Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy?
Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy?
$\mathrm{CaSO}_4$
$\mathrm{BeSO}_4$
$\mathrm{BaSO}_4$
$\mathrm{SrSO}_4$
Solution
Key Idea Hydration energy varies inversely with size and in sulphates of alkaline earth metals lattice energy remains almost constant. The order of size of alkaline earth metals is
$\mathrm{Be}^{2+} < \mathrm{Ca}^{2+} < \mathrm{Sr}^{2+} < \mathrm{Ba}^{2+}$
Thus, the order of hydration energy is$
\mathrm{Be}^{2+} > \mathrm{Ca}^{2+} > \mathrm{Sr}^{2+} > \mathrm{Ba}^{2+}$
Hence, $\mathrm{BeSO}_4$ has the hydration enthalpy higher than the lattice enthalpy.