# Pentane and pentene are both organic compounds containing five carbon atoms. State the molecular formula of pentane and explain why pentane and pentene are not members of the same homologous series.

> Cambridge International IGCSE Chemistry (0620) — 11.1 Formulae, functional groups and terminology · State and Explain · 4 marks

## Mark scheme (4 marks)

1. Correct molecular formula of pentane: C₅H₁₂
2. A homologous series has the same general formula / same functional group
3. Pentane contains only C–C single bonds / is saturated, whereas pentene contains a C=C double bond / is unsaturated
4. Pentane and pentene have different general formulae (CₙH₂ₙ₊₂ vs CₙH₂ₙ) so they belong to different homologous series (alkanes vs alkenes)

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "State and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/pentane-and-pentene-are-both-organic-ae12ba28) · Published by Druglandscape Ltd.