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.
Aluminum is an amphoteric metal i.e it reacts with both acid and base to give hydrogen gas which burns in air with a pop sound.
Nitric acid is a very strong oxidizing agent it leads to the formation of a thin layer of Al2O3(aluminum oxide) on the surface of the aluminum.
Thus, the further reaction is prevented and no hydrogen is liberated.