AQA GCSE Chemistry Chemistry Paper 2 (Higher), 2024: Question 5
12 marks · Standard Demand difficulty · Extended Answer
This question involves analyzing the environmental impacts of burning hydrogen versus natural gas, performing a gas volume calculation, and explaining the fractional distillation process for producing kerosene.
Practise this questionQuestion
Question text
05 This question is about burning fuels in central heating boilers.
In the future, gas central heating boilers may burn hydrogen rather than natural gas.
Table 2 shows information about these fuels when 1 dm3 of the fuel is burned in a
central heating boiler.
Table 2
Fuel
Hydrogen Natural gas
Energy released in kJ 11.9 37.1
Mass of carbon dioxide
0.00 1.83
produced in grams
Mass of water vapour
0.75 1.50
produced in grams
Mass of oxides of nitrogen –4 –4
6.6 × 10 4.9 × 10
produced in grams
05.1 Explain how oxides of nitrogen are produced when burning fuels.
[2 marks]
05.2 Explain one positive impact on the environment of burning hydrogen rather than
natural gas as a fuel.
Use Table 2.
[2 marks]
05.3 Explain one negative impact on the environment of burning hydrogen rather than
natural gas as a fuel.
Use Table 2.
[2 marks]
05.4 Air is 20% oxygen.
Calculate the volume of air needed to provide enough oxygen to react with 3.50 dm3
of hydrogen gas.
The equation for the reaction is
2 H2 + O2 → 2 H2O
[3 marks]
Volume of air = dm3
*0195.*5 Central heating boilers can also burn kerosene.
Kerosene is produced from crude oil in a fractionating column using fractional
distillation.
In the first step, crude oil is heated and hydrocarbon vapours are formed.
Explain how kerosene is produced from these hydrocarbon vapours.
[3 marks]
Mark scheme
Show the mark scheme
Question 5
AO /
Question Answers Extra information Mark
Spec. Ref.
05.1 high temperatures ignore pressure 1 AO1
4.9.3.1
(cause) nitrogen (from air) and 1
oxygen (from air) to react
AO /
Spec. Ref.
ignore references to water
05.2 vapour
less climate change allow less global warming 1 AO1
allow an effect of climate
change for climate change
(because) no carbon dioxide 1 AO3
(produced)
4.7.1.3
4.9.2.4
AO /
Spec. Ref.
05.3 more oxides of nitrogen 1 AO1
(produced)
(so) more acid rain allow an effect of acid rain for 1 AO3
or acid rain
(so) more respiratory problems allow a named respiratory 4.7.1.3
problem for respiratory problems 4.9.3.2
MP2 cannot be linked to an
incorrect gas– from MP1 – –
AO /
Spec. Ref.
05.4 1 AO2
(volume of oxygen = 3.50 × =)
2 4.3.5
1.75 (dm3) 1
4.9.1.1 19
(volume of air =) 1.75 × allow correct use of an 1
incorrectly determined volume of
oxygen
= 8.75 (dm3) 1
AO /
Spec. Ref.
05.5 there is a temperature gradient allow the (fractionating) column 1 AO1
in the (fractionating) column gets cooler going up
(so) kerosene condenses allow (so) the hydrocarbons / 1 AO2
vapours condense
at the level (in the column) allow at the level (in the column) 1 AO1
corresponding to kerosene’s corresponding to the boiling
boiling point (range) point of the hydrocarbons / 4.7.1.2
vapours
for the award of 2 marks for
MP2 and MP3, a reference to
kerosene must be made
Total Question 5 12
How to answer it
Comparing Fuels: Hydrogen vs. Natural Gas
What this question tests
This question assesses your understanding of atmospheric pollutants, interpreting data from tables, gas volume stoichiometry, and the process of fractional distillation for crude oil.
Formation of Nitrogen Oxides
💡 Key Knowledge
- Nitrogen (N₂) is usually unreactive because of its strong triple bond.
- In car engines or boilers, the high temperature provides enough energy for N₂ to react.
✅ Correct Answer
- High temperatures [1 mark]
- Cause nitrogen and oxygen from the air to react [1 mark]
❌ Common Errors
Many students incorrectly state that nitrogen comes from the fuel. Always specify that nitrogen and oxygen come from the air.
Environmental Impacts (Using Data)
🧠 Exam Technique
When a question says "Use Table 2", you must look for a specific difference in the numbers to justify your answer.
✅ 05.2: Positive Impact
Impact: Less global warming / climate change [1 mark]
Reason: No carbon dioxide is produced (Table 2 shows 0.00g for hydrogen) [1 mark]
✅ 05.3: Negative Impact
Impact: More acid rain OR respiratory problems [1 mark]
Reason: More nitrogen oxides are produced (6.6 × 10⁻⁴ is higher than 4.9 × 10⁻⁴) [1 mark]
Calculation: Volume of Air
📐 Step-by-Step Calculation
Equation: 2 H₂ + O₂ → 2 H₂O
- Find the volume of Oxygen: The ratio of H₂ to O₂ is 2:1.
3.50 dm³ ÷ 2 = 1.75 dm³ of O₂ [1 mark] - Calculate the volume of Air: Air is only 20% oxygen. You need to scale up by 5 (or multiply by 100/20).
1.75 dm³ × 5 = 8.75 dm³ [1 mark] - Final Answer: 8.75 dm³ [1 mark]
🧠 Examiner Tip
Even if you get the first step wrong, you can still get "Error Carried Forward" (ECF) marks for the second step if you correctly multiply your (wrong) oxygen volume by 5.
Fractional Distillation of Kerosene
💡 Key Knowledge
Fractional distillation works because different hydrocarbons have different boiling points based on their chain length.
✅ Correct Answer
- There is a temperature gradient in the column (it is cooler at the top) [1 mark]
- Kerosene vapours rise and condense [1 mark]
- This happens at the level corresponding to kerosene's boiling point [1 mark]
🧠 Diagram Description
If asked to draw this, you would show a tall tower with crude oil entering at the bottom as a hot vapour. Kerosene would be collected as a liquid from a tray in the middle of the tower, below petrol but above diesel.
Topics
Chemistry · C3: Quantitative Chemistry · C7: Organic Chemistry · C9: Chemistry of the Atmosphere
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Higher), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.