NaClO4 Medium Research Articles

Complex-formation reactions of aquacobalamin revisited: effect of chloride on the rate and activation parameters

Complex-formation reactions of aquacobalamin were reinvestigated to clarify the role of high chloride concentrations (up to 1 mol dm–3). It was found that high chloride concentrations retard the reactions due to the formation of the less substitution-labile chloro complex, for which the formation constant was found to be 0.8 dm3 mol–1 at 25 °C and ionic strength 1.0 mol dm–3. The pH dependence of the complex formation with hydrazoic acid was also re-examined. Volumes of activation were determined for the reactions with HN3 and N3– in NaClO4 medium and are discussed in comparison with those measured in KCl medium. Direct kinetic evidence for the occurrence of a reverse, acid-catalysed aquation reaction was found and this step is characterised by an activation volume of +8.3 ± 1.6 cm3 mol–1. The results are all in agreement with the concept of a dissociative interchange substitution mechanism.

Potentiometric and spectrophotometric study of the solution equilibria in the nickel(II)–diethanolamine–water system in aqueous sodium perchlorate solutions at 25 °C

The acid–base and complexation equilibria of the system nickel(II)-diethanolamine–water have been studied using and automated potentiometric–spectrophotometric titration system at 25 °C and at four ionic strengths (0.5, 1.0, 2.0 and 3.0 mol dm–3) in NaClO4 medium. The stoichiometric stability constants, obtained at the different ionic strengths, were correlated by means of the modified Bromley methodology and the corresponding thermodynamic constants were: log 0β011= 8.88 ± 0.02, log 0β110= 2.67 ± 0.02 and log 0β120= 4.42 ± 0.05.

Surface Reactions in Aqueous Metal Sulfide Systems: 5. The Complexation of Sulfide Ions at the ZnS-H2O and Pbs-H2O Interfaces

The reactions between hydrous ZnS or PbS surfaces and sulfide ions have been studied. The measurements were performed as potentiometric titrations in 0.1 M NaNO3 or 0.1 M NaClO4 media at 25°C. Besides determining -log[H+] using a glass electrode, log[S2-] was measured with an Ag/Ag2S selective electrode. Synthetically prepared ZnS (predominantly wurtzite) and PbS, as well as the minerals sphalerite and galena, were studied. When adding sulfide ions to acidic or slightly neutral suspensions, bulk precipitation of metal sulfides occurred. The solubility products for the metal sulfides formed were determined and found to be log K(Me2+ + HS- ⇌ MeS(s) + H+) = 10.6 for ZnS and 15.6 for PbS (synthetic preparations). Sulfide additions to neutral and alkaline suspensions resulted in adsorption of H2S, HS-, and S2-. In the PbS-system the best fit was found with a model with the surface complexes ≡SPbSH2, ≡SPbSH-, and ≡SPbS2- without any charge dependent surface complexation constants. In the ZnS-system two models were found to fit experimental data almost equally well. One with the three surface complexes ≡SZnSH2, ≡SZnSH-, and ≡SZnS2- and no charge dependence or one with two surface complexes (≡SZnSH2 and ≡SZnS2-) with charge dependent equilibrium constants. Experimental data were evaluated using the computer program FITEQL. The results explain part of the mechanism behind depression of sulfide minerals in the flotation process.

Polarographic study of uranium(VI)-succinate complexes

The polarographic behavior of uranium(VI)-succinate complexes was studied in 0.5M NaClO4 medium at 30°C at a dropping mercury electrode. It was found that only the doubly charged succinate ion formed the complexes stable enough to be detected. The experimental evidence for this is discussed. The stability constant of uranium(V) (succinate)2 complex was evaluated.

Analysis of the solubility equilibria of yttrium carbonate in aqueous perchlorate media using the Pitzer and Brønsted–Guggenheim–Scatchard ion-interaction models

The solubility of yttrium carbonate has been studied at 25.0 °C by measuring the H+ concentration of yttrium perchlorate solutions in contact with the solid phase and saturated with CO2–N2 gas mixtures. Measurements were made in mixed Y(CIO4)3–NaClO4 media, where the yttrium concentration varied from trace levels up to 1.00 mol dm–3, and the total perchlorate concentration from 0.3 to 3.00 mol dm–3. Some measurements were also made in 0.01 mol dm–3 NaCl using trace concentrations of YIII. The Pitzer model gave an excellent description of the solubility data for the equilibrium Y2(CO3)3(s)+ 6H+⇌ 2Y3++ 3CO2(g)+ 6H2O, in the entire concentration range when using tabulated Pitzer parameters for rare-earth perchlorates as a model for Y(ClO4)3, and experimentally determined values for the additional parameters necessary to describe the mixed electrolyte effects. The equilibrium constants at trace concentrations of yttrium at each perchlorate concentration level investigated were, within the uncertainty of the experiment, the same when using both the Pitzer and Brønsted–Guggenheim–Scatchard method. The same was also the case for the extrapolated equilibrium constants at zero ionic strength, whee log *Ks0 is equal to 21.37 ± 0.26 and 21.68 ± 0.18, respectively.

Stability constants of complexes of uranium/VI/ and plutonium/VI/ with succinate ions

The stability constants of the complexes formed by U/VI/ and Pu/VI/ with succinate ions were determined in 0.5M NaClO4 medium at 30°C following the Bjerrum-Calvin pH titration technique. The stability constants obtained agreed with values reported in literature following the same technique. The values for the second complexes were reported for the first time. U/VI/ complexes were found to have stabilities higher than the corresponding Pu/VI/ complexes in accordance with the acidities of the cations.

ChemInform Abstract: Metal Chloride Equilibria. Part 2. Lead(II) Chloride Complexes.

AbstractResults of investigations of the complex formation equilibria between Pb(II) and Cl‐ ions at 25 °C in 5 m NaClO4 medium using potentiometric methods based on a cell without junction can be explained assuming the reactions shown in the scheme.

The pK * for the dissociation of TRISH+ in NaClO4 media

The stoichiometric dissociation constant, pK*, of TRISH+ has been determined from emf measurements in NaClO4 solutions to 6.0m at 25°C. The results have been used to derive Pitzer coefficients for the interaction of TRISH+ with ClO4−. The coefficients have been compared to the values in NaCl solutions. The values of pK* for TRISH+ can be used to calibrate pH electrodes in NaClO4 solutions using TRIS buffers.

Studies on the Radionuclide Coprecipitation-Solid Solution Formation. The UO2(S)-La(OH)3(S) Coprecipitation as an Analogue for The UO2(S)-Pu(OH)3(S) System

AbstractThe UO2(s)-La(OH)3(s) coprecipitation equilibria have been studied in 0.5 M NaClO4 medium, at 25°C under anoxic conditions. The data obtained in the pH range between 2 and 5, and at different initial La(III)/U(IV) ratios (10%,5%,3%,2% and 1%), is explained by applying the Doerner-Hoskins logarithmic law. The same law can also be used to describe previously collected UO2(s)-Pu(OH)3(s) coprecipitation data. A method is proposed which uses the logarithmic distribution constants and the thermodynamic quantities for the pure phases to describe the solubility of radionuclides under repository conditions.

Metal Complexes with Mixed Ligands. 25. Complex Formation in the Ag(I)--Tris(hydroxymethyl)aminomethane--OH- System in 3.0 M (Na)ClO4 Medium.

Metal Complexes with Mixed Ligands. 25. Complex Formation in the Ag(I)--Tris(hydroxymethyl)aminomethane--OH- System in 3.0 M (Na)ClO4 Medium.

Copper(II) ion hydrolysis in aqueous solution

A copper(II) ion-selective-electrode potentiometric method was used to determine the first and second hydrolysis constants of Cu2+. Special techniques prevented copper(II) hydroxide precipitation, and copper(II) carbonate and cipper(II) organic complexation during the titration of the experimental solution over the pH range 6.8–8.4. The large change in the total copper concentration during the titration due to adsorption of copper onto the vessel walls was accounted for by measuring the total copper concentration at each pH by atomic absorption spectrophotometry. The two hydrolysis constants were determined at 25°C in 0.7 and 0.05m NaClO4 media. The measured stability constants are independent of the copper concentration and yield similar zero ionic strength values. Also, the stepwise equilibrium constants decrease as the ligand number increases.

The Complex Equilibria between Be2+ Ions and 4- or 6-Hydroxysalicylic Acid in 0.5 M NaClO4 Medium.

The Complex Equilibria between Be2+ Ions and 4- or 6-Hydroxysalicylic Acid in 0.5 M NaClO4 Medium.

Potentiometric investigation of complex formation of lead(II) with glycine and dl-alanine

The complex formation of lead(II) with glycine and dl-alanine was investigated at 25°C in 3 mol dm−3 NaClO4 medium by e.m.f. titrations using glass and amalgam electrodes. The e.m.f. measurements were performed in the −log[H+] range between 2.5 and 9. Analysis of the e.m.f. data revealed that PbHL2+ is formed at −log[H+]<5 and PbL+ and PbL2 at higher −log[H+] values in both glycine and dl-alanine systems. The protonation constants of glycine and dl-alanine and the formation constants of the complexes are tabulated in Tables 1 and 2.

Protonation equilibria of marine dissolved organic matter1

Dissolved organic matter isolated by activated charcoal adsorption from river, estuarine, coastal, and open ocean waters was examined by acid‐base titration in 0.7 molal NaClO4 medium. Two types of sites were present in the pH range 2–8. One set of sites with an inflection point at pH 3.5 amounted to 11 µmol of sites per milligram of organic carbon. These sites were present in all samples and showed uniform properties among the samples from different marine environments. A second set of sites with an inflection point at pH 6.5 was present in some samples and amounted to &lt;1 µmol of sites per milligram of organic carbon. These results provide a characterization of the acid‐base equilibria of marine organic matter which is required in an assessment of possible trace metal‐organic interactions in seawater.

A Potentiometric Study on Complex Formation of Cadmium(II) and Lead(II) Ions with Ethylenediaminetetraacetic Acid

Abstract The complex formation of cadmium(II) and lead(II) ions with ethylenediaminetetraacetic acid (EDTA) has been studied potentiometrically in a 1.0 M NaClO4 medium at 25.0 °C by using glass and metal–amalgam electrodes. The results were explained in terms of the formation of the complexes of MHqL with q=3, 2, 1, and 0 for both metals. The corresponding formation constants were determined: for the Cd–EDTA system, logβ101=14.25±0.02, logβ111=17.41±0.02, logβ121=19.71±0.02 and logβ131=21.35±0.02; for the Pb–EDTA system, logβ101=16.50±0.05, logβ111=19.78±0.02, logβ121=21.35±0.02 and logβ131=22.50±0.02, where βpqr=[MpHqLr(2p+q−4r)+]/[M2+]p[H+]q[L4−]r and L denotes the unprotonated molecule of EDTA. The protonation constants of unprotonated EDTA were found to be logβ011=8.63±0.02, logβ021=14.99±0.02, logβ031=17.63±0.02, logβ041=19.87±0.02, logβ051=21.54±0.02, and logβ61=22.70±0.02.

A Potentiometric Study on Complex Formation of Cadmium(H) and Lead(II) Ions with N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic Acid

Abstract The complex formation of cadmium (II) and lead(II) ions with AT-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA) has been studied potentiometrically in a 1.0 M NaClO4 medium at 25.0 °C by using glass and metal–amalgam electrodes. The emf data obtained over the pH range 1 to 10 were explained in terms of the formation of the following species: for the Cd–HEDTA system, CdL− (logβ101=13.21±0.04), CdhL (logβ111=15.61±0.02) and CdH2L+ (logβ121=16.68±0.04); for the Pb–HEDTA system, PbL− (logβ101=14.83±0.02), PbHL (logβ111=16.97±0.02),PbH2L+ (logβ121=17.89±0.02) and PbH3L2+ (logβ131=18.67±0.02), where βpqr=[MpHqLr(2p+q−3r)+/[M2+]p[H+]q[L3−]r and L denotes the unprotonated molecule of HEDTA. Protonation constants of HEDTA were determined as logβ011=9.20±0.01, logβ021=14.72±0.01, logβ031=17.06±0.01, logβ041=18.52±0.01 and logβ051=18.65±0.05.

Equilibrium Studies of L-Ascorbate Ions. IX. Equilibria between Iron(II) Ions, Ascorbate Ions, and Protons in 3 M (Na)ClO4 Medium.

Equilibrium Studies of L-Ascorbate Ions. IX. Equilibria between Iron(II) Ions, Ascorbate Ions, and Protons in 3 M (Na)ClO4 Medium.

Equilibrium Studies of L-Ascorbate Ions. III. Equilibria between Cadmium(II) Ions, Ascorbate Ions, and Protons in 3 M (Na)ClO4 Medium.

Equilibrium Studies of L-Ascorbate Ions. III. Equilibria between Cadmium(II) Ions, Ascorbate Ions, and Protons in 3 M (Na)ClO4 Medium.

The metal complexes of peptides and related compounds. A mixed copper(I)-copper(II) complex of glycylglycylglycine.

The complex formation between copper(I) ions and glycylglycylglycine (H2A+) has been studied in 3.0 M NaClO4 medium at 25° by constant current coulometry using copper amalgam and glass electrodes. In each series of measurements the copper ions were generated into the ligand solution by electrolysis of two phases copper amalgam. The data, shown in Table 2, were treated by graphical methods and by the least squares computer program, Letagrop.It is concluded that the results obtained are consistent by assuming the equilibriaCu++ Cu2++ 2A−⇄ CuICuIIH–3A22−+ 3H+, log β11–32=–3.35 ± 0.04Cu++ A−⇄ CuIA, log β1001= 6.2 ± 0.1 where β is an equilibrium constant.It is assumed that the copper(II)‐equilibria, reported in the previous paper of this series, coexist in solution. On the basis of the equilibrium constants it may be deduced that for pH higher than 6.5 the principal copper(I) complex is CuICuIIH–3A22−. The standard oxidation–reduction potential at pH 7 for the formation of this species from its copper(II) analogue, Cu2H–4A22−, was calculated to be +340 mV.

A Cation-exchange Investigation of the Association between Tris(ethylenediamine)cobalt(III) Ions and Thiosulphate Ions in 2 M NaClO4 Medium.

A Cation-exchange Investigation of the Association between Tris(ethylenediamine)cobalt(III) Ions and Thiosulphate Ions in 2 M NaClO4 Medium.