# Methane, ethane, propane and butane are the first four members of the alkane homologous series. Explain why alkanes are described as 'saturated hydrocarbons' and describe how the boiling points of alkanes change as the number of carbon atoms in the molecule increases, giving a reason for this trend.

> Edexcel A-Level Chemistry (9CH0) — 6.2 Alkanes · Explain · 5 marks

> Alkanes are widely used as fuels. Methane (CH₄) is the main component of natural gas, ethane (C₂H₆) is found in LPG alongside propane (C₃H₈), and butane (C₄H₁₀) is used in portable camping stoves.

## Mark scheme (5 marks)

1. Alkanes are described as 'saturated' because they contain only single (C–C) bonds / no double bonds between carbon atoms
2. Alkanes are hydrocarbons because they contain hydrogen and carbon only / no other elements
3. As the number of carbon atoms increases, the boiling point increases / longer chain alkanes have higher boiling points
4. Larger molecules have stronger intermolecular forces / greater van der Waals forces between molecules
5. More energy is therefore needed to overcome these stronger intermolecular forces, so the boiling point is higher

## Key terms

- [saturated](https://www.gradenine.co.uk/glossary/saturated)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)
- [boiling point](https://www.gradenine.co.uk/glossary/boiling-point)
- [homologous series](https://www.gradenine.co.uk/glossary/homologous-series)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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/methane-ethane-propane-and-butane-are-7733728a) · Published by Druglandscape Ltd.