Ostwald’s dilution law is the application of the law of mass action to weak electrolytes in solution.
A binary electrolyte AB which dissociates into A+ and B– ions.
AB ⇌ A+ + B–
(i) For very weak electrolytes, since α <<< 1, (1 – α) = 1
(ii) Concentration of any ion = Cα = √CK = √K/V
Degree of ionization increases on dilution. Thus, degree of dissociation of a weak electrolyte is proportional to the square root of dilution.