The methods of Zdanovskii‐Stokes‐Robinson (ZSR), Reilly‐Wood‐Robinson (RWR), Pitzer and Correa, to determine water activity in ternary solutions of electrolytes from data for water activity in binary solutions, were analysed. In addition, the first two methods were used to estimate the activity of water in supersaturated binary solutions using data from ternary solutions. Also, the equation of Correa for binary solutions was extrapolated to calculate the activity of water at supersaturation.
The methods were tested using the experimental data (at 25°C) for nine ternary systems, with a common ion, involving the following ions: Li+, Na+, K+, Ca++, Mg++, Cl− and NO3−. Zdanovskii's method gave the best estimations of water activity in ternary systems. The method of Correa gave smaller standard deviations than the methods of Pitzer and RWR with the advantage that its application is simpler. For binary solutions at supersaturation, Correa's method gave better results than the method of ZSR and this, in turn, yielded smaller deviations than the RWR method.
A simple aiialytical function is proposed for the calculation of molar excess Gibbs energy of binary solutions of strong electrolytes in water. Empirical parameters can be easily determined from experimental data reported in the literature. l l i e treatment is extended to ternary solutions and to solid liquid equilibria rising an empirical equation. Absence of solid solutions is assumed.The correlations are applied to the common ion ternary system NaN0,-NaCl-H,O in the temperature range from 0 to 100°C.Predictions of activity coefficients of the binary systems and saturation curves of the ternary system are in good agreement with expcrimental data.nowledge of the behaviour of concentrated K aqueous solutions of strong electrolytes at different temperatures is necessary f o r rational design of separation equipment used in chemical engineering.Recently interest in this field has increased, especially in the treatment of electrolytes mixtures in
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