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

> AQA A-Level Chemistry (7405) — 3.3.1 Introduction to organic chemistry · Describe · 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 the bromine water / bromine water stays orange with the alkane
4. Alkenes have a carbon-carbon double bond, making them unsaturated
5. The double bond makes alkenes more reactive than alkanes (so they react with bromine water whereas alkanes do not)

## Key terms

- [alkene](https://www.gradenine.co.uk/glossary/alkene)
- [alkane](https://www.gradenine.co.uk/glossary/alkane)
- [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" 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/alkenes-and-alkanes-are-both-hydrocarbons-899a7975) · Published by Druglandscape Ltd.