Activity Coefficients of the Systems: NaBr + Na‐Acetate + H₂O and NaBr + Na‐Propionate + H₂O at 25°C. Application of Scatchard's, Pitzer's and Lim's Methods

Abstract

Mean activity coefficients for NaBr in NaBr + Na‐Acetate + H2O and NaBr + Na‐Propionate + H2O mixed systems were determined from the emf measurements of galvanic cells without transport. The measurements were carried out at different total ionic strengths I = INaBr + INaR, between 0.1 and 3.5 mol · kg−1 when R = acetate anion, and between 0.1 and 3.0 mol · kg−1 when R = propionate anion. At each total ionic strength, different ratios INaBr/INaR were studied. These experimental mean activity coefficients were comparatively analyzed by using Scatchard's, Pitzer's and Lim's methods, finding that Lim's models lead to better fittings for these mixed systems. From the LH Lim model (that takes into account the Higher Order Limiting Law, HOLL), activity coefficients of traces for both electrolytes in each mixture were determined and qualitatively analyzed. Finally, the Gibbs excess energy of these mixtures was calculated and also qualitatively analyzed against both the size of the non common electrolyte and the composition of the mixed electrolyte.