Question

Which of the following compounds is readily soluble in water?

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

Answer 1

Answer: (A), (B)

The correct options are
A $BeS{O}_4$
B $MgS{O}_4$

Option (A),(B) are correct.

The solubility of the sulphates in water decreases down the groups $i.e.Be>Mg>Ca>Sr>Ba$.

Thus $BeS{O}_4$ and $MgS{O}_4$ are highly soluble, $CaS{O}_{­}4$ is sparingly soluble but the sulphates of $Sr,Ba$ and $Ra$ are insoluble in water.

The reason is due to the magnitude of lattice energy remains almost constant as the sulphate is so big that small increase in the size of the cation from $Be$ to $Ba$ does not make any difference. Thus hydration energy decreases from $B{e}^{+2}$ to $B{a}^{+2}$ as the size of the cation increase down the group. Hence, the solubilities of sulphates of alkaline earth metals decrease down the group mainly due to the decreasing hydration energies.