# Crude oil is a mixture of hydrocarbons. When a hydrocarbon burns in a limited supply of air, incomplete combustion occurs. Explain why incomplete combustion is considered more dangerous than complete combustion, and state the products formed during each type of combustion of a hydrocarbon.

> WJEC A-Level Chemistry (Wales) — 3.2 Hydrocarbons · Explain · 5 marks

> Crude oil is separated into fractions at an oil refinery. Many of these fractions are used as fuels in homes and vehicles.

## Mark scheme (5 marks)

1. Complete combustion produces carbon dioxide (and water)
2. Incomplete combustion produces carbon monoxide (and water)
3. Incomplete combustion also produces carbon (soot) / unburned particles
4. Carbon monoxide is toxic / poisonous
5. Carbon monoxide is colourless and odourless so cannot be detected by smell / sight, making it more dangerous

## Key terms

- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)
- [complete combustion](https://www.gradenine.co.uk/glossary/complete-combustion)
- [incomplete combustion](https://www.gradenine.co.uk/glossary/incomplete-combustion)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/crude-oil-is-a-mixture-of-ef29ed65) · Published by Druglandscape Ltd.