Q14.47P - Chemistry: Molecular Nature Of Matter And Change

Question

Lithium salts are often much less soluble in water than the corresponding salts of other alkali metals. For example, at 18°C, the concentration of a saturated LiF solution is $\mathbf{1}\mathbf{.}\mathbf{0}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{2}}$M, whereas that of a saturated KF solution is 1.6 M. How would you explain this behaviour?

Step-by-Step Solution

Answer

Lithium fluoride is less soluble than potassium floured because both lithium and fluoride are small in size, due to which their lattice energy increase and the hydration energy decrease.

 

Step1: Solubility

it is defined as the ability of an atom to get hydrated in water. As the atomic size increase, the hydration energy increase. So, caesium has high hydration energy, lithium has low hydration energy, and lattice energy is the inverse of hydration energy.

Step2: Solubility of lithium fluoride

As lithium is less soluble among the alkali metals due to its small size so, in the medium fluoride,both lithium and fluorideions are small in size due to which they have high lattice energy, and the hydration gets decreases,whereas in potassium fluoride; potassium has a large size than lithium and fluoride and ever potassium has high hydration energy than lithium because hydration energy increases down the group so that potassium fluoride is more soluble than lithium fluoride.