Question

\(\mathrm{Al}_{2} \mathrm{O}_{3}\) is amphoteric. What does this mean?

Short answer

An amphoteric substance, such as \(\mathrm{Al}_{2} \mathrm{O}_{3}\) (aluminum oxide), is one that can act as both an acid and a base depending on its environment. It can donate protons (H+) when acting as an acid and accept protons (H+) when acting as a base. For example, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) acts as an acid when reacting with Sodium Hydroxide (NaOH) and as a base when reacting with Hydrochloric Acid (HCl).

Step-by-step solution

Definition of Amphoteric

An amphoteric substance has the ability to act as both an acid and a base depending on its environment. It can donate protons (H+) when acting as an acid, or accept protons (H+) when acting as a base. This dual nature exhibited by the compound differentiates it from regular acids or bases.

Amphoteric Nature of \(\mathrm{Al}_{2} \mathrm{O}_{3}\)(Aluminum oxide)

Aluminum oxide (\(\mathrm{Al}_{2} \mathrm{O}_{3}\)) is an amphoteric substance. This means that it can act as an acid or a base, depending on what it is reacting with. To better understand, let's see how aluminum oxide demonstrates both acidic and basic properties:

Acting as an Acid

When \(\mathrm{Al}_{2} \mathrm{O}_{3}\) reacts with a base, it acts as an acid by donating protons (H+). The reaction of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) with Sodium Hydroxide (NaOH), a strong base, is an example: \[ \mathrm{Al}_{2} \mathrm{O}_{3}(s) + 2\mathrm{NaOH}(aq) + 3\mathrm{H}_{2}\mathrm{O}(l) \rightarrow 2\mathrm{Na}_{3}\mathrm{Al}(\mathrm{OH})^{-}_{4}(aq) \]

Acting as a Base

When \(\mathrm{Al}_{2} \mathrm{O}_{3}\) reacts with an acid, it acts as a base by accepting protons (H+). The reaction of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) with Hydrochloric Acid (HCl), a strong acid, is an example: \[ \mathrm{Al}_{2} \mathrm{O}_{3}(s) + 6\mathrm{HCl}(aq) \rightarrow 2\mathrm{AlCl}_{3}(aq) + 3\mathrm{H}_{2}\mathrm{O}(l) \] In both examples, aluminum oxide demonstrates its amphoteric nature by reacting differently with acids and bases. As such, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is an amphoteric compound.