Which of the following sulphates is sparingly soluble in water ?

Options

A. `BeSO_(4)`
B. `MgSO_(4)`
C. `CaSO_(4)`
D. `BaSO_(4)`

Answer

C

Explanation

The solubility of sulphates in water decreases down the group.
`BeSO_(4) gt MgSO_(4) gt gt CaSO_(4) gt SrSO_(4) gt BaSO_(4)` Thus `BeSO_(4)` and `MgSO_(4)` are soluble but `CaSO_(4)` is sparingly soluble, and the suphates of Sr, Ba, and Ra are virtually insoluble. the significantly higher solubilities of `BeSO_(4)` and `MgSO_(4)` are due to the high enthalpy of hydration of the small `Be^(2+)` and `Mg^(2+)` ions.
Since `SO_(4)^(2-)` ion is relatively large, the lattice enthalpy remains practivally unchanged as smal increase inmetal cation's size doen not make any impact. However, hydration energy decreases appreaciable as the size of metal cation increases from `Be^(2+)` to `Ba^(2+)`, leading to a decrease in the solubility of the sulphates.