Methylamine (CH₃NH₂) can be prepared by the reaction of ammonia with halogenoalkanes. Explain why methylamine is a stronger base than ammonia, and describe what is observed and the type of salt formed when methylamine reacts with dilute hydrochloric acid.

Edexcel A-Level Chemistry (9CH0) — 18.2 Amines, amides and amino acids · Explain · 5 marks · View as Markdown

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

Methylamine (CH₃NH₂) is a primary amine that is a gas at room temperature. It has a pungent smell and is soluble in water.

Model answer (5 marks)

Methylamine is a stronger base than ammonia because the methyl group is electron‑donating; the alkyl group donates electron density towards the nitrogen. This increased electron density on nitrogen makes the lone pair more available and more readily donated to a proton.

When methylamine reacts with dilute hydrochloric acid, it dissolves and reacts to give a colourless solution – no visible precipitate is formed. The nitrogen is protonated to give the positively charged ammonium ion, and the chloride ion remains as the counter‑ion. The product is the ammonium salt methylammonium chloride (CH₃NH₃⁺Cl⁻).

Examiner tips

  • Use the term ‘electron‑donating alkyl group’ to explain the basicity difference. Show that the reaction is a protonation to give an ammonium salt. Mention that the solution remains clear – no precipitate.
  • Use the exact formula CH₃NH₃⁺Cl⁻ and note it is an ammonium salt.

Common mistakes

  • Saying the reaction gives a precipitate or a coloured solution. Confusing the product as a neutral amide rather than an ammonium salt. Using ‘electron‑withdrawing’ instead of ‘electron‑donating’ to explain the basicity.

Mark scheme (5 marks)

  1. Methylamine is a stronger base than ammonia because the methyl group is electron-donating / alkyl groups donate electron density towards the nitrogen
  2. This increased electron density on nitrogen makes the lone pair more available / more readily donated to a proton
  3. Methylamine dissolves / reacts with hydrochloric acid to form a solution (no visible precipitate / colourless solution formed OR the gas fumes / white fumes observed if gas-phase HCl is used)
  4. The product is methylammonium chloride (CH₃NH₃⁺Cl⁻)
  5. The product is an ammonium salt / the nitrogen is protonated to form a positively charged ammonium ion

Key terms in this question

base

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