Application of Kohlrausch's law
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...