Question

State the Kohlrausch law of independent migration of ions. Why does the conductivity of a solution decrease with dilution?

Answer 1

Hint:Conductivity: It is defined as the solution at any particular concentration is the conductance of one unit volume of the solution which is put in between two platinum electrodes with the unit cross-sectional area from a distance of unit length.

Complete step-by-step answer:
-Kohlrausch law of independent migration of ions: According to this law, “At infinite dilution, the dissociation of the electrolyte is complete and hence each ion makes a definite contribution to the equivalent conductivity of the electrolyte irrespective of the nature of other ions associated with it”
${ \Lambda }^{ \infty }{ m }{ =v }^{ + }{ \lambda }^{ \infty + }{ +v }^{ - }{ \lambda }^{ \infty - }$
Where ${ v }^{ + }$ and ${ v }^{ - }$ are the numbers of cations and anions per formula unit of electrolyte respectively ${ \Lambda }^{ \infty }{ + }$ and ${ \Lambda }^{ \infty }{ - }$ are the molar conductivities of the cation and anion at infinite dilution respectively.
-When we dilute the solution, there will be an increase in the volume of the solution but the number of ions that carry charge in a solution remains the same. Consequently, the number of ions per unit volume that carry charge in a solution diminishes. There will be a flow of current when the movement of these charges towards the oppositely charged electrodes, and hence, the conductivity of a solution decreases on dilution.

Additional Information:
Applications of Kohlrausch 's law: Some important applications of the Kohlrausch 's law are given below:
-Determination of ${ \Lambda }^{ \infty }{ m }$ for weak electrolytes
-Determination of the degree of ionization of a weak electrolyte
-Determination of the ionization constant of a weak electrolyte.
-The solubility of a sparingly soluble salt can be determined.

Note: The possibility to make a mistake is that you may think as the volume of the solution increases on dilution, conductivity also increases, but the ions per unit volume are decreasing, so conductivity decreases not increases.