# Alkanes and alkenes are both hydrocarbons. Explain how bromine water can be used to distinguish between an alkane and an alkene, and explain why they react differently with bromine water.

> Eduqas A-Level Chemistry — 2.5 Hydrocarbons · Explain · 5 marks

> A student has two unlabelled test tubes, one containing hexane and one containing hexene. She adds bromine water to each sample.

## Mark scheme (5 marks)

1. The alkene decolourises / decolorises the bromine water (from orange/brown to colourless)
2. The alkane does not decolourise / does not react with bromine water (stays orange/brown)
3. Alkenes contain a carbon–carbon double bond (C=C)
4. The double bond in the alkene allows an addition reaction to occur with bromine
5. Alkanes are saturated (contain only C–C single bonds) so they cannot undergo addition reactions 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 Eduqas A-Level Chemistry](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-and-alkenes-are-both-hydrocarbons-1ca9cc7c) · Published by Druglandscape Ltd.