Buffer standards for the physiological pH of the zwitterionic compound of 3-(N-morpholino)propanesulfonic acid (MOPS) from T = (278.15 to 328.15) K

This paper reports the pH values of five NaCl-free buffer solutions and 11 buffer compositions containing NaCl at I = 0.16 mol · kg⁻¹. Conventional pa_H values are reported for 16 buffer solutions with and without NaCl salt. The operational pH values have been calculated for five buffer solutions and are recommended as pH standards at T = (298.15 and 310.15) K after correcting the liquid junction potentials. For buffer solutions with the composition m₁ = 0.04 mol · kg⁻¹, m₂ = 0.08 mol · kg⁻¹, m₃ = 0.08 mol · kg⁻¹ at I = 0.16 mol · kg⁻¹, the pH at 310.15 K is 7.269, which is close to 7.407, the pH of blood serum. It is recommended as a pH standard for biological specimens.     

(Liquid + liquid) equilibria in {water + acrylic acid + (1-butanol,or 2-butanol,or 1-pentanol)} systems at T = 293.2 K,T = 303.2 K,and T = 313.2 K and atmospheric pressure

(Liquid + liquid) equilibrium (LLE) data for {water + acrylic acid + (1-butanol, or 2-butanol, or 1-pentanol)} at T = 293.2 K, T = 303.2 K, and T = 313.2 K and atmospheric pressure (≈95 kPa) were determined by Karl Fischer titration and densimetry. All systems present type I binodal curves. The size of immiscibility region changes little with an increase in temperature, but increases according to the solvent, following the order: 2-butanol < 1-butanol < 1-pentanol. Values of solute distribution and solvent selectivities show that 1-pentanol is a better solvent than 1-butanol or 2-butanol for acrylic acid removal from water solutions. Quality of data was ascertain by Hand and Othmer-Tobias equations, giving R² > 0.916, mass balance and accordance between tie lines and cloud points. The NRTL model was used to correlate experimental data, by estimating new energy parameters, with root mean square deviations below 0.0053 for all systems.     

Heat capacity and thermodynamic properties of germanium disulfide at temperatures from T = (2 to 1240) K

The heat capacity of polycrystalline germanium disulfide α-GeS₂ has been measured by relaxation calorimetry, adiabatic calorimetry, DSC and heat flux calorimetry from T = (2 to 1240) K. Values of the molar heat capacity, standard molar entropy and standard molar enthalpy are 66.191 J · K^?1 · mol^?1, 87.935 J · K^?1 · mol^?1 and 12.642 kJ · mol^?1. The temperature of fusion and its enthalpy change are 1116 K and 23 kJ · mol^?1, respectively. The thermodynamic functions of α-GeS₂ were calculated over the range (0 ? T/K ? 1250).     

Standard molar volumes and expansibilities of 1,3-alkyl-N-substituted achiral glycolurils in water at T = (278.15 to 318.15) K and p = 0.1 MPa: A comparative analysis

Densities of aqueous solutions of achiral 1,3-dimethylglycoluril (1,3-DMGU) and 1,3-diethylglycoluril (1,3-DEGU) were measured using a hermetically sealed vibrating-tube densimeter, with an uncertainty of 1 · 10⁻⁵ g · cm⁻³, at T = (278.15, 288.15, 298.15, 308.15, and 318.15) K and p = (99.6 ± 0.8) kPa. The solute molality was ranged from (0.06 to 0.39) and from (0.01 to 0.07) mol · kg⁻¹ for the aqueous 1,3-DMGU and 1,3-DEGU, respectively. The standard (at infinite dilution) molar volumes and isobaric expansibilities for the 1,3-dialkyl-N-substituted glycolurils compared in water were calculated and discussed in comparison with the previously derived molar enthalpies and heat capacities of their dissolution (hydration). The temperature-dependent behavior of packing-related hydration effects was described taking into account the structural features of a solute molecule.     

Interaction of biological buffers with electrolytes: Densities of aqueous solutions of two substituted aminosulfonic acids and ionic salts from T = (298.15 to 328.15) K

Biological buffers are of utmost importance for research in biological and clinical chemistry and in oceanography, but they may not be inert enough, thus interfering with the system under study. The N-[Tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS) and N-[Tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO) are useful zwitterionic buffers for pH control as standard buffers in the physiological region of pH 7.7 to 9.1 for TAPS and 7.0 to 8.2 for TAPSO, respectively. In this work, interaction between these zwitterionic compounds and electrolytes of potassium acetate (KAc), potassium bromide (KBr), potassium chloride (KCl), and sodium chloride (NaCl) were investigated through measuring the densities of these buffers in aqueous and in aqueous electrolyte solutions by a high precision vibrating tube digital densitometer from T = (298.15 to 328.15) K under atmospheric pressure. In this series of measurements, the aqueous samples were prepared with various concentrations of the zwitterionic buffers, up to saturated conditions, and over salt concentrations from (1 to 4) mol · dm^?3. The measured densities served to evaluate the cubic expansion coefficients, α(m, T) and the apparent molar volumes, V_?(m, T). An empirical equation was used to correlate quantitatively the experimental densities over the entire concentration ranges.     

Viscosity measurements for squalane at high pressures to 350 MPa from T = (293.15 to 363.15) K

Squalane is being recommended as a secondary reference material for viscometry at moderate to high pressure and at moderate viscosity. As part of this work, a correlation has been developed for atmospheric pressure (Comuñas et al., 2013) [12]. Here we report new experimental high pressure viscosities for squalane (176 data points obtained for temperatures (293.15 to 363.15) K, at pressures up to 350 MPa with a maximum viscosity of 745 mPa · s). These have been determined with four different falling-body viscometers as well as a quartz crystal resonator viscometer. A preliminary high pressure viscosity correlation for squalane is proposed, based on our new data. At pressures up to 350 MPa, this correlation provides an absolute average deviation of 1.5% with a maximum absolute deviation of 8.9%. Comparison is made between the different instruments. In addition, we have also considered the validity of a thermodynamic scaling model.     

Compressed liquid densities for the (n-heptane + n-decane) and (n-octane + n-decane) systems from T = (313 to 363) K

Densities (p, ρ, T, x₁) of two binary n-alkane systems are reported from T = (313 to 363) K in the compressed liquid phase up to 25 MPa over the whole range of composition. The binary mixtures {x₁n-heptane + (1 ? x₁)n-decane} and {x₁n-octane + (1 ? x₁)n-decane} were prepared at compositions of (x₁ = 0.0531, 0.2594, 0.5219, 0.777, 0.952), and (x₁ = 0.0616, 0.2801, 0.5314, 0.7736, 0.9623), respectively. A measuring system based on a vibrating tube densimeter, DMA HPM from Anton Paar with data acquisition system was developed in order to obtain experimental densities. Water and nitrogen were used as reference fluids to calibrate the densimeter. Experimental methodology was checked by comparing the n-heptane and n-decane densities against multi-parameter equations proposed in the literature. Differences between both sets of data show a maximum deviation of 0.07%. Excess molar volumes, isothermal compressibility and isobaric thermal expansivity were computed from experimental densities.     

Partition behaviour of benzoic acid in (water + n-dodecane) solutions at T = (293.15 and 298.15) K

The partition coefficients of benzoic acid in solutions of two immiscible solvents, water and n-dodecane, were measured at temperatures of (293.15 and 298.15) K. The experimental results indicated that at both temperatures the partition coefficients were not constant, but showed linear dependences on the concentration of benzoic acid in water. Dimerization of benzoic acid in n-dodecane and ionization in water were assumed based on the chemical theory and the experimental results verified this assumption quite well. Accordingly the association equilibrium constants of benzoic acid in n-dodecane were obtained by a linear regression. The regression results also showed that there was a very strong dimerization of benzoic acid in n-dodecane over the temperatures and concentration range investigated.     

Viscosities of binary mixtures of some n-ethoxyethanols with ethyl tert-butyl ether at T = (293.15, 298.15, and 303.15) K

Viscosities at T = (293.15, 298.15, and 303.15) K in the binary mixtures of ethyl tert-butyl ether with 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, and 2-[2-(2-ethoxyethoxy)ethoxy]ethanol have been measured over the entire range of mixture compositions. From the experimental data, deviations in the viscosity (Δln η) and excess energies of activation for viscous flow (ΔG^1E) have been calculated. The viscosity data were correlated with equations of Hind et al., Grunberg and Nissan, Auslaender, and McAllister. The results for Δln η and ΔG^1E are discussed in terms of intermolecular interactions and structure of studied binary mixtures.     

Volumetric and viscometric properties of aqueous solutions of N-(2-hydroxyethyl)morpholine at T = (293.15, 303.15, 313.15, 323.15, 333.15) K

Densities, ρ, and viscosities, η, of aqueous solutions of N-(2-hydroxyethyl)morpholine were measured over the entire composition range at T = (293.15, 303.15, 313.15, 323.15, 333.15) K and at atmospheric pressure. The excess molar volumes V^E and viscosity deviations η^E of aqueous solutions were calculated from the experimental results of density and viscosity measurements and fitted to the Redlich–Kister polynomial equation. Apparent molar volumes V?, partial molar volume at infinite dilution V^∞, and the thermal expansion coefficient α were also calculated. The V^E values were found to be negative over the entire composition range at all temperatures studied and become less negative with increasing temperature, whereas the viscosity data η^E exhibited positive deviations from ideal behaviour.     

Solubilities of oleanolic acid and ursolic acid in (ethanol + water) mixed solvents from T = (292.2 to 328.2) K

The solubility of oleanolic acid and of ursolic acid in (ethanol + water) mixed solvents was measured over the temperature range of (292.2 to 328.2) K. The solubility of oleanolic acid and of ursolic acid in the (ethanol + water) mixed solvent systems increase with increasing the mole fraction of ethanol in mixed solvents. The experimental solubility data are correlated by a simplified thermodynamic equation and the modified Apelblat equation.     

(Liquid + liquid) equilibrium of (water + 2-propanol + 1-butanol + salt) systems at T = 313.15 K and T = 353.15 K: Experimental data and correlation

(Liquid + liquid) equilibrium data for the quaternary systems (water + 2-propanol + 1-butanol + potassium bromide) and (water + 2-propanol + 1-butanol + magnesium chloride) were measured at T = 313.15 K and T = 353.15 K. The overall salt concentrations were 5 and 10 mass percent. Ternary (liquid + liquid) equilibrium data for the salt-free system (water + 2-propanol + 1-butanol) were also determined and found to be in good agreement with data from the literature. The NRTL model for the activity coefficient was used to correlate the data. New interaction parameters were estimated, using the Simplex minimization method and a concentration-based objective function. The results are very satisfactory, with root mean square deviations between experimental and calculated compositions of both phases being less than 0.5%.