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Determination of λ0M (limiting molar conductivity) for weak electrolytes It is not possible to determine the λ 0 M for a weak electrolyte by the extrapolation of λ M versus √c plot. But it can be calculated from Kohlrausch’s law. Consider the weak electrolyte CH3COOH. According to Kohlraush’s law, λ 0 CH3COOH = λ 0 H+ + λ 0 CH3COO- ………………………………… (Equation 1) We can experimentally determine the λ 0 M of strong electrolytes such as HCl,CH3COONa and NaCl. From Kohlraush’s law, λ 0 HCl = λ 0 H+ + λ 0 Cl- ……………………………………. (Equation 2) λ 0 CH3COONa = λ 0 Na+ + λ 0 CH3COO- ………………………………… (Equation 3) λ 0 NaCl = λ 0 Na+ + λ 0 Cl- ……………………………………. (Equation 4) Substracting equation 4 from the sum of equations 2 and 3, we get, λ 0 HCl + λ 0 CH3COONa - λ 0 NaCl = λ 0 H+ + λ 0 Cl- + λ 0 CH3COO- + λ 0 Na+ - λ 0 Na+ - λ 0 Cl- = λ 0 H+ + λ 0 CH3COO- = λ 0 CH3COOH Thus by measuring the molar conductance values of NaCl, HCl and CH3COONa, one can easily determi...

Kohlrausch's law of indendent migration of ions states that the molar conductance of infinite dilution (limiting molar conductivity ) is the sum of the individual contributions of the anions and cations of the electrolyte. It can be given in the mathematical form as: λ 0 M = v + λ 0 + + v - λ 0 - λ 0 + and λ 0 - are the limiting molar conductivity of cation and anion respectively. For NaCl, λ 0 M = λ 0 Na+ + λ 0 Cl- And for Al2(SO4)3, λ 0 Al2(SO4)3 =2 λ 0 Al3+ + λ 0 SO4 2-