The molar conductivity at infinite dilution (Λ∞m) can be obtained by extrapolating the above graph of strong electrolytes to zero concentration.
Kohlrausch Law of Independent migration of ions: 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. Thus, if λ°Na+ and λCl– are molar limiting conductivity of the sodium and chloride ions respectively, then the limiting molar conductivity for sodium chloride is given by the equation:
Λ°NaCl = λ°Na + λCl–
In general, if an electrolyte on dissociation gives v+ cations and v– anions then its limiting molar conductivity is given by
Λ° = v + λ°+ + V– λ°–
Here, λ°+ and λ°– are the limiting molar conductivities of the cation and anion respectively.
Kohlrausch’s law helps us to calculate
(i) Determination of molar conductivities of weak electrolytes at infinite dilution.
(ii) Determination of the degree of dissociation of electrolytes.
Degree of dissociation: It is ratio of molar conductivity at a specific countraction ‘C’ to the molar conductivity at infinite dilution. It is denoted by α.
= 1.05 V – 0.0295 x log 80
= 1.05 V – 0.0295 x 1.9031
= 1.05 V – 0.056 = 0.99 V.