Critical Evaluation of the Thermodynamic Properties of Aqueous Calcium Chloride. 1. Osmotic and Activity Coefficients of 0−10.77 mol·kg^-1 Aqueous Calcium Chloride Solutions at 298.15 K and Correlation with Extended Pitzer Ion-Interaction Models

Abstract

Isopiestic vapor-pressure measurements were performed at 298.15 K for CaCl 2 (aq) solutions at 66 molalities from (4.3235 to 10.253) mol‚kg -1 , using H 2 SO 4 (aq) as the reference standard, with emphasis given to the accurate characterization of the osmotic coefficients near and above saturation. Published isopiestic molalities, direct vapor pressures, and emf results for CaCl 2 (aq) have been critically reevaluated and recalculated in an internally consistent manner. This critically-assessed database was used to evaluate the parameters of Pitzer's equations and various extended forms at 298.15 K and 0.1 MPa. Neither the standard equations nor empirically extended versions were able to represent the thermodynamic results over more than part of the molality range without large cyclic systematic deviations. It was possible, however, to obtain essentially quantitative agreement between experiment and model over the full molality range if (1) the presence of CaCl + (aq) ion pairs was included explicitly and (2) higherorder virial terms were included. One such quantitative model is presented here in detail. Without these higher-order virial terms the same model is able to represent the φ(CaCl 2 ) fairly well only to about 8 mol‚kg -1 . The osmotic coefficient of CaCl 2 (aq) goes through a minimum around 0.11 mol‚kg -1 , which is followed by a regular increase with molality to a broad maximum in the supersaturated molality region where φ(CaCl 2 ) is nearly constant at 3.169-3.173 from about (8.5 to 9.5) mol‚kg -1 . It then decreases slightly by about 0.3% at higher molalities.

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].…”

Sit Parameters for 1:2 Electrolytes and Correlation with Pitzer Coefficients

“…Most of these values are taken from Robinson and Stokes 13 and Harned and Howen, 14 but implemented with other more recent data, in particular as concerns magnesium and calcium chlorides, magnesium, calcium and barium nitrate and sulfate salts. [15][16][17][18][19][20] A wide range of salt concentration was considered: for example 0.1 ≤ m ≤ 6 mol kg -1 for calcium salts. Results are reported in TABLES 1-6.…”

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

“…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.…”