Question

Question 10.29 How would you explain the following observations?

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

(ii) BaO is soluble but BaSO4 is insoluble in water,

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

Class XI The s-Block Elements Page 306

Answer 1

hello..
)BeO is almost insoluble in water and BeSO4is soluble in water. Be2+is a small cationwith a high polarising power and O2–is a small anion. The size compatibility of Be2+andO2–is high. Therefore, the lattice energy released during their formation is also veryhigh. When BeO is dissolved in water, the hydration energy of its ions is not sufficient toovercome the high lattice energy. Therefore, BeO is insoluble in water. 
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Answer 2

(i) Lattice energy of BeO is greater than its hydration energy so, it is insoluble in water while in case of BeSO4 , hydration energy is greater than lattice energy, so, it is readily soluble in water.

(ii) Lattice energy of BaO is much smaller than that of its hydration energy, so it is soluble in water .in BaSO4 , Lattice energy predominates over hydration energy so, it is insoluble in water.

(iii) according to Fazan's rule , covalent characters on LI is more than KI . and we know , covalent compound is soluble in covalent compound very easily.
that's why LiI is more soluble than KI in ethanol(covalent compound).