ACE YR IGCSE A TOP APPROACH TO CHEM

12 C (ii) Sodium is a very reactive metal. [1]
Steel is used as the core of an overhead cable to prevent
sagging. This is because steel is strong. Aluminium is a (e) MgO + H O [1]
2
better electrical conductor than steel. CuO + CO [1]
2
13 C 3 (a) Zn + 2HCl ➞ ZnCl + H [1]
2
2
Rusting can be prevented by stopping oxygen from (b) Lighted splint [1]
reacting with iron. Attaching copper to the shipʼs hull Pop sound [1]
cannot prevent rusting because copper is less reactive
than iron. Iron will be reduced to form iron ion and react (c) No reaction [1]
with oxygen. Copper metal is unreactive. It cannot react with
14 A dilute hydrochloric acid. [1]
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X can be zinc. Galvanising is a process of coating steel 4 (a) (i) Carbon is more reactive than zinc. [1]
with zinc.
The metal used to coat steel should be more reactive. (ii) Blast / roast in oxygen to react with zinc
The more reactive metal will lose electrons first. The sulfide. [1]
metal is oxidised. 2ZnS + 3O ➞ 2ZnO + 2SO 2
2
Carbon reacts with oxygen. [1]
Part 2: Structured Questions C + O ➞ CO
2 2
1 (a) (i) Z > X > Y > W [1] Carbon dioxide reacts with more carbon.
(ii) Displacement reaction [1] [1]
(iii) Copper [1] CO + C ➞ 2CO
2
Zinc oxide is reduced by CO. [1]
(b) (i) Sodium hydroxide + hydrogen [1] ZnO + CO ➞ Zn + CO
2
(ii) 2Li + 2HCl ➞ 2LiCl + H 2 Calcium carbonate is added to neutralise
Correct formula for products [1] silicon dioxide. [1]
Balanced equation [1] CaCO + SiO ➞ CaSiO + CO
3 2 3 2
(iii) 2Mg + O ➞ 2MgO (iii) Sulfur dioxide [1]
2
Correct formula for product [1] Carbon dioxide [1]
Balanced equation [1] (iv) The temperature in the blast furnace is
(iv) K + Ag [2] higher than the boiling point of zinc. [1]
+
(c) (i) Any two from: [2] (d) (i) Zinc is more reactive than iron. [1]
• Conduct electricity / heat Zinc loses electrons to form zinc ions. [1]
• Malleable / Ductile Zinc ions react with water and oxygen
• Solid at room temperature instead of iron. [1]
(ii) Any three from: [3] (ii) Sacrificial protection [1]
• Chromium can form coloured Magnesium blocks are also commonly used to
compounds, but calcium does not. protect steel ships.
• Chromium has catalytic activity, but (e) Any one from: [1]
calcium does not. • Coins
• Chromium has variable oxidation states, • Musical instruments
but calcium does not. • Doorknobs
• Chromium can form complex ions, but • Ornaments
calcium does not.
• Chromium is less reactive than calcium. (f) Atoms are of different sizes. [1]
(iii) Add sodium hydroxide. [1] The layers of atoms cannot slide over each other
Chromium turned into a grey-green easily. [1]
precipitate. Calcium turned into a white 5 (a) Any one from:
precipitate. [1] Use: Overhead cable [1]
2 (a) Lead(II) oxide [1] Property: Good conductor of electricity /
Nitrogen oxide [1] Ductile [1]
Or
(b) 2Pb(NO ) ➞ 2PbO + 4NO + O 2 Use: Cooking foil [1]
2
3 2
Correct formula for products [1] Property: Resistant to corrosion [1]
Balanced equation [1] Or
(c) Thermal decomposition [1] Use: Drinks cans [1]
Property: Resistant to corrosion / Light [1]
(d) (i) Sodium nitrite + oxygen [2]



Answers 163







Answers.indd 163 3/4/22 3:54 PM

(b) Any one from: (ii) Sulfur reacts with oxygen to form sulfur
Use: Galvanising iron / steel [1] dioxide and escapes. [1]
Property: Resistant to corrosion [1] S + O ➞ SO [1]
2 2
Or (iii) Silicon dioxide is acidic. [1]
Use: For torch batteries [1] It can be neutralised by calcium oxide.
Property: Conductor of electricity [1] Silicon dioxide + calcium oxide ➞ calcium
(c) Any one from: silicate [1]
Use: Electrical wiring [1] (iv) Phosphorus oxide is acidic. [1]
Property: Good conductor of electricity / It can be neutralised by calcium oxide.
Ductile [1] Phosphorus oxide + calcium oxide ➞
Or calcium phosphate [1]
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Use: Saucepans / saucepan bases [1] (b) (i) Any one from: [1]
Property: Conductor of heat / Malleable / • For buildings
Tough [1]
• Car bodies
(d) Any one from: • Ships
Use: Cutlery / Food containers [1] • Machinery
Property: Resistant to corrosion / Hard / (ii) Particles are arranged in layers. [1]
Waterproof [1] Can slide over each other easily. [1]
Or (iii) More carbon atoms in high-carbon steel.
Use: Medical tools [1] [1]
Property: Resistant to corrosion / Hard / The layers cannot slide over each other. [1]
Waterproof [1]
8 (a) (i) 1 mark for each correct row [3]
6 (a) Iron(III) oxide [1]
Metal
(b) Carbon reacts with oxygen. [1]
The oxidation of carbon is very exothermic. [1] Oxides Iron Magnesium Zinc Copper
Iron(III)
(c) To act as a reducing agent [1] oxide 3 3 7
(d) Add more coke [1] Magnesium
CO + C ➞ 2CO [1] oxide 7 7 7
2
(e) Fe O + 3CO ➞ 2Fe + 3CO 2 Zinc oxide 7 3 7
2
3
Correct formulas [1] Copper(II)
Balanced equation [1] oxide 3 3 3
(f) To remove impurities [1] (ii) Zn + Cu ➞ Zn + Cu [1]
2+
2+
(g) Calcium carbonate + silicon dioxide ➞ calcium [1]
silicate + carbon dioxide [1] (b) (i) magnesium nitrate + zinc [1]
Or
Calcium oxide + silicon dioxide ➞ calcium (ii) ZnCl + H [1]
2
2
silicate [1] (iii) No reaction [1]
Silver is less reactive than potassium.
(h) Iron has a higher density. [1]
(iv) Br + 2Cl [1]
–
(i) Expensive [1] 2
(c) (i) From zinc to lead [1]
(j) (i) Hydrated [1]
iron(III) oxide [1] V
(ii) Any one from: [1]
• Painting Lead Zinc
electrode
electrode
• Greasing Electrolyte
• Coating with plastic of dilute
• Coating with another layer of metal acid
(iii) Prevent oxygen or water from reacting Zinc loses electrons first because it is more
with iron [1] reactive.
7 (a) (i) Carbon reacts with oxygen to form carbon (ii) Metals react by losing electrons. [1]
dioxide and escapes. [1] The more reactive metal will lose electrons
C + O ➞ CO [1] more readily. [1]
2
2
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Answers.indd 164 3/4/22 3:54 PM

(iii) Magnesium, zinc, lead, copper [1] (g) A regular arrangement [1]
of positive ions [1]
(iv) 1.60 V [1]
2.23 V – 0.63 V = 1.60 V and a sea of electrons [1]
9 (a) Zinc is more reactive. [1]
It loses electrons more readily to form zinc 10 Chemistry of the Environment
ions. [1]
Zinc ions react with oxygen and water instead Part 1: Multiple-choice Questions
of iron. [1] 1 B
Iron does not oxidise. [1] The burning of hydrocarbons produces carbon dioxide.
(b) (i) Oxidising agent [1] In a car engine, the temperature is high. Nitrogen and
(ii) Reducing agent [1] oxygen react to form nitrogen dioxide. Hydrocarbons
may contain sulfur. The burning of hydrocarbons
(iii) Iron(III) / Fe [1] containing sulfur produces sulfur dioxide.
3+
2+
(iv) Iron(II) / Fe [1] 2 D
10 (a) Aluminium oxide is dissolved in molten Sulfur dioxide can only be removed through
cryolite. [1] desulfurisation by using limestone.
Cryolite lowers the melting temperature. [1] 3 D
Molten aluminium forms. [1] N – Nitrogen
Anode: P – Phosphorus
K – Potassium
2O ➞ O + 4e [1]
2–
2 4 A
Cathode: Filtration is used to remove the particles. Chlorination is
Al + 3e ➞ Al [1] used to kill bacteria.
3+
(b) Carbon [1] 5 D
reacts with oxygen [1] Gas X is sulfur dioxide. Treating sulfur dioxide with
(c) Any one from: calcium carbonate is called desulfurisation.
Gas Y is carbon monoxide. In a catalytic converter,
Use: Manufacturing aircrafts [1] carbon monoxide reacts with oxygen to form carbon
Reason: Low density / Light [1] dioxide which is less harmful.
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Or
Gas Z is methane. Methane is a greenhouse gas.

Use: Food container [1]
Reason: Resistant to corrosion [1] 6 B
In combustion, oxygen is needed.
(d) (i) 2Al + Fe O ➞ 2Fe + Al O [1] Example: CH + 2O ➞ CO + 2H O
2
3
3
2
2
2
2
4
(ii) Molten iron runs into the cracks and In rusting, oxygen is needed. 4Fe + 3O ➞ 2Fe O 3
2
2
gaps, [1] In extracting aluminium, oxygen is being removed.
and harden [1] 7 B
During photosynthesis, plants take in carbon dioxide and
11 (a) Al O [1] release oxygen.
2
3
(b) Decreases the melting point of alumina [1] During respiration, the lungs take in oxygen.
Alumina melts at 2045°C. Burning needs oxygen. In combustion, a hydrocarbon
Increases the conductivity [1] reacts with oxygen. Therefore, this is the oxidation of
As a solvent / save cost [1] hydrocarbon.
(c) Al + 3e ➞ Al [1] 8 D
3+
There is 21% of oxygen in the air. The amount of oxygen

2O ➞ O + 4e [1]
2–
3
2 is 31.5 cm . Dry air is 100%.
(d) Carbon reacts with oxygen [1] 100 3
Carbon electrodes get eaten away through the Amount of dry air = 21 × 31.5 cm
oxidation of carbon. = 150 cm 3
to form carbon dioxide [1] 9 A
Nitrogen gas is not an air pollutant. Carbon dioxide only
(e) (i) A good conductor of electricity [1] becomes harmful when its concentration is high in the
(ii) Strong [1] air.
Strong steel prevents overhead cables from Carbon monoxide, nitrogen oxide and sulfur dioxide are
sagging. air pollutants.
(f) Any one from: [1] 10 C
• Save energy Desulfurisation is a process for the removal of sulfur
• Reduce carbon dioxide emissions dioxide, but not nitrogen dioxide.
Answers 165




Answers.indd 165 3/4/22 3:54 PM

11 C (b) Cause global warming [1]
Lime kiln is used to produce quicklime, CaO. Carbon dioxide absorbs heat and prevents it
Thermal decomposition: from escaping back into space. [1]
CaCO ➞ CaO + CO 2
3
The raw material, CaCO should be added from Y. (c) Trees use carbon dioxide [1]
3
CO which is released during the process should exit at X in photosynthesis [1]
2
because it is a gas that has very low density.
The product, CaO, is a solid at 600-700 K. It should be (d) Methane [1]
collected at Z. (e) Produce only water [1]
2H + O ➞ 2H O
Part 2: Structured Questions 2 2 2
1 (a) Anhydrous copper(II) sulfate [1] 4 (a) Nitrogen [1]
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White to blue [1] and oxygen react [1]
or at high temperatures in car engines [1]
Anhydrous cobalt(II) chloride [1] (b) N + O ➞ 2NO [1]
2
2
Blue to pink [1] N O , N O and NO are all possible oxides of nitrogen.
2
2
2
2
Note: Must always include the expected result.
Anhydrous = does not contain water (c) Cause acid rain [1]
Oxides of nitrogen are acidic. They dissolve in water
(b) Filter away the fine particles [1] to form nitric acid.
(c) Add chlorine [1] (d) The oxides of nitrogen pass through the
Chlorine kills bacteria. catalytic converter [1]
to form oxygen and nitrogen. [1]
(d) To prevent tooth decay [1] Oxygen reacts with carbon monoxide [1]
Fluorine is commonly used in toothpaste. to form carbon dioxide. [1]
(e) Add carbon [1] Oxygen and nitrogen are the main constituents of
air. They are harmless.
(f) Any two from: [2] Carbon dioxide is naturally occurring and it is less
• Cool hot machinery poisonous than carbon monoxide.
• As a solvent
• Washing (e) Cause respiratory problems [1]
• Move the turbines with steam Particulates can cause health problems for humans
because they irritate the lining of the lungs. The
(g) Does not contain impurities [1] smaller particulates are able to travel deeper into
2 (a) Liquefy the air [1] the lung tissues and cause damage.
Heat and condense the air / Fractional 5 (a) 3 Some of the energy is reflected away as
distillation [1] thermal energy. [1]
Both gases have different boiling points. So, 4 Some thermal energy is lost to space. [1]
fractional distillation is suitable to separate them. 5 Some of the energy is absorbed by greenhouse
(b) Carbon dioxide [1] gases and stays in the atmosphere. [1]
Argon / Any noble gas [1]
Carbon dioxide is not a pollutant. It is released (b) (i) The Earth is warming up. [1]
during respiration. Carbon monoxide is a pollutant. (ii) Climate change [1]
It should not present in the pure air. (iii) Any two from: [2]
(c) (i) Burning of coal / fossil fuel [1] • Droughts
Coal or fossil fuel contains sulfur. • The melting of icebergs
Sulfur reacts with oxygen in burning. • Sea level rises
(ii) Sulfur dioxide dissolves and reacts with • Storms
water [1] • Floods
forms sulfuric acid [1] • The extinction of species
2SO + 2H O + O ➞ 2H SO • Disease transmission
2 2 2 2 4 • Wildfires
(iii) H SO + CaCO ➞ CaSO + CO + H O
4
2
2
2
4
3
[1] (c) Any two from: [2]
(iv) Damage the nervous system [1] • Use wind / waves / tides / fast flowing rivers
to generate energy
3 (a) Carbon monoxide is toxic. [1] • Use nuclear energy
Reduce the amount of oxygen transported to • Use solar energy
the body. [1] • Use hydrogen-oxygen fuel cells
Carbon monoxide will bond with haemoglobin. Less
haemoglobin can take up oxygen for the body. Cells
die of oxygen starvation.
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6 (a) Bleach wood pulp [1] or
(b) Kill bacteria [1] Oxides of nitrogen [1]
Nitrogen and oxygen react in the hot car engine.
(c) (i) A black solid is formed. [1] [1]
Sugar is sucrose, C H O . Water is removed Oxides of nitrogen dissolve in water to form acid rain.
11
12
22
from sucrose leaving the carbon. Carbon is a
black solid. or
(ii) Carbon [1] Lead compounds [1]
Burning of petrol containing lead
[1]
(iii) Any one from: [1] Lead compounds cause brain damage in children, kidney
• Fertilisers and nervous system damage in adults.
• Paint or
• Fibres and plastics Particulates [1]
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• Soap Incomplete combustion [1]
• Detergents Particulates are tiny solid particles formed in an
• Car batteries incomplete combustion of fuels that contain carbon. It
7 (a) Glucose + oxygen ➞ carbon dioxide + water [1] is linked to respiratory problems and cancer.
(b) 6CO + 6H O ➞ C H O + 6O [1] 10 (a) Carbon dioxide [1]
2 2 6 12 6 2 (b) Ammonia [1]
(c) Methane [1] (c) Ethene [1]
Methane is a natural gas. It is also produced by (d) Neon [1]
animals from digestion and anaerobic respiration of (e) Nitrogen [1]
bacteria.
(d) Carbon dioxide is produced in combustion. [1] (f) Chlorine [1]
[1]
(g) Sulfur dioxide
Carbon dioxide absorbs heat. [1]
(h) Hydrogen [1]
(e) Any one from: [1] (i) Carbon monoxide [1]
• Plant more trees 11 (a) Burn sulfur [1]
• Reduce the burning of fossil fuels in the air [1]
• Use solar power or wind power S + O ➞ SO
• Capture greenhouse gases from chimneys 2 2
and bury them underground (b) Stop the growth of bacteria [1]
Buildings or statues made up of limestone, CaCO , (c) Purple [1]
3
will react with acid and release carbon dioxide.
to colourless [1]
(f) The reaction between limestone and acid rain Acidified potassium manganate(VII) is purple.
[1] (d) Sulfurous acid [1]
8 (a) Nitrogen [1] SO + H O ➞ H SO 3
2
2
2
Oxygen [1] (e) Corrode buildings / metal structures / limestone
Argon [1] statues or kill fish / plants [1]
(b) Nitrogen and oxygen react [1] because sulfur dioxide dissolves in water to
at high temperatures in car engines. [1] form acid rain [1]
Oxides of nitrogen dissolve in water to form 12 (a) Heat [1]
nitric acid. [1] Add water [1]
(c) Livestock agriculture / Fermentative digestion
in ruminant animals [1] (b) CaO + H O ➞ Ca(OH) [1]
2
2
Underground gas deposits [1] (c) It is a base. [1]
(d) Photosynthesis [1] Increase the pH of the acidic lake. [1]
Carbon dioxide is used during photosynthesis. (d) (i) Breaking down of a molecule [1]
9 Any three from: by heat [1]
Carbon monoxide [1] (ii) Ca(OH) ➞ CaO + H O [1]
Incomplete combustion [1] 2 2
Carbon monoxide is a poisonous gas. It is bonded with 13 (a) To remove sulfur dioxide [1]
haemoglobin and reduces the concentration of oxygen (b) Sulfur dioxide causes acid rain. [1]
in the blood. (c) A base [1]
or (d) Stays in the soil for a longer time. [1]
Sulfur dioxide [1] 14 (a) Oxygen [1]
Burning of fossil fuels containing sulfur [1] In photosynthesis, 6CO + 6H O ➞ C H O + 6O
Sulfur dioxide dissolves in water to form acid rain. 2 2 6 12 6 2



Answers 167







Answers.indd 167 3/4/22 3:54 PM

(b) Glucose [1] 9 B
The linkage part is at C=C double bond.
(c) Light provides energy. [1]
10 B
(d) Endothermic [1] In addition polymerisation, only one type of monomer
The energy taken in to break bonds is greater than is used, which is an alkene. Alkenes contain C=C double
the energy given out to form bonds. bonds that allow addition polymerisation to happen.
Energy is taken in. [1] In condensation polymerisation, two or more monomers
are used. Different monomers will have different
(e) The rate of reaction increases. [1] functional groups. So, there will be more than one
Light provides energy. [1] functional group in the polymers.
Carbon dioxide and water gain enough energy
to react. [1] Part 2: Structured Questions
1 (a) X: Gasoline / petrol [1]
11 Organic Chemistry Y: Paraffin / kerosene [1]
(b) (i) For cooking [1]
Part 1: Multiple-choice Questions (ii) For making chemicals / plastics [1]

1 A (iii) Waxes / polishes / oil for machinery [1]
Naphtha is a raw material for producing chemicals. (iv) For making tar road [1]
2 A When molecules are large, the fractions
Alkenes can decolourise bromine water from orange to become less runny. It changes from gas at
colourless. the top to solid at the bottom. They are less
An alkene has the general formula of C H . C H and C H flammable. Therefore, the last two fractions
n
2n
3
6
2
4
are alkenes. are not used as fuels.
3 C (c) (i) Contain only [1]
Cracking is the process of breaking down bigger hydrogen and carbon [1]
molecules into smaller molecules and alkenes. (ii) Alkanes have all C–C single bonds. [1]
To get an alcohol, water is added to the alkenes. It is Alkenes have one C=C double bond. [1]
called hydration.
(iii) Add bromine water [1]
4 C Alkane: no change / orange [1]
Hydrogen is a type of fuel that will not produce carbon
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Alkene: decolourised / becomes colourless

dioxide. Water is the only product in the burning of [1]
hydrogen. Bromine water is in orange.
5 A H H H H
The general formula for alkenes is C H . Therefore, the
2n
n
empirical formula should be CH . C C + Br Br Br C C Br
2
6 C H H H H
S and U are alcohols. They are from the same homologous Dibromoethane
series.
R is ethene. 2 (a) The remains of plants and animals that lived
S is ethanol. millions of years ago [1]
T is propanoic acid. can be burned to generate energy [1]
U is propanol.
The fossil fuels are petroleum, coal and natural gas.
7 D (b) Methane [1]
O (c) (i) A family of similar compounds that have
C O the same functional group, so they have
CH 3 CH 2 CH 3
similar chemical properties. [1]
From the structure, the right side of the ester is from a (ii) Any three from: [3]
monomer called methanol. • Same functional group
The left side of the ester is from a monomer called • Same general formula
propanoic acid. • Consecutive members differ by CH
In the naming of an ester, the first part of the name is • Same method of preparation 2
from alcohol and the second part is from carboxylic acid.
Therefore, this ester is called methyl propanoate. • Different physical properties
• Different chain lengths
8 A Note: Can be similarities or differences.
Both nylon and protein are polyamide. They have amide (d) (i) A hydrogen atom in a molecule is replaced
linkage. by a halogen atom. [1]



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Answers.indd 168 3/4/22 3:54 PM

(ii) UV light [1] (d) (i) A process of making a long chain of
Provide the activation energy [1] organic compound [1]
by using one type of monomer [1]
(iii) Chloroethane / dichloroethane /
trichloroethane / tetrachloroethane / (ii) H H
pentachloroethane / hexachloroethane [1]
ClCH CH / ClCH CH Cl / any correct C C
2
2
3
2
number of chlorine atom according to the H H n
named molecule [1]
Note: The question requires the candidate to Correct monomer [1]
write the molecular structure. If the word used Draw the arm to show continuous [1]
is ‘draw’, the candidate should draw as below: Step 1: Draw the structure of ethene but
H H change the C=C double bond to a single bond.
Step 2: Draw the arm at the side of both
Cl C C H carbon atoms.
Step 3: Add brackets and a “n” at the bottom
H H right.
This is an example of a drawn structure. (iii) Polyethene [1]
(e) (i) CH CH CH + 5O ➞ 3CO + 4H O (e) (i) They have the same molecular formula [1]
2
2
2
3
3
2
Correct formula [1] different structural formula [1]
Balanced equation [1] (ii) H H H H H
(ii) Global warming [1]
Carbon dioxide is a greenhouse gas that causes H C C C C C H
global warming. H H H [1]
3 (a) Contains a C=C double bond [1] Tips: Move the functional group which is the
The C=C double bond allows the addition reaction C=C double bond to different locations.
to happen. (f) C H + C H [2]
4
4
10
2
(b) Only one product is formed [1] or
(c) (i) Ethane [1] C H + C H [2]
6
8
3
3
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[1]
The products of cracking include alkanes and
C H
2 6
alkenes.
H H H H Always ensure the total number of carbon and
hydrogen atoms in the products is the same as the
C C + H H H C C H
reactant.
H H H H 4 (a) (i) Fermentation [1]
Nickel [1] (ii) Yeast [1]
(ii) Ethanol [1] 25°C [1]
CH CH OH [1] Yeast is used to catalyse the reaction in the
3 2 absence of air.
H H H H The high temperature used will denature the
yeast.
C C + H O H H C C O H
(iii) High percentage of ethanol [1]
H H H H When the percentage of ethanol reaches a
certain level, the yeast will be denatured.
Phosphoric acid [1]
(b) (i) Adding water [1]
(iii) Dibromoethane [1]
(ii) C H + H O ➞ C H OH
H H H H 2 4 2 2 5
Correct reactants [1]
C C + Br Br Br C C Br Correct product [1]
H H H H [1] (iii) 300°C [1]
60 atm / 6000 kPa [1]
H H H H Phosphoric acid [1]
C C + Br Br Br C C Br (c) Biological method
Advantage [1]
H H H H • Use of renewable resources
UV light [1] Maize or sugarcane is used in fermentation.
These plants can be planted again and again.



Answers 169







Answers.indd 169 3/4/22 3:54 PM

Disadvantage (any one from) [1] A weak acid changes colour to orange /
• Slow yellow. [1]
• Non-recyclable raw materials H and OH are detected by the pH indicator.
+
–
• A lot of land is needed to grow plants (f) (i) Ethyl propanoate [1]
• Need further step to obtain pure ethanol Rules for naming an ester:
The culture broth must be replaced by a new batch The name of the alcohol part is given first, then
even if there is still glucose left. followed by a separate word for the name of
Many plants are needed to produce a small the carboxylic acid part.
percentage of ethanol. So, a lot of land is used to First part ➞ comes from the alcohol
grow crops for the production of ethanol. Second part ➞ comes from the carboxylic acid
The ethanol produced is impure. Fractional
distillation is needed for purification. H H O H H Alcohol
Carboxylic
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Chemical method acid H C C C O C C H
Advantage (any one from) [1]
• Fast H H H H
• Continuous process (ii) Ethanol [1]
• Obtain pure ethanol Propanoic acid [1]
The chemical method is fast. Removing the ethanol (iii) Concentrated sulfuric acid [1]
consistently makes it a continuous process. The
unreacted ethene and steam will be recycled to (iv) H H O H
increase the percentage of yield. Pure ethanol will
be obtained. Therefore, no further steps such as H C C C O C H
fractional distillation are required. H H H
Disadvantage (any one from) [1] Ester linkage [1]
• Use of non-renewable resources A carbon is connected to three other
• Expensive atoms: a single bond to a carbon, a double
• The yield is not high at 300°C. bond to an oxygen, and a single bond to an
Ethene is obtained from petroleum which will run oxygen. [1]
out one day. A great deal of heat is needed because The single-bonded oxygen is connected to
the process which is carried out at the temperature another carbon. [1]
of 300°C will use a lot of energy. This increases the Tips to draw the structure of an ester:
cost. 300°C is a compromised temperature, but the Step 1: Draw the structure of carboxylic acid,
percentage of yield obtained is not high. omitting the OH molecule.
(d) Any one from: [1] Step 2: Connect the alcohol structure to the C
• As a fuel in C=O, with the H removed from the functional
• As a solvent group –OH.
Step 3: Always ensure there is –COO linkage.
5 (a) H O 6 (a) A substance containing very large molecules [1]

H C C O H formed by a lot of small molecules joined
together [1]
H
Correct number of C and H atoms [1] (b) F F F F F
Correct functional group [1]
Ethanoic acids contain two carbon atoms and its C C C C C
functional group is –COOH.
F F F F F
(b) C H 2n + 1 COOH [1] Or any two connected carbon atoms with four
n
(c) (i) Potassium manganate(VII) [1] fluorine atoms [1]
(ii) Change from purple [1]
to colourless [1] (c) F F
–
+
2+
MnO + 8H + 5e ➞ Mn + 4H O C C
4
2
purple colourless
F F
(d) (i) Sodium ethanoate [1] Correct number of C and F atoms [1]
NaOH + CH COOH ➞ CH COONa + H O
3 3 2 Contain 1 C=C double bond [1]
(ii) Neutralisation [1]
(d) Any one from: [1]
(e) A strong acid has a higher concentration of H • High melting point
+
than a weak acid. [1] • Strong / hard
A strong acid changes colour to red. [1] • A conductor of heat
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170 Ace Your Chemistry







Answers.indd 170 3/4/22 3:54 PM

(e) (i) H H H H Physical property [1]
• Tough / strong
C C C C • Insoluble in water
H Cl H Cl • Light
Two repeat units are shown. [1] Or
C–C single bonds [1] Use [1]
• Making tents
(ii) Any one from: [1]
• Water pipes Physical property [1]
• Wellingtons • Tough / strong
• Hoses • Insoluble in water
• Covering for electrical cables • Light
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Or
(f) (i) Do not decompose [1]
by microbes [1] Use [1]
• Making curtains
(ii) Any two from: [2] Physical property [1]
• Do not conduct electricity • Tough / strong
• Unreactive • Insoluble in water
• Light • Light
• Hard / strong
• Not flammable (c) (i) O O
(iii) Any two from: [2] C C O O
• Fill up landfill sites [1]
• Danger to animals (ii) H O O H [1]
• Clog up drains / cause flooding
• Produce greenhouse gases O O
• Produce toxic gases when burnt H O C C O H [1]
• Cause visual pollution
7 (a) Condensation polymerisation (iii) Any one from: [1]
Two types of monomers are used. [1] • Clothing
• Making thread
Addition polymerisation
One type of monomer is used. [1] 8 (a) Amino acid [1]
or (b) O H O H O H
Condensation polymerisation C N C N C N
Make one long chain of molecules and eliminate
one small molecule. [1] Correct amide linkage [1]
Three different amino acids [1]
Addition polymerisation Draw the arm to show continuous [1]
Only one long chain of molecules is formed. [1]
(c) Amide linkage [1]
(b) (i) H H O O
(d) Nylon is made up of two different monomers.
N N C C Protein is made up of more than two types of
monomers. [1]
Correct amide linkage [1] Both sides of the functional group are the same
Draw the arm to show continuous [1] for each monomer in nylon, but monomers in
Correct structure of monomer [1] protein have two different types of functional
(ii) Amide linkage [1] groups in one molecule. [1]
(iii) HCl / hydrochloric acid / hydrogen (e) (i) Breaking down of a molecule [1]
chloride [1] using water [1]
(iv) Use [1] (ii) Protease [1]
• Making ropes (iii) Concentrated hydrochloric acid [1]
Physical property [1] 6 M hydrochloric acid is used in the laboratory
• Tough / strong to hydrolyse proteins. It is boiled for 24 hours.
Or (iv) Paper chromatography [1]
Use [1] 9 (a) A long-chain organic compound [1]
• Making fishing nets and lines which is made of glucose [1]




Answers 171







Answers.indd 171 3/4/22 3:54 PM

(b) It contains C, H and O [1] 11 (a) Condensation [1]
the ratio is 1 : 2 : 1 [1]
(b) O O
(c) O O O C C O O

Correct C–O linkage [1] Correct ester linkage [1]
Draw the arm to show continuous [1] Draw the arm to show continuous [1]
Three repeat units [1] (c) Polyester is formed from dicarboxylic acid and
(d) Water [1] diol monomers. [1]
An ester is formed from monomers with only
(e) Hydrolysis [1] one side carboxyl group and hydroxyl group. [1]

(f) Use paper chromatography [1] (d) Any two from: [2]
Use a locating agent [1] • Disposal in landfill sites
Calculate R value [1] • Accumulation in oceans
f
(g) (i) 2C H OH [1] + 2CO [1] • Formation of toxic gases from burning
2
5
2
Balanced equation [1]
(ii) Without the presence of oxygen [1] 12 Experimental Techniques and Chemical
(iii) Fractional distillation [1] Analysis
Part 1: Multiple-choice Questions
10 (a) They contain carbon and hydrogen [1]
only [1] 1 D
To measure the volumes of two solutions, a pipette
(b) Contain all C-C single bonds [1] is needed. To check if the reaction gives out heat, a
(c) (i) A hydrogen atom is replaced by a halogen thermometer is needed.
atom. [1] 2 B
(ii) UV light [1] D is for titration, C is for filtering away the charcoal, and
(iii) CH CH + Br ➞ CH CH Br [1] + HBr [1] A is for crystallisation.
3
3
3
2
2
(d) (i) Only one product is formed [1] 3 A
A pipette has a smaller diameter. It measures the volume
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H
H
(ii)
H
more accurately compared to a beaker.
H C C C H 4 D
[1] Condenser is used to condense / cool down the water
H Br Br
vapour to water.
(e) H H H H 5 C
Gas Z is denser than air. It cannot move upward.
H C C C C H
6 C
H H [1] If the boiling points of both liquids are below room
But-2-ene [1] temperature, it will exist in gaseous state.
(f) (i) Poly(ethene) [1] 7 A
(ii) First, filter away the copper from the mixture because
H H copper is a solid. Then, heat it to evaporate the excess
water until it reaches its crystallisation point. Lastly, let it
C C cool down and dry to form crystals.
H H n 8 C
Spots 2, 3 and 4 have the same positions as the spots in
Correct monomer [1] the mixture.
Draw the arm to show continuous [1]
9 C
(g) O H O H O H The locating agent is sprayed to visualise the spot as it
can turn the colourless spot into the coloured spot.
C N C N C N 10 A
Correct linkages [1] Water will dissolve the HCl. Concentrated sulfuric acid is
for dehydration. Water will be absorbed.
Draw the arm to show continuous [1]
11 B
(h) Ethanol [1] Na gives a yellow flame. Li gives a red flame. Ca gives
2+
+
+
Butanoic acid [1] an orange-red flame.

Cambridge IGCSE TM
172 Ace Your Chemistry







Answers.indd 172 3/4/22 3:54 PM

12 D (d) Nitric acid
Oxygen: glowing splint re-light / lighted splint burns Nitric acid is made up of H and NO . After the
+
–
3
brighter. reaction is complete, copper ions from copper(II)
Hydrogen: lighted splint makes a squeaky ‘pop’. oxide will chemically join with nitrate ions to form
Chlorine: damp red litmus paper is bleached. copper(II) nitrate.
Carbon dioxide: limewater turns milky / cloudy.
(e) Black solid dissolves. [1]
Part 2: Structured Questions The solution turns blue. [1]
1 (a) Simple distillation [1] Copper(II) oxide is a black solid. Copper(II) nitrate is
blue and it is soluble.
Simple distillation is used to separate liquids with
different boiling points. Salt has a much higher (f) Copper(II) oxide + nitric acid ➞ copper(II)
boiling point than water. Simple distillation is nitrate + water [1]
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suitable to obtain water.
(g) 2Cu(NO ) ➞ 2CuO + 4NO + O
(b) Paper chromatography [1] 3 2 2 2
Carotene and xanthophyll are pigments in leaves. Correct formula for two products [1]
They can be separated using paper chromatography. Balanced equation [1]
(c) Fractional distillation [1] 4 (a) Fractional distillation [1]
Crude oil contains different types of hydrocarbons. (b) Liquefied the mixture of gases [1]
The difference in boiling points can be small. Heat [1]
Fractional distillation is suitable to separate them.
Condense / cool [1]
(d) Crystallisation [1]
Copper(II) sulfate is a salt. (c) The gases have different boiling points. [1]
(e) Diffusion [1] (d) Nitrogen [1]
Oxygen and carbon dioxide have different relative The gas with the lowest boiling point will evaporate
molecular masses. They will diffuse at different first.
speeds. (e) Glass beads increase the surface area. [1]
(f) Filtration [1] It will condense the gases that are not reaching
Barium sulfate is an insoluble salt. Aqueous sodium the boiling point back to the flask. [1]
nitrate is soluble. Filtration is used to separate a This is the way to separate the mixture of gases,
mixture of solid and liquid. especially those with small differences in boiling
points.
2 (a) Simple distillation [1]
(b) Under the flask [1] 5 (a) Paper chromatography [1]
(c) Condenser [1] (b) 2 [1]
(d) To cool the water vapour [1] The 2 spots are not at the same positions as any
and turn into water [1] of the samples 1, 2, 3 and 4. [1]

(e) Heat [1] (c) Different solubilities of substances to the
Condense / cool [1] solvent used. [1]
or
(f) Water has a lower boiling point. [1] The attachment of substances to the paper. [1]
The substance with a lower boiling point evaporates
first. (d) (i) To check if food contains prohibited
colouring [1]
(g) Anhydrous copper(II) sulfate [1] or any correct usage
Change from white to blue [1]
or (ii) Some food colourings are harmful to
Anhydrous cobalt chloride [1] humans [1]
Change from blue to pink [1] or any correct explanation
3 (a) To ensure all acids react [1] 6 (a) Able to dissolve all the samples [1]
All acids need to be reacted to ensure the salt (b) Sample 3 [1]
obtained is pure and contains no acid after
crystallisation. (c) To visualise the spots / To detect the location of

(b) Filtration [1] spots [1]
Copper(II) oxide is a black solid. It can be separated (d) (i) Retention factor [1]
from the acid which is a liquid by filtration. 3.2

(c) Heat [1] (ii) 8.0 = 0.4 [2]
until the crystallisation point is reached or Note: 3.2 [1]; 0.4 [1]
crystals start to form. [1] 8.0




Answers 173







Answers.indd 173 3/4/22 3:54 PM

(iii) Sample 4 [1] Paper chromatography is used to identify amino
1.6 acids.
= 0.2
8.0 (d) Electrolysis [1]
Sample 2 [1] Lithium ions are separated by gaining an
4.8 electron to form lithium [1] at the cathode. [1]
= 0.6
8.0 [1]
7 (a) Draw 3 small circles on the chromatogram. [1] 9 (a) A substance that is composed of two or more
From the lowest to the highest: elements [1]
Yellow, red, blue with correct label [1] chemically combined [1]

(b) Water [1] (b) Must be in the correct order:
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The black ink is water-soluble (it is written in the 1 Dissolving [1]
statement). 2 Filtration [1]
(c) Different solubilities of substances to the 3 Evaporation / Crystallisation [1]
solvent used [1] (c) (i) Condenser [1]
The attachment of substances to the paper [1] Arrow pointing into lower aperture
(d) Draw a horizontal line below the baseline. [1] only [1]
The solvent level should not be above the baseline. Water should go in from the lower aperture.
If the solvent is above the baseline, substances (ii) The stopper is placed over the mouth of
cannot be separated properly.
fractionating column. [1]
(e) The pencil marking cannot dissolve in water. [1] Gases or vapour escape from the mouth of
fractionating column. [1]
(f) Spot the colour on the baseline. [1]
Let the solvent travel until the solvent front. [1] (iii) The mixture is flammable. [1]
Dry the chromatogram. [1] (iv) The temperature of the water bath cannot
8 (a) Add a dilute acid. [1] exceed 100°C. [1]
Filter. [1] Alcohols C and D have boiling points that
Copper does not react or dissolve. / Magnesium are higher than 100°C. [1]
reacts or dissolves, or forms salt. [1] 10 (a) (i) Zn / Zinc ions [1]
2+
Copper metal cannot react with dilute acid because
2+
–
it is not reactive. However, it can react with (ii) Zn + 2OH ➞ Zn(OH) [1]
2
concentrated acid. Magnesium reacts with dilute (b) (i) No reaction / No change [1]
acid.
(b) Diffusion (through a membrane) [1] (ii) A yellow precipitate is formed. [1]
Nitrogen diffuses faster than oxygen. [1] Silver iodide is a yellow solid.
because it has the smallest M . [1] (iii) AgI [1]
M N = 28; M O = 32 r 11 (a) A white [1]
2
r
2
r
or precipitate forms. [1]
Fractional distillation [1] It dissolves in excess of sodium hydroxide. [1]
The mixture of air is cooled and turns into a
+
liquid. [1] (b) NH [1]
4
Nitrogen with a lower boiling point than (c) A pale blue [1]
oxygen will tend to evaporate faster. [1] precipitate forms. [1]
Gases condense to become liquids. It dissolves in excess of ammonia solution [1]
or and turns into deep blue solution. [1]
Burn a named substance [1]
to produce non-gaseous products [1] (d) Add aqueous ammonia [1]
Oxygen reacts / nitrogen does not react. Name (e) Fe [1]
2+
the product of combustion. [1] –
Magnesium can be used. Magnesium burns and (f) Br [1]
reacts with oxygen to form magnesium oxide. (g) A white [1]
Magnesium oxide is a solid. Nitrogen does not react precipitate forms. [1]
with oxygen in the same way.
(h) Add dilute aqueous sodium hydroxide [1]
(c) Chromatography [1] and then some small pieces of aluminium
Use of locating agent / Two acids move at foil. [1]
different rates. / Leucine travels faster than Heat gently. [1]
histidine. / Leucine travels higher up on the
paper / further. [1]


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


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CHEMISTRY






Workbook


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Cambridge IGCSE Ace Your Chemistry is designed to aid students build
TM
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.
Cambridge IGCSE TM ACE YOUR CHEMISTRY
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.

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,
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.


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