An amphoteric oxide is one that can act as a base or as an acid. The non-metallic oxides are generally acidic and the metallic oxides are basic. Metallic oxides are known as amphoteric oxides which display both the basic and acidic nature. Elements that form amphoteric oxides have some metals and some of the non-metals characteristics. Amphoterism is based upon an oxide’s oxidation state. This oxide reacts with base and acid to produce salt and water as the main products.
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)