Question

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

• A. Sodium chloride
• B. Sodium sulphide
• C. Magnesium chloride
• D. Magnesium sulphide

Answer 1

Answer: (D)

Magnesium sulphide. Higher the lattice energy lower the solubility. Out of the four combinations possible, the lattice energy of $MgS$ (bi-bivalent ionic solid) is higher than those of $N{a}_{2}S,MgC{l}_2$ (uni-bivalent or bi univalent ionic solids) and $NaCI$ uni-univalent ionic solids) and hence, $MgS$ is the leas soluble.