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 can react with both acids and bases, producing a salt and water.

Example: Aluminium oxide (Al₂O₃)

1. Reaction with Acid (HCl)

When aluminium oxide interacts with hydrochloric acid, it acts as a basic oxide:

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

This reaction creates a salt (aluminium chloride) and water.

2. Reaction with Base (NaOH)

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

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

or alternatively:

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

Both of these reactions generate a salt and water.

Conclusion:

Because aluminium oxide reacts with both acids and bases to yield a salt and water, it is considered an amphoteric oxide.

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