Solubility of Crystalline Calcium Isosaccharinate

The solubility of calcium isosaccharinate Ca(ISA)₂(c) was determined at 23°C as a function of pH (1–14) and calcium ion molality (0.03–0.52). The similarity of solubility from the over- and undersaturation directions for different equilibration periods indicated that equilibrium in these solutions was reached rapidly (< 7 days) and that these data can be used to develop thermodynamic equilibrium constants. The solubility data were interpreted using the Pitzer ion–interaction model. The logarithms of the thermodynamic equilibrium constants determined from these data were 1.30 for the dominant reaction at pH < 4.5 [Ca(ISA)₂(c) + 2H⁺ Ca²⁺ + 2HISA(aq)], and –2.22 for the dominant reaction at 4.5 [Ca(ISA)₂(c)+ Ca(ISA)₂(aq)]. In addition, the logarithm of the dissociation constant of HISA [HISA(aq) ISA- + H⁺] was calculated to be –4.46.     

The enthalpies of dilution of phosphate solutions at 30°C

The enthalpies of dilution of aqueous solutions of HCl, H₃PO₄, NaOH, NaH₂PO₄, Na₂HPO₄ and Na₃PO₄ in the molality range 0.1 to 1.0 mole-kg^–1 have been determined at 30°C. The relative apparent molal enthalpies _L of HCl, NaOH, NaH₂PO₄ and Na₂HPO₄ have been determined with the aid of an extended form of the Debye-Hückel limiting law. The relative apparent molal enthalpies for Na₃PO₄ solutions have been corrected for hydrolysis. A value of H _H ^o =9525±150 cal-mole^–1 was determined for the heat of hydrolysis of PO ₄ ^–3 . This value gives H ₃ ^o =3815±150 cal-mole^–1 for the ionization of H₂PO ₄ ^– , which is in good agreement with the value of H ₃ ^o =3500±500 cal-mole^–1 determined directly by Pitzer at 25°C. The relative apparent molal enthalpies for H₃PO₄ solutions have been corrected for ionization. A value of H ₁ ^o =–1900±150 cal-mole^–1 was obtained for the heat of ionization of H₃PO₄ to H⁺+H₂PO ₄ ^– . This value is in good agreement with the value of H ₁ ^o =–2031 cal-mole^–1 at 30°C determined by Harned and Owen from the temperature coefficient of the equilibrium constant and H ₁ ^o =–1950±80 cal-mole^–1 at 25°C determined from calorimetry by Pitzer.     

Investigations of crystalline structure of gamma-zirconium phosphate

The -crystalline form zirconium phosphate was investigated. For its lattice parameters was found:a=0.538 nm,b=0.664 nm,c=2.459 nm, =94.2° and basal spacing (d)=1.22 nm. It was determined by IR spectrophotometric method that the phosphate is present in groups of H₂PO ₄ ^– and PO ₄ ^3– of equal quantity. Two moles of crystalline water per formula unit were found where the moles are bound differently. The compound can be characterized by the following chemical formula: Zr(HPO₄)(PO₄)·2H₂O.     

Copper(II) and nickel(II) complexes of N,N′-bis(2-cyanoethyl)-5, 7-dioxo-1,4,8,11-tetra-azacyclotetradecane

Summary Reaction of 5,7-dioxo-1,4,8,11-tetra-azacyclotetradecane with acrylonitrile gives the dicyanoethylated ligand (L). The Cu^II complex [CuLH_-2]·2H₂O has been isolated from basic solution where the macrocycle is deprotonated and acts as a dinegative quadridentate ligand. The ligand L is protonated in acidic solution and the ionisation equilibria can be summarised as LH _inf2 ^sup2+ LH⁺ +H⁺; K₁ LH⁺ L + H⁺; K₂ where pK₁ = 3.05 and pK₂ = 5.94 at 25 °C and I = 0.1 mol dm^-3 (NaNO₃). Complexation with Cu^II can be represented by the equilibria at 25 °C. Cu²⁺ + L [CuLH_-1]⁺ + H⁺; log_{11 – 1} = -3.43 Cu²⁺ + L [CuLH_-2] + 2H²⁺; log_{11 – 2} = -9.18 For Ni^II only the single equilibrium is of importance. Ni²⁺ + L [NiLH_-2] + 2H²⁺; log_{11 – 2} = -14.45     

Ermittlung von Reaktionsgeschwindigkeitskonstanten aus relaxationskinetischen Meßergebnissen,gewonnen bei verschiedenen Ionenstärken

Zusammenfassung Das Dimerisierungsgleichgewicht geladener Moleküle 2M ^zD ^2z wurde als einfaches Modellsystem gewählt, um — unter Verwendung von bei verschiedenen Ionenstärken gewonnenen relaxationskinetischen Meßergebnissen — die Bestimmung ionenstärkenunabhängiger Reaktionsgeschwindigkeitskonstanten und der thermodynamischen Gleichgewichtskonstante zu demonstrieren.

---

Evaluation of rate constants utilizing relaxation data obtained at variable ionic strength

The monomer-dimer equilibrium of charged molecules 2M ^zD ^2z has been used as a simple model to demonstrate how ionic strength independent rate parameters and the thermodynamic equilibrium constant can be determined from relaxation kinetic data obtained at variable ionic strength.

---

---

Mit 3 Abbildungen     

Interaction of bivalent transition metal ions with iminodiacetato-(pentaammine/tetraammine)cobalt(III) ions. A kinetic and equilibrium study

Summary The kinetics of reversible complexation of Ni^II and Co^II with iminodiacetato(pentaammine)cobalt(III), [(NH₃)₅-Co(idaH₂)]³⁺ and Ni^II with iminodiacetato(tetraammine)-cobalt(III), [(NH₃)₄Co(idaH)]²⁺, have been investigated by the stopped-flow technique at 25 °C, pH = 5.7–6.9 and I = 0.3 mol dm ^–3. The reaction paths (NH₃)₅Co(idaH)²⁺+M²⁺(NH₃)₅Co(ida)M³⁺+H⁺ (NH₃)₅Co(ida)⁺+M²⁺(NH₃)₅Co(ida)M³⁺ (NH₃)₄Co(ida)⁺+Ni²⁺(NH₃)₄Co(ida)Ni³⁺ have been identified (idaH = N⁺H₂(CH₂CO₂)₂H, ida = NH(CH₂COO)^2–]. The rate parameters for the formation and dissociation of the binuclear species are reported. The data are essentially consistent with an I _d mechanism. The dissociation rate constants of the binuclear species indicate that Ni²⁺ and Co²⁺ are chelated by the coordinated iminodiacetate moiety.     

Ultraviolet spectroscopic study of ferric hydroxide complexation

Ultraviolet absorbance spectra of ferric ions in 0.68m NaClO₄ were studied as a function of pH at 4.0, 14.9, and 25.0°C. The results provided an evaluation of the stability constant for the formation of FeOH²⁺ which is *₁=[FeOH ⁺][H ⁺]/[Fe ³⁺]. The enthalpy change for the reaction Fe³⁺+H₂O FeOH²⁺+H⁺ was calculated as 10.0±0.3 kcal-mole^–1. Increasing temperature was also found to promote the reaction Fe³⁺+2H₂O Fe(OH) ₂ ⁺ +2H⁺. Our results were combined with the results of other to produce an expression describing the first hydrolysis equilibrium at ionic strengths between 0 and 3m and temperatures between 4.0 and 45.0°C at 1 atm total pressure. At 25°C and 0.68m the ionic strength *₁=1.90×10^-3     

IR-Spectroscopic investigation of the hydration of tetrabutylammonium bromide in methylene chloride

The concentration dependence of the H₂O spectra in solutions of tetrabutylammonium bromide Bu₄NBr in methylene chloride was investigated by IR-spectroscopy. At low salt and H₂O concentrations the equilibrium: Br _f ^– +HOH_fBr^–HOH dominates where f indicates free or not hydrogen-bonded Br^– and H₂O. With increasing salt content, Br^–H–O–HBr^– complexes are present in addition. At high salt and H₂O content, including the saturated aqueous Bu₄NBr solution, H-bonded cyclic dimers seem to be important.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples. December 4–7, 1984.     

Calculations on some phosphate ions by a modified CNDO method

Calculations are presented of the electronic structures of some phosphate ions, namely, H₃PO₄, H₂PO ₄ ^– , HPO ₄ ⁼ , PO ₄ , HPO₃, and PO ₃ ^– . It is shown that the character of the P-O bonds is marked and the 3d orbitals contribute substantially to the bonding. Using the total energy data for the orthophosphate ions, the ratio of the dissociation constants for the ions is calculated and found to be in good agreement with the experimental data.     

Kinetics of the anation reaction of pentaamineaquacobalt(III) by phosphorous acid/hydrogenphosphite

Summary The kinetics of the anation reaction of [Co(NH₃)₅H₂O]³⁺ by H₃PO₃/H₂PO ₃ ^– , to give [CoH₂PO₃(NH₃)₅]²⁺, have been studied at 60, 70 and 80°C, in the acidity range [H⁺](M)=1.5 · 10^–1 –2.0 · 10^–3. Only H₂PO₃ is found to be reactive. The rate data is consistent with an I_d mechanism. The mean value of outer sphere association of [Co(NH₃)H₂O]³⁺ with H₂PO ₃ ^– is 1.5 M^–1. Values of the interchange constants are: 10⁴4k_i(s^–1)= 0.29, 1.47, 5.13, at 60, 70 and 80 °C respectively (H= 1.4 · 10²KJmol^–1, S=8.3 · 10 JK^–1 mol^–1). The first acidity constant of H₃PO₃ at I=1.0 has also been determined: 10²K_a(M)=4.8, 5.2 and 5.5, at 25, 40 and 50 °C respectively.     

Potentiometric Study of Reactions of Titanium Complexes in Phosphate–Perchlorate Acid Solutions

The potentiometric method is used to measure the equilibrium potential in the Ti(IV)/Ti(III) system and determine that monophosphate Ti(IV) complexes and Ti³⁺hydrated complexes dominate in phosphate–perchlorate acid solutions, 4M(H, Na)ClO₄, at of 5 × 10^–2to 4 × 10^–1M. Equations that describe the total electrode reaction are proposed. Decreasing the concentration of free hydrogen ions from 3 to 0.12 M results in the deprotonation of TiO(H₂PO₄)⁺complexes and the formation of TiO(HPO₄) complexes. Equilibrium constants for reactions of the formation of Ti(IV) monophosphate complexes and the protonation of TiO(HPO₄) complex are calculated.     

Thermodynamics of aqueous phosphate solutions: Apparent molar heat capacities and volumes of the sodium and tetramethylammonium salts at 25°C

A Picker flow microcalorimeter and a flow densimeter were used to obtain apparent molar heat capacities and apparent molar volumes of aqueous solutions of Na₃PO₄ and mixtures of Na₂HPO₄ and NaH₂PO₄. Identical measurements were also made on solutions of tetramethylammonium salts to evaluate the importance of anion-cation interaction. The experimental apparent molar properties were analyzed in terms of a simple extended Debye-Hückel model and the Pitzer ion-interaction model, both with a suitable treatment for the effect of chemical relaxation on heat capacities, to derive the partial molar properties of H₂PO ₄ ^– (aq), HPO ₄ ^2– (aq) and PO ₄ ^3– (aq) at infinite dilution. The volume and heat capacity changes for the second and third ionization of H₃PO₄(aq) have been determined from the experimental data. The importance of ionic complexation with sodium is discussed.     

Kinetics of oxidation of hydrogen peroxide by [Mn3 IV(μ-O)4(phen)4(H2O)2]4+ (phen = 1,10-phenanthroline) in weakly acidic aqueous media

In the 3.33–4.95 pH range, buffered with an excess of phenanthroline (phen), [Mn ₃ ^IV (-O)₄(phen)₄(H₂O)₂]⁴⁺ (1) quantitatively oxidises H₂O₂ to O₂; the only manganese product is [Mn ₂ ^III,IV (-O)₂(phen)₄]³⁺ (2), provided a large excess of H₂O₂ is avoided; an excess of H₂O₂ [ > 7 × (1)] reduces (1) to Mn²⁺. When (1) and H₂O₂ were mixed in the stoichiometric molar proportion (1:0.75), the measured second-order rate constant for the reduction of (1) to (2) increased with increasing [H⁺], tending to saturate at lower pH. Added phenanthroline did not affect the rate constant. The results suggest an inner-sphere mechanism, ca. 10 times higher kinetic activity for (1) than for its hydroxo derivative [Mn ₃ ^IV (-O)₄(phen)₄(OH)(H₂O)]³⁺ (1h), and a hydrolysis constant K _a = (2.9 ± 1) × 10^–4 mol dm^–3 for (1) (1h) + H⁺.     

Ion-pair extractions by the use of planar and non-planar extracting solvents

The effect of extracting solvent was studied on the ion-pair extraction reactions with a special interest in the effect of molecular shape (planar or non-planar) of the solvent. The following two reactions were investigated: (HNN)_o + (Q⁺)_W (Q·NN)_o + (H⁺)_W (Extraction I); (Q-ClO₄)_o + (Pi^–)_w (Q·Pi)_o + (ClO ₄ ^– )_w (Extraction II), where HNN, NN^–, Pi^–, and Q⁺ represent 1-nitro-2-naphthol, its base form (1-nitro-2-naphtholate), picrate, and a cationic species, respectively. Above extraction equilibria were confirmed to hold in cases of various extracting solvents including planar solvents (1-chloronaphthalene, etc.) and non-planar solvents (1,2-dichloroethane, chloroform). An approximately linear relationship was found to exist between the extraction constants of Extraction I (logK _ex ^I ) and the Kosower's Z-value of extracting solvents. It was also found that the compatibility between the molecular shape of the ion-pair complexes and that of the extracting solvents affected the extractability to a considerable extent.     

Kinetics of solvolysis and of formation of tetrachloroplatinate(II) in alcohol: Water mixtures

Summary Rate constants are reported for the reaction of [PtCl₄]^2– with hydrochloric-perchloric acid mixtures, in aqueous methanol and aqueous t-butanol at 308.2 K. The observed first-order rate constants are, from their dependence on chloride concentration, divisible into forward and reverse rate constants for the equilibrium: [PtCl₁₄]^2–+H₂O[PtCl₃(OH₂)]^–+Cl^–. The solvent dependence of aquation rates for [PtCl₄]^2– is compared with those for other chlorotransition metal complexes, and discussed in terms of the Grunwald-Winstein method of mechanism diagnosis in organic systems. The solvent dependence of rates of [PtCl₄]^2– formation is compared with the rates of formation of other metal complexes; differences between this platinum reaction and, for example, nickel(II) formation, are rationalised in terms of the reactant charge product difference and consequent solvent permittivity effects on rate trends.     

Coupled diffusion produced by hydrolysis of aqueous potassium phosphate

Conductimetric and diaphragm cell techniques have been used to measure diffusion of aqueous potassium phosphate solutions at 25°C from 0.01 to 0.10 mol-dm^–3 (M). A significant portion of the aqueous K₃PO₄ component diffuses as equimolar amounts of potassium hydrogen phosphate and potassium hydroxide produced by hydrolysis: K₃PO₄+H₂O=K₂HPO₄+KOH. Because OH^– diffuses more rapidly than HPO ₄ ^2– , the total flow of KOH exceeds the flow of K₂HPO₄. The extra flow of KOH constitutes coupled transport of a second solute component. Ternary diffusion coefficients that describe interacting flows of K₃PO₄ and KOH components are reported. At low concentrations where phosphate is strongly hydrolyzed, the molar flux of the KOH component produced by diffusion of K₃PO₄ is six times larger than the flux of the K₃PO₄ component. Binary diffusion coefficients for aqueous K₂HPO₄ solutions are also reported. It is shown that ternary transport coefficients for K₃PO₄ solutions can be estimated from the properties of binary solutions of K₂HPO₄ and KOH.     

Raman Spectroscopy of Aqueous ZnSO4 Solutions under Hydrothermal Conditions: Solubility, Hydrolysis, and Sulfate Ion Pairing

Raman spectra have been measured for aqueous ZnSO₄ solutions under hydrothermal conditions at steam saturation to 244°C; solubility has been recorded as a function of temperature from 25 to 256°C. The high-temperature Raman spectra contained two polarized bands, which suggest that a second sulfato complex, possibly bidentate, is formed in solution, in addition to the 1:1 zinc(II) sulfato complex, which is the only ion pair identified at lower temperatures. Under hydrothermal conditions, it was possible to observe the hydrolysis of the zinc(II) aquo ion by measuring the relative intensity of bands due to SO ₄ ^2– and HSO ₄ ^– according to the equilibrium reaction Zn(OH₂)₆]²⁺ + SO ₄ ^2– [Zn(OH₂)₅OH]⁺ + HSO ₄ ^– The precipitate in equilibrium with the solution at 210°C could be characterized as ZnSO₄ · H₂O (gunningite) by x-ray diffraction (XRD) and Raman and infrared spectroscopy. At 244°C the equilibrium precipitate could be identified as ZnSO₄ (zincosite).     

Solubility and Solubility Product at 22°C of UO2(c) Precipitated from Aqueous U(IV) Solutions

Solubility studies on UO₂(c), precipitated at 90^°C from low-pH U(IV) solutions, were conducted under rigidly controlled redox conditions maintained by EuCl₂ as a function of pH and from the oversaturation direction. Samples were equilibrated for 24 days at 90^°C and then for 1 day at 22^°C. X-ray diffraction (XRD) analyses of the solid phases, along with the observed solubility behavior, identified UO₂(c) as the dominant phase at pH1.2 and UO₂(am) as the dominant phase at pH1.2. The UV-Vis-NIR spectra of the aqueous phases showed that aqueous uranium was present in the tetravalent state. Our ability to effectively maintain uranium in the tetravalent state during experiments and the recent availability of reliable values of Pitzer ion-interactionparameters for this system have helped to set reliable upper limits for the log K ^o value of –60.2 + 0.24 for the UO₂(c) solubility [UO₂(c) + 2H₂O U⁴⁺ + 4OH^–] and of >–11.6 for the formation of U(OH)₄(aq) [U⁴⁺+ 4H₂O U(OH)₄(aq) + 4H⁺]     

Thermodynamic Model for the Solubility of Cr(OH)3(am) in Concentrated NaOH and NaOH–NaNO3 Solutions

The main objective of this study was to develop a thermodynamic model for predicting Cr(III) behavior in concentrated NaOH and in mixed NaOH–NaNO₃ solutions for application to developing effective caustic leaching strategies for high-level nuclear waste sludges. To meet this objective, the solubility of Cr(OH)₃(am) was measured in 0.003 to 10.5 m NaOH, 3.0 m NaOH with NaNO₃ varying from 0.1 to 7.5 m, and 4.6 m NaNO₃ with NaOH varying from 0.1 to 3.5 m at room temperature (22 ± 2°C). A combination of techniques, X-ray absorption spectroscopy (XAS) and absorptive stripping voltammetry analyses, were used to determine the oxidation state and nature of aqueous Cr. A thermodynamic model, based on the Pitzer equations, was developed from the solubility measurements to account for dramatic increases in aqueous Cr with increases in NaOH concentration. The model includes only two aqueous Cr species, Cr(OH) ₄ ^– and Cr₂O₂(OH) ₄ ^– (although the possible presence of a small percentage of higher oligomers at >5.0 m NaOH cannot be discounted) and their ion–interaction parameters with Na⁺. The logarithms of the equilibrium constants for the reactions involving Cr(OH) ₄ ^– [Cr(OH)₃(am) + OH^– Cr(OH) ₄ ^– ] and Cr₂O₂(OH) ₄ ^2– [2Cr(OH)₃(am) + 2OH^– Cr₂O₂(OH) ₄ ^2– + 2H₂O] were determined to be –4.36 ± 0.24 and –5.24 ± 0.24, respectively. This model was further tested and provided close agreement between the observed Cr concentrations in equilibrium with Cr(OH)₃(am) in mixed NaOH–NaNO₃ solutions and with high-level tank sludges leached with and primarily containing NaOH as the major electrolyte.     

Magnetite solubility and phase stability in alkaline media at elevated temperatures

A platinum-lined flowing autocláve facility was used to investigate the solubility behavior of magnetite (Fe₃O₄) in alkaline sodium phosphate and ammonium hydroxide solutions between 21 and 288°C. Measured iron solubilities were interpreted via a Fe(II)/Fe(III) ion hydroxo-, phosphato-, and ammino-complexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A total of 14 iron ion species were fitted. Complexing equilibria are reported for 8 new species: Fe(OH)(HPO₄)^–, Fe(OH)₂(HPO₄)^2–, Fe(OH)₃(HPO₄)^2–, Fe(OH)(NH₃)⁺, Fe(OH)₂(PO₄)^3–, Fe(OH)₄(HPO₄)^3–, Fe(OH)₂(H₂PO₄)^–, and Fe(OH)₃(H₂PO₄)^3–. At elevated temperatures, hydrolysis and phosphato complexing tended to stabilize Fe(III) relative to Fe(II), as evidenced by free energy changes fitted to the oxidation reactions.