Question

Explain Kohlrausch’s law of independent migration of ions. Mention one application of this law.

Hint:

At infinite dilution, ions migrate independently, hence their conductivities can be simply added.

Answer 1

Step 1: Statement of Kohlrausch’s law.
Kohlrausch’s law states that at infinite dilution, the molar conductivity of an electrolyte is the sum of the contributions of its individual ions. Each ion migrates independently of the other.
\[ \Lambda_m^\infty = \lambda^\infty_+ + \lambda^\infty_- \] where,
$\Lambda_m^\infty$ = molar conductivity at infinite dilution
$\lambda^\infty_+$ = limiting molar conductivity of cation
$\lambda^\infty_-$ = limiting molar conductivity of anion
Step 2: Application.
It is used to calculate the molar conductivity of weak electrolytes (like acetic acid) at infinite dilution by using values of strong electrolytes. Example: \[ \Lambda_m^\infty (CH_3COOH) = \Lambda_m^\infty (CH_3COONa) + \Lambda_m^\infty (HCl) - \Lambda_m^\infty (NaCl) \] Conclusion:
Kohlrausch’s law helps in determining the degree of dissociation and dissociation constant of weak electrolytes.