Question
The correct order of the mobility of the alkali metal ions in aqueous solution is
A.
$$L{i^ + } > N{a^ + } > {K^ + } > R{b^ + }$$
B.
$$N{a^ + } > {K^ + } > R{b^ + } > L{i^ + }$$
C.
$${K^ + } > R{b^ + } > N{a^ + } > L{i^ + }$$
D.
$$R{b^ + } > {K^ + } > N{a^ + } > L{i^ + }$$
Answer :
$$R{b^ + } > {K^ + } > N{a^ + } > L{i^ + }$$
Solution :
The correct order of the mobility of the alkali metal ions in aqueous solution is $$R{b^ + } > {K^ + } > N{a^ + } > L{i^ + }$$ due to following order of hydration energy of these ions $$L{i^ + } > N{a^ + } > {K^ + } > R{b^ + }$$ and as the hydration of ion increases, mobility decreases.
$${\text{Hydration enthalpy}} \propto \frac{1}{{{\text{Size of cation}}}}$$