Question

Question 10.23 Why is LiF almost insoluble in water whereas LiCl soluble not only in water but also in acetone?

Class XI The s-Block Elements Page 306

Answer 1

LiF is almost insoluble in water due to high lattice energy. But LiCl is soluble in water due to high hydration energy of Li+ ion.
as you know, according to Fazan's law ,
covalent character increases when increases the size of anion , that's why LiCl is soluble in acetone ( covalent compound ) but LiF is insoluble in acetone .
order of covalent characters are : LiF < LiCl < LiBr < LiI

Answer 2

In Lithium fluoride the lattice enthalpy is very high due to small size of fluoride ions. In this case the hydration enthalpy is very less. Hence, LiF is insoluble in water. Where as in lithium chloride the lattice enthalpy is very small due to large size of chloride ions and hence its hydration enthalpy is high. More over LiCl has partial covalent and partial ionic character due to the polarization of Chloride ion by Lithium ion. Due to its low hydration energy and partial covalent and partial ionic character LiCl is soluble in water as well as acetone.