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Class 9-10, JEE & NEET
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Aluminium dissolves in mineral acids and aqueous alkalies 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, the reaction doesn’t proceed. Explain the reason.
Aluminium reacts both with acid and base to give hydrogen gas which burns in air with a pop sound. Nitric acid forms a thin layer of aluminium oxide on the surface of
aluminium as it is a strong oxidizing agent. Thus, the further reaction is prevented and no hydrogen is liberated.