Limiting Molar Conductivity:

An important relation can be obtained by extrapolating the curve for strong electrolytes figure to c → 0 where all interionic effects are absent. The limiting value obtained by this extrapolation is called the molar conductivity at infinite dilution.

Observing the linearity of Λm versus √c for strong electrolytes in dilute solutions, Kohlrausch suggested the following empirical relation for the variation of equivalent conductance of strong electrolytes with dilution.

Λm = Λ ^∞ - b √c

where b is a constant for the given electrolyte and Λ ^∞   is the molar conductivity of the electrolyte at infinite dilution. The validity of this equation may be seen from the plot for electrolytes like HCl, KCl, etc. To obtain Λ ^∞ of such electrolytes the curve is extrapolated to c → 0 and the intercept so obtained gives the value of Λ ^∞ . The same method cannot be used for obtaining Λ ^∞ for weak electrolytes because of the steep increase in Λ at high dilutions. Λ ^∞  may also be computed from the molar conductivities at infinite dilution of the respective ions, since at infinite dilution, the ions are independent of each other according to the law of independent migration of ions and each contribute its part to the total conductivity, thus,

Λ ^∞ = Λ₊^∞ + Λ_- ^∞                                        

where Λ^∞ and  Λ^∞  are the ionic conductivities at infinite dilution of the cation and anion, respectively.