# Crude oil contains hydrocarbons with different chain lengths. As the length of the hydrocarbon chain increases, the properties of the hydrocarbons change. Describe how the following properties change as the chain length of a hydrocarbon increases, and explain why each property changes in the way it does: (i) boiling point and (ii) viscosity.

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

## Mark scheme (4 marks)

1. Boiling point increases as chain length increases
2. Longer chains have stronger intermolecular forces / more points of contact between molecules, so more energy is needed to separate them
3. Viscosity increases as chain length increases / longer chain hydrocarbons flow less easily
4. Longer chains become more entangled with each other / stronger intermolecular forces between longer chains resist flow

## Key terms

- [hydrocarbons](https://www.gradenine.co.uk/glossary/hydrocarbons)
- [boiling point](https://www.gradenine.co.uk/glossary/boiling-point)
- [viscosity](https://www.gradenine.co.uk/glossary/viscosity)
- [chain length](https://www.gradenine.co.uk/glossary/chain-length)

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/crude-oil-contains-hydrocarbons-with-different-b88859cc) · Published by Druglandscape Ltd.