34.1.3—Basicity of aq. solutions of amines

An amine is a Brønsted–Lowry base: its nitrogen lone pair accepts a proton from water, producing an alkylammonium ion and hydroxide.

The equilibrium is partial, so aqueous amines are weak bases. The position depends on how available the lone pair is and on electron-donating or withdrawing groups.

Ethylamine + H₂O ⇌ ethylammonium ion + OH⁻. The solution is alkaline even though most ethylamine molecules remain unprotonated.

A weak base is not a base that cannot react; it is one whose protonation equilibrium is incomplete.