Kohlrausch’s law of independent migration of ions states molar conductivity of an electrolyte at infinite dilution can be expressed as the sum of the contribution of individual ions. If molar conductivity of cations and anions are represented by λ∞+ and λ∞– respectively.
where v+ and v– are number of cations and anions per formula of electrolyte e.g.,
Λ∞ CaCl2 = λ∞ (Ca2+) + 2 λ∞ (CI–)
Λ = KCl = λ∞ (K+) + λ∞ (CI–)
Uses 1. It is used to find molar conductivity of weak electrolyte at infinite dilution which
cannot be obtained by extrapolation.
2. It is used to calculate degree of dissociation of weak electrolyte at a particular concentration.
Degree of dissociation
where Λm is molar conductivity of weak electrolyte at a particular concentration and Λemis molar conductivity of weak electrolyte at infinite dilution.
= 1.05 V – 0.0295 x log 80
= 1.05 V – 0.0295 x 1.9031
= 1.05 V – 0.056 = 0.99 V.