Real Ionic Solutions in the Mean Spherical Approximation. 3. Osmotic and Activity Coefficients for Associating Electrolytes in the Primitive Model

摘要

Osmotic and activity coefficients for aqueous solutions of pure associating electrolytes are described by a MSA-like theory that includes the following effects: association (ion pairing or chemical) and solvation. The association of ions of opposite charges is described using the BIMSA, based on the Wertheim formalism. As for nonassociating electrolytes, the hydration is taken into account by introducing a cation size and permittivity that are allowed to vary with concentration. New expressions for the osmotic and activity coefficient are given that account for this variation. These equations have been applied to fit data for a variety of aqueous solutions of pure salts at 25 ℃. About 80 new salts have been treated, including perchlorates, nitrates, hydroxides, and sulfates. For some solutions, good fits could be obtained up to very high concentrations, such as 25 mol kg~(-1) for ammonium nitrate and 34 mol kg~(-1) for potassium nitrite. Solutions of NaOH and nitric acid could be described to 10 mol kg~(-1). A description for sulfuric acid has been obtained at low concentration (below 0.1 mol kg~(-1)). Another description has been made for high concentrations (between 6 and 28 mol kg~(-1)) by using a chemically plausible model. In most cases the association constant is of the same order of magnitude as the literature value when available.