Thermodynamic Properties of the KCl+H2O System

Abstract

The thermodynamic properties of the KCl+H2O system were examined in order to provide: (1) an improved equation for the osmotic coefficient as a function of molality and temperature for purposes of isopiestic measurements, (2) a determination of the thermodynamic properties of the standard-state solution process, and (3) a test of the accuracy of the enthalpy of solution values for KCl(cr), a calorimetric standard. New equations that describe the thermodynamic properties of the KCl+H2O system were obtained from previously published measurements for this system. The measured values included in the fitted equations spanned the range of temperature from approximately 260 to 420 K for KCl(aq) and 1.5 K to 1033.7 K for KCl(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of KCl(cr) from 0 K to the melting point, 1045 K, (2) the change in chemical potential for both KCl and H2O in KCl(aq) as a function of temperature, and molality, valid from 260 to 420 K, and (3) standard-state properties for the aqueous solution process. The effect of heat treatment on the determination of enthalpy of solution values was also examined. This examination indicated that the NIST recommendation of heating Standard Reference Material 1655, potassium chloride, at 800 K for a minimum of 4 h prior to its use in calorimeter calibration, should probably not be followed. The heat treatment recommended by the NIST certificate appears, at this point, to have a higher probability of corrupting the sample than improving the accuracy of the measurement.

Isopiestic Determination of the Osmotic and Activity Coefficients of Li2SO4(aq) at T=298.15 and 323.15 K, and Representation with an Extended Ion-Interaction (Pitzer) Model

“…There are several previous studies that reported isopiestic data for Li 2 [10][11][12]14,15] were recalculated for consistency using current critical evaluations of the thermodynamic properties of the reference standards NaCl(aq) [7], KCl(aq) [18], and H 2 SO 4 (aq) [19]. [10,14,15], including the present results from Table 2 (excluding a few measurements as described above), are generally in good agreement.…”

Development of an alkali chloride vapour-generating apparatus for calibration of ultraviolet absorption measurements

“…(2.1) have also been compared with vapour pressures calculated with the commercial HSC Chemistry 7.1 software 14 based on extensive compilation of thermochemical data therein. [15][16][17][18][19][20][21][22][23][24][25][26] In addition, the vapour pressure was calculated utilizing the Clausius-Clapeyron equation…”

Isopiestic Investigation of the Osmotic and Activity Coefficients of {yMgCl2+(1−y)MgSO4}(aq) and the Osmotic Coefficients of Na2SO4⋅MgSO4(aq) at 298.15 K

“…or NaCl(aq) are denoted with a subscript R. The osmotic coefficient of each KCl(aq) and NaCl(aq) reference solution at 298.15 K was calculated using the ion-interaction (Pitzer) model and parameters reported by Archer [8,34].…”

“…The parameters at 298.15 K given in their errata are listed in our Table 3, and were used to calculate values of φ at the 6 experimental concentrations reported in Table 1. were recalculated for consistency using up-to-date ion-interaction models for these reference standards [8][9][10]34], where the CaCl 2 (aq) model of Pitzer et al [10] is based on refitting of results from the critical assessment of Rard and Clegg [41]. Rard and Miller [30,39] generally used two or three isopiestic standards in their isopiestic measurements and the average value of the osmotic coefficient for MgCl 2 (aq) was accepted for each equilibration.…”

“…The isopiestic results of Rard and Miller [30] for the equal molar Na 2 SO 4 + MgSO 4 + H 2 O mixtures were recalculated using Archer's [34] model to calculate the osmotic coefficients of the KCl(aq) reference standard. A comparison of their results to those reported in Table 2 with NaCl(aq) as reference standard indicates essentially complete agreement of the osmotic coefficients over with most of the molality range but with slight differences of 0.2 % at the highest overlapping molalities, which is within the uncertainties of the reference standards and thus the agreement is excellent.…”