Question

The solubility of II group hydroxides increases with molecular weight. This is because:

• A. lattice energy is same but hydration energy decreases down the group.
• B. hydration energy is same but lattice energy decreases down the group.
• C. both lattice and hydration energy increase down the group.
• D. decrease in lattice energy down the group is faster than decrease in hydration energy.

Answer 1

The correct option is D decrease in lattice energy down the group is faster than decrease in hydration energy.

On moving down the group II, the atomic and ionic size increases . The size of $B{e}^{2+}$ is smallest and the size of $B{a}^{2+}$ is highest. As the size increases, the decrease in the lattice energy is much more than the decrease in the hydration energy. Due to this, the solubility increases with increase in the molecular weight on moving down the group. Hence, barium hydroxide is more soluble than beryllium hydroxide.