In chemistry, an amphoteric compound (from Greek amphoteros 'both') is a molecule or ion that can react both as an acid and as a base.
Related words in acid-base chemistry are amphichromatic and amphichroic, both describing substances such as acid-base indicators which give one colour on reaction with an acid and another colour on reaction with a base.
[2] Amphiprotism is exhibited by compounds with both Brønsted acidic and basic properties.
Often such species exists as several structures in chemical equilibrium: In approximately neutral aqueous solution (pH ≅ 7), the basic amino group is mostly protonated and the carboxylic acid is mostly deprotonated, so that the predominant species is the zwitterion H3N+−RCH−COO−.
Many metals (such as zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides.
[6] An amphiprotic molecule (or ion) can either donate or accept a proton, thus acting either as an acid or a base.
The bicarbonate ion, HCO−3, is amphoteric as it can act as either an acid or a base: Note: in dilute aqueous solution the formation of the hydronium ion, H3O+(aq), is effectively complete, so that hydration of the proton can be ignored in relation to the equilibria.