# Octane (C₈H₁₈) is an alkane found in petrol. When octane burns in a limited supply of air, incomplete combustion occurs. Explain why incomplete combustion is considered more dangerous than complete combustion, and describe the products formed in each type of combustion.

> Edexcel A-Level Chemistry (9CH0) — 6.2 Alkanes · Explain · 5 marks

> Petrol engines in cars burn octane, an alkane with the molecular formula C₈H₁₈. The amount of air reaching the engine affects the type of combustion that takes place.

## Mark scheme (5 marks)

1. Complete combustion produces carbon dioxide and water (only)
2. Incomplete combustion produces carbon monoxide (and/or carbon/soot) and water
3. Carbon monoxide is toxic / poisonous
4. Carbon monoxide is colourless and odourless / difficult to detect, making it dangerous
5. Carbon monoxide prevents the blood from carrying oxygen / reduces oxygen transport in the blood

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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/octane-c-h-is-an-alkane-found-c006dc4f) · Published by Druglandscape Ltd.