# 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.

> OCR A-Level Chemistry B: Salters (H433) — DF Developing fuels · Explain · 5 marks

> 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.

## Mark scheme (5 marks)

1. Crude oil is formed over millions of years (from the remains of dead organisms/ancient marine organisms)
2. Crude oil is being used/burned faster than it is being formed/replaced
3. Therefore it will eventually run out / supplies are limited
4. Complete combustion of petrol produces carbon dioxide (CO₂)
5. Carbon dioxide is a greenhouse gas that contributes to global warming / enhanced greenhouse effect / climate change

## Key terms

- [finite resource](https://www.gradenine.co.uk/glossary/finite-resource)
- [fractional distillation](https://www.gradenine.co.uk/glossary/fractional-distillation)
- [complete combustion](https://www.gradenine.co.uk/glossary/complete-combustion)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/petrol-is-a-fuel-obtained-from-d03b943e) · Published by Druglandscape Ltd.