Study Of Mean Activity Coefficients Of Electrolytes In Mixed Solvent

The study of electrolyte solution thermodynamic is a useful tool for the development of other chemical and biological fields and new theories and techniques are based on it solidly. The friendly relation between people and environment was paid more attention in the 21th century. Chemistry and chemical engineering must progress in green chemistry and green technology. The electrolyte solutions play an important role in the supercritical extraction, separation of membrane, ionic liquid. The study of mean activity coefficients of electrolytes in mixed solvent is of important significance in checking the model of statistical mechanics, calculation of activity coefficients between solvent and solute and predication of salt effect on volatile.The method of Electromotive Force (EMF) can determine the EMF of the cell accurately, and gain thermodynamic properties of aqueous solution interiorly. It straightly gets the EMF of the solution by using electrode probe; and it has been used wildly in single electrolyte, mix electrolyte and balanced constant. Under different electrolyte concentration or different solvent conditions, determining the EMF of some system by the method of emf, which get corresponding thermodynamics data according to Nernst equation about the solution theory. The study of electrolyte solution thermodynamics is one of important content in Physical Chemistry. The EMF is becoming the important means to study the solution and the emf is used by many chemists to study the solution thermodynamics properties now.This paper determines EMF of electrolyte in mixed solvents by cells without liquid junction on different composing. Electromotive force measurements of the cell were carried out at the different molalities of KI in the mixtures of CH3OH-H2O containing 0,20,40,60,80 of weight (%) of CH3OH, respectively at 303.15K. Calculations of standard cell potential of each condition were made by using measurements of the extended Debye-Hückel equation and the Pitzer equation. The mean activity coefficients of KI were obtained from the standard potentials by means of the Pitzer equation. The calculated results show that the activity coefficients of KI in methanol-benzene system with constant composition either decrease as its concentration increases, or decrease at first, then they pass a minimum and increase gradually again. At each fixed KI molality, they decreased with an increase of methanol in solvent mixtures. The weak association of KI in methanol was shown.The activity coefficient of salt in mixed solvent with constant composition as a function of vapor-liquid equilibrium data was derived by Ren Yi Sun based on the ternary Gibbs-Duhem equation and two independent test criteria for the thermodynamic consistency of the data has been suggested according to thermodynamics and the Debye-Hückel electrolytic solution theory. The paper gives the thermodynamic equation of effect of salt on vapor-liquid equilibrium at constant liquid composition which contains integral term of the mean activity coefficients of electrolytes in mixed solvent. Recently the determinations of activity coefficients of electrolytes in mixed solvent by EMF measurement in the cells were reported in the literature, but much less attention has been received on non-aqueous mixed systems. Some experimental methods have been developed or perfected for the determinations of activity coefficients of electrolytes in mixed solvent, in which the method of EMF have been reported frequently, nevertheless the method of EMF are mainly adequate for aqueous solution. This paper gives results for mean activity coefficients of electrolytes in non-aqueous solvent by measurement of salt effect on vapor-liquid equilibrium, it not only help realize the essence of salt effect but also introduce a kind of determination method of the mean activity coefficients of electrolytes in mixed solvent. The method of vapor-liquid equilibrium measurement is adequate for non-aqueous mixed solvent particularly. By measuring the vapor-liquid equilibrium of methanol (1) - benzene (2) - NaI and testing the data using the ternary Gibbs-Duhem equation, the experimental results of the vapor-liquid equilibrium with thermodynamics consistency are obtained. It is supposed that the mean activity coefficients of NaI may be represented by power of m1/2. We also calculated using measurements of the Pitzer equation. The calculation results of NaI activity coefficients the show that the activity coefficients of NaI in methanol-benzene system with constant composition either decrease as its concentration increases or decrease at first then they pass a minimum and increase gradually again. This method is applicable to determination of electrolytic activity coefficients in non-aqueous mixed solvents.