Question

(i) A piece of aluminium foil is dropped in dil. hydrochloric acid in a test tube. On bringing a burning match stick near the mouth of the test tube, a pop sound occurs.
(ii) A piece of aluminium foil is dropped in dil. sodium hydroxide in a test tube. On bringing a burning match stick near the mouth of the test tube, again a pop sound occurs.
The product formed in process (ii) is:
A. $AlC{l_3}$
B. NaCl
C. $NaAl{O_3}$
D. None of these

Answer 1

Hint: Aluminium dissolves in mineral acids and aqueous alkalis 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 rest tube, a pop sound indicates the evolution of hydrogen gas. Sodium aluminate is also formed by the action of sodium hydroxide on elemental aluminium which is an amphoteric metal. The reaction is highly exothermic once established and is accompanied by the rapid evolution of hydrogen gas.

Complete step by step answer:
Hydrogen burns with a pop sound because it reacts with compounds or elements around it to release energy. The energy released has kinetic energy that expands and rushes out the test tube to form the “pop” sound. If one lets the hydrogen burn openly in air it will not form a “pop” sound. This pop sound released by hydrogen serves as a distinction test for compounds containing hydrogen such as bicarbonate test.
In the reaction (ii)
$2Al(s) + 2NaOH(aq) + 6{H_2}O(I) \to 2Na + [Al{(OH)_4}](aq) + 3{H_2}(g)$
or
$2Al + 2NaOH + 2{H_2}O \to 2NaAl{O_2} + 3{H_2}$
(Both reactions can occur)
So, the product formed in process (ii) is $NaAl{O_2}$

Therefore, the correct answer is option (C).

Note: Aluminium is an unusual metal in that it reacts not only with acids, but with bases as well. Like Many active metals, aluminium dissolves in strong acids to evolve hydrogen gas and form salts but aluminium also dissolves in strong bases such as sodium hydroxide also commonly known as lye.