Question

(a) State and explain Kohlrausch's law of independent migration of ions. Write an expression for
the molar conductivity of acetic acid at infinite dilution according to Kohlrausch law.

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Answer 1

Kohlrausch's law : The law states that limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cation of the electrolyte.

$\large\rm { \Lambda^{ 0}_{m} (CH_{3} COOH) = \lambda ^{0} _{CH_{3} COO^{-}} + \lambda ^{0} _{H^{+}} }$

Expression: $\large\rm { \Lambda ^{0} _{m} (CH_{3} COOH) = ? }$

$\large\rm { \Lambda ^{0} _{m} (HCl) = 426 \ S \ cm^{2} \ mol^{-1}}$

$\large\rm { \Lambda ^{0} _{m} (CH_{3} COONa) = 91 \ S \ cm^{2} \ mol^{-1}}$

$\large\rm { \Lambda ^{0} _{m} (NaCl) = 126 \ S \ cm^{2} \ mol^{-1}}$

$\large\rm { \Lambda ^{0} _{m} (CH_{3} COOH) = 426+91-126}$

$\large\boxed{\rm { \therefore 391 \ S \ cm^{2} \ mol^{-1}}}$ is the required answer.