Abstract: Isopiestic vapor-pressure measurements were performed at 298.15 K for CaCl2(aq) solutions at 66 molalities from (4.3235 to 10.253) mol·kg-1, using H2SO4(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 CaCl2(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) higher-...

Abstract: H2O activities in supercritical fluids in the system KCl-H2O-(MgO) were measured at pressures of 1, 2, 4, 7, 10 and 15 kbar by numerous reversals of vapor compositions in equilibrium with brucite and periclase. Measurements spanned the range 550–900 °C. A change of state of solute KCl occurs as pressures increase above 2 kbar, by which H2O activity becomes very low and, at pressures of 4 kbar and above, nearly coincident with the square of the mole fraction (xH2O). The effect undoubtedly results primarily from ionic dissociation as H2O density (ρH2O) approaches 1 gm/cm3, and is more pronounced than in the NaCl-H2O system at the same P-T-X conditions. Six values of solute KCl activity were yielded by terminal points of the isobaric brucite-periclase T-xH2O curves where sylvite saturation occurs. The H2O mole fraction of the isobaric invariant assemblage brucite-periclase-sylvite-fluid is near 0.52 at all pressures, and the corresponding temperatures span only 100 °C between 1 and 15 kbar. This remarkable convergence of the isobaric equilibrium curves reflects the great influence of pressure on lowering of both KCl and H2O activities. The H2O and KCl activities can be expressed by the formulas: aH2O = γH2O[xH2O+(1 + (1 + α)xKCl)], and aKCL = γKCl[(1 + α)xKCl/(xH2O +(1 + α)xKCl)](1 + α), where α is a degree of dissociation parameter which increases from zero at the lowest pressures to near one at high pressures and the γ's are activity coefficients based on an empirical regular solution parameter W: ln γi = (1 − xi)2W. Least squares fitting of our H2O and KCl activity data evaluates the parameters: α = exp(4.166 −2.709/ρH2O) − 212.1P/T, and W = (−589.6 − 23.10P) /T, with ρH2O in gm/cm3, P in kbar and T in K. The standard deviation from the measured activities is only ± 0.014. The equations define isobaric liquidus curves, which are in perfect agreement with previous DTA liquidus measurements at 0.5–2 kbar, but which depart progressively from their extrapolation to higher pressures because of the pressure-induced dissociation effect. The great similarity of the NaCl-H2O and KCl-H2O systems suggests that H2O activities in the ternary NaCl-KCl-H2O system can be described with reasonable accuracy by assuming proportionality between the binary systems. This assumption was verified by a few reconnaissance measurements at 10 kbar of the brucite-periclase equilibrium with a Na/(Na + K) ratio of 0.5 and of the saturation temperature for Na/(Na + K) of 0.35 and 0.50. At that pressure the brucite-periclase curves reach a lowest xH2O of 0.45 and a temperature of 587 °C before salt saturation occurs, values considerably lower than in either binary. This double-salt eutectic effect may have a significant application to natural polyionic hypersaline solutions in the deep crust and upper mantle in that higher solute concentrations and very low H2O activities may be realized in complex solutions before salt saturation occurs. Concentrated salt solutions seem, from this standpoint, and also because of high mechanical mobility and alkali-exchanging potential, feasible as metasomatic fluids for a variety of deep-crust and upper mantle processes.

Abstract: Parameters governing the rates of mass transfer of the individual components of four synthetic dense non-aqueous phase liquid (DNAPL) mixtures into the aqueous phase were evaluated. The DNAPL mixtures, composed of toluene and eight polynuclear aromatic hydrocarbons (PAHs), were designed to serve as models for coal tars and creosotes. The reactor employed provided a relatively stable interface between internally mixed but segregated aqueous and DNAPL phases. Two parameters, the aqueous phase concentration at equilibrium and the overall film mass transfer coefficient, were quantified by simulating aqueous concentration profiles with a mass-transfer-limited rate model using a statistical parameter search and data fitting routine. DNAPL phase activity coefficient values for the various compounds derived from equilibrium aqueous phase concentrations were typically within a factor of 2 of Raoult's law prediction of unity; refinement of fugacity ratio estimates for the solid PAHs brought the values even closer t...

Abstract: Isothermal vapor−liquid equilibria (VLE), excess molar enthalpies, , and excess molar volumes, , have been measured for the binary mixtures dimethyl carbonate + methanol, + ethanol, or + propan-1-ol at 313.15 K and at atmospheric pressure. The three mixtures exhibit large deviations from ideality, showing an azeotrope at 0.14, 0.42, and 0.78 mole fraction of dimethyl carbonate, respectively. The VLE data were correlated by the Wilson equation and the appropriate parameters are reported. and values have been correlated using the Redlich−Kister equation by the method of least-squares.

Abstract: Vapor pressures of aqueous solutions of l-amino acids (glycine, l-alanine, l-valine, and l-serine) were measured at various concentrations at 298 K by a differential pressure static method. Activities and activity coefficients of water were determined. The activity coefficients of the amino acids in water were obtained from the activity coefficients of water using the UNIQUAC equation. The obtained activity coefficients of the amino acids were evaluated by comparison of the values obtained by a conventional virial expansion method and the literature data.

Abstract: An equilibrium multicomponent ion exchange model is presented for the ion exchange of group I metals by TAM-5, a hydrous crystalline silicotitanate. On the basis of the data from ion exchange and structure studies, the solid phase is represented as Na3X instead of the usual form of NaX. By using this solid phase representation, the solid can be considered as an ideal phase. A set of model ion exchange reactions is proposed for ion exchange between H+, Na+, K+, Rb+, and Cs+. The equilibrium constants for these reactions were estimated from experiments with simple ion exchange systems. Bromley's model for activity coefficients of electrolytic solutions was used to account for liquid phase nonideality. Bromley's model parameters for CsOH at high ionic strength and for NO2- and Al(OH)4- were estimated in order to apply the model for complex waste simulants. The equilibrium compositions and distribution coefficients of counterions were calculated for complex simulants typical of DOE wastes by solving the equil...

Abstract: Isobaric vapor−liquid equilibrium data at 101.33 kPa are reported for binary systems formed by N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF) with benzene, heptane, hexane, or cyclohexane. Data reduction based on the Van Laar, Wilson, NRTL, and UNIQUAC models provides a correlation for the liquid-phase activity coefficients. All the systems, except for the ones formed with benzene, are strongly nonideal, yielding two phases at low temperatures.

Abstract: The surface tension of aqueous solutions of dodecylammonium chloride–octyl methyl sulfoxide (OMS) and dodecyltrimethylammonium bromide–OMS mixtures was measured as a function of the total molality of surfactants and the composition of OMS. The results were analyzed according to our thermodynamic procedure; the phase diagrams of adsorption and micelle formation and the diagram illustrating the composition relation between the micelle and the adsorbed film at the critical micelle concentration were drawn. The activity coefficient and excess Gibbs energy in the adsorbed film and the micelle were defined and then evaluated from the phase diagrams. They were found to give useful information on the deviation from ideal mixing and intermolecular interaction in the adsorbed film and micelle.

Abstract: Activity coefficients at infinite dilution provide a useful tool for solvent selection in extractive distillation or extraction processes. In this work activity coefficients at infinite dilution for various solutes (alkanes, cycloalkanes, alcohols, aromatic hydrocarbons, xylenes and alkenes) in the solvent 1-octanol were measured at four temperatures, (293.44, 303.45, 313.55, and 323.43) K, with the help of gas−liquid chromatography. The adsorption at the gas−liquid interface between the solutes and the solvent was examined by varying the solvent liquid loading in the columns. Corrected retention values taking adsorption effects into account are determined and are used to calculate the activity coefficients at infinite dilution. These values compare well with various activity coefficients taken from the literature using different techniques and the predicted values using the modified UNIFAC (Dortmund) method. An important application of the present data can be seen in the use of 1-octanol as a solvent for...

Abstract: Dielectric relaxation of water molecules was measured in the frequency range from 0.2 to 20 GHz for aqueous solutions of urea, formamide, alcohols, and saccharides. The relaxation behavior was described well by the Debye equation with a single relaxation process in most cases. The static permittivity of solution and relaxation time of water in solution changed linearly with solute concentration. The relaxation time shift of water molecules through the existence of solute was correlated well to the first virial coefficient of the activity coefficient of water suggesting the close relationship between dielectric relaxation time and aqueous solution structure.

Abstract: The activity coefficients of ZnSO4, MgSO4, CaSO4, and SrSO4 are measured by means of cells with ion-exchange liquid membranes similar to those described in the previous papers of this series. Negative deviations from the limiting law are observed in the dilute region. These deviations are, for ZnSO4, appreciably more important than recent literature has indicated, and the corresponding activity coefficients need to be corrected by about 12%. Pitzer’s theory best-fit coefficients have accordingly been recalculated. The osmotic coefficients are also derived. Accessory information on the hydration state for zinc, magnesium, and sulfate ions, is presented.

Abstract: The activity of aluminum in molten Ti–Al alloy was measured by `free evaporation method'. The specimen was melted and held at constant temperature in an electron beam vacuum furnace. The weight change was measured and converted to the rate of evaporation of constant composition. The Hertz–Knudsen equation was then applied to calculate the vapor pressure of the element, and the activity was obtained by comparing that with the pressure of the pure substance. The activity coefficient at mole fractions of aluminum less than 0.1 is about 0.03 and that for over 0.2 was about 0.1. The activity of titanium was also calculated by integration of the Gibbs–Duhem equation for a binary mixture based on the activity of aluminum.

Abstract: : This report documents a Fortran version of a chemical thermodynamic model for aqueous electrolyte solutions at subzero temperatures, FREZCHEM2, which is a further development of the FREZCHEM model. The model uses thermodynamic data of Spencer-Moller- Weare that permit the calculation of chemical equilibria in the Na-K-Ca-Mg-Cl-S04-H2O system between -60 and 25 deg. C at atmospheric pressure. It applies the Gibbs energy minimization method for chemical equilibrium computation combined with Pitzer equations for activity coefficients and water activity calculation. phases.

Abstract: Apparent molar enthalpies have been determined as a function of concentration by heat conduction calorimetry for aqueous solutions of the phenothiazine drugs chlorpromazine hydrochloride, promethazine hydrochloride, and promazine hydrochloride in the presence of added electrolyte (0.025−0.10 mol dm-3 NaCl). The concentration dependence of the apparent molar enthalpy could be quantitatively described using a mass action model of association based on the Guggenheim equations for the activity coefficients for mixed electrolytes. Derived values of the monomer−counterion interaction coefficient became increasingly negative with increase of salt concentration, suggesting that electrolyte addition promoted association at concentrations below the critical micelle concentration (cmc). Calculations of the fraction of each drug in the form of micelles as a function of concentration further confirmed the tendency for premicellar association. Significant differences in properties were observed between promethazine and...

Abstract: Isobaric vapor-liquid equilibrium data for monocthanolamine (MEA)+water and monoethanolamine (MEA)+ ethanol were measured in an equilibrium cell circulating both the vapor and liquid phases. The measurements of the boiling temperatures and corresponding equilibrium compositions for two binary mixtures were carried out at the atmospheric pressure. The results were checked for thermodynamic consistency by the point test method. The activity coefficients for nonideality of the liquid phase were calculated by using the Wilson, NRTL, and UNIQUAC equations. The fugacity coefficients for nonideality of the vapor phase were calculated from the virial equation of state with the second virial coefficient. The experimental data were verified to be thermodynamically consistent and showed a good agreement with the calculated values.

Abstract: The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.