Conductivity measurements and relative association constants of some 3:1 electrolytes

Conductance measurements are reported for dilute aqueous solutions at 25°C of potassium hexacyanoferrate(III) and of sodium, potassium, rubidium, and cesium octacyanotungstate(V). The results are interpreted in terms of ion-pair formation, and association constants for the formation of these ion pairs are calculated. For the ion pairs MW(CN) ₈ ^2– , the results are: M=Na, 12±8; K, 23±7; Rb, 37±10; and Cs, 51±4M ^–1, at 25°C and zero ionic strength.     

Standard thermodynamic functions of complex formation between Cu2+ and glycine in aqueous solution

Heat effects of the interaction of copper(II) solutions with aminoacetic acid (glycine) are measured by the direct calorimetry at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 against a background of potassium nitrate. Standard enthalpy values for reactions of the formation of aminoacetic acid copper complexes in aqueous solutions are obtained using an equation with a single individual parameter by extrapolating it to zero ionic strength. The standard thermodynamic characteristics of complex formation in the Cu²⁺-glycine system are calculated. It is shown that glycine-like coordination is most likely in Cu(II) complexes with L-asparagine, L-glutamine, and L-valine.     

Thermodynamic characteristics of protolytic equilibria of L-serine in aqueous solutions

The heat effects of the reaction of aqueous solution of L-serine with aqueous solutions of HNO₃ and KOH were determined by calorimetry at temperatures of 288.15, 298.15, and 308.15 K, and ionic strength values of 0.2, 0.5, and 1.0 (background electrolyte, KNO₃). Standard thermodynamic characteristics (Δ_r H ^o, Δ_r G ^o, Δ_r S ^o, ΔC _p ^o) of the acid-base reactions in aqueous solutions of L-serine were calculated. The effect of the concentration of background electrolyte and temperature on the heats of dissociation of amino acid was considered. The combustion energy of L-serine by bomb calorimetry in the medium of oxygen was determined. The standard combustion and formation enthalpies of crystalline L-serine were calculated. The heats of dissolution of crystalline L-serine in water and solutions of potassium hydroxide at 298.15 K were measured by direct calorimetry. The standard enthalpies of formation of L-serine and products of its dissociation in aqueous solution were calculated.     

Chloro Complexes of Mercury(II) in Aqueous Perchlorate Media: Equilibrium and Electronic Absorption Spectra

The literature data on the equilibrium constants of formation of HgCl^– _{3 solv} and HgCl^2– _{4 solv} from HgCl_{2 solv} and Cl^– _solv in aqueous perchlorate–chloride solutions were generalized. The individual electronic absorption spectrum of the trichloro complex of mercury(II) was obtained for the first time, and the effect of the ionic strength on the spectra of di-, tri-, and tetrachloro complexes of mercury(II) was considered. The previously developed procedures for the resolution of absorption spectra into individual bands were found to be suitable for interpretation of spectral changes experimentally observed for solutions as the result of stepwise complexation. The parameters of the absorption bands in the spectra of chloro complexes of mercury(II) were determined.     

Interaction of Gadolinium(III) with Nitrilotrimethylenephosphonic Acid

Interaction of gadolinium(III) with nitrilotrimethylenephosphonic acid is studied by potentiometry in wide range of concentration ratios and pH at 298.15 K and ionic strength of 0.1 (KNO₃). Logarithmic constants of protonation (logK _pr) are 7.88 ± 0.08 and 4.93 ± 0.05 for GdL^3– and GdHL^2–, respectively.     

Binary Diffusion Coefficients for Aqueous Solutions of Lactic Acid

Taylor dispersion equipment installed at the University of Coimbra for the measurement of diffusion in liquids has been tested to ensure adequate accuracy and precision by measuring mutual diffusion coefficients for binary aqueous solutions of sucrose, glycine, lithium chloride, potassium chloride, and hydrochloric acid at 298.15 K. In addition, binary mutual diffusion coefficients for aqueous solutions of lactic acid (not previously reported in the literature) have been measured at 298.15 and 303.15 K and concentrations up to 0.20 mol-dm⁻³.     

Thermodynamics of Ni(II) Complexation with L-Asparagine in Aqueous Solution

Complexation of the Ni²⁺ ion with L-asparagine (HAsn^±) is studied by potentiometric titration at 298.15 K and at the 0.3, 0.5 and 1.0 ionic strength of the solution (KNO₃). The formation of the NiAsn⁺ and NiAsn₂ complexes was established and their stability constants were determined. The thermodynamic stability constants of the mono- and bis(L-asparagine)nickel(II) complexes were obtained by extrapolation to zero ionic strength. The direct calorimetry method was used to measure the heat effect of the L-asparagine reaction with the Ni(II) nitrate solution in different pH intervals at 298.15 K and at the 0.5, 1.0, and 1.5 ionic strength (KNO₃). The standard enthalpies of the NiAsn⁺ and NiAsn₂ formation were found using extrapolation and the equation with one individual parameter. The enthalpies of the formation of the Ni(II) complexes with L-asparagine in aqueous solution were calculated in the standard hypothetically undissociated state.     

Thermodynamics of L-valine complex formation with Cu<Superscript>2+</Superscript> ions in an aqueous solution

Heat effects of mixing of aqueous solutions of Cu(NO₃)₂ and L-valine were measured by the calorimetric method at 298.15 K and a ionic strength of 0.5–1.5 (KNO₃). The standard heat effects of formation of the Cu(II) complexes with L-valine in an aqueous solution were obtained by the extrapolation to the zero ionic strength using the equation with one individual parameter. The standard thermodynamic characteristics of complex formation in the Cu²⁺-L-valine system were calculated.     

Effect of background electrolyte concentration on the heat effects in the processes of formation of L-asparagine complexes with Cu<Superscript>2+</Superscript> ions in aqueous solution

A direct calorimetric method was used to measure the heat effects in the reactions of formation of Cu(II) complexes with L-asparagine in aqueous solutions at 298.15 K and ionic strength 0.5, 1.0, 1.5 (KNO₃). The standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, Δ_r S ⁰) of the processes of complex formation in the system under study were calculated.     

The oxidation of Cu(I) in electrolyte solutions

The rates of oxidation of Cu(I) in air saturated solutions was measured as a function of pH, temperature (5–45°C), and ionic strength (0.5 to 6m) in NaCl and NaCl–NaClO₄ solutions. In pure NaCl solutions, the effect of pH is independent of ionic strength and temperature. The overall rate constant is given by logk=12.32+0.12(pH)–2064/T–3.69I^1/2+ 0.73I The energy of activitation was 39±2 kJ-mol^–1 and is independent of ionic strength. At a constant ionic strength (I=1, 3 and 6m) in NaCl–NaClO₄ mixtures the Cl^– dependence of the rates is attributed to the oxidation of the various forms of Cu(I) in the solution. The rate constants for the oxidation of the various species are found to be functions of ionic strength. At a constant ionic strength (I=1) in NaCl–NaClO₄ solutions, the effect of temperature is independent of the chloride concentration. The effect of Mg²⁺ and HCO ₃ ^– on the oxidation rate was determined as a function of chloride concentration (1 to 6m) at 25°C and pH=8. The addition of Mg²⁺ causes the rate to decrease and the addition of HCO ₃ ^– causes the rate to increase. The possible causes of these effects are discussed. Empirical equations for the rate of oxidation of Cu(I) in Na-Mg-Cl-HCO₃ solutions as a function of composition are used to make reliable estimates of the oxidation in seawater and Red Sea waters.     

The thermodynamic characteristics of complex formation between calcium ions and L-leucine in aqueous solution

Complex formation of L-leucine with calcium ions in aqueous solution was studied by potentiometric titration at 298.15 K and ionic strength values I = 0.5, 1.0, and 1.5 (KNO₃). The formation of the CaL⁺ and CaHL²⁺ complex particles was established and their stability constants were determined. The enthalpies of protolytic equilibria of leucine and formation of calcium ion complexes with leucine were determined calorimetrically at 298.15 K and I = 0.5 (KNO₃). The thermodynamic characteristics of complex formation between calcium ions and L-leucine were calculated.     

Thermochemistry of complex formation of Ni<Superscript>2+</Superscript> with glycyl-L-asparagine in aqueous solutions

The heats of formation of complexes in the glycyl-L-asparagine—Ni²⁺ system were determined by calorimetry in an aqueous solution at ionic strengths of 0.5, 1.0, and 1.5 (KNO₃) and a temperature of 298.15 K. The thermodynamic characteristics of the formation of nickel complexes with dipeptide were determined. The influence of the ligand structure on the complexation thermodynamics in solutions was discussed.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 2, 2005, pp. 143–148.Original Russian Text Copyright © 2005 by Zelenin, Kochergina.     

Enthalpies of Dissolution of Crystalline Naproxen Sodium in Water and Potassium Hydroxide Aqueous Solutions at 298 K

The enthalpies of dissolution of crystalline naproxen sodium in water and aqueous solutions of KOH at 298.15 K are measured by direct calorimetric means in a wide range of concentrations. The acid–base properties of naproxen sodium at ionic strength I ~ 0 and I = 0.1 (KNO₃) and a temperature of 298.15 K are studied by spectrophotometric means. The concentration and thermodynamic dissociation constants are determined. The standard enthalpies of the formation of naproxen sodium and the products of its dissociation in aqueous solution are calculated.     

Acid Catalysis in Reaction of Ozone with Chloride Ions

The kinetics of the interaction of ozone with aqueous solutions of chlorides resulting in Cl₂ evolution to the gas phase was studied. The reaction of O₃ with Cl^– is accelerated by H⁺ ions. The effects of the concentrations of H⁺ and Cl^–, the ionic strength, and temperature (ranged from 7 to 60°C) on the reaction rate were studied. A mechanism explaining the experimental kinetics was proposed. The acid catalysis is due to the formation of the HO₃Cl complex, which is in equilibrium with H⁺, O₃, and Cl^–. The constants of reactions involved in the proposed mechanism were determined.     

Thermodynamics of electrolyte solutions. The system HCl + CaCl2 + H2O at 298.15°K

Activity coefficients of hydrochloric acid have been determined from electromotive-force measurements of cells containing mixtures of hydrochloric acid and calcium chloride at constant total ionic strengthsI=0.1, 0.5, 1.0, 2.0, and 3.0 mole-kg^–1 at 298.15°K. Interpretations based on Scatchard's and Pitzer's equations indicate that Pitzer's equations probably provide a more convenient guide to the thermodynamic properties of the mixed-electrolyte solutions. Activity coefficients for calcium chloride were derived from these equations.     

Thermodynamic characteristics of complex formation in the zinc(II)-glycylglycine system in aqueous solution

The heats of reaction of zinc(II) with glycylglycine at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75 (potassium nitrate as a supporting electrolyte) were determined by calorimetry. The thermochemical results were processed with inclusion of stepwise equilibria. In addition to complexation reactions, “side” protolytic processes were considered. Standard heats of complexation in the system were found by extrapolation to the zero ionic strength by an equation with one individual parameter. The influence of the supporting electrolyte concentration and temperature on the thermodynamic characteristics of the complexation reactions in the glycylglycine-zinc(II) system was considered. The standard enthalpies of formation of ZnGlyGly⁺, Zn(GlyGly)₂, and Zn(GlyGly)₃⁻ species in aqueous solution were calculated.     

Thermodynamics of Formation of Ni(II) Valinate Complexes in Aqueous Solution

Heat effects are determined for complex formation in the system L-valine–Ni²⁺ ion in an aqueous solution at the ionic strength of 0.25, 0.50, and 0.75 (with KNO₃ as a supporting electrolyte) at 298.15, 308.15, and 318.15 K using calorimetric method. Thermodynamic characteristics of formation of the Ni valinate complexes are calculated. The effect of a ligand structure on thermodynamic parameters of complexation reaction in a solution is considered.     

Acid-base and complexation properties of <Emphasis Type="Italic">gem</Emphasis>-diphosphonic and <Emphasis Type="Italic">gem</Emphasis>-diphosphinic acids in aqueous solutions and micellar media of surfactants

Acid-base and complexation properties of gem-disubstituted phosphorus acids, viz., methylenediphosphonic, 1-hydroxyethylidene-1,1-diphosphonic, P,P-diphenylmethylene-diphosphinic, and P, P-diphenyl-1-hydroxyethylidene-1, 1-diphosphinic acids, were studied in aqueous solutions and in the presence of biomimetics (micelles of ionic surfactants). The dissociation constants of the acids and stability constants of complexes with magnesium(II) and copper(II) ions were determined in aqueous solutions and microheterogeneous media containing sodium dodecyl sulfate, cetylpyridinium chloride, or cetylpyridinium nitrate (ionic strength 0.1 mol L^–1, temperature 25°C).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1919–1925, September, 2004.     

Activity coefficients in aqueous mixtures of hydrochloric acid and lanthanum chloride at 25°C

Activity coefficients of hydrochloric acid in aqueous solutions of lanthanum chloride were determined by an emf method at 25°C over an ionic strength range 0.05–3 mol-kg^–1. Harned's rule was obeyed within experimental error by the acid in all the mixtures. However, the fit with Pitzer's equations was not as good as the Harned rule fit, even though the effects of higher-order electrostatic terms were considered. Activity coefficients for the salt in the mixtures were derived using the Pitzer equations and fitted to the Harned equation, whereupon Harned's rule was found to be valid for the salt up to an ionic strength of 0.3 mol-kg^–1 only.     

The thermodynamic characteristics of formation of cobalt(II) ion complexes with D,L-threonine in aqueous solution

The heat effects of interaction of cobalt(II) ions with D,L-threonine in aqueous solution and the corresponding heats of dilution were determined by direct calorimetry at 288.15, 298.15, and 308.15 K and ionic strength values of 0.25, 0.50, and 0.75 (against the background of potassium nitrate). The standard heat effects of formation of CoThr⁺, CoThr₂, and CoThr ₃ ^? complexes were determined by extrapolation to zero ionic strength according to the equation with one individual parameter. The standard enthalpies of formation of complex particles in the hypothetical nondissociated state in aqueous solution were calculated.