Chemistry – Acids, bases and salts - Oxides | e-Consult

Amphoteric oxides react with acids to form a salt and water, behaving as weak acids. They also react with bases to form a salt and water, behaving as weak bases. This dual behaviour is due to the presence of metal ions within the oxide that can accept or donate protons depending on the reaction conditions. The metal ions in amphoteric oxides are typically in higher oxidation states, making them less likely to readily donate protons (like strong acids) or accept protons (like strong bases).

Amphoteric oxides are not considered strong acids or strong bases because their reactivity with both acids and bases is relatively weak. They do not completely donate or accept protons, but rather react to a point where a salt and water are formed.

An example of an amphoteric oxide is zinc oxide (ZnO).

Reaction with a strong base (e.g., NaOH):

ZnO(s) + 2NaOH(aq) + H₂O(l) → Na₂[Zn(OH)₄](aq)

In this reaction, the oxide ions (O^2-) in the zinc oxide react with the protons (H⁺) from the strong base (NaOH) to form the tetrahydroxozincate(II) ion, [Zn(OH)₄]^2-. This demonstrates the basic behaviour of zinc oxide.