Question

How does molar conductivity of a weak electrolyte vary with its concentration in solution?

Answer 1

1. Ordinarily a weak electrolyte does not ionise much in solution. At moderate concentrations, only a few molecules of a weak electrolyte undergo dissociation into ions.
2. Therefore, at moderate concentrations, the concentration of free ions in solution is much less as compared to that of a strong electrolyte.
3. As the concentration of the solution is decreased (i.e., dilution is increased), there is a steep rise in the molar conductivity of the solution of a weak electrolyte.
4. This is due to an increase in the ionisation of the electrolyte. As the solution becomes more and more dilute, more molecules of the weak electrolyte undergo dissociation into free ions, resulting in an increase in the molar conductivity of the solution.
5. The sharp rise in molar conductivity at lower concentrations is due to a sharp increase in ionisation, i.e., due to a sharp increase in the number of free ions in solution.