Electrochemical determination of standard thermodynamic parameters characterizing resolvation of Cu2+ cations in water-acetone mixtures

Standard thermodynamic parameters characterizing the resolvation of the Cu²⁺ ions and the surface potential at the gas-phase/acetone interface, Δχ^Me ₂ ^CO, are determined on the basis of the results of measuring compensating voltages of the Volta circuits by the Kenrick method at 298.15 K and the value of the surface potential at the nonaqueous-solvent/gas phase interface, Δχ _H2O ^S , which was obtained earlier. A comparison of thermodynamic parameters characterizing the resolvation of the copper ions with similar quantities for the calcium and cadmium ions is performed. Specific features pertaining to the solvation of copper ions in a mixed water-acetone solvent are elucidated and the effect of the composition and nature of the mixed solvent on the quantities obtained is determined. A dependence of variations in the thermodynamic parameters characterizing the resolvation of cations on their charge and crystallographic radius is established. The dependence corresponds to the series K⁺, Ca²⁺, Cd²⁺, Cu²⁺.     

The thermodynamic characteristics of resolvation of calcium and cadmium ions in aqueous-ethanolic mixtures

The real and chemical thermodynamic characteristics of resolvation of calcium and cadmium ions in water-ethanol mixtures were determined by measuring the compensation voltages of Volta circuits by the Kenrick method at 295.15 K. The Harkins method was used to substantiate the assumption of a constant surface potential at the nonaqueous solvent/gas phase interface starting with a certain nonaqueous component concentration.     

Thermodynamics of copper ion resolvation in water-isopropanol mixtures by the method of volta potential differences

From results of measuring the compensating voltages of an volta circuit by the Kenrick method at 298.15 K, real and chemical thermodynamic characteristics of copper ion resolvation in water-isopropanol mixtures are determined, as well as the surface potential at the nonaqueous-solvent/gas-phase boundary.     

Thermoelectrochemical determination of standard entropy parameters for hydrogen ion in water-methanol solutions

The initial temperature coefficients are measured for the voltage of a thermogalvanic cell composed of two silver chloride electrodes in water-methanol solutions (WMS) of hydrogen chlorite at 298 K. The experimental results and earlier studies of thermoelectric properties of WMS of alkali metal halides are used to determine the entropy and partial molar entropy of the hydrogen ion moving in solution, the entropy change during its solvation, and the entropy carried by the hydrogen ion and a stoichiometric mixture of H⁺ and Cl^- ions in various WMS. The influence of composition of a mixed solvent on the entropy characteristics of the hydrogen ion is analyzed.     

The thermodynamic characteristics of formation of copper(II) ion complexes with carboxylic acids in aqueous solutions

The heat effects of complex formation between copper(II) ions and malonic, maleic, and succinic acids were measured in an isothermic-shell calorimeter at 298.15 K and several ionic strength values against the background of NaNO₃. The standard thermodynamic characteristics of complex formation in aqueous solutions were calculated.     

Nickel(II), copper(II) and zinc(II) complexes withN-phenylglycine in water-methanol solution

The complex equilibria of the Ni(II), Cu(II), and Zn(II) complexes withN-phenylglycine have been studied by computer analysis of potentiometric data. The mode of coordination has been established by¹H NMR and IR studies.

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Nickel(II), Kupfer(II) und Zink(II)-Komplexe mitN-Phenylglycin in Wasser-Methanol-Lösung

Zusammenfassung Anhand der Computer-Analyse von potentiometrischen Daten wurden die Bildungsgleichgewichte von Nickel(II), Kupfer(II) und Zinc(II)-Komplexen mitN-Phenylglycin untersucht. Zur Bestätigung des Koordinationstyps wurden¹H-NMR- und IR-Messungen vorgenommen.

     

The determination of anionic detergents with the bis (ethylenediamine)copper(II) ion

A method is described for the determination of anionic detergents. The detergent anions are extracted into chloroform as an ion-association compound with the bis(ethylenediamine)copper(II) cation. Determinations are completed by colorimetry or atomic absorption spectrometry. With a 150-ml water sample, the limit or detection is 0.03 μg ml^-1 (as LAS) for colorimetry or 0.06 μg ml^-1 for a.a.s. The method requires only one phase separation step and is highly selective. It is directly applicable to brine and sea-water samples.     

Electrochemical study of potassium and iodide ions resolvation in aqueous methanol mixtures

The results from the compensating voltage measurements of Volta circuits by the Kenrik method at 298.15 K were used to calculate the real primary media effect of potassium and iodide ions and real Gibbs energy of K⁺ and I⁻ transfer from water to aqueous methanol (MeOH) mixed solvent. The surface potential $\Delta \chi _{H_2 O}^{MeOH} $\Delta \chi _{H_2 O}^{MeOH} at non-aqueous solvent/gas interface was found. This value was used to calculate the chemical thermodynamic characteristics of the studied ions. The solvation features of the studied ions were revealed in the aqueous methanol mixed solvent.     

Potentiometric study of the protonation and binary complexation equilibria between the hydrogen ion,copper(II) ion and zinc(II) ion and the picolinate ion in dioxane-water mixtures

Protonation constants of picolinic acid and stability constants of Cu(II) and Zn(II) picolinate complexes were determined potentiometrically in 50% (v/v) dioxane-water solution at 25°C and 0.2 M KNO₃. The values obtained for the constants were: protonation constants for picolinate ion: logβ₁ = 5.36±0.01 and logβ₂ = 6.80±0.04; stability constants for copper(II) complexes: logβ_1.1 = 7.766±0.001 and logβ_1.2 = 16.826±0.007; stability constants for the Zn(II) complexes: logβ_1.1 = 6.10±0.05, logβ_1.2 = 11.47±0.03 and logβ_1.3 = 15.77±0.08. No protonated nor hydroxo-complex was detected in the metal ion-picolinate systems.     

Electrochemical reduction of copper(II) galacturonate

The complexes formed in the interaction between copper(II) anda-andβ-galacturonic acid, in the pH range 2.5–11.0, have been investigated by means of d.c. polarography and cyclic voltammetry. Witha-galacturonic acid, no complex is formed with copper up to pH 6. Between pH 6 and about 9.5, a complex is formed in solution. Above pH 9.5, the complex appears to break up releasing the ligand. In the case of β-galacturanic acid, no complex is formed until pH 3.5, and persists in solution up to a pH of about 9.5. A second complex forms above pH 6.9 and co-exists with the first complex up to pH 9.5. The complexes formed with both forms of galacturonic acid were studied and the stability constant of the coppera-galacturonate determined.     

Electrochemical synthesis of copper(II) carboxylates

A number of copper(II) carboxylates have been synthesized by anodic oxidation of copper. The reactions were found to proceed with current efficiencies of 0.95 to 1.00 eq./Faraday. Reaction products have been characterized by infrared spectral studies and analysis of copper.     

Thermochemical characteristics of transfer of copper(II) and nickel(II) nitrates from water to water-formamide mixtures

The enthalpies of mixing of aqueous solutions of copper(II) and nickel(II) nitrates with water-formamide mixtures were measured calorimetrically at 298.15 K in the entire composition range. The standard enthalpies of transfer of the electrolytes from water to water-formamide mixtures were calculated from these data. The shape of the isotherms of transfer of the electrolytes is discussed on the basis of the calculated enthalpies of transfer of individual ions and contributions to these quantities made by universal, chemical, and electrostatic interactions of ions with the solvents.     

Adsorptive stripping voltammetric determination of copper(II) ion using phenyl pyridyl ketoneoxime (PPKO)

A sensitive and selective procedure is presented for the voltammetric determination of copper(II) ion. The procedure involves an adsorptive accumulation of Cu2+-PPKO on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of reduction current of adsorbed complex at about -0.30 V (vs. SCE). The optimum conditions for the analysis of copper(II) ion include pH (5.8-7.0), 60 microgM PPKO and an accumulation potential of -0.5 V (vs. SCE). The peak current is proportional to the concentration of copper over the range 0.3-76 ng mL(-1) with a detection limit of 0.01ng mL(-1) with an accumulation time of 60 s. The speciation of different forms of complex between copper(II) ion and PPKO, using the Best (Martell program), followed pH measurement were examined. The method was applied to the determination of copper(II) ion content in real samples successfully.     

Simultaneous determination of copper(II) and cobalt(II) by ion chromatography coupled with chemiluminescent detection.

In the absence of any special luminescent reagents, a weakly chemiluminescent emission was observed during the decomposition of hydrogen peroxide, catalyzed by transition-metal ions, such as Cu(II) and Co(II), in basic aqueous solution. The chemiluminescent intensity was significantly enhanced by the addition of ethyldimethylcetylammonium bromide and uranine. The signal-to-noise ratio (S/N) was proportional to the concentrations of Cu(II) and Co(II). Based on these phenomena, a flow-injection chemiluminescent method for the simultaneous separation and determination of Cu(II) and Co(II) was developed. The detection limits of the present chemiluminescent method for Cu(II) and Co(II) were 7.5 and 0.01 ng/ml, respectively. After ion chromatographic separation of Cu(II) and Co(II) by an IonPac CS5A column with oxalic acid and lithium hydroxide monohydrate as the eluent, the present chemiluminescent system was used as a post-column detector for these two transition metal ions in natural water samples.     

Insights into ion specificity in water-methanol mixtures via the reentrant behavior of polymer

In the present work, we have for the first time systematically investigated the ion specific reentrant behavior of poly(N-isopropylacryamide) (PNIPAM) in water-methanol mixtures. Turbidity measurements demonstrate that SCN(-) and ClO(4)(-) depress the reentrant transition, whereas other anions enhance the transition. As the anion changes from chaotropic to kosmotropic, the minimum critical phase transition temperature (T(min)) decreases and the corresponding volume fraction of methanol (X(M)) shifts to a larger value. Our results demonstrate that anion specificity is due to the anionic structure making/breaking effect on water/methanol complexes. Cations are found to have a lesser but still significant effect on the reentrant transition, and as T(min) decreases the corresponding X(M) also shifts to larger values as with the anions. Our studies show that cation specificity is induced by specific interactions between cations and PNIPAM chains. Furthermore, both anion and cation specificities are amplified as X(M) is increased due to the formation of additional water/methanol complexes. Calorimetry measurements demonstrate that the ion specificity is dominated by changes in entropy.     

Thermal characteristics of ammonium nitrate, carbon, and copper(II) oxide mixtures

Ammonium nitrate (AN) has been extensively used as an oxidizer in energetic compositions, and is a promising compound as a propellant and gas generator. It is well-known that metal oxides help to address some of the disadvantages of AN, such as low stability and a low burning rate in these applications. In order to investigate the effects of copper(II) oxide (CuO) on the thermal decompostion of AN mixtures, the thermal characteristics of AN, carbon, and CuO mixtures were measured using simultaneous differential scanning calorimetry and thermogravimetry–differential thermal analysis connected with infrared spectroscopy and mass spectrometry. As a combustible material, activated carbon (AC), and carbon black (CB) were used in this study. In the TG–DTA results for AN/AC/CuO and AN/CB/CuO mixtures in an open cell, an exotherm was observed at approximately 210 and 230 °C, respectively. In addition, the IR and mass spectra of the gases produced from the AN/AC/CuO and AN/CB/CuO mixtures indicated the presence of CO₂. Notably, the effect of CuO addition on the oxidation of the AN/AC/CuO mixture was different from that on the AN/CB/CuO mixture; the oxidation of AC shifted to a lower temperature, while the oxidation of CB shifted to a higher temperature. These results suggest that the effect of CuO on the oxidation of different types of carbon depends on the chemical reactivity of the carbon, which is derived from its physical properties.     

Uncharged encapsulated iron(II) complexes: transfer chemical potentials and solvation in water-methanol and water-t-butanol mixtures

Summary Transfer chemical potentials have been determined from measured solubilities for four uncharged encapsulated iron(II) complexes containing three diimine ligating moieties and O₃BOBu-n and O₃BF capping groups, in H₂O–MeOH andt-BuOH–H₂O solvent mixtures, The trends in transfer chemical potentials are discussed in terms of the natures of the encapsulating ligands, and are compared with those for a selection of other iron(II)-diimine complexes.