AQA GCSE Chemistry Chemistry Paper 1 (Higher), 2022: Question 2
17 marks · Standard Demand difficulty · Extended Answer
Plan an investigation into the temperature change when sodium carbonate reacts with hydrochloric acid, determine the gradient and initial temperature from a graph of the results, and identify features of an exothermic reaction profile.
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Question text
02 Sodium carbonate reacts with hydrochloric acid in an exothermic reaction.
The equation for the reaction is:
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
A student investigated the effect of changing the mass of sodium carbonate powder
on the highest temperature reached by the reaction mixture.
02.1 Plan a method to investigate the effect of changing the mass of sodium carbonate
powder on the highest temperature reached.
[6 marks]
Figure 3 shows a line of best fit drawn through the student’s results.
Figure 3
02.2 Determine the gradient of the line of best fit in Figure 3.
Use the equation:
Change in highest temperature
Gradient =
Change in mass
Give the unit.
[5 marks]
Gradient = Unit
02.3 The initial temperature of the reaction mixture is where the line of best fit would meet
the y-axis.
Determine the initial temperature of the reaction mixture.
Show your working on Figure 3.
[2 marks]
Initial temperature of the reaction mixture =8 °C
02.4 Another student repeated the investigation but added sodium carbonate until the
sodium carbonate was in excess.
Which sketch graph shows the results obtained when sodium carbonate was added
until in excess?
[1 mark]
Tick ( ) one box.
A
B
C
Figure 4 shows a reaction profile for the reaction of sodium carbonate with
hydrochloric acid.
Figure 4
02.5 What do labels X and Y represent on Figure 4?
[2 marks]
X
Y
02.6 How does the reaction profile show that the reaction is exothermic?
Use Figure 4.
[1 mark]
Mark scheme
Show the mark scheme
Question 2
AO/
Question Answers Mark
Spec. Ref
02.1 Level 3: The method would lead to the production of a valid 5–6 AO1
outcome. The key steps are identified and logically sequenced. 4.5.1.1
RPA 4
Level 2: The method would not necessarily lead to a valid 3–4
outcome. Most steps are identified, but the plan is not fully logically
sequenced.
Level 1: The method would not lead to a valid outcome. Some 1–2
relevant steps are identified, but links are not made clear.
No relevant content 0
Indicative content
• measure volume of (hydrochloric) acid
• with a measuring cylinder
• pour (hydrochloric) acid into a suitable container eg
polystyrene cup
• measure the initial temperature (of hydrochloric acid)
• with a thermometer
• add a known mass of sodium carbonate
• measured with a balance
• stir
• measure the highest temperature reached
• repeat with different masses of sodium carbonate
or
add successive masses of sodium carbonate to the same
mixture
• repeat the whole investigation
• use the same starting temperature
• use the same volume of (hydrochloric) acid each time
• use the same concentration of (hydrochloric) acid each time
AO /
Question Answers Extra information Mark
Spec. Ref.
02.2 change in highest temperature allow a tolerance of ± ½ a small 1 AO2
View with square 4.5.1.1
RPA 4
10 Figure 3
corresponding change in mass allow a tolerance of ± ½ a small 1
square
(gradient =)
change in highest temperature allow correct use of an 1
change in mass incorrectly determined change in
highest temperature and / or
change in mass
(gradient =) 1.6 1
°C/g allow °C/gram(s) 1
AO /
Spec. Ref.
02.3 extrapolates line to the y-axis 1 AO2
View with 4.5.1.1
20.6 (°C) allow a tolerance of ± ½ a small 1 RPA 4
Figure 3
square
allow a correctly determined
value from an incorrectly
extrapolated line
alternative approach:
(highest temperature at 1.0 g –
change in highest temperature
per gram =)
22.2 – 1.6 (1) allow correct use of value
determined for gradient in
question 02.2
= 20.6 (°C) (1)
AO /
Spec. Ref.
02.4 C 1 AO3
4.5.1.1
RPA 4
AO /
Spec. Ref.
02.5 (X) energy 1 AO1
4.5.1.2
(Y) (overall) energy change 1
AO /
Spec. Ref.
02.6 (level of) products is below allow the energy decreases 1 AO1
(level of) reactants (overall) 4.5.1.2
allow energy is transferred to
the surroundings
ignore references to bond
making / breaking
Total Question 2 17
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Topics
Required Practicals · Chemistry · Required Practicals · C5: Energy Changes
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Higher), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.