Activity Coefficients of NaCl in Fructose + Water at 298.15 K

Abstract

The mean ionic activity coefficients of NaCl in fructose + water mixtures were experimentally determined at 298.15 K from electromotive force measurements of the following electrochemical cell containing two ion-selective electrodes (ISE): Na−ISE|NaCl(m),fructose(w),H2O(1−w)|Cl−ISE. The molality (m) varied between (0.005 and 3.5) mol kg-1, while the mass fraction of fructose in the mixture (w) was 0, 0.1, 0.2, 0.3, and 0.4. The emf values were analyzed using different models which employed extended Debye−Hückel equations and those of Pitzer, Scatchard, and Sen for describing the variations in activity coefficients with concentration. Results obtained with the different models were in good agreement. The interaction parameters of each model were comparatively analyzed with those of other similar systems reported in the literature, and discussion is presented concerning their variation with properties of the medium, particularly the dielectric constant. The free energy of transfer of the NaCl from the water to the mixed solvent was determined and its variation with the composition of the solvent is discussed in terms of ion−ion and ion−solvent interactions. Also determined was the primary hydration number of the NaCl, which was compared with results from the literature. Finally, the parameters of interaction gij and salting constant ks were estimated.