Aluminium dissovles in mineral acids and aqueous alkalies and thus shows amphoteric character. A place of aluminum foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning match stick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated with concentrated nitric acid. reaction doesn't proceed. Expalin the reason.

Aluminium dissovles in mineral acids and aqueous alkalies and thus sho

1.	Aluminium dissovles in mineral acids and aqueous alkalies and thus shows amphoteric character. A place of aluminum foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning match stick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated with concentrated nitric acid. reaction doesn't proceed. Expalin the reason.
Answer» Solution :Aluminium being amphoteric in nature dissolves both in acids and alkalies evolving `H_(2)` gas which burns with a POP sound `2Al+6HClrarr2AlCl_(3)+3H_(2)` `2Al+NaOH+2H_(2)Orarrunderset("Sodium meta aluminate")(2NaAlO_(2))+3H_(2)` But when Al is TREATED with conc. `HNO_(3)`, a thin protective layer of `Al_(2)O_(3)` is formed on its SURFACE which prevents further action `2Al + 6HNO_(3) RARR Al_(2)O_(3)+6NO_(2)+3H_(2)O`.