Question

How would you explain the following observations? 

(i). BeO is almost insoluble but BeSO₄ is soluble in water. 

(ii). BaO is soluble but BaSO₄ is insõluble in water. 

(iii). LiI is more soluble than KI in ethanol.

Answer 1

(i). Lattice energy of BeO is comparatively higher than the hydration energy. Therefore, it is almost insoluble in water. Whereas BeSO₄ is ionic in nature and its hydration energy dominates the lattice energy.

(ii). Both BaO and BaSO₄ are ionic compounds but the hydration energy of BaO is higher than the lattice energy, therefore it is soluble in water. 

(iii). Since the size of Li⁺ ion is very small in comparison to K⁺ ion, it polarises the electronb cloud of I^- ion to a great extent. Thus LiI dissolves in ethanol more easily than the KI.