Oxford Revise AQA GCSE Combined Science Foundation | Chapter C9 answers

C9: Rate of reaction

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Answers

Extra information

Mark

AO / Specification reference

01.1

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

2

AO2

5.2.2.2

01.2

temperature

1

AO2

5.6.1.2

01.3

\(
\begin{align}
& \frac{45}{60} \\
& = 0.75\ (\textrm{cm}^3/\textrm{s})
\end{align}
\)

1

AO2

5.6.1.1

01.4

faster

more gas produced in the same time/bigger surface area so more frequent collisions

1

1

AO2

5.6.1.1

01.5

balance/top-pan balance/scales

1

AO2

5.6.1.2

02.1

sulfuric acid + sodium carbonate → carbon dioxide + water + sodium sulfate

award one mark if word equation correct but salt name is incorrect

2

AO2

5.4.2.2

02.2

98 g/dm3

1

AO2

5.6.1.2

02.3

volume of carbon dioxide

cm3

1

1

AO2

5.6.1.2

02.4

line is steeper

stops at the same level at original line but sooner

1

1

AO2

5.6.1.2

03.1

independent: surface area of calcium carbonate/lump vs powdered calcium carbonate

dependent: volume of gas released (in 150 seconds)

1

1

AO2

5.6.1.2

03.2

even time points (every 10 s)/regular time intervals/more frequent time intervals

1

AO3

5.6.1.2

03.3

85

1

AO2

5.6.1.2

03.4

all points plotted

allow error carried forward for question 08.3

1

AO2

5.6.1.2

03.5

powdered calcium carbonate has greater surface area

increase in frequency of collisions between calcium carbonate and nitric acid particles

1

1

AO1

5.6.1.3

04.1

sodium chloride

sulfur

1

AO2

5.6.1.2

04.2

measured the time taken for the cross to disappear/solution to become cloudy

1

AO2

5.6.1.2

04.3

use data logger/repeat it

1

AO3

5.6.1.2

04.4

as temperature increases, the rate of reaction

increases/time taken goes down

1

AO3

5.6.1.2

04.5

rate of reaction slow

because energy of most collisions between particles below activation energy

1

1

AO2

5.6.1.3

04.6

one from:

  • concentration of hydrochloric acid
  • concentration of sodium thiosulfate

do not allow concentration on its own

allow add catalyst

1

AO1

5.6.1.2

05.1

four from:

  • add water to a conical flask/beaker
  • place conical flask/beaker onto a balance
  • zero balance
  • add lithium and quickly measure the mass
  • put cotton wool into the spout of the conical flask
  • measure the decrease in mass of lithium as the reaction progresses

accept a method that involves measuring the change in the pH of the solution

one mark for each correct answer up to a maximum of four marks

4

AO1

5.6.1.1

05.2

\((mean)\ rate\ of\ reaction\ =\ \frac{\textrm{change in mass}}{\textrm{time}}\)

1

AO1

5.6.1.1

05.3

g/s

1

AO1

5.6.1.1

05.4

no

1

AO2

5.6.1.2

06.1

hydrogen

1

AO1

5.4.2.1

06.2

decreasing the acid concentration

1

AO1

5.6.1.2

06.3

rate decreases/particles have less kinetic energy

decreases the frequency of collisions between zinc and nitric acid

fewer collisions with activation energy needed

1

1

1

AO1

5.6.1.2

07.1

same shape with same starting and end point, but the peak is lower

1

AO1

5.6.1.4

07.2

double-headed arrow drawn from reactants to peak for the catalysed line

labelled activation energy

1

AO1

5.6.1.4

07.3

enzymes

1

AO1

5.6.1.4

07.4

lowers activation energy

alternative pathway for reaction

1

1

AO1

5.6.1.4

08.1

mass

1

AO2

5.6.1.1

08.2

\(
\begin{align}
& 198\ -\ 170 = 28 \\
& \frac{28}{150} \\
& = 0.19\ \textrm{g/s}
\end{align}
\)

1

1

1

AO1

AO2

5.6.1.1

08.3

Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

1

AO3

5.6

08.4

half points plotted

all points plotted

line of best fit

1

1

1

AO2

AO3

5.6.1.1

08.5

tangent at 20 s

tangent at 100 s

1

1

AO3

5.6.1.1

08.6

slope of tangent at 20 seconds steeper than tangent at 100 seconds

rate of reaction at 20 seconds greater than at 100 seconds

more reactant particles at 20 seconds

so greater frequency of collisions

1

1

1

1

AO2

5.6.1.1

5.6.1.3

09.1

increases reaction rate by providing a pathway with a lower activation energy

1

AO1

5.6.1.4

09.2

B

1

AO1

5.6.1.4

09.3

2H2O2 → 2H2O(l) + O2

one mark for balancing

one mark for state symbols

2

AO1

5.2.2.2

5.3.1.1

09.4

it is a catalyst/regenerated at the end

1

AO2

5.6.1.4

10.1

Level 3: The method is clear and variables are correctly explained.

5-6

AO1

5.6.1.2

Level 2: The method is clear, but variables are absent or incorrect or the method is attempted but not clear and some variables correctly provided.

3-4

Level 1: Either an unclear method (perhaps with some steps missing) or a few variables correctly identified.

1-2

No relevant content.

0

Indicative content:

  • add water to a conical flask/beaker
  • place conical flask/beaker onto a balance
  • put nitric acid into conical flask
  • prepare a bung with gas syringe attached
  • add sodium carbonate
  • put bung in as soon as sodium carbonate is added
  • measure time taken to produce a set volume of carbon dioxide/measure the volume of carbon dioxide produced in set time
  • repeat with different concentrations of nitric acid
  • control variables:
    • same mass of sodium carbonate used
    • same temperature
    • same surface area sodium carbonate/always use solid pieces or powder
    • same volume of nitric acid used
  • independent variable: concentration of nitric acid
  • dependent variable: rate or volume of CO2 /mass of gas produced/pH change

accept an upside-down measuring cylinder as an appropriate method

accept a method that involves measuring the change in mass of sodium carbonate/pH of reaction mixture.

10.2

as the concentration of nitric acid increases, the rate of reaction increases

the higher the concentration, the more acid particles are available in a given volume

so frequency of successful collisions will increase

1

1

1

AO1

AO3

5.6.1.2

10.3

cm3/s

1

AO2

5.6.1.1

10.4

\(
\begin{align}
& \frac{500}{42} = 11.9\\
& = 11.9
\end{align}
\)

1

1

AO2

5.6.1.1

10.5

catalyst/temperature

1

AO1

5.6.1.2

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