# A student cracks decane (C₁₀H₂₂) in the laboratory. The products include octene (C₈H₁₆) and one other substance. The student tests both products with bromine water. Explain what the student would observe in each test and why, and name the other substance produced during cracking.

> AQA A-Level Chemistry (7405) — 3.3.16 Chromatography (A-Level only) · Explain · 5 marks

> Decane is a long-chain alkane that can be cracked to produce smaller, more useful molecules. One product of cracking decane is octene (C₈H₁₆).

## Mark scheme (5 marks)

1. Octene decolourises / turns bromine water from orange to colourless
2. Octene decolourises bromine water because it is unsaturated / has a carbon–carbon double bond
3. The other product does not decolourise bromine water / bromine water stays orange
4. The other product does not react with bromine water because it is an alkane / is saturated / has no double bond
5. The other substance produced is ethane (C₂H₆)

## Key terms

- [cracking](https://www.gradenine.co.uk/glossary/cracking)
- [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/a-student-cracks-decane-c-h-in-9d205a7c) · Published by Druglandscape Ltd.