Question

"Aluminium oxide is an amphoteric oxide." Justify this statement giving chemical equation for the reactions involved.

Answer 1

Amphoteric Oxide – Aluminium Oxide (Al₂O₃)

Definition: An amphoteric oxide is an oxide that reacts with both acids and bases to form salt and water.

Example: Aluminium oxide (Al₂O₃)

1. Reaction with Acid (HCl)

When aluminium oxide reacts with hydrochloric acid, it behaves as a basic oxide:

Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l)

Here, a salt (aluminium chloride) and water are formed.

2. Reaction with Base (NaOH)

When aluminium oxide reacts with sodium hydroxide, it behaves as an acidic oxide:

Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2Na[Al(OH)₄](aq)

or simply:

Al₂O₃(s) + 2NaOH(aq) → 2NaAlO₂(aq) + H₂O(l)

In both reactions, a salt and water are produced.

Conclusion:

Since aluminium oxide reacts with both acids and bases to form salt and water, it is classified as an amphoteric oxide.

General form: Al₂O₃ + HCl/NaOH → salt + H₂O