Question

The solubilities of alkaline earth metal carbonates decrease down the group from $Mg$ to $Ba$ mainly due to a decrease in:

• A. Hydration energies of cations
• B. Inter ionic interaction
• C. Entropy of solution formation
• D. None of the above

Answer 1

The correct option is A Hydration energies of cations

The solubility of the alkaline earth metal carbonates decreases down the group from $Mg$ to $Ba$.
This is because the fact that down the group with increasing size of cation, both the lattice energy and hydration energy decrease. A decrease in lattice energy favours increased solubility, but a decrease in hydration energy favours decreased solubility. These two factors thus change in opposite directions but the effect of hydration energy is more pronounced as the hydration energy changes more rapidly than the lattice energy. Hence, the solubility of compounds become less soluble as the metal gets larger.