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  • Aluminium dissolves in mineral acids and aqueous alkalies and thus shows amphoteric character.

Aluminium dissolves in mineral acids and aqueous alkalis and thus shows amphoteric character. A piece of aluminium foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning matchstick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated nitric acid, reaction does not proceed. Explain the reason.

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Al, when dissolved in acids and alkalis, is amphoteric and thus gives out H2 gas, which can be tested as it burns with a pop sound.

2Al + 6HCl \rightarrow 2AlCl_{3} + 3H_{2}

2Al + 2NaOH + 2H_{2}O \rightarrow 2NaAlO_{2} + 3H_{2}

When the nitric acid becomes passive, the reaction stops, and the thin layer of aluminium oxide ceases the reaction.

2Al + 6HNO_3 \rightarrow Al_{2}O_{3} + 6NO_{2} + 3H_{2}O

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