Question

The solubility order of the chlorides of the alkali metals is

• A. $NaCl>KCl>RbCl>CsCl$
• B. $CsCl>RbCl>KCl>NaCl$
• C. $KCl>NaCl>RbCl>CsCl$
• D. $CsCl>RbCl>NaCl>KCl$

Answer 1

Answer: (D)

The reason why the solubility of most group one metals decreases on descending the group is that the lattice energy only changes slightly, but the free energy of hydration changes rather more. (for e.g.) the difference in lattice energy between $NaCl$ and $KCl$ is $67kJmo{l}^{-1}$, and yet the difference in $\Delta G$ (Hydration) for $N{a}^{+}$and $K^{+}$is $76kJmo{l}^{-1}$. Thus $KCl$ is less soluble than $NaCl$.