AQA GCSE Chemistry Chemistry Paper 2 (Higher), 2023: Question 1
10 marks · Standard Demand difficulty · Short Answer
Analyze the rate of reaction between zinc and sulfuric acid, calculate the mean time taken to collect gas excluding anomalies, identify factors that decrease the rate, and describe the test for hydrogen gas.
Practise this questionQuestion
Question text
01 A student investigated the rate of the reaction between zinc and sulfuric acid.
Hydrogen gas is produced during this reaction.
Figure 1 shows the apparatus.
Figure 1
This is the method used.
1. Add 50 cm3 of sulfuric acid to a conical flask.
2. Add 2.0 g of zinc to the conical flask.
3. Quickly put a stopper in the conical flask and start a timer.
4. Measure the time taken to collect 20 cm3 of gas.
5. Repeat steps 1 to 4 three more times.
01.1 Suggest why the stopper must be put in the conical flask as quickly as possible in
step 3.
[1 mark]
01.2 The student calculated the rate of the reaction for each trial.
Table 1 shows the results of the calculations.
Table 1
Trial 1 Trial 2 Trial 3 Trial 4
Rate of reaction in cm3/s 0.78 0.81 0.68 0.81
Determine the mean time taken to collect 20 cm3 of gas.
Do not include any anomalous results.
Use the equation:
volume of gas collected
mean rate of reaction =
mean time taken
[5 marks]
Mean time taken = s
01.3 The student changed the investigation so that the mean time taken to collect
20 cm3 of gas was greater.
Which two changes would increase the mean time taken to collect 20 cm3 of gas?
[2 marks]
Tick ( ) two boxes.
Use a catalyst
Use a larger conical flask
Use a lower temperature
Use smaller pieces of zinc
Use sulfuric acid of a lower concentration
01.4 Hydrogen gas is produced during this reaction.
Describe the test for hydrogen gas.
Give the result of the test.
[2 marks]
Test
Result
Mark scheme
Show the mark scheme
Question 1
AO /
Question Answers Extra information Mark
Spec. Ref.
01.1 to reduce the escape of gas 1 AO3
4.6.1.1
RPA5
AO /
Spec. Ref.
01.2 (mean rate =) allow
0.78 + 0.81 + 0.81
30.78 + 0.81 + 0.68 + 0.81 1 AO3
0.80 (cm /s) = 0.77 (cm3/ s) for 1 mark
1 AO2
20 allow correct use of incorrectly 1 AO2
0.80 =
mean time taken determined mean rate
AO2
20 1
(mean time taken =)
0.80
AO2
= 25 (s) 1 4.6.1.1
RPA5
alternative approach:
0.78 =
time
or
0.81 = (1)
time
(trial 1 time = =) 25.6 (1)
0.78
(trial 2 and 4 time =
=) 24.7 (1)
0.81
(mean time =) allow correct use of incorrectly
25.6 + (2 × 24.7) determined value(s) for time
(1)
25.6 + 29.4 + (2 × 24.7)
allow
= 25 (s) (1) = 26.1 (s)
for 1 mark
AO /
Spec. Ref.
01.3 use a lower temperature 1 AO1
4.6.1.2
use sulfuric acid of a lower 1
concentration RPA5
AO /
Spec. Ref.
01.4 AO1
MP2 is dependent upon MP1
4.8.2.1
being awarded
(test)
burning / lit splint allow flame 1
do not accept glowing splint
(result)
burns with a (squeaky) pop allow pops 1
sound
Total Question 1 10
How to answer it
Rates of Reaction & Gas Collection (Zinc + Sulfuric Acid)
What this question tests
This question assesses practical skills and theoretical knowledge from AQA GCSE Chemistry Topic 6 (The Rate and Extent of Chemical Change). Specifically, it tests your ability to:
- Explain experimental procedures in gas collection investigations (Required Practical 5).
- Identify anomalous data in a results table and exclude it from mean calculations.
- Rearrange and use the rate of reaction equation to calculate reaction time.
- Identify factors that slow down a chemical reaction (increasing reaction time).
- Recall the chemical test and positive result for hydrogen gas.
Minimising Gas Loss
Suggest why the stopper must be put in the conical flask as quickly as possible in step 3.
✅ Correct Answer
To reduce the escape of gas (or to prevent gas escaping).
1 Mark🧠 Exam Technique
In rate experiments where a gas is produced, the reaction starts the exact millisecond the solid touches the acid. Any delay in sealing the flask means gas escapes into the room instead of going into the measuring cylinder, making your volume measurements inaccurate.
❌ Common Errors
- Writing "to keep it a fair test" (too vague—never gets marks at GCSE).
- Writing "to stop air getting in" (the pressure of the reaction actually pushes air out, so air entering is not the issue).
Calculating Mean Time (5-Mark Calculation)
Determine the mean time taken to collect 20 cm³ of gas. Do not include any anomalous results.
📐 Step-by-Step Calculation
Looking at Table 1, the rates are: Trial 1 = 0.78 , Trial 2 = 0.81 , Trial 3 = 0.68 , Trial 4 = 0.81 .
Trial 3 ( 0.68 cm³/s ) is significantly lower than the others and is the anomaly. Exclude it!
Mean Rate = (0.78 + 0.81 + 0.81) ÷ 3 = 0.80 cm³/s
2 Marks awarded up to here
Given equation: mean rate = volume ÷ mean time
Rearranged: mean time = volume ÷ mean rate
2 Marks awarded for correct rearrangement & substitution
Mean Time = 20 cm³ ÷ 0.80 cm³/s = 25 s
1 Mark for correct final value with units
✅ Final Answer
Mean time taken = 25 s
❌ The "Anomaly" Trap
If you fail to spot the anomaly and include Trial 3 in your average, your mean rate becomes 0.77 cm³/s , leading to a time of 26.1 s . This limits you to a maximum of 4 marks.
Slowing Down the Reaction
Which two changes would increase the mean time taken to collect 20 cm³ of gas?
✅ Correct Answers (Tick 2)
- Use a lower temperature
- Use sulfuric acid of a lower concentration
🧠 Exam Technique: Read Carefully!
The question asks for changes that increase the mean time. An increased time means the reaction takes longer, which means the reaction rate is slower. Do not confuse this with making the reaction faster!
💡 Key Knowledge: Collision Theory
- Lower temperature: Particles have less kinetic energy, move slower, collide less frequently, and with less energy (fewer successful collisions per second).
- Lower concentration: Fewer reactant particles in the same volume, leading to less frequent collisions.
Gas Test for Hydrogen
Describe the test for hydrogen gas and give the result.
✅ Correct Answers
Test: Use a burning / lit splint (or flame).
Result: Burns with a (squeaky) pop sound.
2 Marks (1 for test, 1 for result)❌ Common Errors
- Writing "glowing splint" . This is the test for oxygen (which relights it). A hydrogen test requires an active flame!
- Writing just "squeaky pop" without mentioning the lit splint. You cannot get the result mark if your test is incorrect or missing.
Topics
Chemistry · Required Practicals · C6: The Rate and Extent of Chemical Change · C8: Chemical Analysis · Required Practicals
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Higher), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.