Showing papers in "Journal of Solution Chemistry in 2006"

The Physical Properties of Aqueous Solutions of the Ionic Liquid [BMIM][BF4]

Abstract: We report here the systematic study of the effect of concentration on the physical properties of aqueous solutions of the room-temperature ionic liquid [BMIM][BF4]. The measurements of density, ρ, refractive index △n, viscosity η, specific conductivity κ and surface tension, γ, were made over the whole concentration range. The equivalent conductance Λm was calculated. The observed linear variations of density and refractive index with the molar concentration are established as those of an ideal solution. The surface tension varied most rapidly in the dilute region whereas the viscosity changed much more rapidly in the concentrated region. Two regions with different composition dependences were found after the analyses of the relationship between the conductivity and the concentration of [BMIM][BF4]. A proposed model for a structural change in the mixtures was described. The physical origin of the observed concentration dependence of these properties is discussed. The physical properties of the solutions vary with changes of association between anions and cations and the interaction between [BMIM][BF4] and water.

Refractive Indices, Densities and Excess Molar Volumes of Monoalcohols + Water

Abstract: The refractive index, nD, and density, ρ, of binary mixtures of monoalcohols + water, have been measured at a temperature of 298.15,K and atmospheric pressure. The variation of the refractive indices of these solutions has also been determined with temperature in the range T = (278.15 to 338.15) K and atmospheric pressure. A comparative study has been made of the refractive indices obtained experimentally and those calculated by means of the Lorentz-Lorenz [Theory of Electrons, Dover Phoenix (1952)] and Gladstone-Dale relations [Trans. R. Soc. London 148:887–902 (1858)]; in all cases, the Gladstone–Dale equation was seen to afford values similar to those obtained experimentally. Calculations have been made of the excess molar volumes, VE, and the molar refraction deviations, ΔR, of these mixtures and the differences between the experimental values for refractive index and those obtained by means of the Gladstone–Dale equation. Values of VE were compared with others in the literature. In all cases the VE values were negative, and in all cases, except in the methanol + water, ΔR showed a maximum for x = 0.8.

Solubility and Excess Molar Properties of 1,3-Dimethylimidazolium Methylsulfate, or 1-Butyl-3-Methylimidazolium Methylsulfate, or 1-Butyl-3-Methylimidazolium Octylsulfate Ionic Liquids with n -Alkanes and Alcohols: Analysis in Terms of the PFP and FBT Models 1

Abstract: The solubility of 1-butyl-3-methylimidazolium octylsulfate, [BMIM][OcSO4], has been determined in hydrocarbon (n-hexane, n-heptane, n-octane or n-decane) solutions and alcohol (methanol, 1-butanol, 1-hexanol, 1-octanol or 1-decanol) solutions. Densities and excess molar volumes, V E m, have been determined for 1-methyl-3-methylimidazolium methylsulfate, [MMIM][CH3SO4], solutions with an alcohol (methanol, ethanol or 1-butanol) and with water; for 1-butyl-3-methylimidazolium methylsulfate, [BMIM][CH3SO4], with an alcohol (methanol, ethanol, 1-butanol, 1-hexanol, 1-octanol or 1-decanol) and with water; and for 1-butyl-3-methylimidazolium octylsulfate, [BMIM][OcSO4], with an alcohol (methanol, 1-butanol, 1-hexanol, 1-octanol or 1-decanol) at 298.15 K and atmospheric pressure. The systems exhibit very negative or positive molar excess volumes, V E m, and negative or positive excess molar enthalpies, H E m, as predicted by the Flory–Benson–Treszczanowicz (FBT) model. Our experimental V E m data were used for the description of H E m for solutions of [MMIM][CH3SO4] with the alcohols under study. The simple Prigogine–Flory–Paterson (PFP) model, without including the association of the alcohol, gave slightly worse results. Negative molar excess volumes, V E m, are attributed to hydrogen bonding between the short chain alcohols and ionic liquid and to efficient packing effects. The FBT model overestimates self-association of the alcohol in the solutions under study and shifts the calculated curves to higher alcohol mole fractions. The thermophysical characteristics of [BMIM][OcSO4] were also examined by differential scanning calorimetry (DSC).

Physical and Excess Properties for Binary Mixtures of 1-Methyl-3-Octylimidazolium Tetrafluoroborate, [Omim][BF4], Ionic Liquid with Different Alcohols

Abstract: In recent years, ionic liquids have increasingly gained importance as green solvents. The potential of these organic salts, which are moisture and air stable at room temperature, for new chemical processes and technologies is beginning to be recognized. Research on the thermophysical properties of ionic liquids and their mixtures form the basis for future applications. In this contribution, densities, refractive indices, speeds of sound and dynamic viscosities of 1-methyl-3-octylimidazolium tetrafluoroborate, [Omim][BF4], the room temperature ionic liquid (IL) in binary mixtures with methanol, ethanol, 1-propanol and 2-propanol were measured at 298.15K and atmospheric pressure. The excess molar volumes and molar refraction, isentropic compressibility and dynamic viscosity changes of mixing have been calculated and were satisfactorily correlated by the Redlich–Kister polynomial.

Diffusion Coefficients for Binary, Ternary, and Polydisperse Solutions from Peak-Width Analysis of Taylor Dispersion Profiles

Abstract: Binary mutual diffusion coefficients D can be estimated from the width at half height W 1/2 of Taylor dispersion profiles using D=(ln 2)r 2 t R/(3W 2 h) and values of the retention time t R and dispersion tube radius r. The generalized expression D h=−(ln h)r 2 t R/(3W 2 h ) is derived to evaluate diffusion coefficients from peak widths W h measured at other fractional heights (e.g., (h = 0.1, 0.2,…,0.9). Tests show that averaging the D h values from binary profiles gives mutual diffusion coefficients that are as accurate and precise as those obtained by more elaborate nonlinear least-squares analysis. Dispersion profiles for ternary solutions usually consist of two superimposed pseudo-binary profiles. Consequently, D h values for ternary profiles generally vary with the fractional peak height h. Ternary profiles with constant D h values can however be constructed by taking appropriate linear combinations of profiles generated using different initial concentration differences. The invariant D h values and corresponding initial concentration differences give the eigenvalues and eigenvectors for the evaluation of the ternary diffusion coefficient matrix. Dispersion profiles for polymer samples of N i-mers consist of N superimposed pseudo-binary profiles. The edges of these profiles are enriched in the heavier polymers owing to the decrease in polymer diffusion coefficients with increasing polymer molecular weight. The resulting drop in D h with decreasing fractional peak height provides a signature of the polymer molecular weight distribution. These features are illustrated by measuring the dispersion of mixed polyethylene glycols.

SIT Parameters for 1:1 Electrolytes and Correlation with Pitzer Coefficients

Abstract: The empirical parameters of a two-parameter SIT equation were determined for some 1:1 electrolytes: chlorides, bromides, iodides, nitrates, perchlorates and carboxylates of alkali metals, inorganic acids and bases, and tetralkylammonium halides. A wide range of ionic strengths were considered. Canonical correlation analysis identified correlations between the SIT and Pitzer interaction coefficients for different classes of 1:1 type electrolytes.

Deliquescence Relative Humidity Measurements Using an Electrical Conductivity Method

Abstract: Several methods used in the published literature for determining the deliquescence relative humidity (DRH) of salts and the mutual deliquescence relative humidity (MDRH) of salt mixtures were reviewed. Experiments were conducted to evaluate an electrical conductivity method for determining the DRH of salts and the MDRH of salt mixtures. The electrical impedance of a conductivity cell containing Na2SO4, CaCl2 and NaCl+NaNO3+KNO3 was measured as a function of relative humidity at temperatures up to 70 ∘C. To provide a basis for interpreting the results of the impedance measurements, computer modeling of the specific electrical conductivity of single salts and salt mixtures at 25 ∘C also was performed. The results of the study demonstrated that the electrical conductivity method provides a convenient and accurate method for determining the DRH of single salts and the MDRH of salt mixtures. The derived DRH and MDRH values were in good agreement with those determined using a hygrometer method. The conductivity method, however, is a more reliable technique than the hygrometer method for determining the MDRH of salt mixtures because the conductivity method is insensitive to slight deviations of mixture composition from the eutonic value.

Thermodynamic Investigation of Dimethyl Sulfoxide Binary Mixtures at 293.15 and 313.15 K

Abstract: Densities (ρ), speeds of sound (u), and isentropic compressibilities (kS) of binary mixtures of dimethyl sulfoxide (DMSO) with water, methanol, ethanol, 1-propanol, 2-propanol, acetone and cyclohexanone have been measured over the entire composition range at 293.15 and 313.15 K. The excess molar volumes (VE), the deviations in speed of sound (uE) and the deviations in isentropic compressibility (kSE) have been determined. The VE, uE and kSE values were fitted by the Redlich-Kister polynomial equation and the Ak coefficients as well as the standard deviations (d) between the calculated and experimental values have been derived. The results obtained are discussed from the viewpoint of the existence of interactions between the components of the binary mixtures.

Study of Densities, Viscosities and Ultrasonic Speeds of Binary Mixtures Containing 1,2-Dimethoxyethane and an Alkan-l-ol at 298.15 K

Abstract: The viscosity deviation (Δη), the excess molar volume (VE) and the ultrasonic speed (u) have been investigated from viscosity (η) and density (ρ ) measurements of binary liquid mixtures of 1,2-dimethyoxyethane with methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, hexan-1-ol or octan-1-ol over the entire range of composition at 298.15 K. The excess volumes are negative over the entire range of composition for all of the mixtures with the exception of hexan-1-ol and octan-1-ol. The excess isentropic compressibilities (KSE) and viscosity deviations are negative for all of the mixtures. The magnitudes of the negative values of VE decrease with the number of carbon atoms of the alkan-1-ol. The trend of increasing KSE values with the chain length of the alkanol is similar to that observed in the case of VE. Graphs of VE, Δ η, KSE, Δ u, LfE and ZE against composition are presented as a basis for a qualitative discussion of the results.

Characterization of Heterogeneous Interaction Behavior in Ternary Mixtures by a Dielectric Analysis: Equi-Molar H–bonded Binary Polar Mixtures in Aqueous Solutions

Abstract: The heterogeneous associating behavior of the aqueous binary mixtures of ethyl alcohol, ethylene glycol, glycerol and mono alkyl ethers of ethylene glycol, and aqueous ternary mixtures of equi-molar binary systems (i.e., mono alkyl ethers of ethylene glycol with ethyl alcohol, ethylene glycol and glycerol) have been investigated over the entire concentration range using accurately measured dielectric constants at 25 ∘C. The concentration dependent values of the excess dielectric parameter eE and effective Kirkwood correlation factor geff were determined using the measured values of the static dielectric constant, eo, at 1 MHz and the high frequency limiting dielectric constant e∞ = nD2. The observed eE values in aqueous binary and ternary mixtures are negative over the entire concentration range, which implies the formation of heterogeneous complexes between these molecules that reduces the effective number of dipoles. The stoichiometric ratio corresponding to the maximum interaction in alcohol + water mixtures increases with an increase in the number of hydroxyl groups of the alcohol molecules, but for mono alkyl ethers of ethylene glycol + water mixtures it decreases with the increase in the molecular size of the mono alkyl ethers. In aqueous ternary mixtures the stoichiometric ratio for the maximum extent of heterogeneous interaction is governed by the molecular size of the mono alkyl ethers. It was also found that the strength of the heterogeneous H–bond connectivities in the water + alcohol systems decrease with an increase in the number of hydroxyl groups of the alcohol molecules. However in the case of water + mono alkyl ether binary mixtures and in ternary mixtures, the strength of H–bond connectivities increases with the increase in the molecular size of the mono alkyl ether. An analysis of the geff values confirms that the heterogeneous interaction involves the orientation of molecular dipoles in the studied systems.

Hydrophobic interactions of methylureas in aqueous solutions estimated with density, molal volume, viscosity and surface tension from 293.15 to 303.15 K

Abstract: Density (ρ), viscosity (η), and surface tension (γ) for 0.005–0.25 mol ⋅ kg−1 solutions of urea, 1-methylurea, and 1,3-dimethylurea solutions have been measured at intervals of 0.005 mol ⋅ kg−1. Apparent molal volume (V o, cm3 ⋅ mol−1) and intrinsic viscosity coefficients (B and D) are calculated from the ρ and η values, respectively. Primary data were regressed and extrapolated to zero concentration for the limiting density (ρ 0), apparent molal volume (V φ 0), viscosity (η 0), and surface tension (γ 0) values for solute–solvent interactions. The –CH3 (methyl) groups of N-methylureas weaken hydrophilic interactions and enhance hydrophobic interactions, and the values of the ρ 0 and V φ o reflect the intermolecular forces due to electrostatic charge, whereas the η 0 and γ 0 values reflect the frictional and surface forces. The B values depict the size of hydrodynamic sphere due to heteromolecular forces whereas D shows the effect of concentration. The molar surface energy (ΔE m/sur) for dropwise flow was calculated from the γ values and decreases with concentration and temperature, but increases with –CH3 weakening of the hydrophilic interactions and strengthening the hydrophobic interactions.

Competition between O2 and H2O2 in the oxidation of Fe(II) in natural waters

Abstract: The oxidation rates of nanomolar levels of Fe(II) in seawater (salinity S = 36.2) by mixtures of O2 and H2O2 has been measured as a function of pH (5.8–8.4) and temperature (3–35∘C). A competition exists for the oxidation of Fe(II) in the presence of both O2 (μ mol⋅L−1 levels) and H2O2 (nmol⋅L−1 levels). A kinetic model has been applied to explain the experimental results that considers the interactions of Fe(II) with the major ions in seawater. In the presence of both oxidants, the hydrolyzed Fe(II) species dominate the Fe(II) oxidation process between pH 6 and 8.5. Over pH range 6.2–7.9, the FeOH+ species are the most active, whereas above pH 7.9, the Fe(OH)02 species are the most active at the levels of CO2−3 concentration present in seawater. The predicted Fe(II) oxidation rate at [Fe(II)]0 = 30nmol⋅L−1 and pH = 8.17 in the oxygen-saturated seawater with [H2O2]0 = 50nmol⋅L−1 (log 10 k = −2.24s−1) is in excellent agreement with the experimental value of log 10 k = −2.29s−1 ([H2O2]0 = 55nmol⋅L−1, pH = 8).

Densities and Volumetric Properties of Binary Mixtures of Tetrahydrofuran with Some Aromatic Hydrocarbons at Temperatures from 278.15 to 318.15 K

Abstract: The densities, ρ, of binary mixtures of tetrahydrofuran (THF) with benzene, toluene, o-xylene, m-xylene, p-xylene and mesitylene, including those of the pure liquids, were measured over the entire composition range at the temperatures (278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. From the experimental data, the excess molar volume, V m E, partial molar volumes, \(\bar V\) m,1 ∘ and \(\bar V\) m,2 ∘, and excess partial molar volumes, \(\bar V\) m,1 ∘E and \(\bar V\) m,2 ∘E, at infinite dilution were calculated. The V m E values were found to be negative over the whole composition range for all of the mixtures and at each temperature studied, except for THF + mesitylene, which exhibits a sigmoid trend wherein V m E changes sign from negative to positive as the concentration of THF in the mixture is increased, indicating the presence of specific interactions between THF and aromatic hydrocarbon molecules. The extent of negative deviations in the V m E values follows the order: benzene > toluene > p-xylene > m-xylene > o-xylene > mesitylene. It is observed that the V m E values depend upon the number and position of the methyl groups in these aromatic hydrocarbons.

Apparent Molar Volumes of Symetric and Asymetric Tetraalkylammonium Salts in Dilute Aqueous Solutions

Abstract: The apparent molar volumes, Vφ of tetramethylammonium, tetraethylammonium, tetrabutylammonium, butyltriethylammonium, dibutyldiethylammonium, and tributylethylammonium bromides have been measured at 298.15K in the concentration range from 0.01 to 0.04mol⋅kg−1. The concentration dependence of Vφ is given using the Redlich and Meyer relation. The apparent molar volume at infinite dilution, V∘_φ, and the empirical constant, BV, have been calculated. The CH2-group contribution has been obtained by the additivity rule. The results were interpreted in terms of solute–solvent interactions.

Temperature Dependence of the Solubility of Acetaminophen in Propylene Glycol + Ethanol Mixtures

Abstract: The thermodynamic functions Gibbs energy, enthalpy and entropy of solution, mixing and solvation of acetaminophen in propylene glycol (PG) + ethanol (EtOH) cosolvent mixtures were evaluated from solubility data measured at several temperatures, using the van't Hoff and Gibbs equations. The solubility was greater at 50% m/m of PG at 20.0^C, while it was greater at 80% of PG at 40.0 ^C where m/m refers to mass percent. The solvation of this drug is appreciably greater in the mixtures than in the pure solvents. By means of an enthalpy–entropy compensation analysis, complex behavior was found for the solution. From 0 up to 20% of PG and from 60 up to 100% of PG the solution process is enthalpy driven, whereas from 20 up to 60% of PG it is entropy driven. These facts can be explained in terms of a decrease in the energy required for cavity formation in the solvent for mixtures containing 20–60% of PG.

Kinetics and Mechanism of the Oxidation of Vanillin by Hexacyanoferrate(III) in Aqueous Alkaline Medium

Abstract: The title reaction was investigated in aqueous alkaline medium. A first-order dependence in hexacyanoferrate(III) concentration and a fractional order in both vanillin and alkali were obtained at the concentrations studied. The added product, hexacyanoferrate(II), had a retarding effect on the rate of reaction. Ionic strength and dielectric constant of the reaction medium have little effect on the reaction rate. The effect of temperature on the rate of reaction has also been studied and activation parameters have been evaluated. A mechanism based on the experimental results is proposed and the rate law is derived. The reaction constants are calculated and used to regenerate the kobs values, which are compared with the experimental values.

Studies on Volumetric Properties of Concentrated Aqueous Solutions of the Ionic Liquid BMIBF4

Abstract: In order to test the mole-fraction composition-based models as applied to aqueous solutions of an ionic liquid, the densities of aqueous 1-methyl-3-butylimidazolium tetrafluoroborate (BMIBF4) were measured using a Westphal balance in the concentration range of about 0.2 to 0.85 mole fraction at temperatures from 283.2 to 323.2 K. Values of the apparent molar volumes of concentrated aqueous BMIBF4 solutions were calculated from these densities and were represented with the Pitzer–Simomson and the Pitzer–Simomson–Clegg equations. The values of Pitzer–Simomson parameters and Pitzer–Simomson–Clegg parameters were obtained by fitting to experimental data with small standard deviations.

The Determination of Protonation Constants of Some Amino Acids and Their Esters by Potentiometry in Different Media

Abstract: In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content in contrast those of L-lysine and L-histidine esters.

Mixed-Ligand Complexes of 2-(Aminomethyl)benzimidazole Palladium(II) with Various Biologically Relevant Ligands

Abstract: cis-Dichloro(2-(aminomethyl)benzimidazole)palladium(II), [Pd(AMBI)Cl2], was synthesized and characterized. The stoichiometry and stability constants of the complexes formed between [Pd(AMBI)(H2O)2]2+ with various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA constitutents. The results show the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of the chelate ring size of the dicarboxylic acid complexes on their stability constants is examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. Structural effects of the peptide on the amide deprotonation are investigated. DNA pyrimidinic constituents such as uracil, uridine, thymidine and thymine form 1:1 and 1:2 complexes, whereas purinic constituents such as inosine 5′-monophosphate (5′-IMP) and guanosine 5′-monophosphate (5′-GMP) form only 1:1 complexes. The concentration distribution of the complexes in solution was evaluated. The effect of increasing chloride ion concentration on the formation constant of CBDCA with Pd(AMBI)2+ was reported.

Preferential Solvation in Mixed Solvents

Abstract: The Kirkwood–Buff integrals and the volume-corrected preferential solvation parameters for the first solvation shell of binary mixtures of tetrahydrofuran with many organic solvents, calculated from reported thermodynamic data at the temperatures for which these data were available, are reported. The co-solvents include c-hexane, methyl-c-hexane, n-heptane, i-octane, benzene, toluene, ethylbenzene, 1-chlorobutane, dichloromethane, 1,2-dichloroethane, chloroform, 1,1,1-trichloroethane, tetrachlorom-ethane, tetrachloroethene, hexafluoro benzene, ethanol, 1-propanol, 2-propanol, dibutyl ether, acetic acid, acetone, dimethyl sulfoxide, tetramethylene sulfone (sulfolane), acetonitrile, pyrrolidine, and triethylamine. The preferential solvation parameters of these mixtures are discussed in terms of the interactions that occur.

Densities and Kinematic Viscosities of Ten Binary Liquid Regular Solutions at 308.15 and 313.15 K

Abstract: The densities and kinematic viscosities of 10 binary regular solutions were measured over the entire composition range at 308.15 and 313.15 K. The excess volumes of mixing, absolute viscosities and viscosity deviations were calculated from the experimental data. The viscosity deviations were found to be negative for eight systems. For the two systems, heptane + octane and toluene + ethylbenzene, the viscosity deviations are scattered around zero. The data reported herein were used to examine the predictive capabilities of some viscosity-prediction models; namely, the predictive version of the McAllister model, the GC-UNIMOD model, the generalized corresponding states principle method, and the Allan and Teja correlation. The results of testing these models revealed that the McAllister model predicts the data much better than the other models and has the lowest absolute average deviation of 1.7%.

Physical Properties of the Ternary Mixture Ethanol+Water+1-Butyl-3-Methylimidazolium Chloride at 298.15 K

Abstract: In this work densities, refractive indices, speeds of sound and isentropic compressibilities of the ternary mixture ethanol+water+1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), and of the binary subsystems containing the ionic liquid, have been measured at 298.15 K and atmospheric pressure.

Effect of Ammonium Salts on the Volumetric and Viscometric Behavior of D(+)-Glucose, D(−)-Fructose and Sucrose in Aqueous Solutions at 25°C

Abstract: Apparent molar volumes, Vφ, and viscosity, η, of D(+)-glucose, D(−)-fructose and sucrose in water and in 0.02, 0.05, 0.5, 1.0 and 2.0 mol·kg−1 aqueous solutions of ammonium bromide, tetraethylammonium bromide and tetra-n-butylammonium bromide have been determined at 25 °C from density and efflux time measurements by using a vibrating-tube digital densimeter and a capillary viscometer, respectively. Partial molar volumes, \(\mathop V olimits_{2,m}^o\), at infinite dilution that were extrapolated from the Vφ data were used to obtain the corresponding transfer volumes, \(\Delta_{{\rm tr}} \mathop V olimits_{2,m}^o\), for saccharides from water to different aqueous solutions of co-solutes. The Jones-Dole equation viscosity B-coefficients were obtained from the viscosity data. Positive values of \(\Delta_{{\rm tr}} \mathop V olimits_{2,m}^o\) were obtained for the saccharides in the presence of ammonium bromide, whereas both positive and negative \(\Delta_{{\rm tr}} \mathop V olimits_{2,m}^o\) values were obtained in the presence of tetraethylammonium and tetra-n-butylammonium bromides. The negative \(\Delta_{{\rm tr}} \mathop V olimits_{2,m}^o\) values at very low concentrations have small magnitudes. Volumetric interaction coefficients have been calculated by using the McMillan-Mayer theory and Gibbs energies of activation of viscous flow have been calculated by using Feakin’s transition-state theory equation. The parameters obtained from the volumetric and viscometric studies were used to understand various mixing effects due to the interactions between saccharides and ammonium salts in aqueous solutions.

Excess molar volume and viscosity of isobutyric acid + water binary mixtures near and far away from the critical temperature

Abstract: The excess molar volume VE, shear viscosity deviation Δη and excess Gibbs energy of activation ΔG∗E of viscous flow have been investigated by using density (ρ) and shear viscosity (η) measurements for isobutyric acid + water (IBA+W) mixtures over the entire range of mole fractions at five different temperatures, both near and close to the critical temperature (2.055K ≤ (T−Tc)≤ 13.055K). The results were also fitted with the Redlich–Kister equation. This system exhibited very large negative values of VE and very large positive values of Δη due to increased hydrogen bonding interactions and correlation length between unlike molecules in the critical region and to very large differences between the molar volumes of the pure components at low temperatures. The activation parameters ΔH∗ and ΔS∗ have been also calculated and show that the critical region has an important effect on the volumetric properties.

Modeling of Aqueous 3–1 Rare Earth Electrolytes and Their Mixtures to Very High Concentrations

Abstract: A simple modification to the Pitzer ion–interaction model has been presented for osmotic and activity coefficients of aqueous solutions of highly soluble and highly unsymmetrical electrolytes and their mixtures. The equations extending to the C(3) parameter enable the literature osmotic and activity coefficients of aqueous rare earth nitrates, perchlorates and chlorides at 298.15 K to be represented accurately from infinite dilution to maximum saturation or supersaturation concentrations available. The ionic interactions have also been investigated from the isopiestic measurements on aqueous mixtures Y(NO3)3–La(NO3)3, Y(NO3)3–Pr(NO3)3, Y(NO3)3–Nd(NO3)3, La(NO3)3–Pr(NO3)3, La(NO3)3–Nd(NO3)3 and Pr(NO3)3–Nd(NO3)3 at 298.15 K to near saturation, and the simple modification can represent the new measurements within experimental uncertainty over the full concentration range. In addition, the Zdanovskii-Stokes-Robinson model or partial ideal solution model is obeyed by all the mixtures within isopiestic accuracy, which is consistent with the nature of rare earth elements.

C80 Calorimeter Studies of the Thermal Behavior of LiPF6 Solutions

Abstract: The thermal behavior of several LiPF6 solutions was studied using a C80 calorimeter. It was found that oxygen might react with the solvents and decrease their thermal stability. The dissolution of LiPF6 influences the thermal behavior remarkably with more heat generation and a lower onset temperature. Furthermore, the exothermic peak of LiPF6 based on an electrolyte containing diethyl carbonate (DEC) was found around 185 ∘C, which is 9.5–13.6 ∘C lower than that containing dimethyl carbonate (DMC), which may be due to the relative activity of C2H5— and CH3— in DEC and DMC, respectively.

Experimental Study of the Effect of Temperature, Pressure and Concentration on the Viscosity of Aqueous NaBr Solutions

Abstract: The viscosity of 10 (0.049, 0.205, 0.464, 0.564, 0.820, 1.105, 1.496, 2.007, 2.382, and 2.961 mol ċ kg−1) binary aqueous NaBr solutions has been measured with a capillary-flow technique. Measurements were made at pressures up to 40 MPa. The range of temperature was 288–595 K. The total uncertainty of viscosity, pressure, temperature and composition measurements were estimated to be less than 1.6%, 0.05%, 15 mK, and 0.02%, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous NaBr solutions were studied. The measured values of the viscosity of NaBr(aq) were compared with data, predictions and correlations reported in the literature. The temperature and pressure coefficients of viscosity of NaBr(aq) were studied as a function of concentration and temperature. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for the relative viscosity (η/η0) to calculate accurately the values of viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the results predicted by the Falkenhagen–Dole theory of electrolyte solutions and calculated with the ionic B-coefficient data. The physical meaning parameters V and E in the absolute rate theory of the viscosity and hydrodynamic molar volume V k were calculated using the present experimental viscosity data. The TTG model has been used to compare predicted values of the viscosity of NaBr(aq) solutions with experimental values at high pressures.

Acoustic Study of Solvent Coordination in the Hydration Shells of Potassium Iodide

Abstract: The isentropic compressibilities of aqueous solutions of potassium iodide, from dilute to almost saturated, were determined at 288 to 308 K based on precise measurements of the speed of ultrasound. Using proper correlations, the hydration numbers (h) were calculated as well as the molar volume and compressibility parameters of the hydrated complexes (Vh, βhVh) of water in the hydration shell (V1h, β1hV1h), and of the cavity containing stochiometric mixtures of K+ and I−ions (V2h, β2hV2h). It is revealed that under the studied conditions, the obtained values of h and βhVh are independent of temperature whereas the molar compressibility of the hydration shell βhVh) is independent of concentration. The electrostatic field of the ions is shown to influence the temperature dependence of the molar volume of water in the hydration shell more substantially than a change of pressure alone influences the temperature dependence of the molar volume of pure water.

Precise Conductance Measurements on Dilute Aqueous Solutions of Sodium and Potassium Hydrogenphosphate and Dihydrogenphosphate

Abstract: Precise conductance measurements are reported on dilute aqueous solutions of the sodium and potassium salts of orthophosphoric acid at 25 ∘C. Conductance measurements on solutions of electrolytes such as these phosphate salts that exist in solution as complicated mixtures of ions have previously proved difficult to interpret. To overcome this, a mathematical method has been developed to calculate the concentrations of all the species in the aqueous system M3PO4/M2HPO4/M2HPO4/H3PO4 (M = Na or K) over a continuous range of stoichiometries. The Lee–Wheaton conductance equation has been used to interpret the conductance of these multicomponent solutions in terms of the limiting ionic conductances and concentrations of all the ions in the solution. The limiting molar conductances of the ions H2PO4− and HPO42− and the ion-pair formation constants of these ions with sodium and potassium ions were determine

Transfer Volumes of Glycine, L –Alanine, and L–Serine from Water to 1,2-Butanediol–Water Mixtures at 298.15 K

Abstract: Densities of solutions of glycine, L–alanine, and L–serine have been measured by an oscillating-tube densimeter in 1,2-butanediol–water mixtures with 1,2-butanediol mass fractions ranging from 0 to 0.35 at 298.15 K. Apparent molar volumes and limiting partial molar volumes of each amino acid have been used to obtain the corresponding transfer volumes from water to different concentrations of 1,2-butanediol–water mixtures. The transfer volumes are positive for glycine and L–serine, and both positive and negative for L–alanine over the concentration range studied. The results are interpreted in terms of solute–solvent interactions. Substituent effects are also discussed.