AQA C2 (Chemistry) ANSWERS to questions

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1. (a) 25.4(%)
correct answer with or without working
accept 25(%)
accept 25.433....(%)
allow 26(%) for 1 mark
if incorrect answer 1 mark for identification of 44 as Mr of
useful product
or 173 as total Mr of reactants / products
(b) ignore references to energy / cheaper / profit / cost / efficient
any two sensible ideas from eg:
· no / less waste
· less materials / reactants needed / used
· fewer / no environmental problems or less / no pollution
· better for sustainable development / resources running out
· more useful use of atoms
· less purification / separation of products owtte 2
(c) increase yield 1
more (gaseous) reactant molecule than (gaseous) product molecule owtte 1
accept more molecules on left hand side or converse
accept Le Chatelier based answers for second mark
ignore rate of reaction
(d) reduce yield
allow no yield
less product owtte 1
ignore waste / less efficient
Harrow High School 1

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Y ì2. (a) Pb Cl C O
76 13 2.2 8.8 1
207 35.5 12 16
1 mark for dividing one mass by Ar
allow upside down ratio to lose this mark only
= 0.367 = 0.366 = 0.183 = 0.55 1
1 mark for one correct proportion ­ accept to one d.p. or
rounded up to 1 d.p.…read more

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Cu reacts with oxygen
or Cu is oxidised
this is a poor conductor or gets in the way of 1
free moving electrons or fewer mobile electrons
do not accept electricity
oxygen atoms / oxygen molecules /
oxide ions in metal
do not accept oxygen pockets / bubbles
do not accept macro explanations
prevents / disrupts flow of electrons /
current or fewer mobile electrons
do not accept electricity
(ii) any one from: 1
hydrogen reacts with oxygen
water is formed
hydrogen reduces…read more

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°C from graph) 1
ignore reference to catalyst
any one from: 1
(forward) reaction exothermic
if the temperature is increased the yield of product will
decrease or reaction right to left
2 marks for comments relating to pressure
high / higher / highest pressure 1
(or greater than 450 atm, from graph)
any one from: 1
four reactant molecules but only
two product molecules (owtte)
reverse reaction goes from 2
molecules / moles / volumes to 4
molecules / moles / volumes
increase in pressure…read more

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Mr (SiO2) = 60
if Mr incorrect ecf for max 2
60 g SiO2 28 g Si 1
correct answer for 3 marks
2.14 g SiO2 1 g Si 1
allow 2, 2.1, 2.14 (or anything rounding to 2.14), 2.16 or
a unit is not required but an incorrect unit loses the third
OR Mr (SiO2) = 60 (1)
moles if silicon needed = = 0.0357
mass of SiO2 needed = 0.0357 × 60 (1)
= 2.14 g (1)
allow 2, 2.…read more

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Si H
= 0.05 = 0.…read more

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C 1
accept c
(c) any four from: 4
giant structure / macromolecule / lattice / giant molecule
allow giant molecular / giant atomic structure
each silicon atom joined to four other atoms
(or diagram)
covalent bonds
bonds are strong or large amount of energy needed to break bonds
accept hard to break bonds
large number of bonds to be broken
mention of giant ionic structure or intermolecular forces or
intermolecular bonds max 1 mark
diamond or carbon discussion max 3 marks unless clearly
linked…read more

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(bonds formed =) 2046 (kJ) 1
energy change =
2005 ­ 2046 = (­)41 1
for correct subtraction ignore sign
(ii) (exothermic)
if in part (b)(i) answer is not 41
answer is consequential on endothermic or exothermic
accept correct reasoning for incorrect answer from (b)(i)
energy given out forming new bonds 1
do not accept energy needed to form new bonds
greater than energy put in to break old bonds 1
accept exothermic and more energy given out than taken in
for…read more

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AlX3 1
for 1 mark
Harrow High School 9…read more

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OH­ + H+
cancel 1 mark if equation is balanced incorrectly
H2O 1
award 1 mark only if Na+ and Cl­
included in the balanced equation
(b) (i) 27.…read more


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