Question

What are the applications of Kohlrausch law?

Answer 1

1. Kohlrausch law helps us in the determination of limiting molar conductivities for any electrolyte. Weak electrolytes have lower molar conductivities and lower degree of dissociation at higher concentrations. The graph plotted between molar conductivity and $c\frac{1}{2}$ (where c is the concentration) is not a straight line for weak electrolytes. The molar conductivity of weak electrolyte increases steeply at lower concentrations. Therefore, limiting molar conductivity, ${Ë}_m^0$ cannot be obtained by extrapolation of molar conductivity to zero concentration. Hence, we use Kohlrausch law of independent migration of ions for the determination of limiting molar conductivity, ${Ë}_m^0$ for weak electrolytes.
2. Kohlrausch law also helps us in determining the value of dissociation constant from the value of molar conductivity and limiting molar conductivity for a weak electrolyte at a given concentration.
$\alpha =\frac{\Lambda }{E_m^0}$
Where, $\alpha$ = dissociation constant
$\Lambda$ = molar conductivity
${Ë}_m^0$ = limiting molar conductivity