Study of magnesium nitrate behavior in sodium nitrate solutions at 25°C

Solubility in the system KNO₃-Mg(NO₃)₂-H₂O at 25°C was studied by the isothermal method. Crystallization of potassium nitrate from aqueous solutions was studied. Coefficients of the removal of magnesium nitrate admixture were calculated.     

Second critical micelle concentration of dodecyldimethylbenzylammonium chloride in aqueous solution at 25 °C

Two breaks have been found on the conductivity, refractive index, density and sound velocity against molality plots for aqueous solutions of dodecyldimethylbenzylammonium chloride at 25 °C, in the absence of any additive. The first break corresponds to the critical micelle concentration, cmc. The second, less distinct break, occurring in the molality range of 0.082 to 0.104 mol kg^-1, in dependence on the technique applied, has been ascribed to the second critical micelle concentration, 2nd cmc, responsible for structural transitions of spherical micelles. Values of cmc and 2nd cmc have been also estimated conductometrically for tetradecyltrimethylammonium bromide and dodecylpyridinium chloride. On the basis of available conductometric data it has been shown that the 2nd cmc/cmc ratio varies in the range of 2 to 10 in dependence on the type of 1:1 ionic surfactant. It has been also shown that for a given class of surfactants, the logarithm of 2nd cmc varies linearly with the number of carbon atoms in the alkyl chain ( n= 12, 14 and 16). Both empirical regression coefficients depend upon the class of surfactants considered.     

Dilution enthalpies of alkanols in concentrated aqueous solutions of urea at 25°C

Enthalpies of dilution of some aliphatic alcohols were determined at 25°C in aqueous 7M urea solutions by flow microcalorimetry. The excess enthalpies were expressed as power expansion series in molalities referred to 1 kg of constant composition urea-water mixture. This urea-water mixture was utilized throughout as a mixed solvent. The values of the second enthalpic virial coefficients were all found to be positive and generally lower than the corresponding values in water. Large differences were encountered, as in water, by comparing normal and branched isomeric propanols and butanols. For one system it was possible to measure the third coefficients, which were also positive. The second enthalpic coefficients were found to increase with the molecular weight of the alkanols. These facts suggest that in the presence of a large concentration of urea, the excess enthalpies are mainly determined by apolar interactions. This is surprising and potentially rich in consequences for a better understanding of the interactions among amino acid residues distantly situated in the primary sequences but topologically near in the loops of globular proteins. An analysis, carried out using the Savage-Wood additivity group method, shows that the enthalpic contributions (that appear to play a crucial role in water in making the polar interaction to be favorable) become essentially unfavorable in urea-water solvent. The hypothesis that the peptide-peptide interactions are prevented by the preferential solvation of urea is also discussed.     

Excess enthalpies of aqueous solutions of small peptides at 25°C

Heats of dilution of aqueous solutions of the following di-and tripeptides were determined at 25°C over a wide concentration range: -alanyl-glycine, -alanyl--alanine, DL--alanyl-glycine, glycyl-DL--alanine, L--alanyl-L-alanine, DL--alanyl-DL--alanine, DL--alanyl-DL-valine, DL--alanyl--alanine, glycyl--aminobutyric acid, glycyl-L-leucine and DL--alanyl-glycylglycine. The excess enthalpies H^ex and partial molar relative enthalpies L₂ were calculated and enthalpy coefficients of intermolecular interaction were analysed using the additivity principle of Savage and Wood. The concentration dependence of the enthalpic characteristics of peptide-peptide interactions is discussed based on of their hydrophobicity and hydrophilicity. The three-stage model of peptide association is described using enthalpic coefficients of intermolecular interactions.     

Excess enthalpies of dilute aqueous solutions of model peptides and urea at 25°C

Excess enthalpies of four dilute aqueous solutions each containing urea and a model peptide (N-acetyl-N-methylamides of either glycine or L-alanine, N-acetylamides of either L-valine or L-proline) have been determined by calorimetry. These results are compared with the excess enthalpies of aqueous solutions of amides and other uncharged peptides. The second enthalpic virial coefficients are discussed on the basis of McMillan-Mayer theory and additivity of group interactions. The results confirm the preliminary conclusions of previous works in this series, i.e., that peptideurea interactions are water assisted, and an extra contribution appears when more than one peptidic or amidic group is present on the same molecule.     

Diffusion of levodopa in aqueous solutions of hydrochloric acid at 25 °C

Ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) measured by the Taylor dispersion method are reported for aqueous solutions of {levodopa (l-dopa) + HCl} solutions at 25 °C and HCl concentrations up to 0.100 mol · dm⁻³. The coupled diffusion of l-dopa (1) and HCl (2) is significant, as indicated by large negative cross-diffusion coefficients. D₂₁, for example, reaches values that are larger than D₁₁, the main coefficient of l-dopa. Combined Fick and Nernst–Planck equations are used to analyze the proton coupled diffusion of l-dopa and HCl in terms of the binding of H⁺ ions to l-dopa and ion migration in the electric field generated by l-dopa and HCl concentration gradients.     

Fractal analysis of pit morphology of Inconel alloy 600 in sulphate,nitrate and bicarbonate ion-containing sodium chloride solution at temperatures of 25–100 °C

Pit morphology of Inconel alloy 600 in sulphate (SO₄ ^2-), nitrate (NO₃ ^-) and bicarbonate (HCO₃ ^-) ion-containing 0.5 M sodium chloride (NaCl) solution was analysed in terms of fractal geometry as functions of solution temperature and anion concentration using the potentiostatic current transient technique, scanning electron microscopy, image analysis and ac-impedance spectroscopy. Potentiostatic current transients revealed that the pitting corrosion is facilitated by the increase in solution temperature, irrespective of anion additives, and that it is hindered by the increase in NO₃ ^- and HCO₃ ^- ion concentration, regardless of solution temperature. Above 60 °C, it was also found that the addition of SO₄ ^2- ions impedes pit initiation, but enhances pit growth. The value of fractal dimension D _f of the pits increased with increasing solution temperature and with decreasing NO₃ ^- and HCO₃ ^- ion concentration. Moreover, the value of D _f increased above 60 °C with increasing SO₄ ^2- ion concentration. This is caused by the increase in the ratio of pit perimeter to pit area, implying the formation of pits with micro-branched shape due to the acceleration of the local attack in the pits. From the decrease of the depression parameter with increasing solution temperature, it is inferred that the roughness of the pits increased with increasing solution temperature. In addition, the depression parameter was found to increase with increasing NO₃ ^- and HCO₃ ^- ion concentration. But, above 60 °C, in the case of SO₄ ^2- ion addition, the depression parameter decreased with increasing SO₄ ^2- ion concentration. From the experimental findings, the three-dimensional pit morphology is discussed in terms of the values of D _f of the pits and the depression parameter, with respect to anion concentration and solution temperature.     

Physico-chemical,acoustic and excess properties of glycylglycine–MnCl2 in aqueous ethanol mixtures at different temperatures

Volumetric, acoustic, refractometric, excess and deviation properties of glycylglycine–MnCl₂ in aqueous ethanol mixtures have been reported at T = (288.15 to 318.15) K. Redlich–Kister equation was used to fit the derivate properties. The experimental data of the constituent binaries were analyzed to discuss the nature and strengths of intermolecular interactions. The interdependence of L_f and u has been evolved from Eyring and Kincaid model. The variations in specific acoustic impedance revealed that hydrogen bonding was predominant in the studied binary mixtures. Solvation number indicated structure-breaking tendency of the solute and weakening of local solvent structure.     

Volumetric, rheological, and optical properties of Na-alkylsulfonates aqueous solutions at 29°C

Present paper reports density, relative viscosity and refractive index of sodium salt of 1-heptanesulfonic acid and 1-octanesulfonic acid at 29°C. Density data has been fitted to Masson empirical relation and limiting apparent molar volumes were evaluated. Viscosity A and B coefficients characterizing ion-ion and ion-solvent interactions have been evaluated by fitting viscosity data in Jone-Doles equation. Experimental and calculated properties support the strong ion-solvent interactions in solution.     

Apparent molar and partial molar volumes of aqueous ceric ammonium nitrate solutions at 20, 25, 30, and 35°C

Present paper reports the measured densities (ρ) and refractive indices (n _D) of aqueous solutions of ceric ammonium nitrate (CAN) at 20, 25, 30, and 35°C in different concentrations of solution. Apparent molar volumes (φ_v) have been calculated from the density data at different temperatures and fitted to Massons relation to get limiting partial molar volumes (? _v ⁰ ) of CAN. Refractive index data were fitted to linear dependence over concentration of solutions and values of constant K and n _D ⁰ for different temperatures were evaluated. Specific refractions (R _D) of solutions were calculated from the refractive index and density data. Concentration and temperature effects on experimental and derived properties have been discussed in terms of structural interactions.     

Study of the behavior of chromium(III) in potassium nitrate solutions at 25°C

Solubility in the KNO₃-Cr(NO₃)₃-H₂O system at 25°C was studied by an isothermal method. The existence of solid phases of potassium nitrate and chromium(III) nitrate nonahydrate was confirmed by constructing a phase diagram, chemical analysis, and IR spectroscopy. Crystallization of potassium nitrate from aqueous solutions was studied. Potassium nitrate does not interact with chromium(III) nitrate within the range of micro and macro concentrations. The capture of chromium(III) by KNO₃ crystals is due to adsorption and occlusion of a mother solution.     

Thermodynamic properties of transition metals in aqueous solution: 1. The enthalpies of dilution of some aqueous transition metal chloride solutions at 25°C

Enthalpies of dilution H _D of aqueous solutions of the transition metal chlorides CdCl₂, CoCl₂, CuCl₂, MnCl₂, and NiCl₂ were measured from 1.0 molal to dilute solution at 25°C. The apparent molal enthalpy equations of Pitzer were then fit to the resulting H _D data and the parameters for these equations are presented. The heat of dilution data for CdCl₂ and CuCl₂ were in good agreement with results by other workers.     

Volume properties and structure of aqueous solutions of urea at 263–348 K

The apparent molar volume of urea ? in aqueous solution in the range T = 273–323 K and m = 1–10 (molality) depends linearly on m ^1/2. An equation for ?(m, T) was derived. The partial molar characteristics of urea ? ₂ and water ? ₁ (volume, dilatability, and temperature coefficients of volumes) were calculated. The ?(T) dependences have characteristic points (extrema, inflection points), shifted to the region of lower temperatures for dilute solutions. The ? ₁(T) dependences for 2m and 4m of the urea solution retain the characteristics of the Y ₁(T) of pure water. In these solutions, the proper structure of water is preserved.     

The bulk properties of dioxane solutions in ethylene glycol at 25–75°C

The densities of ethylene glycol solutions of dioxane were measured at 0–20 mol % dioxane at five temperatures ranging from 25 to 75°C. The apparent molar volumes of dioxane in the solutions were studied. The results were compared with similar characteristics of the aqueous solutions of dioxane and ethylene glycol solutions of tetrahydrofuran. In contrast to these systems, the ethylene glycol-dioxane system did not show a minimum of the apparent molar volumes of dissolved nonelectrolytes. The conclusion was drawn that the solvophobic effects were absent in the bulk properties of the ethylene glycol solutions of dioxane because of the low lability of the spatial net of H-bonds of ethylene glycol and peculiarities of the molecular structure of dioxane.     

Efficiency of energy transfer from γ-irradiated ammonium halides in aqueous iodide and nitrate solutions

It is well known that ammonium halide (NH₄X) crystals, on -exposure, store energy in the form of primary and secondary radiolytic products. Such crystals on dissolution in aqueous iodide and nitrate solutions result in oxidation of iodide and reduction of nitrate, respectively. The yields of iodine and nitrite are determined by chemical methods under varying conditions of the amount, dose and particle size of the irradiated ammonium halide salts. The maximum values of the efficiency of energy transfer for oxidation and reduction processes for ammonium halide salts correspond to 40% and 10%, respectively. At low doses, an empirical relation proposed between the percent efficiency of energy transfer and the absorbed dose is valid. The concentrations of inherent oxidizing and reducing species initially present are 7.0×10¹⁸ and 1.0×10¹⁸ per mol of ammonium halide, respectively.     

Molecular interactions in aqueous solutions of polyborates at different acidity based on the Raman spectroscopy data at 25°C

Investigation of aqueous solutions of polyborates LiB(OH)₄, Li₂B₄O₅(OH)₄, and LiB₅O₆(OH)₄ at different acidity has been performed by Raman spectroscopy at 25°C. The geometries and Raman vibrational frequencies of H₃BO₃ in aqueous phase were calculated at different basis sets, and verified the veracity. The calculated characteristic Raman shifts of B(OH)₃, B(OH)₄ ^?, B₃O₃(OH)₄ ^?, B₃O₃(OH)₅ ^2?, B₄O₅(OH)₄ ^2?, and B₅O₆(OH)₄ ^? were assigned to 880.0, 735.33, 599.06, 740.16, 551.67, and 521.04 cm^?1, respectively. Assignments of the bands were tentatively ascribed by comparing the calculated Raman spectrum. The chemical species distribution and the relevant molecular interaction mechanisms in the polyborates solutions were suggested.     

Thermodynamic properties of transition metals in aqueous solution: 3. The heats of mixing aqueous solutions of CdCl2, NiCl2 and ZnCl2 with NaCl at varying ionic strength at 25°C

The heat of dilution of aqueous solutions of ZnCl₂ and the heats of mixing H _m of aqueous solutions of CdCl₂, NiCl₂, and ZnCl₂ with NaCl solutions were measured at 25°C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system.