Petrol is a fuel obtained from crude oil. Crude oil is a mixture of hydrocarbons that can be separated by fractional distillation. Petrol is mainly used as a fuel in car engines, where it undergoes complete combustion. Explain why crude oil is described as a finite resource and outline one environmental problem caused by the complete combustion of petrol.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Crude oil has been used as a major energy source since the mid-19th century. Scientists and engineers continue to search for alternative fuels to replace petrol in vehicles.
Model answer (5 marks)
Crude oil is formed over millions of years from the remains of dead organisms, mainly ancient marine organisms. It is therefore a finite resource because it is being extracted and burned faster than it can be naturally replenished. Consequently, supplies will eventually run out.
The complete combustion of petrol produces carbon dioxide (CO₂). CO₂ is a greenhouse gas that contributes to the enhanced greenhouse effect, leading to global warming and climate change.
The complete combustion of petrol produces carbon dioxide (CO₂). CO₂ is a greenhouse gas that contributes to the enhanced greenhouse effect, leading to global warming and climate change.
Examiner tips
- Use the word ‘finite’ and mention the slow natural formation; link to ‘running out’ for full marks. Mention CO₂ explicitly and its role as a greenhouse gas. Keep the answer concise and use correct terminology.
Common mistakes
- Confusing crude oil with petroleum or not specifying the slow natural formation. Failing to mention CO₂ or describing it only as a ‘gas’ without linking to global warming. Using vague terms like ‘environmental damage’ without specifying the greenhouse effect.
Mark scheme (5 marks)
- Crude oil is formed over millions of years (from the remains of dead organisms/ancient marine organisms)
- Crude oil is being used/burned faster than it is being formed/replaced
- Therefore it will eventually run out / supplies are limited
- Complete combustion of petrol produces carbon dioxide (CO₂)
- Carbon dioxide is a greenhouse gas that contributes to global warming / enhanced greenhouse effect / climate change
Key terms in this question
finite resource · fractional distillation · complete combustion · hydrocarbon
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Developing fuels questions
- A car manufacturer is comparing two fuels for use in a new engine: petrol and li…
- A renewable energy company is developing a biofuel made from fermented plant mat…
- A transport company is considering switching its lorry fleet from diesel fuel to…
- A shipping company is considering switching its large cargo vessels from using h…