ACE YR IGCSE A TOP APPROACH TO CHEM

Format 210mm X 297mm Extent= 184 pgs (9.78 mm) (70gsm paper) Status: CRC Date: 4/3


Cambridge IGCSE TM redue70% DA1303


ACE YOUR

CHEMISTRY





Workbook Cambridge IGCSE TM




Cambridge IGCSE TM Ace Your Chemistry is designed to aid students build
the skills required to succeed in the IGCSE Chemistry Examination. By working
through the questions in the book, students are well equipped with valuable
techniques in answering the examination questions.

This workbook is written distinctively based on the Cambridge IGCSE Chemistry
2020–2022 and 2023–2025 syllabuses for (0620) and (9-1 0971) courses. The
scope, sequence and level of the workbook has been constructed to match the
Cambridge IGCSE Year 10 and Year 11 syllabuses. ACE YOUR CHEMISTRY

A wealth of questions in the book sets a benchmark to prepare students for the
examination-based questions at Extended Level, which include both multiple-
choice and structured questions. In addition, this workbook provides detailed
explanation to all the questions in its answer key. Upon completing the ample
questions in this book, students are on their path in developing the fundamental
scientific skills for progression to Cambridge International AS and A Level, Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
further education, or science-related professions.



About the Author
Lim Mei Sim is an experienced tutor. For over 12 years, she has been teaching Chemistry in accordance TM
with the IGCSE syllabus. She was a University of Malaya graduate with both Bachelor’s Degree Cambridge IGCSE
and Master’s Degree in Science. During her university years, she worked as a laboratory assistant,
guiding undergraduates to complete their experimental assignments. She started her career as a
tutor while she was pursuing her Master’s Degree.

In her 12 years of teaching pathways, she has guided students to excel in IGCSE Chemistry extended ACE YOUR
papers. She conducted intensive chemistry lessons to support students who were striving hard and
needed assistance in a short period of time before the examination. Her students have achieved
outstanding performances with a 100% pass rate in the examination for the past 12 years and the ‘A-score’
rate was over 90%. CHEMISTRY
Currently, she is guiding students in the International Advanced Level for Chemistry.



Workbook






www.dickenspublishing.co.uk
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ISBN: 978-1-78187-261-1

Suite G7-G8, Davina House, 137-149 Goswell Road,
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E-mail: [email protected] Serene Lim Mei Sim

Format 210mm X 297mm TP pg Chem Pgi Status: CRC_ update










Cambridge IGCSE TM



ACE YOUR

CHEMISTRY




Penerbitan Pelangi Sdn Bhd. All Rights Reserved.

Workbook





Serene Lim Mei Sim












© Dickens Publishing Ltd 2022
All rights reserved. No part of this book may be
reproduced, stored in a retrieval system,
or transmitted in any form or by any means,
electronic, mechanical, photocopying, recording
or otherwise, without the prior permission of
Dickens Publishing Ltd.



ISBN: 978-1-78187-261-1
First published 2022




















Dickens Publishing Ltd

Suite G7-G8, Davina House, 137-149 Goswell Road,
London, EC1V 7ET, United Kingdom.
E-mail: [email protected]

Printed in Malaysia

Contents










Preface ii


Assessment Overview iii
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Glossary of Terms Used in Science Exam Papers iv

The Periodic Table of the Elements vi


Contents of Syllabuses 2020–2025 vii


Chapter 1 States of Matter 1



Chapter 2 Atoms, Elements and Compounds 11


Chapter 3 Stoichiometry 24



Chapter 4 Electrochemistry 33


Chapter 5 Chemical Energetics 43



Chapter 6 Chemical Reactions 49


Chapter 7 Acids, Bases and Salts 63



Chapter 8 The Periodic Table 73


Chapter 9 Metals 86



Chapter 10 Chemistry of the Environment 99


Chapter 11 Organic Chemistry 111



Chapter 12 Experimental Techniques and Chemical Analysis 126


Answers 139






viii Contents







Contents.indd 8 3/4/22 12:55 PM

1 States of Matter










Part 1: Multiple-choice Questions
Answer all questions. For each question, there are four possible answers. Choose the best and correct answer.

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Clone May / June 2015 A Durian particles diffuse from a region
of higher concentration to a region of
1 The changes that occur when a substance lower concentration and the smell of
changes its states are shown below. durian is detected by our nose.
W X B Durian particles condense and the
solid liquid gas
Z Y smell of durian is detected by our nose.

Which process, W, X, Y, or Z, occurs in C Air particles diffuse from a region of
each of the following situations? higher concentration to a region of
1 Candle melts. lower concentration and the smell of
2 The level of water in a pool reduces durian is detected by our nose.
under the hot sun. D Durian particles diffuse from a region
3 Ice cubes form in a freezer. of lower concentration to a region of
4 Moisture beads on car windows. higher concentration and the smell of
durian is detected by our nose.
1 2 3 4
5 At room temperature, particles are further
A W X Y Z apart. Which of the following could be the

B W X Z Y particles?
A NaCl
C Y Z X W B Al O 3
2
D X Y Z W C SO 2
D SiO
2
2 In which of the following do the particles 6 The melting and boiling points of four
slide past each other at room temperature? substances are shown. Which substance is
A hand sanitiser in the bottle a liquid at 35°C?
B copper wire of an air conditioner
C methane gas in a household tank substance melting boiling
D plastic of a food container point / °C point / °C
A –210 –196
Clone Oct / Nov 2015 B –150 –29
3 In which of the following changes of the C 39 256
states do the particles change from ‘closely D 30 2203
arranged’ to ‘moving in all directions’?
A gas to liquid C gas to solid 7 Which of the following statements best
B liquid to solid D solid to gas explains the Brownian motion?
A Haze particles move in the air.
4 We can smell the durian from a stall B An apple drops on the floor.
10 metres away from us. Which statement C Water flows down the waterfall.
correctly explains the situation?
D Sand blows by the wind.



Chapter 1 States of Matter 1







Chapter 1.indd 1 3/4/22 11:57 AM

8 Which of the following statements is 1 happens. The particles of tea move
correct about condensation? 2 in hot water.
A The particles lose kinetic energy and
move further away. gap 1 gap 2
B The particles lose kinetic energy and A diffusion slower
move closer together.
C The particles gain kinetic energy and B evaporation slower
move further away. C diffusion faster
D The particles gain kinetic energy and D evaporation faster
move closer together.
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10 In a pressure cooker, the gas particles 1
9 A tea bag is put in a teacup with hot water,
whereas another tea bag is put in a teacup kinetic energy and move faster. The
collisions between the gas particles with
with cold water. After 1 hour, the colour of the walls of pressure cooker 2 the
the water changes.
pressure in it. The food in it is eventually
being cooked.
gap 1 gap 2

A lose increase
Colour change Colour change
in hot water in cold water B lose decrease
after 1 hour after 1 hour
C gain increase
D gain decrease


Part 2: Structured Questions

Answer all questions.

1 Bromine is a halogen. It melts at t°C and boils at 59°C. A sample of pure bromine is slowly
heated from –10°C to 80°C. Its temperature is measured every minute and the results are
shown on the graph.
Temperature / °C
F
80°C

D E



B C
t°C A
–10°C
Time / minutes

(a) Fill in the state symbols in brackets for the chemical reactions that reach equilibrium in
the region DE.
Br ( ) L Br ( ) [2]
2 2
(b) What is true about t°C?






[2]


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2 Ace Your Chemistry







Chapter 1.indd 2 3/4/22 11:57 AM

(c) What is the physical state of region AB?



[1]

(d) If an impure bromine is used, what would happen to the line of the graph?


[1]

(e) Describe the arrangement of particles in region EF.
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[2]
[Total: 8]

2 All metals and non-metals change state.

(a) Calcium is a metal that will change from solid to liquid and then gas.

Melting A
Solid calcium Liquid calcium Gas calcium
Freezing B

(i) State the process each represented by A and B.

A:
[1]

B:
[1]

(ii) Describe, based on the kinetic particle theory, the arrangement and separation of the
particles in the liquid calcium.






[2]

(iii) State two physical properties of gas calcium.





[2]

(b) Chlorine is a green gas that melts at –100°C and boils at –34°C.

(i) Describe the arrangement and movement of particles in chlorine gas.





[3]






Chapter 1 States of Matter 3







Chapter 1.indd 3 3/4/22 11:57 AM

(ii) The graph shows how the pressure of chlorine gas changes when the temperature
increases. The volume is kept constant.

Pressure of
chlorine gas








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Temperature


Describe and explain how the pressure of chlorine gas changes with temperature.








[3]
[Total: 12]


3 Substances can change their states. The changing of state is affected by the temperature.
The observation of an ice cream after 5 minutes is as shown below.


After 5 minutes at
room temperature
A B

(a) Name the change of state of the ice cream.



[1]

(b) Describe the arrangement and movement of particles of ice cream in situation A.








[3]

(c) Explain, in terms of the kinetic particle theory, why ice cream changes from A to B.








[3]








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Chapter 1.indd 4 3/4/22 11:57 AM

(d) Draw the arrangement of particles of ice cream in situation B.











[2]
[Total: 9]
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4 The diagram shows what a scientist sees under a microscope.
Smoke particle












(a) What is this movement called?


[1]

(b) Describe and explain why particles move in this way.









[3]

(c) Aside from smoke in the air, what other evidence for this movement?


[1]

(d) Bromine gas fills up another container after 5 minutes due to the occurrence of diffusion.





After 5 minutes

(i) What is diffusion?








[3]





Chapter 1 States of Matter 5







Chapter 1.indd 5 3/4/22 11:57 AM

(ii) Describe why this happened in the time of 5 minutes.






[2]
[Total: 10]

5 Helium is a type of gas used to fill balloons. The balloons float in the air.


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(a) What is the property of helium that supports its usage?



[1]

(b) Describe and draw the arrangement and movement of particles in helium gas.











[3]

(c) Explain, in terms of the kinetic particle theory, why balloons are inflated.





[2]

(d) If the balloon is kept outside the house under the hot sun, it bursts.
Explain, in terms of the kinetic particle theory, why the balloon bursts.








[3]

(e) The balloon filled with helium deflated faster than the balloon filled with nitrogen. Explain
why.






[2]


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Chapter 1.indd 6 3/4/22 11:57 AM

(f) A long latex balloon is twisted and made into the shape of an animal.







Explain why the balloon can be compressed.





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[2]
[Total: 13]

6 Ammonium chloride is formed when ammonia, NH reacts with hydrochloric acid, HCl.
3
Ammonium chloride





Mineral wool soaked Mineral wool soaked
with ammonia with hydrochloric acid

(a) What is the colour of ammonium chloride?


[1]

(b) Write the chemical equation for the reaction.



[1]

(c) Name the process of the phenomenon above.


[1]

(d) Explain how ammonium chloride is formed.






[2]
(e) Explain why ammonium chloride formed is nearer to the end of the tube containing
mineral wool soaked with hydrochloric acid.






[2]

(f) If the tube is heated, what change will be observed?


[1]



Chapter 1 States of Matter 7







Chapter 1.indd 7 3/4/22 11:57 AM

(g) If hydrochloric acid is replaced by ammonia, what will happen?






[2]
[Total: 10]

Clone Oct / Nov 2010
7 Nitrogen is a gas at room temperature. It is used in packaging food.
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(a) Compare the movement and arrangement of the molecules in solid nitrogen to those in
nitrogen gas.





[3]

(b) Nitrogen gas is flushed into the container and sealed to preserve food.
Use the kinetic theory to explain why the pressure inside the container increases when
the temperature is increased.






[3]
(c) A syringe can be used to measure the rate of diffusion of gases.

Gas
Constant
Gas escapes pressure
through a small applied
hole in the foil
Gas syringe
The results are shown in the table below.

gas temperature / °C rate of diffusion in cm /min
3
chlorine 25 0.63

nitrogen 25 1.00
nitrogen 50 1.05

(i) Why does nitrogen gas diffuse faster than chlorine gas?






[2]

(ii) Nitrogen gas diffuses faster at higher temperatures. Explain why.


[1]
[Total: 9]



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Chapter 1.indd 8 3/4/22 11:57 AM

8 A student carried out an experiment to investigate the melting point of naphthalene and wax.
A heating curve for naphthalene and wax is shown below.

Temperature / °C
90




Naphthalene
80

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70
Wax



60




50
0 2 4 6 8 10
Time / minutes

(a) What is the melting point of naphthalene?



[1]

(b) Compare the differences between arrangement and movement of particles for solid
naphthalene and liquid naphthalene.






[2]

(c) Wax is an impure substance. How to distinguish it from the graph?


[1]
[Total: 4]


Clone May / June 2015
9 Particles diffuse. This is how we can smell the food that is cooking in the kitchen.

(a) Explain, using the kinetic particle theory, why particles diffuse.









[2]






Chapter 1 States of Matter 9







Chapter 1.indd 9 3/4/22 11:57 AM

(b) In the tube below, a white solid is formed when the colourless gases hydrogen bromide
and ethylamine come into contact.

Gives off CH 3 CH 2 NH 2 (g) Gives off HBr(g)



A B C

Cotton wool soaked Cotton wool soaked in
in ethylamine(aq) concentrated hydrobromic acid
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Predict the position, A, B, or C, where the white solid will form. Explain your choice.











[3]
[Total: 5]

Clone May / June 2014
10 Use the kinetic particle theory to explain each of the following.

(a) Pressure increases when a gas is compressed.












[3]

(b) Liquids have a fixed volume but no definite shape. They take the shape of the container.
Gases do not have a fixed volume or a fixed shape. They also take the shape of the container.









Liquid Gas












[3]
[Total: 6]



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10 Ace Your Chemistry







Chapter 1.indd 10 3/4/22 11:57 AM

2 Atoms, Elements and Compounds










Part 1: Multiple-choice Questions
Answer all questions. For each question, there are four possible answers. Choose the best and correct answer.

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1 The diagram shows an atom of an element. C this is a stable arrangement of electrons.
D the nucleon number is 23.

4 Which statement is not true about nucleon
number?
9p
9n A It is also known as mass number.
Key:
p = protons B It is the number of neutrons.
n = neutrons C It is the total number of protons and
neutrons.
How many valence electrons does an ion D It is the total number of subatomic
of this element have? particles in the nucleus.
A 7 C 9
B 8 D 10 5 The diagram shows the outline of the
Periodic Table.
2 Which statement below is correct about
subatomic particles?
A Protons are negatively charged.
B Electrons have a mass of 1.
C Protons and neutrons are in the
nucleus.
D Electrons and protons are in the The following statements are correct
nucleus. about the Periodic Table, EXCEPT
A the zigzag line divides between metals
Clone Oct / Nov 2014 and non-metals.
3 The electronic structure shows it is an B the first vertical column is known as
atom. Group I.
C the third horizontal row is known as
Period 3.
D the elements are arranged in order of
increasing electron number.
11p
12n 6 The diagram shows the electronic structure
Key: of an atom.
p = protons
n = neutrons
The following statements are true about the
atom, EXCEPT
A has the same number of electrons and
protons.
B there is no overall charge.




Chapter 2 Atoms, Elements and Compounds 11







Chapter 2.indd 11 3/4/22 11:59 AM

Based on the electronic structure, the atom 9 The diagrams show the structures of some
should be located at substances.




A B C
D


R S
+ + + + +
7 An element has the electronic configuration + + + + + +
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of 2,8,8,2. + + + + +
Which statement is correct about the T U
element? Which statement is true?
A It is a Group II element. A R and U are covalent compounds.
B It is located in Period 2 of the Periodic B S and T are ionic compounds.
Table. C S has the highest melting point.
C It is a noble gas. D R can conduct electricity.
D It is a non-metal.

Clone Oct / Nov 2015
8 The diagrams show the structures of X, Y
and Z. 10 Ammonia, NH is a covalent compound.
3
Elements share electrons to form bonds.
Which one shows the correct structure?
A –
3+
–
X Y
–



B



Z
C –
Which one is true about X, Y and Z?
3–
X Y Z –
A element mixture compound –

B element compound mixture
C mixture compound element D

compound mixture element
















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12 Ace Your Chemistry







Chapter 2.indd 12 3/4/22 11:59 AM

Part 2: Structured Questions

Answer all questions.

1 The diagrams show the electronic structures of elements V, W, X, Y and Z.


Key
p = protons
n = neutrons
20p
20n
6p 8p 6p
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8n 8n 6n 1p

V W X Y Z

(a) Which atom is a metal?



[1]

(b) Write the electronic configuration of atom V.



[1]

(c) Y and Z combine to form a compound.
What type of bond will they form?



[1]

(d) V and X can react to form an ionic lattice.

(i) What is ionic lattice?





[2]

(ii) Based on the electronic structure, what is the chemical formula of V and X when
they form an ionic compound?



[1]

(iii) Draw the electronic structures of the two ions, V and X present in the ionic compound.
Use dot-and-cross diagrams to show electron arrangements. Show only the outer
shell electrons. Include the charges on the ions.








[3]




Chapter 2 Atoms, Elements and Compounds 13







Chapter 2.indd 13 3/4/22 11:59 AM

(e) In a complete combustion, some products are formed.
Which two atoms will join to form the product of combustion? Name the product.






[2]
(f) Which of the given elements are isotopes? Explain your answer.



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[3]

(g) The isotopes that will decay and give out radiation are called radioisotopes.
Radioisotopes are useful in industry and medicine.
Name a use of radioisotopes in

medicine :

industry :
[2]
[Total: 16]

2 Potassium chloride is an ionic compound.

(a) Write the chemical formula of potassium chloride.



[1]
(b) Describe what happens, in terms of electron loss and gain, when potassium atom reacts
with chlorine atom.






[2]

(c) Describe the structure of solid potassium chloride. You may draw a diagram.





















[2]



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Chapter 2.indd 14 3/4/22 11:59 AM

(d) Explain why potassium chloride has a high melting point.






[2]

(e) Solid potassium chloride cannot conduct electricity, but molten potassium chloride is a
good conductor of electricity. Explain why.



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[2]

(f) Potassium oxide is also an ionic compound.

(i) It has a different ratio of positive and negative ions for the formation. For potassium
oxide, the ratio of potassium ions to oxide ions is 2 : 1. Explain why.








[3]
(ii) Potassium oxide is a base. Suggest a physical test to show it is a base.

test :

result :
[2]
[Total: 14]


3 Carbon dioxide is needed for photosynthesis. It takes up 0.03% of the air composition.

(a) Carbon dioxide is a gas at room temperature. Explain why.


[1]

(b) Carbon atoms and oxygen atoms are bonded together to form carbon dioxide.

(i) What kind of bonding is formed?



[1]
(ii) Use a dot-and-cross diagram to show the electron arrangement in a molecule of
carbon dioxide. Show only the outer shell electrons.









[3]



Chapter 2 Atoms, Elements and Compounds 15







Chapter 2.indd 15 3/4/22 11:59 AM

(c) Carbon dioxide is an acidic oxide. Describe a chemical test to show it is acidic.

test :
[1]

result :
[1]
(d) Carbon dioxide and copper(II) oxide are two different types of compounds.
Carbon dioxide has a low melting point, but copper(II) oxide has a high melting point.
Explain the differences in terms of attractive forces.








[3]
[Total: 10]


4 Diamond and graphite are both allotropes of carbon.
The diagrams show the structures of diamond and graphite.










diamond
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graphite
(a) They are both macromolecules.
Define macromolecule.



[1]

(b) The structures of diamond and graphite are different. Describe the differences between
them.






[2]

(c) Graphite is a good conductor of electricity but not diamond. Explain why.





[2]

(d) Aside from electrical conductivity, write one other property that can show the difference
between them.


[1]



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Chapter 2.indd 16 3/4/22 11:59 AM

(e) Diamond and graphite are useful in our daily life. State one of the uses for each.

diamond :
[1]

graphite :
[1]
(f) Silicon dioxide is another macromolecule.
Describe the structure of silicon dioxide.

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[3]
[Total: 11]

5 Copper is a transition metal. Copper atoms are bonded by metallic bonds.

(a) Describe the lattice structure of copper metal. You may draw a diagram.




















[3]

(b) Copper is a good conductor of electricity. Explain why.



[1]

(c) Name another two properties to show it is a typical metal.





[2]

(d) Copper can be shaped. Explain why.






[2]






Chapter 2 Atoms, Elements and Compounds 17







Chapter 2.indd 17 3/4/22 11:59 AM

(e) Brass is an alloy that is made of copper.

(i) What is alloy?



[1]
(ii) What is another metal used to make brass?



[1]
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(iii) Why is an alloy better than a pure metal for usage?


[1]
[Total: 11]


6 These are some elements in the Periodic Table.
23 S 24 T 27 U 28 V 31 W 32 X 35.5 Y 40 Z
11 12 13 14 15 16 17 18

(a) Choose from the elements above to answer the questions below. An element may be
selected once, more than once or not at all.

(i) Which two elements have the valency of 2?






[2]
(ii) Which element can react with bromine to form an ionic compound in the ratio of 1 : 1?



[1]

(iii) Which element can form 4 single bonds with halogens?


[1]

(iv) Which element forms M when it ionises?
3–

[1]

(v) Which element has the electronic configuration of 2,8,7?


[1]

(b) The elements above are all located in the third period of the Periodic Table.
Explain the statement.






[2]


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Chapter 2.indd 18 3/4/22 11:59 AM

(c) What is the name given to all elements same as Z?



[1]

(d) Z is an unreactive element. Explain why.


[1]

(e) Atom U has the nucleon number of 27.
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(i) What is nucleon number?



[1]
(ii) What is the number of neutrons in atom U?



[1]

(iii) How many electrons are there in atom U?


[1]

(iv) Give a physical property of U.


[1]

[Total: 14]

Clone May / June 2018

7 Uranium, U, atomic number 92, is used as fuel for nuclear power plants.

(a) Uranium bombards with neutrons and splits into barium, atomic number 56 and another
atoms of element Z.

uranium + neutrons ➞ barium + Z

(i) Suggest the identity of element Z.



[1]
(ii) In which period of the Periodic Table is element Z?



[1]
(iii) Predict the number of outer shell electrons in an atom of element Z.



[1]








Chapter 2 Atoms, Elements and Compounds 19







Chapter 2.indd 19 3/4/22 11:59 AM

(b) Two isotopes of uranium are U and U. The nuclei of both isotopes are unstable and
235
238
emit energy when they split up.
(i) State the term used to describe isotopes with unstable nuclei.



[1]
(ii) Complete the table to show the number of protons, neutrons and electrons in the
atoms of the isotopes shown.

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isotope number of protons number of neutrons number of electrons
235 U
238 U

[2]
(c) Uranium is a typical metal.

(i) Suggest two physical properties of uranium.

1
[1]

2
[1]

(ii) Suggest one chemical property of uranium oxide.



[1]
[Total: 9]


Clone Oct / Nov 2015
8 The table below shows the elements in the third period of the Periodic Table, the number of
outer shell electrons, their valency and melting points.

element Na Mg Al Si P S Cl Ar
number of outer
shell electrons 1 2 3 4 5 6 7 8

valency +1 +2 +3 +4 / –4 –3 –2 –1 0
melting point /
°C 98 650 660 1414 317 115 –101 –189


(a) Na, Mg and Al are metals. Describe the structure of a typical metal.








[3]




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Chapter 2.indd 20 3/4/22 11:59 AM

(b) Explain why Na, Mg and Al are good conductors of electricity.



[1]

(c) Which element exists as diatomic molecules of the type X ?
2

[1]

(d) Explain why the valency of argon is 0.
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[1]

(e) Silicon has a similar structure to diamond.
Explain why silicon has the highest melting point in the period.





[2]

(f) Sodium chloride is a crystalline solid with a high melting point. It dissolves in water to
give a neutral solution. Phosphorus trichloride is a liquid at room temperature. It reacts
with water to form an acidic solution.
Suggest an explanation for these differences in the properties.






[2]

(g) Describe how you could show that magnesium oxide is a basic oxide and not an amphoteric
oxide.





[2]

(h) Draw a dot-and-cross diagram to show the bonding in magnesium oxide. Show only the
outer shell electrons.
















[3]
[Total: 15]





Chapter 2 Atoms, Elements and Compounds 21







Chapter 2.indd 21 3/4/22 11:59 AM

9 The table shows the melting points, boiling points and electrical properties of five substances,
A to E.

electrical electrical
melting point / boiling point /
substance conductivity conductivity
°C °C
of solid of liquid
A –7 59 poor poor
B 1083 2567 good good

C 755 1387 poor good
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D 43 181 poor poor
E 1607 2227 poor poor


(a) Which substance in the table has ionic bond? Explain your answer.











[4]

(b) Which substance in the table is a macromolecule?


[1]

(c) Which substance is a liquid at room temperature?



[1]

(d) Substance B is a metal.

(i) Explain why substance B is a good conductor of electricity.


[1]

(ii) Give one chemical property of a metal.



[1]

(e) Which substance is a covalent compound and a solid at room temperature? Explain your
answer.









[3]
[Total: 11]


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Clone May / June 2015
10 Chemical formula provides a way to represent any chemical substance using the symbol of
the elements present in it.

(a) Write the chemical formula for each of the following compounds.

(i) aluminium fluoride


[1]
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(ii) arsenic oxide



[1]

(iii) germanium chloride


[1]

(b) Deduce the formula of each of the following ions.

(i) nitride



[1]

(ii) strontium


[1]

(iii) gallium



[1]
[Total: 6]
































Chapter 2 Atoms, Elements and Compounds 23







Chapter 2.indd 23 3/4/22 11:59 AM

Answers









10 C
1 States of Matter In a pressure cooker, electrical energy changes to heat
energy. The heat energy increases the movement of
Part 1: Multiple-choice Questions particles as it gains kinetic energy. The particles collide
more frequently with the walls of pressure cooker and
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1 B this increases the pressure in it.
1 – W – Melting is a change from solid to liquid.
2 – X – Water evaporates under the sun. Evaporation is Part 2: Structured Questions
a change from liquid to gas.
3 – Z – Water freezes to form ice cubes in the freezer. 1 (a) (l) [1]
Freezing is a change from liquid to solid. (g) [1]
4 – Y – Condensation is a change from gas to liquid. All particles change from solid to liquid, then from
liquid to gas when the temperature increases.
2 A At region CD, it is a liquid. At region EF, it is a gas.
In liquid state, particles slide past each other. Hand Therefore, at DE, it changes from liquid (l) to gas (g).
sanitiser is in liquid state at room temperature.
(b) The temperaure is above –10°C [1]
3 D and below 80°C. [1]
In solids, particles are closely arranged. In gases, particles The only information can be collected from the
are moving in all directions. So, it is changing from solid question is the starting and ending temperature. It
to gas. is always true that t is above –10°C and below 80°C.
4 A (c) Solid [1]
Gas diffuses. Diffusion is a process where particles move
from a region of higher concentration to a region of (d) The line would not be horizontal. [1]
lower concentration. When durian particles reach the When an impure bromine is used, the melting and
nose, it is detected. boiling points will have a wide range, not a sharp
temperature.
5 C
In gases, particles are arranged randomly and further Temperature / °C
apart. SO is a gas at room temperature. A, B, and D are
2
all solids. 110°C E
100°C
6 D D
For a substance to exist in the liquid state at 35°C, the
melting point should be lower than 35°C, and the boiling C
point should be higher than 35°C. Option D fulfils these
criteria. B
7 A A
Brownian motion is the random movement of particles. Time / minutes
Particles move in a zigzag manner when bombarded
with other unseen tiny particles. Haze particles move in (e) Particles are arranged randomly [1]
a zigzag manner while floating in the air. and far apart. [1]
At region EF, bromine is a gas.
8 B
Condensation is a change from gas to liquid. Energy is 2 (a) (i) A – Boiling [1]
lost to allow particles to move closer together. B – Condensation [1]
(ii) Particles are irregularly arranged [1]
and close together. [1]
Tea particles diffuse from a region of higher
concentration, which is from the tea bag to a region (iii) Any two from: [2]
of lower concentration, which is the water. In the hot • Compressible
water, the particles gain more kinetic energy and move • Takes the shape / volume of its container
faster. After 1 hour, the particles are spread throughout • Easily mixes with other gases
the cup. • Diffuses fast
Or any acceptable physical properties






Answers 139







Answers.indd 139 3/4/22 3:54 PM

(b) (i) Particles are irregularly arranged [1] and collide more frequently with the walls of
and far apart. [1] the balloon. [1]
They move in all directions. [1] The pressure inside the balloon increases. [1]
(ii) As the temperature increases, the pressure (e) Helium has a smaller M [1]
increases. [1] and diffuses faster. r [1]
Particles gain energy and move faster. [1] M He = 4; M N = 28
Particles collide with the walls more often. r r 2
[1] (f) Particles are far apart. [1]
Particles can move closer. [1]
3 (a) Melting [1]
6 (a) White [1]
(b) Particles are regularly arranged [1]
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and close together. [1] (b) NH + HCl ➞ NH Cl [1]
4
3
They vibrate on the spot. [1] (c) Diffusion [1]
(c) The particles gain kinetic energy and move (d) Ammonia and hydrochloric acid gas particles
faster [1] diffused from each end [1]
to overcome the forces in between particles. [1] to meet at a point to react. [1]
They move slightly further apart / can move Ammonia is a weak base, and hydrochloric acid
past each other. [1] is a strong acid. They react. It is a neutralisation
The change of state is from solid to liquid. reaction.
(d) (e) Ammonia has a lower relative molecular mass.
[1]
It moves faster. [1]
or vice versa
Particles are close together [1] Relative molecular mass of NH = 14 + 1(3)
irregularly arranged [1] 3 = 17
4 (a) Brownian motion [1] Relative formula mass of HCl = 1 + 35.5
Brownian motion is the random movement of = 36.5
particles. Particles move in a zigzag motion. Note: Must use word of comparison.
(b) Particles that move in a zigzag manner [1] (f) The white spot will form faster. [1]
bombarded / hit [1] Note: Word of comparison must be used.
by unseen tiny particles. [1]
(g) Gas particles still diffuse [1]
(c) Dust particles under the sunlight, [1] Gas particles are constantly moving. Therefore,
or any acceptable answer. diffusion will still happen.
(d) (i) Movement of particles [1] but no white spots form. [1]
from a region of higher concentration [1] But there is no chemical reaction that happens.
to a region of lower concentration. [1] 7 (a)
(ii) Gas particles move in a fast manner. [1] Solid Gas
They collide and bound back quickly in all
directions. [1] Arrangement / Regular / Irregular / [1]
pattern lattice random
5 (a) Lower density than air / lighter than air [1]
Helium has a lower density than the air and this Distance Close Far apart / [1]
property allows balloons filled with helium to float. spread out
(b) Movement Vibrate / Moving [1]
fixed
position
Max 2 marks for a correct drawing.
Arrangement – Irregular / no fixed Note: Comparison must be made. 1 mark is given
arrangement [1], far apart [1] for each comparison.
Movement – Move in all directions [1]
(b) Particles / molecules have more energy / move
(c) Kinetic energy causes gas particles to move. [1] faster, [1]
Particles collide with the walls of the balloon. [1] collide harder / collide more frequently / more
(d) Particles has more kinetic energy and move collisions / collide with more force (with the
faster [1] walls) [1]




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Answers.indd 140 3/4/22 3:54 PM

(c) (i) Nitrogen has a smaller M . [1]
r
M = Relative molecular mass / Relative 2 Atoms, Elements and Compounds
r
formula mass
Relative molecular mass of N = 14 + 14 = 28 Part 1: Multiple-choice Questions
2
Relative molecular mass of Cl = 35.5 + 35.5 = 71
2 1 B
Nitrogen molecules / particles move faster Valence electrons are the electrons in the outer shell
(than chlorine molecules). [1] of an atom. To make this atom an ion, it needs to gain
Note: Word of comparison must be used. 1 electron to form a negative ion, to achieve a stable
(ii) Molecules / particles move faster / have electron arrangement. Therefore, the ion has 8 valence
more energy. [1] electrons in the outer shell.
At higher temperatures, particles have more 2 C
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kinetic energy to move faster. Protons and neutrons are located in the nucleus and
8 (a) 80°C [1] electrons are located outside the nucleus.
(b) 3 C
There is only 1 electron in the outer shell. To achieve a
Solid Liquid stable arrangement, there must be 8 electrons in the

Arrangement Regular Irregular [1] outer shell.
4 B
Movement Vibrate / Moving / [1] Nucleon number is the total number of protons and
fixed slide past neutrons in the nucleus.
position each other
5 D
Note: Comparison must be made. 1 mark is given The elements are arranged in order of increasing proton
for each comparison. number.
(c) There is no horizontal line. [1] 6 B
In a pure substance, the melting and boiling points There are 3 electrons in the outer shell. Therefore,
should show a horizontal line. it should be located in Group III. From the electronic
9 (a) Any two from: [2] structure, there are 3 shells / orbits, it tells that the
element is located in Period 3 of the Periodic Table.
• Particles move randomly in all directions
• collide 7 A
• move from a region of higher concentration The last number in the electronic configuration indicates
to a region of lower concentration the number of electrons in the outer shell. All Group II
elements have 2 electrons in their outer shell.
(b) C [1]
Ethylamine has a lower M r [1] 8 D
M = Relative molecular mass / Relative formula A compound is a substance that contains more than 1
r
mass element chemically bonded together.
A mixture contains more than 1 element / compound
Relative molecular mass of CH CH NH = 45
3
2
2
Relative molecular mass of HBr = 81 that is mixed.
An element consists of only 1 type of atom.
moves faster. [1] 9 A
Note: Word of comparison must be used.
R is a macromolecule. Particles are bonded by covalent
10 (a) Particles move closer together [1] bonds. It has the highest melting point among all. It
in a smaller space [1] has no mobile electrons, therefore it cannot conduct
collide with the walls more often. [1] electricity.
S is a lattice ionic compound. Particles are bonded by
(b) Particles move in all directions / randomly in ionic bonds. It has a high melting point but lower than
both liquid and gas. [1] macromolecules.
No bonds / very weak forces between particles T is a lattice metal. Particles are bonded by metallic
in gas. [1] bonds.
Gas molecules move apart to fill up the entire U is a simple covalent compound. Particles are bonded
volume. [1] by covalent bonds.
or 10 B
There are bonds / forces between particles in Nitrogen has 5 valence electrons. Hydrogen has 1
liquid. [1] valence electron. 3 hydrogen atoms each share their 1
Molecules cannot move apart, so the volume is electron with 3 individual electrons of nitrogen to form 3
fixed. [1] single bonds. Two more paired electrons in nitrogen are
stable.






Answers 141







Answers.indd 141 3/4/22 3:54 PM

Part 2: Structured Questions (c)
K + Cl – K +
1 (a) V [1] – + –
V has 2 electrons in the outer shell. It is a member Cl K Cl
of Group II. It is a metal. K + Cl – K +
(b) 2,8,8,2 [1] Regular arrangement [1]
+
–
(c) Covalent bond [1] of alternating K and Cl [1]
Y and Z are both non-metals. Covalent bonds form
between non-metals. (d) Ionic bond is strong. [1]
(d) (i) A regular arrangement [1] Require a lot of energy to overcome. [1]
Potassium chloride is an ionic compound. Ionic
of alternating positive and negative ions. bond is formed between ions of opposite charge.
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[1]
Lattice = regular arrangement (e) Ions cannot move in solid. [1]
Ionic = alternating positive and negative ions Ions can move in molten. [1]
(ii) CaO [1] – Solid +
Calcium loses 2 electrons to form Ca . Oxygen
2+
gains 2 electrons to form O . + – + – + – + – + – + –
2–
1 atom of Ca is enough to cancel out the – + – + – + – + – + – +
2+
+ – + – + – + – + – + –
charge of 1 atom of O . In the formation of
2–
calcium oxide, the ratio of calcium to oxygen Ions are fixed in the lattice and cannot move
is 1 : 1.
(iii) 2+ 2– – Molten or aqueous solution +
Ca O – + + + – – – – + – –
+ – – + – + – –
+ + + + + + –
+ + + – – – – + – –
Ca has 8 electrons in the outer shell. [1]
2+
O has 6 electrons in the outer shell and Ions can now move and conduct electricity
2–
gains 2 electrons from Ca. [1] (f) (i) Potassium loses 1 electron to form K . [1]
+
Correct charge [1] Oxygen gains 2 electrons to form O . [1]
2–
+
(e) Y and X [1] 2 moles of K is needed to cancel out the
2–
Carbon dioxide [1] charge of 1 mole of O . [1]
In a complete combustion, carbon dioxide is (ii) Dissolve potassium oxide in water and add
formed. Y has the electronic configuration of 2,4. universal indicator / litmus paper / methyl
It is a carbon. X has the electronic configuration of orange / phenolphthalein / pH meter [1]
2,6. It is an oxygen. Turn blue / purple / yellow / pink / > pH 7
W is not the answer because W is carbon-14, which [1]
is radioactive.
Physical test (a qualitative or quantitative test
(f) W and Y [1] that determines the properties of a substance
They have the same number of protons [1] at macroscopic level.)
but different number of neutrons. [1] Universal indicator has a wide range of colour
Both W and Y have the same number of protons, 6, changes giving more accurate pH.
but different number of neutrons, 8 and 6 Litmus paper: acid ➞ red; base ➞ blue / purple
respectively. Methyl orange: acid ➞ red; neutral ➞ orange;
base ➞ yellow
(g) Any one from: Phenolphthalein: acid ➞ colourless; neutral ➞
Cancer treatment / Sterilise medical instrument colourless; base ➞ pink
/ Trace blockage in blood [1] pH meter: gives accurate pH in digit.
Any one from: 3 (a) Its boiling point is below room temperature. [1]
Fuel in nuclear power plant / Trace pipe leakage (b) (i) Covalent bond [1]
[1]
(ii)
2 (a) KCl [1]
O C O
(b) K loses 1 electron to form K . [1]
+
Cl gains 1 electron from the potassium to form
Cl . [1] The correct ratio of carbon to oxygen is
–
1 : 2. [1]
4 sharing electrons at each intersection.
There are 2 intersections. [1]
2 lone pairs on each oxygen. [1]


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Answers.indd 142 3/4/22 3:54 PM

(c) Blow carbon dioxide into limewater [1]
turn cloudy [1] O
Limewater is calcium hydroxide. When carbon
dioxide reacts with calcium hydroxide, calcium O Si O
carbonate is formed. Calcium carbonate is a
precipitate that turns the solution cloudy. O
(d) Carbon dioxide:
• Simple covalent compound 5 (a) + + – + + – + – +
–
• Intermolecular forces / van der Waals forces – – + – + – + – – + – + – +
–
are weak. + – + – + – + – + – + –
–
–
–
• Less energy to overcome. – + – + – + – + + – – +
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Copper(II) oxide: – – –
• Ionic compound A regular arrangement [1]
• Ionic bond is strong. of positive ions [1]
• More energy to overcome. and a sea of electrons / delocalised electrons. [1]
Note: Mark is only given if the following has been
mentioned for both compounds. (b) Has delocalised electrons / free moving electrons
Type of compound [1] [1]
Type of bonding [1] (c) Any two from: [2]
Level of energy required to break the bonds [1] • Shiny
• High density
4 (a) Giant covalent structure [1] • High melting point / boiling point
(b) Diamond: • Malleable / Ductile
• Each carbon atom is bonded to four other • Sonorous
carbons. • Strong
• Tetrahedron (d) Particles are arranged in layers. [1]
Graphite: Particles can slide over each other. [1]
• Each carbon atom is bonded to three other (e) (i) Mixture of a metal with another or more
carbons. metals (or non-metals). [1]
• Layers of hexagonal shape
Note: Show comparisons [2] (ii) Zinc [1]
(iii) More useful / Its properties are improved.
(c) Graphite has free moving electrons. [1] [1]
Diamond has no free moving electron. [1]
6 (a) (i) T and X [2]
(d) Any one from: [1] Valency of an element is the number of
• Diamond is harder. / Graphite is softer. electrons its atoms lose or gain or share, to
• Diamond has a higher melting point. / form a compound.
Graphite has a lower melting point. T = 2,8,2, T formed 2 +
• Diamond is denser. / Graphite is less dense. X = 2,8,6, X formed 2 –
Note: Word of comparison must be used. So, they have the valency of 2.
(e) Any one from: [1] (ii) S [1]
Diamond: Br has a valency of 1. It loses 1 electron to
form Br . To form an ionic compound, charges
–
• Tools for drilling / cutting should be cancelled out.
• Jewellery S = 2,8,1. It has a valency of 1. It forms S .
+
+
–
Any one from: [1] 1 mole of S reacts with 1 mole of Br to form
Graphite: an ionic compound with a 1 : 1 ratio.
• As a lubricant (iii) V [1]
• Pencil V = 2,8,4. V has a valency of 4. It can share the
• Electrode 4 electrons with 4 halogens to form a covalent
compound.
(f) Each silicon atom is bonded to four oxygen (iv) W [1]
atoms. [1] W = 2,8,5. W has a valency of 3. It will gain 3
Each oxygen atom is bonded to two silicon electrons to form W .
3–
atoms. [1] (v) Y [1]
Tetrahedron [1] Y has the number of protons 17. The number
of protons is equal to the number of electrons.
So, the electronic configuration is 2,8,7.




Answers 143







Answers.indd 143 3/4/22 3:54 PM

(b) Period number can be shown by the number of Even though uranium is a metal, it is a poor
shells. [1] conductor of electricity.
The electron distributions of all elements show (ii) Basic / dissolve in acid / reacts with acid [1]
that there are three shells. [1] Uranium is a metal. Metal oxide is basic.
(c) The noble gas [1] 8 (a) Metal ions [1]
Z = 2,8,8. Elements of Group 0. are arranged in lattice [1]
(d) Has stable outer shell [1] with a sea of electrons / delocalised electrons.
(e) (i) Number of protons and number of [1]
neutrons [1] + – + – – + – + – + – +
– + + – + – + – + – +
(ii) 14 [1] – – – – – – – –
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27 – 13 = 14 – + – + – + – + – – + – + – –
(iii) 13 [1] + – + + – + – + +
Number of protons = number of electrons (b) They have mobile electrons. [1]
(iv) Any one from: [1] The moving electrons allow the current to pass
• High melting point / boiling point through.
• Strong / hard (c) Chlorine / Cl [1]
• Shiny At room temperature, halogens are all diatomic.
• Malleable / Ductile Same to these common elements: O , N , H .
• Sonorous 2 2 2
• Conducts electricity (d) Has stable electron arrangement. [1]
Valency is the number of electrons its atoms lose,
7 (a) (i) Krypton [1] gain or share, to form a compound. Argon has a full
Uranium has the atomic number of 92. outer shell. It does not lose, gain, or share.
Uranium is split into barium and Z.
Barium has the atomic number of 56. (e) Atoms are bonded with strong covalent bonds
92 – 56 = 36 [1]
Refer to the Periodic Table, the element with in a giant lattice / macromolecule / giant
the atomic number of 36 is krypton. structure [1]
(ii) Period 4 [1] (f) Any two from: [2]
Refer to the Periodic Table, krypton is located • NaCl is an ionic compound and PCl is a
3
in Period 4. covalent compound.
(iii) 8 [1] • The ionic bond is strong in NaCl and the
Krypton is in Group VIII. So, it has 8 electrons intermolecular force is weak between PCl 3
in its outer shell. molecules.
For questions (a)(ii) and (a)(iii), the electronic • PCl reacts with water and NaCl does not.
configuration can show the answer. 3
The electronic configuration for krypton is (g) MgO with a dilute HCl / H SO / HNO / Acid /
3
2
4
2,8,18,8 (total is 36). Any acidic oxide and NaOH / Alkali / Base /
There are 4 numbers in the configuration Any basic oxide [1]
means it has 4 shells. Thus, it is located in MgO will neutralise the acid but not NaOH /
Period 4. Alkali / Base / Any basic oxide [1]
The last number of electronic configuration Note: Must always include the expected result.
shows the number of outer shell electrons.
(h) 2+ 2–
(b) (i) Radioisotopes [1]
(ii) 235 U: 92, 143, 92 [1] Mg O
238 U: 92, 146, 92 [1]
In an atom, the number of protons and the Mg with 8 electrons (represented by dots) in
number of electrons must be the same. the outer shell. [1]
Calculate the number of neutrons: O with 6 electrons (represented by crosses) and
235 – 92 = 143 2 electrons gained (represented by dots) [1]
238 – 92 = 146 Correct charge [1]
(c) (i) Any two from: [2] Note: Mark all the electrons using either dots or
• High melting point / boiling point crosses.
• Shiny 9 (a) C [1]
• Malleable Ionic bond is strong. [1]
• Ductile Ionic compounds do not conduct electricity in
• High density solids because ions cannot move. [1]
• Hard


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Answers.indd 144 3/4/22 3:54 PM

But they can conduct electricity in liquids
because ions are moving. [1] 3 Stoichiometry
Solid
– + Part 1: Multiple-choice Questions
+ – + – + – + – + – + – 1 B
– + – + – + – + – + – +
+ – + – + – + – + – + – When forming an ionic compound, their charges must
cancel out.
2+
Ions are fixed in the lattice and cannot move X has 2 electrons in the outer shell. It forms X . Y has 7
–
electrons in the outer shell. It forms Y . To cancel out the
Molten or aqueous solution 2+ –
– + charges, 1 mole of X needs 2 moles of Y . Therefore, the
formula is XY .
+ +
– + – – + – – – – + – – 2
–
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+ + – – 2 C
+ + + + + + –
+ + + – – – – + – – Valency means gaining or losing of electrons. Metals
always lose electrons to form positively-charged ions.
Ions can now move and conduct electricity Non-metals gain electrons to form negatively-charged
ions. R is a metal with a valency of 1. It loses 1 electron. T
(b) E [1] is a non-metal with a valency of 2. It gains 2 electrons. 2
2–
+
Macromolecules like diamond, have a high melting moles of R reacts with 1 mole of T to form R T. Charges
2
point. This is because the particles are bonded with are cancelled out in forming an ionic compound.
strong covalent bonds. They are poor conductors of
electricity because there is no free moving electron. 3 D
A 2Na + Cl ➞ 2NaCl
2
(c) A [1] B 2ZnS + 3O ➞ 2ZnO + 2SO 2
2
Room temperature is around 25°C. Substance A C Zn + Ag(NO ) ➞ Zn(NO ) + Ag
3 2
3 2
melts at –7°C and only boils at 59°C. So it is a liquid
at 25°C. 4 D
Relative atomic mass is the average mass of naturally
(d) (i) There are free moving electrons. [1] occurring atoms of an element on a scale where the C
12
The moving electrons allow the current to pass atom has a mass of exactly 12 units.
through. 5 B
(ii) Any one from: [1] MgCO + 2HCl ➞ MgCl + CO + H O
2
3
2
2
• Lose electrons to form positive ions The only gas produced is carbon dioxide. The mole ratio
• React with an acid to form hydrogen gas of MgCO to CO is 1 : 1. Therefore, the number of moles
3
2
and salt of CO is 1.0 mol.
2
• React with a non-metal to form an ionic 6 A
compound Ca + 2H O ➞ Ca(OH) + H
2
2
2
• Form basic oxide Relative atomic mass of Ca = 40
A chemical property is a characteristic of Relative molecular mass of H O = 18
matter that is related to a change in its 4.8 2
chemical composition. Number of moles of Ca = = 0.12 mol
40
(e) D [1] Number of moles of H O = 3.6 = 0.20 mol
Melt at temperatures above room temperature 2 18
[1] The mole ratio of Ca to H O is 1 : 2. Calcium is in excess.
2
Low melting point and does not conduct Therefore, the maximum number of moles of Ca to react
electricity [1] is 0.10 mol.
Covalent compounds have weak intermolecular The mole ratio of Ca to Ca(OH) is 1 : 1. So, the number
2
forces. The melting and boiling points are low of moles of Ca(OH) is 0.10 mol.
2
because less energy is needed to overcome the Relative formula mass of Ca(OH) = 74
2
bonds. Amount of Ca(OH) = 74 × 0.10 mol
2
There is no free moving electron in a covalent = 7.40 g
compound as all electrons are either shared or 7 A
paired up.
4Cr + 3O ➞ 2Cr O 3
2
2
10 (a) (i) AlF [1] Relative atomic mass of Cr = 52
3 Relative molecular mass of O = 32
(ii) As O [1] 2
3
2
(iii) GeCl [1] Number of moles of Cr = 26 = 0.50 mol
4 52
(b) (i) N [1] Number of moles of O = 8 = 0.25 mol
3–
(ii) Sr [1] 2 32
2+
3+
(iii) Ga [1] The mole ratio of Cr to O is 4 : 3.
2
Answers 145
Answers.indd 145 3/4/22 3:54 PM

0.5 mol of Cr needs to react with 0.375 mol of O in a 3. Multiply the empirical formula by the number
2
3 calculated in step 2.
complete reaction. [0.5 mol × = 0.375 mol]. But there
4
is 0.25 mol of O available for the reaction only. So, 2 (a) 0.2 mol [1]
2
oxygen is the limiting agent. Number of moles of Cl = volume 3
The mole ratio of O to Cr O is 3 : 2. 2 24 dm
2 2 3 4.8 dm 3
2
Number of moles of Cr O = 0.25 × = 0.167 mol = 24 dm 3
2 3 3
Relative formula mass of Cr O = 152 = 0.2 mol
3
2
Mass of chromium(III) oxide = 152 × 0.167 mol (b) Relative formula mass of NaOCl = 74.5 [1]
= 25.384 g Number of moles of NaOCl = 0.2 mol [1]
= 25.4 g Mass = 14.9 g [1]
8 A Mass of NaOCl = number of moles × M r
NaOH + HCl ➞ NaCl + H O = 0.2 mol × 74.5
2
Number of moles of NaOH = 0.025 dm × 0.10 mol dm = 14.9 g
–3
3
= 0.0025 mol (c) Number of moles of NaOH = 2 × 0.2 mol
25 cm = 0.025 dm 3 = 0.4 mol [1]
3
The mole ratio of NaOH to NaCl is 1 : 1. number of moles
Relative formula mass of NaCl = 58.5 Volume of NaOH =
Mass of NaCl = 0.0025 mol × 58.5 concentration
= 0.146 g = 0.4 mol –3
2.0 mol dm
9 D = 0.2 dm 3 [1]
Relative formula mass of NaNO = 85
3
1.7 3 (a) 0.05 mol [1]
Number of moles of NaNO = 85 = 0.02 mol Relative formula mass of CaO = 56
3
NaNO ➞ Na + NO 3 – mass
+
3
There are 2 moles of ions formed when 1 mole of NaNO Number of moles of CaO = M
3
r
dissolves. 2.805
1 mole = Avogadro constant = 6.02 × 10 particles = 56
23
Number of particles of NaNO = 0.05 mol
3
23
= 0.02 × 2 × 6.02 × 10 particles
= 0.04 × 6.02 × 10 particles (b) 0.15 mol [1]
23
Number of moles of HCl = concentration × volume
10 C Penerbitan Pelangi Sdn Bhd. All Rights Reserved. 3

= 0.3 mol dm × 0.5 dm
–3
Li PO ➞ 3Li + PO 4 3– = 0.15 mol
+
4
3
3 moles of positive ions are produced.
Number of particles of Li PO = 3 × 6.02 × 10 particles (c) CaO [1]
23
3
4
24
= 1.806 × 10 particles 0.05 mol is 0.025 less than 0.075 mol. [1]
Ratio = CaO : HCl = 1 : 2
Part 2: Structured Questions If CaO is 0.05 mol, HCl should be 0.10 mol. But the
number of moles of HCl is 0.15 mol, it is 0.05 mol in
1 (a) Add up to be 100% [1] excess. CaO is the limiting reagent.
(b) C = 24.30 = 2.03 (d) 5.55 g [1]
12 Relative formula mass of CaCl = 111
H = 4.05 = 4.05 Mass of CaCl = 111 × 0.05 2
2
1 = 5.55 g
Cl = 71.65 = 2.02 [1] 4 (a) Pb(NO ) (aq) + 2KI(aq) ➞ PbI (s) + 2KNO (aq)
35.5 3 2 2 3
Ratio = C : H : Cl = 1 : 2 : 1 [1] Correct formula [1]

[1]
Balance the equation
Empirical formula: CH Cl [1]
2
Steps to calculate empirical formula: Correct state symbols [1]
1. Calculate the number of moles of each atom. Note: Must get the equation correctly, otherwise
2. Get the ratio by dividing the number of moles of cannot do the questions below.
each by the smallest number of moles. (b) (i) 0.02 mol [1]
3. Form the empirical formula. Number of moles of Pb(NO ) = 6.62
331
(c) 99 = 2 [1] 3 2 = 0.02 mol
49.5
Molecular formula = C H Cl [1] (ii) 0.05 mol 8.30 [1]
2
4
2
Steps to get molecular formula: Number of moles of KI = 116
1. Find the relative molecular mass of the molecule
based on empirical formula. = 0.05 mol
2. Divide the molecular formula by the mass (iii) KI / potassium iodide [1]
calculated from step 1. 0.05 mol is more than 0.04 mol. [1]
Cambridge IGCSE TM
146 Ace Your Chemistry
Answers.indd 146 3/4/22 3:54 PM

If Pb(NO ) is 0.02 mol, KI should be 0.04 mol. (c) The amount that contains the same number
3 2
But the number of moles of Kl is 0.05 mol, of units as the number of carbon atoms in
it is 0.01 mol in excess. 12 grams of carbon-12. / 12 g of carbon-12 /
(iv) Relative formula mass of PbI = 334 [1] Avogadro constant / 6.02 × 10 particles /
23
2
6.68 g [1] atoms / molecules [1]
Mass of PbI = 0.02 × 334 = 6.68 g
2 (d) (i) 0.0005 mol [1]
5 (a) Blue / purple [1] Note: Must change cm to dm .
3
3
3
Mg(OH) is alkaline. 1 dm = 1000 cm 3
2
to green [1] Number of moles of K CO = 0.02 × 0.025
3
2
= 0.0005 mol

MgCl is a salt. Salt is neutral.
2 (ii) 0.08 mol dm [1]
–3
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(b) Number of moles of HCl = 0.025 × 3.5 Ratio = K CO : HCl = 1 : 2
3
2
= 0.088 mol [1] Number of moles of HCl = 2 × 0.0005
Note: Must change cm to dm . = 0.001 mol
3
3
1 dm = 1000 cm 3 0.001
3
Number of moles of Mg(OH) = 0.088 Concentration of HCl = 0.0125
2 2 –3
= 0.044 mol [1] = 0.08 mol dm
Ratio = HCl : Mg(OH) = 2 : 1 (e) 720 cm 3 [1]
2 Refer to the number of moles calculated for 7(b).
Concentration of Mg(OH) = 0.044 Ratio = K CO : CO = 1 : 1
2
2
2 0.0205 Volume of CO = 0.03 × 24 dm 3
3
= 2.15 mol dm [1] 2 = 0.72 dm = 720 cm 3
–3
3
(c) Mass of H O = 203 – 95 = 108 [1] 8 (a) C H (g) + 3.5O (g) ➞ 2CO (g) + 3H O(l)
2 2 6 2 2 2
x = 108 = 6 [1] Correct formula [1]
18 Balanced equation [1]
One mole of H O = 18 g
2 (b) Number of moles of C H = 0.2 mol [1]
6
2
6 (a) 34 g [1] Number of moles of CO = 0.4 mol [1]
2
From the information given, we can get the number Volume of CO = 9.6 dm [1]
3
2
of moles of copper. From the information given, calculate the number
6.4
Number of moles of Cu = of moles of ethane.
64 6
= 0.1 mol Number of moles of C H = 30
6
2
Ratio = Cu : AgNO = 1 : 2 = 0.2 mol
3
Number of moles of AgNO = 0.2 mol The gas produced is carbon dioxide.
3
Mass of AgNO = 0.2 mol × 170 Ratio = C H : CO = 1 : 2
3
6
2
2
= 34 g Number of moles of CO = 0.2 × 2 = 0.4 mol
2
(b) Mass of Ag = 0.2 × 108 = 21.6 g [1] Volume of CO = 0.4 × 24 = 9.6 dm 3
2
Percentage of silver formed = 96.3% [1] 9 (a) Relative atomic mass [1]
Ratio = Ag : AgNO = 1 : 1
3
Number of moles of Ag = 0.2 mol (b) Butane is a covalent compound. [1]
Mass of Ag = 0.2 × 108 = 21.6 g Potassium fluoride is an ionic compound. [1]
Formula to calculate the percentage of yield Relative molecular mass is for a covalent compound.
actual yield Relative formula mass is for an ionic compound.
= × 100%
calculated yield (c) (i) 0.0025 mol [1]
20.8 Note: Must change cm to dm .
3
3
= × 100%
21.6 1 dm = 1000 cm 3
3
= 96.3% Number of moles of Y = 0.06 = 0.0025 mol
24
7 (a) K CO (s) + 2HCl(aq) ➞ 2KCl(aq) + CO (g) + (ii) 71 [1]
3
2
2
H O(l) [1] Relative molecular mass of Y = 0.1775
2 0.0025
(b) Number of moles of K CO = 0.03 mol [1] = 71
2
3
4.15 (iii) Chlorine [1]
Number of moles of K CO =
2 3 138 Based on the information given, it is a gas
= 0.03 mol at room temperature. The mass number of
Number of moles of HCl = 0.06 mol [1] chlorine is 35.5. Chlorine is diatomic at room
Ratio = K CO : HCl = 1 : 2 temperature.
2
3
Number of moles of HCl = 2 × 0.03 mol 35.5 × 2 = 71
= 0.06 mol
Answers 147
Answers.indd 147 3/4/22 3:54 PM

(d) Mass of oxide = 2.19 g [1] 2 C
Number of moles of P = 0.054 mol and At the cathode, H will be reduced because it is less
+
number of moles of O = 0.137 mol [1] reactive than Na . Hydrogen is produced. At the
+
–
Ratio = P : O = 1 : 2.5 [1] anode, OH will be oxidised because there is a higher
–
Empirical formula = P O [1] concentration of OH . Oxygen is produced. Hydrogen
2 5 and oxygen are both gases.
Mass of oxide = 3.87 – 1.68 = 2.19 g
1.68 3 D
Number of moles of P = = 0.054 mol OH is oxidised at the anode. Oxygen is formed. H is
+
–
31
2.19 reduced at the cathode. Hydrogen is formed.
Number of moles of O = = 0.137 mol OH + H ➞ H O
–
+
16 2
Divide the number of moles of each by the smallest Water is being removed from the electrolyte.
number of moles. 4 C
0.054 At the cathode, hydrogen ions gain electrons to form
P = = 1 hydrogen gas. It is being reduced. At the anode, chloride
0.054
0.137 ions lose electrons to form chlorine gas. It is being
O = = 2.5 oxidised. Sodium ions and hydroxide ions are left in the
0.054
To round up the number, the ratio number × 2. solution, forming sodium hydroxide. It is alkaline.
Ratio of P : O = 2 : 5 5 B
Solid cannot be used as the electrolyte.
(e) One mole of P O = 110 g [1]
3
2
P O = 220 g [1] 6 C
4 6
10 (a) Number of moles of HCl The only product formed is water which is harmless to
the environment. Hydrogen-oxygen fuel cells are more
= 0.1 dm × 0.1 mol dm efficient than fossil fuels.
3
–3
= 0.01 mol [1]
Number of moles of CaCO 7 A
3

Electrons are supplied from the battery at the cathode.
= 0.01 mol Cations will be attracted to the cathode. Potassium ions
2 are reduced by gaining electrons.
= 0.005 mol [1]
Ratio = HCl : CaCO = 2 : 1 8 C
3
There are 4 ions present in aqueous copper(II) sulfate,

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Mass of CaCO = 0.005 mol × 100 = 0.5 g [1]
2+
2–
+
2+
3 H , Cu , SO and OH . At the cathode, Cu will be
–
4
+
(b) 0.5 × 100% = 89.3% [1] selected instead of H . This is because copper is less
0.56 reactive. Copper is deposited at the cathode. Copper
mass of pure is a brown solid. At the anode, OH will be oxidised.
–
substance Oxygen is produced. Bubbles of gas are seen. H and
+
Percentage of purity = × 100%
mass of impure SO remain in the solution forming sulfuric acid which
2–
4
substance is acidic. As the concentration of sulfuric acid increases,
(c) Molar mass of O = 16 × 3 = 48 g mol [1] the blue aqueous copper(II) sulfate turns paler.
–1
3
Percentage composition of oxygen 9 D
= 48 × 100% In the refining process of an impure copper, a pure
100 copper is placed at the cathode for copper deposition.
= 48% [1] The impure copper is placed as the anode. Since it is the
refining of copper, a copper salt solution should be used.
(d) Number of moles of CO = 0.005 mol [1] Copper(II) sulfate, copper(II) nitrate or any copper salt
2
Number of molecules which is soluble can be used as the electrolyte.
= 0.005 mol × 6.02 × 10 23 At the cathode, copper is deposited, Cu + 2e ➞ Cu. The
2+
= 0.0301 × 10 23 mass increases.
2+
= 3.01 × 10 [1] At the anode, copper is oxidised, Cu ➞ Cu + 2e. The
21
Number of molecules mass decreases.
= number of moles × Avogadro constant
10 B
There are 4 ions present in sodium bromide solution,
–
+
+
–
4 Electrochemistry Na , H , OH and Br . +
+
At the cathode, H will be selected instead of Na . This
is because hydrogen is less reactive. Hydrogen gas is
Part 1: Multiple-choice Questions produced at the cathode. Bubbles of colourless gas
–
1 C are seen. At the anode, Br will be oxidised. Bromine is
In electrolysis, positive ions gain electrons at the cathode produced. Bromine is a reddish-brown liquid.
and negative ions lose electrons at the anode.
Cambridge IGCSE TM
148 Ace Your Chemistry
Answers.indd 148 3/4/22 3:54 PM

Part 2: Structured Questions (e) The copper electrode dissolves and loses
electrons to form Cu at the anode. [1]
2+
1 (a) Molten lithium chloride [1] The rate of removal of Cu and production of
2+
(b) Concentrated hydrochloric acid [1] Cu is the same. [1]
2+
(c) Copper [1] At the anode, the copper electrode will lose
2+
(d) Water [1] electrons to form Cu since it is not inert.
(e) Concentrated aqueous potassium iodide [1] 4 (a) Left: Anode [1]
(f) Hydrogen [1] Right: Cathode [1]
Metal ion is a cation. It will be attracted to the
(g) Oxygen [1] cathode. So, the key should be placed at the
(h) Sodium chloride [1] cathode.
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3+
2 (a) Breakdown of ionic compounds [1] (b) Cathode: Cr + 3e ➞ Cr [1]
3+
in molten or aqueous solution [1] Anode: Cr ➞ Cr + 3e [1]
by the passage of an electric current. [1] (c) To prevent uneven surface [1]
(b) Graphite / Carbon / Platinum [1] (d) Chromium does not stick well on iron. [1]
(c) Clockwise direction [1] (e) The colour of the solution turns purple slowly.
[1]
Ni is attracted to the key. [1]
2+
3+
Chromium will dissolve to form Cr at the
anode. [1]
long line is “+”, short line is “–”. Electrons move Nickel ions from the electrolyte are attracted to the
from “–” to “+”.
cathode before chromium ions from the anode are
(d) 2H + 2e ➞ H [1] enough to plate on the key.
+
2
There are 4 ions in the electrolyte: Chromium(III) nitrate solution is purple.
+
–
H , Na , OH , SO 4 2– Nickel(II) nitrate is bright green.
+
More reactive cations stay as ions. Sodium is more (f) The colour of the metal deposited gets lighter.
reactive than hydrogen. H ions will gain electrons
+
to turn into hydrogen gas. [1]
Nickel is less reactive than chromium, so nickel
(e) Oxygen [1] ions will be attracted to the cathode instead of
2–
–
Anions, OH and SO , are attracted to the anode. chromium ions in the electrolyte. Chromium metal
4
But OH ions release electrons to form oxygen. is silvery gray. Nickel metal is silvery white.
–
(f) 4OH ➞ O + 2H O + 4e [1] (g) Shiny / Look nice / Bright / Attractive [1]
–
2
2
2+
(g) Oxidation [1] 5 (a) Cu ➞ Cu + 2e [1]
loses electrons [1] (b) Oxidation [1]
3 (a) At the cathode, lose electrons [1]
Cu + 2e ➞ Cu [1] (c) Aqueous copper(II) sulfate / nitrate solution
2+
Copper is formed. [1] [1]
At the anode, The electrolyte used should be copper compound
2Br ➞ Br + 2e [1] solution. This is to ensure only copper is obtained.
–
2
Bromine is formed. [1] (d) Mass increases [1]
There are 4 ions in the electrolyte: H , Cu , OH , Br – Copper is deposited.
+
2+
–
More reactive cations stay as ions. Hydrogen is more
reactive than copper. Cu ions will gain electrons to Mass decreases 2+ [1]
2+
turn into copper. Copper dissolves to form Cu , the size of impure
–
–
Br and OH are attracted to the anode. But Br – copper decreases.
releases electrons to form bromine. (e) Sludge / Slag / Impurities [1]
(b) Concentration of water molecules increases. [1] (f) Brass [1]
(g) Any one from: [1]
(c) A brown solid is deposited at the cathode. [1]
Copper is a brown solid. • Harder / stronger
• Higher density

A reddish-brown liquid is formed at the anode. • Better conductor of electricity
[1] • Corrosion resistance
Bromine is a reddish-brown liquid. • Better conductor of heat
(d) Oxygen is formed at the anode. [1] 6 (a) A substance that can be burned [1]
–
–
When the concentration of Br is low, OH will
release electrons to form oxygen. to generate energy [1]
Answers 149
Answers.indd 149 3/4/22 3:54 PM

(b) 2H ➞ 4H + 4e [1] • Paints
+
2
O + 4H + 4e ➞ 2H O [1] • Bleaches
+
2 2
(c) 2H + O ➞ 2H O [1] • Hydrochloric acid
2
2
2
(d) Energy gained to break the bonds = 1362 kJ/mol Sodium hydroxide
[1] Any one from: [1]
Energy lost to form the bonds = 1852 kJ/mol • Soaps
[1] • Detergents
Enthalpy change = –490 kJ/mol [1] • Textiles
(432 × 2) + 498 = 1362 kJ/mol • Paper
(463 × 4) = 1852 kJ/mol • Ceramics
Enthalpy change = energy gained to break the • Dyes
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bonds – energy lost to form the bonds • Medical drugs
= 1362 – 1852 8 (a) Oxygen [1]
= – 490 kJ/mol
Glowing splint [1]
(e) Advantage relight [1]
Any one from: [1] OH will lose electrons.
–
• No pollutant / Only water is formed 4OH ➞ O + 2H O + 4e
–
2
2
• Give out plenty of energy Oxygen is needed in burning. The glowing splint will
• Renewable resources relight when exposed to oxygen.
Disadvantage (b) Copper(II) sulfate contains ions [1]
Any one from: [1] In liquids, ions are moving. [1]
• Can cause explosion with a spark In solids, ions are not moving. [1]
• Hard to store (c) Cathode: Cu + 2e ➞ Cu [1]
2+
• Costly Anode: Cu ➞ Cu + 2e [1]
2+
• Hydrogen filling stations are not yet widely
available 9 (a) Silver [1]
+
7 (a) Na , H , Cl , OH [4] (b) Ag ➞ Ag + e [1]
–
+
+
–
Ag + e ➞ Ag [1]
+
(b) Hydrogen [1]
+
2H + 2e ➞ H [1] (c) The spoon is not totally covered by the solution.
2
[1]
(c) 2Cl (aq) ➞ Cl (g) + 2e If the spoon is not totally soaked in the solution, part
–
2
Correct balanced equation [1] of the spoon will not be plated. The appearance of
Correct state symbols [1] the final product will be less attractive.
(d) Damp litmus paper [1] (d) Any two from: [2]
bleached [1] • Shiny
• Attractive
(e) Titanium cannot react with chlorine gas. [1]
• Prevent rusting
(f) To keep the gases apart [1]
10 (a) Chlorine, [1]
(g) Change from green to purple [1] hydrogen [1]
NaOH is alkaline. [1] and sodium hydroxide [1]
Chlorine gas is produced at the anode. Hydrogen
+
gas is produced at the cathode. (b) Cathode: 2H + 2e ➞ H [1]
2
–
–
Na and OH remain in the electrolyte, forming Anode: 2Cl ➞ Cl + 2e [1]
+
2
–
+
NaOH. Na and OH remain in the solution, forming
NaOH. [1]
(h) Hydrogen Note: Students are encouraged to put both words
Any one from: [1] and equations to describe how the products are
• Make nylon obtained.
• Make hydrogen peroxide
• Make margarine (c) Only hydrogen gas. Chlorine gas and sodium
• As fuel hydroxide are not produced. [1]
At the anode, oxygen will be produced. [1]
Chlorine Na and Cl remain in the solution, forming
–
+
Any one from: [1] NaCl. [1]
• Plastic PVC Water is being removed. [1]
• As a solvent At the cathode, H is less reactive than Na . H gains
+
+
+
• Medical drugs electrons to form hydrogen gas.
• Pesticides
Cambridge IGCSE TM
150 Ace Your Chemistry
Answers.indd 150 3/4/22 3:54 PM

OH will lose electrons instead of Cl since the Energy needed to break the bonds:
–
–
–
concentration of Cl is low. C–H 435 × 4 = +1740 kJ/mol
–
4OH ➞ O + 2H O + 4e O=O 498 × 2 = +996 kJ/mol
2
2
The cathode has no change. H gains electrons, Total = +2736 kJ/mol
+
leaving Na in the solution. Energy needed to form the bonds:
+
H and OH are attracted to the electrodes and turn C=O 803 × 2 = –1606 kJ/mol
+
–
into molecules. So, water molecules (H O) in the O–H 464 × 4 = –1856 kJ/mol
2
solution are being removed. Total = –3462 kJ/mol
Enthalpy change = 2736 – 3462
5 Chemical Energetics = –726 kJ/mol
10 D
Part 1: Multiple-choice Questions This statement is not related to enthalpy change.
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1 D 11 D
The reaction between calcium carbonate and sulfuric Uranium-235 is a radioisotope. It is used to generate
acid is neutralisation. energy. But energy is released through the decay of
Neutralisation is mostly exothermic. Thermal atoms. It does not need to react with oxygen.
decomposition and cracking are both endothermic as
the reactions take in heat to break down the molecules. Part 2: Structured Questions
Rusting is an exothermic reaction as it releases heat. 1 (a) Ag (aq) + Cl (aq) ➞ AgCl(s)
–
+
2 B Correct formula [1]
During photosynthesis, energy from sunlight is absorbed. Correct state symbols [1]
3 B The ionic equation shows the reacting ions in a
The bottom of the flask freezes and this shows that part chemical reaction. The precipitate formed is a solid.
of the flask is cold.
Therefore, this reaction is endothermic. Heat is taken (b) Exothermic [1]
in from the surroundings to break the bonds. In an The temperature increases at the end of the
endothermic reaction, the energy released is lower than reaction. Heat was given out.
the energy absorbed. Exothermic reactions give out heat.
4 C (c)
An exothermic reaction releases heat to the surroundings. AgNO 3 + KCI
N + 3H ➞ 2NH is a reaction in the Haber process.
2
3
2
Making ammonia is an exothermic reaction.
The rest are all endothermic reactions.
5 C AgCI + KNO 3
The energy level diagram shows an exothermic reaction
as the energy level in the molecule reduces. The energy
in the molecules is released to the surroundings. Correct energy level change [1]
The condensation of water vapour releases heat. Energy Correct label [1]
is released when the particles from far apart move
closer. Therefore, it is an exothermic reaction. Arrow pointing down [1]
The energy level decreases since the energy in the
6 B molecules is given out to the surroundings.
Energy is absorbed to break the bonds in order to form
new compounds – glucose and oxygen. (d) The precipitate will form faster. [1]
More particles per unit volume. [1]
7 A Particles collide more frequently. [1]
1 When the enthalpy change is negative, it is an
exothermic reaction. 2 (a)
2 In an exothermic reaction, the reactants have a lower H H
energy than the products. O O O C O H O H
3 In an exothermic reaction, the energy in the molecules H C C O H + O O O C O + H O H
O
H O H
O
is released to the surroundings. Therefore, the reading H H
on the thermometer will increase. All the molecules are displayed, [1]
8 A showing all bonds. [1]
This is a neutralisation reaction. Neutralisation reaction Oxygen and carbon dioxide have double bonds.
is an exothermic reaction. In an exothermic reaction, [1]
energy is released. Therefore, the energy level reduces
after the reaction. (b) Energy taken in to break the bonds
9 B = 4586 kJ/mol [1]
Enthalpy change = energy taken in to break the bonds – Energy given out to form the bonds
energy given out to form the bonds = 5410 kJ/mol [1]



Answers 151







Answers.indd 151 3/4/22 3:54 PM

Enthalpy change = –824 kJ/mol [1] Correct energy level change [1]
(410 × 5) + 347 + 336 + 365 + (496 × 3) = 4586 kJ/mol Correct label [1]
(805 × 4) + (365 × 6) = 5410 kJ/mol Arrow pointing up [1]
Enthalpy change = energy taken in to break the
bonds – energy given out to form the bonds (d) (i) The minimum energy needed by the
= 4586 – 5410 particles [1]
= –824 kJ/mol to start a chemical reaction by collision [1]
(c) Exothermic [1] (ii) The catalyst reduces the activation energy.
The energy given out to form the bonds [1]
is greater than [1]
the energy taken in to break the bonds [1]
6 Chemical Reactions
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3 (a) V [1]
Part 1: Multiple-choice Questions
– + 1 D
(b) (i) Magnesium is more reactive. [1] Keep the concentration of reactants the same will not
More reactive metals will tend to lose electrons change the rate of reaction.
to form ions. 2 C
(ii) Mg ➞ Mg + 2e [1] Based on the graph, experiment 2 has a higher rate of
2+
reaction. Therefore, the molecules in experiment 2 have
(c) (i) Hydrogen [1] more kinetic energy.
In the electrolyte, there are H and Na . The reactions experiments 1 and 2 complete at the
+
+
Na is more reactive. It will stay as an ion in same volume of gas showing that the total volume of
+
the solution. H will gain electrons to form gas collected is the same. This is because the volume of
+
hydrogen gas at the positive pole. reactants has no change.
+
(ii) 2H + 2e ➞ H [1] When a catalyst is used, the rate of reaction increases.
2 The catalyst lowers the activation energy, thus the
(d) (i) Any one from: [1] reaction completes at a higher rate. If a catalyst is added,
• Change the magnesium strip to a more the line should be above experiment 1.
reactive metal e.g. calcium, lithium
• Change the copper strip to a less reactive 3 B
metal e.g. silver, gold The difference between the two experiments is the size
The further apart the metals are in the of magnesium used. In experiment 2, the powdered
reactivity series, the higher the voltage will be. magnesium used has a bigger surface area than the
(ii) Decreases [1] magnesium ribbon. Bigger surface area promotes a
higher rate of reaction.
Zinc is less reactive than magnesium. So, the line plotted for experiment 2 is above the line
(e) (i) Copper, lead, iron, zinc, magnesium [1] plotted for experiment 1 on the graph.
(ii) 0.63 V [1] This shows that the reaction completes at a higher rate /
took shorter time to collect the same amount of gas.
1.1 – 0.47 = 0.63 V
4 (a) Energy taken in to break the bonds 4 A
The smaller the size of a substance, the higher its surface

= 1941 kJ/mol [1] area. The higher surface area exposes more particles for
Energy given out to form the bonds the reaction.
= 1616 kJ/mol [1] 5 D
Enthalpy change = +325 kJ/mol [1] If the bung is not replaced by cotton wool, no gas will
945 + (498 × 2) = 1941 kJ/mol escape. Therefore, the reading on the balance will not show
2 × (201 + 607) = 1616 kJ/mol any changes. The rate of reaction cannot be calculated.
Enthalpy change = energy taken in to break the
bonds – energy given out to form the bonds 6 C
= 1941 – 1616 A catalyst is used to lower the activation energy.
= +325 kJ/mol Therefore, the equilibrium can be achieved faster.
Increasing the temperature will always increase the rate
(b) Endothermic [1] of reaction. (Do not confuse between equilibrium and
(c) rate of reaction.)
N + 3H L 2NH 3
2
2
This symbol “ L ” shows it is a reversible reaction.
2NO 2
Based on the equation, the mole ratio of the reactants
to the product is 4 : 2. A decrease in pressure favours the
direction that produces more gas molecules.
N 2 + 2O 2 Therefore, lowering the pressure will reduce the yield of
ammonia.


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Answers.indd 152 3/4/22 3:54 PM

7 A (c) (i)
Increasing the concentration of reactants increases the
particles per unit volume. The particles collide more
frequently. or
8 B
The forward reaction is endothermic. Increasing
the temperature favours the endothermic reaction. [1]
Therefore, increasing the temperature increases the
yield of products. (ii)
9 D
Oxidation = gaining oxygen, losing electrons, increase in Volume of gas / cm 3
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oxidation number
Reduction = losing oxygen, gaining electrons, decrease in
oxidation number Time / s
[1]
2Mg(s) + O (g) ➞ 2Mg O (s)
2–
2+
2 (iii) The flask is heated:
Oxidation number: 0 –2 More particles have enough energy to
The oxidation number decreases from 0 to –2.
react. [1]
10 A Collision rate increases. [1]
Reduction is a process that shows a decrease in oxidation More successful collisions / The energy
number. gained is greater than the activation
H + O ➞ H O energy. [1]
2 2 2 2
Oxidation number: 0 –1
11 D
The sum of the oxidation numbers in an ion is the same
as the charge on the ion.

Part 2: Structured Questions

1 (a) Carbon dioxide escapes from the flask. [1]
Carbon dioxide is a gas. It will escape through the Powdered calcium carbonate is used:
cotton wool. More particles are exposed for the reaction.
[1]
(b) (i) Mass of flask Collision rate increases. [1]
and contents / g
More successful collisions / The energy
gained is greater than the activation
energy. [1]
T 2 cm 1 cm
Time / s
2 cm
At the end of the line when the line stays 1 cm
stagnant. [1]
2 cm 1 cm
(ii) Mass of flask Surface area Surface area
and contents / g = 6 × (2 × 2) cm 2 = 8 × (6 × (1 × 1)) cm 2
= 24 cm 2 = 48 cm 2
2 (a) Measure the initial weight. [1]
Measure the final weight at the end of the
Time / s reaction. [1]
Its weight is unchanged. [1]
Above the original line [1] (b) The line is above the original line. [1]
Ends at the original line [1] Stop at the same volume of gas collected. [1]
When the concentration of the reactant
decreases by half, the rate of reaction (c) The rate of reaction decreases. [1]
decreases by half too. So, the mass of flask and Less surface area available for the reaction. [1]
its contents decreases slower. Collision rate decreases. [1]
But the amount of products formed does not
change. So, the line will end at the same line. (d) Use a glowing splint [1]
Relit the splint [1]




Answers 153







Answers.indd 153 3/4/22 3:54 PM

(e) (i) A substance that will oxidise another The ratio of the number of molecules of the
substance [1] reactants to the products = 2 : 2
itself being reduced [1] Increasing the pressure will not affect the yield.
(ii) Potassium manganate(VII) [1] (f) Achieve the equilibrium faster [1]
MnO ➞ Mn 2+
–
4
Mn is reduced to Mn . It changes from 5 (a) The reaction can go forward [1]
7+
2+
purple to colourless. and backward [1]
The reaction is reversible.
3 (a) A chemical reaction that obtains energy [1]
from light [1] (b) Endothermic [1]
Energy is taken in [1]
(b) The uncovered part is exposed to light. [1] to break the bonds [1]
Silver bromide on the film decomposes, [1]
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turns into silver which is black. [1] (c) Turns blue [1]
2AgBr ➞ 2Ag + Br 2 6 (a) A chemical reaction in which a more reactive
(c) (i) Photosynthesis [1] metal displaces [1]
(ii) Chlorophyll [1] a less reactive metal from its compounds [1]
2+
2+
Without chloroplasts, photosynthesis cannot (b) Zn(s) + Cu (aq) ➞ Zn (aq) + Cu(s)
be carried out. Correct formula [1]
Correct state symbols [1]
4 (a) Reaction 2 [1]
The energy needed to break the bonds is lower (c) Blue to colourless [1]
[1] Copper(II) sulfate is blue. Zinc sulfate is colourless.
than the energy given out to form the bonds. [1] Zinc is dissolved. [1]
The “–” sign shows that the forward reaction is Zinc is a solid before the reaction starts. It will
exothermic. dissolve when reacting with copper(II) sulfate.
(b) A brown solid is formed. [1]
CO + H 2 O Copper is a brown solid that does not dissolve in a
salt solution.
(d) Copper(II) sulfate is the oxidising agent. [1]
An oxidising agent is a substance that will oxidise
CO 2 + H 2
another substance and itself being reduced.
It gains electrons. [1]
Correct energy level change [1] Electrons are gained in reduction.
Correct label [1] (e) Concentration
Arrow pointing down [1]
Energy is released in exothermic reactions.
The total energy of the products is less than the
total energy of the reactants.
(c) The forward reaction is endothermic. [1]
Higher temperature favours the endothermic
reaction. [1]
Shift the equilibrium to the right. [1] Time / s
The “+” sign shows that the forward reaction is Below the original line [1]
endothermic. Stop at the same place [1]
(d) Increase the temperature [1] (f) More particles have enough energy to react. [1]
The forward reaction is endothermic for reaction Collision rate increases. [1]
3. Increasing the temperature favours the More successful collisions / The energy gained
endothermic reaction.
is greater than the activation energy. [1]
Decrease the pressure [1]
CH (g) + H O(g) L CO(g) + 3H (g) 7 (a) Gain electrons [1]
2
4
2
2+
The ratio of the number of molecules of the Zn gains electrons to form Zn.
reactants to the products = 2 : 4 (b) Zn + 2e ➞ Zn
2+
Lowering the pressure favours the side of Correct formula [1]
equilibrium with more gas molecules.
Balanced equation [1]
(e) The number of molecules is the same on both (c) (i) Carbon [1]
sides of equilibrium. [1] A reducing agent is a substance that will reduce
CO(g) + H O(g) L CO (g) + H (g)
2 2 2 another substance and itself being oxidised.
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Answers.indd 154 3/4/22 3:54 PM

C + O ➞ CO 2 Hydrogen gas:
2
Oxygen is reduced. Carbon is oxidised. Cracking of ethane [1]
(ii) Zinc oxide / ZnO [1] Cracking: Ethane ➞ ethene + hydrogen
An oxidising agent is a substance that will or
oxidise another substance and itself being
reduced. Reacting methane with steam [1]
2+
Zn + 2e ➞ Zn Methane + water ➞ carbon dioxide + hydrogen
(d) Carbon is less reactive than aluminium. [1] (b) Nitrogen and hydrogen are mixed under
200 atmospheres [1]
8 (a) The forward and backward reactions are at the Iron catalyst is used [1]
same rate. [1] at 450°C [1]
The concentrations of the reactants and Gases are compressed in a compressor at a pressure
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products remain unchanged. [1] of 200 atmospheres.
(b) (i) Increases [1] The compressed gases then flow to a bed of hot iron
catalyst at 450°C.
2 [1]
The number of molecules of the reactants (c) To increase the rate of reaction [1]
is more than the number of molecules of (d) Lowering the temperature favours the
the products. [1] exothermic reaction. [1]
Higher pressure favours the side of equilibrium The equilibrium shifts to the right. [1]
with few gas molecules.
The equilibrium will shift to the right, and the (e) The equilibrium shifts to the right. [1]
yield increases. The yield increases. [1]
(ii) Remains the same [1] High pressure favours the side which produces
3 [1] fewer gas molecules. [1]
The number of molecules of the reactants The number of molecules for reactants is 4 and the
and the number of molecules of the number of molecules for product is 2.
products is the same. [1] (f) Low rate of reaction [1]
Increasing the pressure will not give effect
to an equilibrium when the reactants and 11 (a) Fossil fuel / sulfur bed [1]
products have the same number of molecules. (b) Increase the surface area [1]
(iii) Decreases [1] Increase the rate of reaction [1]
1 [1] 2 cm
The number of molecules of the reactants 1 cm
is less than the number of molecules of the 2 cm
products. [1] 1 cm
Higher pressure favours the side of equilibrium
with fewer gas molecules. The equilibrium 2 cm 1 cm
shifts to the left, and the yield decreases. Surface area Surface area
= 6 × (2 × 2) cm 2 = 8 × (6 × (1 × 1)) cm 2
9 (a) Purple [1] = 24 cm 2 = 48 cm 2
to colourless [1]
(b) The oxidation number of manganese reduces (c) S + O ➞ SO [1]
2
2
from +7 [1] (d) The reaction that can move forward and
to +2 [1] backward. [1]
Mn is purple. Mn is colourless.
2+
7+
(e) The equilibrium shifts to the left. [1]
(c) Oxidising agent [1] The higher temperature favours the
(d) Potassium iodide [1] endothermic reaction. [1]
(e) Add sodium hydroxide solution / ammonia(aq) (f) (i) The equilibrium shifts to the right. [1]
[1] The higher pressure favours few gas
Fe – green precipitate [1] molecules. [1]
2+
Fe – brown precipitate [1] (ii) The yield is high at 2 atm. [1]
3+
Fe(OH) is a green precipitate. (g) Vanadium(V) oxide [1]
2
Fe(OH) is a brown precipitate.
3 (h) Add concentrated sulfuric acid [1]
10 (a) Nitrogen gas: Add water [1]
From air [1] SO + H SO ➞ H S O
Nitrogen can be obtained by fractional distillation. 3 2 4 2 2 7
H S O + H O ➞ 2H SO
2 2 7 2 2 4


Answers 155







Answers.indd 155 3/4/22 3:54 PM

12 (a) Zn(s) + CuCl (aq) ➞ ZnCl (aq) + Cu(s) 5 A
2 2
Aluminium oxide is an amphoteric oxide. An amphoteric
oxide can act as both an alkali and an acid. Therefore, it



0 +2 –1 +2 –1 0 neutralises both the acid and base.
1 mark if all oxidation numbers of reactants are 6 B 2+ –

Lead ion (Pb ) and iodide ion (I ) are needed to form
correct. [1] lead iodide.
1 mark if all oxidation numbers of products are
correct. [1] 7 C
Sulfur dioxide is acidic. It cannot neutralise acids.
(b) Yes [1] Zinc oxide is an amphoteric oxide. It neutralises both
The oxidation number of Zn changes from 0 to acids and bases.
+2. [1] Iron(III) oxide is alkaline. It neutralises acids.
It is an oxidation as the oxidation number Carbon monoxide is a neutral oxide. It has pH 7.
increases. [1] 8 D
The oxidation number of Cu changes from +2 pH 1 pH 7 pH 14
to 0. [1]
It is a reduction as the oxidation number Universal Pink / red Green Blue /
decreases. [1] indicator purple
Methyl orange Red Orange Yellow
(c) Zn(s) + Cu (aq) ➞ Zn (aq) + Cu(s) [1]
2+
2+
When writing an ionic equation, spectator ions are Phenolphthalein Colourless Colourless Pink
not needed.
9 D
(d) It is not a redox reaction. [1] Fe reacts with ammonia to form a red-brown
3+
All ions do not show change in oxidation precipitate.
–
number. [1] Cl reacts with silver nitrate to form silver chloride which
is a white precipitate.
Water droplets are formed due to the condensation of
7 Acids, Bases and Salts water. It means the compound is hydrated.
10 B
Part 1: Multiple-choice Questions Copper is less reactive than hydrogen. It cannot react
with dilute acid. However, copper compounds such as
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Metal oxide is basic. So, copper(II) oxide is basic. The copper(II) oxide and copper(II) carbonate react with
reaction between copper(II) oxide and dilute sulfuric dilute sulfuric acid.
acid is a neutralisation reaction. Before copper(II) Zinc, zinc oxide and zinc carbonate react with dilute
oxide is added, there is dilute sulfuric acid in the sulfuric acid.
beaker. Therefore, the pH is less than 7. Since this is a
neutralisation reaction, the salt solution obtained is Part 2: Structured Questions
neutral, which is pH 7. 1 (a) (i) Aluminium oxide [1]
2 B (ii) Carbon monoxide [1]
When dilute sulfuric acid reacts with barium compound, (iii) Calcium oxide [1]
a white precipitate is obtained. The white precipitate is
barium sulfate. (iv) silicon dioxide [1]
Ba (aq) + SO (aq) ➞ BaSO (s) (v) Iron(III) oxide [1]
2+
2–
4
4
When dilute sulfuric acid reacts with carbonate
compound, carbon dioxide is produced. Bubbles are (vi) Sulfur dioxide [1]
seen. (vii) Carbon dioxide [1]
Cu , Zn , NH react with SO will form aqueous
2–
2+
+
2+
4
4
solutions. (b) Add acid [1]
Dilute sulfuric acid does not react with chloride and alkali (suggest an acid and an alkali) [1]
compound. Both give reactions. [1]
3 D (c) Iron(III) oxide is a base. [1]
Magnesium oxide reacts with dilute acid to form a salt 2 (a) Proton donor / H donor [1]
+
and water.
Copper does not react with dilute acid. (b) H SO ➞ H + HSO [1]
+
–
Calcium carbonate reacts with dilute acid to form a salt 2 4 4
–
+
and carbon dioxide. (c) CH COOH L H + CH COO [1]
3
3
4 B (d) A strong acid is ionised completely in water. [1]
A base can be neutralised by an acid to form a salt. It will A weak acid is ionised partially in water. [1]
turn a damp red litmus paper blue.
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Answers.indd 156 3/4/22 3:54 PM

(e) Use pH meter / universal indicator [1] 4 (a) More than enough [1]
pH 1 – 3: A strong acid / red [1] (b) To ensure all of the acid has reacted [1]
pH 4 – 6: A weak acid / yellow / orange [1]
All of the acid must be reacted to get pure crystals.
(c) The solid dissolved. [1]
The solution turned blue. [1]
Copper(II) oxide is a black solid. It will dissolve when
it reacts with the acid to form a soluble copper(II)
sulfate. Aqueous copper(II) sulfate solution is blue.
(d) Copper(II) oxide [1]
An excess of the solid is added. Therefore, the
or residue is copper(II) oxide.
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Set up a simple cell with a voltmeter. [1]
A weak acid shows a low voltage. [1] (e) The crystals started to form. [1]
A strong acid shows a high voltage. [1] (f) Cannot get blue crystals / get a white solid. [1]
Hydrated copper(II) sulfate is blue, anhydrous
V copper(II) sulfate is white.
– + (g) CuO + H SO ➞ CuSO + H O [1]
2
4
2
4
(h) Water molecules present in the hydrated
crystals. [1]
Acid solution
Example: CuSO .5H O
4 2
(i) To remove impurities [1]
or 5 (a) The change of colour indicates the neutralisation
Reacting with a named metal e.g. Mg, Zn, Pb. reaction has completed. [1]
[1]
A strong acid reacts vigorously. [1] (b) Phenolphthalein [1]
A weak acid reacts less vigorously. [1]
(c) when the solution changes colour. [1]
Repeat the experiment with a known amount
of acid without the indicator. [1]
The experiment should be repeated without adding
the indicator.
Heat the solution in an evaporating dish [1]
until crystallisation point is reached. [1]
To ensure crystals are formed, no overheating is
allowed.
(f) A white precipitate is formed. [1]
Sulfate ions react with barium ions to form Rinse and dry with a filter paper. [1]
solid barium sulfate. [1] Another method should be used.
Ba (aq) + SO (aq) ➞ BaSO (s)
2–
2+
4 4 (d) Thymolphthalein will only change colour when
3 (a) Proton acceptor [1] the pH is above 9.3. [1]
(b) Contains hydroxide ions [1] (e) Calcium carbonate is a solid. [1]
NaOH ➞ Na + OH – Another method should be used.
+
(c) Sodium hydroxide is a strong alkali. It is ionised (f) Graphite electrodes [1]
completely in water. [1] The electrodes used must be inert.
Ammonia is a weak alkali. It is ionised partially Dilute sodium chloride solution is used as the
in water. [1] electrolyte. [1]
The concentration of hydroxide ions [1] At the cathode:
is higher in sodium hydroxide [1] 2H + 2e ➞ H [1]
+
2
(d) Nitrate ion [1] At the anode:
–
Add sodium hydroxide and aluminium foil and 4OH ➞ O + 2H O + 4e [1]
2
2
–
+
then heat them. [1] Na and Cl remain in the solution. / Water is
The damp red litmus paper turns blue. [1] being removed. [1]
+
–
Ammonia gas is produced. Ammonia gas is an alkali. H and OH are removed at the electrodes, making
the concentration of NaCl increases.
(e) Neutralises acidic soil / lake [1]
Calcium carbonate is an insoluble alkali. 6 (a) Lead(II) nitrate [1]
Sodium iodide [1]
Answers 157






Answers.indd 157 3/4/22 3:54 PM

All nitrate compounds are soluble. Bubbles formed in ammonium chloride / gases
All sodium compounds are soluble. formed in ammonium chloride turns the damp
or red litmus paper blue. [1]
Any aqueous solution containing both lead Ammonia gas is produced.
ions and iodide ions. [1] (e) Add sodium hydroxide [1]
An aqueous solution is used to make a precipitate. A blue precipitate is formed for copper(II)
(b) Mix the two aqueous solutions [1] bromide [1]
Filter [1] Copper(II) hydroxide is a blue solid.
A precipitate will be collected in a filter paper. or
Rinse [1] flame test [1]
Rinse it with water to ensure a pure salt is obtained. Lithium gives a red flame. / Copper gives a
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blue-green flame. [1]
Dry with an oven [1]
The drying step must be handled carefully to avoid 9 (a) A [1]
overheating. Dilute hydrochloric acid [1]
Hydrochloric acid contains chloride ions.
(c) Pb + 2I ➞ PbI 2 Zinc carbonate + hydrochloric acid ➞ zinc
–
2+
Correct formula [1] chloride + carbon dioxide + water [1]
Balanced equation [1]
(b) C [1]
(d) Spectator ions [1]
Sodium bromide [1]
(e) Will decompose [1] All sodium compounds are soluble.
7 (a) Silver nitrate [1] Pb + 2Br [1]
–
2+
All nitrate compounds are soluble.
(c) B [1]
Potassium bromide [1] Dilute sulfuric acid [1]
Bromide ions must be present to form silver Sulfuric acid contains sulfate ions.
bromide.
2KOH + H SO ➞ K SO + 2H O
2
4
+
–
(b) Ag (aq) + Br (aq) ➞ AgBr(s) Correct formula 2 4 2 [1]
All the formulas of ions and compound are Balanced equation [1]
correct. [1]
All state symbols are correct. [1] 10 (a) Proton donor [1]
completely dissociated in aqueous solution. [1]
(c) Potassium ion [1]
and nitrate ion [1] (b) (i) Barium sulfate [1]
2+
2–
(d) Silver chloride is insoluble. [1] (ii) Ba + SO ➞ BaSO [1]
4
4
(e) Making coloured pigment for paints / Removal (c) (i) Sulfuric acid + sodium hydroxide ➞
of harmful substances when cleaning up waste sodium sulfate + water [1]
–
+
water. [1] (ii) H + OH ➞ H O [1]
2
8 (a) Lighted splint [1] (d) (i) lithium sulfate + water [1]
Oxygen makes the flame burn brighter. / (ii) zinc sulfate + hydrogen [1]
Hydrogen makes a ‘pop’ sound. [1] (iii) copper(II) sulfate + carbon dioxide + water
(b) Add barium chloride [1] [1]
A white precipitate is formed with zinc sulfate.
[1] 8 The Periodic Table
Barium sulfate is a white solid.
or Part 1: Multiple-choice Questions
Dilute sodium hydroxide and aluminium foil 1 A
and heat [1] The most significant differences between metals and
Zinc nitrate turns the damp red litmus paper transition metals are:
blue. [1] Transition metals have variable oxidation states.
Ammonia gas is produced. Transition metals form coloured compounds.
Transition metals can act as catalysts.
(c) Use damp litmus paper [1] Transition metals form complex ions.
Sulfur dioxide bleaches the litmus paper. [1]
Sulfur dioxide is a bleach. 2 B
As going down Group I, reactivity increases.
(d) Add sodium hydroxide [1] As going down Group VII, reactivity decreases.


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Answers.indd 158 3/4/22 3:54 PM

3 B 7 C
Carbon forms a giant covalent structure which has a high
melting point.
Chromium is a transition element. It has a high melting
The atomic radius increases as going down Group I point.
because the number of shells / orbits increases. Caesium is a metal. As going down the group, the melting
As the atomic radius increases down the group, the point decreases. Caesium has a low melting point.
melting point decreases.
The attraction between the nucleus and electrons in the 8 D
outer shell is weaker as the distance increases. The weak The roman number represents the oxidation state of an
attraction also causes them to become more reactive element. It is important because some elements have
when down the group. variable oxidation states. Iron shows two oxidation states,
2Na + 2H O ➞ 2NaOH + H 2 that is +2 and +3. So, (II) and (III) are used in the naming.
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2
NaOH is alkaline. 9 B
4 C W is sodium. Sodium is very reactive. Sodium reacts with
The element located above iodine in the Periodic Table cold water.
is bromine. Bromine is a red-brown liquid at room X is neon. Neon is unreactive.
temperature. Bromine is more reactive than iodine. Y is manganese. Manganese is a transition metal. It has
variable oxidation states.
5 B Z is silicon. Silicon forms macromolecules with oxygen.
The proton number of helium is 2. It is unreactive.
The proton number of beryllium is 4. Beryllium is a 10 A
metal. It can react with oxygen to form beryllium oxide. Hydrogen is flammable. It can trigger an explosion
The proton number of carbon is 6. Carbon reacts with when it gets in touch with fire or sparks. Helium is an
oxygen to form carbon dioxide. unreactive gas. So, it is safe.
The proton number of oxygen is 8. Oxygen can form
diatomic molecules with each other but cannot form Part 2: Structured Questions
oxides. 1 (a) Increasing proton number [1]
The proton number of neon is 10. It is unreactive.
(b) React in the similar way [1]
6 B
Rubidium is Group I element. It reacts with bromine to Have the same number of electrons in the
form an ionic compound. Rb loses 1 electron to form outer shell / Have the same number of valence
–
+
Rb . Br gains 1 electron to form Br . So, the chemical electrons [1]
formula for rubidium bromide is RbBr. Since rubidium is
Group I element, it cannot form a coloured compound. (c) The number of shells [1]
(d)
1 4
H He
hydrogen helium
1 2
7 9 11 12 14 16 19 20
Li Be B C N O F Ne
lithium beryllium boron carbon nitrogen oxygen fluorine neon
3 4 5 6 7 8 9 10
23 24 27 28 31 32 35.5 40
Na Mg Al Si P S Cl Ar
sodium magnesium aluminium silicon phosphorus sulfur chlorine argon
11 12 13 14 15 16 17 18
39 40 45 48 51 52 55 56 59 59 63.5 65 70 73 75 79 80 84
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 [1]
(e) Number of protons + [1] (d) Very explosive [1]
number of neutrons [1]
(e) (i) The reactivity increases down the group.
(f) It shows the characteristics of a non-metal. [1] [1]

(g) Transition elements [1] (ii) Potassium hydroxide [1]
Hydrogen [1]
2 (a) Density increases down the group. [1] 2K + 2H O ➞ 2KOH + H [1]
Number of protons [1] Can be concluded from the observation
2
2
and neutrons increases [1] through the reactions between elements and
Protons and neutrons give the mass to an atom. water.
(b) Lithium [1] (iii) Lighted splint [1]

(c) Any temperature between 60°C and 75°C [1] Burns with a ‘pop’ sound [1]
The melting point of potassium is 63°C.



Answers 159







Answers.indd 159 3/4/22 3:54 PM

3 (a) Have the same number of valence electrons [1] 5 (a) One atom in a molecule [1]
Valence electrons are the electrons in the outer
shell. (b) (i) Have a full outer shell [1]
(ii) Used to fill balloons [1]
(b) Have the tendency to form ions [1] Used to fill light bulbs [1]
by releasing only one valence electron [1] Used in making advertising signs [1]
to achieve a stable electron arrangement in the
outer shell [1] (c) 2,8 [1]
(c) (i) Sodium loses one electron to form a 6 (a) Iron is harder / stronger. [1]
sodium ion. [1] Iron has a higher density. [1]
Chlorine gains one electron to form a Iron has a higher melting point. [1]
chloride ion. [1] Note: Word of comparison must be used.

(ii) + – (b) Forms coloured compounds [1]
Has variable oxidation numbers [1]
Na Cl
Acts as a catalyst [1]
(c) (i) Carbon [1]
Cl with 7 electrons (represented by crosses) (ii) To prevent it to become too brittle [1]
and 1 electron gained (represented by (iii) Any one from: [1]
dots) [1] • Buildings
Correct charge [1] • Ships
Note: Mark all the electrons using either dots • Car bodies
or crosses.
• Machinery
4 (a) Halogens [1]
(d) (i) Brown / Pink [1]
(b) Two atoms in a molecule [1] (ii) The solid is dissolved. [1]
(c) (i) Greenish-yellow [1] Copper(II) oxide is a solid.
(ii) Solid [1] A blue solution is formed. [1]
Copper(II) sulfate is formed. It is a blue solution.
(d) (i) The reactivity decreases as going down the
group. [1] (iii) Electrical wiring [1]
Copper is a good conductor of electricity.

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The valence electrons in the outermost
shell become further away from the 7 (a)
nucleus. [1]
Attracting an electron becomes difficult. Group I II III IV V VI VII
number
[1]
The number of shells increases as going down Element Na Mg Al Si P S Cl
the group. Number
The electrostatic forces of attraction between of valence 1 2 3 4 5 6 7
the outer shell electrons and the nucleus are electrons
weaker as going down the group.
Valency 1+ 2+ 3+ 4+/– 3– 2– 1–
(ii) 2Fe(s) + 3F (g) ➞ 2FeF (s)
3
2
Balanced equation [1] Typical NaCl MgCl AlCl SiCl PH H S HCl
Correct state symbols [1] compound 2 3 4 3 2
(iii) Red-brown [1] solid [1] Correct numbers of valence electrons for all
elements [1]
(iv) Gain one electron to form a stable outer Correct for all valency [1]
shell. [1] Valency is the loss and gain of electrons to achieve
(e) (i) 2KCl + Br 2 a full outer shell.
Correct formula [1] (b) The number of valence electrons = the group
Balanced equation [1] number [1]
Cl is more reactive than Br.
(c) For Na to Al,
(ii) 2KBr + I 2 the valency is the same as the number of valence
Correct formula [1] electrons [1]
Balanced equation [1] because this is the number of electrons lost to
Br is more reactive than I. achieve a full outer shell. [1]
(iii) No reaction [1] For P to Cl,
I is less reactive than Cl. the valency is 8 – [number of valence electrons]



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Answers.indd 160 3/4/22 3:54 PM

or 9 (a) (i) Neon [1]
Valency + valence electrons = 8 [1] Neon is a noble gas. It is monatomic at room
because this is the number of electrons needed temperature because it is unreactive.
to achieve a full outer shell. [1] (ii) Lithium / Beryllium [1]
(d) (i) Basic oxide to amphoteric oxide to acidic All Group I and II elements form a metal
oxide [2] hydroxide which is alkaline when react with
Metal oxide is basic. water.
Non-metal oxide is acidic. 2Li + 2H O ➞ 2LiOH + H 2
2
Aluminium oxide is amphoteric. (iii) Nitrogen [1]
(ii) Ionic bond [1] 78% of the air is nitrogen. 21% is oxygen.
to covalent bond [1] (iv) Oxygen [1]
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Metals form ionic compounds with chlorine. Iron reacts with oxygen to form iron(II) oxide. It
Chlorine forms covalent bonds with non-metals. is known as rusting.
(e) Macromolecule [1] (v) Lithium [1]
Tetrahedral [1] Lithium is a soft metal which is very reactive.
One silicon atom is bonded to four chlorine It must be stored in oil to stop lithium from
atoms. [1] reacting with oxygen in the air.
(f) (vi) Fluorine [1]
(vii) Carbon [1]
Carbon is inert. It does not react in the
H S H
electrolysis but conducts electricity.
(b) (i) BF [1]
3
(ii) BeF [1]
Correct ratio for H and S [1] 2
2 lone pairs and 2 bonded pairs [1] (iii) Li N [1]
3
8 (a) A and F [1] 10 (a) Any one from:
Both have a full outer shell. [1] (i) Fluorine
Element A has only 1 shell. 2 electrons in the outer Physical property: [1]
shell are considered full. • Yellow gas
• Low boiling point
(b) C and E [2] • Poor conductor of electricity / heat
An ionic compound is formed from the reaction
between a metal and a non-metal. To form a • Low density
compound with the formula of XY, the ratio of the • Soluble in water
charges carried must be 1 : 1. Element C has the Chemical property: [1]
valency of +1, and element E has the valency of –1. • Poisonous
The charges cancel out each other to form an ionic
compound that has zero overall charge. • Forms diatomic molecules
• Reacts with hydrogen to form HF
(c) D [1] • Valency / Oxidation state (–1)
Element D has the valency of –3. Fluorine has the • Forms F –
valency of –1. 1 D atom reacts with 3 fluorine atoms • Reacts with metals / named metal
to form a covalent compound with the formula XF .
3 • Reacts with non-metals / named non-
(d) B [1] metal
Diamond is formed by carbon. Carbon has the • An oxidising agent
electronic configuration of 2,4. • Forms acidic oxides
(e) C [1] (ii) Graphite
The electronic configuration of element C is 2,8,1. Physical property: [1]
Number 2 shows the number of electrons in the • A conductor of electricity
first shell. Number 8 shows the number of electrons • Soft
in the second shell. Number 1 shows the number of
electrons in the third shell. • Lubricant
• High melting point / High boiling point
(f) C [1] • Grey black / black solid
Metals are good conductors of electricity in general. • Slippery / Greasy
Element C is Group I element which is a metal. • Brittle / Breaks when subjected to stress
(g) E [1] • Insoluble in water
Element E is Group VII element. Halogens exist in
diatomic at room temperature.



Answers 161







Answers.indd 161 3/4/22 3:54 PM

Chemical property: [1] (iii) Nitrogen and neon
• Reducing agent / Reduces metal oxides / Physical property: [1]
named metal oxide • Nitrogen is diatomic at room temperature,
• Reacts with / burns in air / oxygen but neon is monatomic.
• Forms an acidic oxide (CO ) Chemical property: [1]
2
• Valency / oxidation state of 2 or 4
• Nitrogen reacts with a metal and a non-
(iii) Titanium metal, but neon does not.
Physical property: [1] • Nitrogen has a valency of 3, but neon has
• A conductor of heat / electricity a zero valency.
• High melting point / High boiling point • Nitrogen is colourless, but neon is
• Forms coloured compounds / coloured coloured.
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ions
• Hard / Strong 9 Metals
• High density
• Malleable Part 1: Multiple-choice Questions
• Ductile
• Sonorous 1 B
• Shiny Vanadium is a metal. There are free moving electrons.
Chemical property: [1] 2 B
• Variable or different valency / oxidation Bronze is a mixture of copper and tin.
state / oxidation number 3 C
• Catalytic activity Iron is a metal. There are free moving electrons.
• Forms coloured compounds / coloured 4 A
ions Making an alloy is to strengthen the properties of an
• Forms complex ions / complexes element so that it is more useful.
• Reacts with acids
• An reducing agent 5 D
• Reacts with non-metals Only very reactive metal reacts with cold water.
Potassium is very reactive.
(b) Any one from: 6 C
(i) Oxygen and chlorine The bigger the distance between two metals in the
Physical property: [1] reactivity series, the greater the voltage.
• Chlorine is a coloured gas, but oxygen is
colourless. 7 A
• Chlorine is poisonous, but oxygen is not. A more reactive metal can displace a less reactive metal
from its compound. Sodium is more reactive than
Chemical property: [1] magnesium.
• Chlorine bleaches litmus paper, but 8 C
oxygen does not. Any metal above carbon in the reactivity series cannot
• Chlorine has a valency of 1, but oxygen be reduced by carbon.
has a valency of 2.
9 D
(ii) Lithium and iron Stainless steel is made of iron, nickel and chromium.
Physical property: [1] Mild steel is made of iron and carbon.
• Iron is hard, but lithium is soft. 10 C
• Iron has a higher density than lithium. These are displacement reactions.
• Iron has a higher melting point than Lead cannot react with all metal compounds. So, it is the
lithium. least reactive.
Chemical property: [1] Zinc reacted with all metal compounds. So, it is the most
reactive.
• Iron forms a coloured compound, but Iron reacted with two metal compounds, and tin reacted
lithium forms a white compound. with one metal compound.
• Iron has catalytic activity, but lithium So, iron is more reactive than tin.
does not. Lead < tin < iron < zinc
• Iron has different oxidation states, but
lithium has only 1. 11 A
• Iron is less reactive than lithium. Aluminium is very reactive. It reacts with oxygen to
form aluminium oxide when exposed to air. Aluminium
oxide is a non-porous layer. The acid has to react with
aluminium oxide before reacting with aluminium.



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