Question

Sulphates of Be and Mg are readily soluble in water but sulphates of Ca, Sr and Ba are insoluble. This is due to the fact that:

• A. the greater hydration enthalpies of $B{e}^{2+}andM{g}^{2+}$ overcome the lattice enthalpy
• B. high lattice enthalpy of $B{e}^{2+}$ and $M{g}^{2+}$ makes them soluble in water
• C. solubility decreases from $BeS{O}_4$ to $BaS{O}_4$ due to increase in ionic size
• D. $BeS{O}_4$ and $MgS{O}_4$ are ionic in nature while other sulphates are covalent

Answer 1

The correct option is A the greater hydration enthalpies of $B{e}^{2+}andM{g}^{2+}$ overcome the lattice enthalpy

Due to smaller size their lattice enthalpies are high but their greater hydration enthalpies overcome the lattice enthalpies and they become soluble in water. Ca,Sr and Ba sulphates are insoluble is water due to lower hydration enthalpies.