Question

Mention three application of kohlrausch's law of independent ionic mobility

Answer 1

Determination of for weak electrolytes : The molar conductivity of a weak electrolyte at infinite dilution cannot be determined by extrapolation method. However, values for weak electrolytes can be determined by using the Kohlrausch's equation.

(ii) Determination of the degree of ionisation of a weak electrolyte: The Kohlrausch's law can be used for determining the degree of ionisation of a weak electrolyte at any concentration. If is the molar conductivity of a weak electrolyte at any concentration C and, is the molar conductivity of a electrolyte at infinite dilution. Then, the degree of ionisation is given by,

Thus, knowing the value of , and (From the Kohlrausch's equation), the degree of ionisation at any concentration can be determined.

(iii) Determination of the ionisation constant of a weak electrolyte : Weak electrolytes in aqueous solutions ionise to a very small extent. The extent of ionisation is described in terms of the degree of ionisation In solution, the ions are in dynamic equilibrium with the unionised molecules. Such an equilibrium can be described by a constant called ionisation constant. For example, for a weak electrolyte AB, the ionisation equilibrium is, ⇌ ; If C is the initial concentration of the electrolyte AB in solution, then the equilibrium concentrations of various species in the solution

Answer 2

Answer :

Three application of Kohlrausch's law of independent ionic mobility are :

(1) It is used for the calculation of molar conductivity at infinite dilution for weak electrolytes.

(2) It is used for the calculation of the degree of dissociation.

Formula used : $\alpha=\frac{\Lambda^c_m}{\Lambda^o_m}$

where,

$\alpha$ = degree of dissociation

$\Lambda^c_m$ = molar conductivity of a solution at any concentration

$\Lambda^o_m$ = molar conductivity at infinite dilution

(3) It is used for the calculation of dissociation constant of a weak electrolyte.

Formula used : $K_c=\frac{c\alpha^2}{1-\alpha}$

where,

$K_c$ = dissociation constant

c = concentration of solution

$\alpha$ = degree of dissociation