# Halogenoalkanes can be hydrolysed when heated with aqueous sodium hydroxide solution. A student investigates the hydrolysis of 1-fluorobutane, 1-bromobutane and 1-iodobutane under the same conditions. Explain why the rate of hydrolysis differs between these three compounds, and predict which compound hydrolyses fastest.

> Edexcel A-Level Chemistry (9CH0) — 6.4 Halogenoalkanes · Explain · 5 marks

> Halogenoalkanes undergo hydrolysis when warmed with aqueous sodium hydroxide solution. The carbon–halogen bond must break for the reaction to proceed. Bond enthalpies for C–F, C–Cl, C–Br and C–I bonds decrease in that order down Group 7.

## Mark scheme (5 marks)

1. The rate of hydrolysis depends on the strength (bond enthalpy) of the carbon–halogen bond
2. Going down Group 7 from fluorine to iodine, the carbon–halogen bond becomes weaker / bond enthalpy decreases
3. A weaker bond requires less energy to break, so the carbon–halogen bond breaks more easily
4. Therefore 1-iodobutane hydrolyses fastest because it has the weakest C–halogen bond
5. 1-fluorobutane hydrolyses slowest because it has the strongest C–halogen bond / C–F bond has the highest bond enthalpy

## Key terms

- [halogenoalkane](https://www.gradenine.co.uk/glossary/halogenoalkane)
- [hydrolysis](https://www.gradenine.co.uk/glossary/hydrolysis)

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/halogenoalkanes-can-be-hydrolysed-when-heated-6b685dea) · Published by Druglandscape Ltd.