question_answer 1)

  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 in a test tube and on bringing a burning matchstick near the mouth of the test tube, a pop sound indicate the evolution of hydrogen gas. The same activity when performed with concentrate nitric acid, reaction does not proceed. Explain the reason.

Answer:

Concentrated nitric acid renders aluminium passive (inactive) by forming a protective layer of oxide \[(A{{l}_{2}}{{O}_{3}})\]on the surface. Thus, hydrogen gas is not evolved when aluminium is treated with concentrated\[HN{{O}_{3}}\].