Question

Question 61
Explain the following:

(a) Reactivity of $\text{Al}$ decreases if it is dipped in ${\text{HNO}}_3$.
(b) Carbon cannot reduce the oxides of $\text{Na}$ or $\text{Mg}$.
(c) $\text{NaCl}$ is not a conductor of electricity in the solid state whereas it does conducts electricity in aqueous solution as well as in molten state.
(d) Iron articles are galvanised.
(e) Metals like $\text{Na, K, Ca}$ and $\text{Mg}$ are never found in their free state in nature.

Answer 1

(a) Due to the formation of a layer of oxide i.e., ${\text{Al}}_2{\text{O}}_3$.

$3\text{Al}+4{\text{HNO}}_3⟶3{\text{Al(NO}}_3{)}_2+\text{NO}+2{\text{H}}_2\text{O}$

(b) $\text{Na}$ and $\text{Mg}$ are more reactive as compared to carbon. The two metals have more affinity to oxygen than carbon and thus cannot be reduced by it.

(c) In solid $\text{NaCl}$, the movement of ions is not possible due to its rigid structure but in aqueous solution or molten state, it disassociates into ions which move about and conduct electricity.

(d) The coating of zinc on iron prevents the iron from coming in contact with oxygen in the atmosphere, thus preventing the iron from getting oxidised.

(e) These metals are highly unstable in the free state and thus readily form other compounds.