Question

Why is $\mathrm{ZnO}$ called an amphoteric oxide? Name the other amphoteric oxide.

Answer 1

Metal oxides are basic in nature, and they produce salts when they react with acids. Amphoteric oxides, on the other hand, produce salts when they react with acids and alkalis.

Example: Aluminium oxide (${\mathrm{Al}}_2{\mathrm{O}}_3$).

Zinc oxide $\mathrm{ZnO}$ is known as amphoteric oxide because it can react with both an Acid ($\mathrm{HCl}$) and a Base ($\mathrm{NaOH}$) and forms the respective salts.

$\underset{\mathrm{Zinc}\mathrm{oxide}}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{\underset{\mathrm{acid}}{\mathrm{Hydrochloric}}}{2\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Zinc}\mathrm{chloride}}{{\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}\left(\mathrm{l}\right)$

$\underset{\mathrm{Zinc}\mathrm{oxide}}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{\underset{\mathrm{hydroxide}}{\mathrm{Sodium}}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{zincate}}{{\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}\left(\mathrm{l}\right)$