Partial molar volumes of sodium chloride solutions at 200 bar,and temperatures from 175 to 350°C

High precision densities of sodium chloride solutions at a constant pressure of 200 bar and temperatures between 175°C and 350°C have been measured by a mercury displacement technique. The densities have been converted to apparent molar volumes. The apparent molar volumes decrease with increasing temperature and decreasing concentration whereas the concentration effect increases with temperature. Standard partial molar volumes range from 8.0 cm³-mol^–1 at 175°C to –600 cm³-mol^–1 at 350°C. The results indicate the applicability of the unextended Debye-Hückel limiting law up to concentrations of 0.02 mol-kg^–1.     

Densities and apparent molal volumes of aqueous concentrated calcium chloride solutions from 50 to 200°C at 20.27 bar

Densities of aqueous calcium chloride solutions are reported for molalities up to 6.4 mol-kg^–1 at temperatures from 50 to 200°C and at 20.27 bar. Apparent molar volumes calculated from experimental densities were fitted to the equations of Rogers and Pitzer, and the temperature dependence of the Pitzer parameters were obtained. The standard deviation of fit for the apparent molar volumes is 0.21 cm³-mol^–1 from 50 to 200°C at 20.27 bar.     

Densities and partial molar volumes of aqueous solutions of lithium,sodium, and potassium hydroxides up to 250°C

The densities of aqueous solutions of lithium, sodium and potassium hydroxides were measured up to 3m (mol-kg^–1) with a vibrating tube densimeter from 55 to 250°C an at pressures close to saturation. The apparent molar volumes of the solutions were calculated and the infinite dilution values at each temperature and saturation pressure were obtained by extrapolation. The present data are compared with literature values (for LiOH and KOH below 75°C and over the entire temperature range for NaOH) and with the predictions of a semiempirical model. It is concluded that the high temperature data for NaOH reported here improves the available experimental information on the volumetric properties of this system. The influence of ion association on the volumetric properties of LiOH solutions is also discussed.     

Sodium sulfate solubilities in high temperature aqueous sodium chloride and sulfuric acid solutions—predictions of solubility,vapor pressure,acidity, and speciation

Experimental measurements of the solubility of sodium sulfate in aqueous solutions containing both sodium chloride and sulfuric acid in the temperature range 250 to 374°C are reported. These measurements have been combined with previous data on the solubility of sodium sulfate in water, in aqueous sodium chloride, and in sulfuric acid solutions to produce a comprehensive model describing the solubility of sodium sulfate in such solutions. Calculations and predictions of solubility, vapor pressure, boiling point elevation, acidity, and speciation are presented. This model is of fundamental interest in itself and also is of importance because the precipitation of sodium sulfate may be a contributing factor in enhancing crevice corrosion in metals exposed to high-temperature water containing chloride and sulfate ions as impurities.     

Modified Raoult's law including the solvent structural constant and solute solvation; Aqueous sodium chloride solutions, 25 to 300°C; Other electrolytes and urea, 25°C

The form of Raoult's law is modified to express the activity of water [a(H₂O)] for aqueous electrolyte solutions by the mole fraction of a free (nonsolvating) solvent structural unit raised to the reciprocal power of the solvent structural constant. Relatively close agreement with experiment, is obtained for a(H₂O) of aqueous sodium chloride solutions up to 300°C and nearly saturated concentrations, and of other aqueous electrolyte solutions at 25°C. In an example for aqueous-organic systems, a(H₂O) for urea solutions at 25°C is described with an average deviation of 0.09% for molalities from 0 to 20m (54.6 wt%) by using the necessary (universal) structural constant and a single solvation parameter.     

Thermodynamics of aqueous phosphate solutions: Apparent molar heat capacities and volumes of the sodium and tetramethylammonium salts at 25°C

A Picker flow microcalorimeter and a flow densimeter were used to obtain apparent molar heat capacities and apparent molar volumes of aqueous solutions of Na₃PO₄ and mixtures of Na₂HPO₄ and NaH₂PO₄. Identical measurements were also made on solutions of tetramethylammonium salts to evaluate the importance of anion-cation interaction. The experimental apparent molar properties were analyzed in terms of a simple extended Debye-Hückel model and the Pitzer ion-interaction model, both with a suitable treatment for the effect of chemical relaxation on heat capacities, to derive the partial molar properties of H₂PO ₄ ^– (aq), HPO ₄ ^2– (aq) and PO ₄ ^3– (aq) at infinite dilution. The volume and heat capacity changes for the second and third ionization of H₃PO₄(aq) have been determined from the experimental data. The importance of ionic complexation with sodium is discussed.     

Volumes,heat capacities and solubilities of amyl compounds in decyltrimethylammonium bromide aqueous solutions

Apparent molar heat capacities and volumes of amylamine (PentNH₂) 0.02m, capronitrile (PentCN) 0.02m and nitropentane (PentNO₂) 0.009m in decyltrimethylammonium bromide (DeTAB) micellar solutions, in water and in octane were measured at 25°C. By assuming that their concentration approaches the standard infinite dilution state, heat capacities and volumes were rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase and heat capacity and volume of the additives in both phases are simultaneously derived. The present results are compared to those we have previously obtained for pentanol (PentOH). The thermodynamic properties of PentNH₂ in water and in micellar phase are substantially identical to those of PentOH but different from those of PentCN and PentNO₂ whereas the opposite behavior was observed in their pure liquid state and in octane. The nature of the solvent medium seems to affect the thermodynamic behavior of PentNH₂. Also, the study of the apparent molar heat capacities of the amyl compounds investigated here in micellar solutions as a function of surfactant concentration shows evidence of a maximum at about 0.4m DeTAB, which can be attributed to a micellar structural transition. Accordingly, the solubilities of PentCN and PentNO₂ as a function of the DeTAB concentration drop in the neighborhood of the concentration where heat capacities display the maximum.     

Partial molar heat capacities and volumes of transfer of nucleic acid bases,nucleosides and nucleotides from water to aqueous solutions of sodium and calcium chloride at 25°C

Partial molar heat capacities and volumes of some nucleic acid bases, nucleosides and nucleotides have been measured in 1m aqueous NaCl and CaCl₂ solutions using Picker flow microcalorimeter and a vibrating tube digital densimeter. The partial molar heat capacities of transfer and volumes of transfer from water to the electrolyte solutions were calculated using earlier data for these compounds in water. The values of these transfer parameters are positive. The higher values for transfer to aqueous CaCl₂ solutions reflect the stronger interactions of the constituents of the nucleic acids with Ca⁺² ions than with the Na⁺ ions.