# But-1-ene (C₄H₈) is an alkene. Explain why but-1-ene is classified as an alkene, describe the general formula that links all members of the alkene homologous series, and explain how you could confirm that but-1-ene is unsaturated using a chemical test. Include the expected result of the test.

> Edexcel A-Level Chemistry (9CH0) — 6.3 Alkenes · Explain · 5 marks

> But-1-ene is a colourless gas used in the manufacture of synthetic rubber. Its molecular formula is C₄H₈.

## Mark scheme (5 marks)

1. But-1-ene contains a carbon-to-carbon double bond (C=C)
2. But-1-ene is unsaturated (because of the C=C double bond)
3. The general formula of alkenes is CₙH₂ₙ (which C₄H₈ fits)
4. Add bromine water to but-1-ene
5. Bromine water decolourises / turns from orange-brown to colourless

## Key terms

- [alkene](https://www.gradenine.co.uk/glossary/alkene)
- [unsaturated](https://www.gradenine.co.uk/glossary/unsaturated)
- [general formula](https://www.gradenine.co.uk/glossary/general-formula)
- [homologous series](https://www.gradenine.co.uk/glossary/homologous-series)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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/but-1-ene-c-h-is-an-alkene-explain-4fd47e70) · Published by Druglandscape Ltd.