Question

Give reasons for the following:

Aluminum oxide is amphoteric

Answer 1

Amphoteric oxide:

• Amphoteric oxides are metallic oxides that can react with both acids and bases to form salt and water.
• It exhibits acidic as well as basic characteristics.
• Metals like zinc, tin, lead, aluminum, etc form amphoteric oxides.

Amphoteric nature of aluminum oxide:

• Aluminium oxide exhibits both acidic and basic behavior and has amphoteric nature.

1. Acidic characteristics of aluminum oxide:

$\underset{\mathrm{Aluminium}\mathrm{oxide}}{{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{6\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Aluminium}\mathrm{chloride}}{2{\mathrm{AlCl}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{water}}{3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

In this reaction, aluminum oxide behaves as basic because it reacts with an acid to form salt and water.

ii. Basic characteristics of aluminum oxide:

$\underset{\mathrm{Aluminium}\mathrm{oxide}}{{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{alumininate}}{2{\mathrm{NaAlO}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

In this reaction, aluminum oxide behaves as acidic as it reacts with a base to form salt and water.