Answer for summary questions " C8 Rates & Equilibrium "

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This resource sheet may have been changed from the original. 1
C8 Summary questions
Student Book answers
Question
number
Answer Marks Guidance
1 a carbon dioxide, limewater turns cloudy 1
1 b i calcium carbonate + nitric acid → calcium nitrate + water +
carbon dioxide
1
1 b ii CaCO3(s) + 2HNO3(aq) → Ca(NO3)2(aq) + H2O(l) + CO2(g) 3
1 c used two solutions of nitric acid with different
concentrations,
kept all other variables constant,
in conical flask placed on electric balance,
marble chips added, with cotton wool plug in mouth of
flask,
loss in mass (= mass of gas produced)
monitored for 2.5 minutes, readings every 30 seconds
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1 d both lines drawn as smooth curves and labelled 4
1 e i dependent on tangent drawn on curves on student graph,
accept Rate of A = 0.55–0.65 g/min, Rate of B = 0.25–0.35
g/min
answer in mol/s depends on answer provided in g/min;
accept Rate of A = 2.1–2.5 × 10−4
mol/s and Rate of B =
9.5 × 10−5
–1.3 × 10−4
mol/s
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1
1 e ii rate of reaction in B ≈ half that in A 1
1 f final mass of gas produced in B = half of that produced in
A
1
1 g initial concentration of acid in A = twice concentration of
acid in B
1

2. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 2
C8 Summary questions
Student Book answers
Question
number
Answer Marks Guidance
1 h twice as many acid particles (H+(aq) ions) in A as in B in
same volume of acid,
so twice number of collisions in a given time
between acid particles in solution and particles at surface
of marble chips,
so rate of reaction in A is twice rate in B
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2 a kept temperature, concentration of acid, volume of acid,
mass of zinc constant,
only varied surface area of zinc in each test
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1
2 b hydrogen,
lighted splint pops
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2 c Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) 2
2 d line 1 1
2 e largest pieces 1
2 f steepest line,
rising to same level as other three, levelling off first
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1
2 g The smaller the pieces of zinc, the larger its surface area
and the more zinc particles exposed to react with acid
particles moving randomly in solution.
Therefore, frequency of collision between reactant particles
increases,
causing an increase in rate of reaction.
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1
1
GCSE Chemistry only
2 h 48 cm3
or 0.048 dm3
3

3. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 3
C8 Summary questions
Student Book answers
Question
number
Answer Marks Guidance
3 a substance that increases rate of a reaction
but remains chemically unchanged at end of reaction
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3 b 2H2O2(aq) → 2H2O(l) + O2(g) 3
3 c Measure time to collect a fixed volume of oxygen
using same mass of catalyst
with same surface area
in same volume and concentration of hydrogen peroxide
solution
at same temperature in each test.
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1
1
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1
GCSE Chemistry only
3 d 2.5 cm3
/s = 1.0 × 10−4
mol/s 3 (answer to 2 sig. fig. consistent with data provided)
3 e Filter off insoluble metal oxides after reaction,
wash with distilled water
and dry in a warm oven / leave to dry / dab with filter paper
to dry.
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