Question

What is Kohlrausch’s law? Write its one application with example.

Hint:

Remember: The law is most useful for weak electrolytes, since their molar conductivity at infinite dilution cannot be measured directly.

Answer 1

Step 1: Statement of Kohlrausch’s Law.
Kohlrausch’s law of independent migration of ions states that at infinite dilution, each ion makes a definite contribution to the molar conductivity of the electrolyte, independent of the other ions present. \[ \Lambda_m^\infty = \lambda^0_+ + \lambda^0_- \] where, - \(\Lambda_m^\infty\) = molar conductivity at infinite dilution
- \(\lambda^0_+\) = contribution of cation
- \(\lambda^0_-\) = contribution of anion
Step 2: Application.
It is used to calculate the molar conductivity of weak electrolytes at infinite dilution by using strong electrolytes. Example:
For acetic acid (\(CH_3COOH\)), which is a weak electrolyte: \[ \Lambda_m^\infty (CH_3COOH) = \Lambda_m^\infty (CH_3COONa) + \Lambda_m^\infty (HCl) - \Lambda_m^\infty (NaCl) \] Conclusion:
Kohlrausch’s law helps in determining dissociation constants of weak electrolytes and studying ionic conductivities.