Individual Ionic Activity Coefficients And Salting Constants Of Electrolytes In Pure Water And Saccharide + Water Systems

The activity coefficientγi is an importantly physical and chemical parameter which measures the degree of departure the actual behavior of substance i in solution from ideal or ideally dilute behavior. The activity coefficients of individual ions in electrolyte solutions play an important role in some cases: ionic equilibrium through semipermeable membranes, a basic step in the understanding of biological processes, the design of ion-exchange equipment and geological studies. As a part of the National Nature Science Foundation of China (No.20673033), the major contents of the present work are as follows:1. Activity coefficients of individual ions in aqueous solutions of NaF, NaCl and NaBr were determined at 298.15 K by using ion selective electrodes (ISE). The results show that (i) in aqueous NaF solutions, activity coefficients of both Na~+ and F– decrease with increasing molality of NaF; in aqueous NaCl solutions, activity coefficients of Na~+ first decrease and then increase with increasing molality of NaCl. However, those of Cl– decrease with increasing molality of NaCl; in aqueous NaBr solutions, activity coefficients of both Na~+ and Br– first decrease and then increase with increasing molality of NaBr. (ii) The activity coefficients of Na~+ in different aqueous NaX solutions, at the same molalities of sodium halides, are in the order:γNa +(NaBr)>γ_Na~+(NaCl)>γNa +(NaF). This can be attributed to the fact that in NaX solutions, attractions between Na~+ and X– and repulsions between X– and X– depend on the properties of X– (e.g size).2. Similarly, the individual ionic activity coefficients of sodium halides (NaF, NaCl, NaBr) in saccharide (glucose, frucose and sucrose) + water systems were experimentally determined at 298.15 K. It can be concluded that (i) for NaBr in the mixed solvents (glucose or fructose + water), the activity coefficients of Na~+ first decrease and then increase with increasing molality of NaBr, while those of Br– decrease with increasing molality of NaBr; the similar change trend could be found for the activity coefficients of Na~+ and Cl– in aqueous NaCl solution; under the range of the molilaty of saccharide studied, the activity coefficients of Na~+ and F– decrease with increasing molality of NaF. (ii) Generally, the individual ionic activity coefficients of NaX in glucose solutions decrease with increasing molality of glucose. (iii) For given mixed solvents and mE, the activity coefficients of Na~+ are in the order:γNa +(NaBr)>γ_Na~+(NaCl)>γNa +(NaF). This is possibly due to the electrostatic attractions between Na~+ and X– in solutions, which are primarily dependent on the ionic radius of X– (rBr- > rCl- > rF-). However, the activity coefficients of X~– in aqueous NaX are different. For glucose, the variation trends are similar to those of Na~+ expect for F~–. This is possibly attributed to the self-repulsion of F~– ions which is slightly larger than Cl–. However, the change trend of the activity coefficients of X~– for fructose has not been clear. The order for sucrose is:γF~->γBr~->γCl~-. This can be related to the interaction between sucrose molecules and F~–.3. Salting constants of individual ions and electrolytes for NaX + saccharide + water systems were calculated by means of chemical potentials measured. It's shown that (i) the salting constants of all electrolytes could be splited to the contributions of individual ions (activity of salt constants of ions), which could be expressed by the equation: k S(salt,solute) =∑kS(ion,solute). (ii) The salt constants of a given ion depend on its counterion. This is different from the individual ionic limiting molal conductivity which is independent on counterions.