Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy?
- CaSO4
- BeSO4
- BaSO4
- SrSO4
Answer
(2) BeSO4
Solution
Be2+ is the smallest ion of the group, its hydration enthalpy is very high.
As per NCERT, the greater hydration enthalpies of Be2+ and Mg2+ ions overcome the lattice enthalpy factor, so their sulphates are soluble in water.
Down the group hydration enthalpy decreases faster than lattice enthalpy ⇒ CaSO4, SrSO4, BaSO4 are sparingly soluble.
∴ For BeSO4, hydration enthalpy > lattice enthalpy.
Answer: (2)