Stability of nickel(II) glycylglycinate complexes in aqueous solutions of dimethylsulfoxide at 298.15 K

Stability constants of nickel(II) glycylglycinate complexes in aqueous solutions of dimethylsulfoxide of variable composition (from 0.00 to 0.60 mole fractions DMSO) are determined according to potentiometry at 298.15 K and an ionic strength of 0.1 M (NaClO₄). It is determined that with a rise in the concentration of an organic cosolvent in solution, the stability of nickel(II) complexes with glycylglycinate ion on the whole increases, but the logK _stability = f(X _DMSO) dependences are of a critical character with a maximum of 0.3 mole fractions DMSO. It is demonstrated that the rise in the stability of complexes is related to the destabilization of ligands in the low concentration range of the organic component, while the presence of a maximum is due to the different dynamics of the solvation contributions from reagents during changes in the Gibbs energy of reaction.     

Surface tension and density of mixtures of 1,3-dioxolane+alkanols at 298.15 K: analysis under the extended Langmuir model

Surface tensions (sigma) for [1,3-dioxolane+methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 1-pentanol] and excess molar volumes (v(E)) for [1,3-dioxolane+methanol, ethanol, 1-propanol, 2-propanol, and 2-butanol] at the temperature 298.15 K and normal atmospheric pressure have been determined as a function of mole fractions. The magnitude of these experimental quantities is discussed in terms of the nature and type of intermolecular interactions in binary mixtures. In order to analyze the surface tension behavior, the extended Langmuir (EL) model was used and the results obtained for the systems containing 1,3-dioxolane were compared with those of other formerly published series: [1,4-dioxane+alkanes] and [1,4-dioxane+alcohols].     

Gibbs energy of the resolvation of glycylglycine and its anion in aqueous solutions of dimethylsulfoxide at 298.15 K

Gibbs energies for the transfer of glycylglycine and glycylglycinate ions from water to water-dimethylsulfoxide solvents are determined from the interface distribution of substances between immiscible phases in the composition range of 0.00 to 0.20 molar fractions of DMSO at 298.15 K. It is shown that with a rise in the concentration of nonaqueous components in solution, we observe the solvation of dipeptide and its anion, due mainly to the destabilization of the carboxyl group.     

Excess magnitudes for the benzene + n-dodecane system at 298.15 and 323.15 K

The vapor pressures for benzene + n-dodecane mixtures have been measured using a static apparatus. Values for the excess Gibbs energy have been calculated using a modified form of Barker's method and fitted to a Padé approximant equation. Selection of the most adequate approximant is made according to objective criteria. The results are compared with those corresponding to other benzene + n-alkane systems. The values for the activity coefficient of benzene at infinite dilution calculated from these data agrees very well with the values obtained by gas-liquid chromatography.     

Excess gibbs energies for the benzene + n-hexadecane system at 298.15 and 323.15 K

The vapor pressure of the system benzene +n-hexadecane is measured by means of a static apparatus. Excess Gibbs energies are calculated using a modified Barker's method, and fitted to an equation proposed by Marsh. The regression analysis is based on the principle of maximum likelihood. The selection of the best set of estimates of the parameters is also discussed. The results obtained in this work are compared with those reported by other authors for the same system. Due to the lack of heat capacity data for this system, an approximation to calculate temperature dependence is studied.     

Excess molar volumes and excess viscosities of the n-pentanol-cumene-1,4-dioxane system at 298.15 K

Densities and viscosities were determined for the n-pentanol-cumene-1,4-dioxane system at 298.15 K. From the experimental results, molar excess volumes and excess viscosities were calculated. Different expressions exist in the literature to predict these excess properties from the binary data. The empirical correlation of Cibulka is shown to be the best for this system.     

Surface tension at the boundaries of helium-argon and neon-argon solutions at 108–140 K

The capillary constant was measured and surface tension determined for helium-argon and neon-argon solutions by the differential version of the capillary rise method over the temperature range 108–140 K at pressures up to 4 MPa. The adsorption of helium and neon in interfacial solution layers was calculated.     

Salt effect on vapour-liquid equilibrium in the dimethylsulphoxide-water-0.9 m NaClO4 system at 298.15 K

Isothermal total pressure vs. liquid and vapour composition (P-x-y) equilibrium data are presented for the DMSO-H₂O and DMSO-H₂O-0.9 m NaClO₄ systems. A modified transpiration technique was used to measure the saturated vapour pressures. The compositions of the equilibrium liquid and condensed vapour phases were determined by precision refractometry. The salt appreciably affects the activity coefficients of the solvent components; the effect is discussed in terms of interactions between the DMSO and H₂O molecules and of the preferential solvation of the salt.     

Applicability of corresponding-states group-contribution methods for the estimation of surface tension of multicomponent liquid mixtures at 298.15 K

Corresponding-states group-contribution methods (CSGC-ST1 and CSGC-ST2) have been applied to four binary liquid mixtures (propyl acetate + o-xylene, propyl acetate + m-xylene, propyl acetate + p-xylene and propyl acetate + ethyl benzene); two ternary (benzene + cyclohexane + toluene and n-hexane + cyclohexane + benzene) and two quaternary liquid mixtures (pentane + hexane + cyclohexane + benzene and pentane + hexane + benzene + toluene) at 298.15 K. In this work, the CSGC-ST2 method is modified and extended to multicomponent liquid mixtures. The excess magnitudes of surface tension were also calculated and graphs were plotted using Redlich–Kister method.     

Standard characteristics of thermodiffusion of hydrogen chloride in the water-2-propanol system at 298.15 K

The initial and stationary temperature voltage coefficients for symmetric thermogalvanic cells with silver/silver chloride and quinhydrone electrodes in the HCl-H₂O-2-PrOH system are measured at 298.15 K. From the experimental data obtained, the standard entropies of thermodiffusional transfer of the electrolyte, the standard entropies of moving hydrogen and chlorine ions, and the Soret coefficients of HCl in aqueous solutions of 2-propanol are calculated. The influence of the composition of the mixed solvent and the nature of ions on the entropy characteristics is discussed.     

Enthalpy characteristics of the dissolution of L-valine in water/formamide mixtures at 298.15 K

The thermochemical dissolution of L-valine in solvent mixtures H₂O + (formamide, N-methylformamide, and N,N-dimethylformamide) is studied at an organic component concentration of x₂ = 0–0.35 molar fractions and a temperature of 298.15 K. The experimental data are used to calculate standard enthalpies of dissolution, the transferring of L-valine from water to a mixed solvent, and the enthalpy coefficients of pairwise interactions (h_xy) with organic solvent molecules. The correlation between the enthalpy characteristics of the dissolution of L-valine with the composition of aqueous organic mixtures and the nature of the organic solvent (its physicochemical properties) is determined. A comparative analysis of the values of h_xy of a number of aliphatic L-amino acids in similar solvent mixtures with the hydrophobicity parameters of their side chains is performed.     

Heat capacities of binary cycloalkane mixtures at 298.15 K

Volumetric heat capacities of the six binary mixtures formed from cyclopentane, cyclohexane, cycloheptane and cyclooctane were determined at 298.15 K in a Picker flow microcalorimeter. Excess heat capacities obtained from the results are compred with the temperature variation of excess enthalpies from the literature.     

Activities of the components of glycerol-water binary solutions at 298.15 K

Based on the assumption that there exists a distribution of hydrates over the hydration number, expressions for the hydration number, activity coefficients of the components, and excess Gibbs energy were obtained. It was demonstrated that the van Laar formula for the activity coefficients corresponds to the Poisson distribution of hydrates. It was established that, at a constant ratio of the variance to the mathematical expectation of the distribution of hydrate, the model’s equations adequately describe the available experimental data on the vapor pressure and water activity for the glycerol-water system over the entire concentration range.     

Thermodynamic Properties of Alkanediols+Acetates at 298.15 K

In this work we present experimental values of the density, refractive index, speed of sound, isentropic compressibility and liquid-liquid equilibria of the binary mixtures (methyl acetate, ethyl acetate, propyl acetate, and butyl acetate) with (1,2-ethanediol, 1,2-propanediol, or 1,3-propanediol) at 298.15 K and atmospheric pressure, as a function of mole fraction. From the experimental values, the corresponding excess and deviation values were computed (excess molar volumes, changes of refractive index on mixing, and changes of isentropic compressibility), variable-degree polynomials being fitted to the results. The validity of different estimation methods for predicting the experimental values of physical properties was tested. The limiting partial excess molar volume of the components in each binary mixture was determined by means of predetermined Redlich-Kister parameters. Group contribution method (UNIFAC-Dortmund) was applied in order to compare their capability in predicting the experimental equilibria values. This revised version was published online in July 2006 with corrections to the Cover Date.     

Surface tensions of binary mixtures:2-propanol+dichloromethane and n-pentane+methylacetate at 298.15 K

Densities and surface tensions of 2-propanol+dichloromethane and n-pentane+methylacetate mixtures were determined over the whole composition range at 298.15 K, by the maximum bubble pressure method. Positive excess surface tensions were observed in the first mixture and negative excess surface tensions were observed in the second mixture. Different equations existing in the literature were applied and calculated values were compared with the experimental ones. Hoar and Melford's equations were the best.     

Thermodynamics study of the Cs2SO4-MgSO4-H2O system at the temperature 298.15 K

The Pitzer ion-interaction model has been used for thermodynamics simulation of the ternary system Cs₂SO₄-MgSO₄-H₂O at 298.15 K. The Pitzer ternary mixing parameter $ \psi _{CsMgSO_4 } $ \psi _{CsMgSO_4 } and thermodynamic characteristics for double salt Cs₂SO₄ · MgSO₄ · 6H₂O have been calculated and the theoretical solubilities isotherm has been plotted.     

Excess Gibbs energies of the ternary system ethanol+N,N-dimethylformamide+cyclohexane at 298.15 K

Vapour–liquid equilibrium (VLE) for the ternary system ethanol (EtOH)+N,N-dimethylformamide (DMF)+cyclohexane (Cy) and for the relevant binary mixtures containing DMF have been determined at 298.15 K by headspace gas chromatographic analysis of the vapour phase directly withdrawn from an equilibrium apparatus. Measurements of liquid–liquid equilibria in both binary DMF+Cy and ternary mixtures have been also carried out. The binary VLE data have been described with different correlation equations. The capabilities of different models of either predicting or reproducing the ternary data have been compared. Excess Gibbs energies G^E as well as activity coefficients γ_i of components have been obtained and briefly discussed. While EtOH+DMF behaves almost ideally with slightly negative G^E-values, both EtOH+Cy and DMF+Cy exhibit large positive deviations. The G^Es of the ternary system are positive with the exception of a narrow region in dilute Cy. The excess entropy and the temperature dependence of G^E and γ_i have been calculated in the whole ternary domain from the known excess enthalpy and heat capacity. The predictions by different equations of the effect of temperature on the mutual solubilities of DMF and Cy as well as on the binodal curve of EtOH+DMF+Cy have been compared with experiment.     

Excess enthalpies for the systems acetonitrile-benzene-tetrachloromethane and acetonitrile-dichloromethane-tetrachloromethane at 298.15 K

Nagata, I., Tamura, K. and Tokuriki, S., 1982. Excess enthalpies for the systems acetonitrile-benzene-tetrachloromethane and acetonitrile-dichloromethane-tetrachloromethane at 298.15 K. Fluid Phase Equilibria, 8: 75-86Excess enthalpies at 298.15 K are reported for the binary mixtures acetonitrile-benzene, acetonitrile-tetrachloromethane, benzene-tetrachloromethane, acetonitrile-dichloromethane and dichloromethane-tetrachloromethane, and for the ternary mixtures acetonitrile-benzene-tetrachloromethane and acetonitrile-dichloromethane-tetrachloromethane. The results are analysed by means of an associated-solution theory which includes two types of self-association for acetonitrile, the formation of binary complexes CH₃CN·C₆H₆, CH₃CN·CH₂Cl₂ and C₆H₆·CCl₄, and a physical-contribution term expressed by the NRTL equation.