Degree of ionization and ionization constant

The equilibrium concentration of various species at equilibrium can be represented in terms of degree of ionization as:

Then according to law of mass action,

where 'V' is the volume of the solution in litres containing one mole of the solute. From the above equation it follows that if the concentration decreases, the degree of ionization (a) must increase. Thus, at constant temperature, an electrolyte in solution gets ionized to a larger extent with increasing dilution. This is called Ostwald dilution law. This law is not applicable to solutions of strong electrolytes as they are completely dissociated and there is no equilibrium between the dissociated and undissociated molecules.