Question

In the following sets of reactants which two sets exhibit the amphoteric character of $A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}O$?
Set 1: $A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}O\,(s)$ and $O{{H}^{-}}(aq)$
Set 2: $A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}O\,(s)$ and ${{H}_{2}}O(l)$
Set 3: $A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}O\,(s)$ and ${{H}^{+}}(aq)$
Set 4: $A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}O\,(s)$ and $N{{H}_{3}}(aq)$
(A)- 1 and 2
(B)- 1 and 3
(C)- 2 and 4
(D)- 3 and 4

Answer 1

Hint: The ability of a metal oxide to behave as both an acidic oxide or a basic oxide in a reaction, is what accounts for its amphoteric nature. So, on its reaction with an acid or base, it gains or donates the electrons forming salt and water.

Complete step by step solution:
The amphoteric character is shown by substances which have the ability to act as both, either an acid or a base in a reaction. Further, a metal oxide which on reaction with an acid or base, undergoes the neutralization reaction forming salt and water is known as the amphoteric oxide.
For the given metal oxide of aluminium oxide, to behave as amphoteric it shows reaction with acid and base as follows:
On reaction with hydrochloric acid (having ${{H}^{+}}$ ions), the oxide acts as base forming aluminium chloride salt and water:
$A{{l}_{2}}{{O}_{3}}+6HCl\to 2AlC{{l}_{3}}+3{{H}_{2}}O$
On reaction with sodium hydroxide base (having $O{{H}^{-}}$ ions), the oxide acts as acid forming sodium aluminate sat and water:
$A{{l}_{2}}{{O}_{3}}+2NaOH\to 2NaAl{{O}_{2}}+{{H}_{2}}O$
So, in both of the above reactions, salt and water is formed showing the nature of aluminium oxide to act as acid and base accordingly.

Therefore, the sets of reactants exhibit the amphoteric character of $A{{l}_{2}}{{O}_{3}}.x{{H}_{2}}O$is option (B)- Set 1 and Set 3.

Note: The amphoteric metal oxide behaves as Lewis acid and base, involving the accepting or donating of the electrons by the metal oxide during the reaction. Other metals whose oxide show the amphoteric nature like aluminium are zinc, lead, tin and copper. Whereas, the hydroxides of aluminium and beryllium also show amphoteric character.