# Alkanes and alkenes are both hydrocarbons produced during cracking. Describe how bromine water can be used to distinguish between an alkane and an alkene, and explain why the two types of hydrocarbon give different results in this test.

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

## Mark scheme (5 marks)

1. Add bromine water to each hydrocarbon (sample)
2. The alkene decolourises / turns the bromine water from orange to colourless
3. The alkane does not decolourise / does not change the colour of bromine water (stays orange)
4. Alkenes are unsaturated / have a carbon–carbon double bond
5. The double bond makes alkenes more reactive than alkanes (so alkenes react with bromine / alkanes do not react with bromine water)

## Key terms

- [alkane](https://www.gradenine.co.uk/glossary/alkane)
- [alkene](https://www.gradenine.co.uk/glossary/alkene)
- [bromine water](https://www.gradenine.co.uk/glossary/bromine-water)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-and-alkenes-are-both-hydrocarbons-2e83cb08) · Published by Druglandscape Ltd.