Why is LiF almost insoluble in water whereas LiCl soluble not only in water but also in acetone?
LiF is almost insoluble in water whereas LiCl soluble not only in water but also in acetone.
Explanation:
⇒ The solubility of a compound in water depends on the balance between lattice energy and hydration energy.
Compound | Hydration energy | Lattice energy |
LiCl | -876 kJ mol-1 | -845 kJmol-1 |
LiF | -1019 kJmol-1 | -1005 kJ mol-1 |
⇒ Difference in hydration energy and lattice energy of LiCl:
-876 kJmol-1 – (-845 kJmol-1) = -31 kJ mol-1
⇒ Difference in hydration energy and lattice energy of LiF:
-1019 kJmol-1 – (-1005 kJmol-1) = -14 kJ mol-1
⇒ As a result, difference in lattice energy and hydration energy of LiCl is higher than that of LiF. Hence, LiF is sparingly soluble in water while LiCl is soluble.
⇒ One more reason is that higher the lattice energy, lower will be the solubility. LiF is almost insoluble in water because of much higher lattice energy (-1005 kJ mol-1) than that of LiCl (-845 kJ mol-1).
⇒ Furthermore, Li+ ion can polarise bigger Cl- ion more easily than the smaller F-ion.
⇒ As a result, according to Fajan’s rules, LiCl has more covalent character than LiF and hence is highly soluble in organic solvents like acetone.