# Crude oil is separated into fractions by fractional distillation. Explain why different fractions are collected at different heights in the fractionating column.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 4.2 Crude oil · Explain · 4 marks

> Petrol, kerosene, diesel and bitumen are among the fractions obtained from crude oil. Petrol is collected near the top of the fractionating column, whilst bitumen is collected at the bottom.

## Mark scheme (4 marks)

1. Crude oil is heated and the mixture of hydrocarbons vaporises / rises up the column
2. The column has a temperature gradient — it is hotter at the bottom and cooler at the top
3. Fractions with higher boiling points condense lower down / fractions with lower boiling points rise higher before condensing
4. Longer-chain hydrocarbons have higher boiling points so condense lower down; shorter-chain hydrocarbons have lower boiling points so condense higher up

## Key terms

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

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- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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