The osmotic pressure of the ions and of the undissociated molecules of salts in aqueous solution

Abstract

The concentration of the ions (Ci) and that of the undissociated molecules (CU) are involved in the equation, Ci^2 / Cu = K, expressing the application of the law of mass-action to solutions of electrolytes. Hence the large divergence from this law which strong electrolytes exhibit may be due to the behavior of the ions, to that of the undissociated molecules, or to that of both. This so called anomalous behavior may be simply expressed by saying that for one or for both of these molecular species van't Hoff's law, II = CRT, where II is the osmotic pressure, C is the concentration in mols per unit-volume, R is the gas-constant, and T is the absolute temperature, does not hold; for, if all of the molecular species entering into an equilibrium obey this law, the law of mass-action is a thermodynamic necessity. [1] In this paper is outlined and applied a method for determining the extent to which the ions and the undissociated molecules deviate from van't Hoff's law, that is, for determining the relation between the osmotic pressure of the ions or of the undissociated molecules and their concentration. The significance of the results, particularly as applied to the calculation of the degree of ionization and to the validity of the law of mass-action, is discussed.