The sBlock Elements - Result Question 5
####5. The ease of adsorption of the hydrated alkali metal ions on an ion-exchange resins follows the order :
(a) $Li^{+}<K^{+}<Na^{+}<Rb^{+}$
[2012]
(b) $Rb^{+}<K^{+}<Na^{+}<Li^{+}$
(c) $K^{+}<Na^{+}<Rb^{+}<Li^{+}$
(d) $Na^{+}<Li^{+}<K^{+}<Rb^{+}$
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Solution:
- (b) All alkali metal salts are ionic (except Lithium) and soluble in water due to the fact that cations get hydrated by water molecules. The degree of hydration depends upon the size of the cation. Smaller the size of a cation, greater is its hydration energy.
Relative ionic radii :
$Cs^{+}>Rb^{+}>K^{+}>Na^{+}>Li^{+}$
Relative ionic radii in water or relative degree of hydration:
$Li^{+}>Na^{+}>K^{+}>Rb^{+}>Cs^{+}$
