# Crude oil is a mixture of hydrocarbons. Explain why crude oil is separated into fractions by fractional distillation, and describe how the process works.

> Eduqas GCSE Chemistry — C7 Organic chemistry · Explain · 4 marks

> Crude oil is found trapped in rock beneath the Earth's surface. It is a complex mixture and must be processed before it can be used as fuels and raw materials.

## Mark scheme (4 marks)

1. Different hydrocarbons in crude oil have different boiling points (so they cannot be used directly as the mixture)
2. The crude oil is heated and vaporised / turned into a gas
3. The vapour rises up a fractionating column where there is a temperature gradient (hotter at the bottom, cooler at the top)
4. Hydrocarbons condense / turn back into liquids at different levels and are collected as separate fractions

## Key terms

- [hydrocarbons](https://www.gradenine.co.uk/glossary/hydrocarbons)
- [fractional distillation](https://www.gradenine.co.uk/glossary/fractional-distillation)
- [fractions](https://www.gradenine.co.uk/glossary/fractions)

## Related

- [Revision notes for Eduqas GCSE Chemistry](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/crude-oil-is-a-mixture-of-c2ea0ec5) · Published by Druglandscape Ltd.