CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded
may be different.
Coursebook answers
Chapter 1
Science in context:
Lord of the rings
1
2
Jupiter and Saturn are the biggest of the
planets in our solar system and are made of
hydrogen and helium in the gaseous state.
There is a progression outwards from the Sun
in terms of the structure of the planets. Those
nearest the Sun are rocky and relatively small;
beyond Mars the planets are gaseous.
Hydrogen molecules are the smallest of all
the elements and therefore the forces between
them are very small. The gas needs to be
highly compressed (so that the molecules are
close together) and at a very low temperature
(so that the molecules are moving slowly) in
order for it to condense into a liquid.
Questions
1
2
3
1
4
a
freezing
b
boiling
c
condensation
a
methane
b
ethanol and mercury; they have melting
points below room temperature, but
boiling points above room temperature
c
the impurity lowers the freezing point of
the liquid
a
a volatile liquid is one that evaporates
easily; it has a low boiling point
b
ethanol > water > ethanoic acid;
ethanol is the most volatile, ethanoic acid
is the least volatile
c
B; both the melting point and boiling
point are above room temperature;
therefore, it is a solid
a
if heated strongly then the temperature
rises very quickly, the melting and boiling
points are close together, the liquid stage
is not seen as it boils quickly
b
you would need to heat the solid slowly so
that the temperature rise is not too quick;
you could use an electrical heater so you
can control temperature more carefully;
you could use an oil bath to heat the solid
and carefully control the temperature so it
is kept between the melting point (114 °C)
and boiling point (184 °C) of iodine
Experimental skills 1.1
1
Substance B is a pure substance as the curve is
flat while the substance melts. Substance A is
a mixture as there is no single melting point –
that region of the curve is sloped.
2
Take temperature readings at shorter time
intervals (e.g. every 30 s); use of a digital
thermometer would give more accurate
readings / use of a temperature sensor linked
to a computer would enable the readings to be
taken continuously and enable the graph to be
plotted as the readings were being taken. The
samples can be re-heated and cooled again,
allowing duplicate sets of data to be collected.
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Chapter 1 continued
10 In a the liquid levels are the same as there is
air both inside and outside the porous pot
cylinder; in b hydrogen diffuses into the pot
faster than air molecules diffuse out because
hydrogen molecules have less mass than the air
molecules; this produces an increase in pressure
inside the pot and so the liquid level is pushed
down on the left (and up on the right).
Questions
Temperature / °C
5
80
liquid
freezing
0
solid
–20
Time
6
A = solid; B = energy released;
C = energy absorbed
7
A = solid; B = liquid; C = liquid and gas
(vapour); D = gas
Experimental skills 1.2
1
silver iodide
2
silver nitrate + potassium iodide →
silver iodide + potassium nitrate
3
the rates of diffusion of silver and iodide ions
4
because the rates of diffusion of the ions are
not the same – silver ions are less heavy and so
diffuse slightly more quickly
Questions
8
9
2
Exam-style questions
1
6
7
8
9
Evaporation of bromine takes place as
molecules escape from the surface of the
liquid, the gaseous bromine molecules then
spread throughout the gas jar to completely
fill the container, there are collisions with
air molecules, bromine molecules move
from a region of high concentration to
low concentration and so are completely
mixed with the air and at the same
concentration throughout.
a
Methylamine molecules have a greater
mass than ammonia molecules and so
diffuse more slowly; the white smoke ring
will be more central than for ammonia/
hydrogen chloride, slightly to the right of
centre as methylamine diffuses slightly
faster than hydrogen chloride.
b
hydrogen bromide (from hydrobromic acid)
or hydrogen iodide (from hydroiodic acid)
B [1] ; 2 D [1] ; 3 C [1] ; 4 B [1] ; 5 A [1] ;
a Moving slowly [1] ; close to each other [1] ;
b
They vibrate more quickly ;
[1]
c
evaporation ;
[1]
d
changing from liquid to solid ;
[1]
a
evaporation of the liquid [1] ; and
diffusion of the gas particles [1] ;
b
particles moved more slowly [1] ; because
the temperature was lower [1] ;
a
a solid [1] ; is cooling down [1] ;
b
they are moving more slowly [1] ; and
closer together [1] ;
c
heat comes from the formation of bonds
(interactive forces) between the particles [1] ;
a
ammonia, which is alkaline, reached the
indicator first to change its colour [1] ;
because it moved faster [1] ; because it
was lighter [1] ;
b
C 50 s ;
[1]
rate of diffusion is inversely related to the
molecular mass ; heavier molecules, such
as HCl here, diffuse more slowly than
lighter molecules
Answers A and D are too short ; answer
B too long. Simple proportion would
suggest about 73 s, but the rate of
diffusion is inversely related to the square
root of the molecular mass. Ammonia
molecules diffuse 1.46 times as fast as
hydrogen chloride molecules. ;
[1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 2
Getting started
1
2
‘H’ and ‘O’ are the chemical symbols for
a hydrogen atom and an oxygen atom,
respectively. Water consists of two hydrogen
atoms chemically bonded to one oxygen atom.
When atoms join together like this, they form
a molecule. A molecule must have more than
one atom in it.
You may have heard of protons, neutrons and
electrons; these are subatomic particles, and
they come together to make the many different
types of atom.
Science in context:
Seeing is believing
1
2
The rings are made up of carbon atoms
(not many elements can form rings like
this); carbon is the basis of the molecules
of life because it can form so many
different structures.
There are 19 atoms in all (count all the
corners); arranged in five hexagonal rings.
4
Protons are positively charged and would
therefore repel each other / the presence of the
neutrons counteracts this repulsion and means
that the nucleus can hold together.
5
B
6
21 protons and neutrons; protons and
neutrons are both nucleons
7
Chlorine-37 has two more neutrons in
the nucleus.
8
A nitrogen atom has 7 protons and 7 electrons
and therefore is electrically neutral. All atoms
are electrically neutral.
Worked example 2.1
1
relative atomic mass of iridium is 192
Ar = (191 × 37.3) + (193 × 62.7) / 100 = 192.3
Answer corrected to three significant figures as
this is the accuracy of the data given.
2
That the proportions of the two isotopes
are 50:50 (1:1) as the relative atomic mass is
exactly midway between the masses of the
two isotopes.
Experimental skills 2.1
1
The metal present is responsible for
determining the colour seen in the flame.
The non-metal present is the same in all cases
and so cannot be responsible for the change.
2
It is a physical change.
3
It will be the salt which gave the bluest colour
flame. The results will depend on which salts
you tested.
Questions
1
proton = 1, neutron = 1, electron = 0
(or 1 / 1840)
2
15 protons, 16 neutrons, 15 electrons
3
An element is a substance that cannot be
broken down into anything simpler by
chemical means.
Atoms are the particles that make up all
substances; they are the smallest particle
of an element that shows the properties
of that element; they can join together to
make molecules.
Each element has its own type of atom – the
atoms of an element all have the same number
of protons and electrons.
3
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Chapter 2 continued
4
Questions
9
a
first shell, maximum 2: second shell,
maximum 8
b
2,8,8,2
c
8 in both cases
10 6 in both cases
11 a
5
a
C has more neutrons in the nucleus ;
it has 8 neutrons compared with
6 in 12C
[3]
b
2,6 ;
[1]
c
i
4 ;
[1]
ii
4 ;
[1]
a
It is the outer electrons of an atom that
give rise to its chemical properties.
Same number of electrons in
outer shell ;
[2]
b
(70 × 63) + (30 × 65) / 100 = 63.6 ;
A and C, they have 4 electrons in their
outer shells
b
D, has 8 electrons in its outer shell
c
B, has 7 outer electrons
d
C and D, they have electrons in 3
energy levels
e
14; there are a total of 14 electrons in
the atom, therefore there must be 14
protons in the nucleus as an atom must be
electrically neutral
14
[1 mark for partial working. Answer
alone 2 marks]
[2]
Exam-style questions
1
C ;
[1]
2
A ;
[1]
3
a
b
the number of protons in the nucleus
of an atom ;
mass number is protons + neutrons
[2]
argon has 2 more neutrons ;
c
particle
charge
mass
position in
atom
proton
+
1
in the
nucleus
neutron
0
1
in the
nucleus
electron
−
1/1840 orbiting the
nucleus
[5]
4
[1]
d
hydrogen ;
[1]
e
they both have full/complete
outer shells ;
[1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 3
c
Science in context:
Exploiting the properties
of graphene
1
2
There are two forms of carbon that have been
known for some time: diamond and graphite.
In more recent times the following forms
of carbon have been discovered: fullerenes
(such as C60 and C70), which are sometimes
referred to as bucky balls. This research was
extended to discover tubular forms referred to
as nanotubes. Most recently, the single-layered
form of carbon known as graphene has been
isolated. Many of these recently discovered
forms show a close relationship to graphite in
terms of their properties.
Graphite is a layered structure, with each layer
being a covalently bonded macromolecule.
These layers are very strong and so are very
resistant to forces applied at right angles to the
layer. However, the layers can slide over each
other so a force applied from the side causes
the layers to slip. The strength of graphite
depends on its orientation.
Cl
Mg 2+
7
A
8
A
9
C
10 D
Exam-style questions
1
A ;
2
a
C ;
b
the structure shown is of an ionic
compound ; potassium bromide is the
only ionic compound in the list ;
[2]
a
potassium has lost an electron ;
chlorine has gained an electron ;
3
b
All the atoms of an element contain the same
number of protons (and the same number
of electrons).
2
D
3
C
4
C
5
C
6
a
4
F
2−
O
Na
2
Na +
Na +
O
5
[1]
[2]
diagram showing one shared pair of
electrons between atoms / 3 pairs
non-bonding electrons on each atom ; [2]
Cl
c
covalent ;
d
KCl high melting point / Cl2 low
melting point (or b.p.) ; OR KCl is a solid
at room temperature and Cl2 a gas
[1]
a
in calcium chloride solution the mobile
ions carry the charge in solution / the
ions are fixed in position in the solid ; [2]
b
by melting it ;
c
ionic bonds are strong electrostatic
forces / intermolecular forces in water
are weak interactions ;
[2]
a
graphite has strong covalent bonds
between the atoms in the layers /
delocalised electrons between the
layers of atoms are free to move ;
–
LiF
b
5
[1]
Cl
Li +
–
Cl
Questions
1
–
MgCl
2
[1]
[1]
[2]
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Chapter 3 continued
6
b
graphite has layers which can slide over
each other ;
diamond has a three-dimensional lattice
in which all the atoms are bonded ;
[2]
c
i
ionic solids have oppositely charged
ions that attract each other strongly
but when layers are pushed out of
line the ions repel each other ; in
metals, the metal ions are attracted
to a mobile cloud of electrons and
so the layers of ions can move ; [2]
ii
the charged particles in an ionic solid
are fixed in position
the electrons in a metal lattice are
free to move ; [2]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 4
Science in context:
What’s in a name?
1
Lv = livermorium / Fl = flerovium /
Cn = copernicium
3
f
3Fe + 4H2O → Fe3O4 + 4H2
a
H2 + Cl2 → 2HCl
b
2Cu + O2 → 2CuO
c
Mg + ZnCl2 → MgCl2 + Zn
4
Fl named after the Flerov Laboratory of
Nuclear Reactions in Dubna, Russia, where
the element was discovered in 1998; (honours
the Russian physicist, Georgy Flyorov)
Solid sodium carbonate reacts with
hydrochloric acid solution to give sodium
chloride solution and carbon dioxide gas.
Water, a liquid, is also produced.
5
a
Ag+(aq) + Cl−(aq) → AgCl(s)
b
Ba2+(aq) + SO42−(aq) → BaSO4(s)
a
HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)
Cm = curium and Mt = meitnerium are the
only two elements named after women.
6
H+(aq) + OH−(aq) → H2O(l)
b
176 neutrons
Atoms are only very short-lived and so not
easy to determine the mass number definitively
– may be a number of isotopes.
Study of the chemistry and physics of the
nucleus – structure of the nucleus and
possibility of reaching a zone of more
stable elements.
2HCl(aq) + CuCO3(s) →
CuCl2(aq) + H2O(l) + CO2(g)
2H+(aq) + CO32−(s) → H2O(l) + CO2(g)
Worked examples
4.5 Mass of hydrated magnesium sulfate crystals
= 22.50 − 10.20 = 12.30 g
Mass of dehydrated crystals
= 16.20 − 10.20 = 6.00 g
Worked examples
4.1 a
CH4
b
NCl3
Mass of water combined in crystals
= 12.30 − 6.00 = 6.30 g
4.2 a
MgI2
b
AlBr3
4.6 4.5 g (4.48 rounded to one decimal place)
4.3 a
K3PO4
b
NH4NO3
4.4 2Na + Cl2 → 2NaCl
1
2
Questions
7
Questions
7
2Al + 3Cl2 → 2AlCl3
Lv named in recognition of the Lawrence
Livermore National Laboratory in the
United States.
Cn named after the Polish
astronomer, Copernicus
2
e
a
iron + oxygen → iron(III) oxide
b
sodium hydroxide + sulfuric acid →
sodium sulfate + water
c
sodium + water →
sodium hydroxide + hydrogen
8
a
covalent
b
ionic
c
CH4, NaI, C3H6, ICl3, BrF5, HBr
a
32
b
17
c
98
a
2Cu + O2 → 2CuO
d
119
b
N2 + 3H2 → 2NH3
e
188
c
4Na + O2 → 2Na2O
a
100
d
2NaOH + H2SO4 → Na2SO4 + 2H2O
b
6g
9
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Chapter 4 continued
Exam-style questions
1
A ;
[1]
2
a
H3PO4 (order of elements not critical) ;[1]
b
magnesium carbonate (s) + phosphoric
acid (aq) → magnesium phosphate (aq) +
carbon dioxide (g) + water (l)
([1] for substances and [1] for
state symbols ;)
c
24 + 12 + (3 × 16) = 84
(partially correct calculation = [1] ;)
[2]
d
Relative formula mass is the sum of the
relative atomic masses of the elements
in a compound. ;
[1]
e
(1.2/6) × 21 = 4.2 g
(partial calculation = [1] ;)
[2]
3
C ;
[1]
4
a
C2H4O ;
[1]
b
88 ;
[1]
c
Mg(s) + 2C3H7COOH(aq) →
Mg(C3H7COO)2(aq) + H2(g) ;
(state symbols [1] ; formula of
magnesium butanoate [1] ; balancing [1] ;
correct substances [1] ;)
d
The sum of the relative atomic masses
of the elements in the compound ; [2]
[1 mark if only the simpler terms,
masses or atomic masses are used.]
e
8
magnesium butanoate (or any ionic
compound) is not made up of molecules
and so cannot have a molecular mass ; [1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 5
5.3 mol Mg = 4/24 = 0.167 mol
Getting started
mol acid = 5.48/36.5 = 0.15 mol
The balloons will all contain the same number
of characteristic particles (atoms for B and D /
molecules for A and C).
from equation 1 mol Mg reacts with 2 mol acid
therefore 0.167 mol would react with
0.3 mol acid
Balloon B will fall fastest; the constituent particles
of the gas have the heaviest mass.
Science in context:
Chemical accountancy and
atom economy
HCl is the limiting reagent.
5.4 from equation 2 mol Al gives 2 mol aluminium
chloride (1 : 1 ratio)
mol Al = 4.5/27 = 0.167 mol
1
Other costs: energy costs / safety costs in terms
of the physical plant / level of manpower
needed / cost of unwanted by-products
2
Marketing should consider uses for the
by-products and then convincingly ‘sell’
their usefulness
0.167 mol aluminium chloride = 22.29 g
% purity = (17.8/22.29) × 100 = 79.9%
5.5 Percentage by mass of N = 21.2%
5.6 Percentage by mass of water = 62.9%
Questions
Worked example
4
a
5.1 1
18 g/mol
5
2
0.125 mol
The mole is that amount of substance that
contains 6.02 × 1023 constituent particles (e.g.
atoms, molecules). It is equal to the relative
formula mass (relative molecular mass) of a
substance in grams.
6
The percentage yield of a product from a
reaction is the proportion of the theoretical
yield that is actually obtained. The percentage
purity of the product of a reaction is a
measure of how contaminated the product is.
Questions
1
2
a
0.4 mol
b
2.41 × 10 formula units / 2.41 × 10 Na
ions and 2.41 × 1023 OH– ions
23
23
+
molar ratio of Cu : Fe : S is 1 : 1 : 2
empirical formula = CuFeS2
3
a
molar ratio of C : H : O is 1 : 3 : 1
empirical formula = CH3O
b
molar mass of CH3O = 31
so actual formula is C2H6O2
c
HO
H
H
C
C
H
H
OH
b 18.7%
Worked examples
5.7 a
22 g of carbon dioxide = 0.5 mol
volume of gas = 12 dm3
b
number of moles nitrogen = 1.5 mol
mass of nitrogen = 28 × 1.5 = 42 g
5.8 Molar concentration = 0.1 mol/dm3
5.9 a
mol acid used
= (0.2/1000) × 25 = 0.005 (5 × 10−3) mol
Worked examples
b
molar ratio 1 : 2, so mol NaOH = 0.01 mol
5.2 1
c
0.01 mol NaOH in 10 cm3
32 g methane = 2 mol methane
reacting ratio of methane : oxygen is 1 : 2
reacts with 4 mol oxygen = 64 g of oxygen
9
28.2%
concentration of NaOH solution
= (0.01/10) × 1000 = 1 mol/dm3
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Chapter 5 continued
5
Questions
7
8
9
a
0.02 moles
b
2 moles
c
0.07 moles
a
36 000 cm3
b
1440 cm3
c
12 000 cm3
a
2 mol/dm3
b
0.2 mol/dm3
c
1 mol/dm3
d
0.8 g of NaOH = 0.2 moles; 0.2 mol/dm3
a
0.12/24 = 0.005 mol
[1]
b
0.005 mol
[1]
c
1 mol BaCO3 = 137 + 12 + (16 × 3)
= 197 g
[1]
mass of barium carbonate =
0.005 × 197 = 0.985 g
[1]
% purity = (0.985/1.23) × 100 = 80%
[1]
d
e
Exam-style questions
1
D ;
2
a
b
c
3
4
[1]
40/12, 53.3/16, 6.7/1 = 3.33 : 3.33 : 6.7
empirical formula = COH2
([1] for each step) ;
[3]
molecular formula
= (COH2) × 2 = C2O2H4 ;
[1]
12/60 = 0.2 mol in 250 cm3 /
concentration = 0.2 × 4 = 0.8 mol/dm3 ; [2]
([1] for units) [3]
a
potassium carbonate ;
[1]
b
0.005, 0.005, 0.42 g ;
[3]
c
(0.35/0.42) × 100 = 83.3% ; [2]
a
C3H8
+ 5O2
→ 3CO2 + 4H2O ; [2]
([1] for correct formulae, [1] for balancing)
10
b
volume ratio of propane to carbon
[2]
dioxide is 1 : 3 ; 100 × 3 = 300 cm3 ;
(Wrong answer to part a can be carried
through to gain marks here.)
c
50 cm3 of methane forms 50 cm3 of
carbon dioxide ;
water condenses at room temperature and
pressure so not counted ;
excess of oxygen is 50 cm3 so total
is 100 cm3 ;
[3]
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Chapter 6
3
Getting started
1
Wiring is most often made of copper (due to
high conductivity and flexibility).
2
Wiring is usually covered in plastic coating to
insulate the wires to ensure that the electricity
is conducted to where it is intended to go.
Plastic is used as the insulator as it is generally
flexible which is helpful as it can be easily
manipulated and will not crack.
3
Liquid metals do conduct electricity. Other
liquids that conduct include molten and
aqueous solutions of ionic substances.
Experimental skills 6.1
1
Depends on the equipment available but a
reliable power pack to adjust the voltage
applied is useful / use of an ammeter rather
than a light bulb to detect flow of current.
2
The electrodes would need to be thoroughly
cleaned with sandpaper / washed in propanone
and then dried / weigh the electrodes on as
accurate a balance as is available.
Science in context:
The hydrogen economy
1
2
2H2(g) + O2(g) → 2H2O(g)
Questions
The reaction is exothermic, generating
electrical energy.
4
The fuel cell is considered to be environmentally
advantageous as the only emissions are
water vapour. However, to be considered
carbon-neutral involves a broader range of
considerations. These include the origins of the
raw materials – particularly the hydrogen and
the energy source used to generate it. There is
‘grey hydrogen’ obtained by steam-reforming
natural gas, or from electrolysis of water where
the electricity is produced by fossil fuel power
stations. ‘Green hydrogen’ is hydrogen from the
electrolysis of water using electricity generated
by solar or wind power.
Questions
1
2
11
When a metal conducts electricity it is the
delocalised electrons present in the structure
that move through the metal to carry the
charge / in aqueous solutions of ionic
compounds it is the ions present that move to
carry the charge.
a
potassium at cathode and chlorine
at anode
b
hydrogen at cathode and chlorine
at anode
5
metal is formed at the cathode and a
non-metal at the anode
6
a
the object to be plated is made
the cathode
b
copper(II) sulfate solution
a
2Br−(l) → Br2(g) + 2e−
b
because the lead ions have
gained electrons
7
8
steam-reforming of methane (natural gas)
electrolysis of water using electricity generated
by solar or wind power
a
i, iii, iv and v conduct electricity.
9
b
iii and v are electrolytes (aqueous
solutions of ionic compounds).
10 2H2(g) → 4H+(aq) + 4e−
a
The ionic solid does not conduct as the
ions present cannot move about (they can
only vibrate at fixed positions).
b
Melt it or dissolve it in water.
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Chapter 6 continued
Exam-style questions
1
C ;
[1]
2
A ;
[1]
3
a
B;
b
E;
c
F;
d
D;
e
C ;
a
i
cathode ;
[1]
ii
electrolyte ; [1]
4
5
b
arrows pointing (clockwise) away from
negative and towards positive ;
[1]
c
dilute sulfuric acid ;
[1]
d
carbon or platinum ; [1]
a
i
cathode gains in mass ;
[1]
ii
anode does not change ;
[1]
b
the blue colour would fade to colourless ;[1]
c
4OH− → O2 + 2H2O + 4e−
(correct product [1] ;
balanced equation [1] ;)
d
i
the anode would lose mass [1] ; /
copper anode dissolves to form ions
[1] ; cathode increases in mass [1] ; /
copper deposited on cathode [1] ;
ii
the solution colour would not change
[1] ; / concentration of copper ions in
solution remains the same [1] ;
e
12
[5]
movement of copper ions [1] ; from anode
to cathode [1] ;
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 7
Science in context: Keeping cool!
1
2
CFCs were very stable compounds and
were not degraded (broken down) until they
reached the upper atmosphere where they
released chlorine free radicals. These radicals
reacted with the ozone layer protecting
the Earth from harmful UV radiation.
‘Holes’ appeared in the upper atmosphere,
particularly over the Earth’s poles. CFCs were
banned by the Montreal Protocol. CFCs are
also greenhouse gases.
Use of refrigerants greatly improved food
storage and preservation and allowed for
the long-distance transportation of foods.
Air-conditioning made the workplace much
more comfortable in regions of intense or
extreme climate.
8
bonds made = (4 × 464) + (1 × 498)
enthalpy of reaction
= bonds broken – bonds made = −210 kJ/mol
reaction is exothermic
9
2
a
physical
b
chemical
c
physical
d
physical
a
exothermic
b
exothermic
c
exothermic
d
endothermic
1
B ;
2
a
increase [1] ;
b
physical [1] ;
c
increase [1] ;
d
chemical [1] ;
e
chemical [1] ;
a
effervescence/fizzing/bubbles ;
[1]
b
bubbling stops ;
[1]
c
endothermic [1] ; because the
temperature goes down [1] ;
d
exothermic [1] ; products have less
energy than the reactants [1] ;
a
energy to break bonds = 2253 kJ/mol [1] ;
energy forming bonds = 2346 kJ/mol [1] ;
3
3
A new substance(s) has been formed.
4
an endothermic reaction
For a reaction to take place some bonds in
the reacting substances must first be broken.
Bond breaking is an endothermic process
and therefore there is always a need for some
energy to be supplied by the surroundings to
start off a reaction.
Exam-style questions
Questions
1
bonds broken = (4 × 464) + (2 × 144)
4
difference = 93 kJ/mol [1] ;
correct sign (−) [1] ;
5
Energy / kJ
Zn(s) + CuSO4(aq)
ZnSO4(aq) + Cu(s)
[1]
b
+93 kJ/mol ;
[2]
c
[1] for each correct label
(see Figure 7.15) ;
[2]
made activation energy EA lower ;
[1]
d
Progress of reaction
13
6
The energy of the reactants is lower than the
energy of the products / upwards arrow.
7
Bond breaking is endothermic.
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Chapter 8
Science in context:
Studying incredibly fast reactions
b
There will be more surface area of
the solid exposed to the reactant and
therefore more frequent collisions.
1
c
Greater concentration means there are more
reactant molecules present and so there will
be a greater frequency of collision.
carbon dioxide + water → glucose + oxygen
The photosynthesis reaction maintains
the level of oxygen in the atmosphere and
removes carbon dioxide. The two biochemical
processes of photosynthesis and respiration
maintain the balance between these two gases
that are important for life. Other important
reactions include those involved in the making
of proteins and the copying of DNA.
2
Exam-style questions
1
B ;
2
a
The keys factors in industry are achieving
sufficient product in as economic a way as
possible. The reaction processes used must
give a yield at a reasonable rate as time is
an economic cost. The product must also
be achieved in a system that is safe and
environmentally sustainable.
14
a
rate increases
b
rate increases
c
rate increases
3
2
The reactions that would spoil the food are
slowed down at the lower temperature.
3
at the beginning
4
A catalyst is a substance that speeds up a
chemical reaction but is not itself used up in
the course of the reaction.
5
biological catalyst
6
manganese(IV) oxide
7
changes in temperature and pH
8
The presence of a catalyst decreases the
activation energy of a reaction.
9
a
An increased temperature means that
the particles are moving faster and will
therefore collide more frequently; when
they collide, more particles will have
energy greater than the activation energy
so there will be more collisions that result
in a reaction.
4
because the reaction is complete
(has stopped) ; b
20/30 = 0.67 [1] ; unit cm3/s [1] ;
c
gas syringe ;
d
any two from:
Questions
1
[1]
a
[1]
[1]
•
increase temperature ;
•
smaller pieces of calcium carbonate ;
•
more concentrated acid ;
[2]
the rate of reaction is inversely
proportional to the time for the cross
to disappear ;
[1]
b
as the temperature increases the cross
is obscured (becomes hidden) in a
shorter time / the reaction rate
increases with temperature so the
cross becomes hidden faster ;
[2]
c
the reaction rate increases with an increase
in temperature because the particles
are moving faster and so collide more
frequently [1] ; / the particles have more
kinetic energy and so more collisions
involve energy greater than the activation
energy [1] ; / more collisions produce
a reaction [1] ;
a
smaller particles have a larger surface area
[1] so there are more collisions [1] ;
b
collisions are more frequent [1] ; and
a higher proportion have sufficient energy
to react [1] ;
c
copper acts as a catalyst [1] ; catalysts are
not consumed by the reaction [1] ;
d
hydrogen is a very light gas [1] ; so
the change in mass is not sufficient to
be detected [1] ;
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 9
Getting started
1
A crop is a plant that is grown on a large scale
in order to sell it.
2
This answer will depend on where learners
live but could include a type of cereal, fruits
or vegetables.
3
Crops need sunlight and water but
also nutrients.
4
A fertiliser contains the nutrients that plants
need. It can be added to soil to improve
plant growth.
5
Increasing the temperature favours the
endothermic process, so the equilibrium
position will move to the right. / The
equilibrium counteracts the external
change in conditions so the endothermic
process absorbs the heat being supplied.
a
Hydrogen is obtained by the steamreforming of methane:
CH4(g) + H2O(g) → CO(g) + 3H2(g)
b
burning sulfur or the roasting of metal
sulfide ores such as zinc sulfide
S(s) + O2(g) → SO2(g)
An organic fertiliser is made of a natural
product such as manure. An artificial fertiliser
is manufactured.
Science in context:
Revolutionising food production
2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
6
c
the air
a
450 °C / iron catalyst / 20 000 kPa pressure
b
Increased pressure would produce
more ammonia.
1
Iron is a much more readily available metal
and more economically suitable.
c
Increased temperature would yield
less ammonia.
2
Apart from cost, there are environmental
issues involved in mining for the rarer metals
as such mining often involves development in
environmentally sensitive areas.
d
The unreacted nitrogen and hydrogen are
recirculated so that they can further react
to give more ammonia / so that they react
the second time around (saves producing
more raw materials).
a
to replace nutrients that have been lost
from the soil by plant growth / to increase
crop yield
b
because these are the three elements
needed by plants, which can become used
up in soil
a
nitric acid and ammonia
(ammonium hydroxide)
b
phosphoric acid and ammonia
(ammonium hydroxide)
c
sulfuric acid and ammonia
(ammonium hydroxide)
Questions
1
a
The white powder turns blue.
b
as a test for the presence of water
c
CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)
2
Test to see that it boils at 100 °C.
3
The reverse reaction to form the anhydrous
salt requires heat (is endothermic); therefore,
the reaction to add water back must give out
heat (exothermic).
4
15
5
b
a
i
There is no effect as there are the
same number of moles of gas on both
sides of the equation.
ii
Increasing pressure will move the
position of the equilibrium to the
right, more NO2
7
8
9
They are washed off fields by rain and end
up in streams and rivers / algal growth /
eutrophication / acidification of soils by
excessive use of nitrates.
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Chapter 9 continued
Exam-style questions
1
reversible reaction ;
b
turns green/blue [1] ; and gets hot [1] ;
c
anhydrous [1] ; cobalt chloride
turns pink [1] ;
[1]
2
B ;
[1]
3
C ;
[1]
4
a
advantage: increases rate [1] ;
disadvantage: causes decomposition
of ethanol [1] ;
b
makes particles closer together (more
collisions) [1] ; moves equilibrium to the
right (forward) [1] ;
c
to speed it up ;
[1]
d
none ;
[1]
e
ethanol is constantly removed from the
reactor [1] , which draws reaction to the
right (so reverse reaction doesn’t happen)
[1] ;
a
nitrogen from the air [1] ; hydrogen from
methane/water [1] ;
b
A higher temperature would make the
reaction faster [1] ; but would also move
equilibrium position to the left (move
reaction backwards) [1] ;
c
Higher pressure is costly to produce ; [1]
d
The catalyst becomes poisoned / doesn’t
work as efficiently ;
[1]
e
The catalyst is finely divided or pelleted
to increase the surface area so that more
of the reactant gases can attach and
react together. ;
[1]
5
16
a
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 10
Getting started
•
Oxygen is the gas in the air that is involved in
burning magnesium and hydrogen popping
when ignited.
•
Reduction is the loss of oxygen.
7
Science in context:
Fuelling the international
space programme
1
2
Redox reactions are usually used to drive
an engine or as an explosive reaction. Very
fast reactions / producing a large amount
of energy / rapid expansion in volume. The
products of an explosive reaction are likely
to be gaseous.
1
A, B and D
2
A and B
3
reduction
4
a
b
6
17
9
N2H4(g) + O2(g) → N2(g) + 2H2O(g)
1
An oxidising agent is a substance that
will oxidise (add oxygen to) another
substance and is itself reduced during
a redox reaction. Examples: oxygen /
hydrogen peroxide / chlorine /
potassium manganate(VII)
A reducing agent is an element or
compound that will reduce (remove
oxygen from) another substance and is
itself oxidised during a redox reaction.
Examples: hydrogen / carbon / carbon
monoxide / a reactive metal
Reduction is the gain of electrons; oxidation
is the loss of electrons. During a redox
reaction the oxidising agent gains electrons;
the oxidising agent is itself reduced during
the reaction.
a
No, even in a reaction such as the burning
of magnesium the magnesium is obviously
oxidised, but the oxygen has been reduced
in that it is no longer the free element.
a
+3
b
+5
c
0
d
+3
e
+6
a
Zn2+ ions
b
Br2
c
MnO4−
b colourless to yellow-brown / c purple
to colourless
Exam-style questions
Questions
5
8
b
The definition involving gain or loss of
oxygen is the more straightforward to
understand; but that based on electrons
includes more reactions, and is more
useful in that sense.
a
C ;
[1]
b
B ;
[1]
2
B ;
3
a
F ;
[1]
b
A ;
[1]
c
C ;
[1]
d
B or F ;
[1]
e
D ;
[1]
f
E ;
[1]
g
F ;
[1]
a
potassium manganate(VII) [1] ;
b
iron(II) sulfate [1] ;
c
Fe3+ [1] ;
d
Chlorine is an oxidising agent and so
oxidises iodide ions to iodine molecules
(electrons have been lost). The chlorine
molecules are reduced to chloride ions
(electrons have been gained). ;
[2]
4
[1]
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Chapter 10 continued
5
18
a
+2 ;
[1]
b
−2 ;
[1]
c
0 ;
[1]
d
+4 ;
[1]
e
−3 ;
[1]
f
+6 ;
[1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 11
Science in context:
The significance of language
1
2
Many of these terms come from what
was an impressive age of Islamic science
and mathematics centred around the
Mediterranean (including southern Spain).
Modern terms such as algebra have an Arabic
origin. The period was linked to the practice
of alchemy, which included some truly
experimental science together with the more
mystical aspects and practices.
Strong alkali needs to be removed from soap
as it causes skin burns and can be particularly
dangerous for the eyes. Modern soaps do have
an interestingly wide range of pH. Most are
not actually neutral (pH = 7.0). It is worth
investigating; same are slightly acidic, while
others are mildly alkaline.
6
potassium hydroxide and
ammonium hydroxide
7
a
blue
b
S(s) + O2(g) → SO2(g)
c
magnesium + oxygen → magnesium oxide
8
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) →
2NaAlO2(aq) + H2O(l)
9
2
a
A corrosive substance ‘eats’ things away.
b
citric acid
c
ethanoic acid
a
It changes its colour depending on
whether it is in an acidic or alkaline
solution.
b
alkaline
ii
neutral
iii
alkaline
iv
acidic
3
pH 1 is more acidic (1000 times more acidic
than pH 4).
4
a
H2SO4
b
HCl
a
They are equal.
b
hydroxide ion, OH−
c
i
hydrogen ions and nitrate ions
ii
calcium ions and hydroxide ions
iii
ammonium ions and hydroxide ions
5
19
i
zinc hydroxide or aluminium hydroxide
zinc hydroxide + sodium hydroxide →
sodium zincate + water
Zn(OH)2(s) + 2NaOH(aq) →
Na2ZnO2(aq) + 2H2O(l)
Questions
1
An amphoteric oxide is one that will neutralise
both an acid and an alkali to give a salt and
water only.
or aluminium hydroxide + sodium hydroxide
→ sodium aluminate + water
Al(OH)3(s) + NaOH(aq) →
NaAlO2(aq) + 2H2O(l)
Experimental skills 11.1
1
You need to consider the effectiveness of the
whole tablet and then the mass of powder
used. You need to work out a value for how
much acid has been neutralised per unit mass
of the tablet.
2
For example:
magnesium hydroxide + hydrochloric acid →
magnesium chloride + water
calcium carbonate + hydrochloric acid →
calcium chloride + carbon dioxide + water
Mg(OH)2 + 2HCl → MgCl2 + H2O
3
To make the solid more accessible to the acid
and to speed up the reaction.
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Chapter 11 continued
Questions
10 An acid is a proton donor; a base is a
proton acceptor.
11 a
b
12 a
b
i
CuO(s) + 2HNO3(aq) →
Cu(NO3)2(aq) + H2O(l)
ii
Zn(s) + 2HCl(aq) →
ZnCl2(aq) + H2(g)
Zn has lost electrons and H+ ions
have gained electrons; Zn atoms have
been oxidised.
b
CH3COOH(aq) CH3COO-(aq) +
H+(aq) ([1] ; for equation, [1] ; for
reversible arrow) ;
c
Al2O3 + 6HCl → 2AlCl3 + 3H2O
([1] ; for compounds, [1] ; for balancing)
d
Amphoteric ;
e
marking points as follows:
•
aluminium hydroxide is insoluble
in water ;
•
aluminium hydroxide dissolves in
sodium hydroxide solution /
it is amphoteric ;
•
the reaction is reversible ;
•
hydrochloric acid makes the reaction
go backwards / equilibrium shifts
to left ;
[Max. 3]
HCl(g) + aq → H (aq) + Cl (aq)
+
−
Hydrochloric acid is fully dissociated into
ions (it is a strong acid); ethanoic acid is a
weak acid (only partially dissociated into
ions); so, there will be more ions present
in the hydrochloric acid solution and the
electrical conductivity will be higher.
[1]
Exam-style questions
1
B ;
[1]
2
D ;
[1]
3
a
red ; b
calcium carbonate (s) + hydrochloric acid
(aq) → calcium chloride (aq) + water (l) +
carbon dioxide (g)
([1] ; for compounds, [1] ;
for state symbols. ;)
c
limewater turns milky/cloudy ;
[1]
d
carbon dioxide is an acidic oxide (or
simply acidic) ;
[1]
4
20
[1]
e
metal oxides are basic [1] ; non-metal
oxides are acidic [1] ;
f
test with universal indicator [1] ; note
colour change [1] ; compare with colour
chart to find pH value [1] ;
a
H2SO4(aq) → 2H+(aq) + SO42−(aq)
([1] ; for substances, [1] ; for state
symbols, allow H2SO4(l) and equations
involving water molecules as long as they
are balanced. ;)
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 12
2
Getting started
•
It is sometimes called table salt because people
add salt to their food. The salt is placed in a
container on the table.
•
Salt is necessary for the regulation of many
bodily functions including maintaining the
body’s overall balance of fluid.
•
1
2
2
3
Salt (sodium chloride) is present in the body
and is soluble in water. Loss of salt produces
muscle cramps. It is replaced by drinking
isotonic drinks (isotonic means the same ion
concentration as in our cells).
5
6
7
a
magnesium chloride
b
calcium nitrate
c
zinc sulfate
a
to make sure all the acid is reacted/used up
b
filtration
c
pipette, burette
d
yellow
e
If heated too strongly, the salt could
dehydrate (lose water of crystallisation) or
even decompose.
a
method B
b
sulfuric acid
c
zinc + sulfuric acid → zinc sulfate + water
a
Precipitation is the sudden formation of a
solid when two solutions are mixed, or a
gas passed into a solution.
b
A method in which an acid solution and
an alkali are reacted precisely to produce
a salt solution; the salt can be crystallised
from the solution produced.
c
An ionic equation includes just those ions
and molecules that actually take part in
the reaction.
a
sulfuric acid
b
nitric acid
c
carbonic acid
a
sodium hydroxide and hydrochloric acid
b
calcium hydroxide and nitric acid
c
ammonia (ammonium hydroxide) and
sulfuric acid
a
nitric acid
8
A and C / silver iodide and lead(II) chloride
b
potassium sulfate and ammonium nitrate
9
a
sodium sulfate
b
white
c
Ba2+(aq) + SO42−(aq) → BaSO4(s)
Experimental skills 12.1
1
4
To preserve food / to add flavour (saltiness is
one of the basic human senses) / some cultures
use soy sauce, fish sauce or oyster sauce to
flavour food rather than table salt.
Questions
1
Questions
Salt may be found dissolved in seas and
oceans. Salt can also be found in rocks
(rock salt).
Science in context:
The significance of salt
That the copper oxide was present in
excess / this makes sure that all the acid is
reacted / this is important as the solution is
concentrated by heating after filtration, and
hot, concentrated acid is dangerous.
copper(II) oxide + sulfuric acid → copper(II)
sulfate + water
CuO + H2SO4 → CuSO4 + H2O
21
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Chapter 12 continued
Exam-style questions
1
B ;
2
a
sodium chloride or copper sulfate ;
sodium too reactive and so unsafe /
copper does not react with dilute acids [1]
b
sodium chloride ; [1]
c
barium sulfate ;
[1]
d
potassium carbonate ;
[1]
a
bubbles / effervescence / fizzing ;
[1]
b
to ensure all the sulfuric acid was
reacted / used up ;
[1]
fizzing would stop, or excess
solid remained ;
[1]
3
c
d
filter [1] ; heat to crystallisation
point [1] ; separate/dry crystals [1] ;
4
A ;
5
a
lead nitrate [1] ; sodium, potassium or
other soluble chloride [1] ;
b
mix solutions of the substances [1] ;
filter and keep the residue [1] ;
wash the residue [1] ;
dry the residue [1] ;
a
insoluble calcium sulfate [1] ; stops the
acid reaching the carbonate [1] ;
b
use hydrochloric or nitric acid instead ;[1]
c
sodium, potassium, copper
or magnesium ;
6
22
[1]
[1]
[1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 13
Science in context:
The women behind the
Periodic Table
1
Discuss the historic social and religious
attitudes to the role of women in society in
different parts of the world – their role and
access to education; and opportunity to
pursue an independent career.
2
Consider the modern situation in different
cultures and the development of attitudes,
opportunities and perceptions.
1
potassium hydroxide
2
lithium + water → lithium hydroxide +
hydrogen
a
b
chlorine of the ones available in a school lab
(and fluorine)
5
They all have 8 electrons in their outer shell,
except for helium in the first period, which has
the maximum possible of 2.
7
23
Rubidium will react more strongly with
water than potassium.
a
C
b
PH3
sodium, Na
b
silicon, Si
Alkali metals are soft, transition metals
are hard / alkali metals have low density,
transition metals have high density / alkali
metals have just one valency (oxidation
number), transition metals show variable
oxidation number / alkali metal compounds
are white solids, transition metal compounds
are coloured.
10 D
1
D ;
[1]
2
B ;
[1]
3
a
iodine ;
[1]
b
lithium ; [1]
c
bromine ; [1]
d
potassium [1] ; chlorine [1] ;
a
false ;
[1]
b
false ;
[1]
c
true ;
[1]
d
true ;
[1]
e
true ;
[1]
a
they have coloured compounds [1] ;
they act as catalysts [1] ;
they have variable oxidation states [1] ;
b
CrO is ionically bonded [1] ;
CrO3 is covalently bonded [1] ;
c
amphoteric ;
approximately 40 °C (note that the
difference between one element and the
next is getting smaller as we go down
the group)
4
6
9
a
Exam-style questions
Questions
3
8
4
5
The elements move from metallic character in
the first two or three groups to non-metallic
character; the non-metallic elements in the
centre of the period are giant covalent solids,
moving to simple molecular gases on the right
of the period.
[1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 14
Science in context: Smart alloys
remember that shape!
8
1
9
2
The name is made up of the chemical symbols
of the elements in the alloy: nickel (Ni) and
titanium (Ti), and the initials of the Naval
Ordnance Laboratory (NOL).
They are good conductors of heat and
electricity / flexible without breaking /
corrosion resistant / biocompatible.
Questions
1
2
3
a
24
copper
b
plastic
a
any two from iron, chromium and nickel
b
hardness and corrosion resistance
Exam-style questions
1
C ;
[1]
2
D ;
[1]
3
Property
Metals
Non-metals
They conduct
electricity
True
False
They react with
oxygen in the air
True
True
They are brittle
False
True
They can easily be
bent and shaped
True
False
True
False
can be beaten into sheets / gives a ringing
sound when hit / conducts heat well /
conducts electricity well
b
is an insulator / has a dull surface
a
graphite
b
sodium and potassium
c
mercury
They have high
melting points
d
diamond
[1 mark for each row correct] ;
[5]
a
Its low density ;
[1]
b
Its resistance to corrosion ;
[1]
c
Because of its low density ;
[1]
d
Copper [1] ; Because it is a
better conductor [1] ;
e
Alloy ; Conductor ; Metal ; Mixture ;
[1 mark for each correct answer]
Metals conduct electricity / metals are
malleable and ductile.
4
The fact that there are mobile, delocalised
electrons in the structure of a metal means
that they conduct electricity. Metallic bonding
means that the layers of metal ions in the
structure can move over each other without
the bonding breaking; therefore they are
malleable and ductile.
4
B
5
copper and silver
6
a
metal + water → metal hydroxide +
hydrogen
b
metal + steam → metal oxide + hydrogen
c
i
Mg + H2O → MgO + H2
ii
3Fe + 4H2O → Fe3O4 + 4H2
7
a
a
D
b
brass or steel
5
f
It does not rust/corrode [1] ;
it is an alloy containing chromium
and nickel [1] ;
a
layers of atoms / ions can slide over
each other ;
[4]
[1]
b
the larger atoms prevent layers sliding
over each other. ;
[1]
c
Yes [1] ; Electrons are still free to move
around the metal ions [1] ;
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Chapter 15
Science in context: The search for
longer-lasting battery power
6
1
7
2
Modern batteries depend increasingly on
relatively rare metals such as cobalt. This
means that there is pressure to exploit
mineral deposits in environmentally sensitive
areas, e.g. Alaska. These resources will be
depleted rapidly if batteries continue to be
used disposably.
Graphite rods are used in batteries.
Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)
D
2
a
hydrogen
b
3
1
C ;
2
a
bubbles/fizzing/effervescence [1] ; /
magnesium dissolves [1] ;
b
no reaction (accept very
slow bubbles) ;
2
[1]
iron, unknown metal, magnesium,
calcium [2] ; (one out of order [1] ;)
potassium hydroxide
d
zinc ;
c
sodium + water → sodium hydroxide +
hydrogen
e
burning splint [1] ; pops [1] ;
(glowing splint pops = [1]) ;
d
2K + 2H2O → 2KOH + H2
a
aqueous copper sulfate ; [1]
a
strong and has a low density
b
iron ;
[1]
b
Aluminium is coated with a very thin
oxide layer that protects it from corrosion.
c
Cu(s) + 2AgNO3(aq) →
Cu(NO3)2(aq)+ 2Ag(s) ;
c
copper
3
Carry out the experiments in polystyrene
cups to prevent heat loss or lag the boiling
tube with cotton wool / take more frequent
temperature readings to find the maximum
temperature reached more accurately.
d
4
copper becomes coated with silver
coating ; solution changes from
colourless to blue
[2]
e
zinc is more reactive than copper ;
[1]
a
zinc is the reducing agent / it removes
oxygen from CuO ;
[2]
zinc atoms lose electrons to become
Zn2+ ions / Cu2+ ions gain electrons to
become copper atoms ;
[2]
b
c
4
magnesium + copper(II) sulfate → magnesium
sulfate + copper
5
Magnesium becomes coated with a layer of
copper / the colour of the blue solution fades.
[1]
[1 mark for substances, 1 mark for
balancing, 1 mark for state symbol] [3]
The reaction would be exothermic, but the
rise in temperature would not be as great as
that observed when zinc reacts with copper(II)
sulfate solution.
Questions
25
[1]
c
Experimental skills 15.1
1
This question is speculative – look at the first
letters of the metals in order and see if you
can think of a phrase or sentence!
Exam-style questions
Questions
1
Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)
magnesium is more reactive than zinc
/ it is more ready to form positive
ions than zinc / so it removes oxygen
from copper(II) oxide more readily
than zinc ;
[2]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 16
Science in context:
Mining the ocean floor
1
2
The metallic nodules are rich in the metals in
demand and it would be relatively easy to extract
the required metals. There are various different
sites in different regions of the ocean floor. The
damage to the ocean floor itself through what is
effectively open-cast mining would be significant,
as would the damage to the habitat of marine
species about which we know relatively little.
The dependence on a single land-based source
is open to political and economic dangers;
and could lead to exploitation of the local
population and create socio-economic tensions.
9
Exam-style questions
1
D ;
[1]
2
B ;
[1]
3
a
hematite ;
[1]
b
carbon monoxide ;
[1]
c
because of the high temperature in
the furnace ;
[1]
Experimental skills 16.1
1
The formation of red-brown copper metal.
2
2CuO + C → 2Cu + CO2
4
Questions
1
carbon monoxide
iron(III) oxide + carbon monoxide → iron +
carbon dioxide
Fe2O3 + 3CO → 2Fe + 3CO2
3
silicon(IV) oxide + calcium oxide → calcium
silicate
SiO2 + CaO → CaSiO3
4
26
d
calcium oxide/carbonate [1] ; reacting
with impurities in the ore [1] ;
a
the air ;
[1]
b
it produces the heat needed in
the furnace ; the carbon dioxide is
then reduced in the furnace to give
carbon monoxide
[2]
To combine with the silicon(IV) oxide (sand)
and remove it as slag
CaCO3(s) → CaO(s) + CO2(g)
2
Zinc is more effective because if the surface
layer is broken the zinc will still protect the
steel beneath as it is more reactive than iron
(sacrificial protection) / chromium will not
protect if the layer is broken as it is less
reactive than iron.
Because of the high cost of electricity, which
is needed in large quantities / also the carbon
anodes need replacing regularly.
5
The cryolite lowers the melting point of the
electrolyte / because this makes the temperature
needed to melt the aluminium oxide much lower.
6
Because the oxygen produced at the anode
causes the graphite anodes to burn away as
carbon dioxide.
7
water and air (oxygen) / salt water or acid rain
8
painting / greasing / covering with plastic
5
c
from oxygen ions [1] ; discharged at
the anode [1] ;
d
The carbon anode burns away [1] ;
and so has to be replaced [1] ;
e
It reacts with the silica (silicon dioxide)
impurity in the ore [1] ;
forming calcium silicate slag [1] ;
a
galvanisation ;
[1]
b
it is more resistant to damage but
still protects even if the zinc layer is
scratched or broken ;
[1]
c
the zinc or magnesium is more reactive
than iron [1] ; these metals more readily
form positive ions than iron [1] ; so
they are corroded rather than the iron /
sacrificial protection [1] ;
d
Aluminium does not corrode because it
has a natural surface layer of aluminium
oxide. [1] ; This protects the metal by
preventing it coming into contact
with air. [1] ;
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 17
Science in context: The growing
problem of air pollution
1
2
Possible reasons include population density
(the greater the number of people, the higher
the levels of pollution will tend to be),
presence of particular types of industry (living
closer to large factories will generally mean
poorer air quality), impact of events such as
forest/bush fires, government initiatives to
reduce levels of airborne pollution, etc.
Factors that might encourage more
environmentally friendly options include
education (an understanding of the problems
caused to the environment), tax incentives
(reducing the cost of more environmentally
friendly solutions), cost savings (switching
off electrical equipment when not in use is
both good for the environment and saves
money), etc. Factors that might prevent more
environmentally friendly options include cost
(too expensive), habit (used to always using
the car / not walking), inconvenience (easier
to drive on a wet day than walk), lack of
education, etc.
Questions
1
nitrogen 78%, argon 0.9% and oxygen 21%
2
Harmful to life both on land and in the water /
Increased acidity levels in lakes can kill fish
and other aquatic life / Can kill forests (many
plants are extremely sensitive to pH) / Some
building materials will be damaged/corroded.
3
4
27
8
a
methane + oxygen → carbon monoxide +
water
b
2C6H14 + 13O2 → 12CO + 14H2O
Oxides of nitrogen are formed when nitrogen
from the air reacts with oxygen at a high
temperature (e.g. in a car engine). They are
linked to the formation of acid rain and
photochemical smog.
5
2CO + 2NO → 2CO2 + N2
6
Carbon dioxide: product of the combustion
of fossil fuels. Methane: waste product from
livestock (cattle) and landfill sites.
7
Increased use of fossil fuels.
Rising sea levels so increased flooding and
faster rates of coastal erosion / changes to the
life cycles and migratory patterns of animals
and birds / more severe droughts and crop
failure / drying out of grasslands increases
the frequency and severity of wildfires / more
frequent and severe weather patterns.
Strategies include reducing use of fossil fuels
for transportation and electricity generation
(e.g. by using renewable sources of energy
such as wind and solar) / phasing out of diesel
and petrol cars and replacing with electric cars /
remove CO2 from the atmosphere / reduce
meat consumption / better separation of
household waste.
9
Greenhouse gases absorb and re-emit the
longer wavelength radiation reflected from the
Earth’s surface.
10 Cobalt chloride paper: colour change from
blue to pink. Alternatively, anhydrous
copper(II) sulfate: colour change from white
to blue.
11 Measure melting or boiling point. For pure
water, the melting point is 0 °C and the boiling
point 100 °C.
12 When nitrates and phosphates enter
waterways there is rapid growth of algae.
This can block out sunlight and lead to the
death of aquatic plants, which will reduce
levels of oxygen in the water and so also kill
aquatic animals.
13 Useful metals include calcium (supports the
health of teeth and bones) and iron (needed
for the production of haemoglobin in red
blood cells). Problem metals include lead
(which can cause liver and kidney damage)
and mercury (which has been linked to
damage of the nervous system).
14 The majority of current plastics are not
biodegradable and are creating pollution,
especially in waterways. Biodegradable plastics
will break down naturally.
15 Microplastics removed by filtration using a
fine sand filter. Dissolved organic compounds
removed by an activated carbon filter.
Microbes are removed by disinfection
using chlorine.
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 17 continued
Exam-style questions
1
C ;
2
a
78% ;
[1]
b
Any two from argon, carbon dioxide,
other noble gases (neon, krypton
and helium) ; [2]
i
B ;
[1]
ii
A ;
[1]
iii
C and D ;
[2]
iv
C ;
[1]
c
3
[1]
a
desulfurisation / scrubbing [1] ; using
calcium oxide [1] ;
b
the air [1] ;
c
oxides of nitrogen and sulfur cause acid
rain [1] ; this causes acidic lakes / rivers [1] ;
d
i
ii
e
Not enough oxygen / air for
complete combustion ;
[1]
It is toxic ;
[1]
The toxic gases produced in the engine are
converted into less harmful gases before
they are emitted into the atmosphere. The
process uses a transition metal catalyst [1] ;
2CO + 2NO → 2CO2 + N2 ; [1 mark,
other balanced equations showing
correct substances are acceptable] [1]
4
B ;
5
a
[1]
photosynthesis [1] ;
6CO2 + 6H2O → C6H12O6 + 6O2 ;
[1 mark for substances, 1 mark
for balancing]
28
[2]
b
methane [1] ; livestock or landfill [1] ;
c
They are greenhouse gases [1] ; /
Heat from the Sun passes through the
atmosphere [1] ; / Greenhouse gases
prevent some of it from escaping back
into space [1] ; / The global
temperature increases [1] ; [Max. 3 marks]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 18
7
Science in context:
Building a space elevator
2
The advantages of a space elevator are seen in
terms of the ease of transfer of astronauts and
goods to the space station without the need
for rocket launches from the Earth. Indeed,
subsequent exploration from the space station
would be easier since there would be no
need for the technology to escape the
Earth’s gravity.
These different forms of carbon all conduct
electricity because of the mobile, delocalised
electrons associated with the layered structure
(see Chapter 3).
H
H
C
H
H
H
methane
3
H
H
H
c
propanol
d
butanoic acid
a
CH3CH(OH)CH3
b
CH3CH=CHCH3
c
CH3COOC3H7
Structural isomerism is a property of
compounds that have the same molecular
formula but different structural formulae;
the individual compounds are known as
structural isomers.
C
C
C
C
H
H
H
H
150
H
100
C
H
The bromine water is decolourised from
orange-brown to colourless. There would be
no change if ethane was bubbled into bromine
water. The test is for unsaturation (a C=C):
ethene is unsaturated, but ethane is saturated.
a
a carbon–carbon double bond, C=C
b
a hydroxyl group, –OH
c
a carboxylic acid group, –COOH
50
H
H
C
C
H
H
C
1
B;
2
a
C ;
[1]
b
A and E ;
[2]
c
a carbon–carbon double bond ;
[1]
d
molecule must contain at least one
carbon–carbon double or triple bond ; [1]
e
C3H6 and CH2 ;
O
O
0 1 2 3 4 5 6
Number of carbon atoms
Exam-style questions
C2H5COOH
H
29
H
H
H
6
H
butane
C
5
propene
methane, ethane, propane, butane /
CH4, C2H6, C3H8, C4H10
2
4
9
b
10 There is a steady increase in the boiling point
of the alcohols with increasing chain length.
Questions
1
8
butane
Boiling point / °C
1
a
H
3
B ;
[1]
[2]
[1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 18 continued
4
a
i
H
H
H
H
C
CC
H
HH HH
H
CC
CC HC
H
HH
HH HH HH
H
H
H
H
H
but-1-ene
but-1-ene
b
butane and 2-methylpropane ;
H
HH HH
H
CH3CH(CHCH
)CH
CH(CH3)CH3
3
3 3
C
CH CC CC HC
C
H
H
HH HH
H
butane
H
H
H
H
butane
H
H
H
C
HH
HH
C
H
H
C
CH CC HC
C
H
H
HH
H
H
H
2-methylpropane
2-methylpropane
[2 marks for names, 2 marks
for displayed formulae]
30
[4]
cyclobutane is not an alkene as it
does not contain a carbon–carbon
double bond ;
[1]
H
H
H
but-2-ene
but-2-ene
CH3CH2CHCH
CH3CH
CH2CH3
2
3
2
H
H
H
[2 marks for names, 2 marks
for displayed formulae]
ii
H
CH CC CC CC HC
H
[4]
[1]
c
CnH2n + 2 ;
d
they contain the same functional group
[1] and have similar chemical properties
[1] ; / a consistent trend in certain physical
properties with increasing chain length [1] ;
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 19
4
Science in context:
Molecular envelopes
1
2
The fullerenes, despite the fact that they
contain 60 or 70 carbon atoms per molecule,
are considered to be simple molecular
substances. The forces between these large
simple molecules are relatively weak compared
to covalent bonds.
The nanotubes are enclosed cylinders that can
contain the molecules of medicinal drugs –
protecting the drug molecules from the
environment as they move to the target organ.
The nanotubes are stable, biocompatible
polymers and can be tailored to form
containers that package the drug and carry
it across tissue barriers to the target site. The
nanotubes have free electrons at their surfaces.
The walls of the nanotubes can be modified
to provided water-liking or membrane-liking
surfaces to match the different environments
in the body and the drug involved.
H
5
2
3
Br
C
C
H
H
H
ethane → ethene + hydrogen
6
a
propene + hydrogen → propane
b
C4H8 + H2O → C4H9OH
7
Ethanol is a renewable resource / can reduce
dependence on petroleum imports / can reduce
carbon monoxide emissions / can reduce
environmental pollution, etc.
8
a
yeast, carbohydrate source, water
b
carbon dioxide
c
H
H
H
C
C
H
H
O
H
d
oxidation
a
ethyl ethanoate
b
ethanol + ethanoic acid → ethyl ethanoate
+ water
a
propane + oxygen → carbon dioxide
+ water
b
C3H8 + 5O2 → 3CO2 + 4H2O
a
methane + oxygen → carbon monoxide
+ water
Exam-style questions
b
CO
1
B ;
c
It binds to red blood cells (to the
haemoglobin) and interferes with the
transport of oxygen in the body.
2
a
B ;
[1]
b
C and D ;
[2]
c
A ;
[1]
a
a compound that contains carbon
and hydrogen only ;
[1]
b
no colour change as no reaction ;
[1]
c
ethene and steam are compressed
to 6000 kPa and passed over a
phosphoric acid catalyst at 300 °C ;
[2]
d
as a fuel and as a solvent ;
[2]
e
(addition) polymerisation ;
[1]
a
H
b
H
c
H
H
H
C
C
C
H
H
H H
H Br
C
C
C
H
H
H
9
3
H
H or H
H
Br
H
C
C
C
H
H
H
H
The reaction requires light for it to
take place.
4
31
Br
C2H6 → C2H4 + H2
Questions
1
C2H4Br2
C ;
[1]
[1]
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Chapter 19 continued
5
a
a substitution reaction ;
[1]
b
1,2-dibromoethane ;
[1]
c
advantage: relatively cheap / materials
are renewable [1] ;
disadvantage: product needs
further purification [1] ;
d
acidified potassium manganate(VII) [1] ;
heat under reflux [1] ;
e
ethyl ethanoate ;
H
H
H
C
C
H
H
ethyl
32
H
O
C
O
C
H
H
ethanoate
[1 mark for name, 2 marks
for displayed formula, both
parts correct]
[3]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 20
b
Science in context:
Enzymes that recycle plastics
1
2
PET (a polyester) – the ester link
Use of resources from the petrochemical
industry / uncontrolled littering of the
environment – land, rivers and oceans –
dangers to wildlife / reliable and
environmentally sensitive methods of disposal.
Catalysts are reusable; enable reactions to
take place under milder conditions than
without; enzymes can be very specific and
can be designed/modified to improve reaction
conditions and specificity of product.
O
refinery gas, petrol (gasoline), naphtha,
paraffin (kerosene), diesel, bitumen
2
road surfacing, ships’ engines, car engines,
aircraft fuel (domestic heating)
9
Addition polymerisation takes place when
many molecules of an unsaturated monomer
(e.g. ethene) join together to form a long-chain
polymer.
n
C
C
H
5
6
a
a
b
H
33
a
heat, catalyst
H
H
C
C
H
H
n
O
C
C
O H
H O
O
O
O
C
C
+ H2O
O
the amide link (or peptide link)
O
O
C
C
N
N
H
H
O
O
C
C
N
N
H
H
Proteins are made from 20 different amino
acid monomers; nylon is made from just
two monomers.
10 Simply burning plastic can produce toxic
fumes such as hydrochloric acid from burning
PVC / other toxic compounds can be formed
(e.g. dioxins) / incineration at a precise
temperature range can be used to
destroy plastics.
11 Reuse means simply collecting the containers
and then cleaning and reusing them for the
same purpose / recycling involves shredding
the original article and then making new and
different items from the plastic.
12 Sorting the plastics into their different types /
cleaning the plastic / some plastics are difficult
to recycle because of the dyes that have been
used to give them colour.
H
H
Exam-style questions
C
C
C
1
D ;
CH3
H
Cl
2
a
A ;
[1]
b
A ;
[1]
c
C ;
[1]
H
H
C
H
b
a carbon–carbon double bond
H
H
H
H
H
H
C
C
C
C
C
C
C6H5 H
7
a
c
C10H22 → C8H18 + C2H4
high pressure
O
C
decane → octane + ethene
H
H
O
Catalytic cracking is the thermal decomposition
of a long-chain alkane to a shorter-chain alkane
and an alkene (or an alkene and hydrogen).
H
+
O
H
b
1
4
O
8
Questions
3
nylon – the amide link (or peptide link)
C6H5 H
[1]
C6H5 H
The monomers join together by a reaction
in which a small molecule (usually water)
is eliminated each time a link is made.
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 20 continued
3
4
a
alkanes ;
[1]
b
different boiling points ;
[1]
c
airplane fuel / heating systems ;
[1]
d
i
heat / catalyst ;
[2]
ii
hydrogen ;
[1]
e
C10H22 → C4H8 + 2C3H6 + H2 ;
a
can be broken down into harmless
substances [1] ; by bacteria /
fungi naturally [1] ;
b
they are buried underground / used
as landfill ;
c
they can harm sea life [1] ; /
be consumed by sea creatures and enter
the food chain [1] ;
d
they produce toxic gases when
they burn ;
5
C ;
6
a
b
34
[2]
[1]
[1]
[1]
i
water ;
[1]
ii
condensation polymerisation ;
[1]
i
proteins ;
[1]
ii
they are made by biological cells ; [1]
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 21
Science in context:
Safe drinking water for all
Experimental skills 21.1
1
Residue
1
Portable distillation units. Strengths: Provide
access to distilled water in remote areas
without need for large/expensive equipment
/ May be powered by renewable sources.
Weaknesses: If using solar power, the unit
will only operate under certain conditions /
Produce limited amounts of clean water / May
be limited access to replacement parts if there
is a failure / Would need to be very robust if
used in the field / May require training in safe
use / Could be expensive.
2
It will enable the material to dissolve
more quickly.
3
Salt is ionic and dissolves well in water.
If the solution is concentrated by heat then the
excess solid can be crystallised out. This would
not be a good method for producing iodine
crystals for several reasons. Iodine is toxic and
unlike sodium chloride it has covalent rather
than ionic bonding. Iodine is only partially
soluble in water.
Desalination units. Strengths: Provide
access to drinking water in areas with access
to seawater but limited freshwater / Can
be run continuously / Proven technology.
Weaknesses: May be limited access to parts
if there is a failure / The waste product can
be toxic to marine and coastal ecosystems /
Energy intensive as require high temperature
and pressure / Require training / Could
be expensive.
Experimental skills 21.2
2
Boiling points.
2
100 °C
3
Distillation involves heating the liquid so
that components start to evaporate. As
they evaporate, they travel up through the
apparatus and into the condenser. In the
condenser the temperature is lower and so
the gas will condense. Different fractions
will separate at different temperatures due to
differences in their boiling points.
The filter straw needs to remove particles of
sand / silt / mud and harmful microbes such as
bacteria that can cause disease.
Questions
Questions
1
The temperature should be recorded either
with a thermometer or a digital temperature
probe and meter. The volumes could be
measured with a measuring cylinder or for
greater accuracy a fixed volume could be
measured using a volumetric pipette and a
variable volume by use of the burette.
4
If there are two or more dots in a vertical line
then the substance is a mixture.
5
A substance that remains on the baseline
is insoluble in the solvent used. To improve
the experiment the student needs to use an
alternative solvent, e.g. swapping from water
to ethanol.
The teacher was not correct. The data has
a narrow spread of results and so is precise;
however, it is not accurate as the average of
these results is not very close to the true value.
6
Rf = 2.3/2.8 = 0.82 (to 2 d.p.)
2
3
35
1
Error in the mass is 0.1/1.3 × 100% = 7.7%.
Error in volume is 0.5/10.0 × 100% = 5.0%.
The largest error is in the mass. Random
errors could be reduced by repeating the
experiment several times, checking for and
removing anomalies and then calculating a
mean average.
Rf = distance moved by sample/distance
moved by solvent front
Distance moved by sample
= Rf × distance moved by solvent front
Distance moved by sample
= 0.82 × 9.7 = 8.0 cm.
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 21 continued
Processes for method 2:
Experimental skills 21.3
1
Step a: The baseline needs to be drawn in
pencil, not pen, as the pen could be soluble.
Step c: The solvent should fall between the
bottom of the paper and the baseline; it must
not cover the base line as the samples will
dissolve into the solvent and not travel up
through the paper.
Step d: The solvent should not travel all the
way up but must be stopped just before it gets
to the top of the paper. If this is not done then
samples will continue to travel up the paper.
2
4
heat crushed powder ;
•
forms copper oxide ;
•
heat with charcoal ;
•
wash with dilute acid ;
•
filter and dry ;
a
to be able to measure the volume of
the gas ;
[1]
not sufficiently accurate / can only
measure to nearest cm3 ;
[1]
open the air hole at the base of the
chimney fully ;
[1]
it is fractional distillation /
to know when to change
collecting vessel ;
[1]
b
To reduce the amount of solvent lost
through evaporation.
c
d
Exam-style questions
[1]
[Max. 6 marks]
1
C ;
2
a
tripod [1] ; and evaporating dish/
basin [1] ; the arrow also suggests a
Bunsen burner [1] ;
b
A, C, F, D, B, E ;
c
blue ;
[1]
•
draw a pencil line on the paper ;
d
because copper oxide reacts with acid ; [1]
•
spot some of the solution on the line ;
[Each of the following scores 1 mark]
•
place in the solvent (water) ;
Common starting process:
•
leave until the solvent front reaches
a fixed point ;
•
se a locating agent to make the amino
u
acids visible ;
•
easure distance moved by the
m
different components ;
3
•
crush lump of malachite ;
•
with a pestle and mortar ;
e
[Max. 2 marks]
Processes in method 1:
36
•
5
when crystals form around the edge of
the solution / when crystals form on
a glass rod dipped in the solution ;
[1]
[Each of the following scores 1 mark]
•
dissolve in acid ;
•
named acid ;
•
calculate Rf values ;
•
filter ;
•
•
electrolyse filtrate ;
compare with reference values to identify ;
[Max. 6 marks]
•
recover copper from cathode ;
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 22
light green flame would indicate the presence
of barium ions. Barium sulfate is BaSO4.
Getting started
Criteria for a chemical test might include: It needs
to give a clear result (e.g. a colour change) /
It should be specific (i.e. works for only one
chemical) / Ideally it should be quick and simple
to use / Should not use hazardous chemicals
Reactions students might have seen include:
Standard tests for gases such as hydrogen, oxygen
and carbon dioxide / Standard test for a double
bond (bromine water) / Standard test for an acid
(addition of a carbonate) / Possible tests for the
presence of cations and anions
These tests might be needed by: Companies
monitoring the quality of air or water
/ Government bodies / Health and
safety committees
3
Tap water can contain dissolved ions and
may have given a false positive result, with
the colour being from the impurities and not
the sample. The experimental design can be
improved by using distilled water.
4
C and E
5
The use of state symbols in C shows that this
is a precipitation reaction.
6
AlCl3(aq) + 3NaOH(aq) →
Al(OH)3(s) + 3NaCl(aq)
Experimental skills 22.1
1
A precipitate is an insoluble compound
produced during a precipitation reaction (the
reaction that produces an insoluble salt when
solutions of two soluble salts are mixed).
2
Iron(II) precipitates are green in colour;
iron(III) precipitates are brown in colour.
3
Ammonia is a base.
To ensure their conclusions were valid: To check
results are repeatable / To sample multiple times
Science in context:
Bottled water – finding a solution
to what ions it contains
1
2
Mineral water might be thought of as pure
because it has had no other chemicals added
to it and it has come from a natural source.
Chemically, mineral water is not pure. It is a
mixture, because it contains dissolved impurities.
Questions
7
Iron(II) chloride would initially produce a
green precipitate. Iron(III) chloride would
produce a brown precipitate.
One problem is to ensure that the water does
not contain harmful microbes (these would
normally be removed by disinfection using
chlorine). Another problem is the potential for
changes in composition that may result from
seasonal weather variations.
8
When sodium hydroxide solution is added
to copper(II) sulfate solution, a light blue
precipitate is formed. When dilute ammonia
solution is added to copper(II) sulfate
solution, initially a light blue precipitate is
formed but as more ammonia solution is
added this dissolves and produces a dark
blue solution.
9
A green precipitate could indicate the presence
of either iron(II) or chromium(III) ions and so
their conclusion was not valid. To produce a
valid result, the test should be repeated using
excess sodium hydroxide. If a green precipitate
forms but then redissolves, the sample
contains chromium(III).
Questions
37
1
The nichrome wire probe is cleaned by
placing it alternately in a roaring flame and
concentrated acid. Once clean it can be dipped
in the acid and then into the sample containing
the sodium ions. A positive test for sodium ions
will be the production of a yellow flame.
2
The lilac flame would indicate the presence of
potassium ions. Potassium sulfate is K2SO4.
The red flame would indicate the presence of
lithium ions. Lithium sulfate is Li2SO4. The
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 22 continued
10 Student A’s results would be valid as the
calcium ions would produce an orange-red
flame; no detectable flame colour would
be seen with the zinc or aluminium ions.
Student B’s results would not be valid as both
zinc or aluminium precipitates redissolve in
excess sodium hydroxide. To produce a valid
conclusion student B would need to repeat the
experiment using dilute ammonia solution.
Under these conditions the precipitate
containing zinc ions would redissolve but not
that containing either calcium or aluminium.
18 The pieces of glassware are a volumetric
pipette that adds an accurate, fixed volume of
liquid and a burette, which adds an accurate
but variable volume of liquid.
11 In general, the reaction of a carbonate
with any acid produces carbon dioxide.
Sodium carbonate solution reacts with acids
as follows:
Sodium + sulfuric → sodium + carbon + water
carbonate acid sulfate dioxide
21 The mean titre would only use the results
within 0.10 cm3: i.e. mean titre = (12.15 cm3 +
12.10 cm3 + 12.10 cm3)/3 = 12.12 cm3.
Na2CO3(aq) + H2SO4 (aq) →
Na2SO4 (aq) + CO2(aq) + H2O(l)
Sodium + nitric → sodium + carbon + water
carbonate acid nitrate dioxide
Na2CO3(aq) + 2HNO3 (aq) →
2NaNO3 (aq) + CO2(g) + H2O(l)
12 Acidified silver nitrate would produce a yellow
precipitate with the magnesium iodide and a
white precipitate with the magnesium chloride.
19 Methyl orange and thymolphthalein both
produce clear colour changes at the end-point,
universal indicator does not.
20 Swirling ensures everything is mixed and
also ensures liquid that might have splashed
onto the sides of the flask is returned to
the reaction.
Exam-style questions
1
D;
2
a
b
c
3
[1]
To separate the two components of
the mixture. ;
i
aluminium [1] ; sulfate [1] ;
ii
calcium [1] ; carbonate [1] ;
13 This would negate the results as the sulfuric
acid introduces sulfate ions and so a white
precipitate of barium sulfate is immediately
produced.
14 Al → Al3+ + 3e−
15 a
b
adding
acidified
silver
nitrate
salt
flame
test
slowly
adding
excess
aqueous
sodium
hydroxide
potassium
sulfate
lilac
colour
no reaction no
reaction
barium
bromide
green
colour
no reaction cream
precipitate
lithium
iodide
red
colour
no reaction yellow
precipitate
chromium(III) no colour green
white
chloride
produced precipitate, precipitate
redissolves
Carbon dioxide was present.
Ca(OH)2(aq) + CO2(g) →
CaCO3(s) + H2O(l)
[1]
aluminium sulfate ;
MgI2(aq) + 2AgNO3(aq) →
Mg(NO3)2(aq) + 2AgI(s)
MgCl2(aq) + 2AgNO3(aq) →
Mg(NO3)2(aq) + 2AgCl(s)
[1]
[1 mark for each answer, Max. 6 marks]
16 The gas is not carbon dioxide and it is
not oxygen.
38
17 a
Purple manganate(VII) ions are reduced
to very pale pink manganese(II) ions.
b
The sulfur is oxidised and the manganese
is reduced.
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CAMBRIDGE IGCSE™ CHEMISTRY: COURSEBOOK
Chapter 22 continued
4
a
i
add aqueous sodium hydroxide slowly
until in excess [1] ;
green precipitate which does
not redissolve [1] ;
ii
add acidified barium nitrate [1] ;
white precipitate [1] ;
These two tests can be given in
either order.
b
i
pass gas through lime water [1] ;
lime water turns milky [1] ;
ii
add acidified potassium
manganate(VII) [1] ;
turns colourless [1] ;
These two tests can be given in
either order.
5
39
[Each of the following scores 1 mark]
•
a dd named volume of first vinegar to
a flask ;
•
add a named indicator ;
•
slowly add from a burette ;
•
named alkali ;
•
note volume needed for neutralisation ;
•
repeat with same volume of
second vinegar ;
•
largest volume used (titre) =
most acid. ;
[Max. 6 marks]
Cambridge IGCSETM Chemistry – Harwood, Millington & Lodge © Cambridge University Press 2021