# Petroleum is a mixture of hydrocarbons that is separated into fractions by fractional distillation. Explain how fractional distillation separates petroleum into fractions, and state one use of the fraction that contains the shortest hydrocarbon molecules.

> Cambridge International IGCSE Chemistry (0620) — 11.3 Fuels · Explain · 4 marks

## Mark scheme (4 marks)

1. Petroleum is heated / vaporised and the vapours enter the fractionating column
2. The column has a temperature gradient — hotter at the bottom and cooler at the top
3. Hydrocarbons condense / are collected at the level where the temperature equals their boiling point; shorter-chain / smaller hydrocarbons have lower boiling points and condense / collect higher up the column
4. The fraction with the shortest molecules is used as a fuel for cooking / heating / LPG / refinery gas / Calor gas (accept: used as a fuel in general if shortest-chain fraction is correctly identified as refinery/LPG gas)

## Key terms

- [petroleum](https://www.gradenine.co.uk/glossary/petroleum)
- [fractional distillation](https://www.gradenine.co.uk/glossary/fractional-distillation)
- [fraction](https://www.gradenine.co.uk/glossary/fraction)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](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/petroleum-is-a-mixture-of-hydrocarbons-7dab933d) · Published by Druglandscape Ltd.