Question

Which one of the following alkaline earth metal sulphates has its hydration enthalpy greater than its lattice enthalpy?

• A. $CaS{O}_4$
• B. $BeS{O}_4$
• C. $BaS{O}_4$
• D. $SrS{O}_4$

Answer 1

The correct option is B

$BeS{O}_4$

As we move down the group, size of metal increases. Be has lower size while $S{O}_4^{2-}$ has bigger size, that's why $BeS{O}_4$ breaks easily and lattice energy becomes smaller but due to lower size of Be, water molecules are gathered aroud and hence hydration energy increases.
On the other hand, rest of the metals, i.e. Ca, Ba, Sr have bigger size of sulphates. Hence, $BeS{O}_4$ is the right response.