Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Two-parameter Hu.ckel equations have been determined for the activity coefficient of the salt and for the osmotic coefficient of water in aqueous NaCl or KCl solutions at 0 C from the highly accurate freezing point data of Scatchard and Prentiss (J. Am. Chem. Soc. 1933, 55, 4355.4362), and points were taken in the estimation up to a molality of 0.5 mol Ekg.1. This molality is the upper limit for the use of the data from this method without any corrections to determine thermodynamic activity values for a constant temperature of 0 C. The electrolyte parameters of the Hu.ckel equation are B and b1, and the value obtained for parameter B in the case of both salts is closely the same as that determined in a previous NaCl and KCl study (Partanen, J. I.; Covington, A. K. J. Chem. Eng. Data 2009, 54, 208.219) from the isopiestic and cell potential difference (cpd) data at 25 C. The resulting parameters were tested with the other precise freezing point data existing in the literature for these salts and with the cpd data existing for 0 C. The tests using the latter data reveal that the new parameters apply up to a molality of 1.0 mol Ekg.1. Using the parameter values obtained here for b1 at 0 C and in the previous study at 25 C (see the citation above), a linear dependence of the temperature was determined for this parameter for solutions of both salts. The resulting parameters for B and b1 were tested with the cpd and isopiestic data existing for NaCl and KCl solutions at the temperatures other than 0 and 25 C, and they were observed to be reliable up to a molality of 1.0 mol Ekg.1 in this temperature range. Above 25 C, however, these simple temperature dependences for b1 are probably not sufficient. For a wider range, a quadratic temperature dependence of this parameter was determined for both salt solutions, and these models apply quite well up to 70 C in these dilute solutions. These b1 models were mainly determined from the concentration cell data of Harned and Nims (J. Am. Chem. Soc. 1932, 54, 423.432) and Harned and Cook (J. Am. Chem. Soc. 1937, 59, 1290.1292) for NaCl and KCl solutions measured on cells containing an alkali metal amalgam electrode in the temperature range from (0 to 40) C. These data are not as accurate as the other data used in the present parameter estimation, and therefore, the resulting models are more practical than the linear dependences of b1. The activity and osmotic coefficients from the new Hu.ckel equations are tabulated here at rounded molalities in this wider temperature range, and these values are compared to those regarded as the most reliable in the literature in these connections. Also the activity and osmotic coefficients obtained using the Hu.ckel parameters from Rowland and May (J. Chem. Eng. Data 2014, 59, 2030.2039) are considered here in detail.