Question:
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.
Solution:
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.