Answers to end-of-chapter
questions
Chapter 1 Planet Earth
1
3
a by fractional distillation of liquid air
[2]
b i H—H → 2H
[1]
ii O + H → O—H
[1]
iii endothermic
[1]
c i can be produced from water; doesn’t
produce any pollutants when burnt
[2]
ii not easily/cheaply available
[1]
[Total = 8]
5
a methane
[1]
b Respiration is burning sugar in the cells of the
body to produce energy:
sugar + oxygen → water + carbon dioxide
[3]
c The combustion produces carbon dioxide but,
as crops re-grow, the carbon dioxide is used
by photosynthesis.
[2]
d more burning of fuels producing carbon
dioxide at a faster rate than plants can take
it up
[2]
[Total = 8]
The carbon cycle is part of the natural exchange and
recycling of materials in the environment. It relies
on energy to bring about the changes involved. In
the case of the carbon cycle this energy comes from
chemical changes one of which is photosynthesis –
a photochemical reaction dependent on sunlight.
Discussion could include reference to the major
sources of energy that maintain the temperature
of the planet, i.e. energy from the Sun and from
radioactive decay in the Earth.
2
4
a use cobalt chloride paper – turns from blue
to pink; or use anhydrous copper sulfate
powder – turns from white to blue
[2]
b as a coolant, or any other correct
industrial use
[1]
c a substance that dissolves another to form a
solution
[1]
d i burning coal in power stations or other
correct source
[1]
ii kills fish in lakes, erodes statues/buildings [2]
iii 64
[1]
e 1: filtration to remove solid particles [2]
2: chlorination to kill bacteria/germs [2]
[4]
f 21%
[1]
[Total = 13]
a i decay of vegetation; digestive processes in
animals such as cows
[2]
ii carbon dioxide and water
[2]
b respiration and combustion output carbon
dioxide; photosynthesis consumes carbon
dioxide; these processes balance each other [4]
[Total = 8]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 1
1
Answers to end-of-chapter
questions
Chapter 2 The nature of matter
1
a A: thermometer; B: beaker
[2]
b to keep the temperature the same throughout [1]
c i 48 °C
[1]
ii 72 °C
[1]
d The particles are close together but irregular
[1]; the molecules are able to move about
with slow movement [1].
[2]
e i The third statement is correct: its melting
point is different from pure stearic acid. [1]
ii in testing medicines or food additives, or
other correct
[1]
[Total = 9]
4
a i
5
Both crystals dissolve in water; particles of each
substance diffuse through the water; eventually
particles of the two meet and they react to form
a yellow compound, silver iodide.
[4]
[Total = 4]
6
a An isotope is an atom of an element with
a different nucleon (mass) number but the
same proton number (or the same number of
protons but a different number of neutrons). [1]
b
Both ways of categorising substances have their use
to a chemist.
◆
◆
2
3
Knowing whether a substance is a solid, liquid
or gas at room temperature – and how easily
a substance can change its state – helps us
in handling the different substances and in
separating them and purifying them from
mixtures. It is important to realise that any
substance can exist in any of the three states,
depending on the conditions of temperature
and pressure.
Knowing whether a sample is an element,
compound or mixture helps us in knowing
and predicting the chemical properties of a
substance. These distinctions are mutually
exclusive and therefore are more fundamental
to our understanding.
The word ‘particle’ is needed when talking in
generalisations about the structure and movement
of the constituents of matter. The context should
always be defined to distinguish this scientific use
of the word from the more everyday use when it
can be a speck of dust etc. The one key experiment
where the two uses interact is in the description of
Brownian motion.
Here the unseen motion of atoms and molecules in
a fluid is demonstrated by the jerky, random motion
of the dust particles as they are hit by the submicroscopic particles that make up matter.
One aspect that can be discussed, and needs to
be referred to, is the key definition of the size of
the ‘particles’ involved when the term is used.
Descriptions such as ‘sub-microscopic’ and
‘subatomic’ are useful.
The particles are in fixed positions [1];
they vibrate about their fixed position [1]. [2]
ii Add water, stir to dissolve salt and filter to
obtain sand as the residue.
[3]
b distillation, lower, volatile, condenser, vapour [5]
[Total = 10]
Isotope
Number of
protons
Number of
electrons
Number of
neutrons
50
23
V
23
23
27
51
23
V
23
23
28
c non, medicine, cancer
© Cambridge University Press 2014 IGCSE Chemistry
[3]
[3]
[Total = 7]
Answers to end-of-chapter questions: Chapter 2
1
7
a balloons
[1]
b i nucleus
[1]
ii The third statement is correct: helium has
a complete outer shell of electrons.
[1]
iii 18
[1]
34
[1]
iv 18 Ar
c The atoms are arranged irregularly [1] and
are close together/touching [1].
[2]
[Total = 7]
8
a Bromine slowly evaporates into a gas, the
molecules of the gas spread away from the
liquid until eventually all the space is filled
and the particles move randomly.
[3]
b Diagram 2: Hydrogen in the beaker moves
into the pot faster than the air moves out so
the liquid moves down.
[3]
Diagram 3: Air in the pot moves out of the
pot faster than the surrounding carbon
dioxide moves in so the liquid moves up.
[3]
[Total = 9]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 2
2
Answers to end-of-chapter
questions
Chapter 3 Elements and
compounds
1
2
3
a i
4
a Period 2
b i O
ii F
iii Li
iv C
v Be
vi N
c atoms, protons
Mendeleev knew nothing of atomic structure
and had no concept of proton number (atomic
number). He based his arrangement of the elements
into groups on their atomic masses and the patterns
he saw in their properties. It was his analysis of
the repeated (periodic) patterns in physical and
chemical properties that made his achievement so
remarkable.
This was difficult because not all the elements had
been discovered – for instance, the whole group
of noble gases had not yet been discovered. But he
realised that there were elements that were still to be
found and left gaps for these. Indeed, he predicted
the properties of some elements in anticipation of
their discovery.
Electrical conductivity in metallic elements
and alloys requires that their bonding results in
there being free mobile electrons that can move
through the structure to carry the current. In
other elements and compounds, the electrons are
all held in fixed bonding positions and cannot
move through the lattice. The exception to this
is carbon, in the form of graphite, where there
are electrons free to move between the layered
sheets of the structure. This type of electrical
conductivity can take place in the solid and
liquid states.
There is another form of conductivity – electrolytic
conductivity – which takes place when ionic
compounds are melted or dissolved in water. Here
it is the ions that move between the electrodes to
carry the current. There must be ions present for
this to happen, so covalent liquids (such as ethanol)
cannot conduct in this way. They are made up of
neutral molecules.
© Cambridge University Press 2014 IGCSE Chemistry
lithium + water → lithium hydroxide +
hydrogen [-1 for each error]
[2]
[1]
ii 2Na + 2H2O → 2NaOH + H2
b increasing reactivity from lithium to sodium
to potassium
[1]
lithium floats and fizzes
[1]
sodium floats, fizzes and melts
[1]
potassium floats, fizzes, melts and ignites
[2]
or other correct observations
[Total = 8]
3
[1]
[6]
[2]
[Total = 9]
5
a Br2
[1]
b Particles leave the liquid to become
vapour [1]. Gas particles move into all areas
of the flask [1] by diffusion [1].
[3]
c colourless [1] to orange-brown [1]
[2]
d Iodine is less reactive than bromine.
[1]
e i NaBr
[1]
ii zinc bromide
[1]
iii covalent
[1]
iv A and D
[1]
v because the ions can move to the
electrodes
[1]
[Total = 12]
6
a i
ii
iii
iv
v
D
E
F
B
A
[5]
Answers to end-of-chapter questions: Chapter 3
1
b i
Correct electron structure of the F− ions
(electrons from outer orbit of C moved to
the two F atoms, one electron to each to give
8 electrons in the outer shell of each) [1]
Correct charges on each ion: - on F and
2+ on C [2]
−
F
[C]2+
−
F
[3]
ii high melting point, soluble in water,
conducts when dissolved or molten, brittle
(any two of these possible answers)
[2]
[Total = 10]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 3
2
Answers to end-of-chapter
questions
Chapter 4 Chemical reactions
1
2
a There is a colour change which shows that there
might be a reaction, and new substance(s) are
formed / a gas is given off.
b The most reliable evidence for a chemical
reaction is that a gas is given off which can be
identified as carbon dioxide.
c copper carbonate → copper oxide + carbon
dioxide
zinc carbonate → zinc oxide + carbon dioxide
d Zinc oxide is a white solid which turns yellow
when heated. When cooled, the solid turns
white again.
e No, it is a physical change.
a The definition in terms of oxygen gain or
loss is the most obvious – and is the origin of
the terminology. However, the definition in
terms of electrons is the broader and more
widely applicable of the two. It is relevant to
more situations, including the important ones
involved in electrolysis and the generation of
electricity in batteries.
b Whichever definition is used, it is impossible to
have oxidation taking place without something
else in the reacting mixture being reduced. If
something is gaining oxygen or losing electrons,
then another reactant must be losing the oxygen
or gaining the electrons. This follows the general
principle that matter cannot be created or
destroyed in a chemical reaction.
The processes of oxidation and reduction can
be physically separated in an electrolytic cell, for
instance, but the overall reaction of the cell is still
a redox reaction.
© Cambridge University Press 2014 IGCSE Chemistry
3
a black solid
[1]
b magnesium + carbon dioxide →
magnesium oxide + carbon
[1]
c i carbon dioxide
[1]
ii magnesium
[1]
d MgO + 2HCl → MgCl2 + H2O
[correct formulae but unbalanced = 1]
[2]
e i Zn2+ + Mg → Mg2+ + Zn
[2]
ii Magnesium reduces zinc ions [1] by
donating/giving electrons to them [1]
[2]
[Total = 10]
4
a sulfur + oxygen → sulfur dioxide
[1 for reactants; 1 for product]
[2]
b SO2 is oxidised to SO3 and O3 is reduced
[2]
to O2
c SO3 + H2O → H2SO4
[1]
[Total = 5]
5
a aqueous sodium chloride, copper, graphite
[−1 for each incorrect answer]
[3]
b insulator
[1]
c i anode
[1]
ii negative = zinc [1]; positive = chlorine [1] [2]
iii carbon
[1]
[Total = 8]
6
a carbon/platinum [1] because unreactive [1] [2]
b bubbles [1] at both electrodes [1]
[2]
c hydrogen at cathode [1], chlorine at anode [1] [2]
[Total = 6]
7
a Zn + 2HCl → ZnCl2 + H2
[2]
b i Some elements have more than one
oxidation state.
[1]
[2]
ii 3Cu2+ + 2AsO43− → Cu3(AsO4)2
[Total = 5]
Answers to end-of-chapter questions: Chapter 4
1
Answers to end-of-chapter
questions
Chapter 5 Acids, bases and salts
1
4
a pH 3
[1]
b Add blue (or neutral) [1] litmus [1]; if it
turns red, it is acidic [1].
[3]
c i calcium carbonate + hydrochloric acid →
calcium chloride + carbon dioxide + water
[1 mark for each product]
[3]
ii in a blast furnace for producing iron
[1]
iii lime/calcium oxide, or slaked lime/
calcium hydroxide
[1]
[2]
d Fe + 2HCl → FeCl2 + H2
[Total = 11]
5
a acidic: < 7, any appropriate e.g. SO2
basic: > 7, any appropriate e.g. CaO
neutral: 7, any appropriate e.g. H2O
[6]
b i an oxide/substance that will react with/
dissolve in both acids and alkalis.
[1]
ii any strong acid (e.g. HCl) + any strong
alkali (e.g. NaOH)
[2]
[Total = 9]
6
Step 2: Filter to remove excess solid
[1]
Step 3: Evaporate to crystallisation point
[1]
Step 4: Leave solution to cool [1]; dry crystals
on filter paper [1]
[2]
[Total = 4]
7
a first row: sodium hydroxide; nitric acid
[2]
second row: copper oxide
[1]
third row: silver nitrate; hydrochloric acid
(or soluble chloride salt)
[2]
fourth row: zinc sulfate
[1]
[2]
b i Ag+(aq) + Cl−(aq) → AgCl(s)
ii ZnCO3 + H2SO4 → ZnSO4 + CO2 + H2O [2]
[Total = 10]
The process of dissolving takes place when the
molecules of water are able to break up the lattice
structure of the ions in the solid salt. If the bonding
between the ions in the solid is too strong, then
the water molecules are not able to break up the
structure. The strength of the bonding in an ionic
solid depends on the size and charge of the ions.
There are some guidelines that help us know which
salts are soluble in water and which are not.
2
In understanding the different uses of the word
‘strong’ in these cases, we have to focus on the way
the adjective is being applied.
In the first case, the term is being applied to the
solution – ‘the coffee is strong’ means that it is
concentrated. A weak cup of coffee would have a
low concentration of coffee.
In the second case, the word is applied to the nature
of the acid itself – not the solution – the strong acid
is fully ionised in water. It is therefore possible to
have a dilute solution of a strong acid.
Remember, in chemistry, to use the words
‘concentrated’ and ‘dilute’ when talking about how
concentrated a solution is.
3
a pH 11
[1]
b slaked lime
[1]
c i to help plants grow better (or words to
that effect)
[1]
ii sulfur dioxide [1] from power stations [1]
or nitrogen oxides [1] from car exhausts
[1]; dissolves in rain [1]
[3]
d i neutralisation
[1]
ii Measure the calcium hydroxide/alkali with
a pipette [1], add indicator [1] and add
acid from burette until there is a colour
change [1].
[3]
[Total = 10]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 5
1
Answers to end-of-chapter
questions
Chapter 6 Quantitative chemistry
1
When dealing with reacting substances, the
important thing to realise is that equations define
the number of moles of the substances that react.
A mole of a substance is a defined number of
atoms or molecules.
3
T3(PO4)2 [1]
reaction has finished after 8 cm3 of phosphate
solution has been added (line levels out) [1];
ratio of volumes = 12:8 which is 3:2 in
the formula [1]
[Total = 3]
4
a 72/24 = 3
28/14 = 2
Mg3N2
[2]
b ratio is 0.03: 0.12: 0.09 which is 1: 4: 3
Al4C3 + 12H2O → 4Al(OH)3 + 3CH4
[2]
c i bromine, because 0.07 moles of silicon
requires 0.14 moles of bromine; 25 g of
bromine is 0.16 moles, which is an excess [3]
ii 0.07 moles
[1]
[Total = 8]
5
0.16/24 = 0.0067; 0.0067 × 2 = 0.0134;
0.0134 × 331 = 4.4 g; (4.4/5) × 100 = 88.3%
Do keep the full number of figures in your
calculator through all the steps in a multi-step
calculation, even if you write down answers
that have been rounded
[Total = 4]
6
40/1000 × 2 = 0.08 moles; 0.08/2 = 0.04 moles;
0.04 moles; 0.04 × 238 = 9.52 g
[4]
0.08 moles; 6/119 = 0.05 moles
[1]
This is more than was necessary to react with
all the HCl as 0.05 > 0.08/2
[1]
[Total = 6]
7
a
b
c
d
When dealing with solids, the most obvious
practical way of measuring the amount of a
substance is to weigh it. To make sure we are using
the right proportions of atoms or molecules, we
have to take into account that the atoms of the
elements have different masses. This is done by
using the relative formula masses of the substances
involved in a reaction.
When dealing with gases, the most practical
measure of the amount of a gas is its volume.
Here we are helped by the fact that, in a gas,
the particles are relatively very far apart – a
volume of gas is largely empty space. The volume
occupied by one mole of any gas is the same
whichever gas we are talking of – it is unaffected
by the size of the gas molecules themselves.
When working with reacting gases, we can use
the reacting volumes of gases in calculations –
the balancing numbers in the equation tell us the
reacting ratios; we do not need to work with the
formula masses.
2
a ammonia + sulfuric acid → ammonium
sulfate
[1]
b 8
[1]
c 98
[1]
d 6.6 g
[2]
[Total = 5]
© Cambridge University Press 2014 IGCSE Chemistry
to ensure complete combustion
because it is an acidic gas
20 cm3; 90 cm3; 60 cm3
2CxHy + 9O2 → 6CO2 + 6H2O;
formula = C3H6
[2]
[1]
[2]
[2]
[Total = 7]
Answers to end-of-chapter questions: Chapter 6
1
Answers to end-of-chapter
questions
1
The methods used to prevent explosions from
‘runaway reactions’ are precisely the opposite to
those changes that would speed up the rate of
reaction. The changes used would need to have a
‘dampening’, or inhibitory, effect. The following
changes would all result in a slowing down of a
reaction:
◆
◆
◆
Mass of flask and contents / grams
Chapter 7 How far? How fast?
3
a hydrated iron sulfate → anhydrous iron
sulfate + water
[1]
b endothermic [1]; heat has to be applied
(or words to that effect) [1]
[2]
c pale green
[1]
d It is a reversible reaction [1], hydrated
iron sulfate is formed [1] and heat is also
generated (reaction exothermic) which
produces steam [1].
[3]
e reversible reaction
[1]
f If water is added to anhydrous cobalt chloride
[1], it changes colour from blue to pink [1]. [2]
[Total = 10]
a Carbon dioxide is given off.
[1]
b i somewhere between 600 and 630 s
[1]
ii X placed at the beginning of the curve (see
graph below)
[1]
iii sketch graph to the right of the printed
curve [1] and levelling out above it [1]
(see graph at the top of the next column) [2]
© Cambridge University Press 2014 IGCSE Chemistry
100.3
100.2
100.1
100.0
0
lowering the temperature
adding water to dilute the reactants (see
Workbook Exercise 7.6 for an example)
lowering the pressure of a gas reaction.
100
200
300
400
500
Time / seconds
600
700
c i gets faster
[1]
ii gets faster
[1]
d combustion, small, large
[3]
e i respiration
[1]
ii a substance which speeds up a chemical
reaction
[1]
[Total = 12]
Other methods are also possible.
2
100.4
x
4
a amount of manganese(iv) oxide and
temperature
[2]
b i the higher the concentration, the faster
the reaction
[1]
ii A lower concentration will produce less
oxygen.
[1]
iii 25 or 26 s
[1]
[1]
36 or 37 cm3
c magnesium oxide, copper(ii) oxide,
manganese(iv) oxide, lead(iv) oxide
[1]
[Total = 7]
5
a i
fair test [1]; keep the amount of solution
above the cross the same [1]
ii value for gap: between 120 and 150
iii speed decreases [1] because lower
concentration [1] means fewer
collisions [1]
Answers to end-of-chapter questions: Chapter 7
[2]
[1]
[3]
1
b The reaction is faster [1] because higher
temperature makes particles move more
rapidly [1]; this means more collisions [1]
and harder/more energetic collisions [1].
[4]
[Total = 10]
6
a making fertiliser
[1]
b Methane is reacted with steam/water:
[3]
CH4 + 2H2O → 4H2 + CO2
c High pressure increases the reaction rate
because gas particles are closer together [2].
High pressure ensures that equilibrium is shifted
to the right/forward [1] because the reaction
has fewer molecules on the right [1] and so
the forward reaction reduces pressure [1].
[5]
d i endothermic needs heat/energy to
proceed; exothermic produces
heat/energy
[1]
ii first blank: endothermic; second blank:
6 × 388 = 2328; third blank: exothermic [2]
The exothermic value (heat given out
making bonds) of 2328 is greater than the
endothermic value (the heat taken in to
break bonds) of 944 + 1308 [1].
[3]
[Total = 13]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 7
2
Answers to end-of-chapter
questions
Chapter 8 Patterns and
properties of metals
1
b lithium reaction not exothermic enough to melt
the metal, sodium and potassium melt into a ball,
potassium ignites spontaneously
order of increasing reactivity Li<Na<K
all float on water, all fizz and produce hydrogen,
all leave an alkaline solution
(any five points)
[5]
c i anode: E [1]; electrolyte: A [1]
[2]
ii positive = chlorine; negative = sodium
[2]
iii graphite
[1]
d low melting point, soft/can be cut with knife,
electrical conductivity, etc. (any two)
[2]
[Total = 15]
a Alloys are metals whose composition is
designed to suit the properties required by a
particular use or situation. Properties which
have been significant in the development of
alloys have included:
◆
◆
◆
◆
◆
◆
tensile strength
hardness
resistance to corrosion
electrical conductivity
low melting point
colour.
4
a Zn + H2SO4 → ZnSO4 + H2
[2]
b because energy is produced [1] and electrons
are transferred [1] from a more reactive metal
to a less reactive metal [1]
[3]
c zinc, because it is the more reactive metal
[2]
d change zinc to a more reactive metal; change
iron to a less reactive metal
[2]
[Total = 9]
5
a calcium carbonate → calcium oxide +
carbon dioxide [1]
[2]
Ca(OH)2 → CaO + H2O [1]
b i copper oxide, oxygen and nitrogen
dioxide
[1]
[2]
ii 2NaNO3 → 2NaNO2 + O2
c sodium and calcium
[1]
d copper and silver
[2]
[Total = 8]
b Brass is used in plugs and switches because, even
though it is not as good a conductor as copper, it
is cheaper and harder. It is more resistant to hard
wear and regular use.
2
3
a i copper, zinc, magnesium, calcium
[1]
ii Iron does not react with cold water [1] but
it does react with steam when heated [1]. [2]
b zinc + water → zinc oxide + hydrogen
[1]
c high melting point/boiling point, malleable,
conduct heat, conduct electricity (any three) [3]
d i any sensible answer above 98 °C
[1]
ii decreases
[1]
3
iii any sensible answer above 0.53 g/cm and
[1]
below 1.0 g/cm3 (it floats on water)
[Total = 10]
lithium + water → lithium hydroxide +
hydrogen
ii 2Na + 2H2O → 2NaOH + H2
a i
© Cambridge University Press 2014 IGCSE Chemistry
[2]
[1]
Answers to end-of-chapter questions: Chapter 8
1
Answers to end-of-chapter
questions
Chapter 9 Industrial inorganic
chemistry
1
Although there are some cases where recycling has
significant economic advantages in terms of costs
(for example, the recycling of aluminium), this is
not always the case. The most important argument
for recycling is the conservation of natural
resources, particularly non-renewable resources of
minerals and fuels, for instance.
b carbon burned off by oxygen as carbon
dioxide [1]; phosphorus, etc., react with
calcium oxide/lime to form slag [2]
[3]
c surgical instruments, chemical plant, cutlery
(any of these)
[1]
[Total = 7]
4
acid/base reaction: CaO + SiO2 → CaSiO3
The impact of efficient recycling can be wideranging. The demand for rare metals for the
electronics and media industries puts great pressure
on the need to find new mineral resources and the
development of new mining ventures. This can
bring conflicts with environmental concerns in
some of the most untouched areas of the world.
Efficient recycling could delay some of these
potential clashes of interest.
2
3
a acidic soil
[1]
b nitrogen
[1]
c ammonium sulfate + calcium hydroxide →
ammonia + water + calcium sulfate products
or ‘double decomposition’
[2]
[1]
d CaCO3
[2]
e CaCO3 → CaO + CO2
f water is added
[1]
g N2 + 3H2 2NH3; high pressure, moderate
temperature (or values), catalyst
[4]
h 2SO2 + O2 2SO3; moderate temperature,
catalyst
[4]
[Total = 16]
redox reaction: Fe2O3 + 3CO → 2Fe + 3CO2
(or give the equation with carbon)
Carbon burns to give heat and form
carbon dioxide.
Carbon dioxide reacts with carbon to form
carbon monoxide.
Carbon monoxide reduces hematite to iron.
Limestone decomposes to calcium oxide and
carbon dioxide.
Calcium oxide (lime) reacts with silica to form slag.
(two equations plus three other points of
description)
[Total = 5]
5
oxygen = top left
[1]
slag = right
[1]
molten steel = bottom left
[1]
They are gases.
[1]
They react together to form calcium
phosphate, which is a solid, and form slag,
which floats on the steel.
[3]
c i D
[1]
ii surgical instruments, chemical plant,
cutlery (any of these)
[1]
[Total = 9]
a i
ii
iii
b i
ii
a A: yes will rust, has air and water [1];
B: no, has air but no water [1];
C: no, has air and water but protected/coated
with zinc [1]
[3]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 9
1
6
a i heating/roasting in air
[1]
ii ZnO + C → Zn + CO
[2]
b Zinc is more reactive [1] so it loses electrons
[1] to become an ion [1] more easily.
[3]
[Total = 6]
7
a decomposition
[1]
b so that the ions are free to move
[1]
c to lower the operating temperature by
lowering the melting point, or by lowering
the melting point of the electrolyte
[1]
d B
[1]
e anode = oxygen or carbon dioxide [1];
cathode = aluminium [1]
[2]
f because they burn away [1] in the oxygen [1] [2]
[1]
g Al3+ + 3e− → Al
h pans, cans, power cables, aircraft bodies, etc. [1]
[Total = 10]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 9
2
Answers to end-of-chapter
questions
Chapter 10 Organic chemistry
1
The versatility of carbon lies in its ability to
form chain and ring structures, and to form
multiple bonds with itself and other atoms. The
complexity that arises is important to us in several
different ways:
◆
◆
◆
◆
2
iii add bromine water: but-1-ene – goes
colourless, cyclobutane – no change
[3]
b cracking [1], heating at high temperature or
with a catalyst [1]
[2]
c i 1,2-dibromobutane
[1]
ii butane
[1]
iii butanol
[1]
[Total = 11]
the chemistry of life and the interactions
between carbon-containing molecules that
generate the energy for living cells and the
way of passing genetic information from one
generation to the next
the carbon-containing compounds – from
fossil fuels – that are the fuels of our modern
transport and energy-generating systems
the synthetic and natural polymers that provide
us with food, clothing and structural materials
that support our living and the technologies we
depend on
the novel structures that provide the scope for
developing nanotechnology.
a a family of organic compounds with similar
chemical properties due to the presence of the
same functional group
[1]
b A = alkene; B = alkane; C = alcohol
[3]
c test: bromine water; A: decolorises;
B: no effect
[3]
d heat it with steam [1] and a catalyst [1]
[2]
e fermentation
[1]
[Total = 10]
4
a 10, 65
[2]
b i photochemical or substitution
[1]
ii Isomers are compounds with the
same molecular formula but different
structural formulae.
[2]
iii structural formula of 1-chlorobutane [1]:
H
a i
Isomers are compounds with the same
molecular formula but different structural
formulae.
[2]
ii structural formula of but-2-ene:
H
H
H
H
H
C
C
C
C
H
H
H
H
C
C
C
C
H
H
H
H
Cl
structural formula of 2-chlorobutane [1]:
H
H
H
H
H
C
C
C
C
H
H
Cl
H
H
[2]
c i
potassium manganate(vii) (accept
potassium or sodium dichromate(vi))
[1]
ii butanoic acid
[1]
iii butyl ethanoate [1]
structural formula of CH3COOC4H9 [2]:
H
3
H
H
H
H
H
C
C
C
C
H
H
H
H
O
O
H
C
C
H
H
[3]
[Total = 12]
H
H
© Cambridge University Press 2014 IGCSE Chemistry
[1]
Answers to end-of-chapter questions: Chapter 10
1
5
a i bromine water [1] decolorised [1]
[2]
ii add carbonate or metal e.g. magnesium [1];
[2]
fizzing/gas. CO2 or H2 produced [1]
b ethyl propenoate [1]
correct structure [2]:
H
H
H
C
C
H
H
O
O
H
H
C
C
C
H
[3]
c i
a formula giving the actual numbers of
atoms of each element in the compound
ii two
iii >C=C<
iv structure can be one of following:
[2]
[1]
[1]
HOOC(CH3)C=C(CH3)COOH
or
HOOCCH2CH=CHCH2COOH
or
HOOCCH=CHCH2CH2COOH
© Cambridge University Press 2014 IGCSE Chemistry
[1]
[Total = 12]
Answers to end-of-chapter questions: Chapter 10
2
Answers to end-of-chapter
questions
Chapter 11 Petrochemicals and
polymers
1
The products of burning methane, ethanol and fuels
such as gasoline are the same – the question is more
one of the efficiency and our ability to use the fuels
cleanly. Methane and ethanol are single compounds
but gasoline is a mixture of hydrocarbons and more
difficult to burn completely. Incomplete combustion
gives rise to pollution with carbon monoxide, soot
and particulates.
b heating and cooking; fuel for cars
c molecules contain a double bond;
a compound of carbon and hydrogen only
d i catalytic addition of steam
H
H
ii
H
4
a i
ii
Methane is more environmentally friendly as
it produces less carbon dioxide for the amount
of energy it releases as it has the best/highest
carbon:hydrogen ratio.
b i
ii
iii
a boiling point
[1]
b fuel oil – fuel for home heating; kerosene – jet
fuel; lubricating fraction – waxes and polishes;
naphtha – making chemicals
[4]
c i heat and catalyst
[2]
[1]
ii C14H30 → C2H4 + C12H26
iii H
[1]
H
C
H
C
H
H
iv
[2]
[1]
[2]
H
[2]
[Total = 11]
small molecules (monomers) becoming
chemically joined in a chain (polymer)
In addition polymerisation, joining is
because a double bond breaks, allowing
other atoms to bond. In condensation,
two molecules react with the elimination
of water.
C12H26 → C8H18 + 2C2H4
The method from ethene uses
less chlorine.
electrolysis [1] of brine/concentrated
NaCl solution [1]
correct formula of poly(chloroethene) [1],
with bonds free at each end
H
H
H
H
H
H
C
C
C
C
C
C
H
Cl
H
Cl
H
Cl
[1]
[2]
[1]
[1]
[2]
[2]
[Total = 9]
C
H
d poly(ethene)
[1]
e i steam
[1]
ii a substance that speeds up a reaction
[1]
[Total = 12]
5
a correct display formulae
H
i
O
H
C
a group of hydrocarbons with boiling
points close together
ii C12H26 → C2H4 + C10H22
ii
a i
© Cambridge University Press 2014 IGCSE Chemistry
[1]
[1]
H
[1]
C
O
H
3
O
e monomers, polymers
Ethanol is more environmentally friendly because
it is/can be a renewable fuel. Any carbon dioxide
released can be at least partially removed from the
atmosphere as (for example) the sugar cane used in
fermentation is grown.
2
C
[2]
H
H
C
C
H
H
H
[1]
O
H
Answers to end-of-chapter questions: Chapter 11
1
b i ethyl ethanoate
ii correct display formula showing three
units minimum[2] and ‘loose’ bonds
at ends [1]
OC
C6H4
CO
O
CH2
CH2
[1]
O
OC
C6H4
CO
or
O
O
C
C6H4
C
O
O
CH2
CH2
O
C
O
C6H4
C
[3]
iii When placed in landfill, they do not ‘rot’
away but remain for many years.
[2]
c Nylon has two monomers alternately [1];
a protein chain has different monomers
throughout [1].
[2]
[Total = 10]
© Cambridge University Press 2014 IGCSE Chemistry
Answers to end-of-chapter questions: Chapter 11
2
Answers to end-of-chapter
questions
Chapter 12 Chemical analysis
and investigation
2
1.00
Analysis of the substances we discover and use
in the wide variety of activities that shape our
lives is important in terms of our control of our
environment, the efficient use of resources available
to us and our protection from the harmful effects
of contamination and misuse. Chemical analysis
can be used in industry, medicine, agriculture
and environmental science. We need to know
what chemicals we are dealing with. Analytical
techniques, from the simple to the complex, help
us to do just that. A medical drug company might
need to analyse the painkiller paracetamol, for
instance, in order to maintain the purity of the
product it is marketing. A steel-making company
must check if the content of a batch of steel
matched the customer’s requested composition. An
environmental analyst might have to check river
water for contamination with small amounts of
metal ions, which may be harmful to local wildlife
and also in the drinking water supply.
a arrow under copper oxide
[1]
b black [1] to orange/brown/pink [1]
[2]
c diagram of condenser tube through [1]
cooling jacket [1]
[2]
d extinguished
[1]
[Total = 6]
Total increase in mass / g
1
1.20
0.80
0.60
0.40
0.20
0.00
0
10
20
30
40
Time / min
50
60
70
g reaction finished/copper sulfate gone,
current switched off (any of these)
[1]
[Total = 10]
4
a initial: 25, 26, 23, 24
final: 28, 39, 46, 58
rise: 3, 13, 23, 34 [−1 for each
incorrect value]
[4]
b correct plotting [3] [−1 for each error],
straight line [1] (see graph below)
[4]
c extrapolation of line to 5 [1], correct reading
of temperature (44 °C) from extrapolation [1],
units [1] (see graph below)
[3]
50
3
a
b
c
d
carbon or platinum
cathode (negative electrode)
bubbles
i with an organic solvent – ethanol or
propanone
ii using a hair dryer
e 0.75, 1.00, 1.15, 1.15, 1.15
f correct plotting [2]; two straight lines [1]
[1]
[1]
[1]
[1]
[1]
[1]
[3]
Temperature rise / °C
40
30
20
10
0
© Cambridge University Press 2014 IGCSE Chemistry
1
2
3
4
5
Number of carbon atoms in the alcohol formula
Answers to end-of-chapter questions: Chapter 12
1
6
c correct plotting of points [2], lines [1]
a chromatography
[1]
b line below origin
[1]
c ink’s colours would interfere with the result
(or words to that effect)
[1]
d difference: A had more colours that B [1];
similarity: both contained colour E [1]
[2]
e C, D and E
[1]
[Total = 6]
2.0
a 20, 21, 21, 32, 39, 42, 44, 45, 45
[−1 for each error]
b 20, 21, 21, 24, 32, 36, 37, 38, 38
[−1 for each error]
c correct plotting of points [3] [−1 for each
error], lines [1], labels [1] (see graph below)
d two lines to correct line on graph [1], correct
value (27 °C) from graph [1], correct units [1]
(see graph below)
0
[3]
[5]
0.5
1.0
1.5
2.0
2.5
Time / min
3.0
3.5
4.0
Temperature / °C
e exothermic (or redox or displacement)
reaction
[1]
f i Experiment 1 is twice Experiment 2
(not just more).
[1]
ii Zinc is more reactive than iron.
[1]
g temperature would be higher [1] because
there would be less liquid to heat up [1]
[2]
h increase in temperature slower [1] because
of a smaller surface area [1]
[2]
[Total = 21]
7
a labelled diagram of funnel [1] and filter
paper [1]
b 0.45, 0.95, 1.40, 1.90, 2.35, 2.35
[-1 for each error]
© Cambridge University Press 2014 IGCSE Chemistry
[2]
[2]
5
6
9
Crush a lump of solid [1] using pestle and
mortar [1] then:
Experiment 2
0.0
3
4
Volume of Q / cm3
a named indicator + correct colour [2],
or metal ion solution + correct colour
precipitate [2]
[2]
b fizzy drinks are acidic, chlorine would be
produced, chlorine is toxic (any two)
[2]
c to remove any hazardous chemicals, or
words to that effect
[1]
d litmus paper becomes bleached (not the
silver nitrate test)
[2]
[Total = 7]
metal added
10
2
8
[3]
20
1
d volume of 5 cm3 correctly read from graph
[1]
[Total = 8]
[3]
30
0
1.0
0.0
Experiment 1
40
1.5
0.5
60
50
[3]
2.5
Mass of precipitate / g
5
d temperatures would be higher [1], because
copper is a good conductor [1]
[2]
[Total = 13]
add named acid [1], filter [1], then add a named,
more reactive metal to produce displacement [1]
and obtain copper [1]
or add carbon [1] and heat [1] until pink [1] to
obtain copper [1]
or add named acid [1] and filter [1]; electrolyse
the solution [1] and obtain copper at the
cathode [1]
There are many ways to score, but sequence of
steps must follow sensibly.
[Total = 6]
10 c i white precipitate that dissolves in excess [3]
ii white precipitate, insoluble in excess
[2]
d solid contained water (of crystallisation)
[1]
e ammonia
[1]
f E is not a sulfate [1], contains nitrate
ions [1]
[2]
[Total = 9]
Answers to end-of-chapter questions: Chapter 12
2