ACTIVITY-COEFFICIENTS OF THE SYSTEMS - NABR -ACETATE + H2O AND NABR +NA-PROPIONATE + H2O AT 25-DEGREES-C - APPLICATION OF SCATCHARD PITZERAND LIM METHODS( NA)

Mean activity coefficients for NaBr in NaBr + Na-Acetate + H2O and NaB r + Na-Propionate + H2O mixed systems were determined from the emf mea surements of galvanic cells without transport. The measurements were c arried out at different total ionic strengths I = I(NaBr) + I(NaR), be tween 0.1 and 3.5 mol . kg-1 when R = acetate anion, and between 0.1 a nd 3.0 mol kg-1 when R = propionate anion. At each total ionic strengt h, different ratios I(NaBr)/I(NaR) were studied. These experimental me an activity coefficients were comparatively analyzed by using Scatchar d's, Pitzer's and Lim's methods, finding that Lim's models lead to bet ter fittings for these mixed systems. From the LH Lim model (that take s into account the Higher Order Limiting Law, HOLL), activity coeffici ents of traces for both electrolytes in each mixture were determined a nd qualitatively analyzed. Finally the Gibbs excess energy of these mi xtures was calculated and also qualitatively analyzed against both the size of the non common electrolyte and the composition of the mixed e lectrolyte.