Question

If $N{a}^{+}$ is larger than $M{g}^{2+}$ ion and $S^{2-}$ ion is larger than $C{l}^{-}$ ion, which of the following will be the least soluble in water?

• A. $NaCl$
• B. $N{a}_{2}S$
• C. $MgC{l}_2$
• D. $MgS$

Answer 1

The correct option is D $MgS$

Solubity of a compound in water depends on two factors. They are:
1. lattice energy
2. hydration energy.

When the hydration energy is more than the lattice energy the compound becomes soluble in water.

Lattice energy is directly proportional to the product of the charges on the cation and the anion and inversely proportional to the distance between the charges.

$MgS$ has $M{g}^{2+}$ and $S^{2-}$. The product of charges is the highest and so will be the lattice energy. Hence, $MgS$ is the least soluble.