# Explain why cracking is used in the petrochemical industry to produce alkenes, and describe how bromine water can be used to distinguish an alkene product from an alkane product.

> AQA A-Level Chemistry (7405) — 3.3.15 NMR spectroscopy (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Large/long-chain hydrocarbons are broken down into smaller/more useful molecules
2. Alkenes are produced (from cracking) and are used to make polymers / other chemicals
3. Shorter-chain products are more flammable / better fuels than longer-chain hydrocarbons
4. Bromine water turns from orange to colourless with an alkene
5. Bromine water remains orange / does not change colour with an alkane

## Key terms

- [cracking](https://www.gradenine.co.uk/glossary/cracking)
- [alkenes](https://www.gradenine.co.uk/glossary/alkenes)
- [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 "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/explain-why-cracking-is-used-in-6c418660) · Published by Druglandscape Ltd.