Ethylamine (C₂H₅NH₂) is an amine that reacts with water to form an alkaline solution. Explain why ethylamine is classified as an amine and why its aqueous solution is alkaline.

Eduqas A-Level Chemistry — 4.6 Amines · Explain · 5 marks · View as Markdown

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

Ethylamine is a colourless gas at room temperature with a pungent smell. It is produced industrially and dissolves readily in water.

Model answer (5 marks)

Ethylamine contains a nitrogen atom bonded to carbon atoms, giving it the structure R–NH₂ where R is an ethyl group. The nitrogen has a lone pair of electrons, so it can accept a proton and is therefore a base. Ethylamine is a derivative of ammonia, with one H atom replaced by an ethyl group. When it dissolves in water it accepts a proton from water:

R–NH₂ + H₂O → R–NH₃⁺ + OH⁻

The production of hydroxide ions makes the solution alkaline.

Examiner tips

  • Use the phrase ‘contains a nitrogen atom bonded to carbon’ to show structure.
  • Mention the lone pair and proton‑accepting ability to justify basicity.
  • Show the acid–base reaction with water and the formation of OH⁻.
  • Keep the answer concise – 5 marks, no extra explanation.

Mark scheme (5 marks)

  1. Ethylamine contains a nitrogen atom (bonded to carbon / as part of the molecule)
  2. The nitrogen atom has a lone pair of electrons / can accept a proton
  3. Ethylamine is derived from / related to ammonia, where a hydrogen atom is replaced by a carbon-containing (alkyl) group
  4. Ethylamine reacts with water and accepts a proton (H⁺) from water / acts as a base
  5. This produces hydroxide ions (OH⁻) in solution, making it alkaline

Key terms in this question

amine · alkaline

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