Question

The solubility of metal halides depends on their nature, lattice enthalpy and hydration enthalpy of the individual ions. Amongst fluorides of alkali metals, the lowest solubility of LiF in water is due to

• A. Low ionisation enthalpy of lithium atom
• B. High hydration enthalpy for lithium ions.
• C. The Ionic nature of lithium fluoride
• D. High lattice enthalpy

Answer 1

The correct option is D High lattice enthalpy

Solution:

Solubility mainly depends on two factors - Hydration enthalpy and lattice enthalpy. LiF has highest lattice enthalpy due to comparable size of $L{i}^{+}$ and $F^{-}$ ions. This lattice energy is too high to be compensated by its hydration enthalpy.

Since lattice enthalpy decreases much more than the hydration enthalpy with increasing ionic size for alkali metals, the solubility of LiF is the lowest in water in given group due to the highest lattice enthalpy.Hence the solubility determining factor here is High lattice enthalpy. So, correct answer here is
Option (B)