Question

Why is the molar conductivity of a weak electrolyte much lower than that of a strong electrolyte at moderate concentrations?

Answer 1

1. A weak electrolyte typically ionises very little in solution. Only a small number of molecules of a weak electrolyte dissociate into ions at moderate concentrations.
2. Therefore, the concentration of free ions in solution is significantly lower at moderate concentrations than it is for a strong electrolyte.
3. Due to the low concentration of free ions in solution at moderate concentrations, the molar conductivity of the solution of a weak electrolyte is quite low, much lower than that of a strong electrolyte.
4. The molar conductivity of a weak electrolyte solution increases sharply as the concentration of the solution decreases (i.e., dilution increases).
5. This is because the electrolyte is becoming more ionised. The molar conductivity of the solution rises as the solution gets progressively diluted because more molecules of the weak electrolyte dissociate into free ions.
6. A sharp increase in ionisation, or the quantity of free ions in solution, is the cause of the sharp increase in molar conductivity at lower concentrations.