Strong Negative Synergism of Ion Pair Extinction Coefficients in Chloroform–Acetone and Methylene Dichloride–Acetone Mixtures

The heteroselective preferential solvation of the iodides of N-heterocyclic aromatic cations in acetone–chloroalkane (chloroform and dichloromethane) binary mixtures results in not only a shift in the maxima of outer-sphere charge transfer absorption bands but also a considerable decrease in the molar extinction coefficients of ion pairs.     

Enthalpies of mixing and intermolecular interactions in the 1-octanol-dimethylformamide system at 298–318 K

The heat effects of solution of N,N-dimethylformamide (DMF) and 1-octanol (OctOH) in the DMF (1)-OctOH (2) system are measured over the range of compositions using a variable-temperature isothermal-shell calorimeter at 298, 308, and 318 K. The partial molar enthalpies of the binary mixture components and the enthalpies and heat capacities of mixing are determined. It is found that the amide-alcohol mixing is strongly endothermic and very weakly depends on temperature. The enthalpy and specific heat parameters of binary and ternary interactions between the DMF molecules in OctOH and the OctOH molecules in DMF are determined in terms of the virial expansion technique, and it is shown that the two nonelectrolytes exhibit a tendency to homoassociation.     

Enthalpies and Heat Capacities of Ethyl Acetate Solutions in Water and in Several Organic Solvents at 298–318 K

The enthalpies of solution of ethylacetate (EtOAc) in water, octane and 1-octanol (OctOH) were measured at 298, 308 and 318 K using a precise isoperibol calorimeter. The standard enthalpies and heat capacities of these non-electrolyte solution were computed and compared with the previously obtained ??_sol H ^° and $\Delta C_{p}^{\circ}$ values in N,N-dimethylformamide (DMF). Partial molal heat capacities of EtOAc in water and in organic solvents were calculated and compared with the available literature values.     

Constants of acid‒base equilibria in an aqueous amikacin aminoglycoside solution at 298 K

The acid dissociation constants of form pK₁ = 7.34 ± 0.01, pK₂ = 7.84 ± 0.01, pK₃ = 8.77 ± 0.01, pK₄ = 9.49 ± 0.01, and pK₅ = 10.70 ± 0.02 of cationic amikacin are determined by pH-metric titration at 25°C against the background of 0.1 mol/L KNO₃. K₁, K₂, K₃, and K₄ correspond to the dissociation of protons coordinated to amino groups, while K₅ characterizes the dissociation of the hydroxyl hydrogen atom, testifying to the amphoteric character of amikacin molecules. Applying density functional theory (DFT) with the B3LYP hybrid functional and the 6-311G**++ basis set, the partial charges on the atoms of an amikacin molecule are calculated. It is concluded that the dissociation of H(55)hydrogen atom occurs with a greatest partial charge of +0.53631.     

Thermodynamic characteristics of acid–base equilibria of glycyl-glycyl-glycine in water–ethanol solutions at 298 K

The enthalpies of the acid dissociation of glycyl-glycyl-glycine zwitterions and triglycinium ions are determined calorimetrically in water–ethanol solvents containing 0.0, 0.10, 0.30, and 0.50 molar fractions of ethanol at ionic strengths of 0.1 (maintained by sodium perchlorate) and Т = 298.15 K. It is found that increasing the ethanol content in the solvent enhances the endothermic effect of triglycinium ion dissociation and reduces the endothermic effect of glycyl-glycyl-glycine dissociation. The results are discussed in terms of the solvation thermodynamics.     

Solute–solvent interactions in 2,4-dihydroxyacetophenone isonicotinoylhydrazone solutions in N,N-dimethylformamide and dimethyl sulfoxide at 298–313 K on ultrasonic and viscometric data

The speed of sound (u), density (ρ), and viscosity (η) of 2,4-dihydroxyacetophenone isonicotinoylhydrazone (DHAIH) have been measured in N,N-dimethyl formamide and dimethyl sulfoxide at equidistance temperatures 298.15, 303.15, 308.15, and 313.15 K. These data were used to calculate some important ultrasonic and thermodynamic parameters such as apparent molar volume (V _{? s} ^st ), apparent molar compressibility (K _?), partial molar volume (V _? ⁰ ) and partial molar compressibility (K _? ⁰ ), were estimated by using the values of (V _? ⁰ ) and (K _?), at infinite dilution. Partial molar expansion at infinite dilution, (? _E ⁰ ) has also been calculated from temperature dependence of partial molar volume V _? ⁰ . The viscosity data have been analyzed using the Jones–Dole equation, and the viscosity, B coefficients are calculated. The activation free energy has been calculated from B coefficients and partial molar volume data. The results have been discussed in the term of solute–solvent interaction occurring in solutions and it was found that DHAIH acts as a structure maker in present systems.     

Excess Molar Volume,Viscosity, and Molar Refraction Deviations,and Liquid–Vapor Equilibrium at 303.15 K for Chloroform + Acetonitrile Binary Mixture. An Infrared Study

Excess molar volume, viscosity deviation, and molar refraction deviation for the chloroform #x002B; acetonitrile system at 303.15 K were calculated from binary experimental results of density, viscosity, and refractive index over the whole mole fraction range, respectively. Isothermal vapor–liquid equilibrium data at the same temperature were also obtained and the excess molar Gibbs energy was calculated from these data. Each one of the properties was fitted to a Redlich–Kister type equation using least squares in order to obtain their dependencies on concentration. The presence of intermolecular association complexes was inferred from the viscosity deviations, leading to a 1:1 stoichiometric relationship. The recorded FTIR spectra confirm the existence of this type of hydrogen-bonded complex, making it possible, furthermore, to calculate the heteroassociation constant and enthalpy of formation of the hydrogen bond.     

Concentration Dependences of the Surface Tension and Density of Solutions of Acetone–Ethanol–Water Systems at 293 K

Russian Journal of Physical Chemistry A - Concentration dependences of the surface tension and density of solutions of three-component acetone–ethanol–water systems and the bounding...     

Vapor–liquid equilibrium of nitrogen in an equimolar hexane + decane mixture at temperatures of 258, 273, and 298 K and pressures to 20 MPa

In this work we present experimental results of P, T, x, y, for the vapor–liquid equilibrium of the ternary system: nitrogen in an equimolar hexane+decane mixture at 258, 273, and 298 K in the range 1.5–20 MPa. The solubility of nitrogen in the liquid mixture of hexane+decane is increased when the pressure is increased; however, a considerable change in the solubility values is not observed as a function of temperature in the range studied. We have correlated the experimental results using the Peng–Robinson equation of state. The standard deviation of the fit shows that the data are well correlated (within the experimental error) in the ranges of pressure and temperature studied.     

Ion-solvent and ion-ion interactions of NaCl aqueous and aqueous maltose solutions at 298–323 K on viscosity data

Viscosities of sodium chloride in concentration range 1 × 10^?2 to 9 × 10^?2 ± 0.001 mol dm^?3, have been determined in aqueous and aqueous maltose systems (1.0 to 9.0 wt %) at different temperatures (298 to 323 K). The viscosity data have been analyzed by using Jones-Dole equation and the derived parameters A and B coefficients were also calculated. The data obtained from viscometric studies has been used to investigate the ion-solvent interaction and ion-ion interaction. Thermal effects on the ionic interactions were also examined under the light of transition state theory.     

Dissolution Enthalpy and Entropy of Thiourea in Ethanol at 292–320 K

The dissolution enthalpy and entropy of thiourea in ethanol have been calculated from solubilities of thiourea in ethanol at the mass fractions 0.54–0.88 and temperatures 292–320 K. The data can be used for the synthesis of isopropyl mercaptan.     

Solubility of β-HMX in Acetone + Water Mixed Solvent Systems at Temperatures from 293.15 K to 313.15 K

The solubility of ??-HMX in acetone + water mixed solvents was measured using a synthetic method. The laser monitoring observation technique was used to determine the disappearance of the solid phase in a solid + liquid mixture. All data were measured at atmospheric pressure and at temperatures ranging from (293.15 to 313.15)?K. The effects of solvent composition and temperature on the solubility are discussed. The experimental data were correlated with an empirical equation.     

Solubilities of isobutane in methanol + benzene,methanol + cyclohexane and benzene + cyclohexane mixed solvent solutions at 298 K and 40–102 kPa

The solubilities of isobutane at pressures from 40 to 102 kPa and a temperature of 298.15 K are presented for three mixed solvent solutions: methanol + benzene, methanol + cyclohexane, and benzene + cyclohexane.     

Solubility and dissolution thermodynamics of tetranitroglycoluril in organic solvents at 295–318 K

The solubility data of tetranitroglycoluril in acetone, methanol, ethanol, ethyl acetate, nitromethane and chloroform at temperatures ranging from 295–318 K were measured by gravimetric method. The solubility data of tetranitroglycoluril were fitted with Apelblat semiempirical equation. The dissolution enthalpy, entropy and Gibbs energy of tetranitroglycoluril were calculated using the Van’t Hoff and Gibbs equations. The results showed that the Apelblat semiempirical equation was significantly correlated with solubility data. The dissolving process was endothermic, entropy-driven, and nonspontaneous.     

Thermodynamics of 2,2′-dipyridinium ion and its iron(II) complex in ethanol-water mixtures at 298 K

The enthalpies of formation of 2,2′-dipyridinium ion and tris 2,2′-dipyridyl-iron(II) complex in ethanol-water media at 298 K have been determined by calorimetry and used in calculating thermodynamic parameters.     

Solvation of magnesium chloride and sulfate in aqueous solutions at 278.15–323.15 K

Isoentropy compressibilities of aqueous magnesium chloride and sulfate were determined based on precision measurements of ultrasound velocity, density, and isobaric heat capacity at low to high concentrations at 278.15–323.15 K. The hydration numbers h and the molar parameters of volume and compressibility were calculated based on thermodynamically correct equations for hydration complexes (V _h , β _h V _h ), water in the hydration shell (V _1h , β_1h V _1h ), and the void containing a stoichiometric mixture of ions (V _2h , β_2h V _2h ). The h and β _h V _h values were found to be independent of temperature; the molar compressibility of the hydration sphere (β_1h V _1h ) and the stoichiometric mixture of ions without a hydration shell (β_2h V _2h ) were independent of the concentration under the stated conditions. The effect of the electrostatic field of ions on the temperature dependence of the molar volume of water in the hydration sphere was more significant than the effect of pressure on the temperature dependence of the molar volume of bulk water. This is attributed to changes in the dielectric constant of water in the vicinity of the electrolyte ions.     

SPE–GC–MS Analysis of Chloroform in Drinking Water

In this paper we report a method based on solid-phase extraction (SPE) and subsequent analysis by gas chromatography combined with mass spectrometry for determination of chloroform in potable water. The affinity of chloroform for the resin enables almost complete recovery of the analyte. The analytical method proposed enables evaluation of chloroform levels down to 0.295 g L^–1. The procedure is characterized by lack of interferences, in fact the GC–MS analysis reveals the presence of only one peak, that of chloroform. Use of CDCl₃ as labelled internal standard also makes the procedure suitable for use as a reference analytical method for quantification of chloroform in drinking water.     

Determination of the Distribution of Cupric Chloro-Complexes in Hydrochloric Acid Solutions at 298 K

The distribution of metal-chloro complexes in hydrochloric acid solutions is a fundamental aspect of anion exchange reactions that allows ultrahigh purification during hydrometallurgical processes. However, these exchange reactions are not yet understood in detail. To clarify and improve anion exchange separation so as to obtain a more sophisticated purification process, it is necessary to accurately determine the distribution of metal-chloro complexes. In the present work, cupric-chloro complexes were investigated because copper is one of the most important base metals in modern society. The absorption spectra of solutions of these complexes were acquired at 298 K and analyzed by multivariate curve resolution–alternating least squares method (MCR–ALS), a factor analysis technique widely used in chemometrics. The resulting cupric-chloro complex distributions were fitted with a thermodynamic model using appropriate activity coefficients extended to the concentrated solutions. These calculations employed a modified Debye–Hückel model because the distributions acquired through the model-free MCR–ALS analysis were less meaningful, both physically and chemically. It was concluded that five [Cu^IICl _n ]^2?n species, where n = 0–4, are present in the hydrochloric acid solutions. In addition, cumulative formation constants and pure molar attenuation coefficients were obtained.