Question

Why are $BeS{O}_{4}andMgS{O}_4$ readily soluble in water while $CaS{O}_4,SrS{O}_{4}andBaS{O}_4$ are insoluble?

Answer 1

The hydration enthalpies of $BeS{O}_{4}andMgS{O}_4$ are quite high because of the small size of $B{e}^{2+}andM{g}^{2+}$ ions.

These hydration enthalpy values are higher than their corresponding lattice enthalpies and therefore $BeS{O}_{4}andMgS{O}_4$ are highly soluble in water.

However, hydration enthalpies of $CaS{O}_4,SrS{O}_{4}andBaS{O}_4$ are not very high as compared to their respective lattice enthalpies and hence these are insoluble in water.