Thermodynamic formulation on Ostwald’s law of dilution and the acid dissociation constant Ka

The thermodynamic background of Ostwald’s law of dilution, which gives the acid dissociation constant (Ka), is revealed. The feature of Ka as a constant is understandable in the same context as the equilibrium shift of the gas reaction by pressure. The Ka quantity becomes constant under dilution as far as the solution is an ideal mixture. Because the character depends only on the number of solute particles present, the constant Ka is one of the colligative properties of a dilute solution.