Effect of cadmium and lead adatoms on the reduction kinetics of peroxodisulfate anions at platinized platinum in acid solutions

The reduction of peroxodisulfate anions on a rotating Pt/Pt disk electrode in solutions of sulfuric and perchloric acids with or without cadmium and lead salts is studied. At E _r > 0.2V (RHE) the reduction rate in HClO₄ exceeds that in H₂SO₄, but at E _r < 0.2V, the process in HClO₄ is strongly inhibited upon approaching E _r = 0. Lead adatoms catalyze the process, while cadmium adatoms inhibit it in H₂SO₄ and accelerate it at E _r < 0.2V in HClO₄. The results are interpreted by taking account of the specific adsorption of sulfuric-acid anions and their co-adsorption with cadmium cations, as well as the adsorption of peroxodisulfate anions on the Pt surface modified by lead and cadmium ions in perchlorate solutions.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 137–141.Original Russian Text Copyright © 2005 by Nikiforova, Petrii.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Kinetic study of the aquation of K2 TcBr6 in perchlorate solutions

The aquation of TcBr ₆ ^2– in perchlorate solutions at various hydrogen ion concentrations and ionic strengths has been investigated. Although the same products form in all cases the proportions of the cationic and neutral products depend on the [H⁺] and the ionic strength. Differences in LiClO₄/HClO₄ and NaClO₄/HClO₄ can be attributed to differences in the activities, although at constant ionic strength. A rate constant of 1.75·10^–5 s^–1 was found for the aquation at =1, together with an activation energy of 101.6±12.5 kJ/mol.     

Ultrasonic vibration potentials,apparent molal volumes,and apparent molal heat capacities of 1:1 electrolytes in acetonitrile

The ultrasonic vibration potentials and apparent molal volumes for many inorganic and organic electrolytes were measured in acetonitrile at 25°C and combined to obtain ionic contributions to the standard partial molal volumes V°(ion). Monatomic cations and anions of the same size essentially have the same V°(ion). Their size dependence can be interpreted through Hepler's equation. The apparent molal heat capacities were also measured in acetonitrile and used to derive standard values. Various methods of estimating C _p ⁰ (ion) were investigated and an ionic scale is proposed. It is concluded that C _p ⁰ (ion) of large organic ions are very close to the intrinsic heat capacities of the ions, and the solvation contribution to monatomic ions is positive for both cations and anions.     

Activity coefficients of aqueous perchloric acid

Mean ionic activity coefficients for aqueous perchloric acid at 25°C were obtained from the emf of a HClO₄ concentration cell (m=1×10^–3–1.5) containing a ClO ₄ ^– ion solution electrode and a glass electrode. The results of an application of the Pitzer equations are compared with those previously reported from several different measuring methods. Perchloric acid activity coefficients have been calculated for the mixture HClO₄–NaClO₄. In both cases, good agreement has been obtained between our results and those derived from the isopiestic method.Deceased November 15, 1984.     

Temperature and Concentration Dependence of the Electrical Conductance,Diffusion, and Kinetics Parameters of the Ions in Aqueous Solutions of Sulfuric Acid,Selenic Acid,and Potassium Tellurate

The temperature and concentration dependences of the electrical conductance of aqueous solutions of sulfuric acid, selenic acid, and potassium tellurate were studied. The coefficients of the corresponding empirical equations were determined, and the values of equivalent conductances of the anions were evaluated at infinite dilution at the experimental temperatures. The values of the coefficients in the Fuoss and Onsager equation were evaluated for the three electrolytes at 298 K. The values of the molecular and ionic coefficients of self-diffusion at infinite dilution were calculated in the temperature range 288–318 K. The change of the translational energy Δ E∘_tr. of water molecules in the ionic hydration sphere was determined. The number of water molecules participating in the ionic hydration sphere at 298 K and the changes of Gibbs free energy, enthalpy, and entropy of activation of ionic conductance were calculated. The results obtained were interpreted according to the Samoylov’s theory of positive and negative hydration of ions. The differences observed in the temperature dependences of the mentioned parameters were explained in terms of the different radii and hydration numbers of the ions.     

Some Structural and Thermodynamic Aspects of Solvation of Single Ions. 2. Salt Effects in Aqueous Solutions of 1–1 Electrolytes

The ionic coefficients of the pair interionic interaction in aqueous solutions of 1–1 electrolytes at 298 K were determined from the real activity coefficients of single-charged single ions using the McMillan–Mayer formalism. Analysis of the results of calculations revealed that salt effects are stronger in the case of cations. The weakening of cation hydration (increased negative hydration) and the strengthening of anion hydration (increased positive hydration) enhance the mutual salting of cations and anions. It is shown that the structural effects of hydration produce a strong effect on the interionic interaction in solutions.     

Solvation of thiocyanate complexes of tungsten(VI) by 5-(4-pyridyl) nonane from aqueous hydrochloric acid solutions

5-(4-Pyridyl)nonane has been evaluated as a solvent for trace amounts (<5·10^–5 M) of tungsten(VI) from aqueous chloride-thiocyanate solutions. Remarkable enhancements in metal extractability are observed on the addition of SCN^– to aqueous hydrochloric acid solutions. Extremal partition coefficients are obtained from 0.1 M HCl in 0.2 M KSCN. Diminutions of the metal extractability are produced by relatively high (>0.5 M) SCN^– concentrations and increased concentration of the supporting acid. Slope analysis data, under optimal parameters, indicates the most probable composition of the extractable species as WO₂(SCN)₂·2P_YN. Neutral anions do not have any significant effect on the D values. Behaviour of a number of metal ions has been checked using optimal aqueous conditions of extraction. The investigation shows that the reagent has a great potential for the preconcentration of a number of metal ions including the common toxins.     

Liquid-liquid partition of cobalt between trilaurylamine N-oxide and aqueous thiocyanate solutions

In an attempt to gain an understanding of factors affecting the extraction of cobalt by trilaurylamine oxide, the equilibria between HX+SCN^– (where X=NO ₃ ^– , Cl^–, SO ₄ ^2– ) and benzene solutions of trilaurylamine oxide have been studied. Cobalt is quantitatively extracted by the oxide from aqueous 0.01–1M KSCN in 0.01M concentration of the acids. The extraction mechanism and the possible compositions of the extracted species are discussed. The effect of several anions on the extraction of the element from optimal aqueous solutions are reported and separation factors for a number of metal ions are given. The solvent has a potential for the group preconcentration of toxic metal ions from dilute aqueous solutions.     

Coexistence of Tellurium Cations and Anions in Phosphonium-Based Ionic Liquids

Elemental tellurium readily dissolves in ionic liquids (ILs) based on tetraalkylphosphonium cations even at temperatures below 100 °C. In the case of ILs with acetate, decanoate, or dicyanamide anions, dark red to purple colored solutions form. A study combining NMR, UV-Vis and Raman spectroscopy revealed the formation of tellurium anions (Te_n)²⁻ with chain lengths up to at least n=5, which are in dynamic equilibrium with each other. Since external influences could be excluded and no evidence of an ionic liquid reaction was found, disproportionation of the tellurium is the only possible dissolution mechanism. Although the spectroscopic detection of tellurium cations in these solutions is difficult, the coexistence of tellurium cations, such as (Te₄)²⁺ and (Te₆)⁴⁺, and tellurium anions could be proven by cyclic voltammetry and electrodeposition experiments. DFT calculations indicate that electrostatic interactions with the ions of the ILs are sufficient to stabilize both types of tellurium ions in solution.     

In situ Near-Infrared Spectroelectrochemical Investigation of Redox States of Polyaniline during Growth and Doping

In situ near-infrared (NIR) spectroelectrochemical studies during growth and dedoping/redoping of polyaniline (PANI) in the range between 1200 to 3000 nm are carried out in 1 M aqueous solutions of HCl, H₂SO₄, and HClO₄ acids andp-toluene sulfonic acid (PTSA). The results show three characteristic absorption bands around 1440, 1900, and 2500 nm. The band at 2500 nm is characteristic of mobile charge carriers. The PANI prepared in HClO₄ keeps memory of the size of the doping anion (ClO₄ ^–) and can be redoped only with the same or smaller anions (Cl^– and SO₄ ^2– or HSO₄ ^–) while it cannot be redoped to any significant extent by a larger anion (PTSA^–).     

Ionic Mobility, Phase Transitions, and Superionic Conduction in Solid Solutions (100 ? x)PbF2-xZrF4 and Crystals K2ZrF6, (NH4)2ZrF6, KSnZrF7, and M(NH4)6Zr4F23 (M = Li, Na)

Methods of (¹⁹F, ¹H) NMR and impedance spectroscopy are used to investigate the internal mobility and ionic conduction in solid solutions arising in the system PbF₂-ZrF₄ and polycrystals KSnZrF₇, Li(Na)(NH₄)₆Zr₄F₂₃, and M₂ZrF₆ (M = K, NH₄). Factors responsible for the form of ionic motions and their energetics at 170–550 K are considered. It is established that the phase transitions in these compounds are connected with the crystal transition to a superionic state and that the high ionic (superionic) conductivity of beta phases is due to the diffusion of fluoride ions, ammonium cations, and possibly alkali metal cations. The obtained data testify to a substantial role of chainlike aggregation of anionic groupings and a variableness of structural mechanisms of formation of such chains in fluorozirconates for the development of translational diffusion in these compounds.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 573–582.Original Russian Text Copyright © 2005 by Kavun, Uvarov, Slobodyuk, Goncharuk, Kotenkov, Tkachenko, Gerasimenko, Sergienko.     

Determination of stability constants of U(VI), Np(VI) and Pu(VI) with chloride ions by extraction chromatography

The complex formation of U(VI), Np(VI) and Pu(VI) with chloride ions was studied in HClO₄−HCl solutions at ionic strength of 2.0 and [H⁺]=2.0M by the method of extraction chromatography using dilute HDEHP as the stationary phase.     

Hydrolysis of Protactinium(V). II. Equilibrium Constants at 40 and 60°C: A Solvent Extraction Study with TTA in the Aqueous System Pa(V)/H2O/H+/Na+/ClO− 4

The hydrolysis of protactinium (V) was studied at tracer scale (ca. 10^–12 M) with the solvent extraction method involving the aqueous system: Pa(V)/H₂O/H⁺/Na⁺/ClO^– ₄ at 40 and 60°C for three values of ionic strength. Extraction experiments were conducted using the chelating agent thenoyltrifluoroacetone (TTA) in toluene. Hydrolysis constants are reported for each ionic strength investigated. An SIT modeling is presented and extrapolated constants to zero ionic strength are derived, as well as interaction coefficients involving Pa(V) and perchlorate ions.     

Influence of Anions on Electrochemical Properties of Polypyrrole-Modified Electrodes

The influence of anions ClO₄ ^–, NO₃ ^–, Cl^–, SO₄ ^2–, and DDS^– (dodecyl sulfate) on the cyclic voltammetric response of polypyrrole-modified electrodes is studied. The change in the film composition is examined by electron probe microanalysis. It is established that essential changes in the shape of voltammograms take place during cycling if the anions are not sufficiently freely mobile in the polymer film and insertion of cations from the solution is necessary to guarantee electroneutrality of the system. Some differences between the mobility of Cl^– ions and ClO₄ ^– or NO₃ ^– ions are in good agreement with the results of semi-empirical quantum chemical calculations showing that the interaction of Cl^– and Br^– ions with pyrrole oligomers is stronger than that of NO₃ ^– or ClO₄ ^– ions. Nevertheless, it is established that the peak current determined from voltammograms increases linearly with the increase of the scan rate with very high correlation coefficient. It means that it is possible to describe the behavior of ClO₄ ^–, NO₃ ^– and Cl^– ions in the framework of the model of free ions. The redox behavior of the PPy films doped with anions of low mobility such as SO₄ ^2– and DDS^– depends essentially on the nature of cations in the test solution. It is found that the mobility of cations increases in the row Li⁺ < Na⁺ < K⁺ < Cs⁺. The mobility of DDS^– ions in the PPy in ethanolic solution is significantly higher and their electrochemical properties are quite similar to PPy|Cl or NO₃ ^– film in aqueous solution.     

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.     

Heat capacities of aqueous perchloric acid and sodium perchlorate at 298°K: ΔC p o of ionization of water

We have used a Picker flow calorimeter for measurements leading to apparent molal heat capacities of dilute aqueous solutions of HClO₄ and NaClO₄ at 298°K. Results have been used to derive _c ^° =–27.1J-°K ^–1-mole ^–1 for HClO₄ (aq.), _c ^° =15.2J-°K ^–1-mole ^–1 for NaClO₄ (aq.), and C _p=–213.₈J-°K^–1-mole^–1 for ionization of water.     

Electronic Structure of the Isolated [CuX6]4– Anions in (AguH2)2[CuX6] (X = Cl,Br; Agu is Aminoguanidine) and CuF2

The electronic structures of the isolated [CuX₆]^4– complex anions (X = F, Cl, Br) were studied by the density functional theory and Hartree–Fock methods. The donor–acceptor interactions in similar anions were shown to be accompanied by the formation of square-planar [CuX₄]^2– complexes, and additional axial ligands were coordinated only through ionic bonds.     

Isopiestic measurements on aqueous mixtures of sodium chloride and strontium chloride

Isopiestic measurements have been made on NaCl–SrCl₂ mixtures at 25°C over the ionic strength range 0.6–6 mole-kg^–1. The results are interpreted in terms of current mixed-electrolyte treatments. The mixing behavior in this system is comparatively simple, but the Pitzer treatment is still clearly superior to the other treatments.     

Determination of some elements in Ageratum conyziodes,a tropical medicinal plant, using instrumental neutron activation analysis

1-Hydroxy-2-ethylthioethane, CH₃CH₂SCH₂CH₂OH, (HETE) gave relatively stable intermediate sulfonium cations, with water solutions of mineral acids, which could be extracted into chloroform as ionic associates in the presence of bis(1,2-dicarbollyl)cobaltate anions labeled with ⁶⁰Co independently of the nature of the inorganic anion but depending on the activity of hydrogen ions. The water phase contained buffers and acids HCl, H₂SO₄, H₃PO₄ and HClO₄. The kinetics and mechanism of the reactions have been studied. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ion pairing and the reaction of group IIA metal hexacyanoferrates(II) and peroxodisulfates

The rate of the reaction 2Fe(CN) ₆ ^4– +S ₂ O ₈ ^2– 2Fe(CN) ₆ ^3– + 2SO ₄ ^2– in the presence of Group IIA cations in aqueous solution has been studied over the range of ionic strength from 0.006 to 0.20 M at three temperatures between 5 and 35°C. The results are interpreted by means of the Brønsted⁽²⁾ equation, and it is concluded that the actual reacting species are MFe(CN) ₆ ^2– , and S₂O ₈ ^2– , where M is a Goup IIA metal. The contribution from the nonion-paired species seems to be negligibly small. Rate constants and activation parameters are reported for the observed reaction pathway, and these are compared with those for the same reaction carried out in the presence of alkali metal cations. The results are considered in terms of a mechanism involving cation bridging, and qualitatively this model is consistent with the trends in the results.