Question

In which of the following the hydration energy is higher than the lattice energy

• A. $SrS{O}_4$
• B. $BaS{O}_4$
• C. $MgS{O}_4$
• D. $RaS{O}_4$

Answer 1

The correct option is C

$MgS{O}_4$

Since we are comparing the solubilities of alkaline metal sulphates: we are in fact, talking about the cations from the same group but all having the same counter-anion. So the hydration enthalpy of sulphate is not the deal-breaker. As we go down the group, the hydration enthalpy of the cations decreases with a greater rate (steeper slope). This trend is not mirrored by the lattice enthalpies. $MgS{O}_4$ has a higher hydration energy than lattice energy and is thus the most soluble out of the given alkaline earth metal sulphates.