• # question_answer 72)   Why are $BeS{{O}_{4}}$ and $MgS{{O}_{4}}$ readily soluble in water while$CaS{{O}_{4}}$ and $BaS{{O}_{4}}$ are insoluble?

The solubility of an ionic compound depends on two factors: (i) lattice energy and (ii) hydration energy. These two factors oppose each other. If lattice energy is high, the solubility is low. If hydration energy is high, the ions will have greater tendency to be hydrated and therefore, solubility will be high. The solubility of sulphates decreases on moving down the group. $BeS{{O}_{4}}$and$MgS{{O}_{4}}$ are soluble. This is due to high energy of solvation of smaller $B{{e}^{2+}}$ and $M{{g}^{2+}}$ions.$CaS{{O}_{4}}$is sparingly soluble while $SrS{{O}_{4}}$ and $BaS{{O}_{4}}$ are almost insoluble. This is due to high lattice energy values.