On the charge storage mechanism at RuO<Subscript>2</Subscript>/0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> interface

Comparative study of capacitative properties of RuO₂/0.5 M H₂SO₄ and Ru/0.5 M H₂SO₄ interfaces has been performed with a view to find out the nature of electrochemical processes involved in the charge storage mechanism of ruthenium (IV) oxide. The methods of cyclic voltammetry and scanning electron microscopy (SEM) were employed for the investigation of electrochemical behavior and surface morphology of RuO₂ electrodes. It has been suggested that supercapacitor behavior of RuO₂ phase in the potential E range between 0.4 and 1.4 V vs reference hydrogen electrode (RHE) should be attributed to double-layer-type capacitance, related to non-faradaic highly reversible process of ionic pair formation and annihilation at RuO₂/electrolyte interface as described by following summary equation:

The Influence of Ionic Strength on Yttrium and Rare Earth Element Complexation by Fluoride Ions in NaClO<Subscript>4</Subscript>, NaNO<Subscript>3</Subscript> and NaCl Solutions at 25 °C

Stability constants of the form _F β ₁(M)=[MF²⁺][M³⁺]⁻¹[F⁻]⁻¹ (where [MF²⁺] represents the concentration of a yttrium or a rare earth element (YREE) complex, [M³⁺] is the free YREE ion concentration, and [F⁻] is the free fluoride ion concentration) were determined by direct potentiometry in NaNO₃ and NaCl solutions. The patterns of log_{10  F} β ₁(M) in NaNO₃ and NaCl solutions very closely resemble stability constant patterns obtained previously in NaClO₄. For a given YREE, stability constants obtained in NaClO₄ were similar to, but consistently larger than _F β ₁(M) values obtained in NaNO₃ which, in turn, were larger than formation constants obtained in NaCl. Stability constants for formation of nitrate and chloride complexes ( and _Cl β ₁(M)=[MCl²⁺][M³⁺]⁻¹[Cl⁻]⁻¹) derived from _F β ₁(M) data exhibited ionic strength dependencies generally similar to those of _F β ₁(M). However, in contrast to the somewhat complex pattern obtained for _F β ₁(M) across the fifteen member YREE series, no patterns were observed for nitrate and chloride complexation constants: neither nor _Cl β ₁(M) showed discernable variations across the suite of YREEs. Nitrate and chloride formation constants at 25 °C and zero ionic strength were estimated as log₁₀  and log_{10  Cl} β ₁^o(M)=0.71±0.05. Although these constants are identical within experimental uncertainty, the distinct ionic strength dependencies of and _Cl β ₁(M) produced larger differences in the two stability constants with increasing ionic strength whereby _Cl β ₁(M) was uniformly larger than .     

Mechanistic studies of the reaction of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) with triazines

Bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II), \textFe(\textTPTZ) ₂ ^{2 +} {\text{Fe(\text{TPTZ})}}_{ 2}^{{ 2 { + }}} reacts with 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonicacid)-1,2,4-triazine (PDTS) and 3-(4-(4-phenylsulfonicacid)-2-pyridyl)-5,6-bis(4-phenylsulfonic-acid)-1,2,4-triazine (PPDTS) to give \textFe(PDTS) ₃ ^4- {\text{Fe(PDTS)}}_{ 3}^{ 4- } and \textFe(PPDTS) ₃ ^7- {\text{Fe(PPDTS)}}_{ 3}^{ 7- } respectively. Both of these substitution reactions are fast and their kinetics were monitored by stopped-flow spectrophotometry in acetate buffers in the pH range of 3.6–5.6 at 25–45 °C. Both reactions are first order in \textFe(TPTZ) ₂ ^{2 +} {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} and triazine, and pH has negligible effect on the rate. The kinetic data suggest that these reactions occur in an associative path and a mechanism is proposed considering both protonated and unprotonated forms of PDTS and PPDTS are very similar in reactivity. The kinetic and activation parameters have been evaluated.     

Electrochemical properties of tetravalent Ti-doped spinel LiMn2O4

Ti-doped spinel LiMn₂O₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li( Mn^{3 +} Mn_{1 - x} ^{4 +} Ti_x^{4 +} )O₄ {\hbox{Li}}\left( {{\hbox{M}}{{\hbox{n}}^{3 + }}{\hbox{Mn}}_{1 - x\,}^{4 + }{\hbox{Ti}}_x^{4 + }} \right){\hbox{O}}{}_4 . The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge–discharge results show that the doped sample LiMn_1.97Ti_0.03O₄ exhibits maximum discharge capacity of 135.7 mAh g⁻¹ (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn_1.97Ti_0.03O₄ is 95.0% while the undoped sample LiMn₂O₄ shows only 84.6% retention under the same condition. Additionally, as charge–discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAh g⁻¹, which is much higher than that of the undoped sample of only 82 mAh g⁻¹. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.     

Effect of precompression on isothermal decomposition kinetics of pure and doped potassium bromate

Pure and doped samples of potassium bromate (KBrO₃) were subjected to precompression and their thermal decomposition kinetics was studied by thermogravimetry at 668 K. The samples decomposed in two stages governed by the same rate law (contracting square equation), but with different rate constants, k ₁ (for a α ≤ 0.45) and k ₂ (for α ≥ 0.45), as in the case of uncompressed samples. The rate constants k ₁ and k ₂ decreased dramatically on precompression, the decrease being higher for doped samples. Cation dopants (Ba²⁺, Al³⁺) caused more desensitization effect than the anion dopants ( \textSO₄ ^2- {\text{SO}}_{4}{}^{ 2- } , PO₄ ³⁻) of the same magnitude of charge and concentration. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.     

Thermodynamic Model for ThO<Subscript>2</Subscript>(am) Solubility in Isosaccharinate Solutions

Extensive studies on ThO₂(am) solubility were carried out as functions of a wide range of isosaccharinate concentrations (0.0002 to 0.2 mol⋅kg⁻¹) at fixed pH values of about 6 and 12, and varying pH (ranging from 4.5 to 12) at fixed aqueous isosaccharinate concentrations of 0.008 mol⋅kg⁻¹ or 0.08 mol⋅kg⁻¹, to determine the aqueous complexes of isosaccharinate with Th(IV). The samples were equilibrated over periods ranging up to 69 days, and the data showed that, in most cases, steady-state concentrations were reached in <15 days. The data were interpreted using the SIT model, and required the inclusion of mixed hydroxy-ISA complexes of Th(IV) [Th(OH)ISA²⁺, Th(OH)₃(ISA)₂^-_{2}^{-}, and Th(OH)₄(ISA)₂^2-]_{2}^{2-}] with log ₁₀ K ⁰=12.5±0.5,4.4±0.5 and −3.2±0.5 for the reactions:

Behavior of (La,Sr)CoO3- and La2NiO4-based ceramic anodes in alkaline media: compositional and microstructural factors

The behavior of dense ceramic anodes made of perovskite-type (x = 0.30–0.70; y = 0–0.05; z = 0–0.20) and K₂NiF₄-type (Me = Co, Cu; x = 0–0.20) indicates significant influence of metal hydroxide formation at the electrode surface on the oxygen evolution reaction (OER) kinetics in alkaline solutions. The overpotential of cobaltite electrodes was found to decrease with time, while cyclic voltammetry shows the appearance of redox peaks characteristic of Co(OH)₂/CoOOH. This is accompanied with increasing effective capacitance estimated from the impedance spectroscopy data, because of roughening of the ceramic surface. The steady-state polarization curves of in the OER range, including the Tafel slope, are very similar to those of model Co(OH)₂–La(OH)₃ composite films where the introduction of lanthanum hydroxide leads to decreasing electrochemical activity. La₂NiO₄-based anodes exhibit a low electrochemical performance and poor stability. The effects of oxygen nonstoichiometry of the perovskite-related phases are rather negligible at high overpotentials but become significant when the polarization decreases, a result of increasing role of oxygen intercalation processes. The maximum electrocatalytic activity to OER was observed for A-site-deficient , where the lanthanum content is relatively low and the Co⁴⁺ concentration determined by thermogravimetric analysis is highest compared to other cobaltites. Applying microporous layers made of template-synthesized nanocrystalline leads to an improved anode performance, although the effects of microstructure and thickness are modest, suggesting a narrow electrochemical reaction zone. Further enhancement of the OER kinetics can be achieved by electrodeposition of cobalt hydroxide- and nickel hydroxide-based films. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

Oxygen reduction on a Ru x S y (CO) n cluster electrocatalyst in 0.5 M H2SO4

A ruthenium-sulfur carbonyl cluster electrocatalyst, Ru _x S _y (CO) _n , was synthesized by pyrolysis of Ru₃(CO)₁₂ and elemental sulfur in a sealed ampoule at 300 °C. The pyrolyzed compound was characterized by DSC, FT-IR, XRD and SEM (EDX) techniques. The electrocatalytic activity and kinetic parameters for the molecular oxygen reduction were determined by a rotating ring-disk electrode (RRDE) in a 0.5 M H₂SO₄ solution at 25 °C. The cathodic polarization indicates two Tafel slopes: −0.124 ± 0.002 V dec⁻¹ at low and −0.254 ± 0.003 V dec⁻¹ at high overpotentials, and first-order kinetics with respect to O₂ concentration. From the analysis of Levich plots and RRDE results, the oxygen reduction on Ru _x S _y (CO) _n was determined to proceed mostly via a multielectron transfer path (4e⁻) to water formation ( >94%). Received: 4 March 1999 / Accepted: 26 May 1999     

Methyl thiirane: Kinetic gas-phase titration of sulfur atoms in SX OY systems

The reaction SO + SO →l S + SO₂(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C₃H₆ produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k₂ ? 3.5 × 10^?15 cm³/s at 298 K.     

Electrochemical behaviour of a lead electrode in phosphoric acid

 A lead electrode was studied in 6 and 12 M H₃PO₄. Oxidation of a freshly polished electrode occurred in the −0.5 to −0.3 V vs. SCE range, and led to PbHPO₄ growth on the electrode surface. The dissolution of this layer by electrochemical reduction occurred between −0.5 and −0.7 V. The influence of temperature (20 °C and 65 °C) was investigated and showed that the anodic and the cathodic peaks were increasing, and more markedly for the 12 M H₃PO₄. The ratio Q _cathodic/Q _anodic (Q=electrical charge flowing through the electrode) was equal or close to the unity at 20 °C and decreased as the temperature was increased. The influence of Cl⁻, Br⁻ and I⁻ ions was also evaluated. The addition of Cl⁻ and Br⁻ predominantly led to Pb₅(PO₄)₃Cl and Pb₅(PO₄)₃Br, respectively, while I⁻ led to a mixture of PbI₂ and PbHPO₄. Received: 18 July 1999 / Accepted: 2 November 1999     

Mechanisms for the formation of layered A<Subscript>4</Subscript>B<Subscript>3</Subscript>O<Subscript>12</Subscript> compounds from coprecipitated hydroxocarbonate and hydroxide systems

We have established and analyzed the sequences of phase transitions in synthesis of layered compounds in the A_nB_n–1O_3n family ( \textA₃^\textII\textLnB₃^\textV\textO₁₂ {\text{A}}_3^{\text{II}}{\text{LnB}}_3^{\text{V}}{{\text{O}}_{{12}}} (A^II = Ba, Sr, Ln = La, Nd, B^V = Nb, Ta) and La₄Ti₃O₁₂ with n = 4) from coprecipitated hydroxocarbonate and hydroxide systems, including steps involving the formation, solid-phase reaction, or structural rearrangement of intermediates.     

Constant current anodic stripping chronopotentiometric determination of uranium in uranium mineral ores via accumulation of K<Subscript>2</Subscript>UO<Subscript>2</Subscript>[Fe(CN)<Subscript>6</Subscript>] on the palladium plated aluminum electrode

In the present work the uranyl hexacyanoferrate (K₂UO₂[Fe(CN)₆]) is deposited on the palladized aluminum (Pd-Al) electrode from a \textUO₂^{2 +} + \textFe( \textCN )₆ ^{- 3} {\text{UO}}_{2}^{2 + } + {\text{Fe}}\left( {\text{CN}} \right)_{6}^{ - 3} solution. Then the anodic stripping chronopotentiometry (ASCP) was used to strip the K₂UO₂[Fe(CN)₆] from the Pd-Al surface. The operational conditions including: pH, K₃Fe(CN)₆ concentration, deposition potential, deposition time and stripping current were optimized. The ASCP calibration graph was linear in concentration range 10–460 μM. of \textUO₂^{2 +} {\text{UO}}_{2}^{2 + } and the detection limit was 8.5 μM. The interference of some concomitant ions during the deposition process of K₂UO₂[Fe(CN)₆] was studied. The proposed method was successfully applied for analysis of some uranium mineral ores.     

Electrocatalytic oxidation of nitrite at a terpyridine manganese(II) complex modified carbon past electrode

A carbon past electrode modified with [Mn(H₂O)(N₃)(NO₃)(pyterpy)], ( \textpyterpy = 4￠- ( 4 - \textpyridyl ) - 2,2￠:\text6￠,\text2￠￠- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and nitrite can be determined in the ranges of 5.00 × 10⁻⁶ to 1.55 × 10⁻² mol L⁻¹, with a detection limit of 8 × 10⁻⁷ mol L⁻¹. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10⁻², 0.56× 10⁻⁶, and 7.99 × 10⁻⁶ cm² s⁻¹, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed. This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior, anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Effect of the cathode structure on the electrochemical performance of anode-supported solid oxide fuel cells

The study elementarily investigated the effect of the cathode structure on the electrochemical performance of anode-supported solid oxide fuel cells. Four single cells were fabricated with different cathode structures, and the total cathode thickness was 15, 55, 85, and 85 μm for cell-A, cell-B, cell-C, and cell-D, respectively. The cell-A, cell-B, and cell-D included only one cathode layer, which was fabricated by ( \textLa_0.74 \textBi_0.10 \textSr_0.16 )\textMnO_{3 - d} \left( {{\text{La}}_{0.74} {\text{Bi}}_{0.10} {\text{Sr}}_{0.16} } \right){\text{MnO}}_{{3 - \delta }} (LBSM) electrode material. The cathode of the cell-C was composed of a ( \textLa_0.74 \textBi_0.10 \textSr_0.16 )\textMnO_{3 - d} - ( \textBi_0.7 \textEr_0.3 \textO_1.5 ) \left( {{\text{La}}_{0.74} {\text{Bi}}_{0.10} {\text{Sr}}_{0.16} } \right){\text{MnO}}_{{3 - \delta }} - \left( {{\text{Bi}}_{0.7} {\text{Er}}_{0.3} {\text{O}}_{1.5} } \right) (LBSM–ESB) cathode functional layer and a LBSM cathode layer. Different cathode structures leaded to dissimilar polarization character for the four cells. At 750°C, the total polarization resistance (R _p) of the cell-A was 1.11, 0.41 and 0.53 Ω cm² at the current of 0, 400, and 800 mA, respectively, and that of the cell-B was 1.10, 0.39, and 0.23 Ω cm² at the current of 0, 400, and 800 mA, respectively. For cell-C and cell-D, their polarization character was similar to that of the cell-B and R _p also decreased with the increase of the current. The maximum power density was 0.81, 1.01, 0.79, and 0.43 W cm⁻² at 750°C for cell-D, cell-C, cell-B, and cell-A, respectively. The results demonstrated that cathode structures evidently influenced the electrochemical performance of anode-supported solid oxide fuel cells.     

Thermodynamic properties of the ternary oxides in the Eu–Ru–O system by using solid-state electrochemical cells

The Gibbs free energies of formation of Eu₃RuO₇(s) and Eu₂Ru₂O₇(s) have been determined using solid-state electrochemical technique employing oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following solid-state electrochemical cells have been measured:

Unique (3,12)-Connected Inorganic Lanthanide Cluster Polymer Based on Octahedral Hexanuclear Europium Hydroxide Clusters and Sulfate Anions: Synthesis,Structure, and Luminescence

Abstract  

A (3,12)-connected 3D inorganic luminescent lanthanide hydroxide cluster polymer [Eu₆(μ₆-O) (μ₃-OH)₈(H₂O)₆(SO₄)₄] _n (1) has been hydrothermally synthesized and characterized. The structure can be considered to be constructed by linking 12-connected octahedral hexanuclear lanthanide oxido/hydroxide clusters with 3-connected inorganic SO₄ ²⁻ anions. Presently, it is the first 3D inorganic lanthanide cluster polymer based on octahedral hexanuclear lanthanide cluster with the highest connected binodal network topology. 1 displays red luminescent emission and exhibits the characteristic transitions of the Eu³⁺ ion with a decay lifetime of 196.25 μs in the solid state at room temperature.     

Determination of thermodynamic properties of YRhO3(s) by solid-state electrochemical cell and differential scanning calorimeter

The standard molar Gibbs free energy of formation of YRhO₃(s) has been determined using a solid-state electrochemical cell wherein calcia-stabilized zirconia was used as an electrolyte. The cell can be represented by: ( - )\textPt - Rh/{ \textY₂\textO_\text3( \texts ) + \textYRh\textO₃( \texts ) + \textRh( \texts ) }//\textCSZ//\textO₂( p( \textO₂ ) = 21.21  \textkPa )/\textPt - Rh( + ) \left( - \right){\text{Pt - Rh/}}\left\{ {{{\text{Y}}_2}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right) + {\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right) + {\text{Rh}}\left( {\text{s}} \right)} \right\}//{\text{CSZ//}}{{\text{O}}_2}\left( {p\left( {{{\text{O}}_2}} \right) = 21.21\;{\text{kPa}}} \right)/{\text{Pt - Rh}}\left( + \right) . The electromotive force was measured in the temperature range from 920.0 to 1,197.3 K. The standard molar Gibbs energy of the formation of YRhO₃(s) from elements in their standard state using this electrochemical cell has been calculated and can be represented by: D_\textfG^\texto{ \textYRh\textO₃( \texts ) }/\textkJ  \textmo\textl ^{- 1}( ±1.61 ) = - 1,147.4 + 0.2815  T  ( \textK ) {\Delta_{\text{f}}}{G^{\text{o}}}\left\{ {{\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right)} \right\}/{\text{kJ}}\;{\text{mo}}{{\text{l}}^{ - 1}}\left( {\pm 1.61} \right) = - 1,147.4 + 0.2815\;T\;\left( {\text{K}} \right) . Standard molar heat capacity C^o_p,m C^{o}_{{p,m}} (T) of YRhO₃(s) was measured using a heat flux-type differential scanning calorimeter in two different temperature ranges from 127 to 299 K and 305 to 646 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: $ {*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ $ \begin{array}{*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ \end{array} The heat capacity of YRhO₃(s) was used along with the data obtained from the electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.     

PuPO<Subscript>4</Subscript>(cr,hyd.) Solubility Product and Pu<Superscript>3+</Superscript> Complexes with Phosphate and Ethylenediaminetetraacetic Acid

To determine the solubility product of PuPO₄(cr, hyd.) and the complexation constants of Pu(III) with phosphate and EDTA, the solubility of PuPO₄(cr, hyd.) was investigated as a function of: (1) time and pH (varied from 1.0 to 12.0), and at a fixed 0.00032 mol⋅L⁻¹ phosphate concentration; (2) NaH₂PO₄ concentrations varying from 0.0001 mol⋅L⁻¹ to 1.0 mol⋅L⁻¹ and at a fixed pH of 2.5; (3) time and pH (varied from 1.3 to 13.0) at fixed concentrations of 0.00032 mol⋅L⁻¹ phosphate and 0.0004 mol⋅L⁻¹ or 0.002 mol⋅L⁻¹ Na₂H₂EDTA; and (4) Na₂H₂EDTA concentrations varying from 0.00005 mol⋅L⁻¹ to 0.0256 mol⋅L⁻¹ at a fixed 0.00032 mol⋅L⁻¹ phosphate concentration and at pH values of approximately 3.5, 10.6, and 12.6. A combination of solvent extraction and spectrophotometric techniques confirmed that the use of hydroquinone and Na₂S₂O₄ helped maintain the Pu as Pu(III). The solubility data were interpreted using the Pitzer and SIT models, and both provided similar values for the solubility product of PuPO₄(cr, hyd.) and for the formation constant of PuEDTA⁻. The log ₁₀ of the solubility product of PuPO₄(cr, hyd.) [PuPO₄(cr, hyd.) \rightleftarrows\rightleftarrows Pu³⁺+PO₄^3-\mathrm{Pu}^{3+}+\mathrm{PO}_{4}^{3-}] was determined to be −(24.42±0.38). Pitzer modeling showed that phosphate interactions with Pu³⁺ were extremely weak and did not require any phosphate complexes [e.g., PuPO₄(aq), PuH₂PO₄²⁺\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+}, Pu(H₂PO₄)₂⁺\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{2}^{+}, Pu(H₂PO₄)₃(aq), and Pu(H₂PO₄)₄^-\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{4}^{-}] as proposed in existing literature, to explain the experimental solubility data. SIT modeling, however, required the inclusion of PuH₂PO₄²⁺\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+} to explain the data in high NaH₂PO₄ concentrations; this illustrates the differences one can expect when using these two different chemical models to interpret the data. Of the Pu(III)-EDTA species, only PuEDTA⁻ was needed to interpret the experimental data over a large range of pH values (1.3–12.9) and EDTA concentrations (0.00005–0.256 mol⋅L⁻¹). Calculations based on density functional theory support the existence of PuEDTA⁻ (with prospective stoichiometry as Pu(OH₂)₃EDTA⁻) as the chemically and structurally stable species. The log ₁₀ value of the complexation constant for the formation of PuEDTA⁻ [ Pu³⁺+EDTA^4-\rightleftarrows PuEDTA^-\mathrm{Pu}^{3+}+\mathrm{EDTA}^{4-}\rightleftarrows \mathrm{PuEDTA}^{-}] determined in this study is −20.15±0.59. The data also showed that PuHEDTA(aq), Pu(EDTA)₄^5-\mathrm{Pu(EDTA)}_{4}^{5-}, Pu(EDTA)(HEDTA)⁴⁻, Pu(EDTA)(H₂EDTA)³⁻, and Pu(EDTA)(H₃EDTA)²⁻, although reported in the literature, have no region of dominance in the experimental range of variables investigated in this study.     

The volume and compressibility change for the formation of the LaSO 4 + ion pair at 25°C

The apparent molal volumes (φ_v) and adiabatic compressibilities [φ_K(S)] of La₂(SO₄)₃ solutions have been determined from density and sound speed data at 25°C. The large positive deviations of φ_v and φ_K(S) of La₂(SO₄)₃ from the limiting law have been attributed to the formation of the ion pair LaSO ₄ ⁺ . The observed values of φ_v and φ_K(S) have been used to estimate the change in the apparent molal volume and adiabatic compressibility for the formation of LaSO ₄ ⁺ from $$\Delta \phi (LaSO_4^ + ) = [\phi (obs.) - \phi (2La^{3 + } ,3SO_4^{2 - } )]/\alpha$$ where ?(2La³⁺, 3SO ₄ ^2? ) is the apparent molal volume or adiabatic compressibility of the free ions, and α is the degree of association. The value of \(\Delta \phi _v^o (LaSO_4^ + ) = \Delta \bar V^o (LaSO_4^ + ) = 22.8 \pm 1cm^3 - mole^{ - 1}\) and \(\Delta \phi _{K(S)}^o (LaSO_4^ + ) = \Delta \bar K_S^o (LaSO_4^ + ) = 85 \pm 20 \times 10^{ - 4} cm^3 - mole^{ - 1} - bar^{ - 1}\) at infinite dilution are in reasonable agreement with the values determined from the high-pressure conductance data of Fisher and Davis. The number of hydrated water molecules (ca. 11) associated with the formation of LaSO ₄ ⁺ determined from the volume and compressibility data are in good agreement.     

The Examination of the Activity Coefficients of Cu(II) Complexes with OH<Superscript>−</Superscript> and Cl<Superscript>−</Superscript> in NaClO<Subscript>4</Subscript> Using Pitzer Equations: Application to Other Divalent Cations

The stability constants for the hydrolysis of Cu(II) and formation of chloride complexes in NaClO₄ solution, at 25 °C, have been examined using the Pitzer equations. The calculated activity coefficients of CuOH⁺, Cu(OH)₂, Cu₂(OH)³⁺, Cu₂(OH)₂²⁺, CuCl⁺ and CuCl₂ have been used to determine the Pitzer parameter (β _i ⁽⁰⁾, β _i ⁽¹⁾, and C _i ) for these complexes. These parameters yield values for the hydrolysis constants (log ₁₀ β ₁^*, log ₁₀ β ₂^*, log ₁₀ β _2,1^* and log ₁₀ β _2,2^*) and the formation of the chloride complexes (log ₁₀ β _CuCl^* and that agree with the experimental measurements, respectively to ±0.01,±0.02,±0.03,±0.06,±0.03 and ±0.07. The stability constants for the hydrolysis and chloride complexes of Cu(II) were found to be related to those of other divalent metals over a wide range of ionic strength. This has allowed us to use the calculated Pitzer parameters for copper complexes to model the stability constants and activity coefficients of hydroxide and chloride complexes of other divalent metals. The applicability of the Pitzer Cu(II) model to the ionic strength dependence of hydrolysis of zinc and cadmium is presented. The resulting thermodynamic hydroxide and chloride constants for zinc are and . For cadmium the thermodynamic hydrolysis constants are and . The Cu(II) model allows one to determine the stability of other divalent metal complexes over a wide range of concentration when little experimental data are available. More reliable stepwise stability constants for divalent metals are needed to test the linearity found for the chloro complexes.