Luzheng Zhang

Determination of activity coefficients using a flow EMF method. 1. HCl in methanol-water mixtures at 25, 35 and 45C

AbstractA method to determine activity coefficients of electrolytes in mixed solvent is described which makes use of ion-selective electrode(s) (ISE) and in which a concentrated electrolyte solution is continuously added. Activity coefficients for HCl in methanol-water mixtures containing 0, 10, 20, 30, 50, 70, and 90 weight percent methanol at 25, 35 and 45°C were calculated using the Pitzer equation, and the electromotive force (emf) data of the cell:

Simultaneous prediction of activity coefficients and enthalpy for aqueous electrolyte solutions at high temperatures

pH - glass electrode\backslash HCl in H_2 O - CH_3 OH\backslash AgCl - Ag

Prediction of Activity Coefficients of Electrolytes in Aqueous Solutions at High Temperatures

The experimental results agree well with literature values indicating that the proposed method is procise and reliable.

A further study of solid–liquid equilibrium for the NaCl–NH4Cl–H2O system

Using ion-selective electrode(s) (ISE) the activity coefficients of NaCl in the system NaCl–NH4Cl–H2O at 10, 25, and 40°C were measured by a computer-controlled automatic titration system. The ionic strength fractions of NH4Cl were 0.2, 0.4, 0.6, and 0.8, respectively. It was found that the influence of the NH4+ cation on the Na glass ISE was small enough to be neglected up to 3.0 mol-kg−1. The Pitzer equation was adopted to calculate the activity coefficients of NaCl in this system and compared with the experimental data. Comparison of results indicates that the Pitzer parameters correlated from solubility data are suitable for calculating the activity coefficients for this system within the saturated solutions.

Measurement of Solid−Liquid Equilibria by a Flow-Cloud-Point Method

The model proposed by Lu and Maurer (1993) for aqueous electrolyte solutions is extended to predict activity coefficients and enthalpy simultaneously. The extensive comparison of literature data to the calculated results of using this model shows that the thermodynamic properties of aqueous mixed electrolyte solutions can be predicted accurately up to the solubility limit at high temperature.

Activity Coefficients of HCl in the HCl + NH4Cl + H2O Systems at 298.15 and 313.15 K

The mean activity coefficients of NaCl in the NaCl‐NH 4HCO3‐H2O system, measured by an electrochemical cell using ion-selective electrodes, were used to calculate the mean activity coefficients of NH 4HCO3 in the system through a thermodynamic model. The measurements were made at four temperatures from 293.15 to 308.15 K up to 1.8 mol kg 1 ,a t NH 4HCO3 molality fractions of 0.2 and 0.4. Both sets of values agree with those obtained from Pitzer equation incorporated with chemical reactions. This observation supports the applicability of the existing parameters for calculating mean activity coefficients of this system.