Question

What is the role of dielectric constant for sparingly soluble salt??

Answer 1

The dielectric constant decreases linearly with the concentration of the sparingly soluble salt, in dilute solutions.

Explanation:

The dielectric constant is an indicator of how easily an insulating material can be polarized as a result of an external electric field applied to it. When a sparingly soluble salt is added to water, it will decrease the dielectric constant as more salt is added to the solution, as long as the solution is dilute. The change will be slow compared to the rate at which the salt is added, because sparingly soluble salt is slow to dissolve when placed into solution.

This is an example of dielectric decrement.

There is a formula: `epsilon=epsilon_w-calpha`

`epsilon` is the dielectric of the sparingly soluble salt mixed into water
`epsilon_w` is the dielectric of pure water
c is the concentration of the sparingly soluble salt
`alpha` is the total excess polarization of the ionic species

At higher concentrations the linearity is lost, and the dielectric decrement goes to saturation.

There is more information here:
https://ngavish.net.technion.ac.il/files/2013/01/DielectricConstant_submitted2.pdf