AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Higher), 2019: Question 2

8 marks · High Demand difficulty · Extended Answer

Describe how oxides of nitrogen are formed in car engines and evaluate the carbon footprints of three cars using data on manufacturing and driving emissions.

Practise this question

Question

The question page is headed 'This question is about atmospheric pollutants from fuels.' Question 02.1 asks: 'Fuel burns in a car engine. Describe how oxides of nitrogen are produced in a car engine.' for 2 marks, followed by answer lines. Question 02.2 shows Table 1 comparing three cars, A, B and C, with columns for mass of CO2 produced during manufacture in kg, mass of CO2 produced when driving in kg per km, total mass of CO2 from manufacture plus 40 000 km driving, and total mass of CO2 from manufacture plus 100 000 km driving; the values are A: 14 000, 0.123, 18 920, 26 300; B: 20 000, 0.085, 23 400, 28 500; C: 23 000, 0.044, 24 760, 27 400. Beneath the table the student is asked to 'Evaluate the carbon footprint of the cars. Use information from Table 1.' for 6 marks, with extended writing lines below.
Question text

02 This question is about atmospheric pollutants from fuels.

02.1 Fuel burns in a car engine.

Describe how oxides of nitrogen are produced in a car engine.

[2 marks]

02.2 Table 1 shows the carbon footprint during the manufacture and use of three cars.

Table 1

Mass of CO2 Mass of CO2 Total mass of CO2 Total mass of CO2

Car produced during produced when produced from produced from

manufacture in kg driving manufacture and manufacture and

in kg per km 40 000 km driving 100 000 km

in kg driving in kg

Car A 14 000 0.123 18 920 26 300

Car B 20 000 0.085 23 400 28 500

Car C 23 000 0.044 24 760 27 400

Evaluate the carbon footprint of the cars.

Use information from Table 1.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme states for question 02.1 that one mark is awarded for noting the high temperatures in the engine and one mark for stating that oxygen and nitrogen from the air react or combine; the AO/specification reference shown is AO1 5.9.3.1. For question 02.2, a level-of-response scheme is shown: Level 3 earns 5–6 marks for a clear judgement supported by a sufficient range of logically linked reasons, Level 2 earns 3–4 marks for some linked reasons and possibly a simple judgement, and Level 1 earns 1–2 marks for relevant but unlinked points. Indicative content includes that car C has the highest manufacturing CO2, car A has the highest CO2 per km, car C has the highest total after 40 000 km, car B the highest after 100 000 km, and example judgements that car A has the smallest overall carbon footprint at the stated distances but may eventually have the largest after about 157 895 km because its emissions per kilometre are highest.

AO /

Question Answers Extra information Mark ID

Spec. Ref.

02.1 high temperatures (in the 1 AO1 E

engine) 5.9.3.1

enable oxygen and nitrogen allow combine / bond for react 1

(from air) to react

02.2 E

Level 3: A judgement, strongly linked and logically supported by 5‒6

a sufficient range of correct reasons, is given.

Level 2: Some logically linked reasons are given. There may

also be a simple judgement. 3‒4

Level 1: Relevant points are made. They are not logically

linked. 1–2

No relevant content 0

Indicative content

Examples of relevant points might include:

• car C produces the most CO2 during manufacture

• car A produces the most CO2 per km when driving

• car C produces the most CO2 from manufacture and

40,000km when driving

• car B produces the most CO2 from manufacture and

100,000km when driving

Examples of linked statements might include:

• car A produces least CO2 during manufacture, but most CO2

per km AO3

• car C produces most CO during manufacture, but least CO 5.9.2.2

5.9.2.45.10.2.1

per km

• car A produces least CO2 during manufacture, but car C

produces the least CO2 per km

Examples of judgements might include:

• overall car A has the smallest carbon footprint as it has the

smallest CO2 production during manufacture, the smallest

mass of CO2 after 40,000km of driving and the smallest

mass of CO2 produced after 100,000km of driving.

• car A eventually (after 157,895km) will have the largest

carbon footprint because the mass of carbon dioxide

produced per km is highest.

Total 8

How to answer it

Atmospheric Pollutants from Fuels – Carbon Footprint of Cars

What this question tests

You need to explain how nitrogen oxides form in hot car engines, then compare data from a table to make a clear judgement about which car has the smallest or largest carbon footprint. Credit is given for using numbers accurately, comparing the correct columns, and reaching a supported conclusion.

Question overview

Part (a) is a short recall question on how oxides of nitrogen form in engines.
Part (b) is a 6-mark evaluation using Table 1 to compare carbon dioxide emissions from manufacture and driving.

Part (a): Describe how oxides of nitrogen are produced in a car engine. [2 marks]

✅ Correct answer

High temperatures in the engine cause nitrogen and oxygen from the air to react, producing oxides of nitrogen.

Mark points:
1. high temperatures in the engine
2. nitrogen and oxygen from air react / combine / bond

💡 Key knowledge

  • Air contains nitrogen and oxygen.
  • In a hot engine, these gases can react even though nitrogen is usually unreactive.
  • The pollutant formed is called nitrogen oxides or NOₓ.

🧠 Exam technique

  • Use the word high temperature — this is the key trigger for the reaction.
  • State that the gases come from air.
  • To gain both marks, mention both the condition and the reactants.

❌ Common errors

  • Saying only “fuel burns and makes nitrogen oxides” without explaining how.
  • Forgetting that the nitrogen comes from the air, not the fuel.
  • Writing “nitrogen reacts with carbon” — this is incorrect.

Part (b): Evaluate the carbon footprint of the cars. Use information from Table 1. [6 marks]

💡 Key knowledge from the table

  • Car A has the lowest manufacture CO₂: 14 000 kg.
  • Car C has the highest manufacture CO₂: 23 000 kg.
  • Car A has the highest CO₂ per km while driving: 0.123 kg per km.
  • Car C has the lowest CO₂ per km while driving: 0.044 kg per km.
  • After 40 000 km, the total CO₂ is lowest for Car A: 18 920 kg.
  • After 100 000 km, the total CO₂ is lowest for Car A: 26 300 kg.
  • At both distances given, Car A has the smallest overall carbon footprint.

✅ Strong evaluation points

  • Car A produces the least CO₂ during manufacture.
  • Car C produces the most CO₂ during manufacture.
  • Car A produces the most CO₂ per km when driving.
  • Car C produces the least CO₂ per km when driving.
  • Overall, Car A has the smallest carbon footprint at both 40 000 km and 100 000 km.

📐 Calculations / checking the table

You are not required to calculate the values in the table, but you can use the totals to support your judgement.

  1. At 40 000 km: compare totals
    Car A = 18 920 kg
    Car B = 23 400 kg
    Car C = 24 760 kg
  2. At 100 000 km: compare totals
    Car A = 26 300 kg
    Car B = 28 500 kg
    Car C = 27 400 kg
  3. Conclusion: Car A is lowest in both cases, so it has the smallest carbon footprint in the distances shown.

Units matter: manufacture values are in kg, driving values are in kg per km, totals are in kg.

🧠 Exam technique

  • Make sure your answer is comparative: “higher than”, “lower than”, “least”, “most”.
  • Use the table data directly to back up each point.
  • For top marks, give a clear judgement, not just a list of facts.
  • The best answers link the two parts of the footprint:
    manufacture + driving = total carbon footprint

❌ Common errors

  • Only describing one column, such as manufacture, and ignoring driving.
  • Saying the car with the lowest manufacture CO₂ is always best, without checking total footprint.
  • Mixing up which car has the highest or lowest value.
  • Not giving any numbers from the table.
  • Writing vague comments like “Car A is good” instead of a scientific judgement.

How marks are awarded here

This is a level-marked 6-marker. To reach the top level, you need a clear judgement that is strongly linked to several correct reasons from the table. A high-level response will compare at least two cars, use data accurately, and end with a supported conclusion.

✅ Example 6-mark answer

Car A has the smallest carbon footprint overall in the distances shown. It produces the least CO₂ during manufacture at 14 000 kg, compared with 20 000 kg for Car B and 23 000 kg for Car C. Car A also gives the highest CO₂ per km when driving, at 0.123 kg per km, but its total CO₂ is still the lowest at both 40 000 km and 100 000 km. At 40 000 km Car A produces 18 920 kg, which is less than Car B at 23 400 kg and Car C at 24 760 kg. At 100 000 km Car A still has the lowest total at 26 300 kg, compared with 28 500 kg for Car B and 27 400 kg for Car C. Therefore Car A has the smallest carbon footprint overall.

❌ Big trap to avoid

Do not say “Car C is best because it has the lowest CO₂ per km” without checking the full totals. The question asks you to evaluate the carbon footprint, so you must consider both manufacture and use.

Key exam takeaways

💡 Remember

  • Hot engines can cause nitrogen and oxygen from air to react.
  • Carbon footprint includes emissions from manufacture and use.

🧠 For comparison questions

  • Use the data.
  • Compare all relevant values.
  • End with a judgement.

✅ Best final judgement for this data

Car A has the smallest carbon footprint in the table because it has the lowest manufacture CO₂ and the lowest total CO₂ after both 40 000 km and 100 000 km.

Topics

Chemistry · C9: Chemistry of the Atmosphere

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Higher), 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.