A Conductometric Study of Aqueous Solutions of Some Cyclohexylsulfamates

The electric conductivities of aqueous solutions of the lithium, sodium, potassium and ammonium salts of cyclohexylsulfamic acid were measured from 5 to 35 ^∘C (in steps of 5 ^∘C) in the concentration range 3 × 10⁻⁴ < c/mol-dm⁻³ < 0.01. Data analysis based on a chemical model of electrolyte solutions yielded the limiting molar conductance Λ^∞ and the association constant K_A. Using the known values of the limiting conductances of lithium, sodium and potassium ions, the limiting conductances of the cyclohexylsulfamic ion were evaluated. Total dissociation of the investigated salts in water and negligible hydration of the cyclohexylsulfamate anion are evident.     

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.     

Crystallization and Phase Stability of CaSO<Subscript>4</Subscript> and CaSO<Subscript>4</Subscript> – Based Salts

Summary.  Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO₄·2H₂O), hemihydrate (CaSO₄·0.5H₂O) and anhydrite (CaSO₄). On the one hand the conversion of these phases into each other takes place in nature and on the other hand it represents the basis of gypsum-based building materials. The present paper reviews available phase diagram and crystallization kinetics information on the formation of calcium sulfate phases, including CaSO₄-based double salts and solid solutions. Uncertainties in the solubility diagram CaSO₄–H₂O due to slow crystallization kinetics particularly of anhydrite cause uncertainties in the stable branch of crystallization. Despite several attempts to fix the transition temperatures of gypsum–anhydrite and gypsum–hemihydrate by especially designed experiments or thermodynamic data analysis, they still vary within a range from 42–60°C and 80–110°C. Electrolyte solutions decrease the transition temperatures in dependence on water activity. Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviour, the reason of which is still unclear. However, crystal morphology has a strong influence. Gypsum forms solid solutions by incorporating the ions HPO₄ ²⁻, HAsO₄ ²⁻, SeO₄ ²⁻, CrO₄ ²⁻, as well as ion combinations Na⁺(H₂PO₄)⁻ and Ln³⁺(PO₄)³⁻. The channel structure of calcium sulfate hemihydrate allows for more flexible ion substitutions. Its ion substituted phases and certain double salts of calcium sulfate seem to play an important role as intermediates in the conversion kinetics of gypsum into anhydrite or other anhydrous double salts in aqueous solutions. The same is true for the opposite process of anhydrite hydration to gypsum. Knowledge about stability ranges (temperature, composition) of double salts with alkaline and alkaline earth sulfates (esp. Na₂SO₄, K₂SO₄, MgSO₄, SrSO₄) under anhydrous and aqueous conditions is still very incomplete, despite some progress made for the systems Na₂SO₄–CaSO₄ and K₂SO₄–CaSO₄–H₂O. Corresponding author. E-mail: daniela.freyer@chemie.tu-freiberg.de Received December 17, 2002; accepted January 10, 2003 Published online April 3, 2003     

Electrical Conductance of Some Symmetrical Tetraalkylammonium and Alkali Salts in N,N-Dimethylacetamide at 25°C

Precise measurements of electrical conductances of solutions of tetraethylammonium bromide, tetrapropylammonium bromide, tetrapentylammonium bromide, tetrahexylammonium bromide, tetraheptylammonium bromide, tetraocytylammonium bromide, sodium tetraphenylborate, and potassium tetraphenylborate in N,N-dimethylacetamide at 25^°C are reported for the concentration range 0.005-0.015 mol-dm^–3. The conductance data have been analyzed by the 1978 Fuoss conductance-concentration equation in terms of the limiting molar conductance, the association constant, and the association diameter. The limiting ionic conductances have been estimated from the appropriate division of the limiting molar conductivity value of the reference electrolyte Bu₄NBPh₄. Slight ionic association was found for all these salts in this solvent medium. Tetraalkylammonium ions are found to be unsolvated in N,N-dimethylacetamide, whereas significant solvation has been noticed for sodium and potassium ions.     

Technology of obtaining of potassium dihydrophosphate in the system with salting-out

The technology of producing of potassium dihydrophosphate (and potassium metaphosphate) mineral fertilizer in multicomponent system with salting-out is described; this technology is the result of investigation of multicomponent system K⁺, (C₂H₅)₂NH₂⁺ // Cl⁻, H₂PO₄⁻-H₂O, diagrams of the system condition and technological scheme are given; theoretical estimation of useful product yield agrees with experimental data.     

Conductance of 1,1-electrolytes in acetonitrile solutions from −40° to 35°C

Conductance data for perchlorates of Li⁺, K⁺, Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, iodides of K⁺, Me₄N⁺, i-Am₃BuN⁺, and tetraphenylborates of Na⁺, Bu₄N⁺ and i-Am₃BuN⁺ in acetonitrile solution in the temperature range −40° to 35°C are reported. Λ_° (limiting molar conductance) and K_A (association constant) are evaluated for several temperatures using a conductance equation based on the chemical model of electrolyte solutions including short range forces. Limiting molar ion conductances, λ _ΰ ⁱ , at −35°, −25°, −15°, −5°, 5°, 15° and 25°C are evaluated from temperature dependent limiting transference numbers. Enthalpies and entropies of association, obtained from the temperature dependence of the association constants, are also presented. Dedicated to the memory of Professor Raymond M. Fuoss.     

Transport and thermal characteristics of Cs<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript>

The transport and thermal properties of Cs_{1 − x} Rb _x H₂PO₄ in a wide range of compositions were studied. The binary salts Cs_{1 − x} Rb _x H₂PO₄ (x = 0–0.9) contain solid solutions with a structure of CsH₂PO₄. The binary salts were synthesized by mechanically mixing the starting components and growing crystals by isothermal evaporation from aqueous solutions. The properties of Cs_{1 − x} Rb _x H₂PO₄ salts obtained by different procedures were found to differ considerably. At higher rubidium contents in compounds obtained by mechanical mixing, the superionic transition temperature rose insignificantly, the high-temperature phase conductivity decreased twofold, the low-temperature conductivity increased within the limits of the order of magnitude, and the system of hydrogen bonds was slightly weakened. In Cs_{1 − x} Rb _x H₂PO₄ crystals grown from solutions, the temperature of the superionic transition decreased along with its slowing down, and the low-temperature conductivity increased by more than three orders of magnitude because of the higher contents of residual acid aqueous centers in the structure of the salt. These systems are characterized by increased thermal stability.     

Hydrothermal alteration of BaxMIVxCe2?2 x (PO4)2 [MIV=Zr, Hf] as hosts for minor actinides

Ba_xM^IV _xCe_2−2x (PO₄)₂ [M^IV=Zr, Hf] monazite-like compounds were succesfully synthesized by solid state reaction for x≤0.2 (M^IV=Zr) and x≤0.1 (M^IV=Hf). The low miscibility of BaM^IV(PO₄)₂ (M^IV=Zr, Hf) compounds in CePO₄ was explained on the basis of the monoclinic-to-trigonal phase transition that occurs at 733 K in BaZr(PO₄)₂ and at 798 K in BaHf(PO₄)₂. The hydrothermal alteration of these compounds was tested using a modified MCC-1 static leaching test in acid (1 mol·dm⁻³ HCl) and basic (1 mol dm⁻³ KOH) solutions at 373 K, 473 K and 573 K; both the experimental fluids and the reacted solid specimens were analyzed by different analytical techniques and the reaction mechanisms were elucidated. All the tested compounds are stable in 1 mol·dm⁻³ HCl until 573 K. The stability of the monazites in 1 mol·dm⁻³ KOH is a function of the temperature.     

Ionic Association and Mobility IV. Ionophores in Dimethylsulfoxide at 25°C

The results of conductance measurements on pyridinium picrate, tetraphenylo-sonium picrate, potassium picrate, tetraphenylantimony picrate, tetrapropylam-monium, tetrafluoroborate, tetramethylammonium hexafluorophosphate ion association noncoulombic interaction in dimethyl sulfoxide (DMSO) at 25°C in the concentration range 1–15×10^–4 M are reported. The data were analyzed by the Justice modification of the Fuoss–Hsia equation. Except for pyridinium picrate all salts studied were found to be associated.Application of the Justice Barthel–Bjerrum model of ion association permitted calculation of the noncoulombic portion of the potential of mean force, W _±. Ionic limiting conductances were calculated for six ions using known values of previously determined transport numbers. A table of most current limiting ionic conductances for a variety of ions in DMSO at 25°C has been established.     

Ion Association and Solvation Behavior of Some 1-1 Electrolytes in 2-Ethoxyethanol Probed by a Conductometric Study

Precise measurements of the electrical conductances of solutions of potassium thiocyanate (KCNS), ammonium thiocyanate (NH₄CNS), sodium nitrate (NaNO₃) and ammonium nitrate (NH₄NO₃) in 2-ethoxyethanol (EE) at temperatures 35, 40, 45 and 50,^∘C are reported. The conductance data have been analyzed by the 1978 Fuoss conductance equation. A thermodynamic analysis of the ionic association processes has also been made and the Coulombic forces are found to play a major role in the association processes. The ionic contributions to the limiting equivalent conductances have been determined using the reference electrolyte method. Strong association was found for all these electrolytes in this solvent medium. The cations are found to be substantially solvated in 2-ethoxyethanol, whereas the anions appear to have only weak interaction with the solvent molecules.     

Binary mutual diffusion coefficients of aqueous ammonium and potassium sulfates at 25°C

The diffusion coefficients of aqueous ammonium and potassium ions at infinite dilution differ by only 0.01% at 25°C, so, according to Nernst's law, the binary mutual diffusion coefficients D of pairs of dilute aqueous ammonium and potassium salts should be nearly identical. Yet precise optical interferometric data for ammonium and potassium sulfates contradict this rule: the value of D reported previously for 0.05 mol-L⁻¹ aqueous ammonium sulfate is 0.80×10⁻⁵ cm²-s⁻¹, while the corresponding value for potassium sulfate is 1.24×10⁻⁵ cm²-s⁻¹ about 50% higher. To confirm this surprising result, the diffusion coefficients of the two salts have been measured by the Taylor dispersion technique. The diffusion coefficients of the salts are indeed nearly identical, and the earlier ammonium sulfate data are found to be incorrect.     

Thermodynamics of neptunium(V) complexes with phosphate at elevated temperatures

The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO₄ ²⁻ complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO₄ ²⁻] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO₄ ²⁻ at 25 °C–55 °C were calculated by the temperature coefficient method.     

DDTC-Na-based colorimetric chemosensor for the sensing of cyanide in water

Sodium diethyldithiocarbamate (DDTC-Na) was demonstrated to be a new colorimetric cyanide chemosensor by utilizing an indirect trick. First, some copper ions were added to the colorless aqueous solution of DDTC-Na. Then, the resultant brown solution was studied upon the addition of different anions, including Cl⁻, I⁻, IO₃⁻, SO₄²⁻, NO₂⁻, Br⁻, H₂PO₄⁻, F⁻, SCN⁻, HSO₄⁻, ClO₄⁻ and CN⁻. It was observed by naked eyes that the brown solution changed to colorless immediately after the addition of the trace cyanide, but there were no changes towards other anions, making DDTC-Na a good selective cyanide chemosensor in pure water. Supported by the National Natural Science Foundation of China (Grant Nos. 20674059 & 20402011)     

Determination of americium-243 through its daughter product neptunium-239

The extraction of Np(IV), Zr, Nb, Cs, Ce(III) and Am(III) from nitric acid solutions containing oxalate and phosphate ions by solutions of 1-phenyl-3-methyl-4-benzoylpyrazolon-5 (PMBP) and tri-n-butyl phosphate (TBP) in benzene has been investigated. A solution 0.1M in respect to PMBP and 0.25M in respect to TBP was found to extract 99% of neptunium from aqueous solutions 1M in respect to H₃PO₄ and 0.5M in respect to HNO₃. Under these conditions, the extraction of the other investigated elements does not exceed 0.1%. Based on this finding, a procedure was developed to determine²⁴³Am through its daughter product²³⁹Np in solutions containing large quantities of curium and its fission products. The sensitivity of the procedure is 1·10⁻⁷ mg of²⁴³Am in the sample. The²⁴³Am content is obtained by calculation from measurements of the γ-activity of the extracted²³⁹Np. The purification ratio of²³⁹Np is∼10⁵ from Zr, Nb and Ru, ∼10⁸ from Ce and Cm and >10¹² from Cs.     

Ion-specific swelling behavior of poly(vinyl alcohol) gel prepared by γ-ray irradiation

Poly(vinyl alcohol) gel was prepared by γ-ray irradiation of an aqueous solution of the polymer and its swelling behavior in solutions of the alkali-metal and alkaline-earth-metal salts was investigated. The gel deswelled in solutions containing strongly hydrated anions and swelled in solutions containing strongly hydrated cations. The degree of swelling of the gel was in the following order: SO₄ ²⁻<Cl⁻<Br⁻ ≅ NO₃ ⁻<I⁻ for the anions and K⁺<Na⁺<Li⁺ and Sr²⁺<Ca²⁺<Mg²⁺ for the cations. These results were interpreted in terms of interactions between the polymer and the ions through the hydration layers. Received: 6 November 2000 Accepted: 24 May 2001     

Estimation of the specific content and nature of sorption sites of iron(<Emphasis Type="SmallCaps">III</Emphasis>) and zirconium(<Emphasis Type="SmallCaps">IV</Emphasis>) oxyhydroxides

The sorption of anions H₂PO₄ ⁻, HPO₄ ²⁻, PO₄ ³⁻, [Fe(CN)₆]³⁻, and [Fe(CN)₆]⁴⁻ from aqueous solutions on the surface of Fe^III and Zr^IV oxyhydroxide hydrogels freshly precipitated at pH 4–13 was studied. The region of sorbate concentrations was from 0.00025 to 0.06 mol L⁻¹. The plots of the anion uptakes vs. their equilibrium concentrations are represented by isotherms of the first type, which are well described by the Langmuir equation if the quantity of the amount adsorbed is expressed as mol-site g⁻¹. The maximum uptakes and constants of the Langmuir equation were calculated. The phosphate anions occupy the same number of sorption sites on the sorbents precipitated at different pH. The average specific content of sorption sites for the ferro- and zirconogels in the metastability period is independent of the pH of their precipitation, being 3.1·10⁻³ and 3.2·10⁻³ mol-site g⁻¹, respectively. The [Fe(CN)₆]³⁻ and [Fe(CN)₆]⁴⁻ anions are sorbed only on the positively charged sites of the hydrogels and occupy not more than 2·10 mol-site g⁻¹ in the studied interval of pH of precipitation. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1736—1741, August, 2005.     

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     

Thermodynamics of aqueous solutions of poly ethylene glycol di-methyl ethers in the presence or absence of ammonium phosphate salts

Precise measurements of density and sound velocity at different temperatures ranging from 283.15 to 308.15 K for solutions of PEGDME250, PEGDME500 and PEGDME2000 in water and of PEGDME500 in aqueous solutions of 0.500 mol kg⁻¹ ammonium di-hydrogen phosphate ((NH₄)H₂PO₄) and di-ammonium hydrogen phosphate ((NH₄)₂HPO₄), binodal curves at temperature ranges 293.15-318.15 K for the aqueous PEGDME500 + (NH₄)₂HPO₄, PEGDME500 + (NH₄)₃PO₄, PEGDME2000 + (NH₄)H₂PO₄, PEGDME2000 + (NH₄)₂HPO₄, PEGDME2000 + (NH₄)₃PO₄ and PPG400 + (NH₄)₂HPO₄ two-phase systems, and liquid-liquid equilibrium data at temperature ranges 298.15-318.15 K for the aqueous PEGDME500 + (NH₄)₂HPO₄ and PEGDME2000 + (NH₄)₂HPO₄ two-phase systems have been taken. From the experimental density and sound velocity data, the apparent specific volume, excess specific volume, isentropic compressibility and isentropic compressibility deviation values have been determined and the effect of temperature, charge on the anion of electrolytes and molar mass of PEGDME on the volumetric and compressibility properties of the investigated polymer solutions as well as on the salting-out effect of PEGDMEs produced by ammonium phosphate salts has been studied.     

Conductance of aqueous solutions of cobalticyanides,ferrocyanides, and molybdocyanides of potassium and of tetraalkylammonium lons

The conductances of aqueous solutions of the above-mentioned compounds have been measured in the range of ionic strength between 5×10^?4–10^?1 at 25°C. The decrease in equivalent conductance due to the increase in concentration always becomes smaller with increasing molecular weight of the tetraalkylammonium ions. K₄Fe(CN)₆ is comparable to (Me₄N)₄Fe(CN)₆, K₄Mo(CN)₆ is intermediate between the tetraethyl- and the tetra-n-propylammonium salts, and K₃Co(CN)₆ has a conductance larger than the tetra-n-butylammonium salt. These results are compared with the kinetic salt effects due to the tetraalkylammonium ions.