought Process
At a constant temperature, the rate of movement of gas particles depends on the molecular mass
of the gas particles. The lighter the gas particles, the higher the rate of movement.
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Answer
(i) Balloon containing methane. Methane is the lightest (smallest molecular mass). Hence, the
particles of methane will pass through the small pores of the balloon at the fastest rate.
(ii) Balloon containing carbon dioxide. Carbon dioxide is the heaviest (largest molecular mass).
Hence, the particles of carbon dioxide will pass through the small pores of the balloon at the
slowest rate.
It is insufficient to say the gas is ‘light’ or ‘heavy’ because you need to compare it to the other gases. Use
the words ‘lightest’ and ‘heaviest’.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which of the following statements is not true?
A
B
C
D
2.
( C )
Which statement about the kinetic particle theory is not true?
A
B
C
D
3.
Matter can exist in three states.
A solid has a fixed volume.
A gas cannot be compressed.
A liquid takes the shape of its container.
It
It
It
It
describes the different states of matter.
explains the changes of state.
explains the difference in the properties of solids, liquids and gases.
explains why substances have different solubilities.
( D )
The diagrams below show the arrangement of particles in different states of matter.
1
2
3
Which diagrams represent the correct arrangement of particles in a solid, liquid and gas
respectively?
Solid
Liquid
Gas
1
2
2
3
2
1
3
2
3
3
1
1
A
B
C
D
2
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( D )
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4.
The rate of diffusion of a substance depends on its
1
2
3
relative molecular mass
smell and colour
temperature
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
.
( B )
Use the table below to answer Questions 5 and 6.
Metal
Melting point/°C
Boiling point/°C
A
caesium
29
671
B
potassium
63
774
C
rubidium
39
688
D
sodium
98
883
5.
Which metal remains a liquid over the widest range of temperatures?
( D )
6.
Which metal is most likely to be in the liquid state at 30°C?
( A )
7.
A substance changes from a state where its particles vibrate in fixed positions to a state where
the particles move about freely but are still close to one another.
What change has taken place?
A
B
C
D
8.
Condensation
Evaporation
Freezing
Melting
( D )
The diagram below shows an apparatus for studying the effect of heat on substance X. What is X?
cold
water in
cold
water out
solid X
heat
A
C
Silicon
Iodine
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B
D
Carbon
Oxygen
( C )
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9.
The diagrams below show the particles of hexane at atmospheric pressure but at two different
temperatures. Hexane melts at –95°C and boils at 70°C.
x°C
y°C
What could be the values of x and y?
A
B
C
D
x
–100
–50
0
10
y
0
10
100
–50
( C )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
The interconversions between the three states of matter are represented by the diagram below.
melting
X
Y
Z
(a) Name the process in
(i) X; Boiling/ Evaporation
Freezing
(ii) Y;
(iii) Z.
Condensation
(b) In which of the change(s) of state (X, Y and/or Z) is energy being given out?
Y and Z
2.
In terms of the kinetic particle theory, explain the following.
(a) A liquid can take the shape of its container.
The particles in a liquid are not held in fixed positions and can move freely throughout the liquid.
________________________________________________________________________________
________________________________________________________________________________
(b) A tub of ice is heavier than a tub filled with water vapour.
The particles of ice, a solid, are very closely packed together. The particles of water vapour, a gas,
________________________________________________________________________________
are spread far apart from one another. Thus, ice has a higher density than water vapour of the same
________________________________________________________________________________
volume.
________________________________________________________________________________
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(c) A spray can containing gas should be kept away from fire.
If
a spray can is heated, the gas particles inside it will gain energy and spread out further apart very
________________________________________________________________________________
quickly.
This may cause the can to explode.
________________________________________________________________________________
3.
The boiling point of a liquid depends on the surrounding pressure. The atmospheric pressure at
sea level is 1 atm.
The atmospheric pressure at a base camp on a mountain is 0.40 atm. A mountain climber at the
base camp gently heated several chunks of ice in a saucepan until the water boiled for several
minutes.
(a) At 0.40 atm, ice melts at 0°C and water boils at 68°C. Sketch a graph of temperature against
time for the heating of ice and the boiling of water.
Temperature/°C
(water and water vapour)
68
(water)
0
(ice and water)
Time
(b) On your graph, label where there is
(i) water only;
(ii) a mixture of ice and water;
(iii) a mixture of water and water vapour.
4.
Methanal (HCHO) kills most bacteria. The heating curve of methanal is shown in Figure 1.
Selenium (Se) has both metallic and non-metallic properties. It can convert light energy directly
into electrical energy and is used in solar cells. The cooling curve of selenium is shown in
Figure 2.
Temperature/°C
Temperature/°C
Time/min
1000
900
0
liquid + gas
C
800
D
liquid + gas
700
E
600
–50
F
500
400
liquid + solid
–100
A
B
300
liquid + solid
200
100
Figure 1
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G
H
Time/min
0
Figure 2
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(a) Name the process that occurs from
(i) A–B;
Melting
(ii) C–D;
Boiling
(iii) E–F;
Condensation
(iv) G–H.
Freezing
(b) From Figures 1 and 2, infer the physical states of the substances at room temperature
(30°C).
Physical state of methanal:
Gas
(ii) Physical state of selenium:
Solid
(i)
(c) Solar cells can generate such a large amount of heat energy that the cells heat up to more
than 1000°C. Such cells spoil when they vaporise. At what temperature will a selenium cell
start to spoil?
About 700°C. Selenium will turn into a gas (i.e. vaporise) at around this temperature.
Section C: Free-Response Question
Answer the following question.
*1.
The table below compares the rate of diffusion of some gases to that of helium.
Gas
Relative molecular mass
Rate of diffusion with respect to helium
helium
4
1.0
methane
16
0.5
oxygen
32
0.35
sulfur dioxide
64
0.25
heptane
100
0.2
(a) Define the term ‘diffusion’.
Diffusion is the process by which particles move freely to fill up any available space.
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(b) (i)
Plot a graph of rate of diffusion with respect to helium against the relative molecular
mass.
1.2
Rate of diffusion with respect to helium
1.0
0.8
0.6
0.4
0.2
0
20
40
60
80
Relative molecular mass
100
120
140
(ii) What conclusion can you make from your graph?
The rate of diffusion of a gas is inversely proportional to its relative molecular mass.
(iii) How much faster does helium diffuse compared to a gas with a relative molecular mass
of 40?
From the graph,
Rate of diffusion of gas with relative molecular mass of 40 = 0.28
Number of times rate of diffusion of helium is as fast as that of the gas =
1
0.28
= 3.571
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(iv) What is the relative molecular mass of a gas that diffuses 2.5 times as slow as helium?
Rate of diffusion of the gas : rate of diffusion of helium = 1 : 2.5
Rate of diffusion of the gas = 1
Rate of diffusion of helium 2.5
Rate of diffusion of the gas with respect to helium = 1 × 1 = 0.4
2.5
From the graph, relative molecular mass of the gas = 22
(v) Name a gas that diffuses faster than helium.
Hydrogen (relative molecular mass = 2.0)
(vi) Explain, with a reason, how the results might differ if the experiment is performed at a
higher temperature.
The rate of diffusion of all the gases will increase. An increase in temperature will cause the gas
particles to gain kinetic energy and move faster.
(c) Give an everyday example of diffusion.
The aroma of food being detected from a distance when someone is cooking
(Accept any possible answers.)
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
8
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Describe the solid, liquid and gaseous
states of matter.
1
–
–
1.1
(b)
State the kinetic particle theory.
2
–
–
1.2
(c)
Describe the states of matter using the
kinetic particle theory.
3
2
–
1.2
(d)
Explain the interconversion of states of
matter in terms of the kinetic particle
theory and energy changes.
5, 6, 7, 8, 9
1, 3, 4
–
1.3
(e)
Use diffusion to account for the
movement of particles in liquids and
gases.
–
–
(f)
State examples of daily effects of
diffusion.
–
–
1(c)
1.4
(g)
Explain qualitatively the effect of
molecular mass and temperature on
the rate of diffusion.
4
–
1(b)
1.4
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1(a)
1.4
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Class:
)
Worksheet 2
(
Name:
Date:
Experimental Techniques
for Chapters 2 and 3
ANSWER IT RIGHT!
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
A gas sample contains a mixture of three gases: ammonia, carbon dioxide and methane. The properties
of these gases are shown below.
Gas
Solubility in water
Solubility in sodium hydroxide solution
ammonia
extremely soluble
insoluble
carbon dioxide
slightly soluble
extremely soluble
methane
insoluble
insoluble
(a) What are the steps needed to obtain methane from this gas sample? Explain the purpose of
each step.
You will need to state the steps for separating the gases in the correct sequence (i.e. which gas should
be removed first, second and last).
Thought Process
There are three methods of collecting gases — displacement of water, downward delivery and
upward delivery. The method of collecting a gas will depend on its solubility and density. In order
to obtain methane, ammonia and carbon dioxide must first be removed from the gas mixture.
Answer
Step 1: Pass the gas sample through water.
Purpose: To remove ammonia, which is extremely soluble in water
Step 2: Pass the remaining gases (carbon dioxide and methane) through sodium hydroxide
solution.
Purpose: To remove carbon dioxide, which is extremely soluble in sodium hydroxide solution
Step 3: Collect methane by displacement of water.
Purpose: To remove any residual gases that are slightly soluble in water
(b) Draw a labelled diagram to illustrate your answer in (a).
Your diagram should include all the pieces of apparatus needed for the experiment.
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Answer
gas jar
delivery tube
methane collected
mixture of ammonia,
carbon dioxide and
methane
water trough
conical flask
water
water
sodium hydroxide
solution
• You must label your diagram and make sure that it is large enough to fill up the space given.
• Make sure the apparatus is set up correctly.
– The tube introducing the gases must be immersed in the water or sodium hydroxide solution.
– The exiting tube must not be immersed.
– The apparatus must be air-tight, without any places for the gas to escape.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
The diagram shows three pieces of apparatus
used for measuring volumes of liquids. Which
apparatus can be used to measure 25.0 cm3
of distilled water? (Note: Diagrams are not
drawn to scale.)
A
B
C
D
1
2
1
2
cm3
25 cm3
50 cm3
0
10
30
only
only
and 2
and 3
40
50
1
2.
Gas P can be collected using the apparatus shown.
Based on the diagram only, what can you infer about
gas P?
A
B
C
D
10
It
It
It
It
Worksheet 2
(S)CMWB_02.indd 10
is
is
is
is
denser than air.
insoluble in water.
less dense than air.
soluble in water.
50 cm3
20
2
3 ( C )
gas P
delivery tube
gas jar
( A )
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3.
Which property indicates that a solid is pure?
A
B
C
D
4.
( B )
B
D
Crystallisation
Magnetic separation
Evaporation
Sublimation
( D )
Which statement has to be true in order for two substances to be separated by chromatography?
A
B
C
D
6.
burns completely in oxygen leaving no residue.
has a fixed melting point.
has a fixed volume.
is soluble in water.
Which of the following methods is used to obtain iodine from a mixture of iodine and sodium
chloride?
A
C
5.
It
It
It
It
They
They
They
They
are soluble in the same solvent.
have different boiling points.
have different colours.
have different densities.
( A )
Sodium nitrate decomposes when heated. Which is the best method to obtain crystals of sodium
nitrate from sodium nitrate solution?
A
B
C
D
Chromatography
Distillation
Evaporation to dryness
Crystallisation
( D )
Use the following information to answer Questions 7 and 8.
The diagram shows the apparatus used to obtain water from a solution of blue copper(II) sulfate.
water out
Y
Z
X
water in
W
7.
At which part of the apparatus will the temperature be greater than 100°C?
A
W
B
X
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C
Y
D
Z
( B )
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8.
Which statement about the separation process shown is true?
A
B
C
D
9.
Liquid W changes from colourless to blue.
Liquid X gets darker blue in colour.
The temperature at Y is 100°C at first and then steadily rises as liquid W is collected.
The vapour only starts to condense at Z.
( B )
A substance, Q, has the following properties:
Melting point
Boiling point
Solubility in water
Reaction with water
85°C
130°C
High
None
Which set of apparatus can be used to separate water from a mixture of Q and water?
A
B
C
D
( B )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Six athletes, A, B, C, D, E and F, took part in a race.
Athlete E won the race easily and was suspected
to have taken banned drugs. A sample of his urine
was analysed by chromatography to determine
whether it contained any of the two known banned
drugs, X and Y, which are used to increase physical
performance. The diagram on the right shows the
chromatogram obtained.
(a) The spots on the chromatogram obtained were
colourless. What step was carried out to make
the spots visible?
cm
solvent front
10
9
8
7
6
Key:
X – banned drug X
Y – banned drug Y
E – urine sample of
athlete E
5
4
A locating agent was applied onto the
3
chromatogram.
2
1
0
starting line
X
Y
E
(b) State one factor that determines how far a substance travels on a chromatogram.
Solubility of the substance in the solvent
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(c) What are the Rf values of X and Y?
Rf of X = 7.5 = 0.75
10
3.0
Rf of Y =
= 0.3
10
(d) Has athlete E taken either drug X or Y? Explain your answer.
No. None of the Rf values of the substances in his urine matches those of X and Y.
2.
A scientist carried out an experiment to synthesise a new drug. On his first attempt, he obtained a
white solid, which he named substance S. He decided to examine substance S further by heating
it. The table below shows how the temperature of substance S changed with time during heating.
Time/min
0
1
2
3
4
5
6
7
8
9
10
11
Temperature/°C
30
40
50
60
70
80
90
92
94
96
98
110
(a) Using the data above, plot a graph of temperature against time on the grid provided below.
Temperature/°C
120
100
80
60
40
20
0
1
2
3
4
5
6
7
8
9
10
11
12
Time/min
(b) From your graph, deduce the melting point of substance S.
90–98°C
(c) (i)
The scientist decided to purify substance S further. Explain why the scientist concluded
that substance S was not pure.
Substance S melted over a range of temperatures. It has no fixed melting point.
(ii) Explain why it is important for drugs to be pure.
Impurities in drugs can cause undesirable side effects.
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Section C: Free-Response Questions
Answer the following questions.
1.
Caliche is made up mainly of sodium nitrate, which is soluble in water. You may assume that all the
other substances present in caliche are insoluble in water. Describe the processes for obtaining
pure, dry sodium nitrate crystals from caliche. Explain the purpose of each process.
Step 1: Add water to caliche and stir. This is to dissolve the soluble sodium nitrate to form sodium nitrate
solution.
Step 2: Filter the mixture and collect the filtrate. This is to separate the insoluble substances from the
sodium nitrate solution.
Step 3: Evaporate the filtrate collected. This is to obtain a saturated solution of sodium nitrate.
Step 4: Allow the saturated solution to cool. This is to allow sodium nitrate crystals to form.
Step 5: Filter the mixture and collect the residue. This is to separate the sodium nitrate crystals from the
solution.
Step 6: Press the crystals between a few sheets of filter paper. This is to dry the pure sodium nitrate
crystals obtained.
*2.
Chlorobenzene and bromobenzene are
miscible liquids. Their boiling points are
132°C and 156°C respectively. A student
set up the apparatus shown on the right to
separate chlorobenzene from a mixture of
chlorobenzene and bromobenzene.
(a) Name the method used to separate
chlorobenzene and bromobenzene in
this experiment.
water out
P
B
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The student made an error in
setting up the apparatus. On the
diagram, circle the part in the
apparatus where the error has
occurred.
water in
A
Fractional distillation
(b) (i)
C
mixture of
chlorobenzene and
bromobenzene
distillate
boiling chips
heat from
electric heater
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(ii) What would happen if the student does not correct his mistake? Why?
The apparatus would blow up. Air pressure would build up in the apparatus.
(c) Identify the apparatus labelled A, B and C. In each piece of apparatus, at least one change of
state has occurred. Name these processes.
Apparatus
Process(es)
A: Round-bottomed flask
Evaporation/boiling
B: Fractionating column
Evaporation/boiling and condensation
C: Condenser
Condensation
(d) Assume the apparatus is now set up correctly.
(i)
Sketch a graph to show the temperature at point P against time during the experiment.
Temperature at point P/°C
156
132
0
Time/min
(ii) Explain the temperature changes in the graph you obtained in (d)(i).
When the mixture of chlorobenzene and bromobenzene is heated, its temperature increases
until it reaches 132°C, the boiling point of chlorobenzene. The temperature remains at 132°C
until all the chlorobenzene has distilled over. The temperature then rises until it reaches
156°C, the boiling point of bromobenzene. The temperature remains at 156°C until all the
bromobenzene has distilled over.
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(e) The distillate containing only bromobenzene was contaminated with an unknown liquid, E. Two
layers were observed in the conical flask.
How can the liquids be separated? Explain your answer.
By using a separating funnel. Bromobenzene and E are immiscible and do not dissolve in each other.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
16
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
1
–
–
2.1
–
–
2.2
(a)
Name apparatus for measuring mass,
time, temperature and volumes of
liquids and gases.
(b)
Select suitable apparatus for collecting
a sample of gas.
(c)
Understand the difference between
pure substances and mixtures.
3
2(c)(i)
–
3.1
(d)
Describe methods of separating and
purifying mixtures of a solid and a
liquid.
6
–
–
3.2
(e)
Describe methods of separating and
purifying mixtures of solids.
4
–
1
3.3
(f)
Describe a method to separate and
purify a solvent from a solution.
7, 8, 9
–
–
3.4
(g)
Describe methods of separating and
purifying mixtures of liquids.
–
–
2
3.5
(h)
Describe chromatography and interpret
chromatograms.
5
1(b), 1(c),
1(d)
–
3.6
(i)
Explain the use of a locating agent
in the chromatography of colourless
compounds.
–
1(a)
–
3.6
(j)
Explain the importance of determining
the purity of substances in daily life.
–
2(c)(ii)
–
3.7
(k)
Identify substances and their purity,
given their melting and boiling points.
3
2(a), 2(b),
2(c)(i)
–
3.7
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2
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Class:
)
Date:
Elements, Compounds and Mixtures
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 3
ANSWER IT RIGHT!
Worksheet 3
(
Name:
(a) Complete the table below for comparing the characteristics of compounds and mixtures.
Compounds
Mixtures
Separation
Energy change
Composition
The term ‘compare’ implies that you need to provide both similarities and differences between things or
concepts.
Answer
Compounds
Mixtures
Separation
The components in a compound can
only be separated by chemical
processes (e.g. electrolysis).
The components in a mixture can be
separated by physical processes.
Energy change
A chemical reaction occurs when
a compound is formed. There is
usually an energy change.
There is no reaction when a mixture
is formed. Hence, there is little or no
energy change.
Composition
The elements in a compound are
always combined in a fixed
proportion.
The components can be mixed in
any proportion.
(b) Is tap water a pure compound? Explain your answer.
Answer
A pure compound is made up of only one substance. Tap water is not a pure compound. It contains
other elements or compounds, such as minerals, dissolved in it.
It is a common mistake to think that tap water is pure. It is a mixture of water and other compounds
such as rainwater and dissolved minerals.
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TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Ammonium carbonate is a salt with the chemical formula, (NH4)2CO3. What is the number of
elements in ammonium carbonate?
A
B
C
D
2.
4.
( C )
Which statement is not true about an alloy?
A
B
C
D
3.
2
3
4
5
An alloy is a mixture.
An alloy may contain a non-metal.
The chemical properties of an alloy are similar to the elements that form it.
The physical properties of an alloy are similar to the elements that form it.
Which statements are true about compounds?
1
2
3
4
They can be made from two metals.
They can be made from two non-metals.
They can be made from a metal and a non-metal.
They can be made from another compound.
A
B
C
D
1,
1,
1,
2,
2
2
3
3
and
and
and
and
3
4
4
4
( D )
The diagram below shows two electrical circuits. What could X and Y be if the bulbs light up in both
circuits?
battery
battery
bulb
solid X
A
B
C
D
18
X
copper
sand
silver
sulfur
Worksheet 3
(S)CMWB_03.indd 18
( D )
Y
molten sulfur
molten silver
molten copper
molten sand
bulb
liquid Y
( C )
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5.
PCB is a compound that was used as a coolant. It was banned in 2001 because it is extremely
poisonous. PCB can be made harmless by reacting it with calcium oxide to form calcium chloride,
carbon dioxide and water. What elements must PCB contain?
A
B
C
D
6.
Calcium, carbon and oxygen
Calcium, chlorine and oxygen
Carbon, chlorine and hydrogen
Chlorine, hydrogen and oxygen
Which diagram below represents nitrogen (N2) at room temperature and pressure?
A
7.
C
D
Mercury is a liquid element.
Mercury(II) oxide is a compound.
Oxygen is a gaseous element.
When mercury is heated in oxygen, it will form mercury(II) oxide.
( A )
( B )
Which diagram below represents an incomplete reaction between two elements?
A
9.
B
When mercury(II) oxide is heated, it decomposes to give the elements mercury and oxygen. What
can you deduce from this experiment?
A
B
C
D
8.
( C )
B
C
D
( C )
Shoe polish consists of wax, turpentine (a volatile liquid that does not mix with water) and dyes.
Once applied, shoe polish hardens as the turpentine in it evaporates.
Which of the following statements is true?
A
B
C
D
Shoe polish melts over a range of temperatures.
A clear solution is formed when water is added to shoe polish.
The components of shoe polish can be separated by evaporation to dryness.
The components of shoe polish are always combined in a fixed proportion.
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( A )
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Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Eight elements are listed in the table below. All of them are non-metals.
Element
Chemical symbol
Number of atoms
in one molecule
argon
Ar
(noble gas)
hydrogen
H
2
fluorine
F
2
neon
Ne
(noble gas)
nitrogen
N
2
oxygen
O
2
phosphorus
P
4
sulfur
S
8
(a) Explain what ‘an element’ is.
An element is a pure substance that cannot be broken down into two or more simpler substances by
chemical processes.
(b) Complete the table by filling in the chemical symbols of the eight elements.
(c) Tabulate the non-metals from the table as monatomic, diatomic or polyatomic.
2.
2.
3.
4.
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Diatomic
Polyatomic
argon
neon
hydrogen
fluorine
nitrogen
oxygen
phosphorus
sulfur
The following describes an experiment in which magnesium was heated in air.
1.
20
Monatomic
Magnesium is a grey metal. A piece of magnesium ribbon was placed in a crucible and
weighed.
The crucible was heated and the magnesium ribbon burnt with a very bright flame.
A white solid consisting of magnesium oxide and a small amount of magnesium nitride
was formed.
The white solid and crucible were weighed.
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(a) In this experiment, identify
Magnesium
(i) an element;
(ii) two compounds;
(iii) a mixture.
Magnesium oxide and magnesium nitride
The white solid consisting of magnesium oxide and magnesium nitride
(b) State the evidence to indicate that a chemical change has taken place.
Energy was given off — a bright flame was produced when magnesium was burnt. When magnesium
was heated, new substances such as magnesium oxide and magnesium nitride were formed.
(c) Name two elements that magnesium reacted with.
Oxygen and nitrogen
(d) Magnesium nitride is made up of three atoms of magnesium and two atoms of nitrogen. What
is the formula of magnesium nitride?
Mg3N2
Section C: Free-Response Question
Answer the following question.
1.
Read the article below about methods of food preservation.
Micro-organisms cause food to decay. They require water, and sometimes oxygen, to grow and
reproduce. Many micro-organisms can be killed by heat or chemicals such as sodium chloride,
sodium nitrate, sodium nitrite and sulfur dioxide. Thus, these methods are used for preserving
food.
In preparing canned food, food is first placed in metal cans. These metal cans are usually
made of steel, an alloy, and coated with tin on the inside and the outside. To preserve the food,
air is sucked out of the cans before they are sealed. The cans are then heated under pressure
to kill the micro-organisms inside.
Another method of preservation is salting. Salt (sodium chloride) is added to meat to kill microorganisms. Salting can be done in several ways. Dry-salting involves burying meat in granular
salt, while brine-curing involves soaking meat in concentrated salt solution.
(a) State two differences between compounds and mixtures.
The components in a mixture can be separated by physical methods, while the components of a
compound can only be separated by chemical reactions. The components of a mixture are not fixed in
proportion, while those of a compound are fixed.
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(b) Tabulate the substances mentioned in the article as elements, compounds or mixtures.
Element
Compound
Mixture
oxygen
tin
sodium nitrate
sodium nitrite
sulfur dioxide
water
salt (sodium chloride)
air
steel
salt solution
(c) Air contains nitrogen, oxygen, carbon dioxide and noble gases (mostly argon). Draw a diagram
to represent the components of air.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the relevant
section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
22
Structured
Freeresponse
Textbook
section(s)
to revise
4, 6
1(a), 1(c),
2(a)(i)
–
4.1
–
1(b)
–
4.1
3, 5, 7
2(a)(ii),
2(b), 2(c)
–
4.2
Multiplechoice
(a)
Define an element.
(b)
State the chemical symbols for a number
of elements.
(c)
Define a compound.
(d)
Describe the differences between elements
and compounds.
8
–
1(b), 1(c)
4.2
(e)
Deduce the formula of a compound from
the ratio of elements present.
1
2(d)
–
4.2
(f)
Define a mixture.
2
2(a)(iii)
1(c)
4.3
(g)
Differentiate between compounds and
mixtures.
9
–
1(a), 1(b)
4.3
(h)
Identify substances and their purity, given
their melting and boiling points.
9
–
–
3.7
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Class:
)
Worksheet 4
(
Name:
Date:
Atomic Structure
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 5
ANSWER IT RIGHT!
The figure below shows the electronic structures of five atoms, P, Q, R, S and T.
2p
2n
14p
14n
9p
10n
10p
10n
14p
16n
P
Q
R
S
T
Which of the following statements is correct?
1
2
3
P and S are Group 0 elements in the Periodic Table.
Q and T are isotopes.
R and T have the same nucleon number.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
Not all Group 0 elements have eight electrons in their outer shell. Helium has only two outer electrons.
Thought Process
• Check the number of outer electrons in each atom. In general, elements in the same group have the
same number of outer electrons. Helium in Group 0 is an exception.
• Isotopes are atoms with the same number of protons but different numbers of neutrons.
• The nucleon number is the sum of the number of protons and neutrons in an atom.
Answer
A
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Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
What is the relative mass and charge of a neutron compared to a proton?
C
Relative mass
1
1840
1
1840
1
D
1
A
B
2.
The
The
The
The
nucleon number is the number of neutrons in the nucleus.
nucleon number is the sum of the number of protons and neutrons.
proton number is the number of neutrons in the nucleus.
proton number is the sum of the number of protons and electrons.
( B )
Ra?
226
88
88
138
226
314
A
A
A
A
( B )
phosphorus
phosphorus
phosphorus
phosphorus
They
They
They
They
Worksheet 4
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( C )
atom
atom
atom
atom
has
has
has
has
15 electrons.
15 neutrons.
15 protons, neutrons and electrons.
a mass number of 15.
( A )
Which statement is not true about isotopes of an element?
A
B
C
D
24
Protons only
Electrons and protons
Protons and neutrons
Electrons and neutrons
Phosphorus has an atomic number of 15. Which statement is true?
A
B
C
D
6.
( D )
How many neutrons are there in an atom of radium,
A
B
C
D
5.
–1
1
1840
0
Which statement is true?
A
B
C
D
4.
0
What particles are found in the nucleus of an atom?
A
B
C
D
3.
Relative charge
have
have
have
have
the
the
the
the
same
same
same
same
arrangement of electrons.
chemical properties.
number of protons.
physical properties.
( D )
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7.
Which of the following is correct about the two isotopes of oxygen,
16
8
8.
Electronic configuration
B
0
18
8
O?
18
8
O
2, 8, 6
2, 8, 6
Number of valence electrons
8
8
C
Chemical formula of oxygen gas formed
O2
O3
D
Number of neutrons
8
10
( D )
Elements W, X, Y and Z have proton numbers of 10, 12, 14 and 16 respectively. Which element
does not have the same number of electron shells as the other three?
A
C
9.
A
O and
16
8
W
Y
B
D
X
Z
( A )
Which diagram represents the electronic structure of an oxygen atom?
O
O
O
O
A
B
C
D
( B )
10. The number of valence electrons for the first 12 elements in the Periodic Table, hydrogen to
magnesium, was plotted against their proton numbers. Which of the following is the correct graph?
B
14
12
10
8
6
4
2
Number of
valence electrons
Number of
valence electrons
A
14
12
10
8
6
4
2
1 2 3 4 5 6 7 8 9 10 11 12
Proton number
D
14
12
10
8
6
4
2
Number of
valence electrons
Number of
valence electrons
C
1 2 3 4 5 6 7 8 9 10 11 12
Proton number
1 2 3 4 5 6 7 8 9 10 11 12
Proton number
14
12
10
8
6
4
2
1 2 3 4 5 6 7 8 9 10 11 12
Proton number
( C )
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Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
The table below shows the relative mass and relative charge of three types of subatomic particles.
Relative mass
Relative charge
M
N
O
1
1
x
+1
y
–1
(a) Identify the subatomic particles M, N and O.
Proton
M:
Neutron
N:
O:
Electron
(b) What are the values of x and y?
1
1840
x:
2.
Lithium (Li), sodium (Na) and potassium (K) are in the same group of the Periodic Table. Complete
the table below.
Electronic
configuration
Number of electrons
Number of neutrons
Li
2, 1
3
4
Na
2, 8, 1
11
12
K
2, 8, 8, 1
19
20
Element
7
3
23
11
39
19
3.
0
y:
The electronic structure of a beryllium atom is shown in the diagram below.
+
+
+
Key:
electron
+ proton
neutron
+
(a) Write down the symbol of this element, including its proton number and nucleon number.
9
Be
4
(b) Write down the electronic configuration of beryllium.
2, 2
(c) How many valence electrons are there in an atom of beryllium?
Two
26
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(d) Deduce the group that beryllium belongs to in the Periodic Table.
Group II
4.
Correct each of the following statements.
(a) The nucleus of a fluorine atom 冸 F冹 contains 19 neutrons and 9 protons.
The nucleus of a fluorine atom 冸 F冹 contains 10 neutrons and 9 protons.
(b) The first shell in an atom can hold a maximum of eight electrons.
The first shell in an atom can hold a maximum of two electrons.
(c) A helium atom has eight electrons in its outer shell.
A helium atom has two electrons in its outer shell.
(d) Nitrogen has an atomic number of 7. Therefore, there are seven electrons in the outer shell
of its atom.
Nitrogen has an atomic number of 7. Therefore, there are five electrons in the outer shell of its atom.
5.
The figures below show the electronic structures of six atoms, A to F.
18p
22n
12p
14n
3p
4n
A
B
C
6p
6n
20p
20n
12p
12n
D
E
F
(a) Which atoms
(i)
are isotopes;
(ii) have the same nucleon number;
A and E
(iii) are in the same group of the Periodic Table?
B and F
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B and F
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(b) (i)
Which atom has a mass twice that of atom D?
F
(ii) Using the Periodic Table, identify element D.
Carbon
(c) Atom A has an isotope, Q, with a nucleon number of 38. In the space below, draw the full
electronic structure of Q.
18p
20n
6.
At airports, security officers fire neutrons at luggage to detect any hidden explosives. Most
explosives contain nitrogen-14. When neutrons collide with nitrogen-14, a radioisotope, nitrogen-15,
is formed and high-energy rays are given off. These rays, when detected, indicate the presence of
explosives in the luggage.
(a) (i)
Write down the electronic arrangement of an atom of nitrogen-15.
2, 5
(ii) Using the Periodic Table, name another element that has similar chemical properties as
nitrogen-15.
Phosphorus/ Arsenic/ Antimony
(iii) Explain your answer in (ii).
Phosphorus/ Arsenic/ Antimony is in the same group as nitrogen. Elements in the same group
have the same number of valence electrons and thus share similar chemical properties.
(b) State the similarity in the atomic structures of nitrogen-15 and oxygen-16.
Both nitrogen-15 and oxygen-16 have the same number of neutrons.
28
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Section C: Free-Response Questions
Answer the following questions.
1.
A sample of volcanic rock consists of two isotopes of helium, helium-3 and helium-4, in the following
mass ratio:
3
2
He : 42He = 1 : 99
(a) Explain what is meant by the term ‘isotopes’.
Isotopes are atoms of the same element with the same number of protons but different numbers of
neutrons.
(b) (i)
State the difference between the atomic structures of helium-3 and helium-4.
A helium-3 atom has two protons and one neutron, while a helium-4 atom has two protons and
two neutrons.
(ii) Explain why helium-3 and helium-4 have similar chemical properties.
The chemical properties of an element depend on its outer electrons which are involved in
chemical reactions. Both helium-3 and helium-4 have two outer electrons. Hence, they have
similar chemical properties.
(c) This sample of volcanic rock also contains hydrogen-3.
(i)
Write the symbol of hydrogen-3, showing the atomic and mass numbers.
3
1H
(ii) List one similarity and one difference between hydrogen-3 and helium-3.
Both hydrogen-3 and helium-3 have the same nucleon number. The difference is that hydrogen-3
has two neutrons and one proton, while helium-3 has one neutron and two protons.
2.
The table below shows the nucleon numbers and proton numbers of atoms W, X, Y and Z.
(Note: W, X, Y and Z are not chemical symbols of elements.)
Atom
Nucleon number
Proton number
W
2
1
X
14
6
Y
19
9
Z
37
17
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Draw the electronic structures of atoms W, X, Y and Z.
Atom W
Atom X
1p
1n
6p
8n
Atom Y
Atom Z
9p
10n
17p
20n
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
State the relative charges and relative
masses of a proton, a neutron and an
electron.
1
1(b)
–
5.1
(b)
Describe the structure of an atom.
2
1(a)
–
5.1
(c)
Define proton (atomic) number and
nucleon (mass) number.
3
5(a)(ii), 5(b),
5(c)
–
5.2
(d)
Deduce the numbers of protons,
neutrons and electrons in an atom.
4, 5
2, 4(a), 5(c),
6(b)
1(c)(ii)
5.2
(e)
Interpret and use symbols that
represent an element’s nucleon and
proton numbers X .
4, 10
2, 3(a), 4(a)
6, 7
5(a)(i), 5(c)
1(a), 1(b)
5.3
8, 9, 10
2, 3(b), 3(c),
3(d), 4(b),
4(c), 4(d),
5(a)(iii), 5(c),
6(a)
2
5.4
Learning outcomes
(a)
30
(f)
Define isotopes.
(g)
Use diagrams to describe atoms as
containing
• protons and neutrons in the
nucleus;
• electrons arranged in the electron
shells (energy levels).
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1(c)(i)
5.2
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Class:
)
Worksheet 5
(
Name:
Date:
Chemical Bonding
for Chapters 6 and 7
ANSWER IT RIGHT!
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
Aluminium oxide is a white solid that contains ionic bonds. Due to its hardness and strength, it is
commonly used as an abrasive such as sandpaper.
(a) What do you understand by ‘ionic bond’? Give an example in your answer.
The phrase ‘what do you understand by’ or ‘what is meant by’ implies that a definition should be given.
Answer
An ionic bond is the force of attraction between a positive ion and a negative ion in an ionic
compound. For example, the forces of attraction between aluminium ions and oxide ions make up
the ionic bonds in aluminium oxide.
(b) Draw the electronic structure of an aluminium ion and an oxide ion.
• When asked to draw the electronic structure of an atom or ion, read the question carefully to see whether
you are required to show all the shells or only the outer shell.
• Unless otherwise stated in the question, draw the full electronic structure, showing all the shells.
• When drawing the electronic structure of an ion, write the charge of the ion at the top right-hand corner
of the structure.
Thought Process
• Aluminium is a metal. It loses three valence electrons to attain an octet electronic configuration.
• Oxygen is a non-metal. It gains two electrons to attain an octet electronic configuration.
Answer
Aluminium ion:
3+
2–
Oxide ion:
Al
O
(c) Explain the electrical conductivity of aluminium oxide in the solid and molten states.
Thought Process
Ionic compounds conduct electricity when molten due to the movement of free ions.
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Answer
Aluminium oxide does not conduct electricity in the solid state because the Al3+ and O2– ions
cannot move freely. In the molten state, the ions are free to move about. Hence, aluminium oxide
conducts electricity when molten.
• A common mistake is to state that an ionic compound conducts electricity when molten because ‘the
molecules or ions can move’.
• Remember that a molten ionic compound contains positive and negative ions only, not molecules. It is
these mobile ions (ions which move about) that conduct electricity.
• Another common mistake is to state that an ionic compound conducts electricity when molten because
‘the ions and electrons can move’.
• Remember that there are no free electrons in ionic compounds.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which ion has the same number of electrons as the neon atom?
Ion
O2–
Na+
Cl –
8
11
17
Atomic number
A
B
C
D
2.
( C )
Which of the following is true about the iron(II) ion, Fe2+, and the iron(III) ion, Fe3+?
A
B
C
D
3.
Na+ only
Na+ and Cl –
Na+ and O2–
O2– and Cl –
The compounds they form with the chloride ion, Cl –, have the same chemical formula.
They have the same number of electrons.
They have the same number of protons.
They are formed from the iron atom by losing the same number of electrons.
( C )
Two elements, Z and Y, react to form a compound.
Z
Y
What is the chemical formula of the compound?
A
B
C
D
32
Z2Y
Z2Y3
ZY
ZY2
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( A )
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4.
Indium forms the indium(III) ion with the formula In3+. The sulfate ion has the formula SO42–. What
is the chemical formula of indium(III) sulfate?
A
B
C
D
5.
( B )
How many electrons are shared between the carbon and oxygen atoms in a carbon dioxide
molecule?
A
6.
In(SO4)2
In2(SO4)3
In2SO4
InSO4
B
4
C
6
D
8
10
( C )
The ‘dot and cross’ diagram below shows the arrangement of electrons in the compound XY3. (Only
the outer electrons are shown.)
Y
Y
X
Y
Which elements are likely to be X and Y?
A
B
C
D
7.
Y
chlorine
chlorine
oxygen
oxygen
( B )
Which compound contains both ionic and covalent bonds?
A
B
C
D
8.
X
sulfur
phosphorus
nitrogen
carbon
Ammonia
Ammonium chloride
Hydrogen chloride
Sodium chloride
( B )
Which of the following substances is likely to be potassium chloride?
Substance
Melting point/°C
Electrical conductivity
when molten
Solubility in water
A
–114
nil
soluble
B
180
nil
insoluble
C
772
good
soluble
D
1535
good
insoluble
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( C )
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9.
Which substance in the table below could be methanol?
Electrical conductivity
Substance
Melting
point/°C
Boiling
point/°C
in the liquid state
in aqueous solution
A
–114
–85
nil
good
B
–98
65
nil
nil
C
180
218
nil
nil
D
420
970
good
good
( B )
10. Silicon carbide, SiC, is a very hard solid that melts at 2730°C. Which diagram best represents
its structure?
A
B
C
D
( C )
11. A student carried out tests to find out the electrical conductivity of four substances. The results are
shown below.
Substance P conducts electricity only in aqueous solution.
Substance Q conducts electricity when molten and in aqueous solution.
Substance R conducts electricity in the solid state.
Substance S does not conduct electricity.
Which substances are likely to be P, Q, R and S?
34
P
Q
R
S
A
sulfur
sodium iodide
graphite
hydrogen chloride
B
hydrogen chloride
sodium iodide
graphite
sulfur
C
sodium iodide
hydrogen chloride
graphite
sulfur
D
hydrogen chloride
sodium iodide
sulfur
graphite
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( B )
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Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
(a) The chemical formula of ammonia is NH3. Draw a ‘dot and cross’ diagram to show the
arrangement of the electrons in ammonia. (Only the outer electrons need to be shown.)
N
H
H
H
(b)
O
The structural formula of phosphoric acid is shown on the right. From the
structural formula, deduce the total number of electrons that are shared
between the phosphorus and oxygen atoms.
P
H
There are three single bonds and one double bond between the phosphorus
O
O
O H
H
and oxygen atoms in phosphoric acid. Each bond is formed by the sharing of
two electrons. Thus, the total number of electrons shared between the phosphorus and oxygen atoms
is 5 × 2 = 10.
2.
The table below gives information about the compounds formed between chlorine and some
elements in Periods 2 and 3 of the Periodic Table.
Compound
Boiling point/°C
Compound
Boiling point/°C
LiCl
1380
NaCl
1415
beryllium chloride
480
MgCl2
1410
BCl3
12
AlCl3
120
CCl4
80
silicon tetrachloride
60
NCl3
70
PCl5
80
Cl2O
2
SCl2
60
ClF
–100
Cl2
–34
(a) Write the chemical formula of
(i) beryllium chloride;
BeCl2
(ii) silicon tetrachloride.
SiCl4
(b) Explain why neon and argon do not form compounds.
They have a stable octet electronic configuration and thus do not form compounds.
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(c) Describe how bonds are formed in the compounds below.
(i)
LiCl
A lithium atom loses an electron to a chlorine atom. The lithium and chloride ions formed are held
together by ionic bonds.
(ii) ClF
A chlorine atom shares a pair of electrons with a fluorine atom to form a single covalent bond.
(d) Explain, in terms of structure and bonding, the difference in the boiling points of NaCl and
CCl4.
In NaCl, the Na+ and Cl – ions are arranged in a giant lattice structure and the oppositely charged ions
are held together by strong forces of attraction (ionic bonds). A large amount of energy is needed to
break the strong ionic bonds in NaCl. In CCl4, the CCl4 molecules are held together loosely by weak
intermolecular forces. These intermolecular forces can be easily overcome. Thus, NaCl has a much
higher boiling point than CCl4.
Section C: Free-Response Questions
Answer the following questions.
1.
(a) Magnesium oxide is used as a construction material because of its strength and fire
resistance. Its structure and physical properties are similar to those of sodium chloride. The
lattice structure of magnesium oxide is shown here.
Key:
Mg2+ ion
O2– ion
(i)
Deduce that the chemical formula of magnesium oxide is MgO.
Each Mg2+ ion is surrounded by six O2– ions and vice versa. The overall ratio of Mg2+ ions to
O2– ions is 1 : 1. Thus, the chemical formula of magnesium oxide is MgO.
36
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(ii) Draw a ‘dot and cross’ diagram to show the bonding in magnesium oxide.
2+
Mg
2–
O
(b) The diagram below shows how aqueous sodium chloride can be tested for electrical
conductivity. State the result you would expect to see. Explain your answer.
switch
carbon rod
aqueous sodium chloride
battery
bulb
carbon rod
beaker
The bulb lights up, showing that aqueous sodium chloride conducts electricity. This is because the
sodium and chloride ions are free to move about in aqueous solution.
2.
Silicon and carbon are in Group IV of the Periodic Table. They react with oxygen to form compounds.
Silicon dioxide (SiO2), a white solid, is abundantly found in the Earth’s crust. It is insoluble in
water and has a melting point of 1713°C . It is used in the manufacture of glass and bricks. Carbon
dioxide is a colourless gas present in the atmosphere. It is soluble in water and has a boiling point
of –57°C.
(a) Draw a ‘dot and cross’ diagram to show the bonding in a carbon dioxide molecule. (Only the
outer electrons need to be shown.)
O
C
O
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(b) By comparing the structures of silicon dioxide and carbon dioxide, explain why silicon dioxide
exists as a solid and carbon dioxide as a gas at room temperature.
Silicon dioxide has a giant molecular structure. The silicon and oxygen atoms are held together by
strong covalent bonds. A large amount of energy is required to break these strong bonds. Hence,
silicon dioxide has high melting and boiling points and exists as a solid at room temperature. Carbon
dioxide exists as simple molecules, which are held together by weak intermolecular forces. These
forces are easily overcome. Hence, carbon dioxide has low melting and boiling points and exists as a
gas at room temperature.
(c) Explain why silicon dioxide does not conduct electricity.
All the outer electrons of the silicon and oxygen atoms in silicon dioxide are used for bonding. There
are therefore no free electrons that move through the structure. Hence, silicon dioxide does not
conduct electricity.
3.
Diamond and graphite are allotropes of carbon.
Explain the following in terms of bonding and structure.
(a) Diamond is hard but graphite is soft and slippery.
Diamond forms a three-dimensional structure in which each carbon atom is covalently bonded to four
other carbon atoms, which are in turn bonded to four more carbon atoms. These covalent bonds are
very strong and difficult to break. Thus, diamond is hard. Graphite is made up of layers of carbon
atoms which are held loosely by weak intermolecular forces of attraction. These layers of carbon
atoms slide over each other easily when a force is applied. Thus, graphite is soft and slippery.
(b) Graphite conducts electricity but not diamond.
Graphite is made up of layers of carbon atoms. Each carbon atom has one outer electron that is not
used for bonding. These electrons move freely along the layers from one carbon atom to the next, i.e.
they are delocalised, allowing graphite to conduct electricity. In diamond, all the outer electrons of
the carbon atoms are used to form covalent bonds. There are no free electrons that move through its
structure. Thus, diamond does not conduct electricity.
38
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4.
Aluminium is a malleable metal with a silvery appearance. It has a melting point of 660°C. Due to
its good electrical conductivity, aluminium is used to make electrical transmission lines.
(a) With the aid of a diagram, describe the structure and bonding in aluminium.
In aluminium, the aluminium atoms are held strongly to each other by metallic bonds to form a
giant lattice structure. In the structure, a lattice of positive ions is surrounded by a ‘sea of mobile
electrons’.
(b) Based on your answer in (a), explain why aluminium
(i)
is malleable;
In the aluminium metal lattice, the outer electrons do not belong to any aluminium atom, i.e.
they are delocalised. When sufficient force is applied, one layer of aluminium atoms can slide
over another without disrupting the metallic bonds.
(ii) conducts electricity;
The outer electrons within the aluminium metal lattice are delocalised and able to move freely
within the metal lattice.
(iii) has a high melting point.
A large amount of energy is needed to overcome the strong forces of attraction between
aluminium ions and the 'sea of mobile electrons' in the metal lattice structure.
(c) Draw a ‘dot and cross’ diagram to show the bonding in aluminium fluoride, AlF3. (Only the
outer electrons need to be shown.)
3+
Al
–
3
F
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Describe the stable electronic structure
of a noble gas.
–
2(b)
–
6.1
(b)
Describe the formation of positive ions
(cations) and negative ions (anions) to
achieve the noble gas configuration.
1, 2
–
–
6.2
(c)
Describe how ionic bonds are formed
between metals and non-metals.
7
2(c)(i)
1(a)(ii), 4(c)
6.3
(d)
Deduce the formula of an ionic
compound from the charges on the ions
and vice versa.
3, 4
2(a)
–
6.4
(e)
State that ionic compounds form giant
lattice structures.
–
–
1(a)(i)
6.5
(f)
Deduce the formulae of ionic
compounds from their lattice
structures.
–
–
1(a)(i)
6.5
(g)
Relate the physical properties of ionic
compounds to their lattice structures.
8, 11
2(d)
1(b), 4(b)
6.5
(h)
Describe the formation of a covalent
bond by the sharing of electrons.
5, 6, 7
2(c)(ii)
2(a)
7.1
(i)
Describe the formation of covalent
bonds between non-metallic elements
using ‘dot and cross’ diagrams.
–
1(a)
2(a)
7.1
(j)
Deduce the arrangement of electrons in
covalent molecules.
–
1(a), 1(b)
–
7.1
(k)
Relate the physical properties of
covalent substances to their structure
and bonding.
9, 10, 11
2(d)
2(c), 3
7.2
(l)
Compare the structures of simple
molecular substances and giant
molecular substances to deduce their
properties.
–
–
2(b)
7.2
–
–
3
7.2
–
–
4(a)
7.3
11
–
4(b)
7.3
(m) Compare the bonding and structures of
diamond and graphite to deduce their
physical properties.
40
Multiplechoice
(n)
Describe the structure of metals as
a lattice of positive ions in a ‘sea of
electrons’.
(o)
Relate the physical properties of metals
to their structure.
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Class:
)
Worksheet 6
(
Name:
Date:
Chemical Calculations
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapters 8–10
ANSWER IT RIGHT!
Step 1: Excess iron(III) oxide, Fe2O3, was added to dilute hydrochloric acid, HCl. Iron(III) chloride, FeCl3,
and water were formed as products. The reaction mixture was filtered to remove unreacted
iron(III) oxide and the filtrate was collected.
Step 2: The filtrate obtained in step 1 was added in excess to 30 cm3 of 2.0 mol/dm3 sodium hydroxide
solution, NaOH. A brown precipitate of iron(III) hydroxide, Fe(OH)3, was formed.
(a) Write an ionic equation, including state symbols, to show the reaction in step 1.
• In writing state symbols, do not confuse (l) with (aq).
• The state symbol (l) refers to a pure liquid. In contrast, the symbol (aq) refers to a substance dissolved
in water. For example, molten sodium hydroxide is represented as NaOH(l), while an aqueous solution
of sodium hydroxide is represented as NaOH(aq).
Thought Process
• The first step in writing an ionic equation is to write the balanced chemical equation.
Fe2O3(s) + 6HCl(aq)
2FeCl3(aq) + 3H2O(l)
• Then, rewrite an equation in terms of ions and cancel out the spectator ions.
Fe2O3(s) + 6H+(aq) + 6Cl –(aq)
2Fe3+(aq) + 6Cl –(aq) + 3H2O(l)
Answer
Fe2O3(s) + 6H+(aq)
2Fe3+(aq) + 3H2O(l)
(b) (i) Write an ionic equation for the reaction in step 2.
(ii) Calculate the mass of iron(III) hydroxide precipitated in step 2.
• ‘Calculate’ means that a numerical answer is required.
• When doing calculations, you should show your working.
Thought Process
(ii) Since iron(III) chloride is in excess, sodium hydroxide solution is the limiting reactant. The
amount of product(s) formed is determined by the amount of limiting reactant used.
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Answer
Fe(OH)3(s)
(i) Fe3+(aq) + 3OH–(aq)
(ii) Number of moles of NaOH = concentration in mol/dm3 × volume in dm3
= 2.0 × 30
1000
= 0.06 mol
From the equation, 3 mol of OH– ions react to form 1 mol of Fe(OH)3.
Number of moles of Fe(OH)3 produced = 1 × 0.06
3
= 0.02 mol
Relative formula mass (Mr) of Fe(OH)3 = 56 + (3 × 16) + (3 × 1)
= 107
Mass of Fe(OH)3 = number of moles × molar mass
= 0.02 × 107
= 2.14 g
When calculating relative molecular mass or relative formula mass, make sure that you use relative atomic
masses and not atomic numbers.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which pair of standards is used to measure the relative molecular mass and the relative atomic
mass of a substance?
A
B
C
Relative molecular mass
Relative atomic mass
1 mass of a carbon-12 atom
12
1 mass of a carbon-12 atom
12
1 mass of a carbon-12 atom
12
mass of a hydrogen-1 atom
mass of a hydrogen-1 atom
mass of a hydrogen-1 atom
D
2.
8g
16 g
32 g
64 g
12%
23%
40%
47%
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( C )
Urea, CO(NH2)2, is used as a fertiliser. What is the percentage by mass of nitrogen in urea?
A
B
C
D
42
( A )
What is the mass of oxygen in 74 g of calcium hydroxide, Ca(OH)2?
A
B
C
D
3.
mass of a hydrogen-1 atom
1 mass of a carbon-12 atom
12
( D )
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4.
5.
Which of the following statements about ethanoic acid (CH3COOH) and methyl methanoate
(HCOOCH3) are true?
1
2
3
They contain the same percentage by mass of oxygen.
They have the same empirical formula.
They have the same relative molecular mass.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
( D )
One of the reactions that takes place during the manufacture of iron is as shown:
2CO(g) + O2(g)
2CO2(g)
Which statement about this reaction is true?
A
B
C
D
6.
2 g of carbon monoxide reacts with 1 g of oxygen.
2 mol of carbon dioxide can be obtained from 2 mol of oxygen.
28 kg of carbon monoxide produces 44 kg of carbon dioxide.
88 kg of carbon dioxide can be obtained from 16 kg of oxygen.
( C )
When calcium carbonate is heated strongly, it decomposes into calcium oxide and carbon
dioxide gas.
CaCO3(s)
CaO(s) + CO2(g)
What is the volume of carbon dioxide gas produced at r.t.p. when 10 g of calcium carbonate is
heated strongly?
A
B
C
D
7.
( D )
A student carried out titration of sodium hydroxide with an unknown acid. He found that 20.0 cm3
of 1.5 mol/dm3 of sodium hydroxide exactly reacted with 10.00 cm3 of 1.0 mol/dm3 of the acid.
How many moles of sodium hydroxide would react with one mole of the acid?
A
B
C
D
*8.
0.10 dm3
0.24 dm3
1.00 dm3
2.40 dm3
2
3
4
5
( B )
Tin occurs naturally as tin(IV) oxide, SnO2, in the ore cassiterite. It is extracted by heating the ore
with carbon. The equation for the reaction is:
SnO2(s) + C(s)
Sn(s) + CO2(g)
357 g of tin was obtained from 30.2 kg of cassiterite. What is the percentage yield of tin?
A
B
C
D
0.015%
0.15%
1.5%
15%
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Use the following information to answer Questions 9 and 10.
A sample of seawater contains bromide ions with a concentration of 0.1 g/dm3. When chlorine gas is
bubbled through the sample, bromine gas is obtained. The equation of the reaction is:
2Br–(aq) + Cl2(g)
9.
Br2(g) + 2Cl –(aq)
What volume of chlorine gas is required to produce 0.008 tonne of bromine gas at room
temperature and pressure? (1 tonne = 106 g)
A
B
C
D
50 dm3
100 dm3
1200 dm3
2400 dm3
( C )
*10. What volume of seawater is required to produce 0.008 tonne of bromine gas? (1 tonne = 106 g)
A
B
C
D
20 000 dm3
40 000 dm3
80 000 dm3
160 000 dm3
( C )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
When aqueous sodium sulfate, Na2SO4, was added to aqueous lead(II) nitrate, Pb(NO3)2, lead(II)
sulfate was precipitated.
(a) Write a chemical equation for the reaction. Include state symbols.
Na2SO4(aq) + Pb(NO3)2(aq)
2NaNO3(aq) + PbSO4(s)
(b) Hence, write the ionic equation for the reaction in (a).
Pb2+(aq) + SO42–(aq)
PbSO4(s)
(c) 200 cm3 of 0.1 mol/dm3 lead(II) nitrate solution was mixed with 100 cm3 of 0.1 mol/dm3
sodium sulfate solution.
(i)
What is the limiting reactant in this reaction?
Number of moles of Pb(NO3)2 = volume (dm3) × concentration (mol/dm3)
= 200 × 0.1
1000
= 0.02 mol
Number of moles of Na2SO4 = 100 × 0.1
1000
= 0.01 mol
From the equation, 1 mol of Pb(NO3)2 reacts with 1 mol of Na2SO4.
0.02 mol of Pb(NO3)2 will react with 0.02 mol of Na2SO4.
However, only 0.01 mol of Na2SO4 was used.
Therefore, sodium sulfate is the limiting reactant.
44
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(ii) Calculate the mass of lead(II) sulfate precipitated.
From the equation, 1 mol of PbSO4 is produced from 1 mol of Na2SO4.
Number of moles of PbSO4 = 0.01 mol
Mr of PbSO4 = 207 + 32 + (4 × 16)
= 303
Mass of PbSO4 = number of moles × molar mass
= 0.01 × 303
= 3.03 g
2.
A student was provided with the following solutions:
A: Unknown concentration of sodium hydroxide solution
B: 0.25 mol/dm3 of dilute sulfuric acid
The student titrated 25.0 cm3 portions of A in a conical flask against B in a burette. The results of
the experiment are shown below.
Titration number
Final burette reading/cm
3
Initial burette reading/cm3
Volume of B used/cm
3
1
2
3
19.10
18.70
18.70
0.00
0.00
0.00
19.10
18.70
18.70
(a) Using suitable sets of the titration results, calculate the average volume of the acid used for
complete neutralisation.
Average volume =
18.70 + 18.70
2
= 18.70 cm3
(b) (i)
Write a chemical equation for the reaction between sodium hydroxide solution and dilute
sulfuric acid.
H2SO4(aq) + 2NaOH(aq)
Na2SO4(aq) + 2H2O(l)
(ii) Hence, write the ionic equation for the reaction in (i).
H+(aq) + OH–(aq)
H2O(l)
(c) Calculate the concentration, in mol/dm3, of the sodium hydroxide solution.
Number of moles of H2SO4 = 0.25 × 18.70
1000
= 4.68 × 10–3 mol
From the equation, 1 mol of H2SO4 reacts with 2 mol of NaOH.
Number of moles of NaOH = 2 × 4.68 × 10–3
= 9.36 × 10–3 mol
Concentration of NaOH = number of moles
3
volume in dm
9.36
× 10–3
=
0.025
= 0.374 mol/dm3
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3.
Oxygen is the third most abundant element in the universe by mass. The relative atomic mass of
oxygen is 16. The most stable form of oxygen is the diatomic form, known as dioxygen. The other
form of oxygen, known as ozone, has a relative molecular mass of 48. Ozone at the ground level
is harmful to the human respiratory system. In some countries, the recommended limit of
concentration of ground-level ozone is 1.57 × 10–4 g/m3.
(a) Define ‘relative atomic mass’.
The relative atomic mass of an atom is the mass of one atom of that element compared to 1 of the
12
mass of one carbon-12 atom.
(b) Based on the relative molecular mass of ozone, suggest the molecular formula of ozone.
03
(c) An environmental scientist found that there are 1 × 1018 molecules of ozone in 1 m3 of air.
Has the limit of 1.57 × 10–4 g/m3 been exceeded? Support your answer with relevant
calculations. (One mole of a substance contains 6 × 1023 particles.)
18
Number of moles of ozone in 1 m3 of air = 1 × 1023
6 × 10
= 1.667 × 10–6 mol
Mass of ozone in 1 m3 of air = 1.667 × 10–6 × 48
= 8.00 × 10–5 g
Hence, the limit has not been exceeded.
*4.
Hydrogen fluoride attacks glass and is used to draw on glass. It is prepared by adding concentrated
sulfuric acid to calcium fluoride. The reaction takes place at room temperature.
CaF2(s) + H2SO4(l)
2HF(g) + CaSO4(s)
(a) When 15.6 g of a sample of calcium fluoride was reacted with 12.5 cm3 of 20.0 mol/dm3
sulfuric acid at r.t.p., 7.68 dm3 of hydrogen fluoride was formed.
(i)
What is the limiting reactant in this reaction?
Mr of CaF2 = 40 + (19 × 2)
= 78
Number of moles of CaF2 used = 15.6
78
= 0.2 mol
Number of moles of H2SO4 used = 20.0 × 12.5
1000
= 0.25 mol
From the equation, 1 mol of H2SO4 reacts with 1 mol of CaF2.
0.25 mol of H2SO4 will react with 0.25 mol of CaF2.
However, only 0.2 mol of CaF2 was used.
∴ CaF2 is the limiting reactant.
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(ii) Calculate the theoretical volume of hydrogen fluoride that was formed.
From (a)(i), number of moles of CaF2 used = 0.2 mol
From the equation, 2 mol of HF are produced from 1 mol of CaF2.
Number of moles of HF formed = 2 × 0.20
= 0.40 mol
Theoretical volume of HF formed = number of moles × 24 dm3
= 0.40 × 24
= 9.6 dm3
(b) Calculate the percentage purity of calcium fluoride.
3
Number of moles of HF formed = volume in 3dm
24 dm
7.68
=
24
= 0.32 mol
From the equation, 1 mol of CaF2 produces 2 mol of HF.
Number of moles of pure CaF2 = 0.32
2
= 0.16 mol
Mass of pure CaF2 = number of moles × molar mass
= 0.16 × 78
= 12.48 g
Percentage purity of CaF2 = mass of pure CaF2 in sample × 100%
mass of sample
12.48
× 100%
=
15.6
= 80%
*5.
The recommended dosage of paracetamol for a child weighing 10–16 kg is 160 mg. A brand of
medicine contains 0.20 mol of paracetamol in 1 dm3 of solution. What is the maximum number of
2.5 cm3 spoonfuls of the medicine a parent can safely feed her child, if her child weighs 15 kg?
(Mr: paracetamol = 151)
Number of moles of paracetamol in 1 spoonful (2.5 cm3) of the medicine
= volume (dm3) × concentration (mol/dm3)
= 2.5 × 0.20
1000
= 0.0005 mol
Mass of paracetamol in 1 spoonful of the medicine = number of moles × molar mass
= 0.0005 × 151
= 0.0755 g
= 75.5 mg
Number of spoonfuls of medicine that contains the recommended dosage of paracetamol
= 160
75.5
= 2.12
∴ The maximum number of 2.5 cm3 spoonfuls of the medicine that the parent can feed her child is 2.
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Section C: Free-Response Questions
Answer the following questions.
1.
Hydrated compounds are compounds that contain water of crystallisation. The information of some
hydrated compounds is given in the table below.
Compound
Formula
Percentage by
mass of water/%
hydrated magnesium sulfate
MgSO4.7H2O
51.2
hydrated sodium carbonate
Na2CO3.10H2O
62.9
hydrated zinc nitrate
Zn(NO3)2.xH2O
36.5
(a) Given that one mole of a substance contains 6 × 1023 particles, calculate the number of water
molecules present in 5.00 g of hydrated magnesium sulfate.
Mass of water in hydrated magnesium sulfate = 51.2 × 5.00
100
= 2.56 g
mass in g
molar mass in g/mol
= 2.56
18
Number of moles of water molecules =
= 0.142 mol
Number of water molecules = 0.142 × 6 × 1023
= 8.52 × 1022
(b) When solid hydrated sodium carbonate is heated, the water of crystallisation is given off as
steam. Write a balanced chemical reaction, with state symbols, to represent this change.
Na2CO3.10H2O(s)
Na2CO3(s) + 10H2O(g)
(c) Calculate the value of x in Zn(NO3)2.xH2O.
Mr of Zn(NO3)2.xH2O = 65 + 2(14) + 6(16) + x(18)
= 189 + 18x
Percentage by mass of H2O = (number of H2O molecules) × (Mr of H2O) × 100%
Mr of Zn(NO3)2.xH2O
18x
36.5 =
× 100
(189 + 18x)
18x = 0.365(189 + 18x)
x = 6 (round off to the nearest whole number)
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*2.
The following results were obtained in an experiment to determine the formula of an oxide of
mercury. The oxide is a red solid. It decomposed into its elements when heated at r.t.p. (One mole
of a gas occupies 24 dm3 at r.t.p.)
Mass of empty test tube = 15.45 g
Mass of test tube + oxide of mercury = 17.61 g
Volume of oxygen collected at r.t.p. = 120 cm3
(a) Draw a labelled diagram of the apparatus that can be used to perform this experiment.
gas syringe
oxygen collected
test tube
mercury
oxide of mercury
Bunsen burner
(b) State a precaution to take when performing this experiment.
Conduct the experiment in the fume cupboard.
(c) What observation (other than colour change) indicates that the reaction is complete?
No more oxygen is given off (reading on the gas syringe stays constant).
(d) From the results of the experiment, determine the molecular formula of this oxide of mercury.
(One mole of this oxide of mercury weighs 217 g.)
Mass of oxide of mercury used = 17.61 – 15.45 = 2.16 g
Mass of oxygen produced = ( 120 ÷ 24 dm3) × 32 = 0.16 g
1000
Mass of mercury produced = 2.16 – 0.16 = 2.00 g
Element
Mercury
Oxygen
Mass/g
2.00
0.16
Relative atomic mass
201
16
Number of moles/mol
2.00 = 0.01
201
0.16 = 0.01
16
1
1
Mole ratio
∴ The empirical formula of the oxide of mercury is HgO.
Let the molecular formula of the oxide of mercury be (HgO)n.
Relative mass of the oxide of mercury from empirical formula = 201 + 16 = 217
n=
relative molecular mass of oxide of mercury
= 217 = 1
relative mass of oxide of mercury from empirical formula
217
∴ The molecular formula of the oxide of mercury is HgO.
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
Structured
Freeresponse
(a)
Interpret chemical equations with state
symbols.
5
–
–
8.1
(b)
Write balanced chemical equations
with state symbols.
–
1(a), 2(b)(i)
1(b)
8.1
(c)
Write ionic equations with state
symbols.
–
1(b), 2(b)(ii)
–
8.2
(d)
Define relative atomic mass (Ar).
1
3(a)
–
9.1
(e)
Define relative molecular mass (Mr).
1
–
–
9.2
(f)
Calculate relative molecular mass or
relative formula mass of a substance.
2, 4
–
–
9.2
(g)
Convert number of particles into
number of moles of particles and vice
versa.
–
–
1(a)
9.3
(h)
Perform calculations involving the
number of moles, mass and molar
mass of a substance.
2
3(c)
–
9.3
(i)
Determine the percentage composition
of compounds from given data.
3, 4
–
–
9.4
(j)
Determine the empirical and molecular
formulae of a compound from given
data.
4
3(b)
1(c), 2
9.5
(k)
Perform calculations involving molar
gas volume and the number of moles
of a gas.
–
4(a)(ii)
–
9.6
(l)
Perform calculations involving the
concentration of a solution (g/dm3 or
mol/dm3).
10
–
–
9.7
5
1(c)(ii)
–
10.1
(m) Calculate the masses of reactants and
products by using the mole ratio in a
chemical equation.
50
Multiplechoice
Textbook
section(s)
to revise
(n)
Calculate the volumes of gaseous
reactants and products using the mole
ratio in a chemical equation.
6, 9
–
–
10.2
(o)
Perform stoichiometric calculations
involving the idea of limiting reactants.
–
1(c)(i), 4(a)(i)
–
10.3
(p)
Process the results of volumetric
experiments.
–
2(a), 2(c)
–
10.4
(q)
Perform stoichiometric calculations
involving concentrations of solutions.
7
2(c), 5
–
10.4
(r)
Calculate the percentage yield and
percentage purity of a substance.
8
4(b)
–
10.5
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Class:
)
Worksheet 7
(
Name:
Date:
Acids and Bases
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 11
ANSWER IT RIGHT!
The diagram below shows the set-ups of two experiments.
hydrogen chloride in
dry organic solvent
magnesium ribbon
Experiment I: Magnesium ribbon is
added to HCl in dry organic solvent.
aqueous solution of
hydrochloric acid
magnesium ribbon
Experiment II: Magnesium ribbon is
added to an aqueous solution of HCl.
Explain the likely observations for both experiments. Construct an equation for any reaction that occurs.
• Look out for the term ‘explain’ in the question. Your answer must make use of some reasoning or reference
to a theory to explain why something happens.
• In this case, you need to refer to the factors that affect the properties of acids to explain the difference in
the observations for both experiments.
Thought Process
Recall the role of water in acidity. Acids only display their properties when they are dissolved in water.
Answer
In Experiment I, no change is observed. In organic solvents, HCl exists as covalent molecules. It does
not ionise to form hydrogen ions (H+), which are responsible for the acidic properties. Therefore, HCl in
an organic solvent does not react with magnesium.
In Experiment II, effervescence is observed. In the presence of water, HCl ionises to form hydrogen
ions (H+).
HCl(aq)
H+(aq) + Cl –(aq)
Aqueous HCl thus reacts with magnesium to form magnesium chloride and hydrogen gas.
2HCl(aq) + Mg(s)
MgCl2(aq) + H2(g)
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TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which statement is true for all aqueous solutions of acids?
A
B
C
D
2.
D
( C )
A strong acid has a higher pH value than a weak acid.
A weak acid has a higher concentration of hydrogen ions in solution than a strong acid.
A strong acid is completely ionised in solution while a weak acid is only partially ionised in
solution.
A weak acid reacts faster with metals than a strong acid.
( C )
Ammonium nitrate
Calcium hydroxide
Potassium nitrate
Sodium hydroxide
Acidic
The
The
The
The
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is a soluble base.
reacts with ammonium salts to produce ammonia gas.
reacts with copper(II) sulfate to form two salts.
reacts with dilute nitric acid to form a sodium salt.
( B )
B
Amphoteric
C
Basic
D
Neutral
( B )
Which statement is true at the point where hydrochloric acid is exactly neutralised by sodium
hydroxide solution?
A
B
C
D
52
It
It
It
It
An oxide, Z, reacts with both dilute hydrochloric acid and sodium hydroxide solution to form a salt
and water. What type of oxide is Z?
A
7.
( B )
Which compound should a farmer add to neutralise acidic soil?
A
B
C
D
6.
Acid in car batteries
Bleaching agent
Manufacture of detergents
Manufacture of fertilisers
Which statement is true about a weak acid and a strong acid?
A
B
C
5.
( D )
Which statement about sodium hydroxide is incorrect?
A
B
C
D
4.
have a pH value greater than 7.
react with ammonium chloride to give ammonia gas.
react with copper to give hydrogen.
react with sodium carbonate to give carbon dioxide.
Sulfuric acid has many uses in daily life. Which of the following is not a use of sulfuric acid?
A
B
C
D
3.
They
They
They
They
concentration
concentration
concentration
concentration
of
of
of
of
hydrogen
hydrogen
hydrogen
hydrogen
ions
ions
ions
ions
remains unchanged.
is equal to the concentration of hydroxide ions.
is greater than the concentration of hydroxide ions.
is less than the concentration of hydroxide ions. ( B )
© 2013 Marshall Cavendish International (Singapore) Private Limited
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8.
The tables below show the colours of methyl orange and phenolphthalein at different pH ranges.
Methyl orange
Phenolphthalein
pH range
1–4
4.1–14
pH range
1–10
10.1–14
Colour
red
yellow
Colour
colourless
pink
What would be the colour of each indicator in pure water?
A
B
C
D
9.
Methyl orange
red
red
yellow
yellow
Phenolphthalein
colourless
pink
colourless
pink
( C )
A 1.0 mol/dm3 solution of an acid T has a pH value of 5. Which of the following statements best
describes T?
A
B
C
D
It is a poor conductor of electricity.
It is a weak acid.
It reacts with water to produce a higher concentration of hydrogen ions.
The acid is only slightly soluble in water.
( B )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Below are some reactions of dilute sulfuric acid.
no reaction
Solution T
is formed.
+ sodium
hydroxide
solution
+ metal M
dilute sulfuric acid
+ metal N
Colourless gas P
is given off.
+ sodium
carbonate solution
Colourless gas Q is given
off. Q produces a white
precipitate with limewater.
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(a) Suggest the identities of
(i)
metal M;
Copper/ silver/ gold (any metal below hydrogen in the reactivity series)
(ii) metal N;
Magnesium/ zinc/ iron (any reactive metal except alkali metals)
(iii) gas P;
Hydrogen
(iv) gas Q.
Carbon dioxide
(b) When solution T is evaporated, a white crystalline solid is obtained. Solid T contains 19.17%
sodium, 0.83% hydrogen, 26.67% sulfur and 53.33% oxygen. The relative molecular mass of
T is 120. What is the molecular formula of T?
Element
Na
H
S
O
19.17
0.83
26.67
53.33
23
1
32
16
Number of
moles/mol
19.17 = 0.83
10
0.83 = 0.83
1
26.67 = 0.83
32
53.33 = 3.33
16
Mole ratio
1
1
1
4
Percentage/%
Ar
The empirical formula of T is NaHSO4.
Let the molecular formula of T be (NaHSO4)n.
Relative mass of T from empirical formula = 23 + 1 + 32 + (4 × 16)
= 120
relative molecular mass of T
relative mass of T from empirical formula
= 120
120
n =
=1
∴ The molecular formula of of T is NaHSO4.
2.
Milk of magnesia is a type of medicine which works as an antacid to treat stomach problems.
Milk of magnesia is a mixture of magnesium hydroxide and water. The solubility of magnesium
hydroxide in water is low.
(a) Suggest a reason why a mixture of magnesium hydroxide and water is known as milk of
magnesia.
Magnesium hydroxide does not dissolve easily in water. Hence, magnesium hydroxide and water form
a suspension (and not a solution). The appearance of this suspension is similar to that of milk.
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(b) Suggest how milk of magnesia works as an antacid. Write a chemical equation to support
your explanation.
The magnesium hydroxide in milk of magnesia is alkaline. It reacts with H+ ions in stomach acid
(neutralisation reaction).
Mg(OH)2 + 2H+
Mg2+ + 2H2O or Mg(OH)2 + 2HCl
MgCl2 + 2H2O
(c) Other than the reaction in (b), suggest another reaction which milk of magnesia can undergo.
Write a chemical equation for this reaction.
Milk of magnesia also reacts with ammonium salts (e.g. ammonium chloride) to produce ammonia gas.
Mg(OH)2 + 2NH4+
Mg2+ + 2H2O + 2NH3 or Mg(OH)2 + 2NH4Cl
MgCl2 + 2H2O + 2NH3
Section C: Free-Response Questions
Answer the following questions.
1.
The pH values of solutions can be determined by using Universal Indicator or a pH sensor attached
to a data logger.
Hydrochloric acid (HCl) of different concentrations have different pH values. The table below shows
the pH values and colours of Universal Indicator in hydrochloric acid of different concentrations.
Concentration of HCl
/(mol/dm3)
pH value measured by pH sensor
attached to data logger
Colour of Universal
Indicator
0.1
1.0
red
0.001
3.0
orange
0.00001
5.0
yellow
(a) Using the data in the table, briefly describe how the pH value varies with the concentration of
hydrochloric acid.
The pH value increases as the concentration of hydrochloric acid decreases.
(b) Bernice tried to determine the pH value of 0.1 mol/dm3 sulfuric acid using both the pH sensor
and Universal Indicator. When she measured the pH of the acid using a pH sensor, the data
logger attached showed a value of 0.7.
(i)
Explain why the pH value of 0.1 mol/dm3 sulfuric acid differed from that of 0.1 mol/dm3
hydrochloric acid.
The pH value of a solution is dependent on the concentration of H+ ions. The higher the
concentration of H+ ions, the lower the pH value. 0.1 mol/dm3 hydrochloric acid ionises to give
0.1 mol/dm3 H+ ions. 0.1 mol/dm3 sulfuric acid ionises to give 0.2 mol/dm3 H+ ions. Hence, the
pH value observed for 0.1 mol/dm3 sulfuric was smaller than that for 0.1 mol/dm3 hydrochloric
acid.
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(ii) Bernice concluded that Universal Indicator cannot be used to differentiate between
0.1 mol/dm3 sulfuric acid and 0.1 mol/dm3 hydrochloric acid. Do you agree with her?
Why?
Yes. Both 0.1 mol/dm3 sulfuric acid and 0.1 mol/dm3 hydrochloric acid will give a red colour with
Universal Indicator.
(iii) Bernice also measured the pH of 0.00001 mol/dm3 of ethanoic acid using the pH
sensor. Ethanoic acid is a weak acid. Suggest a likely pH value that she would observe
and explain your answer.
The pH value is likely to be between 5 to 7. Hydrochloric acid is a strong acid which fully
ionises in water. Ethanoic acid is a weak acid which does not fully ionise in water. Hence, the
concentration of H+ ions in 0.00001 mol/dm3 ethanoic acid will be lower than that in
0.00001 mol/dm3 hydrochloric acid. Therefore, the pH value of ethanoic acid will be greater
than 5.
*2.
Barium hydroxide reacts with sulfuric acid to form barium sulfate precipitate. The equation for this
reaction is as follows:
Ba(OH)2(aq) + H2SO4(aq)
BaSO4(s) + 2H2O(l)
In an experiment, 1.0 mol/dm3 sulfuric acid was gradually added to 50 cm3 of barium hydroxide
solution. The mixture was continually stirred with an iron stirrer covered in plastic. The mixture was
connected to an ammeter. The reading was taken after the addition of every 1 cm3 of sulfuric acid.
The graph below shows the results obtained from the experiment.
Current/A
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
End-point
0.05
0
1
2
3
4
5
6
7
8
9
10
3
Volume of sulfuric acid added/cm
(a) Write an ionic equation, including state symbols, for
(i)
the formation of the barium sulfate precipitate;
Ba2+(aq) + SO42–(aq)
BaSO4(s)
(ii) the neutralisation reaction.
H+(aq) + OH–(aq)
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H2O(l)
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(b) State the ions that were present when the following volumes of sulfuric acid were added
to the barium hydroxide solution:
(i)
0 cm3
Ba2+ and OH– ions
(ii) 8 cm3
H+ and SO42– ions
(c) (i)
Mark, on the graph, the end-point of the neutralisation reaction.
(ii) Suggest why the current decreased initially and increased after 5 cm3 of the acid was
added.
The current is directly proportional to the concentration of ions in the solution. As sulfuric acid
was added to barium hydroxide, barium sulfate precipitate was formed, and the concentration
of ions decreased. When exactly 5 cm3 of sulfuric acid was added, neutralisation was complete.
The amount of barium sulfate precipitate formed was at the maximum and the concentration of
ions was at the minimum. When excess acid was added, the concentration of ions increased
causing the current to increase.
(iii) Calculate the concentration, in mol/dm3, of barium hydroxide solution used.
5.0 cm3 of H2SO4 was required for complete neutralisation.
Number of moles of H2SO4 = 1.0 × 5.0
1000
= 0.005 mol
From the equation, 1 mol of Ba(OH)2 reacts with 1 mol of H2SO4.
Number of moles of Ba(OH)2 = 0.005 mol
Concentration of Ba(OH)2 in mol/dm3 = number of moles
3
volume in dm
= 0.005 ÷ 50
1000
= 0.1 mol/dm3
(d) Suggest why the iron stirrer was covered in plastic.
To prevent it from reacting with the acid
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Define acids as substances that produce
hydrogen ions in aqueous solution.
–
–
2(b)(ii)
11.1
(b)
Describe the properties of acids and
their reactions with metals, bases and
carbonates.
1
1(a)
2(d)
11.1
(c)
State the uses of sulfuric acid.
2
–
–
11.1
(d)
Define alkalis as substances that
produce hydroxide ions in aqueous
solution.
7
–
2(b)(i)
11.2
(e)
Describe what is meant by
neutralisation and write the ionic
equation for the neutralisation reaction.
–
2(b)
2(a)(ii),
2(c)(i), 2(c)(ii)
11.2
(f)
Describe the properties of alkalis
and their reactions with acids and
ammonium salts.
3
2
–
11.2
(g)
Distinguish between strong and
weak acids in terms of their extent of
ionisation.
4
–
1(b)(iii)
11.3
(h)
Describe the effects of acids and
alkalis on Universal Indicator.
–
–
1(b)(ii)
11.4
(i)
Describe the use of Universal Indicator
and the pH scale to test hydrogen ion
concentration and relative acidity.
8, 9
–
1(a), 1(b)(i),
1(b)(iii)
11.4
(j)
Describe the reasons for controlling
the pH of soil and the methods used to
reduce excess acidity in soil.
5
–
–
11.4
(k)
Classify oxides as acidic, basic,
amphoteric or neutral based on their
metallic or non-metallic properties.
6
–
–
11.5
(l)
Write balanced chemical equations
with state symbols.
–
2(b), 2(c)
–
8.1
–
–
2(a)
8.2
(m) Write ionic equations with state
symbols.
58
Multiplechoice
(n)
Determine the empirical and molecular
formulae of a compound from given
data.
–
1(b)
–
9.5
(o)
Perform stoichiometric calculations
involving concentrations of solutions.
–
–
2(c)(iii)
10.4
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Class:
)
Worksheet 8
(
Name:
Date:
Salts
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 12
ANSWER IT RIGHT!
Describe the preparation of a pure, dry sample of barium sulfate from barium carbonate.
The term ‘describe’ means that you will need to state the main points of the topic, which may be an experiment
or a phenomenon. You will have to provide a diagram if the question asks for it.
Thought Process
There are three methods of preparing salts:
• Acid + insoluble metal carbonate or base
• Acid + alkali (titration)
• Precipitation
When preparing a salt, there are two questions you must consider:
• Is the salt to be prepared soluble in water?
• Are the starting materials soluble in water?
Barium sulfate is insoluble in water. Thus, you need to use the precipitation method to prepare the salt.
Since the starting material, barium carbonate, is also insoluble in water, the first step is to convert the
starting material to a soluble salt.
Answer
Step 1:
Add excess barium carbonate to dilute nitric acid to produce barium nitrate solution.
BaCO3(s) + 2HNO3(aq)
Ba(NO3)2(aq) + CO2(g) + H2O(l)
Step 2:
Filter to remove unreacted barium carbonate. Collect the filtrate (barium nitrate solution).
Step 3:
Add dilute sulfuric acid (or any soluble sulfate) to the filtrate. A precipitate of barium sulfate
is formed.
Ba(NO3)2(aq) + H2SO4(aq)
BaSO4(s) + 2HNO3(aq)
Step 4:
Filter to collect the precipitate. Wash the precipitate with a small amount of distilled water to
remove impurities and any traces of nitric acid.
Step 5:
Dry the precipitate between a few sheets of filter paper.
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TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which statement is not true for all salts?
A
B
C
D
2.
They contain a metal ion or an ammonium ion.
They contain a negative ion that comes from an acid.
They contain water of crystallisation.
Their names end with ‘–ate’ if they contain oxygen.
Which salt is best prepared by titration?
A
B
C
D
3.
Barium sulfate
Calcium carbonate
Lead(II) nitrate
Potassium chloride
Titrate dilute hydrochloric acid against aqueous lead(II) nitrate.
Evaporate the filtrate until crystals of lead(II) chloride form.
Collect the precipitate of lead(II) chloride by filtration.
Add dilute hydrochloric acid until no more gas is evolved.
Copper(II) carbonate
Iron(II) sulfate
Lead(II) nitrate
Potassium chloride
Observation
A
Add aqueous sodium hydroxide
followed by aluminium foil and boil.
A gas was given off which turned moist
red litmus paper blue.
B
Add dilute hydrochloric acid and
aqueous barium chloride.
A yellow precipitate was formed.
C
Add aqueous sodium hydroxide.
A white precipitate was formed.
D
Add aqueous zinc sulfate.
A white precipitate was formed.
Worksheet 8
(S)CMWB_08.indd 60
( D )
As shown below, a student performed a number of tests on an aqueous solution of lead(II) nitrate.
Which test must be repeated because the student’s observation was wrong?
Test
60
( C )
Dilute nitric acid was added to a colourless solution S. The acidified solution of S reacted with
silver nitrate to give a white precipitate. What is S most likely to be?
A
B
C
D
5.
( D )
Lead(II) chloride is insoluble in water. It can be prepared by reacting dilute hydrochloric acid with
aqueous lead(II) nitrate. Which step is involved in the preparation of lead(II) chloride?
A
B
C
D
4.
( C )
( B )
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6.
Solution X contains two anions. The scheme below shows some reactions of solution X.
solution X
+ dilute HNO3(aq)
colourless solution
+ BaCl2(aq)
white precipitate
+ AgNO3(aq)
white precipitate
What anions are present in X?
A
B
C
D
7.
CO32– and SO42–
CO32– and NO3–
Cl – and SO42–
Cl – and NO3–
( C )
The reaction scheme below shows some reactions of compound Y.
colourless solution
compound Y
+ NaOH(aq)
+ excess HCl(aq)
white precipitate
which dissolves in
excess NaOH(aq)
carbon dioxide gas
What is compound Y?
A
C
Ammonium carbonate
Iron(II) carbonate
B
D
Calcium carbonate
Zinc carbonate
( D )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
The salts of magnesium have many uses. For example, magnesium nitrate is a common fertiliser
and magnesium chloride is used as a dietary supplement for magnesium.
(a) Magnesium nitrate can be prepared by the procedure described below.
1.
2.
3.
4.
5.
6.
7.
Pour 25 cm3 of reagent X into a beaker.
Add solid Y in small portions to X with stirring until no more effervescence is observed.
Heat the mixture and then filter to remove excess Y.
Transfer the filtrate to an evaporating dish and heat the filtrate until it is saturated.
Allow the hot saturated solution to cool and crystallise.
Filter the mixture and collect the magnesium nitrate crystals.
Dry the magnesium nitrate crystals between a few sheets of filter paper.
(i)
Identify X and Y.
X: Dilute nitric acid
Y: Magnesium (or magnesium carbonate)
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(ii) A gas is produced in the preparation of magnesium nitrate described in (a). Write the
formula of this gas.
H2 (or CO2)
(iii) Describe a test that can be used to identify the gas produced.
H2: Insert a lighted splint. The splint will be extinguished with a ‘pop’ sound.
(Or CO2: Bubble the gas through limewater. A white precipitate will be formed.)
(b) Describe a chemical test that can be used to distinguish a solution of magnesium nitrate
from a solution of magnesium chloride.
Add dilute nitric acid followed by silver nitrate to each solution. The solution of magnesium chloride
will form a white precipitate upon reaction with acidified silver nitrate, while magnesium nitrate will not
have any observable change.
*2.
Calcium carbonate is insoluble in water. Calcium sulfate and calcium hydroxide are both sparingly
soluble in water. Four students were each asked to suggest a method for making calcium sulfate
from calcium carbonate:
Method 1: Add dilute nitric acid to calcium carbonate, then add dilute sulfuric acid to the calcium
nitrate solution formed.
Method 2: Add dilute sulfuric acid to calcium carbonate.
Method 3: Heat calcium carbonate strongly to give calcium oxide, then react the calcium oxide with
dilute sulfuric acid.
Method 4: Heat calcium carbonate strongly to give calcium oxide. React the calcium oxide with
water to form calcium hydroxide solution and then add dilute sulfuric acid.
(a) Which method is the most suitable for preparing calcium sulfate? Write the equation(s) for
any reaction(s) involved. Include state symbols.
Method 1. The reactions involved are:
CaCO3(s) + 2HNO3(aq)
Ca(NO3)2(aq) + H2SO4(aq)
Ca(NO3)2(aq) + H2O(l) + CO2(g)
CaSO4(s) + 2HNO3(aq)
(b) Explain why the other three methods are less suitable.
In methods 2 and 3, dilute sulfuric acid and calcium carbonate or calcium oxide react to form an
insoluble layer of calcium sulfate, which prevents further reaction.
In methods 3 and 4, calcium carbonate has to be heated to a very high temperature before it
decomposes. This makes the process difficult and time-consuming.
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*3.
Study the flow chart below.
on heating
green solution W
+ aqueous sodium hydroxide
pungent gas which
turns moist red
litmus paper blue
green precipitate
+ dilute nitric acid
+ aqueous
silver nitrate
+ aqueous
barium nitrate
white precipitate
white precipitate
Identify the two cations and two anions present in green solution W. Quote evidence from the flow
chart to support your answers.
(a) (i)
2+
First cation: Fe
Evidence: Upon addition of aqueous sodium hydroxide, a green precipitate is formed. This
suggests the presence of Fe2+ ions.
+
(ii) Second cation: NH4
Evidence: Upon addition of aqueous sodium hydroxide and on heating, ammonia gas is
given off. This suggests the presence of NH4+ ions.
(b) (i)
2–
First anion: SO4
Evidence: A white precipitate is formed with the addition of acidified barium nitrate. This
suggests the presence of SO42– ions.
(ii) Second anion: Cl
–
Evidence: A white precipitate is formed with the addition of acidified silver nitrate. This
suggests the presence of Cl – ions.
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Section C: Free-Response Questions
Answer the following questions.
1.
One of the steps in the preparation of magnesium sulfate crystals is to react excess magnesium
oxide with dilute sulfuric acid.
(a) (i)
Why is magnesium oxide added in excess?
To make sure all the sulfuric acid has reacted
(ii) The apparatus shown below was used to filter the mixture. Identify residue A and
solution B.
A
B
A:
Unreacted magnesium oxide
B:
Magnesium sulfate solution
(b) After removing residue A, solution B was heated until it became saturated, and then cooled.
The crystals formed were collected and dried between a few sheets of filter paper.
How would you test if the solution is saturated?
Put a clean, dry, and cold glass rod into the solution and then remove it. If crystals form on the glass
rod, the solution is saturated.
(c) Suggest, with a reason, why the crystals should be dried with filter paper and not by heating.
The crystals contain water of crystallisation. If they are heated, the water of crystallisation will be
removed from the salt.
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(d) It was found that when 25.0 cm3 of 1.0 mol/dm3 sulfuric acid was used, the mass of
magnesium sulfate obtained was 1.23 g.
(i)
Write the equation for the reaction between magnesium oxide and sulfuric acid.
MgO(s) + H2SO4(aq)
MgSO4(aq) + H2O(l)
(ii) Calculate the percentage yield of magnesium sulfate obtained.
Number of moles of H2SO4 = 25 × 1.0
1000
= 0.025 mol
From the reaction, 1 mol of H2SO4 produces 1 mol of MgSO4.
Number of moles of magnesium sulfate obtained = 0.025 mol
Mr of MgSO4 = 24 + 32 + (4 × 16)
= 120
Theoretical yield of MgSO4 = number of moles × molar mass
= 0.025 × 120
= 3.00 g
actual yield in g × 100%
theoretical yield in g
= 1.23 × 100%
3.00
Percentage yield of MgSO4 =
= 41%
2.
The solubilities of some salts are shown in the table below.
Salt
Chemical formula
Solubility in water
magnesium chloride
MgCl2
soluble
magnesium fluoride
MgF2
insoluble
magnesium phosphate
Mg3(PO4)2
insoluble
silver chloride
AgCl
insoluble
silver nitrate
AgNO3
soluble
silver sulfate
Ag2SO4
insoluble
(a) State the method for preparing silver chloride. Explain your answer.
Precipitation can be used to prepare silver chloride as it is an insoluble salt.
(b) From the table above, identify two salts that can be used to prepare silver chloride.
The salts are magnesium chloride and silver nitrate.
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(c) Describe the preparation of silver chloride from the two salts named in (b).
The magnesium chloride solution and silver nitrate solution are mixed in a beaker. The two solutions
react to give a precipitate, silver chloride. The mixture is then filtered and the precipitate (silver
chloride) is collected. The precipitate is washed with a little distilled water and dried on a piece of
filter paper.
(d) Write a balanced equation, including state symbols, for the reaction in (c).
MgCl2(aq) + 2AgNO3(aq)
Mg(NO3)2(aq) + 2AgCl(s)
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
66
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Define a salt.
1
–
–
12.1
(b)
Describe the general rules for the
solubility of common salts in water.
–
–
2(a), 2(b)
12.1
(c)
Suggest a suitable method and
starting materials for preparing a salt.
2
1(a)(i), 2
2(a), 2(b)
12.2
(d)
Describe the methods of separation
and purification in preparing salts.
3
–
1(a), 1(b),
1(c), 2(c)
12.2
(e)
Describe the tests to identify cations.
5, 7
3(a)
–
12.3
(f)
Describe the tests to identify anions.
4, 6, 7
1(b), 3(b)
–
12.3
(g)
Describe the tests to identify gases.
–
1(a)(iii)
–
12.3
(h)
Write balanced chemical equations
with state symbols.
–
2(a)
1(d)(i), 2(d)
8.1
(i)
Calculate the percentage yield and
percentage purity of a substance.
–
–
1(d)(ii)
10.5
(j)
Describe the properties of acids and
their reactions with metals, bases and
carbonates.
–
1(a)(ii)
–
11.1
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Class:
)
Worksheet 9
(
Name:
Date:
Oxidation and Reduction
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 13
ANSWER IT RIGHT!
(a) The reaction between ammonium perchlorate, NH4ClO4, and aluminium metal is used to propel
space shuttles. The equation for the reaction is shown below.
6NH4ClO4(s) + 10Al(s)
4Al2O3(s) + 2AlCl3(s) + 12H2O(l) + 3N2(g)
(i) State the oxidation numbers of nitrogen and chlorine in ammonium perchlorate.
(ii) Identify the oxidising agent in the above reaction. Give a reason for your answer.
Oxidation state is also known as oxidation number.
Thought Process
(i) Ammonium perchlorate consists of the polyatomic ions NH4+ and ClO4–. The sum of the
oxidation states or numbers of the atoms in a polyatomic ion is equal to the charge on the ion.
To calculate the oxidation number of nitrogen, look at the NH4+ ion. NH4+ carries a +1 charge
and the oxidation number of hydrogen is +1.
To calculate the oxidation state of chlorine, look at the ClO4– ion. ClO4– carries a –1 charge
and the oxidation number of oxygen is –2.
(ii) An oxidising agent causes another substance to be oxidised and is itself reduced.
Answer
(i) Let the oxidation number of nitrogen be x.
Since NH4+ has a +1 charge and the oxidation number of hydrogen is +1,
x + 4(+1) = +1
x = –3
Thus, the oxidation number of nitrogen in NH4ClO4 is –3.
Let the oxidation number of chlorine be y.
Since ClO4– has a –1 charge and the oxidation number of oxygen is –2,
y + 4(–2) = –1
y = +7
Thus, the oxidation number of chlorine in NH4ClO4 is +7.
• When writing the oxidation state or number, the sign ‘+’ or ‘–’ should be included. For example, the
oxidation state (number) of hydrogen is +1 and not 1.
• Note that oxidation state is not written in the same way as the charge on an ion. For example, the oxide
ion is written as ‘O2–’ where ‘2–’ indicates the charge on the ion, but the oxidation state of oxygen is
written as ‘–2’.
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(ii) Ammonium perchlorate is the oxidising agent. It oxidises aluminium to aluminium oxide and
aluminium chloride. The oxidation number of aluminium increases from 0 in Al to +3 in Al2O3
and AlCl3.
(b) Air bags have saved thousands of lives since their introduction in the early 1980s. When a car
fitted with air bags brakes suddenly and rapidly, sodium azide, NaN3, in the air bag decomposes
to produce nitrogen gas. The nitrogen gas causes the air bag to inflate. The equation for the
decomposition of sodium azide is shown below.
2NaN3(s)
(i)
2Na(s) + 3N2(g)
State, with a reason, what has been reduced in this reaction.
• ‘State’ requires a concise answer. There is no need to give supporting reasons unless the question
asks for it.
• In this case, the question is accompanied by the phrase ‘with a reason’. This means that an explanation
is required.
(ii) Calculate the volume, in cm3, of nitrogen gas produced when 6.5 g of sodium azide
decomposes at r.t.p.
Thought Process
(i) A substance is reduced if its oxidation state decreases after the reaction.
Answer
(i) Sodium in sodium azide, NaN3, has been reduced because there is a decrease in the oxidation
number from +1 to 0.
(ii) Mr of NaN3 = 23 + 3(14) = 65
Number of moles of NaN3 =
mass in g
= 6.5 = 0.1 mol
molar mass in g/mol
65
From the equation, 3 mol of N2 is produced from 2 mol of NaN3.
Number of moles of N2 produced = 3 × 0.1 = 0.15 mol
2
Volume of nitrogen produced = number of moles × 24 dm3
= 0.15 × 24
= 3.6 dm3
= 3600 cm3
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
The equation below shows the reaction that occurs between iron(III) chloride and hydrogen sulfide.
2FeCl3(aq) + H2S(g)
2FeCl2(aq) + 2HCl(aq) + S(s)
Which element is oxidised in the reaction?
A
C
68
Iron
Hydrogen
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B
D
Chlorine
Sulfur
( D )
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2.
The following equation shows the reaction that takes place on photographic film:
2AgBr(s)
2Ag(s) + Br2(g)
What can be deduced from the equation?
A
B
C
D
3.
( B )
barium sulfate + potassium chloride
Barium chloride + potassium sulfate
Potassium hydroxide + hydrochloric acid
potassium chloride + water
Potassium iodide + chlorine
potassium chloride + iodine
Silver nitrate + potassium chloride
silver chloride + potassium nitrate
( C )
Aqueous potassium iodide
colourless to brown
colourless to brown
no change
no change
Acidified potassium manganate(VII)
no change
purple to colourless
no change
purple to colourless
( D )
Why does the colour of aqueous potassium iodide change to brown when chlorine gas is bubbled
through it?
A
B
C
D
8.
2KCl(s) + 3O2(g)
2KClO3(s)
Cl2(g) + 2NaOH(aq)
NaCl(aq) + NaClO(aq) + H2O(l)
Cl2(g) + H2(g)
2HCl(g)
NaCl(aq) + AgNO3(aq)
AgCl(s) + NaNO3(aq)
What colour changes occur when sulfur dioxide is passed through aqueous potassium iodide and
acidified potassium manganate(VII) separately?
A
B
C
D
7.
( D )
Which reaction is a redox reaction?
A
B
C
D
6.
Copper in Cu2O and Cu
Iron in FeO and Fe2O3
Manganese in MnO2 and KMnO4
Sulfur in SO3 and H2SO4
In which reaction does the oxidation state of chlorine increase by one?
A
B
C
D
5.
( D )
In which pair of substances does the named element have the same oxidation state?
A
B
C
D
4.
The bromide ions are reduced to bromine molecules.
Light is needed for the reaction to take place.
The silver ions are oxidised to silver atoms.
Electrons are transferred from the bromide ions to the silver ions.
A compound is formed between chlorine and potassium iodide.
Chlorine oxidises iodide ions to iodine.
Iodine is reduced by chlorine.
Potassium chloride, which is brown, is formed.
( B )
Hydrogen peroxide reacts with acidified potassium iodide to form iodine as one of the products. It
also turns acidified potassium manganate(VII) from purple to colourless.
Which statement is true about hydrogen peroxide in both reactions?
A
B
C
D
Hydrogen
Hydrogen
Hydrogen
Hydrogen
peroxide
peroxide
peroxide
peroxide
acts as both an oxidising agent and a reducing agent.
acts only as a reducing agent.
acts only as an oxidising agent.
is neither an oxidising agent nor a reducing agent.
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9.
Which reactions are oxidation reactions?
C2H5OH
2
CH3CHO
A
C
1
CH3CO2H
B
D
1 and 2
2 and 3
3
CH3CO2Na
1 and 3
1, 2 and 3
( A )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Gold (Au) can form ions with the oxidation states of +1 and +3.
(a) Write down the chemical formulae of two chlorides that gold can form.
AuCl and AuCl3
(b) (i)
When copper is added to gold(III) chloride solution, gold in the chloride solution is
displaced by copper. Write the chemical and ionic equations for the reaction between
copper and gold(III) chloride.
Chemical equation: 3Cu(s) + 2AuCl3(aq)
3+
Ionic equation: 3Cu(s) + 2Au (aq)
3CuCl2(aq) + 2Au(s)
3Cu2+(aq) + 2Au(s)
(ii) State, with a reason, which substance has been oxidised in this reaction.
Copper has been oxidised. It has lost two electrons to form Cu2+. The oxidation state of copper
increased from 0 to +2.
(c) (i)
When a solution containing gold(I) ions is gently heated, solid gold is precipitated
together with gold(III) ions. Write an ionic equation for this reaction.
3Au+(aq)
2Au(s) + Au3+(aq)
(ii) State whether the gold(I) ions have been oxidised or reduced in this reaction.
The Au+ ions have been both oxidised and reduced.
(d) Gold(III) ions are powerful oxidising agents. How do you test for the presence of an oxidising
agent?
Add aqueous potassium iodide to the solution to be tested. The solution changes from colourless to
brown if an oxidising agent is present.
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2.
(a) The diagram below shows the oxidation states of sulfur as an element and in the compounds
sulfuric acid, sulfur trioxide and sulfur dioxide. Identify the substances A, B, C and D.
Oxidation state
+6
+5
+4
+3
+2
+1
Substance
0
A
B
C
D
A:
Sulfur
B:
Sulfur dioxide
C:
Sulfur trioxide/sulfuric acid
D:
Sulfuric acid/sulfur trioxide
(b) The equations below represent the stages in the manufacture of nitric acid from nitrogen.
N2(g) + 3H2(g)
2NH3(g)
4NH3(g) + 5O2(g)
4NO(g) + 6H2O(l)
2NO(g) + O2(g)
2NO2(g)
4NO2(g) + 2H2O(l) + O2(g)
(i)
4HNO3(aq)
Sketch a diagram, similar to the one in (a), to show the oxidation states of nitrogen in
the substances N2, NH3, NO, NO2 and HNO3.
Oxidation state
+6
+5
+4
+3
+2
+1
0
–1
N2
NH3
NO
NO2
Substance
HNO3
–2
–3
–4
(ii) From your diagram in (i), state if nitrogen has been oxidised or reduced in each stage of
the manufacturing process.
N2
(
reduced
)
NH3
(
oxidised
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)
NO
(
oxidised
)
NO2
(
oxidised
)
HNO3
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3.
Study each pair of equations and determine whether each statement is true or false. Explain your
answer.
CO2(g)
(a) C(s) + O2(g)
2H2S(g) + O2(g)
2H2O(l) + 2S(s)
Oxygen acts as an oxidising agent in both reactions.
True. Oxygen causes C and H2S to be oxidised to CO2 and S respectively.
(b) 2FeCl2(aq) + Cl2(g)
2NaCl(aq) + F2(g)
2FeCl3(aq)
2NaF(aq) + Cl2(g)
The oxidation state of chlorine has decreased to –1 in both reactions.
False. In the second reaction, the oxidation state of chlorine has increased from –1 in NaCl to 0
in Cl2.
(c) N2(g) + 3H2(g)
2Na(s) + H2(g)
2NH3(g)
2NaH(s)
Hydrogen acts as a reducing agent in both reactions.
False. Hydrogen acts as a reducing agent in the first reaction. It causes nitrogen to be reduced to
ammonia due to the gain of hydrogen. On the other hand, hydrogen acts as an oxidising agent in the
second reaction. It causes sodium to be oxidised to sodium ions due to the loss of electrons.
Section C: Free-Response Questions
Answer the following questions.
1.
Ethanoic acid, CH3COOH, is the main compound found in vinegar. It has a sour taste and a
distinctive pungent smell. Ethanoic acid undergoes many different reactions. When ethanoic acid
reacts with a reducing agent, lithium aluminium hydride (LiAlH4), ethanol is formed. The chemical
equation for this reaction is shown below.
CH3COOH(aq)
LiAlH4
CH3CH2OH(aq)
Reaction I
When ethanoic acid reacts with magnesium metal, the products obtained are a salt (magnesium
ethanoate) and hydrogen gas. The chemical equation for this reaction is shown below.
2CH3COOH(aq) + Mg(s)
(CH3COO)2Mg(aq) + H2(g)
Reaction II
When ethanoic acid reacts with sodium hydroxide, the products are a salt (sodium ethanoate) and
water. The chemical equation for this reaction is shown below.
CH3COOH(aq) + NaOH(aq)
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CH3COONa(aq) + H2O(l)
Reaction III
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(a) Explain, in terms of gain or loss of oxygen and hydrogen, why the conversion of ethanoic acid
to ethanol is a reduction reaction.
It is a reduction reaction because ethanoic acid, CH3COOH, has lost oxygen and gained hydrogen to
form ethanol, CH3CH2OH.
(b) Identify the elements that are oxidised and reduced in Reaction II. State the changes in the
oxidation states of these elements during the reaction.
Hydrogen is reduced. The oxidation state of H decreases from +1 in CH3COOH to 0 in H2.
Magnesium is oxidised. The oxidation state of Mg increases from 0 in Mg to +2 in (CH3COO)2Mg.
(c) Is Reaction III a redox reaction? Explain your answer.
No. None of the elements in the reaction are reduced or oxidised.
(d) When ethanoic acid reacts with potassium carbonate, the products obtained are a salt
(potassium ethanoate), carbon dioxide and water.
(i)
Write a balanced chemical equation for this reaction. Include state symbols.
2CH3COOH(aq) + K2CO3(aq)
2CH3COOK(aq) + H2O(l) + CO2(g)
(ii) State the oxidation state of carbon in potassium carbonate and in carbon dioxide.
The oxidation state of carbon is +4 in both K2CO3 and CO2.
*2.
(a) Explain, with an example, why there cannot be an oxidation reaction without a corresponding
reduction reaction.
Take the reaction between copper and silver nitrate as an example:
Cu(s) + 2AgNO3(aq)
Cu(NO3)2(aq) + 2Ag(s). Copper has been oxidised as it has lost two electrons
to form copper(II) ions. The electrons lost must be gained by another substance. The silver ions in
silver nitrate have gained the electrons to form silver atoms. The silver ions have been reduced. This
example shows that oxidation and reduction always take place together.
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(b) Explain why solutions of strong reducing agents, such as iron(II) chloride, have a short shelf
life when exposed to the air. Write an equation to support your explanation.
Since iron(II) chloride is a strong reducing agent, it is easily oxidised. When iron(II) chloride is exposed
to the air, it is oxidised by oxygen in the air. In the reaction, iron(II) ions lose electrons to form iron(III)
ions. The equation for the reaction is Fe2+
Fe3+ + e–.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
74
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Define
• oxidation as the gain of oxygen;
• reduction as the loss of oxygen.
9
3(a)
1(a)
13.1
(b)
Define redox reactions.
–
–
2(a)
13.1
(c)
Define
• oxidation as the loss of hydrogen;
• reduction as the gain of hydrogen.
1, 9
3(c)
1(a)
13.2
(d)
Define
• oxidation as the loss of electrons;
• reduction as the gain of electrons.
2
1(b)(ii),
1(c)(ii), 3(c)
2(b)
13.3
(e)
Define
• oxidation as an increase in oxidation
state;
• reduction as a decrease in oxidation
state.
1, 3, 4
1(b)(ii),
1(c)(ii), 2,
3(b)
1(b), 1(d)(ii)
13.4
5
–
1(c)
13.5
6, 7, 8
1(d), 3(a),
3(c)
–
13.6
(f)
Identify redox reactions.
(g)
Test for oxidising agents and reducing
agents using aqueous potassium iodide
and acidified potassium manganate(VII).
(h)
Deduce the formula of an ionic
compound from the charges on the
ions and vice versa.
–
1(a)
–
6.4
(i)
Write balanced chemical equations
with state symbols.
–
1(b)(i)
1(d)(i)
8.1
(j)
Write ionic equations with state
symbols.
–
1(b)(i), 1(c)(i)
–
8.2
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Class:
)
Worksheet 10
(
Name:
Date:
Metals
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 14
ANSWER IT RIGHT!
(a) Brass is an alloy of copper and zinc. Explain why brass is harder than pure copper.
Thought Process
The physical properties of a substance depend on its structure. The difference in hardness
between brass (an alloy) and copper (a metal) is due to their different atomic arrangements.
Answer
The atoms in pure copper are packed regularly in layers. When a force is applied, the layers of
atoms can slide over one another easily. Thus, pure copper is soft. In brass, the copper and zinc
atoms are of different sizes. This breaks up the regular arrangement of atoms in pure copper,
which makes it harder for the layers to slide over one another when a force is applied. Hence,
brass is harder than pure copper.
• It is a common mistake to think that brass (an alloy) is harder and stronger than copper (a pure metal)
because copper forms strong bonds with zinc.
• The hardness of an alloy is due to the different sizes of the constituent atoms of the alloy.
(b) Explain the electrical conductivity of zinc in the solid state.
Thought Process
The electrical conductivity of a substance depends on its type of chemical bonding and its physical
state.
Answer
Zinc is a metal. Zinc atoms are held by metallic bonds, which consist of positive zinc ions
surrounded by a ‘sea of mobile electrons’. This means that the outer electrons are free to move
through the entire metal structure. Thus, zinc can conduct electricity in the solid state.
• It is too vague to write ‘metals conduct electricity because the electrons move through the entire metal
structure’.
• Note that metals conduct electricity due to the movement of their outer electrons only.
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(c) Carbon steels are alloys of iron and carbon. How does the carbon content of steel affect the
properties of steel?
Thought Process
Whether a steel is malleable or brittle will depend on the proportion of carbon in the steel.
Answer
Mild steel has low carbon content. It is strong and malleable. High-carbon steel has high carbon
content. It is strong but brittle. Thus, the higher the content of carbon, the more brittle the steel.
This is a question on comparing the different physical properties of high-carbon steel and mild steel
(low-carbon steel).
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
What is an alloy?
A
B
C
D
2.
A
A
A
A
mixture
mixture
mixture
mixture
of a metal with one or a few other elements
of a non-metal with one or a few other elements
that must contain carbon
that must contain iron
( A )
Which diagram shows the structure of an alloy?
A
B
C
D
( B )
3.
76
What are the advantages of recycling metals?
1
2
3
Conserves fossil fuels
Reduces air and water pollution
Always requires less time and money
A
C
1 and 2
2 and 3
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B
D
1 and 3
1, 2 and 3
( A )
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4.
The positions of some metals in the reactivity series are shown below.
Least reactive
Most reactive
iron
>
tin
>
lead
>
silver
In which beaker will there be no reaction?
A
B
Sn
Pb(NO3)2(aq)
5.
Sn
AgNO3(aq)
D
Fe
SnCl2(aq)
( B )
Calcium carbonate (limestone) removes the basic impurities.
Carbon is oxidised to carbon monoxide by carbon dioxide.
Carbon monoxide oxidises iron(III) oxide to iron(II) oxide.
Molten iron floats on the molten slag.
( B )
Which of the following uses is incorrect?
A
B
C
D
7.
SnCl2(aq)
C
Which statement about the production of iron from iron(III) oxide in the blast furnace is correct?
A
B
C
D
6.
Pb
Cast iron for woks
Galvanised steel for cutlery
Stainless steel for hospital equipment
Steel for cans and containers
( B )
A metal, M, takes part in the reactions shown by the following chemical equations:
2M + O2
M + 2HCl
MO + C
2MO
MCl2 + H2
heat
no reaction
Which metal could M be?
A
B
C
D
*8.
Iron
Lead
Magnesium
Zinc
( C )
Hydrogen was passed over 1.0 g of heated copper(II) oxide. What is the colour and mass of the
product obtained?
A
B
C
D
Colour of product
black
black
reddish-brown
reddish-brown
Mass of product
more than 1.0 g
less than 1.0 g
more than 1.0 g
less than 1.0 g
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Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Metals were added in excess to aqueous solutions of different metal nitrates. The table below
records the observations obtained. A tick (✓) indicates a reaction. A cross (✗) indicates no reaction.
Aqueous metal
nitrate
Metal
Copper(II)
nitrate
(blue)
Magnesium
nitrate
(colourless)
Nickel(II)
nitrate
(green)
Silver nitrate
(colourless)
Zinc nitrate
(colourless)
✗
✗
✓
✗
✓
✓
✓
✓
✗
Copper
Magnesium
✓
Nickel
✓
✗
Silver
✗
✗
✗
Zinc
✓
✗
✓
✗
✓
(a) Place the metals in order of their reactivity, starting with the most reactive metal.
Magnesium, zinc, nickel, copper, silver
(b) Which metal and aqueous metal nitrate would react to give the following colour changes?
(i)
Blue to green:
Nickel and copper(II) nitrate
Copper and silver nitrate
(ii) Colourless to blue:
(c) Apart from colour changes, state two other observations that would indicate that a chemical
reaction has taken place.
A precipitate is observed on the surface of the metal added. The reaction mixture becomes warmer
(due to the increase in temperature during the reaction).
2.
(a) What are the conditions that can cause iron to rust?
The presence of air (oxygen) and water
(b) Explain why rusting is an example of oxidation.
During rusting, iron gains oxygen./ The oxidation state of iron increases from 0 to +3.
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(c) (i)
Car bodies can be protected from rusting by painting and sacrificial protection. Explain
how the two methods work.
Painting and sacrificial protection coat the iron of the car body with a layer of paint and a more
reactive metal (e.g. zinc) respectively. These layers protect the iron from being exposed to the
air, thus preventing moisture and oxygen in the air from reacting with the iron. In sacrificial
protection, the more reactive metal corrodes instead of iron.
(ii) What will happen if the paint on a galvanised car body is scratched off? Explain your
answer.
The car body will not rust. Zinc is more reactive than iron, so the zinc that remains will corrode
instead of iron.
3.
The following list shows some elements in order of reactivity.
Least reactive
Most reactive
potassium > magnesium > carbon > iron > tin > gold
(a) Some reactions of the metals are summarised in the table below.
(i)
Metal
Reaction with water or steam
Reaction with dilute acids
potassium
violent reaction with cold water
explosive
magnesium
violent reaction with steam
fast
iron
slow reaction with steam
slow
tin
slow reaction with steam
slow
gold
no reaction with water or steam
no reaction
From the table, deduce the position of hydrogen in the reactivity series.
Between tin and gold
(ii) Based on your answer in (a)(i), deduce a general rule for the reactivity of metals with
water and dilute acids.
Only metals that are more reactive than hydrogen will react with water and dilute acids.
(b) Why does gold occur mostly as pure gold in the Earth’s crust, while potassium only occurs
as potassium compounds?
Gold is very unreactive and therefore occurs naturally uncombined as a metal. Potassium is very
reactive. It reacts easily with substances such as water, air and acids in the surroundings to form
compounds.
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(c) Based on the order of reactivity of the elements, state the method that is most likely used to
extract the following metals from their compounds.
(i)
Reduction by carbon
(ii) Tin from tin(IV) oxide:
4.
Electrolysis
Magnesium from molten magnesium chloride:
The table below gives the densities and melting points of substances used in the blast furnace, at
normal atmospheric pressure.
Substance
Density/(g/cm3)
Melting point/°C
calcium carbonate
2.71
decomposes at 850°C
calcium oxide
3.35
2600
calcium silicate
2.50
1530
carbon
2.25
4000
iron
7.80
1539
iron(III) oxide
5.24
1566
magnesium oxide
3.58
2900
The diagram below shows the temperatures in a blast furnace.
waste gases
A
700°C
1100°C
1600°C
hot air
hot air
B
C
Some elements, including those used in the blast furnace, are shown below in decreasing order of
reactivity.
Ca > Mg > Fe > C > H > Ti
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(a) Name the substances that are fed into the furnace at A.
Calcium carbonate, carbon and iron(III) oxide
(b) This reaction takes place at the base of the furnace:
C(s) + O2(g)
CO2(g)
How is the carbon dioxide formed immediately reduced to carbon monoxide?
Excess carbon (coke) is present in the furnace. This reduces the carbon dioxide to carbon monoxide:
CO2(g) + C(s)
2CO(g)
(c) Write the equation for the reduction of iron(III) oxide by carbon monoxide.
Fe2O3(s) + 3CO(g)
(d) (i)
2Fe(l) + 3CO2(g)
Why is the temperature of the slag coming out of B much lower than 1530°C?
It contains impurities that lower its melting point.
(ii) Use the data from the table to explain why slag floats on top of molten iron.
Slag (calcium silicate) is less dense than molten iron.
(iii) Why is it useful for slag to float on top of the molten iron?
This protects the molten iron from oxidation by the hot air.
(e) (i)
The furnace is lined with magnesium oxide bricks. Suggest one physical property and
one chemical property of magnesium oxide that make it a suitable material.
Physical property: Magnesium oxide has a high melting point (it is a refractory substance).
Chemical property: It does not react with any of the substances in the furnace.
(ii) Why might the furnace explode if damp substances were added at A?
Iron and carbon would reduce the water (steam) to hydrogen. Hydrogen gas and air form an
explosive mixture.
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Section C: Free-Response Questions
Answer the following questions.
1.
Aluminium is the most abundant metal in the Earth’s crust. It has a low density and is corrosionresistant.
In a laboratory, some experiments involving aluminium were set up.
aluminium
strip
aluminium
strip
aqueous
iron(II)
nitrate
aqueous
calcium
nitrate
Experiment 1
Experiment 2
Experiment 3
aluminium
strip
rubbed with
sandpaper
aluminium
strip
rubbed with
sandpaper
aqueous
iron(II) nitrate
aqueous
calcium
nitrate
Experiment 4
Changes were only observed in Experiment 3.
(a) Describe the observations you would see in Experiment 3. Write a balanced chemical equation
for this reaction.
A grey deposit (iron) is formed on the aluminium strip. The pale green solution of iron(II) nitrate slowly
turns colourless.
2Al(s) + 3Fe(NO3)2(aq)
Al2(NO3)3(aq) + 3Fe(s)
(b) Suggest why a reaction occurred in Experiment 3 but not in Experiment 1.
When aluminium is exposed to air, a thin surface layer of aluminium oxide is formed. This oxide
layer prevents the aluminium from reacting with other reagents. Hence, no reaction took place in
Experiment 1. In Experiment 3, this layer of aluminium oxide was removed by the sandpaper and the
aluminium came into contact with aqueous iron(II) nitrate. Aluminium displaced iron from the solution
because aluminium is more reactive than iron.
(c) Based on the experimental results, arrange aluminium, calcium and iron in increasing order
of reactivity.
Iron, aluminium, calcium
(d) The carbonates of calcium and iron decompose on heating. Based on your answer in (c),
deduce the thermal stability of aluminium carbonate. Explain your answer.
Aluminium carbonate decomposes into aluminium oxide and carbon dioxide upon heating. Its thermal
stability is similar to those of iron(II) carbonate and calcium carbonate, both of which decompose into
the metal oxide and carbon dioxide when heated.
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2.
Steel is an alloy of iron with carbon and/or other metals. It is made from cast iron extracted from
the blast furnace. Steel has many uses and properties.
(a) With the aid of diagrams, explain the difference between steel and iron in terms of structure.
Structure of steel
Structure of iron
In iron, atoms are packed regularly in layers. All the atoms are of the same size. In steel, the
arrangement of atoms is not regular due to the different atom sizes of the different elements.
(b) Explain how the difference in structures in (a) accounts for the difference in physical properties
of steel and iron.
The regular arrangement in iron makes it easy for the layers of atoms to slide over each other
when a force is applied. Thus, iron is soft. The different sizes of atoms in steel disrupt the regular
arrangement of atoms. The layers cannot slide over each other easily. Thus, steel is harder and
stronger than iron.
(c) Carbon steel is a main category of steel. There are two types of carbon steel —
high-carbon steel and mild steel. State how the compositions of high-carbon steel and mild
steel account for their properties and uses.
High-carbon steel has high carbon content, which makes it strong but brittle. It is used to manufacture
cutting and boring tools. Mild steel has low carbon content, so it is soft and malleable. It is used to
make car bodies and machinery.
(d) Recycling metals helps to conserve natural resources and has many advantages. Discuss
some problems faced in metal recycling.
Recycling metals can be extremely costly. It is sometimes more expensive than extracting the
metal from the earth. Recycling metals can pollute the environment. For example, air pollutants are
produced in the process of recycling lead–acid batteries. It takes time and effort for communities to
adopt recycling as a lifestyle. Thus, it is not immediately effective.
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WORK ON IT!
Circle the question(s) that you have answered incorrectly. Then, revisit the relevant section(s) in the
textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
Structured
Freeresponse
(a)
Explain what an alloy is.
1
–
–
14.1
(b)
Identify the diagrams of structures of
metals and alloys.
2
–
2(a)
14.1
(c)
Explain the difference in the properties of
alloys and their constituent metals.
–
–
2(b)
14.1
(d)
Determine the order of reactivity of some
metals from the reactions of metals with
water, steam and dilute hydrochloric acid.
7
3(a)
–
14.2
(e)
Relate the reactivity of metals to their
tendency to form positive ions by
• the displacement of metals from their
salt solutions;
• the reaction of a metal with the oxide
of another metal.
4
–
1(a), 1(b)
14.3
(f)
Determine the order of reactivity of
metals from the reduction of metal oxides
with carbon and hydrogen.
7, 8
–
–
14.3
(g)
Describe the action of heat on metal
carbonates and explain how their thermal
stability is related to the reactivity series.
–
–
1(d)
14.3
(h)
Deduce the order of reactivity of metals
when given a set of experimental results.
–
1, 3(a)
1(c)
14.3
(i)
Relate the method of obtaining the metal
from its ore to its position in the reactivity
series.
–
3(b), 3(c)
–
14.4
(j)
Describe and explain the reactions
involved in the extraction of iron in the
blast furnace.
5
4
–
14.4
(k)
Identify and describe steel as an alloy.
–
–
2(a)
14.5
(l)
Describe how the properties of steel vary
with the amount of carbon or other metals
added to iron.
–
–
2(c)
14.5
6
–
2(c)
14.5
(m) State the uses of steel.
84
Multiplechoice
Textbook
section(s)
to revise
(n)
Describe the conditions necessary for
rusting to occur.
–
2(a)
–
14.6
(o)
State how rusting can be prevented.
–
2(c)
–
14.6
(p)
State why there is a need to recycle metals.
3
–
–
14.7
(q)
Discuss the issues related to recycling
metals.
–
–
2(d)
14.7
(r)
Define oxidation as the gain of oxygen.
–
2(b)
–
13.1
(s)
Define oxidation as an increase in
oxidation state.
–
2(b)
–
13.4
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Class:
)
Worksheet 11
(
Name:
Date:
Electrolysis
Go through the worked example. Use the tips to guide you in understanding and answering the
questions.
for Chapter 15
ANSWER IT RIGHT!
(a) The electrolysis of dilute sodium chloride solution was carried out with inert electrodes. The gases
produced were collected.
(i)
Construct ionic half-equations for the reactions that take place at the electrodes.
• The term ‘construct’ requires you to make use of information given to write your answer.
• In this case, you will need to use the information ‘dilute sodium chloride solution’ to write the ionic
half-equations.
(ii) Draw a labelled diagram to show the apparatus used for this experiment.
Thought Process
(i) • The ions present in dilute sodium chloride solution are Na+, Cl –, H+ and OH–.
• At the anode, OH– ions are discharged by losing electrons to form oxygen gas and water.
• At the cathode, H+ ions are discharged by gaining electrons to form hydrogen gas.
Answer
O2(g) + 2H2O(l) + 4e–
(i) At the anode: 4OH–(aq)
+
At the cathode: 2H (aq) + 2e–
H2(g)
• Take note of the type of solution that is being electrolysed — the products of electrolysis of dilute NaCl,
concentrated NaCl and molten NaCl are different.
• For example, if concentrated or molten NaCl are electrolysed, chlorine gas instead of oxygen gas will be
the product at the anode.
(ii)
oxygen gas
hydrogen gas
carbon anode
carbon cathode
dilute sodium
chloride solution
battery
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(b) A metal object is to be electroplated with copper. Suggest what can be used as the anode, cathode
and electrolyte.
Thought process
• The metal object to be electroplated is made the cathode.
• The anode is the source of the plating metal.
• The electrolyte is an aqueous salt solution of the plating metal.
Answer
Cathode: metal object to be electroplated
Anode: pure copper
Electrolyte: copper(II) sulfate solution
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
In which of the following experiments will the bulb not light up?
A
B
sodium chloride
solution
C
dilute sulfuric
acid
D
mercury
molten sulfur
( D )
2.
Which of the following molten electrolytes requires only one mole of electrons to produce one mole
of metal atoms during electrolysis?
A
C
3.
Product formed at the cathode
chlorine
hydrogen
oxygen
potassium
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B
D
Iron(II) chloride
Potassium bromide
( D )
What changes take place when concentrated potassium chloride solution is electrolysed using
inert electrodes?
A
B
C
D
86
Calcium chloride
Magnesium bromide
Solution produced
neutral
alkaline
acidic
neutral
( B )
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4.
Copper(II) sulfate solution is electrolysed using carbon electrodes. Which of the half-equations
below represents the reaction at the cathode?
A
B
C
D
5.
2H+(aq) + 2e–
H2(g)
4OH–(aq)
2H2O(l) + O2(g) + 4e–
Cu2+(aq) + 2e–
Cu(s)
SO42–(aq)
SO2(g) + O2(g) + 2e–
( C )
Cells A and B show the electrolysis of dilute hydrochloric acid and copper(II) chloride solution
respectively.
carbon
dilute
hydrochloric
acid
copper
copper(II)
chloride solution
Cell A
Cell B
Which of the statements below is true?
A
B
C
D
6.
( A )
A spoon to be silver-plated is made the cathode in an electrolytic cell. Which of the following could
be used as the anode and the electrolyte?
A
B
C
D
*7.
Oxygen gas is given off at the carbon anode in cell A.
Hydrogen gas is given off at the copper cathode in cell B.
The OH– ions in cell A accept electrons from the anode.
The size of the copper anode in cell B increases.
Anode
carbon
carbon
silver
silver
Electrolyte
dilute hydrochloric acid
silver nitrate solution
dilute hydrochloric acid
silver nitrate solution
( D )
Consider the simple cell shown below. Which of the following changes will occur?
V
Mg (negative electrode)
salt bridge
Mg(NO3)2(aq)
A
B
C
D
Oxygen gas is produced at the copper electrode.
The blue colour of the copper(II) sulfate solution deepens.
Hydrogen gas is produced at the magnesium electrode.
The copper electrode is coated with a layer of brown solid.
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Cu (positive electrode)
CuSO4(aq)
( D )
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Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
(a) Explain what is meant by the term ‘electrolysis’.
Electrolysis is the process of using electricity to break down or decompose a compound (usually an
ionic compound in the molten state or in aqueous solution).
(b) The following solutions are electrolysed using carbon electrodes. Predict the products.
Products
Electrolyte
at the anode
(i)
copper(II) chloride solution
copper solid
oxygen gas
(ii)
silver nitrate solution
silver solid
oxygen gas
(iii)
potassium sulfate solution
hydrogen gas
oxygen gas
(iv)
molten sodium chloride
molten sodium
chlorine gas
The diagrams below show two types of cells.
+
e–
>
–
Cu electrode X
v
e–
>
e–
>
e–
>
2.
at the cathode
Cu electrode Y
porous
pot
Mg
–
+
CuSO4(aq)
Cu
CuSO4(aq)
Cell I
Cell II
(a) On the above diagrams,
(i) label the positive and negative electrodes of cells I and II with ‘+’ or ‘–’ signs;
(ii) indicate the direction of electron flow in cells I and II.
(b) Write ionic half-equations for the reactions that occur at
(i)
electrodes X and Y in cell I;
At electrode X: Cu(s)
Cu2+(aq) + 2e–
At electrode Y: Cu2+(aq) + 2e–
Cu(s)
(ii) the magnesium and copper electrodes in cell II.
At the magnesium electrode: Mg(s)
At the copper electrode: Cu2+(aq) + 2e–
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Mg2+(aq) + 2e–
Cu(s)
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3.
Consider three simple cells, A, B and C, as shown below. Each cell contains sodium chloride
solution as the electrolyte.
v
v
Pb
v
Mg
Fe
Pb
NaCl(aq)
Pb
Ag
NaCl(aq)
Cell A
Cell B
NaCl(aq)
Cell C
(a) Identify the positive and negative terminals of each of these cells. Match the following voltages
to the cells: 0.31 V; 0.93 V; 2.25 V.
Cell
A
B
C
Positive terminal
Negative terminal
Voltage/V
Pb
Fe
0.31
Pb
Mg
2.25
Ag
Pb
0.93
(b) Explain the following observations in cell A.
(i)
The iron electrode decreases in size.
Iron is more reactive than lead. Hence, iron atoms lose electrons to form iron(II) ions, which go
into the solution.
(ii) Bubbles of gas are produced at the lead electrode.
Hydrogen ions present in the aqueous solution gain electrons and are reduced to hydrogen gas
at the lead electrode.
(c) What is the direction of electron flow in cell C? Give your reason.
Electron flow in cell C is from the lead electrode to the silver electrode. Electrons flow from the more
reactive metal (lead) to the less reactive metal (silver).
Section C: Free-Response Questions
Answer the following questions.
*1.
An iron object is electroplated with chromium as shown in the diagram below.
chromium (anode)
chromium(III)
nitrate solution
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iron object
(cathode)
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(a) Explain the chemical changes that occur at the
(i)
anode;
NO3– and OH– ions migrate to the anode. Since chromium is a reactive electrode, the chromium
anode dissolves, producing chromium(III) ions.
(ii) cathode.
Cr3+ and H+ ions migrate to the cathode. Chromium is formed rather than hydrogen gas because
Cr3+ ions accept electrons more readily than hydrogen ions. The iron object at the cathode
becomes coated with a layer of chromium.
(b) Explain why the concentration of the electrolyte remains the same throughout the
electroplating process.
The chromium(III) ions that are discharged at the cathode come mainly from the chromium anode.
There is no net loss of chromium(III) ions from the chromium(III) nitrate solution. Thus, the
concentration of the electrolyte remains the same.
(c) Give two uses of electroplating metals.
It prevents the corrosion of metals and improves their appearance.
*2.
The set-up shown was used to compare the reactivity of four metals, P, Q, R and S. Metal strips P,
Q, R and S and a copper plate were first cleaned with sandpaper. Each metal strip was then clipped
onto the wet filter paper and the voltmeter reading was recorded.
V
metal strip
under test
filter paper soaked with
sodium chloride solution
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connecting
wire
copper plate
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A summary of the voltmeter readings obtained is shown in the table below.
Metal strip
Direction of electron flow in the external circuit
Voltmeter reading/V
P
P to Cu
+0.80
Q
Cu to Q
–2.20
R
R to Cu
+1.40
S
S to Cu
+0.30
(a) Give a reason why the metal strips and copper plate must first be cleaned with sandpaper.
To remove any oxide layer formed on the metal surface, to ensure better electrical conductivity
(b) From the results in the table,
(i)
arrange the metals in order of increasing reactivity;
Q, S, P, R
(ii) state how the positions of the metals in the reactivity series affect the magnitude of
voltage.
The further apart the metals are from copper in the reactivity series, the greater the magnitude
of voltage.
(c) (i)
Given that R is an element in Group II of the Periodic Table, what is observed if it is
placed in copper(II) sulfate solution?
A reddish-brown solid is deposited. The solution turns from blue to colourless.
(ii) Write an ionic equation for the reaction.
R(s) + Cu2+(aq)
Cu(s) + R2+(aq)
(d) State and explain any difference in the voltmeter readings if the experiment is repeated using
filter paper soaked with the organic solvent methylbenzene.
The voltmeter reading will be zero for all four metals. This is because methylbenzene is a covalent
compound and does not conduct electricity.
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
92
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Define electrolysis.
–
1(a)
–
15.1
(b)
Describe electrolysis as evidence of
the structure of ionic compounds in the
solid, molten and aqueous states.
1
–
–
15.1
(c)
Describe the electrolysis of molten
sodium chloride using inert electrodes.
–
1(b)(iv)
–
15.2
(d)
Predict the products of the electrolysis
of a molten ionic compound.
2
–
–
15.2
(e)
Construct ionic equations for the
reactions occurring at the electrodes
during electrolysis.
4
2(b)
–
15.2
(f)
Predict the products of the electrolysis
of an aqueous electrolyte using the
idea of selective discharge of ions.
3, 5
1(b)(i),
1(b)(ii),
1(b)(iii), 2(b)
–
15.3
(g)
Describe the purification of copper by
the electrolysis of aqueous copper(II)
sulfate using copper electrodes.
–
2(a)(i)
–
15.4
(h)
Describe the electroplating of metals
and its uses.
6
–
1
15.4
(i)
Describe how electricity can be
produced from simple cells, in relation
to the reactivity series and redox
reactions.
7
2(a)(ii), 3
2(b)
15.5
(j)
Relate the physical properties of ionic
compounds to their lattice structures.
–
–
2(a)
6.5
(k)
Relate the physical properties of
covalent substances to their structure
and bonding.
–
–
2(d)
7.2
(l)
Write ionic equations with state
symbols.
–
–
2(c)(ii)
8.2
(m) Relate the reactivity of metals to their
tendency to form positive ions by
• the displacement of metals from
their salt solutions;
• the reaction of a metal with the
oxide of another metal.
–
–
2(c)(i)
14.3
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Class:
)
Worksheet 12
(
Name:
Date:
The Periodic Table
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 16
ANSWER IT RIGHT!
(a) (i) Write the chemical formula of rubidium carbonate.
(ii) Explain what is observed when rubidium carbonate is added to dilute sulfuric acid.
Thought Process
Rubidium is a Group I element and forms Rb+ ions. It undergoes similar reactions to other Group I
elements.
Answer
(i) Rb2CO3
(ii) Rubidium carbonate dissolves in sulfuric acid and effervescence occurs.
Write down physical observations, i.e. what you see, hear or feel. An answer such as ‘a gas is given off’
is not acceptable.
(b) (i)
Based on the position of silicon in the Periodic Table, deduce the chemical formula of silicon
chloride.
(ii) Draw a ‘dot and cross’ diagram to show the bonding in silicon chloride. Show only the outer
electrons.
Thought Process
(i) Silicon is a Group IV element. It has four valence electrons. It will form four covalent bonds
with chlorine atoms to attain the stable octet electronic configuration.
Answer
(i) SiCl4
(ii)
Cl
Cl
Si
Cl
Cl
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(c) Chromium is a transition element. List two properties of chromium.
• ‘List’ implies that no elaboration is needed on the points you write down.
• You should only list the number of points that is required.
Answer
Chromium has a high density and high melting and boiling points. It forms coloured compounds.
Remember that transition elements are not coloured. It is their compounds (oxides, hydroxides or salts)
that are coloured.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
A bar chart for some elements is shown below. What should the label for the x-axis be?
Element
Sc
Ca
K
Ar
Cl
S
0
A
B
C
D
2.
20
Group number of the element
Number of electrons in the outermost shell of the element
Nucleon number of the element
Proton number of the element
Group
Group
Group
Group
II
IV
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15
( D )
III elements form negative ions.
II elements form positive ions.
I elements are reactive metals.
0 elements are gases.
( A )
An element has a proton number of 5. Which group of the Periodic Table does the element belong
to?
A
C
94
10
Which statement about elements in the Periodic Table is not true?
A
B
C
D
3.
5
B
D
III
V
( B )
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4.
What is the similarity between the elements carbon, nitrogen and oxygen?
A
B
C
D
5.
They
They
They
They
have the same number of electrons.
form negative ions with the same charge.
are in the same period of the Periodic Table.
are in the same group of the Periodic Table.
( C )
The diagram below shows the electronic structure of a molecule of YZ. What could Y and Z be?
Key:
Y
valence electron
of atom Y
valence electron
of atom Z
Z
A
B
C
D
6.
Z
chlorine
oxygen
oxygen
sodium
( A )
Which halogens are gases at room temperature and pressure?
A
B
C
D
7.
Y
chlorine
hydrogen
oxygen
oxygen
Bromine and fluorine
Bromine and iodine
Chlorine and fluorine
Chlorine and iodine
( C )
The table below shows some properties of two elements from Group I.
Element
Relative atomic mass
Sodium
23
Potassium
39
Melting point/°C
Boiling point/°C
Density/(g/cm3)
883
63
0.86
Which prediction is most likely to be correct?
A
B
C
D
The density of sodium is 1.53 g/cm3.
The melting point of sodium is 39°C.
The melting point of sodium is 98°C.
The boiling point of potassium is 1347°C.
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*8.
R, S, T and V represent some elements in the simplified Periodic Table below. Which statement is
true? (Note: R, S, T and V are not chemical symbols of the elements.)
S
R
T
V
transition elements
A
B
C
D
*9.
S and T have the same number of valence electrons.
R and V react to form an ionic compound.
The oxide of R is insoluble in water.
V is the most powerful oxidising agent of the four elements.
( B )
D, E and F are in the same period of the Periodic Table. The oxide of D reacts with water to form a
solution with a pH less than 7. The oxide of E reacts with water to form a solution with a pH greater
than 7. The oxide of F is soluble in both hydrochloric acid and aqueous sodium hydroxide. What is
the order of elements D, E and F in terms of increasing proton number? (Note: D, E and F are not
chemical symbols of elements.)
A
C
D, E, F
E, D, F
B
D
D, F, E
E, F, D
( D )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
(a) What determines the position of an element in the Periodic Table?
The proton number of the element and the number of valence electrons in the atom of
the element
(b) Indium (In) is in Group III and Period 5 of the Periodic Table.
(i)
In the diagram below, which shows a simplified version of the Periodic Table, mark the
symbol of indium (In).
O
Cl
In
transition elements
(ii) How many valence electrons does indium have?
Three
(iii) Predict whether indium conducts electricity. Give a reason for your answer.
Indium conducts electricity as it is a metal.
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(iv) Write the chemical formulae of indium chloride and indium oxide.
Indium chloride:
InCl3
Indium oxide:
In2O3
(v) Indium chloride reacts with water to form insoluble indium hydroxide and hydrogen
chloride gas. Write an equation for the reaction of indium chloride with water. Include
state symbols.
InCl3(aq) + 3H2O(l)
2.
In(OH)3(s) + 3HCl(g)
Carbon and silicon belong to the same group of the Periodic Table.
(a) Carbon and silicon react with hydrogen to form methane, CH4, and silane, SiH4, respectively.
(i)
Without referring to the Periodic Table, state the group in which carbon and silicon are
found. Explain how you arrived at your answer.
Group IV. Both carbon and silicon have the oxidation state +4 in their compounds. This means
that they have four valence electrons and hence belong to Group IV.
(ii) Methane is used as a fuel. It forms carbon dioxide and water when burnt. Predict the
products that are formed when silane burns in oxygen.
Silicon dioxide and water
(b) The chemical formula of sodium carbonate is Na2CO3. Predict the formula of sodium silicate.
Na2SiO3
3.
Caesium, an element in Group I of the Periodic Table, is a liquid at room temperature. It is used in
atomic clocks. Atomic clocks are very accurate time-measurement devices.
Caesium reacts explosively with cold water and also reacts with ice at −110°C.
(a) Describe the trend in the melting points of Group I elements down the group.
The melting points of Group I elements decrease down the group.
(b) State the chemical formulae of
(i)
CsCl
caesium chloride;
(ii) caesium sulfide;
Cs2S
(iii) caesium sulfate;
Cs2SO4
(iv) the products of the reaction between caesium and water.
CsOH and H2
(c) Explain why caesium reacts with ice at −110°C but lithium does not.
The reactivity of Group I metals increases down the group. Caesium is below lithium in the Periodic
Table. Thus, it is more reactive than lithium.
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4.
Element X has the electronic configuration 2, 8, 7. Element Y is above X in the Periodic Table.
(a) Which element, X or Y,
(i)
X
has a higher boiling point;
(ii) has a lighter colour;
Y
(iii) will displace the other element from its salt solution?
Y
(b) Element Z is an unreactive element. It is found next to X in the Periodic Table.
(i)
Which group does Z belong to?
Group 0
(ii) In terms of electronic configuration, explain why X is reactive but not Z.
X is reactive because its outer shell contains seven electrons and it needs to accept only one
electron to form a stable octet electronic configuration. Z is unreactive as its atoms have fully
filled outer shells and thus do not gain or lose electrons.
Section C: Free-Response Questions
Answer the following questions.
1.
(a) Sodium, potassium and rubidium are Group I metals. Explain the following properties of the
Group I metals. Write equations, if any, to support your explanation.
(i)
Group I metals are powerful reducing agents.
Reducing agents give away electrons. Sodium, potassium and rubidium give away their valence
electrons readily to form ions with a charge of +1: Na
Na+ + e–
(ii) Freshly cut potassium rapidly tarnishes in air.
Potassium is a very reactive metal. It reacts with oxygen in the air to form a layer of potassium
oxide: 4K(s) + O2(g)
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2K2O(s)
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(iii) Rubidium reacts more vigorously with water than potassium does.
The reactivity of Group I metals increases down the group. The equation for the reaction of
rubidium with water is: 2Rb(s) + 2H2O(l)
2RbOH(aq) + H2(g)
(b) Group 0 elements are known as noble gases. They are the least reactive elements in the
Periodic Table.
(i)
Explain the unreactivity of noble gases.
Noble gases are unreactive because their atoms have fully filled outer shells.
(ii) State one use of a noble gas in daily life and explain its importance.
Argon is used to fill electric bulbs. It provides an inert atmosphere to protect the filament from
oxidation in air.
2.
(a) Chlorine, bromine and iodine are halogens. They react in the gaseous state with hydrogen to
form hydrogen halides. Their reactions are summarised in the table below.
Halogen
(i)
Conditions and rate of reaction
chlorine
rapid reaction in the presence of light
bromine
slow reaction when heated in the presence of a catalyst
iodine
no reaction unless very strongly heated
Write a chemical equation for the reaction between hydrogen and bromine.
H2(g) + Br2(g)
2HBr(g)
(ii) Based on the data given, state whether chlorine, bromine or iodine is the strongest
oxidising agent.
Chlorine
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(b) An experiment was carried out by adding solutions of halogens A, B and C to each of their
halide solutions. The results of the experiment are shown in the table below. A tick (✓)
indicates a reaction. A cross (✗) indicates no reaction.
Halide solution of A
Halide solution of B
Halide solution of C
✓
✗
Solution of halogen A
Solution of halogen B
✗
Solution of halogen C
✓
✗
✓
The three halogens are chlorine, bromine and iodine. Based on the results given above,
(i)
arrange A, B and C according to an increasing order of reactivity and identify A, B and C;
B
Order of reactivity:
Bromine
A:
A
<
C
<
Iodine
B:
Chlorine
C:
(ii) write ionic equations for the reactions that took place.
Br2(aq) + 2I–(aq)
2Br –(aq) + I2(aq)
Cl2(aq) + 2Br –(aq)
Cl2(aq) + 2I–(aq)
3.
2Cl –(aq) + Br2(aq)
2Cl –(aq) + I2(aq)
The graph below shows the melting points and boiling points of the first 20 elements in the Periodic
Table.
Temperature/°C
5000
boiling point
melting point
4000
3000
2000
1000
0
1
--1000
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Proton number
(a) Circle the melting and boiling points of three alkali metals.
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(b) Compare the melting points of the alkali metals and other metals.
The melting points of the alkali metals are lower than those of other metals.
(c) Compare the boiling points of the alkali metals with those of other metals.
The boiling points of the alkali metals are lower than the boiling points of other metals.
(d) Rubidium is found below potassium in the Periodic Table. Predict whether rubidium has a
higher or lower boiling point than potassium. Explain your answer.
The boiling point of rubidium should be lower than that of potassium. This is because the boiling
points of alkali metals decrease down the group.
*4.
A catalyst is a substance which increases the speed of reaction. Iron and its compounds are often
used as catalysts in chemical reactions. One such example is iron(III) chloride, FeCl3. It can be
used to catalyse the reaction between sodium thiosulfate, Na2S2O8, and potassium iodide, KI.
The reaction is broken down into two steps in the presence of iron(III) chloride. The ionic equations
for these two steps are:
Step 1: 2Fe3+(aq) + 2I–(aq)
Step 2: 2Fe2+(aq) + S2O82–(aq)
2Fe2+(aq) + I2(aq)
2Fe3+(aq) + 2SO42–(aq)
(a) Based on the equations given above, write the ionic equation for the uncatalysed reaction
between Na2S2O8 and KI.
S2O82–(aq) + 2I–(aq)
2SO42–(aq) + I2(aq)
(b) The equations in steps 1 and 2 show that iron forms ions with different oxidation states. Iron
is an example of a transition metal.
(i)
Give two other examples of transition metals found in the Periodic Table.
Manganese and copper (Accept any two possible answers.)
(ii) State two other properties of transition metals.
They have high melting and boiling points and form coloured compounds.
(c) Suggest why, unlike iron(II) chloride, calcium chloride cannot be used to catalyse the reaction
between sodium thiosulfate and potassium iodide.
Iron forms compounds with variable oxidation states (+2, +3) but calcium does not (only +2).
(d) Iron is used as a catalyst in many industrial processes. Give an example of these processes.
Haber process for the manufacture of ammonia (Accept any other possible answer.)
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
Structured
Free-response
Textbook
section(s)
to revise
(a)
Describe the Periodic Table as
an arrangement of the elements
according to proton (atomic) number.
1
–
–
16.1
(b)
Describe the change in metallic
properties of the elements across a
period of the Periodic Table.
9
–
–
16.2
(c)
Relate the position of an element in
the Periodic Table to its proton number
and electronic structure.
3, 4, 5, 8
1(a), 1(b)(i)
3(a)
16.2
(d)
Describe the relationship between
group number, number of valence
electrons and metallic/non-metallic
properties.
8
1(b)(ii),
1(b)(iii)
–
16.2
(e)
Explain the similarities between the
elements in the same group of the
Periodic Table.
–
2
–
16.2
(f)
Relate the ionic charge of an element
to its group number.
1
1(b)(iv), 2(b)
–
16.2
(g)
Describe the physical and chemical
properties of Group I elements.
2, 7
3
1(a), 3(b),
3(c)
16.3
(h)
Predict the properties of Group I
elements using the Periodic Table.
7
–
3(d)
16.3
(i)
Describe the physical and chemical
properties of Group VII elements.
6
4(a)
2(a)(ii), 2(b)
16.4
(j)
Predict the properties of Group VII
elements using the Periodic Table.
–
4(b)(i)
–
16.4
(k)
Describe the Group 0 elements as
unreactive.
–
4(b)(ii)
–
16.5
(l)
Describe the lack of reactivity of the
noble gases in terms of electronic
structure.
–
–
1(b)(i)
16.5
–
–
1(b)(ii)
16.5
(m) Describe the importance of the
noble gases in providing an inert
atmosphere.
102
Multiplechoice
(n)
Describe the properties of the
transition elements.
–
–
4(b), 4(c)
16.6
(o)
State that many transition elements
and their compounds are good
catalysts.
–
–
4(c), 4(d)
16.6
(p)
Write chemical equations with state
symbols.
–
1(b)(v)
1(a)(ii),
1(a)(iii), 2(a)(i)
8.1
(q)
Write ionic equations with state
symbols.
–
–
1(a)(i),
2(b)(ii), 4(a)
8.2
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Class:
)
Worksheet 13
(
Name:
Date:
Energy Changes
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 17
ANSWER IT RIGHT!
When 1.0 mol of propane is burnt in excess oxygen, 2220 kJ of heat is liberated.
C3H8(g) + 5O2(g)
3CO2(g) + 4H2O(g)
∆H = –2220 kJ
(a) Explain why heat energy is liberated when propane burns in oxygen.
Thought Process
The energy change in a chemical reaction depends on whether the energy absorbed during bond
breaking is greater or less than the energy released during bond making.
Answer
Heat energy is liberated because the energy absorbed during bond breaking is less than the energy
released during bond making.
A common mistake in students’ answers is to say that energy is needed to form a bond. The fact is, heat
energy is taken in to break a bond and given out during bond making.
(b) Calculate the heat liberated when 2.5 mol of propane is burnt in excess oxygen.
Thought Process
The amount of heat energy released is directly proportional to the amount of propane used.
Answer
Heat liberated = 2.5 × 2220
= 5550 kJ
(c) Find the mass of propane needed to produce 1665 kJ of heat on burning.
‘Find’ is a general term. It means to calculate, measure, determine and so on.
Answer
Number of moles of propane used = 1665
2220
= 0.75 mol
Mr of propane (C3H8) = (3 × 12) + (8 × 1)
= 44
Mass of propane used = number of moles × molar mass
= 0.75 × 44
= 33 g
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TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which of the following processes is exothermic?
A
B
C
D
2.
( C )
Which of the following does not involve an endothermic change?
A
B
C
D
3.
Decomposition by heat of zinc carbonate into zinc oxide and carbon dioxide
Formation of glucose and oxygen during photosynthesis
Conversion of glucose to carbon dioxide and water during respiration
Sublimation of dry ice
An iron nail rusting in air
A few drops of ethanol drying up
A potted plant making food in sunlight
A candle melting
( A )
A thermometer is placed in water and the temperature is measured at room temperature
(Figure 1). A liquid, X, is then added to the water and the temperature is measured again
(Figure 2).
34
32
30
28
26
24
Figure 1
28
26
24
22
20
18
Figure 2
What conclusion can be drawn from Figures 1 and 2?
A
B
C
D
The
The
The
The
process of mixing liquid X and water is exothermic.
temperature increased by 3.5°C.
temperature decreased by 4.0°C.
graph that shows the temperature changes after X is added to water should be:
Temperature/°C
room
temperature
Time/min
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( D )
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4.
5.
The reaction between hydrogen and oxygen to form water occurs in three stages. In which stages
are the signs of the enthalpy changes correctly shown?
1
2
3
4H(g) + 2O(g)
2H2(g) + O2(g)
4H(g) + 2O(g)
2H2O(g)
H2O(g)
H2O(l)
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
( B )
The thermochemical equation for the formation of nitrogen monoxide (NO) in a car engine is
shown below.
1 N (g) + 1 O (g)
NO(g)
∆H = +90.5 kJ
2
2
2
2
This implies that
A
B
C
D
6.
∆H = positive
∆H = positive
∆H = negative
.
the product has more energy than the reactants
the total energy change for bond making is greater than that for bond breaking
the formation of the N–O bond in an NO molecule is an endothermic process
heat energy is released to the surroundings during the reaction
( A )
Which of the statements about the hydrogen–oxygen fuel cell is correct?
A
B
C
D
The electrolyte is dilute sulfuric acid.
At the positive electrode (cathode), oxygen is reduced to hydroxide ions.
At the negative electrode (anode), hydrogen is reduced to water.
H2O(l).
The overall reaction is: H+(aq) + OH–(aq)
( B )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
(a) (i)
The table below shows the heat of combustion of some fuels. The heat of combustion is
the amount of heat produced when 1.0 mol of a fuel is burnt completely in air. Complete
the table by calculating the heat energy liberated when 1.0 g of each fuel is completely
burnt.
Fuel
Molecular
formula
Relative
molecular
mass
hydrogen
H2
2
–286
–143
methane
CH4
16
–890
–56
ethanol
C2H6O
46
–1371
–30
butane
C4H10
58
–2877
–50
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Heat of
Heat liberated/(kJ/g)
combustion/(kJ/mol)
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(ii) Give three advantages of using hydrogen as a fuel.
It is a renewable energy resource. It is pollution free because only water is produced when
hydrogen burns. It gives out the most heat per gram of fuel.
(b) (i)
What is a fuel cell?
A fuel cell is a chemical cell in which reactants are continuously supplied to produce electricity.
(ii) In what way is a fuel cell different from an electrolytic cell in terms of energy changes?
In a fuel cell, chemical energy is converted into electrical energy. In an electrolytic cell, electrical
energy is converted into chemical energy.
2.
The bond energies of some bonds are given in the table below.
Bond
H–H
Cl–Cl
H–Cl
C–C
C–H
C–Cl
Bond energy/(kJ/mol)
436
243
432
348
413
330
The equation for the reaction between methane (CH4) and chlorine (Cl2) to produce chloroform
(CHCl3) and hydrogen chloride (HCl) is shown below.
H
H C H + 3Cl Cl
H
Cl
H C
Cl + 3H Cl
Cl
(a) Calculate the overall enthalpy change of the above reaction.
From the equation above,
Number of moles of C–H bonds broken = 3
Number of moles of Cl–Cl bonds broken = 3
Total energy absorbed for bond breaking = (3 × 413) + (3 × 243)
= 1968 kJ
Number of moles of C–Cl bonds formed = 3
Number of moles of H–Cl bonds formed = 3
Total energy released for bond making = (3 × 330) + (3 × 432)
= 2286 kJ
∆H = Total energy absorbed for bond breaking – total energy released for bond making
= 1968 – 2286
= –318 kJ
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(b) Hence, deduce whether the reaction is endothermic or exothermic.
The overall enthalpy change of the reaction has a negative value. This indicates that the reaction is
exothermic.
*3.
The reaction between A and B to produce C and D is reversible. This means that the reaction can
proceed in both directions: the forward reaction, where A and B react to form C and D; and the
backward reaction, where C and D react to form A and B.
A+B
C+D
The energy profile diagram below shows the energy changes as the forward reaction proceeds.
Energy
E3
E2
A+B
E1
C+D
Progress of reaction
(a) What does each of the following energy changes represent?
(i)
E2 – E1 : The enthalpy change for the forward reaction
(ii) E3 – E1 : The activation energy for the backward reaction
(iii) E3 – E2 : The activation energy for the forward reaction
(b) Based on the energy profile diagram given, explain whether the forward reaction is
exothermic or endothermic.
It is an exothermic reaction because the energy of the reactants is greater than the energy of the
products.
(c) Based on your answer in (b), deduce whether heat is given out or taken in when C and D react
to form A and B.
Since the forward reaction is exothermic, the backward reaction must be endothermic. Therefore, it is
deduced that heat is taken in during the backward reaction.
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Section C: Free-Response Questions
Answer the following questions.
1.
When 1.0 mol of ethanol, CH3CH2OH, is completely burnt in oxygen, 1367 kJ of heat is liberated.
CH3CH2OH(l) + 3O2(g)
(a) (i)
∆H = –1367 kJ
2CO2(g) + 3H2O(g)
In terms of bond breaking and bond making, explain why the combustion of ethanol is
exothermic.
The energy released in forming the bonds in CO2 and H2O molecules is greater than the energy
absorbed for breaking the bonds in CH3CH2OH and O2 molecules.
(ii) What is the application of this reaction in the motor industry?
This reaction is used to power cars.
(iii) Sketch the energy profile diagram for the combustion of ethanol.
Energy
Ea
CH3CH2OH +3O2
⌬H = –1367 kJ
2CO2 + 3H2O
Progress of reaction
(b) Calculate the mass of ethanol required to produce 411 kJ of heat.
1 mol of ethanol produces 1367 kJ of heat.
Number of moles of ethanol required to produce 411 kJ of heat = 411
1367
= 0.3 mol
Mr of ethanol (CH3CH2OH) = (2 × 12) + (6 × 1) + 16
= 46
Mass of ethanol required = number of moles × molar mass
= 0.30 × 46
= 13.8 g
(c) When 1.0 mol of propanol, CH3CH2CH2OH, is burnt completely in oxygen, x kJ of heat is
liberated. Would you expect the value of x to be greater or smaller than 1367? Explain your
answer.
The value of x is expected to be greater than 1367. Each molecule of propanol contains more carbon
and hydrogen atoms than ethanol. The combustion of 1.0 mol of propanol thus produces more CO2
and H2O molecules and more heat is liberated.
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*2.
(a) In an experiment, 25.0 cm3 of hydrochloric acid was placed in an insulated container. Aqueous
sodium hydroxide of concentration 1.0 mol/dm3 was then added to the acid, 2.0 cm3 at a
time. The mixture was then stirred and the highest temperature reached was recorded after
each addition. The graph below shows the results of the experiment.
Temperature/°C
35
30
25
20
15
10
5
0
(i)
2
4
6
8
10
12
14
16
18
Volume of NaOH added/cm3
State why the reaction is exothermic.
The temperature of the mixture increased during the experiment.
(ii) From the graph, what was the maximum temperature reached and volume of sodium
hydroxide added?
31.5°C, 11.0 cm3
(iii) Calculate the concentration, in mol/dm3, of hydrochloric acid used in the experiment.
Number of moles of NaOH added = 1.0 × 11
1000
= 0.011 mol
NaOH(aq) + HCl(aq)
NaCl(aq) + H2O(l)
From the equation, 1 mol of HCl reacts with 1 mol of NaOH.
Number of moles of HCl = number of moles of NaOH
= 0.011 mol
Volume of HCl = 25.0 cm3
= 0.025 dm3
Concentration of HCl in mol/dm3 = number of moles
3
volume in dm
0.011
=
0.025
= 0.44 mol/dm3
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(b) When 1.0 mol of hydrochloric acid reacts with 1.0 mol of aqueous sodium hydroxide, 57 kJ
of heat energy is given out.
(i)
Write the ionic equation for the reaction.
H+(aq) + OH–(aq)
H2O(l)
(ii) Deduce the heat energy given out when 100 cm3 of 2.0 mol/dm3 sulfuric acid reacts
with 200 cm3 of 2.0 mol/dm3 aqueous potassium hydroxide. (Hint: Calculate the number
of moles of water formed.)
Number of moles of H2SO4 used = 2.0 × 100
1000
= 0.2 mol
2H+(aq) + SO42–(aq)
H2SO4(aq)
From the equation, 1 mol of H2SO4 produces 2 mol of H+.
Therefore, number of moles of H+ = 2 × 0.2
= 0.4 mol
Number of moles of KOH used = 2.0 × 200
1000
= 0.4 mol
Number of moles of H2O formed = 0.4 mol
Heat energy given out = 0.4 × 57
= 22.8 kJ
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the relevant
section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
110
Textbook
section(s)
to revise
Multiplechoice
Structured
Freeresponse
1, 2, 3, 4,
5
2(b), 3
1(a)(ii), 1(b),
1(c), 2(a)(i),
2(a)(ii)
17.1
(a)
Describe enthalpy change in terms of exothermic
and endothermic changes.
(b)
Describe bond breaking and bond making as
endothermic and exothermic respectively.
–
–
1(a)(i)
17.2
(c)
Explain overall enthalpy changes in terms of the
energy involved in bond breaking and bond making.
–
2
1(a)(i),
2(b)(ii)
17.2
(d)
Draw energy profile diagrams to represent
exothermic and endothermic reactions and show
the activation energies of reactions.
–
3
1(a)(iii)
17.3
(e)
Describe hydrogen as a potential fuel, which
reacts with oxygen in a fuel cell to produce
electricity.
6
1
–
17.4
(f)
Perform calculations involving the number of
moles, mass and molar mass of a substance.
–
–
1(b)
9.3
(g)
Perform stoichiometric calculations involving
concentrations of solutions.
–
–
2(a)(iii),
2(b)(ii)
10.4
(h)
Describe what is meant by neutralisation and write
the ionic equation for the neutralisation reaction.
–
–
2(b)(i)
11.2
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Class:
)
Worksheet 14
(
Name:
Date:
Speed of Reaction
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 18
ANSWER IT RIGHT!
(a) Zinc powder was added to excess dilute hydrochloric acid. The volume of hydrogen gas produced
was recorded at regular time intervals. The graph below shows the results of the experiment.
Volume of H2/cm3
80
60
40
20
0
50
100
150
200
Time/s
(i) At what time did the reaction stop? Why?
(ii) Estimate the time required for half the mass of zinc to react with dilute hydrochloric acid.
Explain your answer.
The term ‘estimate’ implies an approximate calculation of the amount or value, based on the information
given (in this case, the graph).
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Thought Process
(i) The horizontal portion of the curve shows that the reaction has stopped.
Answer
(i) 175 s. The reaction stopped because all the zinc metal had reacted.
(ii) Total volume of hydrogen produced = 74 cm3
If half the mass of zinc has reacted, the volume of hydrogen produced will be 37 cm3.
From the graph, the time taken to produce 37 cm3 of hydrogen is 35 s.
(b) The reaction between zinc and dilute hydrochloric acid is catalysed by copper(II) sulfate, CuSO4.
(i) Define the term ‘catalyst’.
‘Define’ requires you to state the meaning of the term.
(ii) Sketch the graphs of the volume of hydrogen produced against time for the reaction between
zinc and dilute hydrochloric acid with and without copper(II) sulfate.
• The term ‘sketch’ implies that your curve need not be accurately drawn on graph paper.
• However, the shape of your curve must be correct. Your curve may need to display some important
values. In this case, both graphs should start from the origin and show the same final volume of
hydrogen.
Answer
(i) A catalyst is a substance which increases the speed of a chemical reaction and remains
chemically unchanged at the end of the reaction.
(ii) Volume of H2/cm3
with CuSO4
without CuSO4
0
Time/s
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
When excess magnesium ribbon is added to dilute hydrochloric acid, the reaction gradually
becomes slower and finally stops. Which of the following statements best explains this
observation?
A
B
C
D
112
The concentration of the hydrochloric acid decreases until it finally becomes zero.
The magnesium ribbon is slowly being coated with an insoluble layer of magnesium chloride.
The magnesium ribbon gradually becomes smaller.
The temperature of the reaction mixture gradually decreases as the reaction proceeds. ( A )
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2.
Excess hydrochloric acid is added to a given mass of calcium carbonate. A graph of volume of
carbon dioxide produced against time is plotted.
Volume of CO2/cm3
40
30
20
10
0
1.0
2.0
3.0
4.0
Time/min
Which of the following statements about this experiment is true?
A
B
C
D
3.
50.0 cm3 of 1.0 mol/dm3 sulfuric acid
50.0 cm3 of 1.0 mol/dm3 hydrochloric acid
50.0 cm3 of 1.0 mol/dm3 nitric acid
100.0 cm3 of 1.0 mol/dm3 ethanoic acid
( A )
The time taken for 5.0 g of marble chips to react completely with 50 cm3 of dilute hydrochloric
acid was 10 minutes. The time taken for the same experiment would be longer than 10 minutes if
.
A
B
C
D
5.
( A )
Which of the following acids reacts the fastest when 1.0 g of magnesium powder is added to it?
(Assume that all the experiments are carried out at the same temperature.)
A
B
C
D
4.
At 2.4 minutes, all the calcium carbonate has reacted.
The reaction is complete after 3.0 minutes.
The speed of the reaction is fastest at 3.0 minutes.
The time taken for half the mass of calcium carbonate to react is 1.1 minutes.
the reaction was carried out using smaller pieces of marble chips
concentrated hydrochloric acid was used
distilled water was added to the reaction mixture
a catalyst was added to the reaction mixture
( C )
The gases, Q and R, react according to the equation:
Q(g) + R(g)
T(g)
piston
The reaction mixture is placed in a container at room
temperature as shown in the diagram. Which of the
following actions can speed up the formation of gas T?
A
B
C
D
Adding an inert gas to the mixture
Using a bigger container
Lowering the piston in the container
Placing the container in water at 0°C
mixture of
Q and R
( C )
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6.
7.
Manganese(IV) oxide, MnO2, catalyses the decomposition of hydrogen peroxide to form oxygen
and water. Which of the following statements about manganese(IV) oxide are true?
1
2
3
4
It causes hydrogen peroxide molecules to move faster.
It decreases the activation energy of the reaction.
It remains chemically unchanged after the reaction.
Its mass remains unchanged after the reaction.
A
C
1 and 2
3 and 4
( D )
Process
cracking
manufacture of ammonia
manufacture of margarine
removal of air pollutants from exhaust gases
Catalyst
calcium oxide
iron
nickel
platinum
( A )
Catalase is an enzyme commonly found in living cells. It increases the rate of decomposition
of hydrogen peroxide found in human bodies into water and oxygen gas. Which of the following
statements about catalase is most likely to be correct?
A
B
C
D
9.
1 and 3
2, 3 and 4
Catalysts are commonly used to speed up industrial processes. Which of the following is incorrect?
A
B
C
D
8.
B
D
It
It
It
It
operates effectively at all temperatures.
operates most effectively over a certain range of pH.
increases the activation energy of the decomposition of hydrogen peroxide.
increases the yield of products from the decomposition of hydrogen peroxide.
( B )
A substance, X, is added to a reaction mixture. The energy profile diagram below shows the effect
of X on the reaction.
Energy
without X
with X
reactants
products
Progress of reaction
Which of the following observations are not true?
114
1
2
3
The enthalpy change of the reaction decreases.
The activation energy of the reaction remains unchanged.
The reaction takes a shorter time to complete.
A
C
1 and 2
2 and 3
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B
D
1 and 3
1, 2 and 3
( A )
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*10. An experiment involving the decomposition of
10.0 cm3 of hydrogen peroxide of concentration
0.4 mol/dm3 was carried out at 30°C. The results
are represented by Graph I on the right.
Volume of O2/cm3
II
I
The experiment was repeated under different
conditions and the results are represented by
Graph II. Which of the following would produce
Graph II? (The mass of manganese(IV) oxide used in
both experiments was 1.0 g.)
Time/min
Experiment
Volume of hydrogen
peroxide/cm3
Concentration of
hydrogen peroxide/
(mol/dm3)
Temperature/°C
A
10.0
0.25
30
B
12.5
0.40
30
C
20.0
0.25
28
D
20.0
0.40
40
( C )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Three experiments were carried out to study the effect of particle size on the speed of reaction
between marble chips (CaCO3) and hydrochloric acid. The graphs below show how the volume of
carbon dioxide gas given off varied with time. In each experiment, a fixed volume of hydrochloric
acid and excess marble chips were used.
Volume of CO2/cm3
R
I
II
Q
III
P
0
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Time/min
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(a) State two variables that must be kept constant during the experiments.
The temperature at which the reaction occurs and the concentration of hydrochloric acid
(b) At which point, P, Q or R, on Graph I was the reaction most vigorous?
Point P
(c) Why does Graph I become horizontal at point R?
At point R, all the hydrochloric acid has been used up and the reaction has stopped. Thus, the total
volume of carbon dioxide gas produced remains constant.
(d) Which graph represents the experiment using
large marble chips;
Graph III
(ii) small marble chips;
Graph II
(iii) powdered marble?
Graph I
(i)
(e) In another experiment, 1.0 g of calcium carbonate powder was reacted with excess hydrochloric
acid at 25°C to produce v cm3 of carbon dioxide. The volume of carbon dioxide produced
against time is represented by Graph X.
Volume of CO2/cm3
2v
Y
v
X
0
Time/min
Graph Y was obtained when the experiment was repeated under different conditions. Suggest
two changes in the conditions that will produce Graph Y.
The mass of calcium carbonate powder used is 2.0 g. The experiment is carried out at a
temperature higher than 25°C./ Hydrochloric acid of a higher concentration is used.
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*2.
Wine slowly turns sour when it is exposed to air. This is due to the reaction between ethanol in the
wine and oxygen in the air to form ethanoic acid.
ethanoic acid + water
ethanol + oxygen
However, when a piece of red-hot platinum wire is suspended over ethanol vapour as shown below,
a sour smell is quickly detected and the wire continues to glow for some time.
red-hot
platinum wire
ethanol vapour
mixed with air
ethanol
(a) Deduce the role of the platinum wire in this experiment. Give a reason for your answer.
The platinum wire acts as a catalyst. It increases the speed of the reaction.
(b) Explain why the platinum wire continues to glow for some time.
The reaction between ethanol and oxygen is an exothermic process. The heat energy given out by the
reaction continues to heat the platinum wire.
(c) Sketch the energy profile diagram for the conversion of ethanol to ethanoic acid with and
without the platinum wire.
Energy
without the platinum wire
with the platinum wire
ethanol +
oxygen
Ea’
Ea
ethanoic acid
+ water
∆H = negative
Progress of reaction
(d) Use your answer in (c) to explain the effect of the platinum wire on the reaction between
ethanol and oxygen.
The activation energy of the reaction is lowered. Hence, Ea’ is less than Ea.
The enthalpy change of the reaction, ∆H, remains unchanged.
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(e) In the industrial preparation of alcoholic drinks, sugar or starch is converted into alcohol
with the use of enzymes. During the conversion, the temperature is not allowed to go above
37°C or below 14°C. Give a reason for this condition.
When the temperature is too high, the enzymes will be denatured. When the temperature is too low,
the enzymes will become inactive.
*3.
Our stomachs secrete hydrochloric acid. Antacid tablets can reduce excess acidity in our
stomachs. A student carried out six experiments to study the speed of reaction between an antacid
tablet and excess hydrochloric acid.
Volume used in the
mixture/cm3
Acid
Water
Temperature at
the start of the
experiment/°C
1
10
40
2
20
3
Experiment
Time taken for the tablet to react
completely with the acid/s
Crushed tablet
Whole tablet
20
30
35
30
22
24
30
30
20
28
18
21
4
30
20
22
22
25
5
20
30
20
26
32
6
10
40
29
24
29
(a) How would the student know that the tablet had reacted completely with the acid?
When the tablet had dissolved completely in the acid
(b) Explain why the total volume of the acid–water mixture was kept constant in all the experiments.
The total volume was kept constant so that the concentration of the acid in each experiment would be
proportional to the volume of acid used.
(c) Using the results of the experiments in the table, explain the effect each of the following
actions had on the speed of reaction between the acid and the tablet.
(i)
Crushing the tablet
The speed of reaction increased. For each experiment, the time taken for the tablet to react was
always shorter for the crushed tablet than for the whole tablet.
(ii) Increasing the temperature
The speed of reaction increased. Comparing the results of Experiments 2 and 5 (or 3 and 4),
where the concentration of the acid was kept constant, a shorter time was needed for the tablet
to react completely when the temperature was increased.
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(iii) Increasing the concentration of the acid
The speed of reaction increased. Comparing the results of Experiments 1 and 5, where the
temperature was kept constant, the time taken for the tablet to react completely was shorter
when the volume (and hence concentration) of acid used was higher.
Section C: Free-Response Questions
Answer the following questions.
1.
Marble chips (calcium carbonate) react with dilute hydrochloric acid according to the equation:
CaCO3(s) + 2HCl(aq)
CaCl2(aq) + H2O(l) + CO2(g)
A conical flask containing marble chips and dilute hydrochloric acid was placed on an electronic
balance. The decrease in the mass of the reaction mixture was recorded at half-minute intervals.
The results of this experiment are shown in the table below.
Time/min
Total loss in mass/g
0.0
0.00
0.5
0.13
1.0
0.24
1.5
0.33
2.0
0.40
2.5
0.46
3.0
0.50
3.5
0.50
4.0
0.50
(a) Using the information from the table, calculate the volume, in cm3, of carbon dioxide produced
at room temperature and pressure in 1.5 minutes. (1.0 mol of any gas occupies 24 dm3
at r.t.p.)
Mass of carbon dioxide produced in 1.5 min = total loss in mass from the reaction after 1.5 min
= 0.33 g
Mr of CO2 = 12 + (2 × 16)
= 44
mass
molar mass
= 0.33
44
Number of moles of CO2 =
= 0.0075 mol
Volume of CO2 produced = number of moles × 24 000 cm3
= 0.0075 × 24 000
= 180 cm3
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(b) Using the information from the table, show that the speed of the reaction decreased with
time.
The rate of mass loss indicates the speed of reaction, i.e. how quickly the marble chips reacted with
hydrochloric acid.
Mass loss between 0–0.5 minutes = 0.13 – 0.00
= 0.13 g
Mass loss between 2–2.5 minutes = 0.46 – 0.40
= 0.06 g
Mass loss between 2.5–3.0 minutes = 0.50 – 0.46
= 0.04 g
The rate of total mass loss decreased as the reaction proceeded. This shows that the speed of the
reaction decreased with time.
(c) Explain why the speed of the reaction decreased with time.
As the reaction proceeded, the concentration of hydrochloric acid and the amount of marble chips
decreased. This caused the frequency of effective collisions between hydrochloric acid and marble
chips to decrease. Hence, the speed of reaction decreased.
(d) Suggest another method to measure the speed of the reaction.
Measure the volume of carbon dioxide produced at half-minute intervals.
2.
When aqueous sodium thiosulfate (Na2S2O3) and hydrochloric acid are mixed, a yellow precipitate
of sulfur is produced. The solution becomes increasingly cloudy as more sulfur is formed.
Na2S2O3(aq) + 2HCl(aq)
S(s) + 2NaCl(aq) + SO2(g) + H2O(l)
Four experiments were carried out to study the effect of the concentration of sodium thiosulfate
on the speed of reaction. Only the concentration of sodium thiosulfate was changed for each
experiment.
conical flask
HCl(aq) and Na2S2O3(aq)
white paper with a cross
The time taken for the cross on the paper to disappear from view was recorded.
Experiment
Time taken/s
(a) (i)
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B
C
D
110
80
50
40
Write the ionic equation for the reaction between sodium thiosulfate and hydrochloric
acid.
S2O32–(aq) + 2H+(aq)
120
A
S(s) + SO2(g) + H2O(l)
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(ii) Explain, in terms of collisions between particles, how the concentration of sodium
thiosulfate affects the speed of reaction.
When the concentration of sodium thiosulfate is increased, there are more S2O32– ions and this
increases the frequency of effective collisions between S2O32– ions and H+ ions. The speed of
reaction thus increases.
(b) Deduce which experiment had used sodium thiosulfate with the highest concentration.
Explain your answer.
Experiment D. It took the shortest reaction time which implies that the concentration of sodium
thiosulfate used was the highest compared to that used in other experiments.
(c) Suggest two conditions that should be kept constant when carrying out the experiments.
The temperature of the reactants and the concentration of hydrochloric acid
*3.
Explain each of the observations below in term of collisions between particles.
(a) Nitrogen reacts more vigorously with hydrogen at pressures above 200 atmospheres than at
1 atmosphere.
At high pressures, the nitrogen and hydrogen molecules are closer together. Thus, effective collisions
occur more frequently and this increases the speed of reaction.
(b) Placing a light stick (or glow stick) in hot water makes it glow more brightly.
In hot water, the temperature is higher and reacting particles in the light stick gain energy and move
about with greater speed, thus colliding with one another more frequently. As a result, effective
collisions occur more frequently and the speed of reaction increases, causing the light stick to glow
more brightly.
(c) When a piece of raw liver is dropped into hydrogen peroxide, there is a rapid reaction and
oxygen gas is liberated.
Enzymes present in the liver catalyse the decomposition of hydrogen peroxide to produce oxygen
gas. Enzymes are biological catalysts. The presence of enzymes lowers the activation energy of the
reaction. As a result, more reacting particles possess energy equal to or greater than the activation
energy. Effective collisions occur more frequently and hence the speed of reaction increases.
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
(a)
Explain that reactions can occur at
different speeds.
(b)
Describe the different methods that
can be used to investigate the speed
of reaction.
(c)
Describe how the speed of reaction
can be affected by concentration,
pressure, particle size and
temperature.
Structured
Freeresponse
1, 2
–
–
18.1
–
–
1(d)
18.2
3, 4, 5, 10
1(d), 3(c)
–
18.3
(d)
Explain the effects of these factors in
terms of collisions between particles.
–
–
1(c), 2(a)(ii),
3(a), 3(b)
18.3
(e)
Suggest a suitable method to
investigate the effect of a particular
variable on the speed of reaction.
–
1(a), 1(e),
3(b)
2(c)
18.3
(f)
Interpret experimental data from
investigations on the speed of
reaction.
2, 10
1(b), 1(c),
1(d), 3(a),
3(c)
1(b), 1(c),
2(b)
18.3
(g)
Define catalysts and describe the
effect of catalysts (including enzymes)
on the speed of reaction.
6, 9
2(a)
–
18.4
(h)
Explain the effect of catalysts on the
speed of reaction in terms of collisions
between particles.
–
–
3(c)
18.4
(i)
Relate the increase in speed of
reaction to pathways with lower
activation energies.
6, 9
2(c), 2(d)
3(c)
18.4
(j)
State that some compounds act
as catalysts in a range of industrial
processes.
7
–
–
18.4
(k)
State that enzymes are biological
catalysts.
8
2(e)
3(c)
18.4
(l)
Write ionic equations with state
symbols.
–
–
2(a)(i)
8.2
–
–
1(a)
9.6
(m) Perform calculations involving molar
gas volumes and the number of moles
of a gas.
122
Multiplechoice
Textbook
section(s)
to revise
(n)
Describe enthalpy change in terms of
exothermic and endothermic reactions.
–
2(b)
–
17.1
(o)
Draw energy profile diagrams to
represent exothermic and endothermic
reactions and show the activation
energies of reactions.
–
2(c)
–
17.3
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Class:
)
Worksheet 15
(
Name:
Date:
Ammonia
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 19
ANSWER IT RIGHT!
The reaction between nitrogen and hydrogen to form ammonia is a reversible reaction.
N2(g) + 3H2(g) ⇌ 2NH3(g)
The graph below shows the percentage yield of ammonia at different pressures and temperatures.
Percentage yield of NH3/%
100
200 °C
90
80
400 °C
70
60
500 °C
50
40
30
20
10
0
200
400
600
Pressure/atm
800
1000
(a) What is the percentage yield of ammonia at 400°C and 300 atm?
Answer
50%
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(b) Deduce, from the graph, the optimal conditions for the synthesis of ammonia from nitrogen
and hydrogen. Give a reason for your answer.
‘Deduce’ requires you to make use of the information provided to answer the question.
Thought Process
The graph shows two important facts:
• An increase in temperature decreases the yield of ammonia.
• An increase in pressure increases the yield of ammonia.
Hence, the conditions for obtaining a good yield of ammonia are a low temperature and a high
pressure.
Answer
The optimal conditions for the maximum yield of ammonia are 200°C and 600 atm. The graph
shows that the lower the temperature and the higher the pressure, the higher the yield of ammonia.
The yield of ammonia at 200°C does not increase at pressures above 600 atm.
• Do not get confused over speed of reaction and yield.
• An increase in temperature increases the speed of reaction. However, for some reversible reactions, an
increase in temperature decreases the yield.
• Thus, for such reactions, it is best to use a low temperature to increase the yield and a catalyst to
increase the speed of reaction.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
When 1 mol of nitrogen reacts with 3 mol of hydrogen under suitable conditions, how many moles
of ammonia will be obtained?
A
B
C
D
2.
124
Exactly 2 mol
Exactly 4 mol
Less than 2 mol
More than 4 mol
Which of the following shows the optimal conditions for manufacturing ammonia in the Haber
process?
Volume ratio of H2 : N2
Temperature/°C
Pressure/atm
Catalyst
A
1:3
250
450
platinum
B
1:3
450
250
iron
C
3:1
250
450
platinum
D
3:1
450
250
iron
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( C )
( D )
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3.
Which of the following statements about the Haber process is incorrect?
A
B
C
D
4.
In the Haber process, the yield of ammonia can be increased by
A
B
C
D
5.
( A )
.
increasing the pressure to 300 atm
increasing the temperature to 1500°C
using a mixture containing three parts of nitrogen to one part of hydrogen
using platinum as a catalyst
( A )
Which of the following mixtures produces ammonia when heated?
A
B
C
D
6.
A high temperature will increase the yield of ammonia.
It is not possible to obtain a 100% yield of ammonia.
Nitrogen is reduced by hydrogen in the process.
An iron catalyst is used to increase the speed of the reaction.
NH4NO3 + Al
NH4NO3 + NaCl
CO(NH2)2 + HCl
CH3COONH4 + Ba(OH)2
( D )
Which of the following salts will produce the greatest mass of ammonia when heated with aqueous
sodium hydroxide?
A
B
C
D
0.2 mol (NH4)2SO4
0.2 mol (NH4)3PO4
0.5 mol NH4Cl
0.5 mol NH4NO3
( B )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Ammonia is manufactured industrially by the Haber process. The raw materials used are nitrogen
and hydrogen. The Haber process is a reversible reaction.
(a) What is meant by a ‘reversible reaction’?
A reversible reaction is a reaction that can go both forward and backward at the same time.
(b) Write the chemical equation for the Haber process.
N2(g) + 3H2(g)
⇌
2NH3(g)
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(c) Briefly describe how ammonia gas can be obtained from aqueous sodium hydroxide and
ammonium dichromate(VI), (NH4)2Cr2O7. Write a balanced chemical equation for the reaction.
Ammonia is displaced from ammonium dichromate(VI) when the salt is heated with sodium hydroxide.
The equation for this reaction is:
(NH4)2Cr2O7(s) + NaOH(aq)
2.
NH3(g) + H2O(l) + Na2Cr2O7(aq)
Ammonia is widely used in the agricultural industry. It is used for manufacturing fertilisers such as
ammonium nitrate, NH4NO3, and ammonium phosphate, (NH4)3PO4. The fertilisers are a source of
nitrogen, which is required for plants to grow healthily.
(a) Calculate the percentage of nitrogen in ammonium nitrate.
Mr of ammonium nitrate, NH4NO3 = 14 + (4 × 1) + 14 + (3 × 16)
= 80
Mass of nitrogen in 1 mol of NH4NO3 = 2 × 14
= 28 g
mass of nitrogen in 1 mol of NH4NO3
× 100%
Mr of NH4NO3
= 28 × 100%
80
Percentage of nitrogen in ammonium nitrate =
= 35%
(b) A farmer added ammonium nitrate to soil that has been recently treated with calcium
hydroxide.
(i)
State one purpose of adding calcium hydroxide to the soil.
To neutralise excess acidity / increase the pH of the soil so that crops can grow healthily
(ii) Explain what happens when ammonium nitrate is added to the soil.
Calcium hydroxide will react with ammonium nitrate to form ammonia gas, which then escapes
into the atmosphere. This will cause a loss of nitrogen from the soil.
(iii) Write an equation for your answer in (b)(ii).
2NH4NO3(aq) + Ca(OH)2(aq)
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2NH3(g) + 2H2O(l) + Ca(NO3)2(aq)
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Section C: Free-Response Question
Answer the following question.
1.
The diagram below shows the Haber process for manufacturing ammonia.
process X
nitrogen
N2 : H2 = 1 : 3
process Y
converter
condenser
liquid
ammonia
hydrogen
unreacted nitrogen and
hydrogen recycled
(a) (i)
Name the processes X and Y for obtaining nitrogen and hydrogen.
Process X: Fractional distillation of liquid air
Process Y: Cracking of petroleum
(ii) Briefly describe how the mixture of nitrogen and hydrogen gases is converted into
ammonia in the converter.
The mixture of gases is compressed to 250 atm. The gases are then heated to 450°C and
passed over finely divided iron, which acts as a catalyst in the reaction. Ammonia gas is formed
as the product.
(iii) Suggest one advantage of recycling unreacted nitrogen and hydrogen in the reaction.
Recycling the unreacted gases allows more gases to react and thus helps to save costs.
(b) (i)
What volume of ammonia is expected to be produced when 36 dm3 of nitrogen
reacts with 72 dm3 of hydrogen in the reaction? (All volumes are measured at room
temperature and pressure.)
⇌
N2(g) + 3H2(g)
2NH3(g)
From the equation, 3 volumes of H2 react with 1 volume of N2.
72 dm3 of H2 will react with 24 dm3 of N2.
However, 36 dm3 of N2 is used. Therefore, H2 is the limiting reactant.
Volume of ammonia produced = 2 × 72
3
= 48 dm3
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(ii) The actual volume of ammonia produced in the reaction is less than the value obtained
in (b)(i). Explain this fact.
The reaction between nitrogen and hydrogen is a reversible process. Thus, some of the
ammonia produced will be converted back into nitrogen and hydrogen.
(iii) Explain, in terms of collisions between molecules, how an increase in pressure would
increase the speed of the reaction.
When the pressure is increased, the number of collisions between nitrogen and hydrogen
molecules per unit volume increases, leading to more effective collisions. Hence, the speed of
the reaction increases.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
128
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
State that some reactions, such as the
formation of ammonia, are reversible.
1
1(a), 1(b)
1(b)(ii)
19.1
(b)
Describe the manufacture of ammonia
from nitrogen and hydrogen.
2
–
1(a), 1(b)(ii)
19.2
(c)
Describe the operating conditions in
the manufacture of ammonia in the
Haber process.
2, 3, 4
–
1(a)(ii)
19.2
(d)
Describe the displacement of ammonia
from its salts.
5
1(c), 2(b)(ii),
2(b)(iii)
–
19.3
(e)
Write balanced chemical equations with
state symbols.
–
2(b)(iii)
–
8.1
(f)
Perform calculations involving the
number of moles, mass and molar
mass of a substance.
6
–
–
9.3
(g)
Determine the percentage composition
of compounds from given data.
–
2(a)
–
9.4
(h)
Perform stoichiometric calculations
involving the idea of limiting reactants.
–
–
1(b)(i)
10.3
(i)
Describe the reasons for controlling
the pH of soil and the methods used to
reduce excess acidity in soil.
–
2(b)(i)
–
11.4
(j)
Describe how the speed of reaction can
be affected by concentration, pressure,
particle size and temperature.
–
–
1(b)(iii)
18.3
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Class:
)
Worksheet 16
(
Name:
Date:
The Atmosphere and Environment
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 20
ANSWER IT RIGHT!
(a) Every year, a large quantity of coal is burnt as a fuel to produce electricity and heat. When coal
undergoes combustion, carbon dioxide and water vapour are produced. Discuss the effects of
carbon dioxide on the environment.
• ‘Discuss’ implies that a critical account of the issues on a topic is involved.
• In this case, the topic is ‘carbon dioxide’ and the issue to be discussed is ‘effects on the environment’.
Answer
Carbon dioxide is a greenhouse gas, which retains heat in the atmosphere. This produces a
warming effect called the greenhouse effect, which maintains a uniform temperature on the
Earth’s surface. This is important for sustaining life on Earth.
However, human activities like the burning of fossil fuels and deforestation can cause carbon
dioxide to build up rapidly in the atmosphere. This will result in global warming, which may lead to
negative consequences, such as a decrease in crop yields due to droughts.
(b) Coal also contains small quantities of sulfur. Describe the health and environmental problems
caused by sulfur when coal is burnt.
Answer
When sulfur-containing coal is burnt, sulfur dioxide is produced. Sulfur dioxide irritates the eyes
and causes breathing difficulties. It dissolves in rainwater to form acid rain. Acid rain damages
metal bridges and marble buildings. It also reduces the pH of water in rivers and lakes to below 4,
which kills fish and other aquatic life.
Do not confuse sulfur with sulfur dioxide. A common mistake is to state that ‘sulfur dissolves in water to
form acid rain’. In fact, sulfur does not react with water.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
One of the gases in clean, dry air contains two double covalent bonds in its molecule. What is the
composition (by volume) of this gas?
A
0.03%
B 1%
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C
21%
D
78%
( A )
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2.
3.
Which air pollutant is correctly matched with its source and effect on the environment?
5.
Source
Effect on the environment
A
carbon monoxide
incomplete combustion of petrol
acid rain
B
methane
decay of vegetable matter
global warming
C
sulfur dioxide
volcanic eruption
global warming
D
ozone
photochemical reaction
acid rain
( B )
When coal burns, sulfur dioxide is produced. Which of the following pairs of chemicals is used to
remove sulfur dioxide present in flue gases?
A
C
4.
Air pollutant
CaSO4 and CaCO3
CaO and CaSO4
B
D
CaSO3 and CaSO4
CaCO3 and CaO
( D )
Which of the following statements about ozone are correct?
1
2
3
4
The ozone layer filters out some of the harmful ultraviolet radiation from the Sun.
Ozone is an air pollutant in the upper layer of the atmosphere.
The depletion of the ozone layer is caused by chloroalkanes such as CH2ClCCl3.
Compounds such as CFCl3 destroy the ozone layer.
A
C
1 and 3
1, 2 and 3
B
D
1 and 4
2, 3 and 4
( B )
Which of the following can cause an increase in the Earth’s average temperature?
1
2
3
Photosynthesis of plants
Burning of fuels in power stations
Respiration of plants and animals
A
C
1 and 2
2 and 3
B
D
1 and 3
1, 2 and 3
( C )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
(a) Name one air pollutant that
(i)
nitrogen dioxide
reacts with hydrocarbons to form ozone;
(ii) causes the depletion of the ozone layer;
chlorofluorocarbons (CFCs)
carbon monoxide
(iii) reacts with haemoglobin in blood.
(b) (i)
Describe how sulfur dioxide causes the formation of acid rain.
Sulfur dioxide dissolves in water to form sulfurous acid (H2SO3). In the presence of oxygen in the
air, sulfurous acid is slowly oxidised to sulfuric acid (H2SO4).
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(ii) Write balanced equations for the reactions in (b)(i).
SO2(g) + H2O(l)
H2SO3(aq)
2H2SO3(aq) + O2(g)
2.
2H2SO4(aq)
Hydrocarbons can get into the air from the incomplete combustion of fuels such as petrol,
kerosene or diesel. The table below shows the concentration of hydrocarbons in the air in a big
city from 1984 to 1995. The concentration is measured in parts per billion (ppb).
Year
1984
1985
1986
1987
1988
1989
Concentration/ppb
1630
1690
1650
1670
1660
1550
Year
1990
1991
1992
1993
1994
1995
Concentration/ppb
1560
1520
1450
1480
1480
1460
(a) Plot a graph based on the data provided in the table.
Concentration of
hydrocarbons/ppb
1700
1600
1500
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1400
Year
(b) Cars are now manufactured with catalytic converters to reduce air pollution.
(i)
What are the catalysts used in catalytic converters?
Platinum and rhodium
(ii) Based on your graph in (a), deduce the year in which it became compulsory for cars to
be fitted with catalytic converters. Explain your answer.
1989. There was a sharp drop in the concentration of hydrocarbons in the air in 1989.
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(c) Unburnt hydrocarbons contain mainly octane, C8H18. The following reaction occurs when
unburnt hydrocarbons pass through a catalytic converter.
C8H18(g) + xO2(g)
(i)
yCO2(g) + 9H2O(g)
What are the values of x and y?
x = 12.5 or 25; y = 8
2
(ii) Calculate the volume of carbon dioxide produced at r.t.p. when 285 g of octane is passed
through the catalytic converter.
Mr of C8H18 = (8 × 12) + (18 × 1)
= 114
Number of moles of C8H18 = 285
114
= 2.5 mol
C8H18(g) + 12.5O2(g)
8CO2(g) + 9H2O(g)
From the equation, 1 mol of C8H18 produces 8 mol of CO2.
Number of moles of CO2 produced = 8 × 2.5
= 20 mol
1.0 mol of any gas occupies 24 dm3 at r.t.p.
Volume of CO2 produced = 20 × 24
= 480 dm3
Section C: Free-Response Questions
Answer the following questions.
1.
(a) “Ozone is a protector and a pollutant.” Comment on this statement.
It is true that ozone is a protector. In the upper atmosphere, ozone filters out some of the harmful
ultraviolet radiation from the Sun. It is also true that ozone is a pollutant. In the lower atmosphere,
ozone forms photochemical smog which irritates the eyes and lungs and causes breathing difficulties.
(b) The structural formula of Freon-113, a chlorofluorocarbon, is shown below.
Cl F
F
C
C
F
Cl Cl
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(i)
Describe how Freon-113 causes the depletion of the ozone layer.
In the presence of sunlight, Freon-113 decomposes to form chlorine atoms. Chlorine atoms
react with ozone molecules to form chlorine oxide and oxygen, thus destroying the ozone layer.
(ii) Explain why the depletion of the ozone layer is harmful to humans.
As the ozone layer filters some of the harmful UV radiation from the Sun, the depletion of the
ozone layer will cause more UV radiation to reach the Earth’s surface. Too much UV radiation
can cause skin cancer, genetic mutations and eye damage.
2.
(a) Explain how the processes in the carbon cycle maintain the level of carbon dioxide in the
atmosphere.
In the carbon cycle, respiration, combustion of fuels, and decay and bacterial decomposition release
carbon dioxide into the atmosphere, while photosynthesis and ocean uptake remove carbon dioxide
from the atmosphere.
(b) How is global warming related to the greenhouse effect?
Greenhouse gases such as carbon dioxide trap some of the infrared radiation from the Sun. Heat
energy is thus retained in the atmosphere. This produces a warming effect called the greenhouse
effect. The rapid build-up of greenhouse gases increases the greenhouse effect. This leads to an
increase in the Earth’s average temperature, a phenomenon known as global warming.
(c) State three effects of global warming.
The rapid evaporation of water from the Earth’s surface; the melting of large quantities of ice in the
North and South Poles, which causes the rising of ocean levels and flooding in low-lying countries;
a decrease in crop yields due to droughts
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(d) Describe the effects of large-scale cutting down of forests on global warming.
Large-scale cutting down of forests reduces the number of trees. As a result, carbon dioxide is
being added to the atmosphere more quickly than photosynthesis can remove the excess gas. This
increased amount of carbon dioxide traps more heat in the Earth’s atmosphere and causes global
warming.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
134
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Describe the composition by volume of
gases present in dry air.
1
–
–
20.1
(b)
Name some common air pollutants and
state their sources.
2
1(a)
–
20.2
(c)
Describe the effects of some air
pollutants on health and the
environment.
2
1(a)(ii), 1(b)
1(a)
20.2
(d)
Describe the reactions involved in
catalytic converters to remove
combustion pollutants.
–
2(a), 2(b)
–
20.3
(e)
Describe the reactions used to reduce
the effect of acid rain and in flue gas
desulfurisation.
3
–
–
20.3
(f)
Discuss the importance of the ozone
layer.
4
–
1(a)
20.4
(g)
Discuss the problems involved with the
depletion of the ozone layer.
4
1(a)(ii)
1(b)
20.4
(h)
Describe the basic processes of the
carbon cycle.
–
–
2(a)
20.5
(i)
State that greenhouse gases such as
carbon dioxide and methane may
contribute to global warming.
5
–
2(b), 2(d)
20.5
(j)
Discuss the possible effects of an
increase in global warming.
–
–
2(c)
20.5
(k)
Write balanced chemical equations
with state symbols.
–
1(b)(ii), 2(c)(i)
–
8.1
(l)
Calculate the volumes of gaseous
reactants and products using the mole
ratio in a chemical equation.
–
2(c)(ii)
–
10.2
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Class:
)
Date:
An Introduction to Organic Chemistry
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 21
ANSWER IT RIGHT!
Worksheet 17
(
Name:
The table below shows the boiling point ranges of petroleum gas and petrol.
Substance
Boiling point range/°C
petroleum gas
below 40
petrol
40–75
(a) Explain why petroleum gas and petrol do not boil at a fixed temperature.
Thought Process
Only pure substances have fixed boiling points.
Answer
Petroleum gas and petrol are mixtures of hydrocarbons and not pure substances. Hence, they
boil over a range of temperatures.
(b) State the uses of petroleum gas and petrol.
Answer
Petroleum gas and petrol are used as fuels. Petroleum gas is used as a fuel for cooking and
heating. Petrol is used as a fuel in cars.
(c) Suggest a method to distinguish between petroleum gas and petrol.
• The term ‘suggest’ implies that there is no unique answer to the question.
• There is more than one way to distinguish between petroleum gas and petrol.
Thought Process
• We can use a chemical or physical method to distinguish between two substances.
• As petroleum gas and petrol are chemically similar (both are hydrocarbons), they can be
distinguished by a physical method.
Answer
Petroleum gas and petrol can be distinguished by their boiling points. Petroleum gas has a lower
boiling point range than petrol.
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TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
2.
Which of the following statements about a homologous series are correct?
1
2
3
All members undergo similar chemical reactions.
All members have the same functional group.
All members have the same physical properties.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
Which of the following pairs of compounds belongs to the same homologous series?
A
H H H
H H H H
H C C C H
H C C C C H
H
H
H H H
H H H H
H C C C H
H C C C C H
B
C
D
H H H H
H H
H O
H
H O
H O
H
H
H C C O C H
H
H
( A )
Which of the following statements about natural gas is correct?
A
B
C
D
It
It
It
It
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H C C O H
H H
H C C O H
136
H
H
H C C O H
3.
( A )
is obtained by the fractional distillation of crude oil.
is a renewable source of energy.
consists mainly of methane gas.
produces large amounts of soot on combustion.
( C )
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4.
The fractional distillation of a sample of crude oil produces fractions A to D. The boiling point
ranges of the fractions are given below. Which fraction has the largest molecules?
Fraction
Approximate boiling point range/°C
A
20–40
B
40–120
C
120–160
D
160–250
( D )
5.
Which statement about the fractional distillation of petroleum is correct?
A
B
C
D
6.
Liquid petroleum is pumped into the fractionating column.
The petroleum fraction collected at the top of the column has the largest relative molecular
mass.
The petroleum fraction collected at the bottom of the column has the lowest range of boiling
points.
Each petroleum fraction collected is a mixture of compounds.
( D )
Which of the following petroleum fractions is correctly matched to its use?
A
B
C
D
Fraction
bitumen
naphtha
lubricating oil
diesel oil
Use
as feedstock for the petrochemical industry
for making roads
for making polishes and waxes
as jet fuel
( C )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
(a) What is meant by ‘hydrocarbons’?
Hydrocarbons are organic compounds that contain only hydrogen and carbon.
(b) 3.0 g of a hydrocarbon was found to contain 2.4 g of carbon. What is the empirical formula of
the hydrocarbon?
Mass of hydrogen in the hydrocarbon = 3.0 – 2.4
= 0.6 g
Element
Carbon
Hydrogen
Mass/g
2.4
0.6
Relative atomic mass
12
1
Number of moles/mol
2.4 = 0.2
12
0.6 = 0.6
1
1
3
Mole ratio
∴ The empirical formula of the hydrocarbon is CH3.
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2.
Chloromethane is the first member of the homologous series of chloroalkanes. The table below
gives information about chloromethane and the next two members.
(a) Deduce the full structural formula of chlorobutane and predict its physical properties.
Name
Formula
H
Boiling point/°C
Solubility in water
–23.8
insoluble
12.5
insoluble
46.6
insoluble
> 46.6
insoluble
H C Cl
chloromethane
H
H H
H C C Cl
chloroethane
H H
H H H
H C C C Cl
chloropropane
H H H
H H H H
chlorobutane
H C C C C Cl
H H H H
(b) When chloromethane is boiled with sodium hydroxide solution, methanol is obtained.
H
H
H C Cl + NaOH
H C O H + NaCl
H
Chloromethane
H
Methanol
Deduce the name of the organic product obtained when chloropropane is boiled with sodium
hydroxide solution. Write an equation for this reaction, showing the full structural formulae of
the organic compounds.
H H H
H C C C
H H H
Cl + NaOH
H C C C O H + NaCl
H H H
3.
H H H
Propanol
The pie charts below show the energy sources used by countries A and B.
natural gas
hydropower
coal
hydropower
natural
gas
crude
oil
biomass
Country A
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biomass
coal
nuclear power
crude
oil
Country B
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(a) Name the renewable and non-renewable sources of energy used by country A.
Hydropower, biomass
Renewable sources:
Coal, natural gas, crude oil
Non-renewable sources:
(b) Which country, A or B, is a better model for Singapore to follow in terms of the types of energy
sources used? Give two reasons to justify your answer.
Country A. It uses more renewable energy sources (hydropower and biomass) and fewer
non-renewable energy sources (coal, natural gas and crude oil) than country B.
Section C: Free-Response Question
Answer the following question.
1.
The diagram below represents a fractionating column where petroleum is separated into various
fractions.
X
Y
petroleum
vapour
(a) (i)
Z
Explain how petroleum fractions are separated in the fractionating column.
Petroleum is heated into a vapour in the furnace and passed into the fractionating column.
As the hot vapour rises up the column, it begins to cool and condense. Petroleum fractions
with lower boiling points are collected at the top of the column as gases and those with higher
boiling points are collected at the lower sections of the column.
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(ii) Match X, Y and Z with the petroleum fractions naphtha, kerosene and lubricating oil.
X:
(b) (i)
Naphtha
Kerosene
Y:
Z:
Lubricating oil
Can simple distillation be used to separate petroleum into various fractions? Why?
No. It is difficult to separate mixtures of liquids with boiling points that are close to one another
by simple distillation.
(ii) State the main difference between the apparatus used for fractional distillation and
simple distillation.
A fractionating column is used in fractional distillation but not in simple distillation.
(c) Describe the issues relating to the competing uses of petroleum as an energy source and
chemical feedstock.
About 90% of all the petroleum produced is used as fuel to generate heat and electricity. Another 10%
is used as chemical feedstock for the manufacture of petrochemicals and medicines. Petroleum is a
non-renewable resource and the Earth’s petroleum reserves are finite. With the supply of petroleum
decreasing rapidly, there is a growing need for its conservation.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
140
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
1, 2
1(a), 2
–
21.1
(a)
Define a homologous series.
(b)
Describe petroleum as a mixture of
hydrocarbons.
5
–
–
21.2
(c)
Name natural gas and petroleum as
sources of energy.
3
3(a)
–
21.2
(d)
Describe the fractional distillation of
petroleum.
4, 5
–
1(a)(i), 1(b)
21.2
(e)
Name the petroleum fractions and
state their uses.
6
–
1(a)(ii)
21.2
(f)
Describe the issues related to the
competing uses of petroleum.
–
3(b)
1(c)
21.3
(g)
Determine the empirical and
molecular formulae of a compound
from given data.
–
1(b)
–
9.5
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Class:
)
Worksheet 18
(
Name:
Date:
Alkanes and Alkenes
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 22
ANSWER IT RIGHT!
(a) What is meant by ‘unsaturated hydrocarbons’?
• When asked to define a term consisting of two words, you have to define both words.
• In this case, ‘hydrocarbons’ as well as ‘unsaturated’ has to be defined.
Answer
Hydrocarbons are organic compounds containing only the elements carbon and hydrogen.
Unsaturated hydrocarbons are hydrocarbons that contain one or more carbon–carbon double bonds.
(b) The structural formulae of six hydrocarbons are shown below.
A
B
C
CH2
H H H H H
CH2
CH
CH2
CH
CH2
CH2
H C C C C C H
H H
H
D
H H H H H
H C C C C C H
H H H H H
CH2
CH2
E
F
H
CH2
H
H C H
H C H
H
H
H H
H C C C C H
H H H H
(i)
CH2
H H
H C C C C H
H H
Classify these hydrocarbons as saturated or unsaturated hydrocarbons.
• ‘Classify’ means putting things in groups based on common characteristics.
• In this case, the common characteristic to consider is whether the hydrocarbons contain the C=C bond.
(ii) Which of these hydrocarbons are isomers?
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Thought Process
(i) Saturated hydrocarbons do not contain C=C bonds, whereas unsaturated hydrocarbons
contain one or more C=C bonds.
(ii) Isomers are compounds with the same molecular formula but different structural formulae.
Answer
(i) Saturated hydrocarbons: C, D and E
Unsaturated hydrocarbons: A, B and F
(ii) A, C and F; D and E
Note that isomers need not belong to the same homologous series. For example, A is an alkene, whereas
C is a cycloalkane.
(c) B is called cyclohexene. It is a hydrocarbon with a cyclic structure. Deduce the molecular and
structural formulae of cyclohexane.
Thought Process
‘Cyclo’ suggests a cyclic structure. ‘Hexane’ refers to a saturated hydrocarbon with six carbon
atoms per molecule.
Answer
Molecular formula: C6H12
CH2
Structural formula:
CH2
CH2
CH2
CH2
CH2
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which statement about methane and ethane is correct?
A
B
C
D
2.
Relative molecular mass of P
70
70
72
72
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( D )
Alkanes P and Q have the molecular formulae CxH12 and C14Hy respectively. What are the relative
molecular masses of P and Q?
A
B
C
D
142
They are liquids at room temperature.
They are unsaturated hydrocarbons.
They have the general formula CnH2n.
They contain carbon and hydrogen only.
Relative molecular mass of Q
194
196
198
200
( C )
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3.
Alkenes L and M are isomers. Which statement about L and M is incorrect?
A
B
C
D
4.
6.
( D )
They are soluble in water.
They have different general formulae.
Octane is more viscous than hexadecane.
Octane is more flammable than hexadecane.
( D )
Which of the following reactions is correctly matched with the type of reaction?
1
2
3
4
Reaction
C2H5OH
C2H4 + H2O
C2H4 + Cl2
C2H4Cl2
C2H4 + 3O2
2CO2 + 2H2O
C8H18
C2H4 + C6H14
A
B
C
D
1 and 2
1 and 3
1, 3 and 4
2, 3 and 4
Type of reaction
addition
substitution
redox
substitution
( B )
Which statement about the reaction of ethene with hydrogen is correct?
A
B
C
D
7.
have the same empirical formula.
have the same molecular formula.
contain the same percentage by mass of carbon.
have the same boiling point.
Octane (C8H18) and hexadecane (C16H34) are used as fuels. Which statement about these two
alkanes is correct?
A
B
C
D
5.
They
They
They
They
The
The
The
The
reaction is catalysed by sunlight.
reaction is carried out at 60 atm.
product has a lower molecular mass than ethene.
product is an alkane.
( D )
The structural formula of 2-butene is shown below.
H H H H
H C C C C H
H
H
2-Butene reacts with steam to form a product, Z. What is the structural formula of Z?
H H H H
A
H H H H
B
H C C C C H
H C C C C O H
H H H H
C
H
H H H H
H
H
H
H
C
C
C
C
H
H
OH H
D
H
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H
H
H
H
H
C
C
C
C
H
OH OH H
H
( C )
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*8.
The alkene, C4H8, reacts with bromine to form the following compound.
H
H
C
H
H
H
H C
C
C Br
H Br H
What is the structural formula of the alkene?
A
B
H H H H
H H H H
H C C C C H
H C C C C H
H H
C
H
D
H
H
H C H
H
H
H C H
H
H H
H C C C H
H
H C C C C H
H
( C )
H H
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
The molecular formulae of six hydrocarbons are shown below.
C6H14
C7H14
C7H16
C8H16
C9H20
C10H20
(a) Which of these hydrocarbons are alkanes?
C6H14, C7H16, C9H20
(b) Which of the alkanes in (a)
(i)
has the highest boiling point;
C9H20
(ii) gives out the least heat (per mole) on complete combustion;
C6H14
(iii) burns with the smokiest flame?
C9H20
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(c) 20 cm3 of C8H16 was burnt in 300 cm3 of oxygen.
(i)
Write a balanced chemical equation for this reaction.
C8H16(l) + 12O2(g)
8CO2(g) + 8H2O(g)
(ii) What is the volume of oxygen that remained unreacted at the end of the reaction?
(All volumes are measured under the same conditions.)
From the above equation, 1 mol of C8H16 reacts with 12 mol of O2.
Volume of oxygen reacted = 12 × volume of C8H16
= 12 × 20
= 240 cm3
Volume of oxygen that remained unreacted = 300 – 240
= 60 cm3
2.
(a) (i)
Draw the full structural formula of butane.
H H H H
H C C C C H
H H H H
(ii) Draw the full structural formula of the isomer of butane.
H H H
H C C C H
H
H
H C H
H
(b) On complete combustion, 1.0 mol of alkane P produces 3.0 mol of carbon dioxide. P reacts
with chlorine under UV light to produce Q and hydrogen chloride. The relative molecular mass
of Q is 78.5.
(i)
What is the molecular formula of alkane P? Explain how you arrived at your answer.
The general formula of an alkane is CnH2n+2. Since alkane P contains three carbon atoms per
molecule, the molecular formula of P is C3H(2×3)+2, i.e. C3H8.
(ii) Show that the molecular formula of Q is C3H7Cl.
The equation for the reaction of P, C3H8, with chlorine under UV light is:
C3H8 + Cl2
UV light
C3H7Cl + HCl
Relative molecular mass of C3H7Cl = (3 × 12) + (7 × 1) + 35.5
= 78.5
Thus, the molecular formula of Q is C3H7Cl, as confirmed by the equation and relative molecular
mass given.
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(c) Dichloromethane, CH2Cl2, is a volatile liquid. It is used as a solvent to dissolve a wide range
of organic compounds. In the food industry, it is used to remove caffeine, a stimulant found
in coffee. Dichloromethane undergoes a photochemical substitution reaction with chlorine
gas to form trichloromethane.
(i)
Why is the reaction described as a ‘photochemical substitution reaction’?
The reaction takes place only in the presence of ultraviolet light/sunlight and a hydrogen atom in
the dichloromethane molecule is substituted by a chlorine atom.
(ii) Write an equation for this reaction.
CH2Cl2(l) + Cl2(g)
3.
UV light
CHCl3(l) + HCl(g)
An experiment is carried out in the school laboratory using the apparatus as shown below.
broken porous pot
containing aluminium oxide
mixture of gases
glass wool soaked
in liquid petroleum
heat
water
A petroleum fraction containing a mixture of hydrocarbons, C12H26 and C18H38, is used for the
experiment. The equations for the reactions that take place are as follows:
C12H26
C18H38
(a) (i)
C6H12 + C4H8 + X
C10H20 + C8H16 + Y
Name the above process and state its purpose.
Cracking. It breaks down hydrocarbons with long carbon chains into smaller molecules.
(ii) What is the application of this process in the industry?
To produce more useful fractions such as petrol, ethene and hydrogen, which are in high
demand
(b) Identify X and Y in each of the above equations.
X is ethane, C2H6. Y is hydrogen, H2.
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*4.
The flow chart below shows the reactions of a hydrocarbon, L.
+ Cl2(g)
UV light
hydrocarbon M
C3H7Cl + HCl
+ H2 200°C, Ni
+ steam
colourless liquid P
hydrocarbon L
+ excess O2
colourless gas Q
colourless gas R
(a) Identify L and M and draw their full structural formulae.
(i)
Propene
L:
(ii) M:
Full structural formula of L:
Full structural formula of M:
H H H
H H H
H C C C H
H C C C H
H
(b) (i)
Propane
H H H
Write an equation for the formation of P from L, showing the full structural formulae of P
and L.
H H H
H C C C H + H2O
H
H
L
H
H
H
C
C
C
H
OH H
H
P
(ii) State the conditions for the reaction.
Temperature: 300°C; pressure: 60 atm; catalyst: phosphoric(V) acid
(c) At room temperature, Q is a gas and R is a liquid. Identify Q and R.
Q is carbon dioxide and R is water.
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Section C: Free-Response Questions
Answer the following questions.
1.
The table below shows the boiling points (in kelvin) of five hydrocarbons. (The kelvin (K) is the S.I.
unit for temperature.)
Hydrocarbon
A
B
C
D
E
Number of carbon atoms per molecule
2
3
4
5
6
160
250
267
303
337
Boiling point/K
(a) Plot a graph of boiling point against number of carbon atoms for these hydrocarbons.
Boiling point/K
350
300
250
200
150
100
(b) (i)
2
3
4
5
Number of carbon atoms per molecule
6
Four of the five hydrocarbons are alkenes. Which hydrocarbon is not an alkene?
B
(ii) Explain your answer in (i).
The boiling points of the members of a homologous series gradually increase with the number of
carbon atoms in each molecule. Only B does not fall within the graph, hence it is not an alkene.
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(c) The boiling point of an alkene is 160 K. Calculate the relative molecular mass of the product
obtained when this alkene reacts with excess aqueous bromine.
From the table given, the alkene is ethene, C2H4.
C2H4 + Br2
C2H4Br2
Relative molecular mass of the product, C2H4Br2 = (2 × 12) + (4 × 1) + (2 × 80)
= 188
(d) The mass of 0.125 mol of an alkene is 7.0 g.
(i)
Identify this alkene.
Relative molecular mass of the alkene = 7.0
0.125
= 56
The general formula of an alkene is CnH2n.
12n + 2n = 56
14n = 56
n =4
There are four carbon atoms in each molecule of the alkene.
∴ The alkene is butene.
(ii) What is the boiling point of this alkene?
267 K
2.
(a) What is meant by ‘polyunsaturated’ when applied to food products?
It means that the food products contain polyunsaturated fats and oils. The hydrocarbon chains in
these fats and oils contain more than one carbon–carbon double bond.
(b) Describe how margarine is produced.
Margarine is produced by the addition of hydrogen to unsaturated vegetable oil (hydrogenation).
A temperature of 200°C and a nickel catalyst are needed for hydrogenation to occur.
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(c) The structure of a fat molecule is represented as follows:
C17H27
rest of the fat molecule
hydrocarbon
chain
Is the fat molecule saturated or unsaturated? Explain your deduction.
Assuming that the fat molecule is saturated, the formula of its hydrocarbon chain should be
C17H(2×17)+1, that is, C17H35. However, the hydrocarbon chain has the formula C17H27, which is eight
hydrogen atoms fewer than that of a saturated hydrocarbon chain. This implies that the hydrocarbon
chain contains four C=C bonds and the fat molecule is unsaturated.
*3.
Dienes are alkenes with two carbon–carbon double bonds. An example of a diene is butadiene,
which has the molecular formula C4H6.
(a)
Draw the full structural formula of butadiene.
H H H H
H C C C C H
(b) (i)
Compare butadiene and butane in terms of structure and reactivity.
Both butadiene and butane contain only carbon and hydrogen. Butadiene contains
carbon–carbon double bonds, whereas butane contains only carbon–carbon single bonds.
Butane is generally unreactive, whereas butadiene is very reactive.
(ii) Suggest a method to distinguish between butadiene and butane. In each case, describe
what would be observed and write an equation for any reaction that occurs.
Aqueous bromine can be used. When butadiene is added to aqueous bromine, the
reddish-brown bromine solution decolourises immediately.
H H H H
H C = C C = C H + 2Br2
H H H H
H C C
C C H
Br Br Br Br
H H H H
(Or H C = C C = C H + Br2
H H H H
H C C
C = C H)
Br Br
When butane is added to aqueous bromine, the reddish-brown solution remains unchanged.
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(c) Student A predicts that butadiene forms butene during hydrogenation, whereas student B
predicts the product to be butane. Both their predictions are correct.
(i)
What is meant by ‘hydrogenation’?
Hydrogenation is the addition of a hydrogen molecule to a carbon–carbon double bond.
(ii) Explain the two different predictions made by students A and B. Write equations to
support your explanation.
Student A’s prediction is based on the partial hydrogenation of butadiene, i.e. only one of the
C=C bonds is hydrogenated.
H H H H
H H H H
H C C C C H + H2
H C C C C H
H H
Butene
Student B’s prediction is based on the complete hydrogenation of butadiene, i.e. both C=C
bonds are hydrogenated.
H H H H
H H H H
H C C C C H + 2H2
H C C C C H
H H H H
Butane
(d) A 20 cm3 gaseous mixture contains methane and butadiene. On complete combustion,
44 cm3 of carbon dioxide is produced.
(i)
Write balanced chemical equations for the complete combustion of methane and
butadiene.
CH4(g) + 2O2(g)
2C4H6(g) + 11O2(g)
CO2(g) + 2H2O(g)
8CO2(g) + 6H2O(g)
(ii) Calculate the volumes of methane and butadiene in the gaseous mixture.
Let the volume of CH4 be v cm3.
Thus, volume of C4H6 = (20 – v) cm3
From the equations,
1 volume of CH4 produces 1 volume of CO2 and 1 volume of C4H6 produces 4 volumes
of CO2.
Volume of CO2 produced by methane = v cm3
Volume of CO2 produced by butadiene = 4(20 – v) cm3
Total volume of CO2 produced = 44
v + 4(20 – v) = 44
v + 80 – 4v = 44
3v = 36
v = 12
Volume of CH4 = 12 cm3
Volume of C4H6 = 20 – 12
= 8 cm3
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
152
Structured
Freeresponse
Textbook
section(s)
to revise
1, 2
1(a), 2(b)(i)
–
22.1
Multiplechoice
(a)
Describe the alkanes as a homologous
series of saturated hydrocarbons with
the general formula CnH2n+2.
(b)
Name the first four alkanes.
–
4(a)(ii)
–
22.1
(c)
Describe the characteristics of the
alkane homologous series.
–
1(b)
–
22.1
(d)
Draw the structures of the first four
branched and unbranched alkanes.
–
2(a)(i),
4(a)(ii)
–
22.1
(e)
Define isomerism and identify isomers.
3
2(a)(ii)
–
22.1
(f)
Explain why alkanes show a gradation
in their physical properties down the
homologous series.
4
1(b)
–
22.2
(g)
Describe the chemical properties of
alkanes.
–
1(c)(i),
2(b)(ii), 2(c)
3(d)(i)
22.2
(h)
Describe the alkenes as a homologous
series of unsaturated hydrocarbons with
the general formula CnH2n.
–
–
1(a), 1(b),
3(a)
22.3
(i)
Name the first three alkenes.
–
4(a)(i)
1(d)
22.3
(j)
Describe the characteristics of the
alkene homologous series.
–
–
1(b)
22.3
(k)
Draw the structures of the first three
branched and unbranched alkenes.
7, 8
4(a)(i), 4(b)(i)
–
22.3
(l)
Describe the chemical properties
of alkenes.
5, 6, 7
4(b), 4(c)
1(c), 3(c),
3(d)(i)
22.4
(m) Describe the manufacture of alkenes
and hydrogen.
–
3(a)(i), 3(b)
–
22.5
(n)
Explain the importance of cracking.
–
3(a)(ii)
–
22.5
(o)
Describe the differences between
saturated and unsaturated
hydrocarbons.
–
–
3(b)
22.6
(p)
Define the term ‘polyunsaturated’ when
applied to food products.
–
–
2(a), 2(c)
22.7
(q)
Describe the manufacture of margarine.
–
–
2(b)
22.7
(r)
Write balanced chemical equations with
state symbols.
–
1(c)(i),
2(c)(ii)
3(d)(i)
8.1
(s)
Calculate relative molecular mass or
relative formula mass of a substance.
–
–
1(c), 1(d)(i)
9.2
(t)
Calculate the volumes of gaseous
reactants and products using the mole
ratio in a chemical equation.
–
1(c)(ii)
3(d)(ii)
10.2
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)
Worksheet 19
(
Name:
Date:
Alcohols and Carboxylic Acids
Go through the worked example. Use the tips to guide you in understanding and answering the
questions.
(a) (i)
for Chapter 23
ANSWER IT RIGHT!
Outline the steps involved for the conversion of glucose to ethanoic acid. Write equations
for all the reactions involved.
The term ‘outline’ means to give a brief answer without going into details.
(ii) Describe and explain the observation when copper(II) oxide is added to ethanoic acid. Write
an equation for the reaction.
Thought Process
(i) Ethanoic acid is obtained from the oxidation of ethanol, which is produced by the fermentation
of glucose.
(ii) Copper(II) oxide is a base. It reacts with ethanoic acid to form a salt and water.
Answer
(i) Step 1: Fermentation of glucose to form ethanol
Mix a glucose solution with yeast and keep the mixture at about 37°C for a few days.
Ethanol is produced.
C6H12O6(aq)
yeast
37°C
2C2H5OH(aq) + 2CO2(g)
Step 2: Oxidation of ethanol to ethanoic acid
Heat the ethanol obtained in step 1 with a mixture of potassium manganate(VII)
solution and dilute sulfuric acid. Ethanol is oxidised to ethanoic acid.
C2H5OH(aq) + 2[O]
CH3COOH(aq) + H2O(l)
(ii) Copper(II) oxide dissolves in ethanoic acid to form a blue solution of copper(II) ethanoate
and water.
CuO(s) + 2CH3COOH(aq)
(CH3COO)2Cu(aq) + H2O(l)
• Take note of the charge on the metal ion when you write the formulae of the salts of carboxylic acids.
• For example, copper exists as Cu2+ ions in copper(II) salts. Thus, the formula of copper(II) ethanoate is
(CH3COO)2Cu, not CH3COOCu.
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(b) Determine the relative molecular mass of a carboxylic acid containing six carbon atoms per
molecule.
The term ‘determine’ implies that the required quantity cannot be measured directly, but is obtained
through calculation using a formula.
Thought Process
Use the general formula CnH2n+1COOH to determine the molecular formula of the carboxylic acid
with six carbon atoms per molecule.
Answer
The general formula of a carboxylic acid is CnH2n+1COOH.
Substituting n = 5 into the formula, we have C5H(2×5)+1COOH, that is, C5H11COOH.
Thus, the molecular formula of the acid is C6H12O2.
Relative molecular mass of C6H12O2 = (6 × 12) + (12 × 1) + (2 × 16) = 116
• When counting the number of carbon atoms in a carboxylic acid, take note to include the carbon atom
of the –COOH group.
• In this case, the carboxylic acid with six carbon atoms is C5H11COOH, not C6H13COOH.
(c) 2.22 g of a carboxylic acid required 15.0 cm3 of 2.0 mol/dm3 aqueous sodium hydroxide for
complete reaction. Identify the carboxylic acid and draw its full structural formula.
When asked to draw the full structural formula or displayed formula, you must show all the bonds
between the atoms in the molecule.
Answer
3
Number of moles of NaOH = concentration in mol/dm3 × volume in cm
1000
15.0
= 2.0 ×
1000
= 0.03 mol
CnH2n+1COOH(aq) + NaOH(aq)
CnH2n+1COONa(aq) + H2O(l)
From the equation, 1 mol of CnH2n+1COOH reacts with 1 mol of NaOH.
Number of moles of CnH2n+1COOH = number of moles of NaOH
= 0.03 mol
mass
Mr of CnH2n+1COOH =
number of moles
= 2.22
0.03
= 74
12n + 2n + 1 + 12 + (2 × 16) + 1 = 74
14n = 28
n=2
The molecular formula of the acid is C2H5COOH.
Thus, the carboxylic acid is propanoic acid. Its full structural formula is:
H H O
H C C C O H
H H
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TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
Which organic compound does not belong to the same homologous series as the following
compound?
H
A
C
2.
H
OH H
C
C
C
H
H
H
CH3OH
C6H11OH
B
D
H
C5H11OH
C7H15OH
Which of the following compounds will be produced when wine is left exposed to the air for a period
of time?
A
B
O
H C O H
C
O
O
CH3 C O H
D
C2H5 C O H
H
CH3 C O H
H
3.
5.
Fermentation of glucose
Combustion of ethanol
Oxidation of propanol
Reaction of ethanoic acid with sodium carbonate
( C )
The oxidation of ethanol produces ethanoic acid and water. In this reaction, one molecule of
.
ethanol
1
2
3
4
loses one hydrogen atom
loses two hydrogen atoms
gains one oxygen atom
produces two molecules of water
A
C
1 and 2
2 and 3
B
D
1 and 4
2, 3 and 4
( C )
A carboxylic acid, Z, has a relative molecular mass of 60. What is the next member after Z in the
homologous series?
A
C
Methanoic acid
Propanoic acid
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( B )
Which of the following reactions does not produce carbon dioxide?
A
B
C
D
4.
( C )
B
D
Ethanoic acid
Butanoic acid
( C )
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6.
When compound P is heated with acidified potassium manganate(VII), compound Q is obtained.
The full structural formula of Q is shown below.
H H H O
H C C C C O H
H H H
Q
What are P and Q?
A
B
C
D
7.
Q
propanoic acid
butanoic acid
propanoic acid
butanoic acid
( D )
Compound X reacts with aqueous sodium carbonate to form a product with the molecular formula
HCO2Na. What is X?
A
C
8.
P
propanol
propanol
butanol
butanol
Methanol
Methanoic acid
B
D
Ethanol
Ethanoic acid
( C )
The properties of an organic compound, R, are shown below.
• It reacts with aqueous sodium hydroxide.
• It reacts with sodium carbonate.
• It has no reaction with bromine solution.
What could be the structure of R?
H H H
A
H C C C O H
H H H
H H O
B
H C C C O H
H H
H H H O
C
H C C C C O H
H
H O
D
H H
H C C O C C H
H
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H H
( B )
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Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
The structural formulae of six organic compounds are shown below.
A
B
H
H H
H H H
H C O C C H
H
C
H O
H C C C O H
H H
H C C O C H
H H H
E
D
H
H C C C O H
H H
H
F
H H H O
H H O
H
H H H O
H C C C C O H
H
H C C C C O C H
H H H
H
H
(a) Name the organic compounds B, C, D and E.
(i) B:
Propanol
(ii) C:
Methyl ethanoate
(iii) D:
Propanoic acid
(iv) E:
Butanoic acid
(b) Identify two pairs of isomers.
A and B; C and D
(c) Suggest a chemical test to distinguish between C and F.
Add aqueous bromine to each compound. C will have no reaction with aqueous bromine but F will
decolourise aqueous bromine.
(d) (i)
Outline a method to obtain E in the laboratory.
Add a mixture of potassium manganate(VII) solution and dilute sulfuric acid to butanol and heat
the mixture. The organic compound produced is E (butanoic acid).
(ii) Write an equation for the reaction in (d)(i), showing the full structural formulae of all the
organic compounds.
H H H H
H C C C C O H + 2[O] heat
H H H H
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H H H O
H C C C C O H + H2O
H H H
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2.
(a) From the molecular formulae of the organic compounds below, draw the structural formulae
of these compounds and name them.
(i)
(iii) C2H4O (an ester)
CH4O (an alcohol)
O
H
esterification
H C O H
H
H C O C H
H
H
methyl methanoate
methanol
(iv) HCO2Na (a salt)
(ii) CH2O2 (a carboxylic acid)
O
(b) (i)
O
+ NaOH(aq)
H C O H
H C ONa
methanoic acid
sodium methanoate
Is ethanoic acid a strong or weak acid? Explain your answer.
It is a weak acid as it ionises only partially to give hydrogen ions in aqueous solution.
(ii) Write an equation for the reaction between calcium carbonate and ethanoic acid.
CaCO3(s) + 2CH3COOH(aq)
3.
(CH3COO)2Ca(aq) + H2O(l) + CO2(g)
The flow chart below shows some reactions involving ethanol.
red solution
colourless solution W
yeast
+X
ethanol
dilute H2SO4,
heat
litmus
solution
colourless solution Y
+ C3H7OH
concentrated
H2SO4, heat
colourless solution Z
(a) Identify each of the following:
(i)
W:
(iii) Y:
Glucose
(ii) X: Potassium manganate(VII) solution
Ethanoic acid
Propyl ethanoate
(iv) Z:
(b) Draw the full structural formula of Z.
H H H
O H
H C C C O C C H
H H H
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H
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4.
(a) The structure of an organic compound, Q, is shown below.
H H H
O H H
H C C C O C C C H
H H H
(i)
H H
Name the compound Q.
Propyl propanoate
(ii) Describe how you would synthesise Q in the school laboratory.
Mix propanol with propanoic acid and add a few drops of concentrated sulfuric acid to the
mixture. Heat the mixture in a water bath. Then pour the reaction mixture into a beaker of water.
Q (propyl propanoate) formed will float on top of the water.
(iii) Write an equation for the reaction in (a)(ii).
C3H7OH(aq) + C2H5COOH(aq)
C2H5COOC3H7(aq) + H2O(l)
(b) State two commercial uses of esters.
They are used as solvents for cosmetics, perfumes and glues, and in the preparation of artificial food
flavourings.
Section C: Free-Response Questions
Answer the following questions.
1.
(a) Ethanol can be produced by the hydration of ethene or the fermentation of sugar. Complete
the table below.
Reaction
Hydration of ethene
Source of raw materials
Ethene is obtained from the
cracking of petroleum.
Sugar is obtained from
sugarcane.
Catalyst for the reaction
Phosphoric(V) acid, H3PO4
Yeast
Temperature and pressure
300°C, 60 atm
37°C, atmospheric pressure
Speed of reaction
Fast
Slow
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Fermentation of sugar
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(b) State one difference between the physical properties of ethene and ethanol.
Ethene is a gas at room temperature, but ethanol is a liquid at room temperature.
(Or: Ethene is insoluble in water but ethanol is soluble in water.)
(c) Perfumes and deodorants often contain large amounts of ethanol. Suggest two reasons why
ethanol is used in these products.
Ethanol is a good solvent (it dissolves many substances that are not soluble in water).
Ethanol is volatile (it evaporates easily at room temperature).
*2.
Gasohol is used as car fuel in some countries such as Brazil, Canada and Thailand. It is a mixture
of liquid gasoline and ethanol. Gasoline consists mainly of octane, C8H18.
(a) Write equations for the complete combustion of ethanol and octane.
C2H5OH(aq) + 3O2(g)
2CO2(g) + 3H2O(g)
2C8H18(l) + 25O2(g)
16CO2(g) + 18H2O(g)
(b) Suggest a chemical test to distinguish between ethanol and octane.
Add acidified potassium manganate(VII) to each compound and heat. The solution containing
ethanol will turn from purple to colourless. Octane will have no reaction with acidified potassium
manganate(VII).
(c) A sample of gasohol vapour in the car engine contains 25% ethanol and 75% octane. What
is the volume of carbon dioxide produced on the complete combustion of 20 dm3 of gasohol
vapour?
Volume of ethanol in the sample = 25% × 20
= 5 dm3
Volume of octane in the sample = 75% × 20
= 15 dm3
From the equations in (a), 1 mol of C2H5OH produces 2 mol of CO2. 1 mol of C8H18 produces 8 mol
of CO2.
Volume of CO2 produced by C2H5OH = 2 × 5
= 10 dm3
Volume of CO2 produced by C8H18 = 8 × 15
= 120 dm3
Total volume of CO2 = 10 + 120
= 130 dm3
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*3.
The table below gives information about the first four members of the carboxylic acid homologous
series.
Carboxylic acid
Melting point/°C
Boiling point/°C
methanoic acid
8
101
ethanoic acid
17
118
propanoic acid
–21
141
butanoic acid
–8
164
(a) State the trend in the melting and boiling points of the carboxylic acids down the series, if any.
The change in the melting points of the acids does not show a regular pattern while the boiling points
increase gradually down the series.
(b) (i)
What is the relative molecular mass of pentanoic acid?
The molecular formula of pentanoic acid is C4H9COOH, i.e. C5H10O2.
Relative molecular mass of pentanoic acid = (5 × 12) + (10 × 1) + (2 × 16)
= 102
(ii) Predict the boiling point of pentanoic acid.
Increase in boiling point between carboxylic acids with three and four carbon atoms
= 164 – 141
= 23°C
Expected boiling point of the carboxylic acid = 164 + 23
= 187°C
(c) A sample of a carboxylic acid was analysed and found to contain 0.24 g of carbon, 0.04 g of
hydrogen and 0.16 g of oxygen.
(i)
What is the empirical formula of this carboxylic acid?
Element
C
H
O
Mass/g
0.24
0.04
0.16
Relative atomic mass
12
1
16
Number of moles/mol
0.24 = 0.02
12
0.04 = 0.04
1
0.16 = 0.01
16
2
4
1
Mole ratio
The empirical formula of the carboxylic acid is C2H4O.
(ii) Deduce the name and molecular formula of the carboxylic acid.
Butanoic acid, C4H8O2 (or C3H7COOH)
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WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the relevant
section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
Structured
Freeresponse
(a)
Describe alcohols as a homologous series
containing the –OH group.
1
–
1(b)
23.1
(b)
Name and draw the structures of the first
four unbranched alcohols.
–
1(a)(i), 2(a)(i)
–
23.1
(c)
Describe the combustion and oxidation
reactions of alcohols.
2, 3, 4, 6
1(d), 3(a)(ii),
3(a)(iii)
2(a), 2(b)
23.2
(d)
Describe the formation of ethanol from the
catalytic addition of steam to ethene and the
fermentation of glucose.
3
3(a)(i)
1(a)
23.3
(e)
State some uses of ethanol.
–
–
1(c)
23.4
(f)
Describe carboxylic acids as a homologous
series containing the –COOH group.
5
–
3(a), 3(b)
23.5
(g)
Name and draw the structures of the first
four unbranched carboxylic acids.
–
1(a)(iii), 1(a)(iv),
2(a)(ii)
3(c)(ii)
23.5
(h)
Describe carboxylic acids as weak acids.
–
2(b)(i)
–
23.6
(i)
Describe the reactions of carboxylic acids
with reactive metals, carbonates and bases.
3, 7, 8
2(a)(iv),
2(b)(ii)
–
23.6
(j)
Describe the formation of ethanoic acid from
the oxidation of ethanol.
6
1(d), 3(a)(iii)
–
23.7
(k)
Describe the formation of esters from the
reaction of carboxylic acids with alcohols.
–
1(a)(ii), 2(a)(iii),
3(a)(iv), 3(b), 4(a)
–
23.8
(l)
State some uses of esters.
–
4(b)
–
23.8
–
2(b)(ii)
2(a)
8.1
(m) Write balanced chemical equations with
state symbols.
162
Multiplechoice
Textbook
section(s)
to revise
(n)
Calculate relative molecular mass or relative
formula mass of a substance.
–
–
3(b)(i)
9.2
(o)
Determine the empirical and molecular
formulae of a compound from given data.
–
–
3(c)
9.5
(p)
Calculate the volumes of gaseous reactants
and products using the mole ratio in a
chemical equation.
–
–
2(c)
10.2
(q)
Describe the properties of acids and their
reactions with metals, bases and carbonates.
–
3(a)(iii)
–
11.1
(r)
Define isomerism and identify isomers.
–
1(b)
–
22.1
(s)
Describe the chemical properties of alkanes.
–
–
2(a), 2(b)
22.2
(t)
Describe the alkenes as a homologous
series of unsaturated hydrocarbons with the
general formula CnH2n.
–
–
1(b)
22.3
(u)
Describe the differences between saturated
and unsaturated hydrocarbons.
–
1(c)
–
22.6
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Class:
)
Worksheet 20
(
Name:
Date:
Macromolecules
Go through the worked example. Use the tips to guide you in understanding and answering
the questions.
for Chapter 24
ANSWER IT RIGHT!
(a) An example of biodegradable plastic is poly(lactic acid) (PLA). It is produced from renewable
resources such as potato peels. The monomer of poly(lactic acid) is lactic acid. Potato peels are
first converted to glucose, which is then converted to lactic acid. The structural formula of lactic
acid is shown below.
CH3 O
HO
C
C
OH
H
(i) What is the chemical reaction that occurs when lactic acid is converted to poly(lactic acid)?
(ii) Write an equation to show the polymerisation of lactic acid.
(iii) Suggest one advantage and one disadvantage of using biodegradable plastics.
Thought Process
(i) • Lactic acid does not contain any C=C bond. Therefore, it cannot undergo addition
polymerisation.
• Lactic acid contains two functional groups, the hydroxyl group (–OH group) and the carboxyl
group (–COOH group).
• Hence, lactic acid can undergo condensation polymerisation to form a polyester.
Answer
(i) Condensation polymerisation
(ii)
CH3 O
CH3 O
HO
C
H
C
OH + HO
C
C
OH
removal of H2O
molecules
H
CH3 O
O
C
H
C
CH3 O
O
C
C
H
(iii) Advantage: Disposal of biodegradable plastics does not cause land pollution as these plastics
can be decomposed by bacteria.
Disadvantage: These plastics are not durable as they decompose easily.
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(b) (i) Nylon is used to make fishing lines. State two other uses of nylon.
(ii) State one disadvantage of using nylon for making fishing lines.
(iii) Nylon was invented as a substitute for silk, which was in short supply during World War II.
“Nylon is a better material for manufacturing items than silk.” Comment on this statement.
• ‘Comment’ is meant as an open-ended instruction.
• You need to recall or infer points of interest relevant to the context of the question.
• In this case, your answer could discuss whether nylon, a non-biodegradable material, is always better.
Thought Process
(iii) Nylon is a synthetic fibre that is non-biodegradable, while silk is a natural material that is
biodegradable.
Answer
(i) Nylon can be used in making parachutes and sleeping bags.
(ii) Nylon is non-biodegradable. Thus, fishing lines made of nylon can cause pollution, as they do
not decompose when thrown away.
• Do not simply write ‘nylon fishing lines cause pollution’ or ‘nylon fishing lines are dangerous to sea life’.
• You need to be more precise by describing nylon as being ‘non-biodegradable’.
(iii) Nylon is strong and can be drawn into long, thin strands without breaking. Thus, it is a better
material than silk for making items such as ropes and nets. However, in some instances,
biodegradable materials such as silk are more useful. For example, fishing lines often break
and get lost in the sea. If they are made of nylon, which is non-biodegradable, they may pollute
the sea as they do not decompose.
TEST IT!
Section A: Multiple-Choice Questions
Choose the correct answer and write its letter in the brackets provided.
1.
A section of the structure of a polymer is shown below.
F
Cl
F
Cl
C
C
C
C
Cl H Cl H
Which of the following shows the monomer of this polymer?
A
C
164
Cl H
Cl
F
C
C
C
C
F
Cl
H
H
Cl
F
F
Cl
C
C
C
C
Cl H
F
H
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B
D
( A )
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2.
Which of the following shows the correct polymer that can be obtained from the given monomer?
A
B
Monomer
Polymer
H H
H H H H
H C C H
C C C C
H H
H H H H
H Cl
Cl H Cl H
C
C
C
Cl H
C
D
3.
C
C
H Cl H Cl
CH3 Cl
CH3 H
CH3
H
C
C
C
C
C
C
H
H
Cl
H
Cl
H
H H
H H
H O C C O H
O C C O
H H
H H
Which of the following monomers reacts with H
A
O
O
O
O
H to form a synthetic fibre?
H
CH3(CH2)5
O
N H
H
D
H O C C6H4 C O H
4.
( B )
B
C6H5 C O H
C
C
H
H N (CH2)6 N H
( C )
A section of the structure of a macromolecule is shown below.
O
O H
H O
O H
H
C
C N
N C
C N
N
Which of the statements about this macromolecule is correct?
A
B
C
D
It is formed by addition polymerisation.
H O
O H
The repeat unit is N C
Its monomers are HOOC
Its monomers are HOOC
C N
N .
COOH and H O
COOH and NH2
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H
O H.
NH2.
( D )
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5.
A polymer is made from the monomers shown below.
H
H
O
H N (CH2)4 N H
O
H O C (CH2)4 C O H
Which of the following is produced when the monomers react?
A
B
C
D
6.
Hydrogen gas
Ammonia gas
A polyester
Water
( D )
Which of the following materials are non-biodegradable?
1
2
3
4
Poly(propene)
Nylon
Terylene
Wool
A
B
C
D
1 and 2
2 and 4
1, 2 and 3
1, 3 and 4
( C )
Section B: Structured Questions
Answer the following questions in the spaces provided.
1.
Teflon is used to coat the surfaces of non-stick frying pans. It is a macromolecule formed by the
addition polymerisation of tetrafluoroethene. The formula of tetrafluoroethene is given below.
F
F
C C
F
F
(a) Explain the term ‘addition polymerisation’ using Teflon as an example.
Addition polymerisation occurs when unsaturated monomer units, i.e. tetrafluoroethene, join together
to form a long-chain molecule, i.e. Teflon, as the only product without the loss of any molecules or
atoms.
(b) Draw part of the structure of the Teflon polymer, showing three repeat units.
F
F
F
F
F
F
C C C C C C
F
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F
F
F
F
F
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(c) Calculate the percentage of carbon in a Teflon molecule.
The repeat unit of Teflon is:
F
F
C C
F
F
Relative molecular mass of a repeat unit (C2F4) = (2 × 12) + (4 × 19)
= 100
Percentage of carbon in the repeat unit = 2 × 12 × 100
100
= 24%
Percentage of carbon in Teflon = 24%
2.
(a) Deduce the structural formulae and names of the monomers for the following polymers.
Polymer
Monomer
Structural formula:
H
H
H
H
H
H
C
C
C
C
C
C
Cl
H
Cl H Cl H
Poly(chloroethene)
Name:
Chloroethene
Structural formula:
H
C6H5 H
C6H5
H
C6H5
C
C
C
C
C
C
H
H
H
H
H
H
Polystyrene
Name:
Styrene
(b) State two uses of poly(ethene).
For making plastic bags/ toys/ buckets/ clingfilm
(c) ,(i)
Explain why nylon is classified as a polyamide and Terylene, a polyester.
Nylon is a polyamide because it contains many amide linkages, CONH .
Terylene is a polyester because it contains many ester linkages, COO .
(ii) Nylon and Terylene are examples of synthetic fibres. State two uses of synthetic fibres.
For making clothes/ sleeping bags/ curtains/ parachutes/ fishing lines
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3.
Poly(carbonates) are used in the manufacture of compact discs. The structure of a poly(carbonate)
is shown below.
O
C O
O
O
O C O
O C O
O
(a) Draw the repeat unit of a poly(carbonate).
O
C O
O
(b) One of the two monomers used to prepare the poly(carbonate) is phosgene. Its structural
formula is:
O
Cl C Cl
Draw the structure of the other monomer.
H O
(c) (i)
O H
What type of reaction is used to make poly(carbonates)?
Condensation polymerisation
(ii) What is the inorganic side-product in this reaction?
Hydrogen chloride
*4.
(a) Two monomer molecules are shown below. They are used to make a polymer, Y.
O
O
H O C
(i)
C O H
H O
O H
Draw the structure of Y, showing two repeat units.
O
O
C
C O
O
O C
O
C O
O
(ii) Name a synthetic polymer that has a similar structure as Y. Give a reason for your
answer.
Terylene. Both polymers are polyesters.
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(b) When a macromolecule, Z, is boiled with dilute hydrochloric acid, it breaks down to form two
organic products. The structural formulae of the two products are shown below.
O
O
H O C
(i)
H
C O H
H N
H
N H
Deduce whether Z is an addition polymer or a condensation polymer.
Condensation polymer
(ii) Draw the structure of Z, showing two repeat units.
O
O H
H O
O H
H
C
C N
N C
C N
N
Section C: Free-Response Question
Answer the following question.
1.
(a) (i)
Describe the formation of poly(propene).
The monomer for making poly(propene) is propene. Propene undergoes addition polymerisation
under high temperature and pressure and in the presence of a catalyst to form poly(propene).
(ii) Write an equation to show the reaction described in (i).
CH3 H
CH3 H
nC
C
C
C
H
H
H
H
Propene
n
Poly(propene)
(b) Poly(propene) is used for making plastic bottles. State two advantages and one disadvantage
of using plastic bottles instead of glass bottles.
Plastic bottles are lighter than glass bottles and they do not break easily. However, they are
non-biodegradable and thus cause land pollution when disposed of.
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(c) An addition polymer contains 2000 monomer units which are alkene molecules. The relative
molecular mass of the polymer is 84 000. Identify the monomer used.
Relative molecular mass of the monomer = 84 000
2000
= 42
The general formula of an alkene is CnH2n.
Relative molecular mass of CnH2n = 42
12n + (2 × 1)n = 42
14n = 42
n =3
The monomer is propene, C3H6.
WORK ON IT!
In the table below, circle the question(s) that you have answered incorrectly. Revisit the
relevant section(s) in the textbook to strengthen your understanding of the key concept(s).
Question number(s)
Learning outcomes
170
Multiplechoice
Structured
Freeresponse
Textbook
section(s)
to revise
(a)
Describe the structure of
macromolecules.
–
1(a)
–
24.1
(b)
Describe the addition polymerisation of
ethene to form poly(ethene).
–
1(a)
1(a)
24.2
(c)
Deduce the structure of a polymer from
its monomer and vice versa.
1, 2
1(b), 2(a),
3(a), 3(b),
4(a)(i),
4(b)(ii)
–
24.2
–
2(b)
–
24.2
3, 4, 5
3(c), 4(b)
–
24.3
(d)
State some uses of poly(ethene).
(e)
Describe the formation of nylon
and Terylene by condensation
polymerisation.
(f)
Describe nylon as a polyamide and
Terylene, a polyester.
–
2(c)(i),
4(a)(ii)
–
24.3
(g)
State some uses of synthetic fibres
such as nylon and Terylene.
–
2(c)(ii)
–
24.3
(h)
Describe the problem of pollution
caused by the disposal of plastics.
6
–
1(b)
24.4
(i)
Calculate the relative molecular
mass or relative formula mass of a
substance.
–
–
1(c)
9.2
(j)
Determine the percentage composition
of compounds from given data.
–
1(c)
–
9.4
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Class:
)
Trial Examination
(
Name:
Date:
Trial Examination
PAPER 1
Answer all questions.
1.
An isotope of element Z forms an ion, Z3–. The Z3– ion has 18 electrons and 17 neutrons.
What is element Z?
A
B
C
D
2.
Argon
Nitrogen
Oxygen
Phosphorus
(
)
Benzoic acid occurs naturally in some plants. It is widely used in the food industry as a food
preservative. The melting and boiling points of benzoic acid are shown below.
• Melting point: 122°C
• Boiling point: 249°C
Which of the following occurs when benzoic acid at 2000°C is cooled to 100°C?
A
B
C
D
3.
Distance between particles
increases
increases
decreases
decreases
Energy of particles
increases
decreases
decreases
increases
(
)
(
)
(
)
A student is asked to confirm the presence of Ca2+ and I– ions in a salt solution.
Which of the following observations is incorrect?
A
B
C
D
4.
Test
add ammonia solution
add sodium hydroxide solution
add barium chloride solution
add dilute sulfuric acid
Observation
no precipitate
white precipitate, insoluble in excess
yellow precipitate
white precipitate
A substance, X, has the following properties:
• Melting point: 3550°C
• Does not conduct electricity
Which of the following substances is likely to be X?
A
B
C
D
Diamond
Graphite
Copper
Poly(ethene)
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5.
The diagram below shows the electrons present in the outer shell of element R.
What is the chemical formula of the sulfate of R?
R
A
B
C
D
6.
R(SO4)2
R2SO4
R2(SO4)3
R3(SO4)2
(
)
(
)
(
)
The positions of elements X and Y in the Periodic Table are shown below.
X
Y
Which of the following is true about the two elements?
A
B
C
D
7.
Which of the following equations is not balanced?
A
B
C
D
8.
X has a higher melting point than Y.
X reacts more vigorously with water than Y.
The carbonates of X and Y are insoluble in water.
The chlorides of X and Y are covalent molecules.
2Na2O
4Na + O2
Al(OH)3 + 3HCl
AlCl3 + 3H2O
Fe2O3 + 2CO
2Fe + 3CO2
C6H12O6
2C2H5OH + 2CO2
The thermite reaction is highly exothermic. It is thus used for welding steel in railway lines. The
equation for the thermite reaction is shown below.
2Al(s) + Fe2O3(s)
Al2O3(s) + 2Fe(s)
What is the mass of iron(III) oxide, Fe2O3, needed to produce 3.0 mol of iron, Fe?
A
B
C
D
9.
(
)
(
)
Which of the following statements is true for all metals?
A
B
C
D
172
60 g
120 g
180 g
240 g
They
They
They
They
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are solids at room temperature and pressure.
have high melting points.
are denser than water.
are conductors of electricity.
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10. Which of the following changes has a positive ∆H value?
A
B
C
D
2NaOH(aq) + H2(g)
2Na(s) + 2H2O(l)
NaOH(aq) + HCOOH(aq)
HCOONa(aq) + H2O(l)
2HBr(g)
H2(g) + Br2(g)
H2O(l)
H2O(s)
(
)
(
)
11. A steel spoon is electroplated with copper in an electrolytic cell.
Which of the following statements is correct?
A
B
C
D
The electrolytic cell contains molten copper(II) sulfate.
The anode is pure copper.
Oxygen gas is liberated at the anode.
Copper dissolves to form Cu2+ ions at the cathode.
12. Alkaline cells convert chemical energy to electrical energy. They are commonly used in portable
audio devices. The reactions that occur at the electrodes of an alkaline battery are shown below.
ZnO(s) + H2O(l) + 2e–
Electrode X: Zn(s) + 2OH–(aq)
Electrode Y: 2MnO2(s) + H2O(l) + 2e–
Mn2O3(s) + 2OH–(aq)
Which of the following statements is correct?
A
B
C
D
Electrical energy is produced by the neutralisation reaction.
Zinc acts as the oxidising agent in the alkaline cell.
Oxidation occurs at electrode X.
The oxidation number of manganese decreases from +5 to +3.
(
)
13. An experiment was carried out to study the reaction between calcium carbonate (in excess) and
10 cm3 of 0.2 mol/dm3 hydrochloric acid at 25°C. Graph I shows the results of the experiment.
Volume of CO2/cm3
II
I
Time/min
Which set of conditions will produce Graph II?
Volume of
HCl/cm3
Concentration of
HCl/(mol/dm3)
Temperature/°C
A
20
0.2
20
B
20
0.1
25
C
30
0.2
30
D
10
0.1
30
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)
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14. Which reactant has undergone a reduction reaction to form the product?
Reactant
SO2
HCl
H+
CuO
A
B
C
D
Product
SO3
Cl2
H2
CuSO4
(
)
15. The enzyme, catalase, is used in the rubber industry to convert latex to foam rubber. It can also
be used as a catalyst in the decomposition of hydrogen peroxide.
2H2O2(aq)
catalase
2H2O(l) + O2(g)
The energy profile diagram for the catalysed and uncatalysed decomposition of hydrogen peroxide
is shown below.
Energy
E4
E3
E2
2H2O2(aq)
2H2O(l) + 02(g)
E1
Progress of reaction
Which of the following represents the activation energy in both reactions?
A
B
C
D
Catalysed reaction
E3 – E1
E3 – E2
E4 – E1
E4 – E2
Uncatalysed reaction
E4 – E1
E4 – E2
E3 – E1
E3 – E2
(
)
16. The reaction between lead(II) acetate and potassium chromate produces a yellow precipitate of
lead(II) chromate. Which of the following is true about the solubilities of the salts?
A
B
C
D
Lead(II) acetate
soluble
soluble
insoluble
insoluble
Potassium chromate
soluble
soluble
insoluble
insoluble
Lead(II) chromate
soluble
insoluble
insoluble
soluble
(
)
(
)
17. Which process is used to obtain hydrogen for the manufacture of ammonia?
A
B
C
D
174
Cracking of petroleum
Fractional distillation of liquid air
Fractional distillation of petroleum
Haber process
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18. Tin is below iron and above copper in the reactivity series. Which of these statements correctly
describes iron, tin and copper?
1
2
3
Their sulfates are soluble in water.
Their oxides can be reduced by carbon on heating.
Their oxides can be reduced by hydrogen on heating.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
(
)
19. 10.0 cm3 of 1.0 mol/dm3 ethanoic acid, CH3COOH, is slowly added to 20.0 cm3 of 1.0 mol/dm3
sodium hydroxide, NaOH, containing methyl orange. The reaction mixture is constantly stirred.
glass rod
10.0 cm3 of
1.0 mol/dm3 CH3COOH
20.0 cm3 of
1.0 mol/dm3 NaOH
and methyl orange
Which of the following statements is true about this experiment?
A
B
C
D
The pH of the reaction mixture is less than 7.
The colour of the indicator remains unchanged.
A precipitate of sodium ethanoate is formed.
0.02 mol of water is produced.
(
)
20. 0.02 mol of the hydroxide of a metal, M, requires 15.00 cm3 of 2.0 mol/dm3 sulfuric acid for
complete neutralisation.
What is the chemical formula of the salt produced?
A
B
C
D
MSO4
M(SO4)3
M2SO4
M2(SO4)3
(
)
21. Which of the following pairs of reactants is correctly matched with the colour change that occurs
during the reaction?
A
B
C
D
Reactants
chlorine gas and potassium iodide solution
ethanol and acidifed potassium manganate(VII)
zinc metal and copper(II) sulfate solution
iron metal and dilute sulfuric acid
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Colour change
brown to colourless
colourless to purple
blue to colourless
colourless to yellow
(
)
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22. The symbols of two elements, X and Y, are shown below.
23
11 X
16
8Y
When X reacts with Y, compound Z is formed. What is the molar mass of compound Z?
A
B
C
D
39 g/mol
55 g/mol
62 g/mol
94 g/mol
(
)
(
)
(
)
23. Which of the following contains at least two compounds?
A
B
C
D
Brass
Diamond
Petrol
Ammonium nitrate
24. A mixture containing aqueous sodium chloride and aqueous copper(II) sulfate is distilled.
water out
distillation flask
NaCl(aq) and CuSO4(aq)
water in
distillate
Which of the following is correct?
176
Temperature of
solution in the
distillation flask/°C
Thermometer
reading/°C
Distillate
A
100
100
aqueous sodium chloride
B
> 100
100
aqueous copper(II) sulfate
C
> 100
100
water
D
> 100
> 100
no distillate
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25. A solid mixture contains 1.0 mol of hydrated iron(II) sulfate, FeSO4.7H2O, and 0.5 mol of hydrated
nickel(II) sulfate, NiSO4.6H2O.
How many moles of ions are found in the solution when the solid mixture is completely dissolved
in water?
A
B
C
D
2
3
4
10
(
)
(
)
(
)
26. Four experiments are carried out to determine the conditions that cause the rusting of iron.
NaCl(aq)
NaCl(aq)
silver
iron
lead
Beaker 1
iron
Beaker 2
NaCl(aq)
NaCl(aq)
copper
iron
Beaker 3
zinc
iron
Beaker 4
In which beaker will the rusting of iron be observed?
A
B
C
D
Beaker 1 only
Beaker 4 only
Beakers 2 and 4
Beakers 1, 2 and 3
27. Which of these reactions does not occur in the blast furnace during the extraction of iron?
A
B
C
D
2CO
C + CO2
CaCO3
CaO + CO2
CaO + SiO3
CaSiO4
Fe2O3 + 3CO
2Fe + 3CO2
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28. The mass of magnesium used in the experiment below is 1.0 g.
magnesium
gas Q
glass wool
soaked in
water
heat
water
What is the mass of the product formed and the identity of gas Q?
A
B
C
D
Mass of product
more than 1.0 g
more than 1.0 g
less than 1.0 g
less than 1.0 g
Gas Q
hydrogen
oxygen
hydrogen
oxygen
(
)
29. L, M and N are Period 3 elements. They form different types of oxides as shown below.
Element
Type of oxide
L
basic
M
amphoteric
N
acidic
Which of the following shows the correct order of the elements in terms of increasing proton
number?
A
B
C
D
L, M, N
L, N, M
N, M, L
N, L, M
(
)
(
)
30. Which of the following reactions can be used to prepare lead(II) chloride?
A
B
C
D
Pb(s) + 2HCl(aq)
PbCl2(s) + H2(g)
Pb(NO3)2(aq) + 2HCl(aq)
PbCl2(s) + 2HNO3(aq)
PbCO3(s) + 2HCl(aq)
PbCl2(s) + H2O(l) + CO2(g)
PbO(s) + 2HCl(aq)
PbCl2(s) + H2O(l)
31. When compound Q is heated, a colourless gas is liberated and a white residue is obtained. The
colourless gas forms a white precipitate with limewater.
Which of the following could be compound Q?
A
B
C
D
178
Calcium nitrate
Calcium carbonate
Copper(II) carbonate
Copper(II) nitrate
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(
)
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32. Consider the set-up of a simple cell as shown below.
V
magnesium
iron
NaCl(aq)
Which statement about this simple cell is correct?
A
B
C
D
The
The
The
The
iron electrode is the negative terminal.
electrons flow from the iron electrode to the magnesium electrode.
solution turns green after some time.
magnesium electrode decreases in size.
(
)
(
)
33. Which of the following statements about methane is correct?
1
2
3
It is a colourless, odourless gas.
It is a greenhouse gas.
It causes the depletion of the ozone layer.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
34. A given volume of propane produces 13.2 g of carbon dioxide on complete combustion. What is
the mass of water produced in the reaction?
A
B
C
D
7.2 g
13.2 g
21.6 g
28.8 g
(
)
35. Ethanoic acid is a 1 acid. It is prepared by the 2 of ethanol. The reaction between ethanoic
acid and methanol produces an ester called 3 . Esters are used as 4 .
A
B
C
D
1
strong
strong
weak
weak
2
oxidation
reduction
oxidation
reduction
3
methyl ethanoate
ethyl methanoate
methyl ethanoate
ethyl methanoate
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4
flavourings
fuels
flavourings
fuels
(
)
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36. Which of the following pairs of organic compounds are not isomers?
O
H O
A
H C C O H
H C O CH3
H
H
H H H
B
H C C C O H
H H
H C O C C H
H H H
H
H H
H H H H
H
H
H C C C C H
H C C
C
C H
H
H C H
H H
H
D
H H H H
H
H C C C C H
H H C H H
H H H H
H C
C
C H
H H C H H
H
(
)
(
)
37. Aspirin is used to relieve pain. The structural formula of aspirin is shown below.
O
H
H
C
C
C
C
C
OH
C
C
O
H
C
CH3
O
H
Which of the following statements about aspirin are correct?
180
1
2
3
It contains an ester group.
It reacts with sodium carbonate solution.
It reacts with acidified potassium manganate(VII) on heating.
A
B
C
D
1 and 2
1 and 3
2 and 3
1, 2 and 3
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38. An organic compound, X, is found in coconut oil. It has the molecular formula C17H31COOH. What
can be deduced about X?
A
B
C
D
It
It
It
It
is
is
is
is
an alcohol.
an ester.
a saturated carboxylic acid.
an unsaturated carboxylic acid.
(
)
39. A student carried out some tests on compound Y. The structural formula of Y is shown below.
H H H H H
H C C C C C O H
H
H H
Which of the following observations is incorrect?
A
B
C
D
Aqueous bromine was decolourised when Y was added to it.
Effervescence was observed when sodium carbonate was reacted with Y.
The colour of acidified potassium manganate(VII) changed from purple to colourless when it
was heated with Y.
A sweet, fruity smell was detected when Y was heated with a mixture of methanoic acid and
concentrated sulfuric acid.
(
)
40. Which of the following statements about nylon is correct?
A
B
C
D
It is obtained by addition polymerisation.
The monomers of nylon are HOOC– –COOH and HO– –OH.
Each repeat unit in the nylon polymer contains two nitrogen atoms.
The combustion of nylon produces hydrogen chloride gas.
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)
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PAPER 2
Section A
Answer all questions in this section.
1.
The diagram below shows the positions of eight elements in the Periodic Table. (Note: The letters
do not represent the chemical symbols of the elements.)
H
A
E
B
D
C
F
G
(a) State the group that H belongs to in the Periodic Table.
[1]
(b) Write the electronic configuration of
(i) A;
(ii) D.
[1]
[1]
(c) State the element that
(i) gains three electrons when it forms an ion;
(ii) forms compounds with oxidation states +2 and +3;
(iii) has four valence electrons.
[1]
[1]
[1]
(d) Write the chemical formula of the compound formed when A and F combine.
[1]
[Total: 7 marks]
2.
Since 1992, it has been compulsory for all new petrol-fuelled vehicles in Singapore to be fitted
with catalytic converters in the car exhaust systems.
(a) The diagram below shows three air pollutants that are passed through a catalytic converter.
They are converted to three other gases. Identify these gases.
[2]
• unburnt hydrocarbons
• nitrogen dioxide
• carbon monoxide
catalytic
converter
• gas P
• gas Q
• gas R
(b) In terms of oxidation and reduction, state and explain the reactions that occur when unburnt
hydrocarbons pass through the catalytic converter.
[2]
(c) (i)
Write an equation for the reaction between nitrogen dioxide and carbon monoxide in the
catalytic converter.
[1]
(ii) Calculate the total volume of gaseous products obtained when 10 cm3 of nitrogen dioxide
reacts with 50 cm3 of carbon monoxide.
[2]
(d) (i) Name another air pollutant that may also be found in car exhaust fumes.
(ii) Write an equation to show how this substance is formed in car engines.
[1]
[1]
[Total: 9 marks]
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3.
An alkene, L, has a relative molecular mass of 42.
(a) What is its
(i) molecular formula;
(ii) empirical formula;
(iii) structural formula?
[2]
[1]
[1]
(b) M is a polymer produced from L.
(i) Draw the structure of M, showing three repeat units.
(ii) Name the type of chemical reaction that is used to produce M.
(iii) Suggest a use for M.
[2]
[1]
[1]
[Total: 8 marks]
4.
The diagram below shows the arrangement of outer electrons in a compound consisting of three
elements.
(a) State whether each of the following statements about this compound is true or false.
(i) It could be hydrogen cyanide, HCN.
(ii) It is a covalent compound.
(iii) It can conduct electricity.
(iv) It is an unsaturated hydrocarbon.
[2]
(b) Draw a similar diagram to show the arrangement of outer electrons in ethene, C2H4.
[3]
[Total: 5 marks]
5.
Ammonia is obtained by the Haber process.
(a) State the raw materials and conditions required for the Haber process.
[3]
(b) The graph of percentage yield of ammonia against temperature at pressures of 300 atm,
400 atm and 500 atm is shown below.
Yield of ammonia/%
100
500 atm
400 atm
300 atm
0
400 500 600 700 800
Temperature/°C
(i) What is the effect of pressure on the yield of ammonia?
[1]
(ii) The graph above shows that a lower temperature gives a higher yield of ammonia.
However, a lower temperature is not used in the Haber process. Explain why.
[1]
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(c) (i)
A factory manufactures ammonia to make fertilisers. When 2.8 tonnes of nitrogen were
used in the manufacturing process, 2.55 tonnes of ammonia were produced. Calculate
the percentage yield of ammonia. (1.0 tonne = 106 g)
[2]
(ii) Suggest why the percentage yield of ammonia calculated in (c)(i) is not 100%.
[1]
(d) Calcium hydroxide is sometimes used in agriculture to neutralise excess acidity in the soil.
However, it may react with nitrogenous fertilisers such as ammonium nitrate and release
ammonia gas into the atmosphere.
Write an equation, with state symbols, for the reaction between calcium hydroxide and
ammonium nitrate.
[2]
[Total: 10 marks]
6.
A reaction scheme is shown below.
heat
white powder
X
white residue Y
(when cold)
+
colourless
gas
+ HNO3(aq)
white precipitate Z,
soluble in excess
NH3(aq)
+ NH3(aq)
colourless
solution
+ limewater
white
precipitate
(a) Identify X, Y and Z.
[2]
(b) Outline the steps for the preparation of X, starting from Y.
[3]
[Total: 5 marks]
7.
The diagram below shows six elements, which are found in Period 3 of the Periodic Table. (The
letters A–F in the diagram do not represent the chemical symbols of the elements.)
23
11 A
28
14 B
31
15 C
32
14 D
32
15 E
37
17 F
(a) (i) Which of these elements have similar chemical properties?
(ii) State a reason for your answer in (a)(i).
[1]
[1]
(b) Deduce the number of protons, neutrons and electrons in the ion formed from F.
[2]
(c) Which element
(i) forms an oxide with a giant molecular structure;
(ii) is made up of a lattice of positive ions in a ‘sea of electrons’?
[1]
[1]
[Total: 6 marks]
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Section B
Answer three questions in this section.
The last question is in the form of an either/or question. Answer only one of the alternatives.
8.
Aluminium is used extensively for the construction of aircraft because of its low density and
resistance to corrosion.
Aluminium is extracted industrially from bauxite, an ore which contains aluminium oxide. The
diagram below shows the electrolytic cell used for the manufacture of aluminium. The electrolyte
is a mixture of molten aluminium oxide and cryolite, Na3AlF6. The function of cryolite is to lower the
melting point of aluminium oxide so that electrolysis can be carried out at a lower temperature.
carbon anode
carbon cathode
molten aluminium oxide
and cryolite
molten aluminium
tapping
hole
(a) State, with ionic half-equations, whether oxidation or reduction occurs at the
(i) carbon anode;
(ii) carbon cathode.
[2]
[2]
(b) Explain why
(i) the anodes in the electrolytic cell have to be replaced from time to time;
(ii) the melting point of aluminium oxide has to be lowered.
[2]
[2]
(c) During the extraction of aluminium from aluminium oxide, 128 tonnes of oxygen were
produced. Calculate the mass, in tonnes, of aluminium produced. (1 tonne = 106 g)
[2]
[Total: 10 marks]
9.
(a) Honeycombs in a beehive are made of beeswax, which is commercially used to make wax
paper, candles, cosmetics and polishing materials such as shoe polish and furniture polish.
Beeswax is a mixture of esters (about 74%), hydrocarbons (about 20%) and other substances
(about 6%). The esters are made from long-chain carboxylic acids and alcohols.
An ester found in beeswax has the following structural formula:
O
CH3(CH2)14
C O (CH2)29CH3
(i)
Write the chemical formulae of the organic compounds that can be used to form this
ester. State the conditions for the reaction.
[2]
(ii) Student A predicts that beeswax will melt at a constant temperature of about 62°C.
Student B predicts that it will melt at a temperature range of 62–66°C, while student C
predicts that it will melt at a temperature range of 1000–1200°C.
Which student is correct? Give reasons for your answer.
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[3]
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185
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(b) Amides are a homologous series of organic compounds containing nitrogen atoms. With the
exception of methanamide, amides are solids at room temperature and pressure. The table
below shows some information on the first two amides.
Name
Chemical formula
methanamide
HCONH2
Full structural formula
O H
H C N H
H O H
H C C N H
CH3CONH2
ethanamide
H
When ethanamide is boiled with aqueous sodium hydroxide, the following reaction occurs:
H O H
H O
H C C N H + NaOH
H
(i)
H C C ONa + NH3
H
An amide with four carbon atoms is boiled with excess aqueous sodium hydroxide.
Name the amide and organic product formed. Write an equation for the reaction, showing
the full structural formulae of the organic compounds.
[3]
O H
(ii) Name another organic compound that contains the
uses.
C N
group and state one of its
[2]
[Total: 10 marks]
EITHER
10. (a) In Experiment 1, 0.1 mol/dm3 aqueous sodium hydroxide was added slowly from a burette to
25.0 cm3 of hydrochloric acid in a conical flask. The changes in pH during the titration were
recorded by a pH probe attached to a computer as shown in Figure 1.
pH
14
12
10
8
6
4
2
0
20
40
10
30
Volume of NaOH added/cm3
Figure 1
186
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Experiment 2 was then carried out using 0.05 mol/dm3 aqueous sodium hydroxide instead.
Using the information in Figure 1, calculate the concentration, in g/dm3, of the
hydrochloric acid in the conical flask.
[4]
(ii) What is the volume of aqueous sodium hydroxide required to reach the end-point in
Experiment 2?
[1]
(i)
(b) Phosphoric acid, H3PO4, contains three hydrogen atoms. It forms three types of sodium salts,
NaH2PO4, Na2HPO4 and Na3PO4, upon reaction with aqueous sodium hydroxide.
A titration was carried out by adding 0.1 mol/dm3 aqueous sodium hydroxide slowly to
25.0 cm3 of 0.1 mol/dm3 phosphoric acid. The graph in Figure 2 shows the changes in pH
during the titration.
pH
14
12
10
8
6
4
2
50
25
75
Volume of NaOH added/cm3
Figure 2
Find the mole ratio of the acid and base used when 25.0 cm3 of 0.1 mol/dm3 aqueous
sodium hydroxide is added to 25.0 cm3 of 0.1 mol/dm3 phosphoric acid.
[2]
(ii) Using your answer in (b)(i), write an equation for the reaction between the acid and
base used.
[1]
(iii) The pH value of a salt formed during the titration can be obtained from the mid-point
of the vertical part of the titration curve. Hence, estimate the pH values of the salts,
NaH2PO4 and Na2HPO4, from Figure 2.
[2]
(i)
[Total: 10 marks]
OR
10. (a) The primary source of tin is the ore, cassiterite, which contains tin dioxide. Cassiterite is
mixed with coke and heated to a high temperature of about 1360°C in the furnace.
Predict three reactions that occur in the furnace. Write equations, including state symbols,
for these reactions.
[3]
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(b) The diagram below shows the set-up used to investigate the reduction of three metal oxides
with hydrogen.
metal oxide
hydrogen
gas burning
dry hydrogen
The table shows the appearance of each metal oxide before the experiment.
Experiment
Metal oxide
Colour of oxide at
room temperature
1
lead(IV) oxide
brown
2
aluminium oxide
white
3
copper(II) oxide
black
(i) Predict the colour change that would be observed in each experiment.
[3]
(ii) The following table shows the mass of lead(IV) oxide and lead at the start and end of the
experiment.
Mass of lead(IV) oxide at the start of the experiment/g
4.78
Mass of lead at the end of the experiment/g
4.14
Show that the empirical formula of the oxide used is PbO2.
[2]
(iii) Describe a chemical test to distinguish between aluminium oxide and copper(II) oxide.
Give a reason for your answer.
[2]
[Total: 10 marks]
188
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Answers to Trial Examination
Paper 1
1.
D
6.
A
11.
B
16.
B
21.
C
26.
D
31.
B
36.
D
2.
C
7.
C
12.
C
17.
A
22.
C
27.
C
32.
D
37.
A
3.
C
8.
D
13.
A
18.
D
23.
C
28.
A
33.
A
38.
D
4.
A
9.
D
14.
C
19.
B
24.
C
29.
A
34.
A
39.
B
5.
C
10.
C
15.
B
20.
D
25.
B
30.
B
35.
C
40.
C
Paper 2
Section A
1. (a) Group VIII/ 0
(b) (i) 2, 1
(ii) 2, 8, 4
(c) (i)
(ii)
(iii)
(iv)
2.
E
C
D
A2F
(a) Water vapour, nitrogen, carbon dioxide
[Three correct: 2 marks; two correct: 1 mark]
(b) Unburnt hydrocarbons react with oxygen and are oxidised to carbon dioxide. [1] Oxygen is
reduced to form water. [1]
(c) (i) 2NO2(g) + 4CO(g)
N2(g) + 4CO2(g)
(ii) The limiting reagent is nitrogen dioxide.
From the equation 2NO2(g) + 4CO(g)
N2(g) + 4CO2(g),
2 mol of NO2 react with 4 mol of CO to produce 1 mol of N2 and 4 mol of CO2.
∴ Volume of N2 produced = 10 = 5 cm3
2
4
Volume of CO2 produced = × 10 = 20 cm3 [1]
2
Total volume of gaseous products = 5 + 20 = 25 cm3 [1]
(d) (i) Sulfur dioxide
(ii) S(s) + O2(g)
3.
(a) (i)
SO2(g)
The general formula of an alkene is CnH2n.
Mr of L (CnH2n) = 42
12n + 2n = 42
n = 3 [1]
Therefore, the molecular formula of L is C3H6. [1]
© 2013 Marshall Cavendish International (Singapore) Private Limited
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Answers to Trial Examination
189
8/27/12 8:21 PM
(ii) CH2
H H H
(iii)
H C C C H
H
(b) (i)
CH3 H
CH3 H
CH3 H
C
C
C
C
C
C
H
H
H
H
H
H
[Correct repeat unit: 1 mark; three repeat units: 1 mark]
(ii) Addition polymerisation
(iii) For making plastic bags
4.
(a) (i) True
(ii) True
(iii) False
(iv) False
[Four correct: 2 marks; two correct: 1 mark]
(b)
H
H
C
H
C
H
Arrangement of C and H atoms is correct. [1]
Number of electrons shared between carbon atoms (C=C) is correct. [1]
Number of electrons shared between carbon and hydrogen atoms (C–H) is correct. [1]
5.
(a) Raw materials: nitrogen and hydrogen [1]
Conditions: temperature of 450°C, pressure of 250 atm, iron catalyst
[Three correct: 2 marks; two correct: 1 mark]
(b) (i) At constant temperature, the higher the pressure, the greater the yield of ammonia.
(ii) A lower temperature will result in a slower reaction, which is not desirable for the
large-scale production of ammonia.
(c) (i)
N2(g) + 3H2(g) 2NH3(g)
Mr of NH3 = 14 + (3 × 1) = 17
Mr of N2 = 2 × 14 = 28
From the equation,
Theoretical yield of ammonia = 2.8 × (2 × 17) = 3.4 tonnes [1]
28
actual
yield
× 100% = 2.55 × 100% = 75% [1]
Percentage yield =
3.4
theoretical yield
(ii) The reaction between nitrogen and hydrogen is reversible. Hence, it is not possible to
obtain 100% yield of ammonia.
190
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(S)CMWB_Answer.indd 190
© 2013 Marshall Cavendish International (Singapore) Private Limited
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(d) Ca(OH)2(aq) + 2NH4NO3(aq) [1]
6.
2NH3(g) + Ca(NO3)2(aq) + 2H2O(l) [1]
(a) X is zinc carbonate; Y is zinc oxide; Z is zinc hydroxide.
[Three correct: 2 marks; two correct: 1 mark]
(b) Step 1: Dissolve Y (zinc oxide) in dilute nitric acid. [1]
Step 2: Filter to remove excess Y. Collect the filtrate. [1]
Step 3: Add excess aqueous sodium carbonate. Filter to obtain residue X
(zinc carbonate). [1]
7.
(a) (i) Elements C and E (or B and D)
(ii) They are isotopes.
(b) 17 protons, 20 neutrons, 18 electrons
[Three correct: 2 marks; two correct: 1 mark]
(c) (i) B or D
(ii) A
Section B
8. (a) (i)
Oxidation occurs at the anode. The oxide ion is oxidised to oxygen. [1]
2O2–(l)
O2(g) + 4e– [1]
(ii) Reduction occurs at the cathode. The aluminium ion is reduced to aluminium. [1]
Al3+(l) + 3e–
Al(l) [1]
(b) (i)
The oxygen gas liberated during electrolysis reacts with the carbon anodes to form
carbon dioxide. [1] The anodes gradually erode and thus have to be replaced. [1]
(ii) Heat energy is required to melt the electrolyte. [1] If the melting point is lowered, less
heat energy will be needed to maintain the electrolyte in the molten state. [1]
(c) 2Al2O3(l)
4Al(l) + 3O2(g)
Mr of O2 = 2 × 16 = 32
6
Number of moles of O2 = 128 × 10 = 4 × 106 mol
32
From the equation,
Number of moles of Al = 4 × 4 × 106 = 16 × 106 mol [1]
3
3
Ar of Al = 27
Mass of Al = 16 × 106 × 27 = 144 × 106 g = 144 tonnes [1]
3
9.
(a) (i)
CH3(CH2)14COOH and CH3(CH2)29OH. [1] Add a few drops of concentrated sulfuric acid to
a mixture of the carboxylic acid and alcohol and warm. [1]
(ii) Student B is correct. [1] Beeswax is a mixture of esters and hydrocarbons and will
melt over a range of temperatures. [1] Esters and hydrocarbons are simple covalent
compounds and melt at low temperatures. [1]
(b) (i)
H H H O H
H C C C C N H + NaOH
H H H
Butanamide [1]
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H H H O
H C C C C ONa + NH3 [1]
H H H
Sodium butanoate [1]
Answers to Trial Examination
191
8/27/12 8:21 PM
(ii) The organic compound is nylon. [1] It is used to make fishing nets/ clothing/ curtains/
parachutes/ sleeping bags. [Any one use: 1 mark]
EITHER
Volume of sodium hydroxide required for the titration = 15.00 cm3 [1]
Number of moles of NaOH = 0.1 × 15.00 = 0.0015 mol
1000
NaOH + HCl
NaCl + H2O
From the equation,
Number of moles of HCl = 1 × 0.0015 = 0.0015 mol [1]
Concentration of HCl in mol/dm3 = number of moles
volume in dm3
= 0.0015 × 1000 = 0.06 mol/dm3 [1]
25.0
Mr of HCl = 1 + 35.5 = 36.5
Concentration of HCl in g/dm3 = 0.06 × 36.5 = 2.19 g/dm3 [1]
(ii) Volume of NaOH required to neutralise 0.0015 mol of HCl in Experiment 2
= 0.0015
0.05
= 0.03 dm3
= 30.00 cm3 [1]
10. (a) (i)
Number of moles of NaOH = 0.1 × 25.0 = 0.0025 mol
1000
Number of moles of H3PO4 = 0.1 × 25.0 = 0.0025 mol
1000
Mole ratio of NaOH : H3PO4 = 0.0025 : 0.0025 [1] = 1 : 1 [1]
(ii) NaOH(aq) + H3PO4(aq)
NaH2PO4(aq) + H2O(l)
(iii) The pH of NaH2PO4 is about 4.0 (mid of pH range 2.4–5.6). [1]
The pH of Na2HPO4 is about 9.2 (mid of pH range 7.6–10.8). [1]
(b) (i)
OR
10. (a) Carbon is oxidised to form carbon dioxide: C(s) + O2(g)
CO2(g) [1]
Carbon dioxide reacts with more carbon to form carbon monoxide: C(s) + CO2(g)
2CO(g) [1]
Tin dioxide is reduced by carbon monoxide to form tin: SnO2(s) + 2CO(g)
Sn(l) + 2CO2(g) [1]
(b) (i)
Lead(IV) oxide turns grey. [1] Aluminium oxide remains white. [1] Copper(II) oxide turns
reddish-brown. [1]
(ii) Mass of oxygen = 4.78 – 4.14 = 0.64 g
Number of moles of lead in lead(IV) oxide = 4.14 = 0.02 mol
24
Number of moles of oxygen in lead(IV) oxide = 0.64 = 0.04 mol
16
Mole ratio of Pb : O = 0.02 : 0.04 = 1 : 2 [1]
Empirical formula of the oxide used in the experiment is PbO2. [1]
(iii) Add aqueous sodium hydroxide to aluminium oxide and copper(II) oxide separately and
heat. Aluminium oxide is an amphoteric oxide, which is soluble in aqueous sodium
hydroxide. [1] Copper(II) oxide is a basic oxide and thus will not dissolve in aqueous
sodium hydroxide. [1]
192
Answers to Trial Examination
(S)CMWB_Answer.indd 192
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While every effort has been made to contact copyright holders of material reproduced, we have been unsuccessful in some
instances. To these copyright holders, we offer our sincere apologies and hope they will take our liberty in good faith. We would
welcome any information which would enable us to contact the copyright holders/owners involved.
(S)CMWB_IFC&IBC(TE).indd 1
7
6
5
21
45
Sc
b
23
51
V
24
52
Cr
55
Mn
26
56
Fe
27
59
Co
88
Radium
Ra
227
89
Actinium
Ac
57
226
56
Lanthanum
139
La
Yttrium
39
Barium
137
Ba
Strontium
38
89
Y
88
Sr
Scandium
Calcium
20
a
X
72
b = proton (atomic) number
X = atomic symbol
a = relative atomic mass
†
Hafnium
178
Hf
Zirconium
40
91
Zr
Titanium
73
90
Thorium
Th
232
Cerium
58
140
Ce
Tantalum
181
Ta
Niobium
41
93
Nb
Vanadium
184
W
59
91
Protactinium
Pa
Preseodymium
141
Pr
Tungsten
74
42
Molybdenum
96
Mo
Chromium
75
92
U
Uranium
238
Neodymium
60
144
Nd
Rhenium
185
Re
Technetium
43
99
Tc
Manganese
25
76
93
Neptunium
Np
Promethium
61
Pm
Osmium
190
Os
Ruthenium
44
101
Ru
Iron
77
94
Pu
Plutonium
62
Samarium
Sm
150
Iridium
Ir
192
Rhodium
45
103
Rh
Cobalt
28
59
Ni
106
Pd
Nickel
78
95
Am
Americium
Europium
63
152
Eu
Platinum
195
Pt
Palladium
46
The volume of one mole of any gas is 24 dm3 at room temperature and pressure.
Key
*
22
48
Ti
29
64
Cu
30
65
Zn
157
Gd
Gold
197
Au
Silver
96
Curium
Cm
Gadolinium
64
79
47
108
Ag
Copper
80
97
Bk
Berkelium
Terbium
65
159
Tb
Mercury
201
Hg
Cadmium
48
112
Cd
Zinc
81
98
Cf
Californium
Dysprosium
66
162
Dy
Thallium
Tl
204
Indium
49
In
115
Gallium
31
Ga
70
Ca
40
27
Al
Boron
Aluminium
13
5
Magnesium
12
*58-71 Lanthanoid series
†90-103 Actinoid series
87
Fr
Francium
55
Caesium
Cs
133
Rubidium
37
Rb
85
Potassium
19
K
39
Sodium
24
Mg
Beryllium
Second edition 2013
11
23
Na
4
11
B
165
Ho
Lead
207
Pb
Tin
99
Es
Einsteinium
Holmium
67
82
50
119
Sn
Germanium
32
73
Ge
Silicon
28
Si
Carbon
14
6
12
C
83
Bi
100
Fm
Fermium
Erbium
68
167
Er
Bismuth
209
Antimony
51
122
Sb
Arsenic
33
75
As
Phosphorus
31
P
Nitrogen
15
7
14
N
169
101
Md
Mendelevium
69
Thulium
Tm
84
Polonium
Po
Tellurium
52
128
Te
Selenium
34
79
Se
Sulfur
32
S
Oxygen
16
8
16
O
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Level Theory Workbook by Oxford University Press Pte Ltd
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Marshall Cavendish is a registered trademark of Times Publishing Limited.
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7
addressed to the Publisher.
1
Original edition first published in 2001 as Chemistry Matters for GCE ‘O’
V
173
Yb
102
No
Nobelium
Ytterbium
70
85
At
Iodine
Astatine
53
175
Lu
Rn
Radon
Xenon
103
Lr
Lawrencium
Lutetium
71
86
54
Xe
131
I
127
84
Kr
Argon
Krypton
36
18
40
Ar
Neon
20
Ne
Helium
10
2
4
He
0
Bromine
35
Br
80
Chlorine
Cl
35.5
Fluorine
17
9
19
F
VII
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First published 2007
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© 2001 Oxford University Press Pte Ltd
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is the companion workbook to the revised best-selling Chemistry Matters for
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Strengthens conceptual understanding
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