Oxford Revise AQA GCSE Chemistry | Chapter 12 answers

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Chapter 12: Rate of reaction

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Answers

Extra information

Mark

AO / Specification reference

01.1

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

1

AO1

4.6.1.4

01.2

B

1

AO1

4.6.1.4

01.3

2H2O2 → 2H2O(l) + O2

one mark for balancing

one mark for state symbols

2

AO1

4.2.2.2

4.3.1.1

01.4

it is a catalyst/regenerated at the end

1

AO1

4.5.1.2

02.1

half points plotted correctly

all points plotted correctly

points plotted at (0, 0) (30, 21) (60, 38) (90, 52) (120, 58) (150, 61) (180, 61)

1

1

AO2

4.6.1.1

02.2

line of best fit correctly drawn

must be a curve

1

AO3

4.6.1.1

02.3

 \(
\begin{array}{l}
{\rm{rate\ }} = {\rm{\ gradient\ of\ tangent\ drawn\ at\ }}100\\
= \frac{{18}}{{80}}\\
= 0.225\\
= 0.23\left( {{\rm{c}}{{\rm{m}}^3}/{\rm{s}}} \right)
\end{array}
\)

1

1

1

1

AO2

4.6.1.1

02.4

concentration of acid is less at 100 seconds

1

AO3

4.6.1.1

03.1

start the timer and add the acid at the same time

1

AO3

4.6.1.2

03.2

the temperature will be the actual temperature at which the reaction occurs

1

AO3

4.6.1.2

03.3

judging exactly when the cross disappears varies slightly from person to person

1

AO3

4.6.1.2

03.4

the one at 45 °C

1

AO2

4.6.1.2

03.5

as temperature increases, rate also increases

1

AO1

4.6.1.2

03.6

increasing the temperature increases the frequency of collisions

more particles have energy above the activation energy

1

1

AO1

4.6.1.3

04.1

one of the products (carbon dioxide) is a gas which escapes from the flask

1

AO1

4.3.1.3

04.2

do not remove the paper because doing this makes the mass lower

than it would be as a result of loss of carbon dioxide gas alone

1

1

AO3

4.6.1.2

04.3

the smaller the calcium carbonate pieces, the faster the reaction

powder has the highest surface area to volume ratio

so collisions are more frequent

1

1

1

AO1 × 1

AO2 × 2

4.6.1.2

4.6.1.3

05.1

hydrogen

1

AO1

4.4.2.1

05.2

decreasing the acid concentration

1

AO1

4.6.1.2

05.3

rate decreases

1

AO1

4.6.1.2

06.1

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO2

4.4.3.5

06.2

Level 3: The variables are correctly identified and the account is clearly written and well-structured.

5-6

AO1 × 2

AO2 × 2

AO3 × 2

4.6.1.1

4.6.1.2

Level 2: The variables are mainly correct, although there might be one or two errors. The account is written fairly clearly, and may be somewhat disorganised.

3-4

Level 1: One or two of the variables are correctly identified. The account is not written clearly, and consists of isolated points rather than one coherent piece of work.

1-2

No relevant content.

0

Indicative content

  • temperature increased/size of pieces decreased/acid concentration increased/surface area of magnesium increased
  • because in P, more gas is produced in a given time at first (than Q)
  • kept constant: correct two from: acid concentration, size of magnesium pieces, acid concentration
  • because these are the control variables
  • kept constant: mass and volume of both substances/amount of limiting reactant
  • because total volume of hydrogen gas produced is the same

07.1

move delivery tube so that its end is not in the acid

to avoid acid going up the delivery tube

allow other suitable reasons

1

1

AO3

4.6.1.2

07.2

 \(
\begin{array}{*{20}{l}}
{\frac{{{\rm{91}}}}{{\rm{5}}} = 18.2}\\
\begin{array}{l}
= 18\\
{\rm{c}}{{\rm{m}}^{\rm{3}}}{\rm{/min}}
\end{array}
\end{array}
\)

1

1

1

AO2

4.6.1.1

07.3

increase

powder has bigger surface area

1

1

AO3

4.6.1.4

08.1

half points plotted correctly

all points plotted correctly

line of best fit drawn

1

1

1

AO2

AO3

4.6.1.2

08.2

100, 65

1

AO3

4.6.1.2

08.3

more reactant particles at the start of the reaction

greater frequency of collisions

as reaction progresses, more reactant particles become product particles

therefore frequency of collisions

1

1

1

1

AO1

4.6.1.3

08.4

tangent drawn at 60 seconds

gradient of tangent calculated

1

1

AO2

AO3

4.6.1.1

09.1

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

5-6

AO1

4.6.1.2

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

  • 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 surface area sodium carbonate/always use solid pieces or powder
  • same volume of nitric acid used

independent variables:

  • concentration of nitric acid

dependent variables:

  • rate/volume of CO2

accept an upside-down measuring cylinder as an appropriate method

accept a method that involves measuring the change in mass of sodium carbonate

09.2

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

the higher the concentration the more acid particles are available

so frequency of successful collisions will increase

1

1

1

AO1

AO3

4.6.1.2

09.3

cm3/s

1

AO2

4.6.1.1

09.4

 \(
\begin{array}{l}
\frac{{500}}{{42}} = 11.904\\
= 11.9
\end{array}
\)

1

1

AO2

4.6.1.1

09.5

catalyst/temperature

1

AO2

4.6.1.2

10.1

increase the number of hydrochloric acid particles

so frequency of collisions increased

1

1

AO1

4.6.1.3

10.2

particles move faster so increases the frequency of collisions

increases the energy of the particles

so more particles have energy greater than the activation energy

so more collisions are successful

1

1

1

1

AO1

4.6.1.3

10.3

time on x-axis, turbidity on y-axis

curve starts high and decreases

higher temperature has steeper curve

both curves finish at the same point

1

1

1

1

AO2

4.6.1.2

11.1

2H2(g) + 4OH−(aq) → 4H2O(l) + 4e−

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO1

4.5.2.2

11.2

O2(g) + 2H2O(l) + 4e− → 4OH−(aq)

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO1

4.5.2.2

11.3

fuel cells do not need to be electrically recharged, but rechargeable batteries do

no pollutants are produced at the pint of use from either type of cell

hydrogen is highly flammable, but the substances in rechargeable batteries are not

hydrogen is difficult to store

accept other sensible suggestions

1

1

1

1

AO3

4.5.2.1

4.5.2.2

12.1

no atoms/mass are lost or made during a chemical reaction

so the mass of products is equal to the mass of reactants

1

1

AO1

4.3.1.1

12.2

Pb(NO3)2(aq) + 2NaI(aq) → PbI2(s) + 2NaNO3(aq)

one mark for formulae and state symbols of reactants

one mark for formulae and state symbols of reactants

or

one mark for correct formulae

one mark for correct state symbols

one mark for balancing

3

AO2

4.4.3.5

12.3

Mr of lead iodide = 207 + 127 +127 = 461

\(
6.68{\rm{\ g\ of\ lead\ iodide\ is\ }}\frac{{6.68}}{{461}} = 0.014{\rm{\ mol}}
\)

0.014 mol of lead iodide made from (0.014 × 2 =) 0.028 mole sodium iodide

Mr of sodium iodide = 23 + 127 = 150

150 × 0.028 = 4.2 g

1

1

1

1

1

AO1 × 2

AO2 × 3

4.3.2.2

13.1

fluorine – 2,7

neon – 2,8

1

1

AO2

4.1.1.7

13.2

Group 7 – atoms have 7 electrons in outer shell; reactive because atoms gain one electron in reactions to achieve full outer shell/stable electronic structure

Group 0 – atoms have full outer shell;

unreactive because this arrangement is stable

1

1

AO1

4.1.2.4

4.1.2.6

13.3

increases from top to bottom of both groups

1

1

AO1

4.1.2.4

4.1.2.6

14.1

buckminster fullerene

allow ‘buckyball’

1

AO1

4.2.3.3

14.2

both – three covalent bonds per carbon atom

graphite – giant layer structure

buckminsterfullerene – spherical structure

1

1

1

AO1

4.2.3.2

4.2.3.3

14.3

two from

  • high boiling point
  • hard
  • does not conduct electricity

explanation for hard and high boiling point: each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure

explanation for does not conduct electricity:

no charged particles that are free to move

one mark for each correct property (maximum of two)

one mark for each correct explanation (maximum of two)

4

AO1

4.2.3.1
⌃
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