Bromoethane can be converted into ethanol by reacting it with aqueous sodium hydroxide solution. Describe and explain what happens during this reaction, including the type of reaction taking place and the role of the aqueous sodium hydroxide solution.

AQA A-Level Chemistry (7405) — 3.3.3 Halogenoalkanes · Describe and explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Bromoethane is a halogenoalkane with the molecular formula C₂H₅Br. When it is warmed with aqueous sodium hydroxide solution, ethanol is produced.

Model answer (5 marks)

Bromoethane undergoes hydrolysis.
The C–Br bond is broken.
The hydroxide ion (OH⁻) substitutes the bromine atom.
Aqueous sodium hydroxide provides the OH⁻ ion that replaces Br.
Ethanol is the organic product formed.

Examiner tips

  • Use the word "hydrolysis" to show the reaction type. Show the bond breaking and substitution clearly. Mention that NaOH supplies OH⁻. State the product as ethanol.

Common mistakes

  • Saying the reaction is "nucleophilic substitution" without linking it to hydrolysis. Forgetting to mention that NaOH supplies the OH⁻ ion. Calling the product "ethanol" but not explaining the bond change.

Mark scheme (5 marks)

  1. Bromoethane undergoes hydrolysis
  2. The C–Br bond breaks / is broken
  3. The hydroxide ion (OH⁻) replaces / substitutes the bromine atom (Br)
  4. The aqueous sodium hydroxide acts as a source of hydroxide ions (OH⁻) / provides the OH⁻ ion that replaces the bromine
  5. Ethanol is the organic product formed

Key terms in this question

aqueous sodium hydroxide

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