# Alkanes are described as saturated hydrocarbons. Explain what this means and describe how the boiling point and flammability of alkanes change as the length of the carbon chain increases. Use your knowledge of alkane properties to explain why shorter-chain alkanes make better fuels.

> AQA A-Level Chemistry (7405) — 3.3.2 Alkanes · Explain · 5 marks

## Mark scheme (5 marks)

1. Alkanes contain hydrogen and carbon atoms only (are hydrocarbons)
2. Saturated means alkanes have no carbon–carbon double bonds (all single C–C bonds)
3. As the carbon chain gets longer, the boiling point increases
4. As the carbon chain gets longer, the alkane becomes less flammable (shorter chains are more flammable)
5. Shorter-chain alkanes make better fuels because they are more flammable / ignite more easily / have a lower boiling point so vaporise more readily

## Key terms

- [saturated](https://www.gradenine.co.uk/glossary/saturated)
- [hydrocarbons](https://www.gradenine.co.uk/glossary/hydrocarbons)
- [alkanes](https://www.gradenine.co.uk/glossary/alkanes)
- [boiling point](https://www.gradenine.co.uk/glossary/boiling-point)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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/alkanes-are-described-as-saturated-hydrocarbons-1e83837b) · Published by Druglandscape Ltd.