Re-Evaluation of the Thermodynamic Activity Quantities in Aqueous Sodium and Potassium Chloride Solutions at 25 °C

Abstract

The Hu ¨ckel equation is used to correlate the experimental activities of dilute NaCl and KCl solutions up to a molality of about 1.0 mol • kg -1 . The two parameters of this equation are dependent on the electrolyte and are B [which is simply related to the ion-size parameter (a*) in the Debye-Hu ¨ckel equation] and b 1 (which is the coefficient of the linear term in molality and related to hydration numbers of the ions of the electrolyte). In more concentrated solutions up the saturation for both electrolytes, an extended Hu ¨ckel equation was used, and it contains, additionally, a quadratic term with respect to the molality with parameter b 2 . The values of parameters B and b 1 for dilute KCl solutions were determined from the cell potential differences measured by Hornibrook et al. on concentration cells with transference (J. Am. Chem. Soc. 1942, 64, 513-516). With these values of KCl, the corresponding parameter values for NaCl solutions were determined from the isopiestic data of Robinson for NaCl and KCl solutions (Trans. R. Soc., N. Z., 1945, 75, 203-217). Only the data points for NaCl molalities less than 1.4 mol • kg -1 were included in this determination. The resulting parameter values were successfully tested with all reliable cell potential and isopiestic data in the literature for dilute NaCl and KCl solutions. For more concentrated solutions, new values of parameters b 1 and b 2 were determined for the extended Hu ¨ckel equations of NaCl and KCl, but the same values of parameter B were used as for dilute solutions. For these more concentrated NaCl solutions, the values of parameters b 1 and b 2 were determined from the vapor pressure data of Olynyk and Gordon (J. Am. Chem. Soc. 1943, 65, 224-226), which cover the molality range (2.3 to 6.1) mol • kg -1 . With these values for NaCl, the corresponding parameter values for more concentrated KCl solutions were determined from the isopiestic data of Robinson for this pair of electrolytes (see the citation above), where all experimental points were included in the determination. The resulting extended Hu ¨ckel equations were thoroughly 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 Hu ¨ckel equations up to the saturated solutions. Reliable activity and osmotic coefficients of NaCl and KCl can, therefore, be calculated by using the Hu ¨ckel and extended Hu ¨ckel equations determined in this study. The values obtained by these equations are probably the most accurate values available, and they have been tabulated at rounded molalities. The activity and osmotic coefficients obtained from the new equations were compared with the values suggested by Robinson (see citation above), with those calculated by using the Pitzer equations of Pitzer and Mayorga (J.

Re-evaluation of the thermodynamic activity quantities in aqueous alkali metal nitrate solutions at T= 298.15 K

“…In the previous studies, it was found that the following Hückel equations apply very well to the thermodynamic properties of NaCl [11], KCl [11], LiCl [19], RbCl [20], CsCl [20], and alkali metal bromide [21] solutions at least up to a molality of 1 mol Á kg À1 :…”

“…In more concentrated solutions, the following extended Hückel equations were used here as earlier [11,[18][19][20][21] for the activity and osmotic coefficients:…”

“…Usually, the points where the alkali metal nitrate molality is less than 1.5 mol Á kg À1 could be included in the determination. The Hückel parameters needed in the estimation from the isopiestic results for KCl were taken from the results of a previous study [11] where NaCl and KCl solutions are considered. The resulting parameter values were tested with the data used in the parameter estimation.…”

“…These activity and osmotic coefficients were compared to those of the previous investigations (some of which, in addition to Robinson and Stokes' values [2], have achieved wide acceptance). Activity coefficient deviations in this comparison are presented as the cell-potential deviations for galvanic cells without a liquid junction (in the same way as in references [8,11,18]) and the osmotic coefficient deviations are presented as vapour pressure deviations (as in references [11,[19][20][21]). …”

Development of intermolecular potential models for electrolyte solutions using an electrolyte SAFT-VR Mie equation of state

“…The experimental data for γ exp ±,m at salt saturation are obtained from [91][92][93][94][95][96][97][98][99][100], and the values of K sp calculated from Equation (55) or taken from [101] are presented in Table 10. We predict the solubility limits at 298 K and 1.01 bar for a number of aqueous salt solutions using the solubility equation with the solubility product obtained from both Equations (42) and (55); the results are presented in Table 11 alongside the experimental solubility data [70,[102][103][104].…”