chapter 5 electrochemistry class 12 chemistry textbook solution

4. Answer the following :

i. What is Kohrausch law of independent migration of ions? How is it useful in obtaining molar conductivity at zero concentration of a weak electrolyte ? Explain with an example.


1. Kohlrausch's law states that "at infinite dilution, each ion migrates independently of the co-ion and contributes to the total molar conductivity of an electrolyte, irrespective of the nature of other ions to which it is associated." 2. Both cations and anions contribute to the molar conductivity of the electrolyte at zero concentration. Therefore, \(\Lambda_0\) is the sum of the molar conductivity of cations and that of anions at zero concentration. Hence, \(\Lambda_0 = \lambda_+^0 + \lambda_-^0\), where \(\lambda_+\) and \(\lambda_-\) are the molar conductivities of cations and anions, respectively. \(n_+\) and \(n_-\) are the number of moles of cations and anions specified in the chemical formula of the electrolyte. 3. Determining the molar conductivity of a weak electrolyte at zero concentration: - This theory is particularly useful for calculating \(\Lambda_0\) values of weak electrolytes based on those of strong electrolytes. - For example, \(\Lambda_0\) of acetic acid can be calculated by knowing those of HCl, NaCl, and CH₃COONa as described below:
\(\Lambda_0(HCl) + \Lambda_0(CH₃COONa) - \Lambda_0(NaCl)\) \[= \lambda_{H^+}^0 + \lambda_{Cl^-}^0 + \lambda_{CH_3COO^-}^0 + \lambda_{Na^+}^0 - \lambda_{Na^+}^0 - \lambda_{Cl^-}^0\]
\[= \lambda_{H^+}^0 + \lambda_{CH_3COO^-}^0 = \Lambda_0(CH_3COONa)\]
\(\Lambda_0(CH_3COONa) = \Lambda_0(HCl) + \Lambda_0(CH_3COONa) - \Lambda_0(NaCl)\).
Because \(\Lambda_0\) values of strong electrolytes, HCl, CH₃COONa, and NaCl, can be determined by the extrapolation method, the \(\Lambda_0\) of acetic acid can be obtained.

chapter 5 elctrochemistry textbook solution page 118