ANSWERS 345
UNIT 1 ANSWERS
CHAPTER 1
1 ▶ a melting b freezing
c subliming/sublimation d subliming/sublimation
2
▶ a
solid liquid gas
Note: Solids should have regularly packed particles
touching. Liquids should have most of the particles
touching at least some of their neighbours, but with
gaps here and there, and no regularity. Gases should
have the particles well spaced.
b Solids: vibration around a fixed point. Liquids:
particles can move around into vacant spaces, but
with some diculty because of the relatively close
packing.
c Evaporation: Some faster moving particles break away
from the surface of the liquid. Boiling: Attractive forces
are broken throughout the liquid to produce bubbles
of vapour.
3
▶ a i A – gas; B – liquid; C – solid; D – liquid; E – solid
ii A – gas; B – solid; C – solid; D – liquid; E – solid
iii A – gas; B – liquid; C – solid; D – gas; E – solid
b A, because it is a gas.
c It sublimes and therefore is converted directly from a
solid to a gas without going through the liquid stage.
d D – because it has a lower boiling point the forces of
attraction between particles will be weaker therefore it
will also evaporate more easily than substance B (the
only other substance that is a liquid at 25 °C).
4
▶ a The ammonia and hydrogen chloride particles have
to diuse through the air in the tube, colliding with air
particles all the way.
b i Its particles will move faster.
ii It would take slightly longer for the white ring to
form, because the gas particles would be moving
more slowly at the lower temperature.
c Ammonia particles are lighter than hydrogen chloride
particles and so move faster. The ammonia covers
more distance than the hydrogen chloride in the same
time.
d i Ammonium bromide.
ii The heavier hydrogen bromide particles would
move more slowly than the hydrogen chloride
particles, and so the ring would form even closer
to the hydrobromic acid end than it was to the
hydrochloric acid end. The ring will also take
slightly longer to form because of the slower
moving particles.
5 ▶ Sodium chloride dissolves in water to form a solution.
The water is called the solvent and the sodium chloride
is the solute. If the solution is heated to 50 °C some
of the water evaporates until the solution becomes
saturated and sodium chloride crystals start to form.
6
▶ a
0
0
20 40 60 80 100
temperature/°C
solubility/g per 100
g water
120
10
20
30
40
50
60
b 94 +/−1 g per 100 g
The values obtained in this question and in c depend
on the line of best fit. In the exam there will always be
some tolerance – a range of values will be accepted.
c From the graph, the solubility at 30
o
C is 10 g per 100 g
of water.
40
____
100
× 10 = 4 g
Therefore 4 g of sodium chlorate will dissolve.
d i 53 +/−1 °C
ii The solubility at 17
o
C is 7 ±1 g per 100 g, therefore
20 − 7 = 13 g must precipitate out of the solution.
Answers of 13 ±1 g are acceptable.
CHAPTER 2
1 ▶
Element Compound Mixture
hydrogen magnesium oxide sea water
calcium copper(II) sulfate honey
blood
mud
potassium iodide
solution
2
▶ a mixture b mixture c element
d element e compound f compound
3
▶ Substance X is the pure substance – it melts at a fixed
temperature. Substance Y is impure – it melts over a
range of temperatures.
4
▶ a crystallisation b (simple) distillation
c fractional distillation d chromatography
e filtration
5
▶ For example: Stir with a large enough volume of cold water
to dissolve all the sugar. Filter to leave the diamonds on
the filter paper. Wash on the filter paper with more water to
remove any last traces of sugar solution. Allow to dry.
6
▶ a M b R
c 0.45 ±0.01 (measure to the centre of the spot and
remember to measure from the base line and not from
the bottom of the paper)
d G and T e P
346 ANSWERS
g 82, lead
h
6 ▶ Palladium is a metal and so is likely to have any of the
following properties:
• good conductor of electricity
• forms a basic oxide
• is shiny when polished or freshly cut
• is malleable
• is ductile
• is a good conductor of heat
The first two are mentioned specifically on the syllabus.
7
▶ They have a full outer shell (energy level) and so they
have no tendency to form compounds by losing/gaining
electrons or sharing electrons.
8
▶ Argon and potassium OR iodine and tellurium.
The elements would then be in a dierent group in the
Periodic Table. They would not have the same number
of electrons in the outer shell as other members of the
group and would react in a completely dierent way. For
example, potassium would be in Group 0 with the noble
gases, and argon, which is very unreactive, would be in
Group 1, with the highly reactive alkali metals.
CHAPTER 5
1 ▶ a Fe + 2HCl → FeCl
2
+ H
2
b Zn + H
2
SO
4
→ ZnSO
4
+ H
2
c Ca + 2H
2
O → Ca(OH)
2
+ H
2
d 2Al + Cr
2
O
3
→ Al
2
O
3
+ 2Cr
e Fe
2
O
3
+ 3CO → 2Fe + 3CO
2
f 2NaHCO
3
+ H
2
SO
4
→ Na
2
SO
4
+ 2CO
2
+ 2H
2
O
g 2C
8
H
18
+ 25O
2
→ 16CO
2
+ 18 H
2
O
h Fe
3
O
4
+ 4H
2
→ 3Fe + 4H
2
O
i Pb + 2AgNO
3
→ Pb(NO
3
)
2
+ 2Ag
j 2AgNO
3
+ MgCl
2
→ Mg(NO
3
)
2
+ 2AgCl
k C
3
H
8
+ 5O
2
→ 3CO
2
+ 4H
2
O
2
▶ a 44 b 60 c 142 d 132
e 286; (The common mistake would be not to multiply
the whole water molecule by 10. So the mass of the
10H
2
O is 180. Students will commonly and wrongly
come up with 36 for this by multiplying the H
2
by 10
but not the O as well. Work out the mass of the whole
H
2
O first and then multiply it by the number in front.
That way you won’t make this mistake.)
f 392
3
▶ a 13.9% b 35%
c 21.2%; (Be careful of the cases where there are two
nitrogen atoms in the fertiliser (all except KNO
3
). The
masses of the nitrogen in those cases will be 28 and
not 14.)
CHAPTER 3
1 ▶ a the nucleus b electrons
c proton d proton and neutron
2
▶ a 9
b sum of protons + neutrons in the nucleus
c 9 p, 10 n, 9 e
d The protons and electrons have equal but opposite
charges. The atom has no overall charge, therefore
there must be equal numbers of protons and
electrons.
3
▶ a 26 p, 30 n, 26 e
b 41 p, 52 n, 41 e
c 92 p, 143 n, 92 e
4
▶ a Atoms with the same atomic number but dierent
mass numbers. They have the same number of
protons, but dierent numbers of neutrons.
b 35Cl: 17 p, 18 n, 17 e; 37Cl: 17 p, 20 n, 17 e
5
▶
6 × 7 + 93 × 7
_____________
100
= 6.93
6
▶
24 × 78.99 + 25 × 10.00 + 26 × 11.01
__________________________________
100
= 24.32
7
▶
204 × 1.4 + 206 × 24.1 + 207 × 22.1+ 208 × 52.4
__________________________________________
100
= 207.241
8 ▶ a 77 protons, 114 neutrons, 77 electrons
b Iridium-193 has 2 more neutrons in the nucleus.
c More iridium-193 because the relative atomic mass is
closer to 193 than 191.
9
▶ This statement is true – it only applies to 1 element,
hydrogen (
1
H).
CHAPTER 4
1 ▶ a i strontium ii chlorine iii nitrogen
iv caesium v neon
b metals: caesium, molybdenum, nickel, strontium, tin
non-metals: chlorine, neon, nitrogen
2
▶
Na
abc
Si S
3 ▶ a 2, 7 b 2, 8, 3 c 2, 8, 8, 2
4
▶ a 5 b 7 c 4 d 8
5
▶ a A, F b A
c C and D because 5 shells are occupied
d C because there are 7 electrons in the outer shell
(energy level)
e B, D
f Calcium – it has 20 electrons and therefore must
have 20 protons in the nucleus. The atomic number
is therefore 20. Calcium is the element with atomic
number 20.
ANSWERS 347
c
Na S O
Combining
mass
3.22 g 4.48 g 3.36 g
No. of
moles of
atoms
3.22
_____
23
= 0.14
4.48
_____
32
= 0.14
3.36
_____
16
= 0.21
Ratio of
moles
(divide by
smallest
number)
1
simplifies
to 2
1
2
1.5
3
Empirical formula is Na
2
S
2
O
3
d
Carbon Hydrogen Bromine
Given % 22.0 4.6 73.4
No. of
moles of
atoms
22.0
_____
12
= 1.833
4.6
___
1
= 4.6
73.4
_____
80
= 0.9175
Ratio of
moles
(divide
by
smallest
number)
2 5 1
Empirical formula is C
2
H
5
Br
8
▶ a The mass of oxygen is 2.84−1.24 = 1.60 g
P O
Combining mass 1.24 g 1.60 g
No. of moles of
atoms
1.24
_____
31
= 0.04
1.60
_____
16
= 0.10
Ratio of moles 1 2.5
Whole numbers must be used, therefore multiply by 2
to get the empirical formula P
2
O
5
.
b P
2
O
5
has an M
r
of 142
284
____
142
= 2
Therefore there must be two lots of the empirical
formula in a molecule.
Molecular formula is P
4
O
10
9 ▶ a
Carbon Hydrogen Oxygen
Given % 66.7 11.1 22.2
Combining
mass in
100 g
66.7 g 11.1 g 22.2 g
No. of
moles of
atoms
66.7
_____
12
= 5.558
11.1
_____
1
= 11.1
22.2
_____
16
= 1.3875
Ratio of
moles
(divide by
smallest
number)
4 8 1
Empirical formula is C
4
H
8
O
4
▶ In each case, work out the M
r
by adding up the relative
atomic masses (A
r
values), and then attach the unit “g” to
give the mass of 1 mole.
a 27 g
b 331 g
c 4.30 × 16 = 68.8 g
d 0.70 × 62 = 43.4 g
e 0.015 × 85 = 1.275 g
f 0.24 × 286 = 68.64 g Don’t forget the water of
crystallisation
Strictly speaking the answers to d), e) and f) shouldn’t
be quoted to more than 2 significant figures, because
the number of moles is only quoted to that precision.)
5
▶ In each case, work out the mass of 1 mole as above, and
then work out how many moles you’ve got in the stated
mass. You can use the equation:
number of moles =
mass
______________
mass of 1 mole
a
20
___
40
= 0.5 mol
b
3.20
_____
160
= 0.0200 mol
c
2000
_____
79.5
= 25.2 mol; Don’t forget to convert kg to g!
d
50
______
249.5
= 0.2 mol
e
1 000 000
_________
56
=
17 900 mol (or 17 857, although this is precise
to more significant figures than the A
r
).
f
0.032
______
64
= 5.0 × 10−4 mol (0.0005 mol)
6
▶ a 4 × 58.5 = 234 g
b
37
___
74
= 0.5 mol
c
1000
_____
40
= 25 mol
d 0.125 × 79.5 = 9.94 g (9.9375 g)
e
4
___
0.1
= 40 g
f
1
________
0.004 g
= 250 g
7 ▶ a
P H
Combining mass 9.39 g 0.61 g
No. of moles of
atoms
9.39
_____
31
= 0.30
0.61
_____
1
= 0.61
Ratio of moles 1 2
Empirical formula is PH
2
b
K N O
Combining
mass
5.85 g 2.10 g 4.80 g
No. of
moles of
atoms
5.85
_____
39
= 0.15
2.10
_____
14
= 0.15
4.80
_____
16
= 0.3
Ratio of
moles
1 1 2
Empirical formula is KNO
2
348 ANSWERS
already been used when you worked out that 2 mol Fe
formed 2 mol FeBr
3
– do not use it again. The equation
for working out the mass is
mass = number of moles × mass of 1 mole).
14
▶ a
1.0
____
190
= 0.0053 mol
b 0.0053 mol
c 0.0053 × 48 = 0.25 g
d number of moles of NaCl = 0.0053 × 4 = 0.0212 mol
mass of NaCl = 0.0212 × 58.5 = 1.2 g
e You can carry out a moles calculation as above:
1 tonne = 1 000 000 g
moles of TiCl
4
=
1 000 000
_________
190
= 5300 mol
moles of Ti = 5300 mol
mass of Ti = 5300 × 48 = 254 400 g
Alternatively, you can reason that, if 1 g TiCl
4
forms
0.25 g Ti, 1 tonne TiCl
4
will form 0.25 tonne Ti.
15
▶ mass of 1 mole of AlCl
3
= 27 + 3 × 35.5 = 133.5 g
moles of Aluminum chloride =
2.67
______
133.5
= 0.0200 mol
moles of AgCl = 3 × 0.0200 = 0.0600 mol
mass of 1 mole of AgCl = 108 + 35.5 = 143.5 g
mass of AgCl = 0.0600 × 143.5 = 8.61 g
16
▶ a mass of 1 mol Cr
2
O
3
= 2 × 52 + 3 × 16 = 152 g
number of moles of Cr
2
O
3
=
50
____
152
= 0.33 mol
number of moles of Al = 2 × 0.33 = 0.66 mol
mass of Al = 0.66 × 27 = 17.8 g
b number of moles of Cr = 2 × 0.33 = 0.66 mol
mass of Cr = 0.66 × 52 = 34.3 g
c 5 kg is 5000 g
number of moles of Cr
2
O
3
=
5000
_____
152
= 33 mol
number of moles of Cr = 2 × 33 = 66 mol
mass of Cr = 66 × 52 = 3430 g or 3.43 kg
Alternatively, we can reason that 5 kg is 100 times
as much as 50 g. If we start with 100 times as much
Cr
2
O
3
, we will make 100 times as much Cr.
d 5 tonnes is 5 000 000 g
number of moles of Cr
2
O
3
=
5 000 000
_________
152
= 33 000 mol
number of moles of Cr = 2 × 33 000 = 66 000 mol
mass of Cr = 66 000 × 52 = 3 430 000 g or 3.43 tonnes
Alternatively, we can reason that, if 5 kg of Cr
2
O
3
produces 3.43 kg Cr, then 5 tonnes of Cr
2
O
3
will
produce 3.43 tonnes of Cr.
17
▶ a mass of 1 mol CuO = 63.5 + 16 = 79.5 g
number of moles of CuO =
4.00
_____
79.5
= 0.0503 mol
number of moles of CuSO
4
= 0.0503 mol
number of moles of CuSO
4
.5H
2
O = 0.0503 mol
mass of 1 mol CuSO
4
.5H
2
O = 63.5 + 32 + 4 × 16 + 5 ×
(16 + 2) = 249.5 g
mass of CuSO
4
.5H
2
O = 0.0503 × 249.5 = 12.55 g
b The mass of the empirical formula is 4 × 12 + 8 × 1
+ 16 = 72. Since this is equal to the relative formula
mass, the molecular formula is the same as the
empirical formula, that is C
4
H
8
O.
10
▶ You know the mass of anhydrous sodium sulfate (1.42 g).
You can work out the mass of water of crystallisation
(3.22 − 1.42 g = 1.8 g).
You can work out the mass of 1 mole of sodium sulfate,
Na
2
SO
4
= 142 g;
and the mass of 1 mole of water = 18 g.
Number of moles of sodium sulfate =
1.42
_____
142
= 0.01 mol.
Number of moles of water =
1.8
___
18
= 0.1 mol.
So for every 1 mole of sodium sulfate, there are 10 moles
of water.
The value of n is 10.
11
▶ mass of anhydrous calcium sulfate = 44.14 − 37.34 = 6.80 g
mass of water of crystallisation = 45.94 − 44.14 = 1.80 g
mass of 1 mole of calcium sulfate, CaSO4 = 136 g
number of moles of sodium sulfate =
6.80
_____
136
= 0.05 mol
mass of 1 mole of water = 18 g
number of moles of water =
1.8
___
18
= 0.1 mol
number of moles of water = 0.1 = 2
number of moles of calcium sulfate 0.05
the value of n = 2
12
▶ a 0.36 mol
b From the chemical equation, the number 2 in front
of the HCl indicates that 2 mol HCl react with 1 mol
CaCO
3
, therefore 0.4 mol CaCO
3
react with
2 × 0.4 = 0.8 mol HCl.
c 6 mol HCl react to form 3 mol H
2
S
Therefore the number of moles of H
2
S is half the
number of moles of HCl.
0.4 mol HCl form 0.2 mol H
2
S
d 3 mol CO form 2 mol Fe
The number of moles of Fe is
2
__
3
the number of moles
of CO.
0.9 ×
2
__
3
= 0.6 mol iron
e 0.8 ×
3
__
2
= 1.2 mol hydrogen
13
▶ a number of moles of iron =
10
___
56
= 0.179 mol
b From the chemical equation, the number of moles of
bromine that reacted with this number of moles of iron
is
3
__
2
× 0.179 = 0.277 mol.
c From the chemical equation, the number of moles of
FeBr
3
will be the same as the number of moles of iron
= 0.179 mol.
d mass of 1 mol FeBr
3
= 56 + 3 × 80 = 296
mass of FeBr
3
= 0.179 × 296 = 53 g
(A common mistake here is to multiply the number
of moles of FeBr
3
by the mass of 2FeBr
3
. The 2 has
ANSWERS 349
2 ▶ a 2.0 × 24 = 48 dm
3
(48 000 cm
3
)
b 0.10 × 24 = 2.4 dm
3
(2400 cm
3
)
c 1 × 10
−3
× 24 = 0.024 dm
3
(24 cm
3
)
3 ▶ a 200 cm
3
of chlorine is
200
_______
24 000
= 0.00833 mol
(be careful with units here – if the volume is in cm
3
you
must use 24 000 as the molar volume)
mass of 1 mol of Cl
2
= 2 × 35.5 = 71 g
mass of 0.00833 mol Cl
2
= 0.00833 × 71 = 0.592 g
b mass of 1 mol of O
2
= 2 × 16 = 32 g
number of moles of O
2
= 0.
16
___
32
= 0.005 mol
0.005 mol O
2
has a volume of 0.005 × 24 000 =
120 cm
3
(0.12 dm
3
)
c 1 dm
3
of the gas is
1
___
24
= 0.0417 mol
the mass of 0.0417 mol is 1.42 g
mass of 1 mol of the gas =
1.42
_______
0.0417
= 34.1 g
4
▶
0.240
______
24
= 0.0100 mol
From the chemical equation, the number of moles of H
2
is
the same as the number of moles of Mg: 0.0100 mol.
volume of hydrogen = 0.0100 × 24 = 0.24 dm
3
(240 cm
3
)
5
▶
1
___
24
= 0.0417 mol O
2
From the chemical equation, the number of moles of
KNO
3
is twice the number of moles of O
2
2 × 0.0417 = 0.0833 mol
mass of 1 mol KNO
3
= 39 + 14 + 3 × 16 = 101 g
mass of 0.0417 mol KNO
3
= 0.0833 × 101 = 8.42 g
6
▶ mass of 1 mol MnO
2
= 55 + 2 × 16 = 87 g
number of moles of MnO
2
=
2.00
_____
87
= 0.0230 mol
from the chemical equation: 1 mol MnO
2
produces
1 mol Cl
2
number of moles of Cl
2
produced = 0.0230 mol
volume of Cl
2
produced = 0.0230 × 24000 = 552 cm
3
(0.552 dm
3
)
7
▶ mass of 1 mol H
2
SO
4
= 98 g
number of moles of H
2
SO
4
4.90
_____
98
mol = 0.0500 mol
this number of moles is in 1 dm
3
of solution
concentration = 0.0500 mol/dm
3
(0.0500 to show that the
answer is precise to 3 significant figures)
8
▶ mass of 1 mol KOH = 39 + 16 + 1 = 56 g
mass of 0.200 mol = 0.200 × 56 = 11.2 g
concentration = 11.2 g/dm
3
9 ▶ In each of these questions the number of moles is given by:
number of moles = volume in dm
3
× concentration in
mol/dm
3
to convert a volume in dm
3
to cm
3
divide by 1000
a
25.0
_____
1000
× 0.100 = 0.00250 mol
b
200
_____
1000
× 0.200 = 0.0400 mol
b the theoretical yield is 12.55 g
the actual yield is 11.25 g
11.25
______
12.55
× 100 = 89.64%
18
▶ a mass of 1 mol ethanol = 2 × 12 + 6 × 1 + 16 = 46 g
number of moles of ethanol =
20.0
_____
46
= 0.435 mol
number of moles of ethyl ethanoate = 0.435 mol
mass of 1 mol ethyl ethanoate = 4 × 12 + 2 × 16 + 8 ×
1 = 88 g
mass of ethyl ethanoate = 0.435 × 88 = 38.3 g
b theoretical yield = 38.3 g
actual yield = 30.0 g
percentage yield =
30.0
_____
38.3
× 100 = 78.3%
19
▶ a 0.5 mol HCl would react with 0.25 mol Na
2
CO
3
.
There is more than 0.25 mol Na
2
CO
3
, therefore Na
2
CO
3
is in excess.
b 0.02 mol O
2
would react with
0.02
_____
5
= 0.004 mol C
3
H
8
.
There is more than 0.004 mol C
3
H
8
, therefore C
3
H
8
is
in excess.
c 28 g of CO is
28
___
28
= 1 mol
1 mol CO would react with
1
__
3
= 0.33 mol Fe
2
O
3
.
There is more than 0.33 mol Fe
2
O
3
, therefore Fe
2
O
3
is
in excess.
d 16 g O
2
is
16
___
32
= 0.5 mol
16 g SO
2
is
16
___
64
= 0.25 mol
0.25 mol SO
2
would react with 0.125 mol O
2
There is more than 0.125 mol O
2
, therefore O
2
is in excess.
20 ▶ a 1.0 g of CaCO
3
is
1.0
_____
100
= 0.010 mol
0.010 mol CaCO
3
would react with 2 × 0.010 =
0.020 mol HCl
There is less than 0.020 mol HCl, therefore there is
not enough HCl to react with all the CaCO
3
. Therefore
CaCO
3
is in excess.
b To calculate the number of moles of CO
2
you must use
the number of moles of HCl because not all the CaCO
3
reacted.
moles of HCl = 0.015 mol
moles of CO
2
= 0.5 × 0.015 = 0.0075 mol
mass of CO
2
= 0.0075 × 44 = 0.33 g
(If you got the answer 0.44 g you used the number of
moles of CaCO
3
. CaCO
3
was in excess; therefore not
all of it will react.)
CHAPTER 6
1 ▶ a
2.4
___
24
= 0.10 mol
b
480
____
24
= 20 mol
c
100
______
24000
= 0.00417 mol
d
1500
______
24000
= 0.0625 mol
350 ANSWERS
b mass of 1 mol CaCO
3
= 100 g
number of moles of CaCO
3
=
10.0
_____
100
= 0.100 mol
from the chemical equation 0.100 mol CaCO
3
reacts
with 2 × 0.100 = 0.200 mol HCl
volume (dm
3
) =
number of moles (mol)
______________________
concentration (mol/dm
3
)
volume =
0.200
______
2.00
= 0.100 dm
3
or 100 cm
3
16 ▶ In each of these questions the number of moles is given by
number of moles = volume in dm
3
× concentration in mol/dm
3
to convert a volume in dm
3
to cm
3
divide by 1000
a no. of moles of NaOH solution =
25.0
_____
1000
× 0.100 mol =
0.00250 mol
the equation shows that you need the same number of
moles of nitric acid = 0.00250 mol
concentration (mol/dm
3
) =
number of moles (mol)
_____________________
volume (dm
3
)
20.0 cm
3
is
20.0
_____
1000
= 0.0200 dm
3
concentration =
0.00250
________
0.0200
= 0.125 mol/dm
3
b no. of moles of nitric acid =
30.0
_____
1000
× 0.100 mol =
0.00300 mol
the equation shows that you need half the number
of moles of sodium carbonate = 0.5 × 0.00300 =
0.00150 mol
concentration (mol/dm
3
) =
number of moles (mol)
_____________________
volume (dm
3
)
25.0 cm
3
is
25.0
_____
1000
= 0.0250 dm
3
concentration =
0.00150
________
0.0250
= 0.0600 mol/dm
3
c no. of moles of potassium carbonate solution =
25.0
_____
1000
× 0.250 mol = 0.00625 mol
the equation shows that you need twice the number of
moles of ethanoic acid = 2 × 0.00625 = 0.0125 mol
concentration (mol/dm
3
) =
number of moles (mol)
_____________________
volume (dm
3
)
12.5 cm
3
is
12.5
_____
1000
= 0.0125 dm
3
concentration =
0.0125
_______
0.0125
= 1.00 mol/dm
3
17 ▶ a no. of moles of hydrochloric acid =
18.8
_____
1000
× 0.0400 mol
= 0.000752 mol (7.52 × 10
−4
)
the equation shows that you need half the number of
moles of calcium hydroxide
number of moles of calcium hydroxide = 0.5 ×
0.000752 = 0.000376 mol (3.76 × 10
−4
)
concentration (mol/dm
3
) =
number of moles (mol)
_____________________
volume (dm
3
)
25.0 cm
3
is
25.0
_____
1000
= 0.0250 dm
3
concentration =
0.000376
_________
0.0250
= 0.0150 mol/dm
3
c
75.0
_____
1000
× 0.150 = 0.01125 mol
d
22.4
_____
1000
× 0.280 = 0.00627 mol
10
▶ concentration (mol/dm
3
) =
number of moles (mol)
_____________________
volume (dm
3
)
a concentration =
0.100
______
2
= 0.0500 mol/dm
3
b volume in dm
3
=
25.0
_____
1000
= 0.050 dm
3
concentration =
0.0200
_______
0.0250
= 0.800 mol/dm
3
c volume in dm
3
=
27.8
_____
1000
= 0.0278 dm
3
concentration =
0.00150
________
0.0278
= 0.0540 mol/dm
3
11 ▶ volume (dm
3
) =
number of moles (mol)
______________________
concentration (mol/dm
3
)
a
0.500
______
0.100
= 5.00 dm
3
(5.00 indicates that the answer is to
3 significant figures)
b
0.00500
________
0.0200
= 0.250 dm
3
(250 cm
3
)
c
0.0200
_______
0.500
= 0.0400 dm
3
(40.0 cm
3
)
12
▶ no. of moles of copper(II) sulfate =
20
_____
1000
× 0.100 =
0.00200 mol
equation shows that 1 mol CuSO4 produces 1 mol BaSO
4
no. of moles BaSO
4
formed = 0.00200 mol
mass of 1 mol BaSO
4
= 137 + 32 + 4 × 16 = 233 g
mass of 0.00200 mol BaSO
4
= 0.00200 × 233 = 0.466 g
13
▶ 25.0 cm
3
of 2.00 mol/dm
3
HCl contains
25.0
_____
1000
× 2.00 mol =
0.0500 mol
From the chemical equation, the number of moles of
CaCO
3
that reacts is half the number of moles of HCl,
that is 0.5 × 0.0500 = 0.0250 mol.
mass of 1 mol CaCO
3
= 100 g
mass of 0.0250 mol CaCO
3
= 0.0250 × 100 = 2.50 g
number of moles of CO
2
= 0.0250 mol
volume of CO
2
= 0.0250 × 24 000 = 600 cm
3
14 ▶ number of moles of hydrogen peroxide =
30.0
_____
1000
× 0.0200
= 0.000600 mol (6.00 × 10
−4
)
from the chemical equation, the number of moles of O
2
produced is half the number of moles of H
2
O
2
number of moles of O
2
= 0.000300 mol (3.00 × 10
−4
)
volume of oxygen = 0.000300 × 24 000 = 7.20 cm
3
15 ▶ a no. of moles of NaOH solution =
25.0
_____
1000
× 0.400 mol =
0.0100 mol
the equation shows that you need half as many moles
of sulfuric acid = 0.00500 mol
volume (dm
3
) =
number of moles (mol)
______________________
concentration (mol/dm
3
)
volume =
0.00500
________
0.200
= 0.0250 dm
3
or 25.0 cm
3
ANSWERS 351
3 ▶
a formula b name
i magnesium Mg
2+
ii strontium Sr
2+
iii potassium K
+
iv oxygen O
2−
oxide
v sulfur S
2−
sulfide
vi caesium Cs
+
vii chlorine Cl
−
chloride
viii iodine I
−
iodide
ix aluminium Al
3+
x calcium Ca
2+
xi nitrogen N
3−
nitride
4
▶ PbO NaBr
MgSO
4
ZnCl
2
K
2
CO
3
(NH
4
)
2
S
Ca(NO
3
)
2
Fe(OH)
3
FeSO
4
CuCO
3
Al
2
(SO
4
)
3
Ca(OH)
2
CoCl
2
CaO
AgNO
3
FeF
3
NH
4
NO
3
RbI
Na
2
SO
4
Cr
2
O
3
5 ▶ a The electrostatic forces of attraction between
oppositely charged ions are strong and require a lot of
energy to break.
b The ions are held tightly in place in the giant lattice
structure and are not free to move.
c The ions are free to move (it is important to use the
word ions here; any mention of electrons will score 0
in an exam).
6
▶ Potassium chloride will have a lower melting point than
calcium oxide. The charges on the ions in KCl (K
+
and Cl
−
)
are lower than in CaO (Ca
2+
and O
2−
). There are weaker
electrostatic forces of attraction between oppositely
charged ions in KCl than in CaO; these forces require less
energy to break than the forces in CaO.
CHAPTER 8
1 ▶
a MgO ionic
b CH
3
Br covalent
c H
2
O
2
covalent
d FeCl
2
ionic
e NaF ionic
f HCN covalent
2
▶ a A pair of electrons that is shared between two atoms.
The atoms are held together because the nucleus of
each is attracted to the shared pair.
b mass of 1 mol Ca(OH)
2
= 40 + 2 × (16+1) = 74 g
there are 0.0150 mol in 1 dm
3
the mass of 0.0150 mol is 0.0150 × 74 = 1.11 g
therefore the concentration is 1.11 g/dm
3
18 ▶ a 0.1 mol HNO
3
reacts with 0.05 mol Na
2
CO
3
. There is
more than this present, therefore Na
2
CO
3
is in excess.
b no. of moles of Na
2
CO
3
=
20.0
_____
1000
× 0.100 mol =
0.00200 mol
0.0200 mol HNO
3
reacts with 0.0100 mol Na
2
CO
3
.
There is less than this present, therefore HNO
3
is in
excess.
c no. of moles of Na
2
CO
3
=
25.0
_____
1000
× 0.300 mol =
0.00750 mol
no of moles of HNO
3
=
20.0
_____
1000
× 0.400 mol =
0.00800 mol
0.00800 mol HNO
3
reacts with 0.00400 mol Na
2
CO
3
. There
is more than this present, therefore Na
2
CO
3
is in excess.
CHAPTER 7
1 ▶ a i An atom or group of atoms which carries an
electrical charge.
ii Attractions between positively and negatively
charged ions holding them together.
b Correct electronic structures for:
i Na 2,8,1 and Cl 2,8,7
ii Li 2,1 and O 2,6
iii Mg 2,8,2 and F 2,7.
Diagrams (similar to those in the chapter) showing
transfer of electrons, and the charges and
electronic structures of the ions formed (or words
to the same eect).
In (i), show 1 electron transferred from Na to Cl
leaving Na
+
[2,8]
+
and Cl
–
[2,8,8]
In (ii), show 2 lithium atoms each giving 1 electron
to O leaving 2 × Li
+
(2)
+
and O
2
–
[2,8]2
In (iii), show 1 Mg giving an electron each to 2
fluorines leaving Mg
2+
[2,8]
2+
and 2 × F
–
[2,8]
–
2 ▶ a
K
+
F
–
b
Br Ca
–
Br
–2+
c
I Mg
–
I
–2+
352 ANSWERS
(It doesn’t matter what variations of colours or dots
and crosses are used. In the chloroethane case, the
Cl could equally well have been drawn together with
either of the other two hydrogen atoms on the right-
hand carbon atom.)
4
▶ Carbon dioxide has a simple molecular structure; diamond
has a giant covalent structure. When carbon dioxide
sublimes, only the weak intermolecular forces of attraction
must be broken – but when diamond sublimes, the strong
covalent bonds must be broken. A lot more energy is
required to break the strong covalent bonds in diamond
than the weak intermolecular forces in carbon dioxide.
5
▶ a
Simple molecular because it is a liquid at room
temperature. Only weak intermolecular forces of attraction
must be broken to melt solid hexane. Compounds with
giant structures have high melting points and boiling
points and will be solids at room temperature.
b Pentane has a lower boiling point. The intermolecular
forces of attraction are weaker in pentane because the
relative formula mass is lower. Weaker intermolecular
forces require less energy to break.
c It will not conduct electricity because there are no ions
present and all the electrons are held tightly in atoms
or covalent bonds.
6
▶ a To break apart diamond, strong covalent bonds must
be broken, which requires a large amount of energy.
Much less energy is required to break the weak forces
of attraction between the layers in graphite.
b C
60
fullerene has a molecular structure but graphite
has a giant structure. To melt C
60
fullerene, only weak
intermolecular forces must be broken, but to melt
graphite strong covalent bonds must be broken.
Much less energy is required to break the weak
intermolecular forces in C
60
fullerene than the strong
covalent bonds in graphite.
c
Each C atom in graphite only forms 3 bonds so there is one
electron left over on each on each atom. These delocalised
electrons are free to move throughout the layers.
d All the outer shell electrons in diamond are held tightly
in covalent bonds and unable to move around.
7
▶ (Weakest intermolecular forces of attraction) hydrogen,
phosphorus trifluoride, ammonia, ethanol, water,
ethanamide (strongest intermolecular forces of attraction).
Higher intermolecular attractions produce higher boiling
points – more energy has to be supplied to overcome
stronger forces of attraction between molecules.
8
▶ a Nitrogen usually forms 3 bonds because it has 5
electrons in its outer shell. Each N forms 1 bond to F,
therefore there must be a double bond between the
two N atoms. Formation of a double bond results in
each N having 8 electrons in its outer shell.
b
N N
F
F
b (It doesn’t matter whether students use dots or
crosses or just dierent colours- or what positions (N,
S, E, W) the hydrogens occupy in the H
2
S or PH
3
.)
Cl Si Cl
Cl
ii
i
iv
iii
Cl
H
H
S
H H
H
P
H
H
H
C H
c i
O O
ii
N N
3 ▶ a
CH
H
H
C
H
H
H
b
CC
H
H
H
H
c
CH
H
H
C
Cl
H
H
ANSWERS 353
CHAPTER 10
1 ▶ cathode anode
a lead bromine
b zinc chlorine
c hydrogen iodine
d sodium iodine
e copper chlorine
f hydrogen chlorine
g hydrogen oxygen
h hydrogen oxygen
2
▶ a Mg
2+
+ 2e
−
→ Mg
b Al
3+
+ 3e
−
→ Al
c 2Br
–
→ Br2 → 2e
–
d 2O2
–
→ O2 + 4e
–
e 2Cl
–
→ Cl2 + 2e
–
f Ni2
+
+ 2e
−
→ Ni
g 4OH
–
→ O2 + 2H2O + 4e
–
h 2H2O → O2 + 4H
+
+ 4e
–
i 2H2O + 2e
–
→ H2 + 2OH
–
3 ▶ a Ions weren’t free to move.
b anode
c iodine: 2I
–
(l) → I
2
(g) + 2e
–
d K+(l) + e
–
→ K(l)
e anode: bromine
cathode: sodium
f anode: 2Br
−
→ Br
2
+ 2e
−
cathode: Na
+
+ e
−
→ Na
4
▶ a i Pb
2+
(l) + 2e
–
→ Pb(l)
ii 2Br
–
(l) → Br
2
(g) + 2e
–
iii oxidised: bromide ions. Reduced: lead(II) ions.
b i 2H
+
(aq) + 2e
–
→ H
2
(g)
ii 2Cl
–
(aq) → Cl
2
(g) + 2e
–
iii oxidised: chloride ions. Reduced: hydrogen ions.
c i 2H
+
(aq) + 2e
–
→ H
2
(g)
ii 2Br
–
(aq) → Br
2
(aq or l) + 2e
–
iii oxidised: bromide ions. Reduced: hydrogen ions.
d i Cu
2+
(aq) + 2e
–
→ Cu(s)
ii 4OH
–
(aq) → 2H
2
O(l) + O
2
(g) + 4e
–
iii oxidised: hydroxide ions. Reduced: copper(II) ions.
e i 2H
+
(aq) + 2e
–
→ H
2
(g)
ii 4OH
–
(aq) → 2H
2
O(l) + O
2
(g) + 4e
–
iii oxidised: hydroxide ions. Reduced: hydrogen ions.
f i Mg
2
+(l) + 2e
–
→ Mg(s or l)
ii 2I
–
(l) → I
2
(g) + 2e
–
iii oxidised: iodide ions. Reduced: magnesium ions.
g i 2H
+
(aq) + 2e
–
→ H
2
(g)
ii 2Cl
–
(aq) → Cl
2
(g) + 2e
–
iii oxidised: chloride ions. Reduced: hydrogen ions.
(It doesn’t matter what variations of colours or dots
and crosses are used. The F atoms could also be
drawn in dierent positions.)
9
▶ a
Cl
BCl
Cl
b The B atom does not have 8 electrons in its outer shell.
CHAPTER 9
1 ▶ a
+
–
–
+
–
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
++
–
+
–
+
–
+
–
+
sea of
delocalised
electrons
lattice of metal ions
–
–
b
2+ 2+ 2+
2+ 2+ 2+
2+ 2+ 2+
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
––
sea of delocalised
electrons
lattice of metal ions
(The diagrams should show at least 9 ions but can be
of any size beyond that. Electrons could be shown
ase
−
.)
2
▶ a Mg 2, 8, 2. The two outer electrons will be lost from
each Mg atom to form the sea of delocalised electrons.
There will be a regular arrangement of Mg
2+
ions.
b Na will form Na
+
ions, Mg will form Mg
2+
ions and Al
will form Al
3+
ions. There will be stronger electrostatic
attraction between the metal ions and the delocalised
electrons when the charge on the ion is higher. Al
3+
has
the strongest attraction between the metals ions and
the delocalised electrons, therefore most energy has to
be supplied to overcome the forces of attraction.
c Delocalised electrons are free to move.
d The layers of metal ions are able to slide over each
other without changing the bonding.
3
▶ a giant covalent
b molecular
c molecular
d giant ionic
e giant metallic
f molecular
g giant metallic
Cl
BCl
Cl
354 ANSWERS
The diagram below would only score 1 mark – for the
random arrangement
c number of protons: 1 (1)
number of neutrons: 2 (1)
number of electrons: 1 (1)
d i 2, 5 (1)
ii
N
H
H
H
three covalent bonds shown, each with a dot and
a cross (1)
the remaining 2 electrons on N (1)
e NH
4
SO
4
is incorrect (1) because the ammonium ion is
NH
4
+
and the sulfate ion is SO
4
2−
f fractional distillation (1)
2 ▶ a The elements in the Periodic Table are arranged in
order of atomic number (1). The vertical columns are
called groups (1) and contain elements which have the
same number of electrons (1) in their outer shell (1).
b H (1) and Ar (1)
c i The second property is not a property of metals.
Metal oxides are basic (1)
and would react with acids rather than with alkalis
such as sodium hydroxide. (1)
ii The grey circles represent silicon atoms. (1)
A silicon atom has 4 electrons in its outer shell and
will form 4 covalent bonds. (1)
An oxygen atom has 6 electrons in its outer shell
and will only form 2 covalent bonds. (1)
(Note: although some of the ‘grey atoms’ only
appear to form 2 bonds this is because only part
of the giant structure is shown. None of the ‘red
atoms’ form 4 bonds.)
iii SiO
2
would be a solid at room temperature
because it has a giant structure. (1)
A lot of energy is required to break all the strong
covalent bonds. (1)
3
▶ a idea of electron transfer (1)
electron transfer from Sr to Br (1)
the correct number of electrons transferred (1)
b high melting point (1)
strong electrostatic forces of attraction between
oppositely-charged ions (1)
require a lot of energy to break (1)
c The relative atomic mass of an element is the weighted
average mass of the isotopes of the element. (1)
It is measured on a scale on which a carbon-12 atom
has a mass of exactly 12. (1)
d
50.69 × 79 + 49.31 × 81
______________________
100
(1)
79.99 (1)
e Sr(NO
3
)
2
(1)
5
▶ The melting point of S is too high to reach using a
Bunsen, and so you would have to test a solution in water.
On the other hand, T would melt easily, and won’t
dissolve. Heat it until it melts.
6 V
odes
bulb
S solution
small beaker
DC power supply
6 V
odes
bulb
molten
pyrex dish
or crucible
(You could also do the electrolysis of the solution using the
more complicated apparatus in the chapter, but since there
is no need to collect anything, there isn’t much point.)
If the substances are electrolytes, the bulbs will light up,
and there will be signs of activity around the electrodes
(gases given o, solids deposited, etc).
6
▶ a Cu
2+
(aq) + 2e
−
→ Cu(s)
b i The Cu
2+
(aq) ions are responsible for the blue
colour and these are removed from the solution,
therefore the blue colour fades.
water dissociates
H
2
O ⇋ H
+
+ OH
−
Oxygen is produced at the anode. The half
equation for this is:
4OH
−
→ 2H
2
O + O
2
+ 4e
−
Because the OH
−
is removed from solution, more
water must dissociate to replace them. This
produces an excess of H
+
ions in solution, so the
solution is acidic.
ii There is no change in colour because the
concentration of Cu
2+
(aq) remains the same; when
1 Cu
2+
(aq) ion is removed at the cathode another
one replaces it at the anode.
There is no change in acidity because the OH
−
ions
are not removed from the solution to form oxygen.
END OF UNIT 1 QUESTIONS
1 ▶ a −255 °C (1) The temperature is between the melting
point and boiling point.
b
Particles randomly arranged
(1) and mostly touching
each other. (1)
ANSWERS 355
From the chemical equation, the number of moles of
Fe
2
O
3
is half the number of moles of FeS
2
.
number of moles of Fe
2
O
3
= 2000 mol (1)
Mr of Fe
2
O
3
= 2 × 56 + 3 × 16 = 160
mass of Fe
2
O
3
= 2000 × 160 = 320 000 g or 320 kg (1)
b From the chemical equation 4000 mol FeS
2
produces
8000 mol SO
2
. (1)
volume = 8000 × 24 = 192 000 dm
3
(1)
c i 2SO
2
+ O
2
→ 2SO
3
all formulae correct (1)
correct balancing (1)
ii From the equation 2 mol SO
2
react with 1 mol
O
2
. So the number of moles of O
2
will be half as
many. Therefore the number of moles of O
2
will be
4000 mol. (1)
volume = 4000 × 24 = 96 000 dm
3
(1)
For the second mark we could just reason that
since half as many moles are required, then the
volume will also be half.
9
▶ a A saturated solution is a solution which contains
as much dissolved solid as possible at a particular
temperature. (1)
b number of moles =
32.8
_____
1000
× 0.100 = 3.28 × 10
−3
mol or
0.00328 mol (1)
c From the chemical equation, the number of moles of
Sr(OH)
2
is half the number of moles of HCl.
number of moles of Sr(OH)
2
= 1.64 × 10
−3
or
0.00164 mol (1)
volume of Sr(OH)
2
in dm
3
is
25
_____
1000
= 0.025 dm
3
(1)
concentration of Sr(OH)
2
=
0.00164
________
0.025
= 0.0656 mol/dm
3
(1)
d M
r
of Sr(OH)
2
= 88 + 2 × (16 + 1) = 122
mass of Sr(OH)
2
in 1 dm
3
of solution is 122 × 0.0656 =
8.00 g (1)
1 dm
3
is 1000 cm
3
, therefore mass of Sr(OH)
2
present
in 100 cm
3
or 100 g of water is one tenth of this, that is
0.800 g (1)
e (The three points in bold are essential and then 1 mark
each for 2 further points.)
an empty evaporating basin is weighed (1)
some of the strontium hydroxide solution is poured
into the evaporating basin (1)
care must be taken to not pour in any solid (1)
weigh the evaporating basin and strontium
hydroxide solution (1)
the evaporating basin is heated over a tripod and
gauze using a Bunsen burner (1)
until all the water is driven o / heat to constant mass (1)
weigh the evaporating basin and solid strontium
hydroxide (1)
10
▶ a Number of moles of sodium hydroxide =
25.0
_____
1000
× 0.100
= 2.50 × 10
−3
mol or 0.0025 mol (1)
From the chemical equation, the number of moles of
sulfuric acid is half of this.
4
▶ a Diamond has a giant covalent structure (1), where all
the atoms are held together by strong covalent bonds
– a lot of energy is required to break these bonds. (1)
b i Graphite has the higher melting point. (1)
Graphite has a giant structure but C
60
fullerene has
a simple molecular structure. (1)
To melt graphite, all the strong covalent bonds
between carbon atoms must be broken – this
requires a lot of energy. (1)
To melt C
60
fullerene, only the weak intermolecular
forces of attraction must be broken – this requires
less energy. (1)
ii Graphite has delocalised electrons. (1)
Delocalised electrons are free to move (throughout
the structure). (1)
iii C
60
has a molecular structure rather than a giant
structure. (1)
Electrons cannot move between molecules. (1)
5
▶ a
OO
(1)
The correct diagram is above. (There is a double bond
between the O atoms.)
b K
2
O is the correct formula (1)
c
OCO
(1)
The correct diagram is above. (Carbon forms 4 bonds
and oxygen forms 2 bonds.)
6
▶ a mass of lead = 24.16 − 17.95 = 6.21 g (1)
b mass of oxygen = 24.80 − 24.16 g = 0.64 g (1)
c Pb O
combining masses 6.21 g 0.64 g
no of moles of atoms 6.21/207 0.64/16 (1)
= 0.03 = 0.04
ratio of moles 3 : 4 (1)
empirical formula: Pb
3
O
4
(1)
7
▶ a number of moles of copper =
2.00
_____
63.5
= 0.0315 mol (1)
From the chemical equation, the same number of
moles of copper(II) nitrate will be produced.
number of moles of Cu(NO
3
)
2
is 0.0315 mol (1)
M
r
of Cu(NO
3
)
2
= 63.5 + 2 × (14 + 3 × 16) = 187.5
mass of Cu(NO
3
)
2
= 187.5 × 0.0315 = 5.91 g (1)
b The student would use crystallisation. (1)
Heat the solution in an evaporating basin to drive
o some of the water until the solution becomes
saturated. (1)
Allow to cool then filter o the crystals that form. (1)
c percentage yield =
actual yield
_______________
theoretical yield
× 100
=
5.23
_____
7.61
× 100 (1)
= 68.7% (1)
8
▶ a M
r
of FeS
2
= 56 + 2 × 32 = 120
480 kg is 480 000 g
number of moles of FeS
2
=
480 000
________
120
= 4000 mol (1)
356 ANSWERS
ii Some gas could have escaped from the apparatus
/ there was a leak in the apparatus / they could
have used less than 0.15 g limestone / they used
a dierent concentration of hydrochloric acid that
had too low a concentration / they used too low a
volume of hydrochloric acid. (1)
e All the hydrochloric acid has been used up. (1)
There is no more hydrochloric acid to react with any
additional limestone, so no more gas can be produced. (1)
f 0.42 g (1)
(This is the point at which the two lines cross because
this is the point at which adding any more CaCO
3
does not produce any more gas.)
g i CaCO
3
(s) + 2HCl (aq) → CaCl
2
(aq) + H
2
O (l) +
CO
2
(g)
ii Number of moles of CO
2
=
91
______
24000
= 3.79 ×
10
−3
mol or 0.00379 mol. (1)
From the chemical equation, the number of moles
of CaCO
3
is the same as the number of moles of
CO
2
.
Number of moles of CaCO
3
is 3.79 × 10
−3
mol or
0.00379 mol. (1)
Mr of CaCO
3
is 40 + 12 + 3 × 16 = 100
mass of CaCO
3
= 0.00379 × 100 = 0.379 g (1)
iii
0.379
______
0.42
× 100 (1)
= 90 % (1)
You have worked out above the mass of limestone
that reacts with the hydrochloric acid is 0.42 g. The
volume of CO
2
produced by this mass of limestone
is 91 cm
3
. 91 cm
3
of CO
2
is produced by 0.379 g
of CaCO
3
, therefore this is the mass of CaCO
3
present in 0.42 g of limestone.
UNIT 2 ANSWERS
CHAPTER 11
1 ▶ They have the same number of electrons in the outer
shell (1 electron) and all react in the same way.
2
▶ a A = lithium
b B = potassium; C = hydrogen; D = potassium
hydroxide
c 2K(s) + 2H
2
O(l) → 2KOH(aq) + H
2
(g)
d The paper goes blue/purple.
e Lots of heat evolved. Melting point of potassium is low.
f E is sodium and F is sodium oxide
sodium + oxygen → sodium oxide
4Na(s) + O
2
(g) → 2Na
2
O(s)
3
▶ a FALSE b TRUE c TRUE
d FALSE, the formula of lithium chloride is LiCl
4
▶ a More dense. Density increases down the group.
b 1
Number of moles of sulfuric acid = 1.25 × 10
−3
mol or
0.00125 mol (1)
Volume of sulfuric acid in dm
3
= 0.0200 dm
3
(1)
Concentration of sulfuric acid is
0.00125
________
0.0200
= 0.0625 mol/
dm
3
(1)
b i lattice of positive ions (1)
sea of delocalised electrons (1)
electrostatic attraction between the positive ions
and delocalised electrons (1)
ii the layers of positive ions/atoms (1)
can slide over each other (1)
iii number of moles =
100
_____
1000
× 0.0625 = 0.00625 mol
or 6.25 × 10
−3
mol (1)
iv 0.100 g of Mg is
0.100
______
24
= 0.00417 mol or 4.17 ×
10
−3
mol (1)
Therefore the sulfuric acid is in excess because
only 0.00417 mol would be required to react with
all the Mg and there is more present than this. (1)
v The number of moles of magnesium must be used
to work out the number of moles of H
2
because
the sulfuric acid is in excess.
From the chemical equation, the number of moles
of H
2
is the same as the number of moles of Mg.
The number of moles of H
2
is 0.00417 mol or 4.17
× 10
−3
mol. (1)
volume of hydrogen = 0.00417 × 24000 = 100 cm
3
(1)
vi the percentage yield =
94
____
100
× 100 = 94% (1)
c i hydrogen gas (1)
ii 4OH
−
→ O
2
+ 2H
2
O + 4e
−
OR 2H
2
O → O
2
+ 4H
+
+ 4e
−
for formulae for all species correct (1)
for correctly balanced (1)
11 ▶ a measuring cylinder/pipette/burette (1)
b volume is 33 cm
3
(1)
c
0
0
0.60.50.40.3
mass of limestone/g
volume of gas/cm
3
0.20.1
100
70
80
90
60
50
40
30
20
10
plotting points correctly (2)
line of best fit (1)
d i Student 3’s result (1)
The volume of gas recorded is too low and does
not lie on the line of best fit. (1)
ANSWERS 357
f Cl
2
(aq) + 2At
−
(aq) → At
2
(s) + 2Cl
−
(aq)
The chlorine is reduced in this reaction because it
gains electrons. The At
−
is oxidised in the reaction
because it loses electrons. Oxidation and reduction
both occur, therefore it is a redox reaction.
3
▶ a Cl
2
(g) + F
2
(g) → 2ClF(g)
b
F Cl
c F
2
< ClF < Cl
2
The boiling point increases as the relative molecular
mass increases and the strength of the intermolecular
forces increases.
d i ClF
3
ii ClF
3
(g) + 2H
2
O(l) → 3HF(aq) + HCl(aq) + O
2
(g)
CHAPTER 13
1 ▶ a 78.1% b 21.0 % c 0.04% d 0.9%
2
▶ a 95 − 80 = 15 cm
3
of oxygen
15
___
95
× 100 = 15.8%
b The answer is less than expected. The apparatus was
not left long enough; there was not enough time for all
the oxygen in the air to react. The experiment could be
improved by leaving the apparatus set up for longer.
3
▶ a The student should follow a procedure such as:
• Weigh a boiling tube.
• Pour 1 g of the metal carbonate into the boiling
tube and weigh the boiling tube again.
• Connect a delivery tube to the boiling tube.
Connect the other end of the delivery tube to a gas
syringe or put in to a measuring cylinder filled with
water.
• Heat the boiling tube.
• Allow the apparatus to cool.
• Record the volume of gas collected.
• Re-weigh the boiling tube and contents.
b Carbon dioxide.
c PbCO
3
(s) → PbO(s) + CO
2
(g)
d Thermal decomposition.
e Sodium carbonate is more thermally stable than
the other carbonates; it does not decompose when
heated.
f The M
r
of PbCO
3
is 267, whereas the M
r
of CuCO
3
is
123.5.
1 g of CuCO
3
is more moles than 1 g of PbCO
3
– more
than twice as many moles.
When more moles of solid are heated, more moles of
gas will be produced, so a greater volume of gas will
be produced.
g The mass goes down because CO
2
is given o. In the
first experiment the mass goes down by 0.15 g, which
must be the mass of 89 cm
3
of gas.
c Edexcelium hydroxide and hydrogen.
d More reactive than francium. Reactivity increases
down the group.
Reactivity increases as the size of the atom increases.
aAn edexcelium atom is larger than a francium atom.
The outer electron would be more easily lost from
edexcelium – it is less strongly attracted by the nucleus.
e 2Ed + 2H
2
O → 2EdOH + H
2
f Alkaline, because OH
−
ions are formed.
g Ed
2
O
CHAPTER 12
1 ▶ a
F
b
A fluorine atom has 7 electrons in its outer shell – the group
number indicates the number of outer shell electrons.
c
F
H
d There are weaker intermolecular forces of
attraction between fluorine molecules than between
chlorine molecules. Weaker forces require less energy
to break. The intermolecular forces are weaker
because fluorine has a lower relative molecular mass.
e No reaction because chlorine is less reactive than
fluorine and therefore cannot displace it.
2
▶ a
At
Astatine atom
At
–
Astatide ion
At At
Astatine molecule
b Astatine would be a solid – melting point increases
down the group and iodine is a solid.
c Reactivity decreases down the group so astatine
would be less reactive than iodine.
Astatine is a larger atom than iodine and so has a
lower attraction for electrons.
d pH 1−2
e Caesium astatide would be a colourless/white solid
because it is an ionic compound. It would probably be
soluble in water because many ionic compounds are
soluble in water and most of the alkali metal halides are
soluble in water (e.g. sodium chloride, potassium iodide
etc.).
358 ANSWERS
6 ▶ a X is between iron and hydrogen in the reactivity series.
It displaces hydrogen from dilute hydrochloric acid,
and copper from copper(II) sulfate, and so must be
above hydrogen and copper. It won’t displace iron
from iron(II) sulfate, and so must be below iron.
b i yes: X nitrate and silver
ii no reaction
iii no reaction (at least, not in the short term)
iv yes: X chloride and copper
v yes: X sulfate and hydrogen
7
▶ a hydrogen
b aluminium chloride
c 2Al(s) + 6HCl(aq) → 2AlCl
3
(aq) + 3H
2
(g)
d Aluminium is covered by a very thin, but very strong,
layer of aluminium oxide which prevents the acid
getting at the aluminium underneath. On heating,
the acid reacts with the oxide and removes it. The
aluminium then shows its true reactivity, and produces
a vigorous reaction.
8
▶ Drop a very small piece into cold water. If it reacts, judge
its reactivity relative to K, Na, Ca or Mg.
If it doesn’t react, add a small piece to dilute hydrochloric
acid and warm if necessary. Rapid reaction in the cold
would place it as ‘similar to magnesium’. A few bubbles
of hydrogen in the cold, but more on heating would place
it as ‘similar to iron or zinc’.
If there is no reaction, then it is ‘below hydrogen’.
9
▶ a The iron/steel must be exposed to oxygen (air) and water.
b Painting prevents the oxygen and water from coming
into contact with the iron/steel.
c It is iron/steel coated with zinc.
d It would take much longer before the car went rusty.
Zinc is more reactive than iron and so corrodes in
preference to the iron. The zinc prevents iron rusting
even when the coating is scratched. When paint is
scratched the steel underneath will rust – this will not
happen when the steel is galvanised, therefore the life
of the car is extended.
10
▶ a
Pearsonium
chloride
solution
Mollium
chloride
solution
Rosium
chloride
solution
Amelium
chloride
solution
pearsonium
7 7 7 7
mollium
3 7 3 3
rosium
3 7 7 7
amelium
3 7 3 7
b mollium > amelium > rosium > pearsonium
c mollium + pearsonium chloride → mollium chloride +
pearsonium
CHAPTER 15
1 ▶ Iron is below carbon in the reactivity series and so can be
extracted by heating with carbon.
From the first experiment:
1 cm
3
of gas has a mass of
0.16
_____
89
= 0.00180 g
100 cm
3
has a mass of 100 × 0.00180 = 0.180 g
h The student did not heat the carbonate for long
enough so not all the carbonate decomposes.
Some of the gas escaped/leaked from the apparatus.
4
▶ Carbon dioxide is one of the gases responsible for the
greenhouse eect. These gases absorb IR (infrared)
radiation that has been emitted from the Earth’s surface.
They then re-radiate it in all directions, warming the
atmosphere. Heating of the atmosphere could lead to
climate change.
CHAPTER 14
1 ▶ a sodium, aluminum, iron, copper
b i magnesium oxide, copper
ii Mg(s) + CuO(s) → MgO(s) + Cu(s) (Include state
symbols in all equations for preference.)
iii Copper(II) oxide (CuO) has been reduced to
copper (Cu) because it has lost oxygen - reduction
is the loss of oxygen.
iv Copper(II) oxide (CuO) is the oxidizing agent
because it oxidizes the magnesium (gives oxygen
to it) and is, in the process, reduced.
c i Zinc is higher in the reactivity series because it
takes the oxygen from the cobalt(II) oxide
ii A reducing agent is a substance which reduces
something else. Zinc removes oxygen from the
cobalt(II) oxide. Removal of oxygen is reduction.
iii Zinc because it gains oxygen - oxidation is gain of
oxygen.
d aluminium, manganese, chromium (Statement 1: Al is
above Cr. Statement 2: Mn is below Al. Statement 3:
Mn is above Cr. Putting this together gives the final
list.)
2
▶ a oxidised; gain of oxygen
b reduced; loss of oxygen
c oxidised; loss of electrons
d reduced; gain of electrons
3
▶ Magnesium is above lead because it removes the oxygen
from the lead(II) oxide.
4
▶ a Either: grey iron filings become coated with brown
solid. Or: solution fades from blue to colourless (very
pale green).
b iron (Fe) has been oxidised (to Fe
2
+) because it has
lost electrons - oxidation is loss of electrons.
c Fe(s) + CuSO
4
(aq) → FeSO
4
(aq) + Cu(s)
5
▶ a nickel, copper, silver
b i Either: colour of solution changes from blue to
green. Or: nickel becomes coated with brown
solid.
ii Ni(s) + CuSO
4
(aq) → NiSO
4
(aq) + Cu(s)
iii Ni(s) + Cu
2+
(aq) → Ni
2+
(aq) + Cu(s)
Nickel has been oxidised by loss of electrons.
ANSWERS 359
c High-carbon steel is brittle and not very malleable so
it would be dicult to make it into the correct shapes
for car bodies. It would also not bend/deform very
well during a crash – the fact that mild steel deforms
upon impact (because it is malleable) is important
for absorbing some of the force upon impact (from
a Physics point of view, the change in momentum
occurs over a longer period of time).
CHAPTER 16
1 ▶
methyl orange phenolphthalein litmus
a yellow pink blue
b red colourless red
2
▶
solution pH strongly
acidic
weakly
acidic
neutral weakly
alkaline
strongly
alkaline
potassium
iodide
7
3
propanoic
acid
4.2
3
sodium
carbonate
9.5
3
potassium
hydroxide
13
3
iron(III)
chloride
2.4
3
nitric acid
1.3
3
3
▶ a Na
2
O + 2HNO
3
→ 2NaNO
3
+ H
2
O
b 2KOH + H
2
SO
4
→ K
2
SO
4
+ 2H
2
O
4
▶ Neutralisation – reaction a) involves an acid reacting with
a base (sodium oxide) and reaction b) involves an acid
reacting with an alkali (KOH).
5
▶ Measure out 25.0 cm
3
of potassium hydroxide solution
using a pipette. Transfer the potassium hydroxide solution
to a conical flask. Add a few drops of an indicator. Put
the sulfuric acid into the burette. Add the acid to the alkali
until the indicator changes colour.
CHAPTER 17
1 ▶ a copper(II) oxide, copper(II) hydroxide, copper(II)
carbonate
b CuO(s) + H
2
SO
4
(aq) → CuSO
4
(aq) + H
2
O(l) Cu(OH)
2
(s)
+ H
2
SO
4
(aq) → CuSO
4
(aq) + 2H
2
O(l) CuCO
3
(s) +
H
2
SO
4
(aq) → CuSO
4
(aq) + CO
2
(g) + H
2
O(l)
2
▶ a A = copper; B = copper(II) oxide; C = copper(II) sulfate;
D = copper(II) carbonate; E = carbon dioxide;
F = copper(II) nitrate
b i CuO(s) + H
2
SO
4
(aq) → CuSO
4
(aq) + H
2
O(l)
ii CuCO
3
(s) + 2HNO
3
(aq) → Cu(NO
3
)
2
(aq) + CO
2
(g) +
H
2
O(l)
3
▶ a i Description could include: Silvery metal. Colourless
acid. Slow bubbles of gas on warming. Formation
of green solution. Possible disappearance of nickel
if very small quantities were used.
Fe
2
O
3
(s) + 3C(s) → 2Fe(l) + 3CO(g)
Aluminium is above carbon in the reactivity series and so
heating aluminium oxide with carbon will not produce a
reaction. Aluminium must be extracted by electrolysis.
Al
3+
+ 3e
−
→ Al
2
▶ a Sodium is high in the reactivity series, and so will need
to be produced by electrolysis. It can be manufactured
by electrolysing molten sodium chloride using suitable
electrodes (industrially, carbon anode, steel cathode),
keeping the sodium and chlorine apart to prevent them
from reacting back to give sodium chloride again.
Sodium would be released at the cathode:
Na
+
(l) + e
–
→ Na(l)
b It needed the discovery of electricity.
c Any other metals high in the reactivity series – e.g.
potassium, lithium, calcium, magnesium.
3
▶ Because lead is below iron in the reactivity series it is
also below carbon. Lead can be extracted from its ore by
heating with carbon.
4 ▶ a Chromium(III) oxide contains the Cr
3+
ion. The oxide
ion has the formula O
2−
, therefore the formula of
chromium(III) oxide is Cr
2
O
3
.
Cr
2
O
3
+ 2Al → 2Cr + Al
2
O
3
b Al is the reducing agent because it takes the O away
from the Cr
2
O
3
– it reduces it.
c Chromium is less reactive than aluminium because the
aluminium is able to take the oxygen away from the
chromium oxide.
5
▶ a 2FeTiO
3
+ 7Cl
2
+ 6C → 2TiCl
4
+ 2FeCl
3
+ 6CO
b TiCl
4
+ 2Mg → MgCl
2
+ Ti
c Magnesium is more reactive than titanium as it is
able to take the chlorine away from the TiCl
4
; the
magnesium is able to reduce the TiCl
4
.
d Magnesium is more reactive than carbon, so it could
be extracted from its ore by electrolysis or by heating
with a more reactive metal such as sodium.
e Titanium is more expensive than magnesium. Although
it is expensive to extract magnesium using electrolysis,
the magnesium is used in the extraction of titanium,
therefore titanium must be more expensive.
6
▶ a i It has a low density. (Note: saying that it has a low
density is usually better than just saying it is light)
ii Alloys are stronger than the pure metals. Alloys
contain some atoms of dierent sizes; this makes
it more dicult for the layers of positive ions to
slide over each other.
iii Advantages:
An aluminium body is lighter than a steel body and
so the car will use less fuel. An aluminium body
will not corrode.
Disadvantage:
Aluminium is more expensive than steel.
b i a good conductor of electricity and ductile (can be
drawn out into wires)
ii does not react with water and malleable (can be
hammered into shape)
360 ANSWERS
7 ▶ a A solution of any soluble silver salt (silver nitrate is
always used) plus a solution of any soluble chloride
including dilute hydrochloric acid
Ag
+
(aq) + Cl
–
(aq) → AgCl(s).
b A solution of any soluble calcium salt (calcium chloride
or nitrate) plus a solution of a soluble carbonate
(sodium, potassium or ammonium carbonate).
Ca
2+
(aq) + CO
3
2–
(aq) → CaCO
3
(s)
c A solution of a soluble lead(II) salt (most commonly,
lead(II) nitrate) plus a solution of any soluble sulfate
including dilute sulfuric acid
Pb
2+
(aq) + SO
4
2–
(aq) → PbSO
4
(s).
d A solution of a soluble lead(II) salt (most commonly,
lead(II) nitrate) plus a solution of any soluble chloride
including dilute hydrochloric acid.
Pb
2+
(aq) + 2Cl
–
(aq) → PbCl
2
(s)
8
▶ Mix solutions of barium chloride or barium nitrate and
sodium carbonate, potassium carbonate or ammonium
carbonate. Filter, wash and dry the precipitate.
Ba
2+
(aq) + CO
3
2–
(aq) → BaCO
3
(s)
9
▶ a A: dilute sulfuric acid + solid zinc (or zinc oxide,
hydroxide or carbonate)
H
2
SO
4
(aq) + Zn(s) → ZnSO
4
(aq) + H
2
(g)
or H
2
SO
4
(aq) + ZnO(s) → ZnSO
4
(aq) + H
2
O(l)
or H
2
SO
4
(aq) + Zn(OH)
2
(s) → ZnSO
4
(aq) + 2H
2
O(l)
or H
2
SO
4
(aq) + ZnCO
3
(s) → ZnSO
4
(aq) + H
2
O(l) + CO
2
(g)
b C: solutions of a soluble barium salt + soluble sulfate
(including H
2
SO
4
)
Ba
2+
(aq) + SO
4
2–
(aq) → BaSO
4
(s)
There is no point in writing full equations for precipitation
reactions like this. The ionic equation is always easier.
c B: dilute nitric acid + potassium hydroxide or
carbonate solution
HNO
3
(aq) + KOH(aq) → KNO
3
(aq) + H
2
O(l)
or 2HNO
3
(aq) + K
2
CO
3
(aq) → 2KNO
3
(aq) + H
2
O(l) +
CO
2
(g)
d A: dilute nitric acid + solid copper(II) oxide or
hydroxide or carbonate.
2HNO
3
(aq) + CuO(s) → Cu(NO3)2(aq) + H2O(l)
or 2HNO
3
(aq) + Cu(OH)
2
(s) → Cu(NO
3
)
2
(aq) + 2H
2
O(l)
or 2HNO
3
(aq) + CuCO
3
(s) → Cu(NO
3
)
2
(aq) + H
2
O(l) +
CO
2
(g)
(Unlike the other simple acids, nitric acid also reacts
with copper metal, but it doesn’t produce hydrogen,
and is not on the Edexcel International GCSE syllabus.
Any equation using copper to produce hydrogen
should be disallowed.)
e C: solutions of a soluble lead(II) salt (normally the
nitrate) + a soluble chromate(VI). (Since you don’t
know anything specifically about chromates, choose
one of sodium, potassium or ammonium chromate (VI)
– these are bound to be soluble because all sodium,
potassium and ammonium salts are soluble.)
Pb
2+
(aq) + CrO
4
2–
(aq) → PbCrO
4
(s)
10
▶ a acid: H
3
O
+
base: CO
3
2−
b acid: H
2
SO
4
base: MgO
c acid: HNO
3
base: NH
3
Pops with lighted splint held to mouth of tube.
ii hydrogen
iii Ni(s) + H
2
SO
4
(aq) → NiSO
4
(aq) + H
2
(g)
b i Description could include: Green solid. Colourless
acid. Bubbles of gas produced in the cold.
Formation of green solution. Green powder
disappears if excess acid is used.
Testing for gas: Bubble through lime water to give
a white precipitate (milky, cloudy).
ii NiCO
3
(s) + 2HCl(aq) → NiCl
2
(aq) + CO
2
(g) + H
2
O(l)
iii CO
3
2–
(s) + 2H
+
(aq) → CO
2
(g) + H
2
O(l)
Some teachers may prefer to write this as:
NiCO
3
(s) + 2H
+
(aq) → Ni
2+
(aq) + CO
2
(g) + H
2
O(l)
4
▶ soluble insoluble
sodium chloride lead(II) sulfate
zinc nitrate calcium carbonate
iron(III) sulfate lead(II) chloride
potassium sulfate copper(II) carbonate
aluminium nitrate silver chloride
ammonium chloride barium sulfate
magnesium nitrate calcium sulfate (almost
insoluble)
sodium phosphate nickel(II) carbonate
potassium dichromate(VI) chromium(III) hydroxide
5
▶ a Dilute sulfuric acid in a beaker/flask. Heat gently. Add
copper(II) oxide a little at a time until no more reacts.
Filter into an evaporating basin. Evaporate gently
until a sample will crystallise on cooling. Leave to
crystallise. Separate and dry crystals.
b i CuO(s) + H
2
SO
4
(aq) → CuSO
4
(aq) + H
2
O(l)
ii CuSO
4
(aq) + 5H
2
O(l) → CuSO
4
.5H
2
O(s)
6
▶ a using a pipette: Need to be able to measure the
volume of sodium carbonate solution accurately
so that exactly the same volume can be used later
without the indicator.
few drops of methyl orange were added: An indicator
to show when the solution becomes ‘neutral’. (In fact
the colour change happens around pH 4. The pH
changes very quickly around the end point for the
indicator, and the dierence in volume of acid added
to take the pH from the desired pH 7 to the actual pH
4 for the indicator will be a fraction of a drop.)
until the solution became orange: Exactly the right
volume of acid has been added (the ‘neutral’ colour for
methyl orange).
without the methyl orange: Otherwise the crystals
would be contaminated by methyl orange.
evaporated until… Shows when the solution is
suciently concentrated to crystallise on cooling. If a
sample will crystallise, so will the bulk of the solution.
left to cool… Crystals form on cooling because the
solubility of the sodium sulfate is lower in the cold.
b i Na
2
CO
3
(aq) + H
2
SO
4
(aq) → Na
2
SO
4
(aq) + CO
2
(g) +
H
2
O(l)
ii Na
2
SO
4
(aq) + 10H
2
O(l) → Na
2
SO
4
.10H
2
O(s)
ANSWERS 361
b Take a sample and add any named dilute acid. If the
crystals are free of potassium carbonate, there won’t
be any fizzing.
8
▶ a Add a few drops of the liquid to some anhydrous
copper(II) sulfate. If the colour changes from white to
blue then water is present.
b The boiling point of the liquid must be measured. If
the liquid boils at 100 °C it is pure water. The freezing/
melting point can also be measured – pure water
freezes/melts at 0 °C.
c The test-tube becoming warm indicates that an
exothermic reaction has occurred. An exothermic
reaction with sodium hydroxide solution could mean
that the colourless liquid is an acid – neutralisation
reactions are exothermic. The fact that there is no
other visual reaction indicates that there is no metal
present that has an insoluble hydroxide.
The second test indicates that the solution does
not contain carbonate ions – carbonate ions would
produce fizzing with dilute hydrochloric acid.
The third test indicates that no sulfate ions are present
– the solution cannot be sulfuric acid.
The last test indicates the presence of chloride ions.
With the results of the other tests, this suggests that
the solution is dilute hydrochloric acid.
The student could confirm this by adding an indicator,
to see whether the liquid is acidic.
END OF UNIT 2 QUESTIONS
1 ▶ a They all have 1 electron in the outer shell. (1)
b Potassium oxide. (1)
c The piece of lithium floats; hydrogen gas is formed;
the final solution is alkaline.
d i it forms a 1+ ion in compounds; it reacts with
water and air
ii The density increases from lithium to sodium but
decreases from sodium to potassium (1)
The trend is not clear for the whole group (1)
2
▶ a Because there will be no reaction (1)
between a halogen and its halide ion / chlorine cannot
reaction with chloride ions / bromine cannot reaction with
bromide ions / iodine cannot reaction with iodide ions (1)
b
potassium
chloride
solution
potassium
bromide
solution
potassium
iodide
solution
chlorine
solution
orange
solution
formed
brown
solution
formed
bromine
solution
no reaction brown
solution
formed
iodine
solution
no reaction no reaction
c chlorine + potassium bromide → potassium chloride +
bromine (1)
d acid: H
2
SO
4
base: H
2
O
e acid: HCl base: NH
3
f acid: CH
3
COOH base: NH
3
CHAPTER 18
1 ▶ a chlorine b ammonia c carbon dioxide
d hydrogen e oxygen
2 ▶ a
Clean a nichrome or platinum wire by dipping it into
concentrated hydrochloric acid and then into a flame until
no colour shows. Moisten the wire with concentrated
hydrochloric acid, dip it into the solid, and then back into
flame. Lithium ions give a red flame colour.
b Warm the solid very gently with sodium hydroxide
solution. Test any gases given o with a piece of damp
red litmus paper. If it turns blue, ammonia is being
given o from an ammonium compound.
c Make a solution in pure water. Add dilute hydrochloric
acid + barium chloride solution. A white precipitate
shows the sulfate ions.
d Add dilute hydrochloric acid or dilute nitric acid. (Not
sulfuric acid which forms an insoluble layer of calcium
sulfate around the calcium carbonate, which stops the
reaction.) Look for a colourless odourless gas turning
limewater milky.
e Make a solution in pure water. Add dilute nitric acid +
silver nitrate solution. A yellow precipitate shows the
iodide ions.
3
▶ a A = iron(III) chloride; B = iron(III) hydroxide;
C = silver chloride
b B: Fe
3+
(aq) + 3OH
–
(aq) → Fe(OH)
3
(s) or: FeCl
3
(aq) +
3NaOH(aq) → Fe(OH)
3
(s) + 3NaCl(aq)
C: Ag
+
(aq) + Cl
–
(aq) → AgCl(s) or 3AgNO
3
(aq) +
FeCl
3
(aq) → 3AgCl(s) + Fe(NO
3
)
3
(aq)
4
▶ a D = iron(II) sulfate; E = iron(II) hydroxide;
F = barium sulfate
b E: Fe
2+
(aq) + 2OH
–
(aq) → Fe(OH)
2
(s)
or: FeSO
4
(aq) + 2NaOH(aq) → Fe(OH)
2
(s) + Na
2
SO
4
(aq)
F: Ba
2+
(aq) + SO
4
2–
(aq) → BaSO
4
(s)
or BaCl
2
(aq) + MgSO
4
(aq) → BaSO
4
(s) + MgCl
2
(aq)
5
▶ a G = potassium carbonate; H = potassium nitrate;
I= carbon dioxide (Note: g could also be potassium
hydrogen carbonate, but, because hydrogen
carbonates haven’t been covered in the course, a
student is unlikely to come up with it.)
b CO
3
2–
(s) + 2H
+
(aq) → CO
2
(g) + H
2
O(l) or K
2
CO
3
(s) +
2HNO
3
(aq) → 2KNO
3
(aq) + CO
2
(g) + H
2
O(l)
6
▶ a
J = ammonium bromide; K = ammonia; L = silver bromide
b Ag
+
(aq) + Br
−
(aq) → AgBr(s)
7
▶ a Dissolve the mixture in the minimum possible amount
of hot water, and then allow it to cool again. The small
amount of the more soluble potassium carbonate will
stay in solution, but crystals of potassium nitrate will
be formed on cooling. Filter these o, and wash them
on the filter paper with a small amount of very cold
water. Allow them to dry.
362 ANSWERS
4 ▶ a Put dilute sulfuric acid into a beaker and heat it on a
tripod and gauze using a Bunsen burner.(1)
Add excess copper(II) oxide (1)
Filter o the excess copper(II) oxide (1)
b Test: add hydrochloric acid followed by barium
chloride solution (1)
Positive result: white precipitate (1)
c copper(II) hydroxide (1)
d i In a new line: Any 2: Concentration of copper(II)
sulfate (1)
Volume of copper(II) sulfate solution (1)
How finely divided the metal is (1) (if the metal is
very finely divided it will react more quickly and the
heat will be given out more quickly, so there is less
chance for heat to be lost to the surroundings. This
will give a more accurate value for the temperature
change)
ii Zinc > nickel > silver (1)
iii The temperature rise would be zero (1)
Copper will not react with copper(II) sulfate /
copper ions (1)
iv The mass of 1 mole of zinc (65 g) is very similar to
the mass of 1 mole of nickel (59 g) (1)
Because the student used the same mass of each
metal, the number of moles of nickel and zinc is
very similar. (1)
Because silver does not react it does not matter
how much the student uses (1)
v Nickel gets oxidized. (1)
Ni loses electrons to form Ni
2+
and oxidation is
loss of electrons. (1)
e Heat the solution to drive o the water and form
(small) crystals of hydrated copper(II) sulfate. (1)
Keep heating the solid. (1)
f i Dip a piece of (nichrome) wire into concentrated
hydrochloric acid and then into the solid. (1)
Put the solid into the blue/roaring/non-luminous
flame of a Bunsen burner. (1)
ii blue-green (1)
5
▶ a An ore is a sample of rock that contains enough of a
mineral for it to be worthwhile to extract the metal. (1)
b
thermal decomposition neutralisation redox
reaction 1
3
reaction 3
3
c MoO
3
+ 3C → Mo + 3CO
products (1)
balancing (1)
d carbon is the reducing agent (1)
it reduces the MoO
3
by removing the oxygen (1)
e Molybdenum is below carbon in the reactivity series (1)
Carbon must be more reactive than molybdenum to
be able to take the oxygen away from molybdenum
oxide.(1)
d Cl
2
(aq) + 2Br
−
(aq) → 2Cl
−
(aq) + Br
2
(aq)
Cl
−
(aq) (1)
Br
2
(aq) (1)
balancing (1)
e chlorine gains electrons to form chloride ions (1)
bromide ions lose electrons to form bromine (1)
gain of electrons is reduction and loss of electrons is
oxidation (1)
f i 5Cl
2
(1)
ii test: damp litmus paper/universal indicator paper (1)
positive result: the paper is bleached (goes white) (1)
iii test: add dilute nitric acid (1) followed by silver
nitrate solution (1)
positive result: white precipitate (1)
3
▶ a nitrogen (1)
b i The oxygen in the air is used up as it reacts with
the iron. (1)
Water is pushed in by the atmosphere to take its
place/the pressure in the measuring cylinder is
reduced. (1)
ii All the oxygen has reacted and so there is nothing
to react with the iron.
iii Hydrated iron(III) oxide. (1)
iv There is no oxygen present (1); Oxygen is required
for the splint to burn. (1)
v The total amount of oxygen present in the original
sample of air is 94 − 75 = 19 cm
3
of oxygen. (1)
9 cm
3
of oxygen is used up after one day, therefore
there is 19 − 9 = 10 cm
3
of oxygen still present
after one day. (1)
This is in a total volume of 85 cm
3
(1) (reading on
the measuring cylinder).
Percentage oxygen =
10
___
85
× 100 = 11.8 %. (1)
vi These will produce hydrogen when they react with
the water present (1)
Hydrogen gas will take up space in the measuring
cylinder, therefore the volume change will not
show the volume of oxygen used up. (1)
vii Suggest one change that the student could make
to the apparatus so he does not have to wait so
long for the results. (1)
Use more iron filings/more finely-divided (higher
surface area) iron filings/warm the apparatus. (1)
c Sulfur reacts with oxygen. A teacher burns a piece of
sulfur in a gas jar of oxygen.
i blue
ii S + O
2
→ SO
2
(1)
iii the litmus solution will be red (1)
No-metal oxides are acidic and dissolve in water (if
soluble, like SO
2
) to form acidic solutions. (1)
d i 4Na + O
2
→ 2Na
2
O ii hydroxide ion (1)
all formulae (1)
balancing (1)
ANSWERS 363
Named indicator added e.g. methyl orange/
phenolphthalein but not universal indicator. (1)
Acid/alkali added to alkali /acid acid until indicator
changes colour (1)
Procedure repeated without indicator using same
volumes. (1)
Sodium carbonate/sodium hydrogencarbonate could
also be used instead of sodium hydroxide.
c i
0
0
121086
time/minutes
volume of gas/cm
3
42
20
14
16
18
12
10
8
6
4
2
all point plotted correctly (2) −1 for each mistake
line of best fit (1)
ii the point at 6 minutes (1); 10.8 ± 0.2 cm
3
(1)
iii as the time increases the volume of gas increases (1)
directly proportional relationship (1)
just stating that the volume is directly proportional
to the time scores (2)
iv test: burning splint (1)
positive result: squeaky pop (1)
UNIT 3 ANSWERS
CHAPTER 19
1 ▶ a A reaction in which heat energy is given out to the
surroundings.
Correctly balanced equations for any two
exothermic reactions e.g. any combustion reactions
(metals, hydrogen, hydrocarbons, etc, in oxygen),
neutralisation reactions involving oxides or hydroxides
and acids, magnesium and acids. For example, 2H2(g)
+ O2(g) → 2H2O(l) or NaOH(aq) + HCl(aq) → NaCl(aq)
+ H2O(l)
b
energy
progress of the reaction
C
7
H
16
+ 11O
2
7CO
2
+ 8H
2
O
ΔH = –4817
kJ/mol
f Because aluminium has to be extracted from its ore
using electrolysis. (1)
Electrolysis is very expensive because it uses a large
amount of electricity, therefore aluminium is more
expensive than carbon. (1)
g Add sodium hydroxide solution and warm. (1)
If ammonium ions are present a colourless gas will be
given o that turns moist red litmus paper blue. (1)
6
▶ a Mix together solutions (1) of lead(II) nitrate and sodium
sulfate (1). Filter the mixture (1) Wash the residue with
distilled/pure water (1); Leave the solid in a warm oven
to dry. (1)
b Because lead(II) iodide is yellow and insoluble in
water.(1)
The precipitate could just be lead(II) iodide. (1)
7
▶ a
Cl
H
Dot and cross in the covalent bond. (1)
All other electrons. (1)
b A proton/hydrogen ion/H
+
is transferred from the HCl
to the water. (1)
HCl is an acid because it donates a proton/hydrogen
ion/H
+
(1)
H
2
O is a base because it accepts a proton/hydrogen
ion/H
+
(1)
c
Reagent Solid or
solution?
Salt Other
product
magnesium solid hydrochloric
acid
magnesium
chloride
hydrogen
copper(II)
oxide
solid hydrochloric
acid
copper(II)
chloride
water
sodium
hydroxide
solution hydrochloric
acid
sodium
chloride
water
silver
nitrate
solution hydrochloric
acid
silver
chloride
nitric acid
d i a white precipitate is formed (1)
ii hydrochloric acid contains chloride ions (1)
Will always give a positive test for chloride ions. (1)
e CuCO
3
(s) + 2HCl(aq) → CuCl
2
(aq) + H
2
O(l) + CO
2
(g)
reactants (1)
products (1)
balance (1)
8
▶ a iron(II) (1) chloride (1)
b B = iron(II) hydroxide (1) Fe(OH)
2
(1)
c D = iron(III) hydroxide (1) Fe(OH)
3
(1)
d redox (1)
The iron(II) is oxidised to iron(III) (1)
9
▶ a Na
2
SO
4
(1)
b Sodium hydroxide solution/sulfuric acid is measured
out using a pipette and put into conical flask/beaker. (1)
Sulfuric acid/sodium hydroxide placed in burette. (1)
364 ANSWERS
c is the specific heat capacity of the water (it is the
water that is being heated)
c = 4.18 J/g/
o
C
Temperature change of water = ΔT = 55.0 − 19.0 =
36.0 °C
Heat evolved = Q = mcΔT = 100 × 4.18 × 36.0 J =
15 048 J = 15.0 kJ to 3 significant figures
d Mass of hexane burnt = 35.62 − 35.23 g = 0.39 g
Heat evolved per gram =
15.048
_______
0.39
= 38.6 kJ/g to 3
significant figures
The combustion reaction is exothermic, therefore heat
energy released per gram = −38.6 kJ/g
e Number of moles of hexane, C
6
H
14
burnt =
n =
mass (m)
__________________________
relative molecular mass (Mr)
=
0.39
_____
86
= 0.00453 mol
The molar enthalpy change of combustion of hexane (DH)
=
heat energy change (Q)
___________________________________
number of moles of ethanol burned (n)
=
15.048
________
0.00453
= 3320 kJ/mol to
3 significant figures
The combustion reaction is exothermic, therefore
ΔH = −3320 kJ/mol
f Any two from: Misreading one of the weighings of
the spirit burner so that it looked as if less hexane
had been burnt than was really the case; misreading
the thermometer to give a final temperature higher
than it should have been; adding less than 100 cm
3
of water to the flask, so that the temperature went up
more than it should because the heat was going into a
smaller volume of water.
g Any two from: Heat loss to the surroundings; heat
is lost to warm up the copper calorimeter or the
thermometer; incomplete combustion of the fuel.
7
▶ a Heat energy change = Q = mcΔT
Mass of solution being heated = m = 50 g, the mass of
the lithium chloride is relatively small and it is ignored
in the calculation.
c is the specific heat capacity of the diluted solution of
lithium chloride, which we assume to be the same as
the heat capacity of water c = 4.18 J / g /
o
C
Temperature change of water = ΔT = 33.5 − 17.0 =
16.5 °C
Heat evolved = Q = mcΔT = 50 × 4.18 × 16.5 J =
3448.5 J = 3.45 kJ to 3 significant figures
b Number of moles of lithium chloride dissolved =
n =
mass (m)
________________________
relative formula mass (Mr)
=
5.15
_____
42.5
= 0.121 mol
c The enthalpy change of solution
ΔH =
heat energy change (Q)
_________________________________________
number of moles of lithium chloride dissolved (n)
=
3.45
______
0.121
= 28.5 kJ/mol to 3 significant figures
The dissolving of lithium chloride is exothermic,
therefore ΔH = -28.5kJ/mol
c Energy is needed to break the bonds in heptane and in
oxygen. Energy is released when new bonds are made
to produce the carbon dioxide and water. More energy
is released when the new bonds are made than was
used to break the old ones.
2
▶ a A reaction in which heat energy is absorbed from the
surroundings.
b
energy
progress of the reaction
2NO
N
2
+ O
2
ΔH = +180
kJ/mol
3 ▶ a exothermic b exothermic c endothermic
d exothermic e endothermic f exothermic
4 ▶ The cans have two chambers. The outer one contains
the beverages or food to be heated. The inner chamber
contains calcium oxide and water. The calcium oxide
and water are kept separate by a seal. Pushing a button
on the bottom of the can breaks the seal and allows the
calcium oxide and water to come into contact. You get
the reaction below which is exothermic.
CaO(s) + H
2
O(l) → Ca(OH)
2
(s)
5
▶ a Bonds broken: 4 × C−H = 4 × (+413) = +1652 kJ
1 × Br−Br = + 193 kJ
total = +1845 kJ
Bonds made: 3 × C−H = 3 × (−413) = −1239 kJ
1 × C−Br = − 290 kJ
1 × H−Br = − 366 kJ
total = −1895 kJ
Overall change = +1845 − 1895 = −50 kJ (exothermic)
b Bonds broken: 1 × H−H = +436 kJ
1 × Cl−Cl = +243 kJ
total = +679 kJ
Bonds made: 2 × H−Cl = 2 × (−432) = −864 kJ
Overall change = +679 − 864 = −185 kJ (exothermic)
c Bonds broken: 2 × H−H = 2 × (+436) = +872 kJ
1 × O=O = +498 kJ
total = +1370 kJ
Bonds made: 4 × O−H = 4 × (−464) = −1856 kJ
Overall change = +1370 − 1856 = −486 kJ (exothermic)
d Bonds broken: 1 × N
≡
N = +944 kJ
3 × H−H = 3 × (+436) = +1308 kJ
total = +2252 kJ
Bonds made: 6 × N−H = 6 × (−388) = −2328 kJ
Overall change = +2252 − 2328 = −76 kJ (exothermic)
6
▶ a Her first two results weren’t reliable. There was too
much dierence between them.
b Any two from: Wear a lab coat; avoid touching the hot
copper can; tie long hair back.
c Heat energy change = Q = mcΔT
Mass of water being heated = m = 100 g
ANSWERS 365
c At the very beginning of the reaction. The reaction can
only happen when acid particles collide with the solid
dolomite. Numbers of acid particles per unit volume are
greatest at the beginning of the reaction before any get
used up. Therefore the greatest number of collisions per
second and the fastest reaction is at the beginning.
d
70 seconds (read this o the graph and allow some
tolerance depending on the size of graph paper available.)
e Volume produced within the first 80 seconds = 55 cm
(The average rate =
55
___
80
= 0.688 cm
3
/s to 3 significant
figures)
f i There would be a lower initial rate; same volume of
gas.
ii There would be a lower initial rate; half the volume
of gas (50 cm
3
).
iii The initial rate would be the same; half the volume of
gas (50 cm
3
). (The initial rate depends on the original
concentration of the acid that is still the same.)
iv The initial rate would be faster; same volume of gas.
2
▶ a Time taken for the reaction would increase. A reaction
happens when acid particles collide with the magnesium.
The concentration of acid is less, so there is less number
of acid particles per unit volume. There will be fewer
collisions per second, and therefore a slower reaction.
b Time taken for the reaction would decrease. The acid
particles are moving faster and so collide with the
magnesium more often. Reaction only happens if the
energy of the collision equals or exceeds activation
energy. At higher temperatures more acid particles have
energy greater than or equal to the activation energy, so
a greater proportion of the collisions are successful.
c Answers could include: Acid will be used up quickly
immediately around the magnesium – stirring brings
fresh acid into contact with it; bubbles of hydrogen form
around the magnesium, preventing acid from reaching
it – stirring helps to dislodge the bubbles; bubbles of
hydrogen lift the magnesium to the surface (sometimes
above the surface) of the acid, lowering contact between
acid and magnesium – stirring helps to prevent this.
d
energy
progress of the reaction
Mg and H
2
SO
4
MgSO
4
and H
2
Δ
H
(enthalpy change)
activation
energy
3 ▶ a Reactions only happen if collisions have energies
equalling or exceeding activation energy. Catalysts
provide an alternative route for the reaction with a lower
activation energy. More particles now have energy
greater than or equal to the activation energy, so there
will be more successful collisions per unit time.
d Any two from: Heat loss to the surroundings; heat
is lost to warm up the solution container or the
thermometer; incomplete transfer of the salt from the
weighing boat into the water; some salt crystal does
not dissolve completely in water.
8
▶ a The number of moles of NaOH(n) =
concentration(C) × volume(V) = 0.50 ×
200
_____
1000
= 0.10 mol
b Heat given out by the reaction = Q = mcΔT = 300 ×
4.18 × 4.5 = 5643 J = 5.64 kJ to 3 significant figures
Here we assume the density of the reaction mixture is
the same as water and the specific heat capacity of
the mixture is the same as heat capacity of water.
c The enthalpy change of neutralisation
ΔH =
heat energy change (Q)
________________________________
number of moles of NaOH reacted (n)
=
5.65
_____
0.10
= 56.4 kJ/mol to 3 significant figures
The neutralisation reaction is exothermic, therefore ΔH
= −56.4 kJ/mol.
d
energy
progress of the reaction
2NaOH + H
2
SO
4
Na
2
SO
4
+ 2H
2
O
ΔH
e As double the amount of reactants react, the amount
of heat energy released from the reaction doubles.
The same amount of solution gets heated up so the
temperature rise should double.
CHAPTER 20
1 ▶ a
cotton
gas syringe
weighing bottle
containing dolomite
side-arm flask
50
cm
3
of dilute
hydr
ochloric acid
Collection of gas over water into an inverted measuring
cylinder is an acceptable alternative. Pieces of dolomite
are put in a weighing bottle into the conical flask before
the reaction starts. This is to make sure that the reaction
can be started without losing any carbon dioxide.
b Graph should be completely smooth with the axes
properly labelled.
0
0
400250 300 350200150
time/seconds
Volume of CO
2
produced over time
volume of gas/cm
3
10050
120
100
80
60
40
20
366 ANSWERS
c Using a catalyst increases the rate of the reaction,
as it provides an alternative pathway for the reaction
with lower activation energy. More particles will have
energy greater than or equal to the activation energy so
there will be more successful collisions per unit time.
More products will be made quickly and relatively low
temperature and pressure can be used in the presence
of a catalyst. This saves energy and money. Adding a
catalyst has no eect on the position of equilibrium,
as the rate of the forward reaction and the rate of the
reverse reaction are increased by an equal amount.
5
▶ a A high pressure favours the reaction producing
fewer moles of gas, shifting the position of equilibrium
to the right hand side.
b Very high pressures are expensive to produce for
two reasons: all the reaction vessels and pipework
have to be built much more strongly, and it takes a
lot more energy to drive the compressors producing
the very high pressures. The extra ammonia produced
isn’t worth the extra cost, so a compromise of 200
atmospheres pressure is used.
c At a low temperature. Lower temperature favours the
forward exothermic reaction, shifting the position of
equilibrium to the right hand side to produce more
ammonia.
d At low temperatures the reaction is extremely slow
even in the presence of a catalyst. 450 °C is chosen
because it gives a compromise between the rate and
the yield of the reaction.
END OF UNIT 3 QUESTIONS
1 ▶ a
Br
H
correct number of outer shell electrons for both H and
Br (1)
sharing of 1 pair of electrons between the two atoms (1)
b
bond bond energy / kJ/mol
H−H 436
Br−Br 196
H−Br 368
Bonds broken: 1 × H−H = +436 kJ
1 × Br−Br = + 196 kJ
total = +632 kJ
Bonds made: 2 × H−Br = − 736 kJ
Overall change = +632 − 736 = −104 kJ (exothermic)
c i and ii
Δ
H
progress of the reaction
H
2
+ Br
2
activation
energy
energy
2HBr
a line labelled
with product
name or formula
below the line of
reactants (1)
b To find out whether it speeds the reaction up: You
could do this most simply by having two test-tubes
with equal volumes of the same hydrogen peroxide
solution side-by-side. Add some copper(II) oxide to
one and look for the faster production of bubbles.
To show that it is unchanged: Use a known mass
of copper(II) oxide. When the reaction stops, filter
through previously weighed filter paper, allow to dry,
and re-weigh. Show that the mass of copper(II) oxide
is unchanged. (If it had changed, and you hadn’t
lost any during the separation process, it must have
reacted in some way.)
c
Δ
H
(enthalpy change)
energy
progress of the reaction
reactants
catalysed route
products
activation
energy
with a
catalyst
activation energy
without catalyst
original
route
CHAPTER 21
1 ▶ a The reversible symbol ‘⇌’ shows that the reaction can
go both ways. The reactants can form products and
the products can react to form the reactants.
b White solid decomposes to form colourless gases.
c Ammonium chloride, ammonia and hydrogen chloride
2
▶ a Right
b Left
c Left
d No change
e No change
3
▶ a ‘Dynamic’ means that the reactions are still happening
and the rate of the forward reaction is equal to the
rate of the reverse reaction. ‘Equilibrium’ means that
the concentrations of the reactants and the products
remain constant.
b The proportion of sulfur trioxide will increase. An
increase in pressure shifts the position of equilibrium
to the right because this side has fewer moles of
moles of gas molecules.
c The position of equilibrium shifts to the right.
A decrease in temperature favours the forward
exothermic reaction.
4
▶ a Less carbon monoxide and hydrogen would be
produced. (A high pressure favours the reverse
reaction, as the left hand side of the reaction has
fewer number of moles of gas molecules.)
b A high temperature favours the endothermic forward
reaction and shifts the position of equilibrium to the
right hand side of the reaction.
ANSWERS 367
Re-weigh the solid and the mass should be the
same as before if it acts as a catalyst (1).
g Shallower curve than the original (1). but the end
volume remains the same (1).
h Shallower curve than the original (1) and only 30 cm
3
(half the volume) of gas is produced (1).
4
▶ a the mass (1). and the surface area / the size (1).
b To let the gas escape but keep the liquid inside the
conical flask. (1)
c i B
ii
0
0
100 1208060
concentration of acid/%
time/seconds
4020
600
500
400
300
200
100
correct labelling of axes with units (1)
correct points plotted (2)
a smooth curve of best fit, going through all but
one point (1)
iii 150 seconds
iv C
d i The mass of CO
2
given o is directly (1)
proportional (1) to the concentration of the acid.
ii Increasing the concentration of the acid increases
the rate of reaction. (1) This is because there are
more acid particles within a fixed volume (1) so the
frequency of successful collision between the acid
and the marble chip increases (1).
5
▶ a i The gas particles have more kinetic energy (1)
so more particles have energy greater than or
equal to the activation energy (1). There are more
successful collisions per unit time (1).
ii The rate increases (1) as gas particles are closer
together and there are more frequent collisions (or
more successful collisions per unit time) (1).
iii Reactions happen on the surface of the catalyst (1)
and gauzes have greater surface area (1).
b
The use of a catalyst increases the rate of the reaction
without itself being used up (1). It saves money which
would be spent on increasing temperature or pressure (1).
6 ▶ a reversible reaction (1), enthalpy change (1)
b The forward reaction is endothermic. (1)
c
Δ
H
progress of the reaction
2NO + O
2
activation
energy
energy
2NO
2
use of single-headed arrows to represent activation
energy (1) and enthalpy change (1), as shown
2
▶ a i 19.3 (1), 16.6 (1), 2.7 (1)
ii A
b i Q = mcΔT = 100.0 × 4.2 × (23.2 – 15.9) = 3.066 kJ
calculation of temperature change (1)
using the correct mass (100 g, award mark if 105 g
is used) (1)
correct answer for Q (1)
ii n = mass of calcium chloride/M
r
=
5
_____________
(40 + 35.5 *2)
=
5
____
111
= 0.0450 mol to 3 significant figures.
calculation of M
r
(1)
correct answer to 2–4 significant figures (1)
iii ΔH =
3.066
_______
0.0450
= 68.1 kJ/mol to 3 significant figures.
The molar enthalpy change is −68.1 kJ/mol as the
dissolving is exothermic.
dividing Q by n (1)
correct answer (must have a negative sign) (1)
c heat loss to the surrounding air through beaker (1)
some magnesium chloride is left on the weighing boat/
did not dissolve in water completely (1)
3
▶ a 2H
2
O
2
(aq) → 2H
2
O(l) + O
2
(g)
correct formulae of reactants and products (1)
correct balancing (1)
b To prevent the loss of oxygen at the beginning of the
reaction. (1)
c
0
0
350250 300200150
time/seconds
volume of o
xygen/cm
3
10050
70
60
50
40
30
20
10
correct labelling of axes with units (1)
correct points plotted (2)
a smooth curve of best fit, going through all of the points (1)
d i 125 seconds
ii 43 cm
3
iii
53
____
150
= 0.353 cm
3
/sec
correct numerical answer (1)
correct unit (1)
e Reaction has stopped (1) because all the hydrogen
peroxide is used up (1).
f i B (1)
ii Weigh a sample of manganese(IV) oxide and add
to hydrogen peroxide (1). Oxygen is produced at a
faster rate with manganese(IV) oxide than without
(1). Filter the reaction mixture and dry the solid (1).
368 ANSWERS
iv
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
v
H
H
C
H
O
H
vi
H
H
C
H
H
C
H
C
H
H
HC
H
H
vii
H
H
CC
C
H
C
H
H
H
H
H
viii
H
H
CC
H
H
C
H
H
C
H
H
C
H
H
2 ▶ a The existence of molecules with the same molecular
formula but dierent structural formulae.
b
CH
3
CH
2
CH
2
CH
3
butane
CH
3
CH
3
CH
CH
3
2-methylpropane
(In these and subsequent formulae, if you aren’t asked
specifically for displayed formulae, these quicker
forms are acceptable.)
c
CH
3
CH
2
CH
2
CH
2
CH
2
CH
3
hexane 2-methylpentane
CH
3
CHCH
2
CH
2
CH
3
CH
3
2,2-dimethylbutane
CH
3
CH
2
CHCH
2
CH
3
CH
3
CH
3
CHCHCH
3
CH
3
CH
3
CH
3
CCH
2
CH
3
CH
3
2,3-dimethylbutane3-methylpentane
CH
3
d
CH
2
CH
3
CH
2
CH CHCH
3
CH
3
CH CH
2
CH
3
C
(2-methylpropene)but-2-enebut-1-ene
CH
3
e
CH
2
CH
2
CH
2
CH
2
CH
3
CH
CH
2
CH
2
d i Increasing the temperature favours the forward
endothermic reaction. (1)
The position of equilibrium shifts to the right. (1)
The reaction mixture becomes more colourless. (1)
ii
Increasing the pressure favours the left hand side of the
reaction as it has fewer moles of moles of gases. (1
)
The position of equilibrium shifts to the left. (1)
The reaction mixtures becomes more brown. (1)
e No change in the position of equilibrium (1) The use of
a catalyst increases the rate of both the forward and
reverse reaction equally (1).
7
▶ a A and D
b i Increasing the pressure favours the right hand side
of the reaction which has fewer moles of moles of
gas molecules. (1)
The position of equilibrium shifts to the right. (1)
The yield of NH
3
increases. (1)
ii As temperature increases, the percentage of NH
3
at equilibrium decreases. (1)
iii ΔH for the forward reaction is negative. (1)
Increasing temperature favours the reverse
endothermic reaction. (1)
iv Increasing temperature increases the rate of
reaction. (1)
More particles will have energy greater than or
equal to the activation energy. (1)
The frequency of successful collisions increases. (1)
UNIT 4 ANSWERS
CHAPTER 22
1 ▶ a i methane
ii propane
iii hexane
iv propene
v ethene
vi but-1-ene
vii propan-1-ol
viii butan-2-ol
b i
H
H
C
H
H
C
H
H
ii
H
H
C
OH
H
C
H
H
C
H
H
iii
H
H
C
H
C
H
C
H
H
C
H
H
ANSWERS 369
f Any between n = 5 – 10 for C
n
H
2n+2
g i 2C
4
H
10
+ 13O
2
→ 8CO
2
+ 10H
2
O
ii Carbon monoxide is poisonous as it reduces the
blood’s ability to carry oxygen around the body.
2
▶ a The sulfur (or sulfur compound) burns to make sulfur
dioxide. The sulfur dioxide reacts with water and
oxygen in the atmosphere to produce sulfuric acid that
falls as acid rain.
b The spark in the engine causes nitrogen to react with
oxygen to give various oxides of nitrogen.
c Sulfur dioxide reacts with water and oxygen in the
atmosphere to produce sulfuric acid. The sulfuric acid
in acid rain can react with calcium carbonate and
corrode the buildings.
3
▶ a Crude oil produces too many larger hydrocarbons /
not enough of the more useful smaller ones. Smaller
alkanes can be used as fuel for cars. Cracking also
produces alkenes that can be used to make polymers.
b Heat the vaporised fraction in the presence of a silicon
dioxide or aluminium oxide catalyst at 600-700 °C.
c C
11
H
24
→ 2C
2
H
4
+ C
7
H
16
d Any other valid cracking equation starting with C
11
H
24
.
For example:
C
11
H
24
→ C
2
H
4
+ C
9
H
20
or C
11
H
24
→ C
2
H
4
+ C
3
H
6
+ C
6
H
14
or lots of other variants. In each case, at least one
hydrocarbon should be an alkane (C
n
H
2n + 2
), and at
least one an alkene (C
n
H
2n
).
4
▶ This is entirely open to your imagination and ability
to think both logically and laterally. It is impossible to
suggest ‘right’ answers.
CHAPTER 24
1 ▶ a Contains only C-C single bonds and has no double or
triple bonds.
b i C
11
H
24
ii Liquid
iii C
11
H
24
(l) + 17O
2
(g) → 11CO
2
(g) + 12H
2
O(l)
iv 2C
11
H
24
+ 23O
2
→ 22CO + 24H
2
O
Carbon monoxide is poisonous, as it reduces the
ability of the blood to carry oxygen around the
body.
2
▶ a C
5
H
12
b C
4
H
10
c C
6
H
14
3 ▶ a
H
H
C
H
H
C
H
C
H
H
C
H
H and
H
H
C
H
H
C
H
C
H
C
H
H
HH
H
CH
HC
H
H
3 ▶ a i (first answer is shown in the textbook as an
example)
ii
CH
3
CH
2
CHCH
3
OH
iii
CH
3
CHCH
2
OH
CH
3
iv
CH
3
CCH
3
OH
CH
3
b
CH
3
CH
3
OCH
2
CH
2
CH
3
, CH
3
CH
2
OCH
2
CH
3
, CH
3
OCHCH
3
These compounds are known as ethers.
4
▶ a addition
b combustion
c addition
d substitution
e combustion
f substitution
5
▶ a C, it contains element other than carbon and hydrogen.
b
C
H
H
H
CH
H
H
c
H
H
C
H
H
C C
H
H
d C
n
H
2n+2
e Same functional group / similar chemical properties;
Shows a gradation in physical properties; Each
member diers from the next by a −CH
2
−.
f C
5
H
12
+ 8O
2
→ 5CO
2
+ 6H
2
O
CHAPTER 23
1 ▶ a Carbon and hydrogen.
b The crude oil (mixture of hydrocarbons) is heated until
it boils. The vapour passes into a fractionating column.
The temperature is higher at the bottom of the column
than at the top. Dierent fractions condense and
are drawn o at dierent heights in the column. The
hydrocarbons with the highest boiling points (longer
chains) condense towards the bottom of the column.
The smaller hydrocarbon molecules travel further up
the column until they condense and are drawn o.
c Gasoline – petrol for car; Diesel – fuel for lorries or
buses
d Any two from: refinery gas, kerosene, fuel oil or
bitumen.
e The average size of the molecules in gasoline is
smaller than in diesel. Diesel is darker in colour and
more viscous than gasoline.
370 ANSWERS
c
H
H
C
H
H
C
C
H
C
H
H
H
H
H H
CC
H
C
H
H
C
H
,
HH
H H
CC
H
C
H
H
C
H
,
H
d
CH
2
CH
2
CH
2
CH
2
CH
3
CH
CH
2
CH
2
2 ▶ a a carbon-carbon double bond
b
H
H
C
H
C
H
H
C
H
c
H
H
C
H
Br
C
H
H
C
H
BrH
H
C
H
C
H
H
C+ Br
2
H
d i CH
3
CH
3
+ Br
2
(g) → CH
3
CH
2
Br + HBr(g)
ii In this (substitution) reaction, one of the hydrogens
has been replaced by a bromine during the
reaction. In the previous (addition) reaction,
nothing was lost when the two molecules
combined together.
3
▶ a 1,2-dichloropropane CH
2
ClCHClCH
3
b ethane CH
3
CH
3
4
▶ a Cracking.
Conditions: 1) The presence of a silicon dioxide (silica)
or aluminium oxide (alumina) catalyst 2) heat the
vaporized alkanes at high temperatures of 600 – 700 °C.
b Test: shake with bromine water
Result with propane: no colour change (solution
remains orange)
Result with propene: solution changes colour from
orange to colourless
5
▶ a CH
3
CH
2
CH
2
CH
2
OH or CH
3
CH
2
CH(OH)CH
3
butan-1-ol butan-2-ol
b CH
3
CH
2
CH
2
CH
2
Cl or CH
3
CH
2
CHClCH
3
1-chlorobutane 2-chlorobutane
c CH
3
CH
2
CHBrCH
2
Br
1,2-dibromobutane
CHAPTER 26
1 ▶ a i CH
3
OH
ii CH
3
CH
2
CH
2
OH
b Any 2 of the following:
H
H
C
H
H
C
H
C
H
C
H
H
C
H
H
H
HC
H
H
H
H
C
H
H
C
H
H
C
H
H
C
H
C
H
H
C
H
H
H
H
H
C
H
H
C
H
H
C
H
C
H
H
C
H
H
C
H
H
H
H
H H
C
H
H
C
H
C
H
H
C
H
H
C
H
H
C
H
H
4 ▶ a UV light
b Substitution
c
H
H
C Br Br
H
H
C
H
H+ H
H
C
HBr
Br
H
H
C
H
+
5 ▶ a C
4
H
10
+ Cl
2
→ C
4
H
9
Cl + HCl
b CH
3
CH
2
CH
2
CH
2
Cl CH
3
CH(Cl)CH
2
CH
3
1-chlorobutane 2-chlorobutane
CHAPTER 25
1 ▶ a i Any two from: same general formula; same
functional group or similar chemical properties;
shows a gradation in physical properties; each
member diers from the next by a –CH
2
–.
ii Compounds containing one or more carbon
carbon double or triple bond.
b i Starting: orange; Finishing: colourless
ii
H
H
C
Br Br
H
C
H
1,2-dibromoethane
ANSWERS 371
3 ▶ a
H
H
H
C
H H
H
C C
O
O
b Orange to green.
c Propan-1-ol is very flammable and should not be
heated with an open flame. The vapour can easily
catch fire when heated with a Bunsen burner.
d i bubbles/fizzes/eervescence; Mg decreases in size
Mg(aq) + 2CH
3
COOH(aq) → (CH
3
COO)
2
Mg(aq) +
H
2
(g)
ii bubbles/fizzes/eervescence
Na
2
CO
3
(aq) + 2CH
3
COOH(aq) → 2CH
3
COONa(aq)
+ CO
2
(g) + H
2
O(l)
4
▶ a CH
3
COOH + NaHCO
3
→ CH
3
COONa + CO
2
+ H
2
O
b Neutralisation.
c Bubbles will form.
CHAPTER 28
1 ▶ a i CH
3
COOCH
2
CH
3
ii CH
3
CH
2
CH
2
COOCH
2
CH
2
CH
2
CH
3
b i
H
H
C
H
O
O
C
H
C
H
H
C
H
H
C
H
H
ii
H
H
C
H
H
C
H
O
O
C
H
C
H
H
C
H
H
c i Methyl propanoate.
ii Ethyl methanoate.
2
▶ a CH
3
COOCH
2
CH
3
CH
3
COOCH
2
CH
2
CH
3
CH
3
CH
2
COOCH
2
CH
3
CH
3
CH
2
COOCH
2
CH
2
CH
3
b • Add 1 cm
3
of ethanoic acid and 1 cm
3
of ethanol
into a boiling tube, then add a few drops of
concentrated sulfuric acid.
• Warm at about 80 °C.
• Allow the contents of the tube to cool. When cool,
pour the mixture into a beaker containing sodium
carbonate solution.
• A layer of ester will separate and float on top of the
water.
• Repeat with other combinations of acid and
alcohol.
c Esters can be detected by smelling the product: gently
waft the odour towards nose. For example, propyl
ethanoate smells like pear.
d Food flavourings and perfumes.
3
▶ a Alcohol Carboxylic acid
Methanol Propanoic acid
CH
3
OH CH
3
CH
2
COOH
b Propan-1-ol Methanoic acid
CH
3
CH
2
CH
2
OH HCOOH
b i
H
H
C
H
H
C
H
OH
ii
H
H
C
H
H
C
H
H
C
H
H
C
H
OH
c i Butan-1-ol
ii Ethanol
2
▶ a
C
H
H
H
CO
H
H
H
b Any two from: 300 °C; 60–70 atmosphere pressure;
phosphoric acid catalyst
c i Sugar cane
ii Yeast provides the enzyme (biological catalyst) for
the reaction; 30–40 °C is the optimum temperature
for the reaction. If the temperature is too low, the
rate of the reaction is too slow. If the temperature
is too high, the enzyme will be denatured; In the
presence of air (aerobic conditions), enzymes
in the yeast produce carbon dioxide and water
instead of ethanol.
iii Countries like Brazil have plenty of land and warm
climate to grow sugar cane. There is also a lack of
crude oil resource in these countries, so it is too
expensive to hydrate ethene to produce ethanol.
d C
2
H
5
OH + 3O
2
→ 2CO
2
+ 3H
2
O
3
▶ a C
6
H
12
O
6
→ 2C
2
H
5
OH + 2CO
2
b i potassium dichromate(VI) in dilute sulfuric acid
ii orange to green
iii CH
3
CH
2
OH + 2[O] → CH
3
COOH + H
2
O
c C
2
H
5
OH → C
2
H
4
+ H
2
O
CHAPTER 27
1 ▶ a i CH
3
COOH
ii CH
3
CH
2
CH
2
COOH
b i
H
H
C
H
O
ii
H
H
H
C
H H
H
C C
O
O
c i Butanoic acid
ii Ethanoic acid
2
▶ C
372 ANSWERS
f Drawing the molecule to show its relationship with the
structure of the polymer as drawn in the question:
C
H
H
C
C
CH
3
OCH
3
O
g Either: buried in landfill sites because there would
be no emission of poisonous carbon monoxide or
no carbon dioxide to contribute to global warming
or no sulfur dioxide to contribute to acid rain. Or:
incineration because no space is filled up for landfills
or energy can be generated to provide heat for oce
buildings.
3
▶ a Condensation polymer
b
O
O
O
C
H andHO
C
H
O
H
O
4 ▶ a
C C
6
H
4
C O CH
2
CH
2
O C C
6
C
4
C
CH
2
CH
2
OO
O O O O
b
n HO CH
2
CH
2
OH + n HO C C
6
H
4
O
C OH
O
CH
2
CH
2
O
O
C
6
H
4
O O
C C n + 2n H
2
O
5 ▶ a Drawing 1,6-diaminohexane as:
N H
H
N
H
H
and hexandioic acid as:
C O H
O
COH
O
i In a condensation reaction, when two molecules
join together a small molecule is lost in the
process. When the two molecules above join
together, a molecule of water is lost every
time they come together. In a condensation
polymerisation reaction, this happens repeatedly.
C O H
O
COH
etc etc
water
O
N H
H
N
H
H
ii
C
O
N
H
N
H
C
O
c Butan-1-ol Ethanoic acid
CH
3
CH
2
CH
2
CH
2
OH CH
3
COOH
4
▶ a
H
H
C
H
O
H
C
H
H
C
H
H
O
C
b Ethanoic acid.
c By heating with potassium dichromate(VI) in dilute
sulfuric acid.
d CH
3
COOH(l) + CH
3
CH
2
OH(l) ⇌ CH
3
COOCH
2
CH
3
(l)
+ H
2
O(l)
e Heat at about 80 °C with a few drops of concentrated
sulfuric acid as a catalyst.
5
▶ Test 1: Take out 3 cm
3
of each of the three samples and
put them into three separate test-tubes. Add a few pieces
of Mg or a spatula tip worth of Na2CO3 solid into each of
the test-tubes. The one that bubbles contains ethanoic
acid.
Test 2: To the remaining two samples, take out another
3cm
3
of each and put them into two separate boiling
tubes. Add a few drops of potassium dichromate(VI)
in dilute sulfuric acid. Heat the boiling tubes in a warm
water bath. The one that changes colour from orange to
green contains ethanol.
CHAPTER 29
1 ▶ a Unsaturated: containing one or more carbon carbon
double or triple bond.
Hydrocarbon: compounds containing carbon and
hydrogen only.
b C
2
H
4
+ 3O
2
→ 2CO
2
+ 2H
2
O
c Ethene can be used to make addition polymer
polyethene, which is used for making plastic bags,
milk bottles etc.
2
▶ a Joining up of lots of little molecules (the monomers) to
make one big one (a polymer).
b
H
H
C
H
C
H
H
C
H
c (The “continuation” bonds at each end are an
important part of this structure. Marks will be lost in an
exam if they are omitted.)
CH
3
CH
3
CH
3
C
H
H
C
H
C
H
H
C
H
C
H
H
C
H
d Joining two or more molecules together without
anything being lost in the process.
e
C
n
n
H
C
6
H
5
C
H
H
C
H
C
6
H
5
C
H
H
ANSWERS 373
ii
Br
Br
C
H
C
H
HH
C
H
Ho
ror
H
Br
Br
CC
H H
C
HH
H
Br
Br
C
H
C
H
HH
C
H
H
c
H
BrBr
C
CH
2
CHCH
2
CH
3
+ Br
2
C
HHH
C
H
H
C
H
H
d i B and D
ii C
n
H
2n+2
iii Same functional group / same or similar chemical
properties. (1)
Shows a trend in physical properties. (1)
Or Each member diers from the next by a –CH
2
–
unit. (1)
e i Poly(chloroethene) or polyvinylchloride (1)
ii
Cl
H
C
H
H
C
iii They are inert. (1)
Or non-biodegradable. (1)
Or if they are burned, they release toxic gases
including carbon monoxide or hydrogen chloride. (1)
iv No colour change / bromine water remains
orange. (1)
Polymer of compound A is saturated / contains no
C=C bond. (1)
f i UV light (1)
ii Substitution. (1)
iii
Cl
C
H
C
H
HHH
C
H
H and H
Cl
C
H
C
H
HH
C
H
H
3 ▶ a C H O
Mass (in 100 g) 55 9 36
/A
r
/12 /1 /16
Number of moles 4.58 9 2.25
/smallest number of moles /2.25 /2.25 /2.25
Ratio 2 4 1
The empirical formula is C
2
H
4
O.
b i There will be four more CH
2
groups in the “box”
in the part of the diagram which comes from the
dioic acid.
ii The bonding between the two monomers will be
identical, as will the size of the diamine.
END OF UNIT 4 QUESTIONS
1 ▶ a D (1)
b Used as liquefied petroleum gas / domestic heating or
cooking. (1)
c Gasoline. (1)
d Crude oil is separate into fractions by fractional
distillation. (1)
It is heated until it boils and the vapour enters a
fractionating column (1), which is cooler at the top
and hotter at the bottom (1). The fractions with a lower
boiling point condense nearer to the top of the column
and can be tapped o / the fractions with a higher
boiling point condense nearer to the bottom of the
column and can be tapped o (1).
e As the number of carbon atoms increase, the boiling
point of a hydrocarbon increases. (1)
This is because the intermolecular forces increases so
it takes more energy to break them during boiling. (1)
f 2C
15
H
32
+ 31O
2
→ 30CO + 32H
2
O
correct formulae of products (1)
correct balancing of the equation (1)
g i
O O
C
ii C
h i 600–700 °C (1); silica / alumina as a catalyst,
accept ‘aluminium oxide / silicon dioxide /
aluminosilicate / zeolite or the correct formulae. (1)
ii To make more of the smaller-chain fractions, for
example, gasoline to use as petrol. (1)
To produce more alkenes that can be used for
making polymers (plastics). (1)
iii C
9
H
20
(1)
iv The compound contains one or more carbon –
carbon double or triple bond. (1)
v
H
H
C
H
C
H
H
C
H
C
H
H H
H
C
H
CC
H
H
H
H
CH
2 ▶ a E contains an element that is not carbon or hydrogen. (1)
b i 1,3-dibromopropane 1 mark for dibromopropane
374 ANSWERS
6 ▶ a
C
H
H
C
CH
3
CH
3
H
C
H
H
CH
3
C
H
C
H
H
C
H
b
CH
2
CH
NH
2
CO
c i In condensation polymerisation, two dierent
types of monomers are used (1)
A small molecule such as water or hydrogen
chloride is produced in condensation
polymerisation as well as the polymer (1)
ii
C
O
C
O
CH
2
CH
2
O CH
2
O
d i A polyester that is biodegradable (1)
ii C
7
▶ a i Phosphoric acid (1); 300 °C or 60–70 atm pressure.
(1)
ii Bond breaking 4 × C−H + 1 × C=C + 2 × O−H =
4 × 412 + 612 + 2 × 463 = 3186 kJ/mol. (1)
Bond forming 5 × C−H + 1 × C−C + 1 × C−O + 1
× O−H =
5 × 412 + 1 × 348 + 1 × 360 + 1 × 463 = 3231 kJ/
mol. (1)
Overall 3186 – 3231 = −45 kJ/mol. (1)
iii
energy
ΔH = –45
kJ/mol
C
2
H
5
OH
C
2
H
4
+
H
2
O
b i Fermentation (1)
ii To provide the enzyme (zymase) which speeds up
the reaction. (1)
iii In the presence of oxygen, yeast would produce
carbon dioxide and water rather than ethanol. (1)
iv Warm climate or plenty of land to grow sugar
canes (1); Lack of oil resources to produce ethane.
(1)
c i Dilute sulfuric acid (1); Heating. (1)
ii CH
3
CH
2
OH + 2[O] → CH
3
COOH + H
2
O
iii Orange (1) to green. (1)
iv Mg(s) + 2CH
3
COOH(aq) → (CH
3
COO)
2
Mg(aq) +
H
2
(g)
1 mark for the correct formulae of products; 1
mark for correct balancing.
d i Water is formed in the reaction. (1)
ii Pour the reaction mixture into water (or sodium
carbonate solution) (1); The alcohol and the acid
will dissolve but the ester will float on the surface
of water. (1)
b 2 × 12 + 4 × 1 + 1 × 16 = 44
88
___
44
= 2
The molecular formula is C
4
H
8
O
2
.
c
HC
H
C
H
HHH
C
H
O
C
O
H
butanoic acid (1)
d (l) (l)
CH
3
CH
2
CH
2
COOH + CH
3
OH ⇌ CH
3
CH
2
CH
2
COOCH
3
+ H
2
O
Methylbutanoate (l)
4
▶ a Test ‘Add bromine water’
Result with compound 1 Solution changes colour from
orange to colourless
Result with compound 2 Solution stays orange
b 1 mark for the correct structure; 1 mark for the
continuation bonds
c Poly(but-2-ene) (1)
5
▶ a i 1 mark for the ester linkage; 1 mark for the correct
structure of butyl and ethanoate group
H
C
H
HH
C
H
C
H
HHH
C
H
H
C
H
O
O
C
ii Potassium dichromate. (VI); Dilute sulfuric acid. (1);
Heat. (1)
b
H
2
CCH
2
HC
OH
O
CH
3
(CH
2
)
4
C
HO
c i The reaction is reversible. (1)
ii Concentrate sulfuric acid. (1)
d No eect on the position of equilibrium. (1); Catalyst
increase the rate of the forward reaction and the rate
of the reverse reaction equally. (1)
e
HC
H
O H
HC
O H+ 3
HC
H
glycerol ethanoic acid
O
H
HC
H
H
C
O
O C
H
H
HC
H
H
C
O
O C H+ 3H
2
O
HC
H
H
C
O
O C
H
H
HO
OH
CC +H
H
HC
H
O H
HCO H+ 3
HC
H
glycerol ethanoic acid
O H
HC
H
H
C
O
O C
H
H
HC
H
H
C
O
O C H+ 3H
2
O
HC
H
H
C
O
O C
H
H
HO
OH
CC +H
H