Question

Which of the following statements is correct?
(A) Molar conductivity of a strong electrolyte decreases with dilution.
(B) Molar conductivity of a strong and weak electrolyte decreases with dilution
(C) Molar conductivity of a weak electrolyte decreases with dilution
(D) Molar conductivity of a strong and weak electrolyte increases with dilution.

Answer 1

Hint: Molar conductivity of a strong and weak electrolyte increases with dilution. The dissociation of a weak electrolyte and strong electrolyte increases with dilution giving more ions, its molar conductance increases with dilution. The solution of weak and strong electrolyte is diluted, the volume of the solution increases, hence equivalent conductivity increases.

Complete answer:
Molar conductivity of a strong and weak electrolyte increases with dilution. On dilution as volume of solution increases. Thus, the number of ions per ml decreases and hence conductivity decreases. Molar conductivity is defined for one mole of ions. Thus on dilution, ions get more apart and mobility of ions increases which leads to increase in molar conductivity of the solution.
For weak electrolytes, however, the molar conductivity strongly depends on concentration: The more dilute a solution, the greater its molar conductivity, due to increased ionic dissociation. For a weak electrolyte molar conductance in dilute solution increases sharply as its concentration in solution is decreased.
As the dilution increases, the dissociation of the electrolyte increases, hence the total number of ions increases, therefore, the molar conductivity increases.
So, the correct answer is (D) molar conductivity of a strong and weak electrolyte increases with dilution.

Note:
Kohlraush's law helps to find molar conductivity of a weak electrolyte at infinite dilution. A Kohlraush's law can be defined as the equivalent conductivity of an electrolyte at infinite dilute is equal to total conductance of the anions and cations.