Re-evaluation of the Thermodynamic Activity Quantities in Aqueous Solutions of Uni-univalent Alkali Metal Salts of Aliphatic Carboxylic Acids and Thallium Acetate at 25 ℃

摘要

The Huckel equation, which was used in this study to correlate the experimental activities of dilute solutions of uni-univalent alkali metal salts of aliphatic carboxylic acids up to a molality of about 1 mol·kg~(-1), contains two parameters that are dependent on the electrolyte: B (closely related to the ion-size parameter a* in the Debye-Huckel equation) and b1 (the coefficient of the linear term with respect to the molality, related to the hydration numbers of the ions of the electrolyte). For thallium acetate solutions, this equation applies up to a molality of 3.5 mol·kg~(-1). In more concentrated solutions of these electrolytes, in the best case up to a molality of about 7.5 mol·kg~(-1), an extended Hiickel equation was used. It contains additionally a quadratic term with respect to the molality, and the coefficient of this term is the parameter b2. All parameter values for the Hiickel equations of lithium, sodium, and potassium acetate were determined from isopiestic data measured by Robinson for solutions of these salts against KCl solutions (J. Am. Chan. Soc. 1935, 57, 1165-1168), and all parameters for rubidium, cesium and thallium acetate solutions were obtained from the osmotic coefficients reported by Robinson for solutions of these salts (J. Am. Chem. Soc. 1937, 59, 84-90). All Huckel parameters for sodium formate, propionate, butyrate, and valerate were determined from the results of isopiestic measurements of Smith and Robinson (Trans. Faraday Soc. 1942, 38, 70-78) in which these salts were measured against KCl solutions, and the parameters for the extended Hiickel equation of potassium formate solutions were solved from the recent vapor pressure data of Beyer and Steiger (J. Chem. Eng. Data 2010, 55, 830-838). The Hiickel parameters of primary sodium and potassium salts of malonic, succinic, and adipic acids were determined from the isopiestic data measured by Stokes (J. Am. Chem. Soc. 1948, 70, 1944-1946) in which these salts were measured against NaCl solutions. The resulting parameter values were tested with the vapor pressure and isopiestic data existing in the literature for the solutions of these organic salts. Most of these data support well the recommended Hiickel parameters at least up to a molality of 3.0 mol·kg~(-1) for all of the salt solutions considered. Reliable activity and osmotic coefficients for solutions of these electrolytes can therefore be calculated using the new Hiickel equations, and they have been tabulated at rounded molalities. The activity and osmotic coefficients obtained from these equations were compared to the values suggested by Robinson and Stokes (Electrolyte Solutions, 2nd ed.; Butterworths: London, 1959), to those calculated using the Pitzer equations with the parameter values of Pitzer and Mayorga (J. Phys. Chem. 1973, 77, 2300-2308), and to those calculated using the extended Hiickel equations of Hamer and Wu (J.Phys. Chem. Ref. Data 1972, 1, 1047-1099).