1-bromopropane can be converted into propan-1-ol. Describe what happens when 1-bromopropane is reacted with aqueous sodium hydroxide solution, and explain why bromine forms a precipitate when silver nitrate solution is added to the reaction mixture after the reaction is complete.

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).

Model answer (5 marks)

1-bromopropane is heated with aqueous NaOH.
The C–Br bond is broken and the Br⁻ ion is displaced – a nucleophilic substitution (S_N2) occurs.
Propan-1-ol is produced.
After the reaction, Br⁻ ions remain in solution.
Adding AgNO₃ gives a cream/pale yellow precipitate of AgBr.

Examiner tips

  • Use the word "heated" to show the reaction conditions. Mention "S_N2" to justify the mechanism. State that Ag⁺ reacts with Br⁻ to give AgBr, the colour of the precipitate.

Common mistakes

  • Failing to mention the substitution mechanism. Not specifying that AgBr is the precipitate. Using the wrong colour description (e.g. blue instead of cream).

Mark scheme (5 marks)

  1. 1-bromopropane is heated with aqueous sodium hydroxide solution
  2. The C–Br bond is broken / the bromine is displaced / substitution reaction occurs
  3. Propan-1-ol is formed as the product of the reaction
  4. Bromide ions are present in solution after the reaction
  5. Silver nitrate reacts with bromide ions to form a cream/pale yellow precipitate of silver bromide

Key terms in this question

precipitate · aqueous sodium hydroxide

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