Acidobasic properties of molten potassium tetrahalogenogallates (X=Cl,I)

Molten potassium tetrachlorogallate and potassium tetraiodogallate were studied in terms of halogenoacidity, based on X^? ion-exchange. Titration of KX solution with GaX₃ were achieved and characterized by the shift of cathodic voltammetric curves. Autodissociation constants K_i,X/mol² kg^?1 were determined: ?log K_i,Cl=4.25±0.05 and ?log K_i,I=2.6±0.05, as well as the solubility values of KX: 0.41±0.02 and 0.80±0.02 mol kg^?1 for KCl and KI respectively.     

Densities of Melts of the System KF?K2MoO4?B2O3

The density of melts of the system KF? K₂MoO₄? B₂O₃ was measured. The molar volume in the binary system KF? K₂MoO₄ deviates only little from the ideal course, which indicates the extended thermal dissociation of the congruently melting additive compound K₃FMoO₄. In the KF? B₂O₃ binary system the formation of KBF₄ and K₂B₄O₇ leads to the volume expansion, like in the K₂MoO₄? B₂O₃ system, where the volume expansion may be described by the formation of the heteropolyanions [BMo₆O₂₄]^9?. The significant deviation from the ideal behaviour in the ternary system KF? K₂MoO₄? B₂O₃ refers to the pronounced interaction, most probably due to the substitution of oxygen atoms in the coordination sphere of the heteropolyanion with the fluorine ones.     

The detection of potassium sulfate in excess of potassium pyrosulfate

X-Ray diffraction, infrared, and raman spectroscopic methods were investigated for the detection of K₂SO₄ in excess of K₂S₂O₇ in solid solutions.The X-ray diffraction lines of K₂SO₄ were found to be overlapped by the diffraction pattern of K₂S₂O₇ and infrared studies indicated that K₂SO₄ absorption bands corresponded to regions of strong absorption in K₂S₂O₇. The detection of sulfate could not be carried out by the X-ray diffraction and infrared methods. However, the raman method indicated that a strong and narrow K₂SO₄ band at 981 cm^?1 could unambiguously be used for the detection of sulfate in solid solutions of K₂SO₄ in K₂S₂O₇, as pyrosulfate showed no absorption around this band.     

A multi-pumping flow system with on-line photochemical conversion and improved sensitivity for phosphorus fractionation in freshwaters

A flow-based procedure with solenoid micro-pumps was developed for phosphorus fractionation (dissolved organic and inorganic phosphorus) in freshwaters. The spectrophotometric detection was based on the formation of molybdenum blue and the organic species were on-line photo-converted to orthophosphate. The analytical response was linear within 10 and 75?µg?L^?1 with a detection limit of 2.0?µg?L^?1 (99.7% confidence level). Coefficient of variation of 1.8% (50?µg?L^?1 P, n?=?20) and sampling rate of 40 determinations per hour were achieved. Per determination, 160?µg (NH₄)₆Mo₇O₂₄, 10?µg SnCl₂, 640?µg K₂S₂O₈ and 10?mg NaOH were consumed, generating 2.0?mL of waste. Slopes of analytical curves obtained for four different organic phosphorus species agreed with those obtained for orthophosphate, indicating quantitative conversion. The results for freshwater samples agreed with those obtained by the AOAC reference procedure at 95% confidence level. The organic matter did not interfere in the photo-oxidative process. The proposed procedure is a fast and environmentally friendly alternative for the phosphorus fractionation in freshwaters.     

Study and Application of Polarographic Catalytic Wave of Chlordiazepoxide in the Presence of Persulfate

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Pyrochlore and Perovskite Potassium Tantalate: Enthalpies of Formation and Phase Transformation

Alkali niobates and tantalates are currently important lead‐free functional oxides. The formation and decomposition energetics of potassium tantalum oxide compounds (K₂O?Ta₂O₅) were measured by high‐temperature oxide melt solution calorimetry. The enthalpies of formation from oxides of KTaO₃ perovskite and defect pyrochlores with K/Ta ratio of less than 1 stoichiometry—K_0.873Ta_2.226O₆, K_1.128Ta_2.175O₆, and K_1.291Ta_2.142O₆—were experimentally determined, and the values are (?203.63±2.92) kJ mol^?1 for KTaO₃ perovskite, and (?339.54±5.03) kJ mol^?1, (?369.71±4.84) kJ mol^?1, and (?364.78±4.24) kJ mol^?1, respectively, for non‐stoichiometric pyrochlores. That of stoichiometric defect K₂Ta₂O₆ pyrochlore, by extrapolation, is (?409.87±6.89) kJ mol^?1. Thus, the enthalpy of the stoichiometric pyrochlore and perovskite at K/Ta=1 stoichiometry are equal in energy within experimental error. By providing data on the thermodynamic stability of each phase, this work supplies knowledge on the phase‐formation process and phase stability within the K₂O?Ta₂O₅ system, thus assisting in the synthesis of materials with reproducible properties based on controlled processing. Additionally, the relation of stoichiometric and non‐stoichiometric pyrochlore with perovskite structure in potassium tantalum oxide system is discussed.     

Kinetics of the potassium persulfate-initiated inverse emulsion polymerization of sodium acrylate solutions

The kinetics of the K₂S₂O₈-initiated inverse emulsion polymerization of aqueous sodium acrylate solutions in kerosene with Span 80 as the emulsifier has been studied. The conversion-time curves are S-shaped. The following expressions have been obtained for the maximum rate of polymerization and the molecular weight of the polymers under the experimental conditions investigated: R_max ∞ [K₂S₂O₈]^0.78[sodium acrylate]^1.5[Span 80]^0.1, (OVERLINE)M(/OVERLINE)_u ∞ [K₂S₂O₈]^−0.37[sodium acrylate]^2.9[Span 80]^−0.2. The activation energy for the maximum rate of polymerization is 94.8 kJ mol^−1. The results suggest a monomer–droplet–nucleation mechanism for the system studied. © 1996 John Wiley & Sons, Inc.     

Kinetics and mechanism of the reaction between thiosulfate and chlorite ions at 90°C

The kinetics of the oxidation of S₂O₃^2? by ClO₂^? have been studied in aqueous alkaline solution at 90⁰C using classical titrimetric methods to follow the course of the reaction. The reaction takes place according to the stoichiometry S₂O₃^2? + 2ClO₂^? + 2OH^? = 2SO₄^2? + 2Cl^? + H₂O even in large S₂O₃^2? excess. There is some indication of a complex reaction pattern, but 70% of the ClO₂^? disappearance can be best described by the autocatalytic rate equation -d[ClO₂^?]/dt = k[S₂O₃^2?] [ClO₂^?] [H⁺] with k = (1.3 ± 0.2) ×10⁸ M^?2 sec^?1. The mechanism is explained by postulating nucleophilic attack of S₂O₃^2? on HClO₂ to form a chlorine-containing intermediate.     

Preparation and electrochemical properties of nano-sized cryptomelane particles for the formation of potentiometric potassium ion sensors

The potentiometric response of 100-nm spherical K_1.3Mn₈O₁₆ particles versus K⁺ ions has been studied in aqueous media using a polymeric technology. The stoichiometry of this material evolves in potassium nitrate solution towards K_1.08Mn₈O₁₆. A stable and reversible response has been obtained with a sensitivity of 47 mV dec^?1 in the range from 8?×?10^?5 to 1 mol·L^?1, and a rather good selectivity towards Li⁺, Na⁺, Mg²⁺ and Ca²⁺ $\left( {{\text{log K}}_{{{{\text{K}}^{\text{ + }} } \mathord{\left/ {\vphantom {{{\text{K}}^{\text{ + }} } {{\text{X}}^{n + } }}} \right. \kern-0em} {{\text{X}}^{n + } }}} \approx - {\text{3}}} \right)$ . We assume that this potentiometric response is the result of the ability of K_1.08Mn₈O₁₆ to specifically adsorb K⁺ ions.     

Kinetics and mechanism of decomposition of intermediate complex during oxidation of pectate polysaccharide by potassium permanganate in alkaline solutions

The kinetics of decomposition of an [Pect·Mn^VIO₄^2?] intermediate complex have been investigated spectrophotometrically at various temperatures of 15–30°C and a constant ionic strength of 0.1 mol dm^?3. The decomposition reaction was found to be first‐order in the intermediate concentration. The results showed that the rate of reaction was base‐catalyzed. The kinetic parameters have been evaluated and found to be ΔS^≠ = ? 190.06 ± 9.84 J mol^?1 K^?1, ΔH^≠ = 19.75 ± 0.57 kJ mol^?1, and ΔG^≠ = 76.39 ± 3.50 kJ mol^?1, respectively. A reaction mechanism consistent with the results is discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 67–72, 2003     

Oxoacidity reactions in molten LiCl+KCl eutectic (at 470°C): Potentiometric study of the equilibria of exchange of O2− between Al(III) systems and carbonate and water systems

The reactions between aluminium chloride and oxide anion were studied in molten LiCl+KCl eutectic at 470°C. For that purpose, a pO^2? indicator electrode made with a membrane in yttria-stabilized zirconia has been used and tested by means of a carbonate ion whose dissociation constant, 10^?2.15 atm, was determined. Then, the electrode has allowed us to obtain the formation constant of AlO⁺ (solvated by Cl^?) and the solubility product of Al₂O₃ (S): 10^10.7 and 10^?27.4, respectively (molality scale). The equilibrium constant of the following system: 2HCl (g)+O^2? agH₂O (g)+2Cl^? has also been determined: 10^?9.93 atm mol kg^?1. The conditional solubility of alumina in LiCl+KCl melt is discussed.     

Electrolytically generated sulfur dioxide anion radical S2O·−4, its absorption coefficient and some of its decay reactions

The electrochemical reduction of SO₂ in dimethylformamide at Pt electrodes finally leads to the red species S₃O^2?₆ via the blue complex S₂O^·?₄. The UV-VIS absorption coefficients are determined: ?(S₂O^·?₄) = (224 ± 25) × 10⁵ cm² mol^?1; ?(S₃O^2?₆) = (0.64 + 0.07) × 10⁵ cm² mol^?1. A calculation of the complexing constant of SO₂ with free SO^·?₂ radical based on potential shifts confirms this constant to be in the range of 200–700 1 mol^?1.Two potentiometric titration methods (viz: with allylbromide and tetraethylammoniumtribromide) for analysis of electrolytically generated S^III-oxo-anions in DMF are presented. Reactions of those anions with aromatic aldehydes and trials for trapping of possibly formed SO are described.     

Electrocatalytic Reduction of Peroxy Disulfate on the Palladized Aluminum Electrode Modified by Prussian Blue: Application to the Analysis of Decolorizing Powders

The mechanism of catalytic reduction of peroxydisulfate on the palladized aluminum electrode modified by Prussian blue (PB/Pd‐Al) was studied. The charge transfer‐rate limiting step as well as overall reduction reaction of S₂O₈^2? is found to be a one‐electron and two‐electron abstraction respectively. The modified electrode is exploited for the hydrodynamic amperometry of peroxydisulfate. It is found that the calibration graph is linear in the S₂O₈^2?concentration range 5×10^?6–1.5×10^?3 mol L^?1. The detection limit of the method was 2.4×10^?6 mol L^?1 S₂O₈². The method was successfully used for the determination of S₂O₈^2? in decolorizing powders     

Alginate polyelectrolyte ionotropic gels. XVIII. Oxidation of alginate polysaccharide by potassium permanganate in alkaline solutions: Kinetics of decomposition of intermediate complex

The kinetics of decomposition of [Alg · Mn ^VIO₄^2?] intermediate complex have been investigated spectrophotometrically at a constant ionic strength of 0.5 mol dm^?3. The decomposition reaction was found to be first-order in the intermediate concentration. The results showed that the rate of reaction was base-catalyzed. The kinetic parameters have been evaluated and found to be ΔS^? = ?103.88±6.18 J mol^?1 K^?1, ΔH^? = 51.61 ± 1.02 kJ mol^?1, and ΔG^? = 82.57 ± 2.86 kJ mol^?1, respectively. A reaction mechanism consistent with the results is discussed. © 1993 John Wiley & Sons, Inc.     

Interaction of zinc oxide clusters with molecules related to the sulfur vulcanization of polyolefins ("rubber")

The vulcanization of rubber by sulfur is a large‐scale industrial process that is only poorly understood, especially the role of zinc oxide, which is added as an activator. We used the highly symmetrical cluster Zn₄O₄ (T_d) as a model species to study the thermodynamics of the initial interaction of various vulcanization‐related molecules with ZnO by DFT methods, mostly at the B3LYP/6‐31+G* level. The interaction energy of Lewis bases with Zn₄O₄ increases in the following order: CO62H₄3H₆2S₂<1,4‐C₅H₈2O2S3N?CH₃COO^?. The corresponding binding energies range from ?57 to ?262 kJ mol^?1. However, Brønsted acids react with the Zn₄O₄ cluster with proton transfer from the ligand molecule to one of the oxygen atoms of Zn₄O₄, and these reactions are all strongly exothermic [binding energies [kJ mol^?1] in parentheses: H₂O (?183), MeOH (?171), H₂S (?245), MeSH (?230), C₃H₆ (?121), and CH₃COOH (?255)]. The important vulcanization accelerator mercaptobenzothiazole (C₇H₅NS₂, MBT) containing several donor sites reacts with the Zn₄O₄ cluster with proton transfer from the NH group to one of the oxygen atoms of ZnO, and in addition the exocyclic thiono sulfur atom and the nitrogen atom coordinate to one and the same zinc atom, resulting in a binding energy of ?247 kJ mol^?1. A second isomer of [(MBT)Zn₄O₄] with a strong O? H???N hydrogen bond rather than a Zn? N bond is only slightly less stable (binding energy ?243 kJ mol^?1). The NH form of free MBT is 36 kJ mol^?1 more stable than the tautomeric SH form, while the sulfurized MBT derivative benzothiazolyl hydrodisulfide C₇H₅NS₃ (BtSSH) is most stable with the connectivity >CSSH.     

Mechanistic Aspects of Ligand Substitution on the Hydroxopentaaquarhodium(III) Ion in Aqueous Solution by Sulfur‐Containing Bioactive Ligands

The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k₁ ～10^?3 s^?1 and k₂ ～10^?5 s^?1) and activation parameters (for thioglycolic acid: ΔH₁^≠ = 22.4 ± 3.0 kJ mol^?1, ΔS₁^≠ = ?220 ± 11 J K^?1 mol^?1, ΔH₂^≠ = 38.5 ± 1.3 kJ mol^?1, ΔS₂^≠ = ?204 ± 4 J K^?1 mol^?1; for 2‐thiouracil: ΔH₁^≠ = 42.2 ± 2.0 kJ mol^?1, ΔS₁^≠ = ?169 ± 6 J K^?1 mol^?1, ΔH₂^≠ = 66.1 ± 0.5 kJ mol^?1, ΔS₂^≠ = ?124 ± 2 J K^?1 mol^?1; for glutathione: ΔH₁^≠ = 47.2 ± 1.7 kJ mol^?1, ΔS₁^≠ = ?155 ± 5 J K^?1mol^?1, ΔH₂^≠ = 73.5 ± 1.1 kJ mol^?1, ΔS₂^≠ = ?105 ± 3 J K^?1 mol^?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as      

Photocatalytic decolorization of methyl orange solution with potassium peroxydisulfate

Increasing environmental pollution caused by toxic dyes due to their hazardous nature is a matter of great concern. It has been generally agreed that methyl orange (MO) can be effectively degraded in aerated K₂S₂O₈ homogeneous reaction system using near-UV irradiation. In this paper photocatalytic degradation of MO solutions with K₂S₂O₈ was investigated, with particular attention on the possible underlying mechanisms. This report has shown decolorization efficiency of MO increases with the increasing of the dosage of the catalyst. There is no optimal amount of catalyst in our case, where special attention was paid on the nature of the photocatalyst itself. The current research revealed that the decolorization reaction is a pseudo first-order reaction when the concentration of MO is below 20 mg L⁻¹ and the decolorization reaction is zero-order reaction when the concentration of MO is above 100 mg L⁻¹, but the Langmuir-Hinshewood kinetic model does not describe this. The influence of IO₄⁻, BrO₃⁻ and H₂O₂ were investigated in detailed. Several observations indicate that the mechanism is not involved in hydroxyl radical attacks in MO degradation with K₂S₂O₈ by UV irradiation. The possible underlying mechanisms are direct oxidation of the MO by S₂O₈²⁻ and hydrogen attraction by SO₄^•−.      

Interaction of calcium ion with sodium triphosphate determined by potentiometric and calorimetric techniques

The stoichiometry of the interaction of Ca²⁺ with sodium triphosphate was determined using a Ca²⁺ sensitive electrode, divalent ion sensitive electrode, a glass electrode and by titration calorimetry, A 2:1 and 1:1 complex of Ca²⁺ and P₃O^5?₁₀ is found when titrating calcium chloride with sodium triphosphate by the calcium ion sensitive electrode and tritation calorimetry. However, only by titration calorimetry is the 2:1 and 1:1 complex found when titrating sodium triphosphate with calcium chloride. Thermodynamic value (log K, ΔH and ΔS) are reported for the formation of CaP(in3)O^?3₁₀ and Ca₂P₃O^?₁₀ in aqueous solution.     

Chemical and electrochemical studies of the oxide ion-oxygen reaction in equimolar sodium nitrate+potassium nitrate

Manometric and potentiometric studies of the oxide ion+oxygen reaction in molten alkali nitrate are reported. Sufficient oxygen was found to be absorbed by alkali nitrate melts after addition of Na₂O to convert virtually all of the added O^2? ion to O₂^2? and O₂^? ions. The equilibrium constant and the temperature dependence of the reaction 2 O₂^?=O₂+O₂^2? was determined over a temperature range of 250–400°C. The value of the equilibrium constant determined by the method used was found to depend on whether Na₂O, Na₂O₂, or NaO₂ was used as the starting material. Stabilized zirconia tubes were studied for use as oxide ion probes in these melts. In oxygen-containing melts the zirconia/melt interface was shown to respond to added Na₂O or NaO₂ in a manner similar to the response of a platinum wire dipped into the melt. This response is shown to be the expected one, for the cells studied. When nickel chloride was added to oxygen-saturated melts which contined Na₂O, a reaction was found to occur which resulted in the effective loss of two oxide ions from the melt for each nickel ion which was added.