Pairwise Gibbs function cosphere–cosphere group interaction parameters for alkylammonium salts in aqueous solutions at 298 K; solubilities of hydrocarbons in aqueous salt solutions

Abstract

Excess Gibbs functions G^E(aq; T; p), mean ionic activity coefficients γ_± and practical osmotic coefficients ϕ for dilute aqueous salt solutions are expressed in terms of pairwise ion–ion interaction parameters. These parameters are calculated from β°-terms defined by Pitzer's equations which describe the dependences of (ϕ–1) on molalities of salts in solution. Procedures are described which re-express pairwise ion–ion interaction parameters in terms of pairwise group interaction parameters. The method derives from the procedures used by Savage and Wood in their analysis of the thermodynamic properties of aqueous solutions containing neutral solutes. An extension of these procedures is developed for the properties of salt solutions. A quantitative description emerges of deviations from ideal of the properties of salt solutions based on the concept of cosphere overlap. Data for ammonium, alkylammonium and azoniaspiroalkane salts are used to calculate interaction parameters g(i↔j) between groups i and j involving N⁺, CH₂, Br^–, I^–, Cl^– and F^–. Derived parameters predict, with reasonable success, the general pattern for Setschenow coefficients for hydrocarbons in aqueous salt solutions.