Question

Explain the determination of molar conductivity of a weak electrolyte at infinite dilution or zero concentration using Kohlrausch’s law.

Answer 1

Molar conductivity of a weak electrolyte at infinite dilution or zero concentration cannot be measured experimentally.

Consider the molar conductivity (∧₀) of a weak acid, CH₃COOH at zero concentration. 

By Kohlrausch s law, 

\(∧_{0CH_3COOH}\)= \(\lambda^0_{CH_3COOH^-}\)+ \(\lambda^0_{H^+}\) where \(\lambda^0_{CH_3COO^-}\) and \(\lambda^0_{H^+}\) are the molar ionic conductivities of CH₃COO^- and H⁺ions respectively.

If \(∧_{0CH_3COONa,}\)∧_0HCl and ∧_0NaCl are the molar conductivities of CH₃COONa, HCl and NaCl respectively at zero concentration, then by 

Kohlrausch’s law,

Now,

Hence, 

From ∧₀ values of strong electrolytes,∧₀ of a weak electrolyte CH₃COOH, at infinite dilution can be calculated.