Amphoteric oxides and hydroxides share the property of being able to behave as acids. An amphoteric oxide is one that can act as either an acid or a base. Generally, non-metallic oxides are acidic and metallic oxides are basic. Metallic oxides, which show the basic as well as acidic nature, are known as amphoteric oxides. Elements that form amphoteric oxides have some characteristics of metals and some of the non-metals.
Amphoteric oxides react with both acids and alkalis to form salt and water. Examples of amphoteric oxides are zinc oxide and aluminum oxide.
ZnO(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l)
ZnO(s) + 2NaOH(a) → Na2ZnO2(aq) + H2O(l)
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l)