Volumes of ions, ion pairs, and electrostriction of alkali halides in aqueous solutions at 25°C

Millero (1971) (FJM) has made an exhaustive and lucid review of the development of our understanding of the molal volumes of strong electrolytes in aqueous solutions. The data on molal volumes of alkali halide solutions were described by an empirical extended Debye–Hückel equation (valid up to about 4 m) based on the idea of complete dissociation (c.d.) and the constants of the equation have been tabulated. Recently, Krumgalz et al. (1996) (KPP) have established a much more elaborate equation (valid from zero to saturation), also based on the assumption of c.d. for the available volumetric data. On the other hand, Heyrovská (1996) has shown, based on the idea of partial dissociation (p.d.), that the molal volume of a typical strong electrolyte like NaCl( aq) at all concentrations is simply the sum of the volumes of the solvent, ion pairs, ions and electrostriction. The sum of the last two corresponds to the “partial molal volume at infinite dilution”, tabulated by FJM. In this paper, the molal volumes of all alkali halides calculated back from the parameters of the Harned and Owen (1958) (HO) and KPP equations have been shown to be in conformity with the simpler and more meaningful interpretation based on the idea of p.d., as in the case of NaCl(aq). All the results have been presented in the form of graphs and tables.