Limiting Activity Coefficients for Aqueous Solutions
Measurement techniques for limiting activity coefficients ($\gamma\sp\infty$) are reviewed with respect to aqueous solutions. Literature values for $\gamma\sp\infty$ of solutes in water at 25$\sp\circ$C were compiled and critically evaluated to form a database of high confidence for 120 compounds. Predictive expressions for $\gamma\sp\infty$ were analyzed for aqueous systems. The use of other thermodynamic measurements such as inverse solubility and hexadecane-water and octanol-water partition coefficients were also evaluated as methods for obtaining $\gamma\sp\infty$ of solutes in water. A database of inverse solubility of solutes in water was compiled. Differential ebulliometry was used to measure $\gamma\sp\infty$ over a modest range of temperatures for three solvents in water and water in six solvents. The data were used to demonstrate the limitations of several current excess Gibbs energy expressions in representing both vapor-liquid and liquid-liquid equilibrium data from $\gamma\sp\infty$ measurements. A new technique for measuring limiting activity coefficients of low relative volatility solutes was developed based on measuring the change in the dew point temperature of a solvent with the dilute addition of a solute. This dew point method was used to measure $\gamma\sp\infty$ for three solutes in water over a range of temperatures. The low $\gamma\sp\infty$ values for these solutes indicate solvation occurring in the mixture. Ideal chemical theory was used to model the measured dew point temperatures.
Engineering, Chemical, Environmental Sciences
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign