Enthalpies of Dilution of Cobalt–Amine-Type Salts in Aqueous Solutions at 25°C

The enthalpies of dilution for aqueous solutions of [Co(en)₃]Br₃, [Co(pn)₃]Cl₃, and [Co(tn)₃]Cl₃ (where en = 1,2-diaminoethane, pn = 1,2-diaminopropane, and tn = 1,3-diaminopropane) have been measured at 25°C, and up to m = 1 mol-kg^–1, using an isoperibol calorimeter by the long-jump method. Relative apparent molar enthalpies L have been extracted as an empirical equation relating L and m. Previously reported experimental data and theoretical predictions in the restricted primitive model (RPM) for 3:1 and 1:3 aqueous electrolytes are shown together with the new experimental material.     

Sorption–Spectrometric Determination of Palladium in Chloride Solutions

A sorption–spectrometric method was developed for the determination of palladium in solutions of complex composition using cellulose filters impregnated with trioctylamine with the subsequent formation of the colored compound of palladium with 4-(2-pyridylazo)resorcinol on the filter. It was demonstrated that conditions for the preconcentration of palladium coincide with conditions for the formation of colored compounds (green and red forms of palladium complexes) in the sorbent phase. The highest selectivity is observed for the formation of the green form; in this case, the determination of palladium is not affected by the interference from large amounts of concomitant elements (macrocomponents of ores). Palladium was determined on filters by diffuse reflectance spectrometry with the calculation of chromaticity characteristics and by a test scale. The detection limits were 0.5 (green form) and 0.3 (red form) g of palladium on the filter. High precision of results of the determination of palladium (RSD < 5%) is attained in a wide range of its concentrations.     

Thermodynamic Studies of Amino Acid–Denaturant Interactions in Aqueous Solutions at 298.15 K

As proteins and other biomolecules consisting of amino acid residues require external additives for their dissolution and recrystallization, it is important to have information about how such additives interact with amino acids. Therefore we have studied the interactions of simple model amino acids with the additives urea and guanidine hydrochloride in aqueous solutions at 298.15 K, using vapor pressure osmometry. During the measurements, the concentration of urea was fixed as ∼2 mol⋅kg⁻¹ and that of guanidine hydrochloride was fixed as ∼1 mol⋅kg⁻¹ whereas the concentrations of amino acids were varied. The experimental water activity data were processed to get the individual activity coefficients of all the three components in the ternary mixture. Further, the activity coefficients were used to get the excess Gibbs energies of solutions and Gibbs energies for transfer of either amino acids from water to aqueous denaturant solutions or denaturant from water to aqueous amino acid solutions. An application of the McMillan-Mayer theory of solutions through virial expansion of transfer Gibbs energies was made to get pair and triplet interaction parameter whose sign and magnitude yielded information about amino acid–denaturant interactions, relative to their interactions with water. The pair interaction parameters have been further used to obtain salting constants and in turn the thermodynamic equilibrium constant values for the amino acid–denaturant mixing process in aqueous solutions at 298.15 K. The results have been explained in terms of hydrophobic hydration, hydrophobic interactions and amino acid–denaturant binding.     

Solubility in the manganese perchlorate–urea–perchloric acid–water system at 25°С

Heterogeneous equilibria in the manganese perchlorate–urea–perchloric acid–water quaternary system at 25°С were studied by investigating solubility. The crystallization regions were determined for the initial solid components, eutonic compositions of ternary systems constituting the quaternary system, binary compounds of urea with manganese perchlorate and perchloric acid, and also two new coordination compounds containing simultaneously manganese perchlorate, urea, and perchloric acid: Mn(ClO₄)₂ · 4CO(NH₂)₂ · HClO₄ and Mn(ClO₄)₂ · 2CO(NH₂)₂ · HClO₄.     

Interaction in the nickel perchlorate–acetamide–perchloric acid–water system at 25°С

Heterogeneous equilibria in the nickel perchlorate–acetamide–perchloric acid–water quaternary system at 25°С were studied by studying solubility. The crystallization regions were determined for the initial solid components, eutonic compositions of the ternary systems constituting the quaternary system, binary compounds of acetamide with nickel perchlorate and perchloric acid, and also two new coordination compounds containing simultaneously nickel perchlorate, acetamide, and perchloric acid: Ni(ClO₄)₂ · 4CH₃CONH₂ · HClO₄ and Ni(ClO₄)₂ · 2CH₃CONH₂ · HClO₄.     

Interaction in the zinc perchlorate–urea–perchloric acid–water system at 25°С

Heterogeneous equilibria in the zinc perchlorate–urea–perchloric acid–water quaternary system at 25°С were studied by investigating solubility. The crystallization regions were found for the initial solid components, eutonic compositions of the ternary systems constituting the quaternary system, binary compounds of urea with zinc perchlorate and perchloric acid, and also two new coordination compounds containing simultaneously zinc perchlorate, urea, and perchloric acid: ZnClO₄ · 4CO(NH₂)₂ · HClO₄ and ZnClO₄ · 2CO(NH₂)₂ · HClO₄.     

Enthalpies of Dilution of Some Aqueous Transition Metal Sulfate Solutions at 25°C

Enthalpies of dilution of aqueous solutions of the transition metal sulfates CoSO₄, MnSO₄, and NiSO₄, were measured from 1.5 to 0.2 mol-kg^–1 at 25°C. The apparent molal enthalpy equations of Pitzer were fit to the resulting data and the parameters for these equations presented.     

Copper(II)–Ammonia Complexation Equilibria in Aqueous Solutions at Temperatures from 30 to 250°C by Visible Spectroscopy

The spectra of copper(II)–ammonia solutions in 2 mol-kg^–1 NH₄NO₃(aq) were recorded as a function of pH with a new UV–visible flow cell, capable of operating at conditions up to 325°C and 300 bars. Equilibrium constants for the formation of copper(II)–ammonia complexes Cu(NH₃)_n ²⁺, 1 n 4, from 30 to 150°C were determined by evolving factor analysis and nonlinear least-squares regression. Measurements at higher temperatures were limited by thermal decomposition of NH₄NO₃(aq). The formation constants of Cu(NH₃)_n ²⁺ decrease with temperature, consistent with extrapolations of literature data from measurements below 100°C. Measurements above 150°C were carried out in 0.5 mol-kg^–1 CF₃SO₃H (aq), at the very high ammonia concentrations required to avoid the precipitation of CuO(s). The spectra are consistent with Cu(NH₃)₄ ²⁺ as the predominant species, based on extrapolations of peak maxima and molar absorptivities from lower temperatures. Shifts in the spectra of Cu²⁺ and the Cu(NH₃)_n ²⁺ species to higher wavelength and increases in molar absorbance with increasing temperature are discussed in terms of the structure of the complexes.     

Determination of Stoichiometric Dissociation Constants of Benzoic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant K_m of benzoic acid in dilute aqueous NaCl and KCl solutions at 25°C from the thermodynamic dissociation constant K_a of this acid and from the ionic strength I_m of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study and the equations for K_m were based on the single-ion activity coefficient equations of the Hückel type. The existing literature data obtained by conductance measurements and by electromotive force (EMF) measurements on Harned cells were first used to revise the thermodynamic value of the dissociation constant of benzoic acid. A value of K_a = (6.326 ± 0.005) × 10^-5 was obtained from the most precise conductivity set [Brockman and Kilpatrick] and this value is supported within their precisions by the less precise conductivity set of Dippy and Williams and by the EMF data set measured by Jones and Parton with quinhydrone electrodes. The new data measured by potentiometric titrations in a glass electrode cell were then used for the estimation of the parameters of the Hückel equations of benzoate ions. The resulting parameters were also tested with the existing literature data measured by cells with and without a liquid junction. The Hückel parameters suggested here are close to those determined previously for anions resulting from aromatic and aliphatic carboxylic acids. By means of the calculation method based on the Hückel equations, K_m can be obtained almost within experimental error at least up to I_m of about 0.5 mol-kg_-1 for benzoic acid in NaCl and KCl solutions.     

Densities and Partial Molar Volumes of Some Amino Acids and Diglycine in Aqueous n-Propanol Solutions at 25°C

Apparent molar volumes, V , of glycine, DL--alanine, DL--amino-n-butyric acid, L-valine, L-leucine, and diglycine in water and in 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 m _B [molality of n-propanol in water (mol-kg^–1)] aqueous solutions of n-propanol have been obtained from densities of their solutions at 25 °C measured by using a precise vibrating-tube digital densimeter. The calculated partial molar volumes of amino acids and diglycine at infinite dilution, V _2,m ^o , have been used to obtain the corresponding transfer volumes, _tr V _2,m ^o , from water to different n-propanol–water mixtures. _tr V _2,m ^o values are positive for glycine, DL-- alanine, and diglycine (except at lower concentration 1.0 m _B ), negative for L-valine, and both positive and negative for the remaining amino acids over the concentration range studied. The side-chain contributions and hydration numbers have been calculated from V _2,m ^o data. Interaction coefficients have also been obtained from the McMillan–Mayer approach and the data have been interpreted in terms of various interactions.     

On Gold(I) Complexes and Anodic Gold Dissolution in Sulfite–Thiourea Solutions

Processes involving gold(I) complexes were studied in sulfite–thiourea (TU) solutions. It is shown that at pH >5 the complex [\( {\text{AuTU}}_{2}^{ + } \)] undergoes irreversible decomposition followed by deprotonation and formation of a solid phase. From the data of pH in mixed solutions, the equilibrium constants were evaluated: \( {\text{Au}}({\text{SO}}_{3} )_{2}^{3 - } + i{\text{TU}} \rightleftharpoons {\text{Au}}({\text{SO}}_{3} )_{2 - i} {\text{TU}}_{i}^{2i - 3} + i{\text{SO}}_{3}^{2 - } \), log₁₀ β ₁ = ?1.2, log₁₀ β ₂ = ?3.6. Some aspects of the anodic dissolution of gold in mixed sulfite–thiourea solutions are considered. With the help of the carbonate buffer system the change of the anodic current density j _a was studied at high pH; j _a (pH) has a maximum at pH 11.6–11.9 for E _a = 0.3–0.6 V (vs. NHE). At pH > 12.0, the j _a values decrease sharply. Possible mechanisms of anodic gold dissolution, as well as the role of sulfite, are discussed.     

Phase Diagrams of Fullerenol-d–LaCl3–H2O and Fullerenol-d–GdCl3–H2O Systems at 25°С

Russian Journal of Physical Chemistry A - Isothermal phase diagrams of ternary systems fullerenol-d–LaCl3–H2O and fullerenol-d–GdCl3–H2O at 25°C are studied via...     

Volumetric Properties of Amino Acids in Aqueous N-methylacetamide Solutions at 298.15 K

The apparent molar volumes (V _φ ) of glycine, L-alanine and L-serine in aqueous 0 to 4 mol⋅kg⁻¹ N-methylacetamide (NMA) solutions have been obtained by density measurement at 298.15 K. The standard partial molar volumes (V_f⁰)V_{\phi}^{0}) and standard partial molar volumes of transfer (D_trV_f⁰)\Delta_{\mathrm{tr}}V_{\phi}^{0}) have been determined for these amino acids. It has been show that hydrophilic-hydrophilic interactions between the charged groups of the amino acids and the –CONH– group of NMA predominate for glycine and L-serine, but for L-alanine the interactions between its side group (–CH₃) and NMA predominate. The –CH₃ group of L-alanine has much more influence on the value of D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0} than that of the –OH group of L-serine. The results have been interpreted in terms of a co-sphere overlap model.     

Kinetics of Crystalline Iodine Dissolution in Ethanol at Room Temperature and at 60°С

The kinetics of crystalline iodine dissolution in ethanol at room temperature and 60°C is studied using the electronic absorption spectra of iodine solutions. Dissolution is shown to proceed for more than three months. It is found that the process begins with the formation of hydroiodic acid HI and is complete with the formation of I ₃ ^? anions.     

Electrical Double Layer on Liquid Sn–Ga Alloy in Aqueous Solutions

Double-layer parameters of a liquid Sn–Ga electrode in aqueous electrolyte solutions are studied. It is shown that Sn in the alloy with Ga is a surface-active component and is forced out onto a surface layer of the electrode. The double-layer parameters of an Sn–Ga electrode (8 at. % Sn), which are measured in the experimentally accessible range of charges, differ radically from the parameters of Ga electrodes and are close to those of Sn electrode. Hence, an Sn–Ga electrode containing 8 at. % Sn simulates electrochemical properties of a liquid Sn electrode. The difference between reciprocal electronic capacitances of Hg and Sn and a corrected electrochemical work function of Sn are determined. It is shown that the chemisorption interaction of an Sn–Ga electrode with water molecules is virtually absent at charges more negative than –7 C/cm². A potential drop on uncharged Sn, which is associated with water chemisorption, is –20 mV. Thus, the hydrophilicity of Sn is slightly higher than that of Hg, Bi–Ga, Pb–Ga, and Tl–Ga and significantly lower than that of In–Ga, Cd–Ga, and Ga.     

Conversion of Heterocycles of The Dihydrothiazine–Thiazoline Series in Aqueous Solutions

When heterocycles of the dihydrothiazine–thiazoline series are treated with an aqueous solution of base, they undergo ring opening, leading to formation of ureidoalkanethiols. Study of solvolysis of the heterocycles when treated with ammonia permitted us to observe a novel heterocyclic ring opening reaction, occurring with formation of 2(3)-guanidinoalkanethiols. We have developed a novel preparative method for obtaining 2(3)-guanidinoalkanethiols.     

Electrical Double Layer on Liquid Bi–Ga Alloys in Aqueous Solutions

Double-layer characteristics of a liquid bismuth–gallium electrode are studied in aqueous electrolyte solutions. Based on the results obtained it is shown that Bi in an alloy with Ga is a surface-active component and forced out to the electrode surface layer. For electrode charges q –5 C/cm², the double layer characteristics of Bi–Ga electrodes approach those of a bismuth electrode. Thus, with respect to its electrochemical properties, a Bi–Ga electrode containing 0.25 at. % Bi simulates a liquid bismuth electrode. The corrected electrochemical work function is determined for bismuth. The close values of the difference of zero-charge potentials on mercury and bismuth in water and the difference of corrected electrochemical work functions for these metals points to the very low hydrophilicity of the Bi–Ga electrode, which approaches the value for mercury at negative electrode potentials. Taking into account that the Bi–Ga electrode displays no semimetallic properties, the similarity of the electric double layer (EDL) parameters for the Bi–Ga alloy and solid pure Bi indicates that the semimetallic properties of bismuth make no contribution to the EDL characteristics of the alloy in the studied range of negative charges q –5 C/cm².     

Electroconduction,Association, and Ion–Molecular Interactions in Nickel Chloride Solutions in Methanol at 5–55°C

Results of a conductimetric investigation of nickel chloride in methanol at 5–55°C and electrolyte concentrations of 0.1–5 mM are presented. Limiting equivalent conductivities by Ni²⁺ and Cl^– and constants of ionic association in the first step with the formation of ionic pair NiCl⁺ are determined for asymmetric electrolytes using an extended Lee–Wheaton equation. In dilute nickel chloride solutions in methanol the association of ions in the second step is inessential. The size of dynamic solvation sheaths of the ions and the short-range non-coulombic interion potential suggest that the Ni²⁺ ion forms a kinetically and energetically stable solvated complex with the nearest solvation layer being 400 pm thick and virtually temperature-independent. The nearest kinetically stable solvation sheath of the Cl^– ion comprises mostly hydroxyl groups of methanol molecules and its stability is severely dependent on temperature.     

Quaternary Liquid–Liquid Equilibria for Aqueous Systems Containing Dimethyl Carbonate at 298.15 K

Experimental tie-line data for two ternary systems, water + dimethyl carbonate + methanol or ethanol, and two quaternary systems, water + dimethyl carbonate + toluene + methanol or ethanol were investigated at 298.15 K and atmospheric pressure. The experimental liquid–liquid equilibrium data were correlated using a modified UNIQUAC activity coefficient model with binary and ternary as well as quaternary parameters. The calculated results were further compared with those obtained from an extended UNIQUAC model.     

Volumetric and Surface Properties of Short Chain Alcohols in Aqueous Solution–Air Systems at 293?K

From measurements of the surface tension, density, viscosity and light scattering of aqueous solutions of methanol, ethanol and propanol at 293?K, their activity in the surface monolayer, surface excess concentration, and apparent and partial molar volume were determined. The surface excess concentration of alcohols at the water?Cair interface was determined from the Gibbs equation by using both the alcohol's activity and their molar fraction in the bulk phase and recalculated by using the Guggenheim?CAdam equation. The values of the surface excess concentration determined from the Gibbs equation were also applied to determine the standard Gibbs energy of alcohol adsorption at the water?Cair interface from Langmuir??s equation and compared to those determined from that of Aronson and Rosen.