# Ethene and ethane are both hydrocarbons containing two carbon atoms. Explain why ethene is described as an unsaturated hydrocarbon and describe one chemical test that distinguishes ethene from ethane, including the expected results for each compound.

> OCR A-Level Chemistry B: Salters (H433) — 4.1 Basic concepts and hydrocarbons · Explain · 5 marks

> Alkenes such as ethene are produced during the cracking of longer-chain hydrocarbons from crude oil. Unlike the alkanes produced alongside them, alkenes have different chemical properties due to their structure.

## Mark scheme (5 marks)

1. Ethene is unsaturated because it contains a carbon–carbon double bond (C=C)
2. Ethane is saturated because it contains only single bonds / no double bonds
3. The test uses bromine water
4. Ethene decolourises / turns the bromine water from orange/brown to colourless
5. Ethane does not decolourise the bromine water / bromine water stays orange/brown with ethane

## Key terms

- [unsaturated](https://www.gradenine.co.uk/glossary/unsaturated)
- [saturated](https://www.gradenine.co.uk/glossary/saturated)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/ethene-and-ethane-are-both-hydrocarbons-9c20f953) · Published by Druglandscape Ltd.