Re-Evaluation of the Thermodynamic Activity Quantities in Aqueous Lithium Chloride Solutions at 25 °C up to a Molality of 6.0 mol·kg−1

Abstract

The Hückel equation used in this study to correlate the experimental activities of dilute LiCl solutions up to a molality of about 1.0 mol·kg−1 contains two parameters being dependent on the electrolyte: B [that is related closely to the ion-size parameter (a*) in the Debye−Hückel equation] and b1 (this parameter is the coefficient of the linear term with respect to the molality, and this coefficient is related to hydration numbers of the ions of the electrolyte). In more concentrated solutions up to a molality of 6.0 mol·kg−1, an extended Hückel equation was used. It contains additionally a quadratic term with respect to the molality, and the coefficient of this term is the parameter b2. The values of parameters B and b1 for dilute LiCl solutions were determined from the isopiestic data measured by Robinson and Sinclair for KCl and LiCl solutions (J. Am. Chem. Soc. 1934, 56, 1830−1835) by using the Hückel parameters determined recently by Partanen and Covington for dilute KCl solutions (J. Chem. Eng. Data 2009, 54, published ASAP July 24, 2008). The resulting parameter values were tested with the sparse cell potential and isopiestic data existing in the literature for dilute LiCl solutions. In more concentrated solutions, new values of parameters b1 and b2 were determined for the extended Hückel equation of LiCl but the same value of parameter B was used as for dilute solutions. The values of b1 and b2 for LiCl were determined from the isopiestic data measured by Robinson for NaCl and LiCl solutions (Trans. Faraday Soc. 1945, 41, 756−758) by using the extended Hückel equation determined recently by us for concentrated NaCl solutions (see the citation above). The resulting extended Hückel equation was tested with all reliable experimental data presented in the literature on the basis of electrochemical, isopiestic, and direct vapor pressure measurements. Most of these data can be reproduced within experimental error by means of the extended Hückel equation up to a molality of 6.0 mol·kg−1. Reliable activity and osmotic coefficients for LiCl solutions can, therefore, be calculated by using the new Hückel equations, and they have been tabulated here at rounded molalities. The activity quantities obtained from these equations were compared to the values suggested by Robinson and Stokes (Trans. Faraday Soc. 1949, 45, 612−624), to those calculated by using the Pitzer equations of Pitzer and Mayorga (J. Phys. Chem. 1973, 77, 2300−2308), of Kim and Frederick (J. Chem. Eng. Data 1988, 33, 177−184), and of Marshall et al. (J. Chem. Eng. Data 1995, 40, 1041−1052), and to those calculated by using the extended Hückel equation of Hamer and Wu (J. Phys. Chem. Ref. Data 1972, 1, 1047−1099).