Question

Identify the amphoteric oxide from the following?

• A. Aluminium oxide (${\mathrm{Al}}_2{\mathrm{O}}_3$)
• B. Sulphur dioxide (${\mathrm{SO}}_2$)
• C. Phosphorous pentaoxide (${\mathrm{P}}_2{\mathrm{O}}_5$)
• D. Calcium oxide ($\mathrm{CaO}$)

Answer 1

The correct option is A

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

The explanation for the correct answer:

Option (A) Aluminum oxide (${\mathbf{Al}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}$)

1. Amphoteric oxides react with both acids and alkalis to form salt and water.
2. Aluminium oxides react with both acids and bases, So it is considered amphoteric oxides.
3. The reaction of aluminum oxides with acids: $\underset{\mathrm{Aluminum}\mathrm{Oxide}}{2{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{6\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Aluminum}\mathrm{Chloride}}{2{\mathrm{AlCl}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$.
4. The reaction of aluminum oxides with bases: $\underset{\mathrm{Aluminum}\mathrm{Oxide}}{{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{Hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{Aluminate}}{2{\mathrm{NaAlO}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$.
5. Hence, option (A) is correct.

The explanation for the incorrect answer:

Option (B) Sulphur dioxide (${\mathbf{SO}}_{\mathbf{2}}$)

1. Sulphur dioxide is considered to be an acidic oxide because of its high oxidation state and also reacts only with bases.
2. The reaction of sulphur dioxide with bases: $\underset{\mathrm{Sulfur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Sodium}\mathrm{Hydroxide}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{Sulfite}}{{\mathrm{Na}}_2{\mathrm{SO}}_3\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}$
3. Hence option (B) is incorrect.

Option (C) Phosphorous pentaoxide (${\mathbf{P}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{5}}$)

1. Phosphorous pentaoxide is considered to be acidic oxide because of its maximum oxidation state and its reactivity only with bases.
2. The reaction involved: $\underset{\mathrm{Phosphorous}\mathrm{pentaoxide}}{{\mathrm{P}}_2{\mathrm{O}}_5\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Phosphoric}\mathrm{acid}}{4{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)}$.
3. Hence option (C) is incorrect.

Option (D) Calcium oxide ($\mathbf{CaO}$)

1. Calcium oxide is a basic oxide, although it reacts only with acids.
2. Reaction involved: $\underset{\mathrm{Calcium}\mathrm{Oxide}}{\mathrm{CaO}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Calcium}\mathrm{Chloride}}{{\mathrm{CaCl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}$
3. Hence option (D) is incorrect.

Therefore, aluminium oxide reacts with both acid and bases it is amphoteric, so option (A) is correct.