Ion—solvent interaction: viscosity of ternary electrolytes in dioxane-water mixtures at 35°

The viscosities of the chlorides, bromides and nitrates and perchlorates of Mg²⁺ and Ba²⁺, of the chlorides and nitrates of Ca²⁺ and Sr²⁺, and of the sulphates of Na⁺ and K⁺ at mass fraction of dioxane, 10, 20 and 30% have been measured at 35°. The values of the constant A and B of the viscosity equation indicate ion—ion and ion—solvent interaction respectively. The ion-solvent interaction is found to be of the order NO^?₃ > ClO^?₄ > Br^? > Cl^? and K⁺ > Na⁺.     

Variations in the Composition of Bromine Water During Oxidation Reactions

A cubic equation has been derived that permits calculation of the composition of aqueous bromine solutions in terms of HOBr, BrO^?, Br₂, Br^?₃ and Br^? as a continuous function of the pH, the initial oxidant concentration and the mole fraction of oxidant consumed. The calculations were performed by computer for the pH range 0–14 at bromine concentrations (c₀) of 10^?1 to 10^?7 M. Throughout the course of an oxidation at pH 0 and c₀= 10^?4, bromine water is pure Br₂. No Br^?₃ exists at c₀ < 10^?3. In the pH range 4–6, dilute bromine solutions are pure HOBr (+ equimolar Br^?). For pH > 10, bromine water is pure BrO^?, while at pH < 7, no BrO^? is present. These conditions are unchanged during oxidant consumption.     

An Equilibrium Study of Reactions Involving a Cationic Surfactant and Various Counterions: Prediction of Ion Selectivity

Abstract

The thermodynamic equilibrium constants for the reactions between the cationic surfactant, ethylhexadecyldimethylammonium bromide, EHDA-Br, and various anions were determined using spectrophotometric and specific ion electrode measurements. The sequence of stability of EHDA⁺ in the presence of the anions X^? studied is Br^? > F^? > H₂PO₄ ^? > NO₃ ^? > C₆H₅O^? > I^?. The sequence of stability of EHDA-X is the reverse of this. The EHDA⁺ stability sequence is the same as the order of selectivity expected during foam fractionation from published results for Br^?, I^?, NO₃ ^?, and for H₂PO₄ ^? and C₆H₅O^?, i.e., I^? preferred over NO₃ ^?, which is preferred over Br^?, etc. The stability and selectivity sequences are interrelated by the steric hindrance of EHDA⁺ in the presence of the anions X^? at the bubble surface.     

Models for Interactions between Ionic Surfactants and Nonsurface-Active Ions in Foam Fractionation Processes

Abstract

Interactions are analyzed between an ionic surfactant and nonsurface-active ions (colligends) of opposite charge being separated in foam fractionations. Surfactant selectivity for competing colligends is determined in terms of models based on surfactant—colligend ion pair formation in the feed solution to a foam fractionation unit, based on colligend-surfactant counterion exchange at the gas-solution, bubble interfaces, and based on surface exchange coupled with ion pair formation in the bulk solution. Accurate, continuous-flow, single-equilibrium-stage foam fractionation data for NO^? ₃, BrO^? ₃, CIO^? ₃, and I^?, each versus Br^?, the counterion of the ethylhexadecyldimethylammonium cation, are used to discriminate among the models. Based on a detailed statistical analysis of the selectivity coefficients determined by two interaction models for each of the four colligends, the hypothesis of colligend-counterion exchange at the gas-solution interface is shown to be valid and that of solution ion pair formation is not substantiated. The surface exchange model provides selectivity coefficients which are quite constant over a tenfold concentration range and yet which are very sensitive to data inaccuracies.     

A cationic surfactant as a soluble ion exchanger in the continuous foam fractionation of nitrate; iodide,and bromide

An experimental investigation is presented of the continuous foam fractionation of NO₃^? versus Br^? and of T^? versus Br^? with a quaternary ammonium surfactant at concentrations of the order 1.8 × 10^?4M. An equation is derived to enable the computation of anion selectivity coefficients from foam fractionation data. The key assumptions of the derivation are verified experimentally. The selectivity coefficient for NO₃ versus Br^? is 1.56 ± 0.28 and for I^? versus Br^? is 5.85 ± 1.81, established from 40 continuous-flow experiments. Precipitation of EHDA-I is indicated at the highest ratios of the bulk solution concentrations of I^? and Br^?. significantly, both selectivity coefficients are independent of the fraction of the exchanger occupied by the preferred ion, indicating an exchanger activity coefficient ratio of unity, and are independent of ionic strength. The counterion present markedly influences the surfactant distribution coefficient.     

Conductance of LiBr solutions in acetonitrile in the presence of sulphur dioxide

The effect of SO₂ on the transport properties of LiBr in acetonitrile is studied by conductometric measurements. The specific conductivity of a 0.08 M LiBr solution rises ca. 2.5 fold upon the addition of 0.4 M SO₂. The physical properties of the solvent, the equivalent conductivity, the Walden number change but insignificantly in this SO₂ concentration range, whereas the association constant decreases considerably. It is concluded that the ion-dipole interaction Br^? + SO₂ = SO₂.Br^?, which raises the concentration of the conducting species and consequently lowers the apparent association constant, is basically responsible for the enhancement of the specific conductivity of LiBr in the mixed solvent acetonitrile with SO₂, used currently in practical Li/SO₂ batteries.     

EXTRACTION OF INDIUM( III) FROM BROMIDE AND THIOCYANATE MEDIA WITH 1-PHENYL-3-HETHYL-1-BENZOYLPYRAZOL-5-ONE; EFFECT OF LIPOPHILIC AMMONIUM SALTS

1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HL) in toluene extracts In(III) from ClO₄ ^?, (Br^?, CIO ClO₄ ^?, ) and Br^? media according to the extraction equilibria (1) and (2). Tri-n-octylmethylammonium bromide (B⁺Br^?) induces a medium synergic effect for Br^? and (Br^?,NO₃ ^?) media, which is cancelled in ClO₄ ^?medium. It corresponds to the extraction of (B⁺InBr_xL_4-x) ion pairs. On the contrary, from SCN^? or (SCN^?,ClO₄ ^?) media, In is extracted by HL according to only (1) and no synergism is obtained with tri-n-octylammonium salt.

These results are compared with those obtained with Cl^? and (C1^?,ClO₄ ^?) aqueous media. They are to a great extent explained by taking into account the complexing of In³⁺ by aqueous inorganic anions, the lipophilicity of the diverse species and the anionic exchanges in the B⁺X^? ion pairs.     

Observation of specific optical phonon modes dominating Li ion diffusion in γ-LiAlO2 ceramic

In γ-LiAlO₂ ceramic, Li ion diffusion plays a key role both in tritium release as a solid tritium breeder material in nuclear fusion and in phase stability as a matrix material in molten carbonate fuel cells (MCFC). Yet fundamental understanding of the diffusive process in γ-LiAlO₂ is still missing, especially considering the interaction of the lattice dynamics and Li ion motion. Herein, we demonstrated that two specific optical phonon modes are coupled with Li ion diffusion in γ-LiAlO₂, by investigating the temperature-dependent lattice dynamics via Raman scattering experiments, as well as first-principles calculations and neutron diffraction experiments (ND). The high-temperature ND experiments showed that γ-LiAlO₂ undergoes partial Li ion disordering in Li sublattice at high temperature. Notably, the lattice dynamics studies demonstrated that B₁ mode at 226 cm^?1 and A₁ mode at 263 cm^?1 are responsible for Li ion motion through the oscillation of Li–O in <010> and <001> direction, respectively. Our results further suggest that the behavior of tritium release and phase stability in γ-LiAlO₂ at elevated temperature may be controlled by tuning the two specific phonon modes through photon/electron-phonon coupling.     

Electrolytic conductivity—the hopping mechanism of the proton and beyond

The hopping mechanism of electrolytic conductivity is analyzed, employing mixtures of two solvents: one that sustains the hopping mechanism and the other that does not inhibit it directly, but interferes with it by diluting the solvent that sustains hopping.Measurement of the equivalent conductivity shows that the excess proton conductivities of H₃O⁺ and OH⁻ increases with increasing temperature, although the number of hydrogen bonds is known to decrease.In mixtures of acetonitrile with water, proton hopping does not start until a threshold concentration of about 20 vol.% water has been reached, while no such threshold concentration is observed upon addition of methanol to acetonitrile. It is concluded that in the former the proton is transferred to a cluster of water molecules, which can be formed only if there is enough water in the solvent mixture. This observation leads to the concept of mono-water, which is the state of water molecules when they constitute a small minority in the solvent mixtures, as opposed to bulk water, which consists of clusters of variable sizes.Systems in which a hopping mechanism of heavy ions has been observed include Br⁻/Br₂ and I⁻/I₂. In these cases the triple ions Br₃⁻ and I₃⁻, respectively are formed, and serve as the mediators for the transfer of the simple halogen ion. A very large increase of conductivity was observed upon solidification of the Br⁻/Br₃⁻ system, probably caused by favorable linear alignment of ions in the solid.The conductivity of acidified methanol decreases upon addition of water, because the affinity of the proton to water is higher than to methanol, thus water can act as a scavenger for protons. This behavior exemplifies a general observation, namely that conductivity by hopping can only occur when the Gibbs energy of the system does not change significantly following ion transfer; otherwise the ions would be trapped in the more stable state, hindering further propagation by hopping.The dependence of the Walden product on temperature can serve as an experimental criterion for hopping. A distinct decline of the product λ⁰ × η with increasing temperature is a clear indication of the occurrence of a hopping (non-Stokesian) mechanism of electrolytic conductivity.     

The oxidation of aqueous sodium sulphite solutions

In this paper new experimental work on the kinetics of the absorption of oxygen in an aqueous solution of sodium sulphite with cobaltous sulphate as a catalyst, has been presented and compared with already published data. It is shown that the reaction of oxygen with sodium sulphite is zero order in sulphite, first order in cobalt and second order in oxygen for 2 × 10⁴ N/m² <p_O2 < 10⁵ N/m², 150°C <T < 60°C, 3 × 10^?6 kmol/m³ <c_Co⁺⁺ < 3 × 10^?3 kmol/m 7.50 < pH < 8.50 and 0.4 kmol/m² <c_SO2-- < 0.8 kmol/m³. The reaction rate constant can be varied by more than two decades by changing the cobalt concentration, pH and temperature.The specific interfacial areas, a, and mass transfer coefficients, k_L, measured by DeWaal and Beek [14, 15] using an incorrect kinetic model of this reaction, are reinterpreted with the results of the present kinetic investigation. It is shown that their values of a and k_L are a factor 2.2 too low and too high, respectively, but that their values of k_La are correct.     

Electrode reactions of nickel(II) at mercury electrodes in aqueous solutions of pyridine at high ionic strengths

At high ionic strength the ion pair (NiPy²⁺₄, nX^?) or complex (NiPy₄X₂), n = 0, 1, 2; X^? = Cl^?, Br^?, SCN^?, N^?₃, F^?, NO^?₃, ClO^?₄; is adsorbed at the surface of mercury electrode. Under specified conditions in chloride, bromide, and thiocyanates solutions the electroreduction is preceded by a crystallization of a complex on the electrode surface. The inductive role of specifically coadsorbed Cl^? ions is discussed.     

Anionic polymerization of styrene in triglyme-benzene mixtures

Living anionic polymerization of styrene was kinetically investigated in triglyme-benzene mixtures. At low concentrations of triglyme the overall propagation rate constant, k_p, was much larger than at the same concentration of monoglyme (DME) in DME-benzene mixtures. The Szwarc-Schulz plot did not have negative slopes for lithium and sodium salts at triglyme contents of 5～20vol%, and no contribution of free anions to the propagation was observed for the sodium salt. The sodium ion pair was more highly reactive than the lithium ion pair; thus at 25°C, the ion pair rate constant, k′_p, for the lithium salt was 43, 102, 135 and 165 M^?1sec^?1 at triglyme concentrations of 5, 10, 15, and 20%, respectively, while that for the sodium salt was 410, 920, and 1460 M^?1sec^?1 in 5, 10, and 15% triglyme, respectively. The dissociation constant, K, for the lithium salt was 2·4×10^?11, 1·9×10^?10 and 1·3×10^?9 M in 10, 15, and 20% triglyme, respectively and the free ion rate constant, k″_p, was 2～2·5×10⁴ M^?1sec^?1 for the lithium salt.     

Interaction of polystyryl radical with Cu(DMF)2Br2

The kinetics of 2,2′-azobisisobutyronitrile (AIBN) initiated polymerization of styrene in N,N-dimethylformamide (DMF) at 60°C were investigated in the presence of dibromo(N,N-dimethylformamide)copper(II) complex. The complex was prepared in situ by mixing tetrakis (N,N-dimethylformamide)copper(II) perchlorate with LiBr in the molar ratio of 1 : 2. The equilibrium constant for [Cu(DMF)₄]²⁺ + 2Br^? ? Cu(DMF)₂Br₂ + 2DMF was calculated by the limiting logarithmic method as 1.80 × 10³ L² mol^?2. The velocity constant at 60°C for the interaction of polystyryl radical with Cu(DMF)₂Br₂ is 7.46 × 10⁴ L mol^?1 s^?1.     

Influence of Some Hofmeister Anions on the Krafft Temperature and Micelle Formation of Cetylpyridinium Bromide in Aqueous Solution

In this work, the effect of some Hofmeister anions on the Krafft temperature (T_K) and micelle formation of cetylpyridinium bromide (CPB) have been studied. The results show that more chaotropic anions increase, while the less chaotropic ones lower the T_K of the surfactant. More chaotropic I^? and SCN^? form contact ion pairs with the cetylpyridinium ion and reduce the electrostatic repulsion between the CPB molecules. As a result, these ions show salting‐out behavior, with a consequent increase in the T_K. In contrast, less chaotropic Cl^? and NO₃^? increase the activity of free water molecules and enhance hydration of CPB molecules, showing a decrease in the T_K. A rather unusual behavior was observed in the case of SO₄^2? and F^?. These strong kosmotropes shift from their usual position in the Hofmeister series and behave like moderate chaotropes, lowering the T_K of the surfactant. Because of the high charge density and the strong tendency for hydration these ions preferentially remain in the bulk. Rather than forming contact ion pairs, these ions stay away from the CPB molecules, decreasing the T_K of the surfactant. In term of decreasing the T_K, the ions follow the order NO₃^? > SO₄^2? > Cl^? > F^? > Br^? > SCN^? > I^?. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to the screening of the micelle surface charge by the excess counterions. The decreasing trend of the CMC in the presence of the salts follows the order SCN^? > I^? > SO₄^2? > NO₃^? > Br^? > Cl^? > F^?.     

Electrochemical oxidation of hydrogen peroxide at a bromine adatom-modified gold electrode in alkaline media

Bromine (Br)-adatom (Br_(ads)) was in situ fabricated onto polycrystalline gold (Au (poly)) electrode in Br⁻-containing alkaline media. The surface coverage of Br_(ads) (Γ_Br) varied only in the submonolayer coverage within the investigated potential window under potentiodynamic condition because of the coadsorption of hydroxyl ion (OH⁻) in alkaline media. The in situ fabricated Br_(ads)-submonolayer-coated Au (poly) electrode was successfully used for the electrochemical oxidation of hydrogen peroxide (H₂O₂). About five times higher oxidation current was achieved at the modified electrode as compared with the bare electrode. The enhancement of the electrode activity towards the electrochemical oxidation of H₂O₂ was explained based on the enhanced electrostatic attraction between the anionic HO₂⁻ molecules and Br_(ads)-adlayer-induced positively polarized Au (poly) electrode surface.     

Potentiels biioniques de membranes liquides fortement dissociees

The liquid membranes are solutions in nitrobenzene of alkyl-trimethyl-ammonium salts which, in the concentration range studied, have a dissociation coefficient higher than 0·9. Biionic potentials obtained when opposing Cl^??Br^?, Br^??I^? and Br^??Pi^? are studied. The values of the parameters appearing in the mathematical expression of biionic potentials (ion mobility, standard chemical affinity of transfer from water to nitrobenzene) are determined.     

Ion flotation and solvent sublation of cobalt cyanide complexes

An experimental investigation into the batch ion flotation of cobalt complex anions with the cationic surfactant, cetylpyridinium chloride is described. The concentration ratio of cetyl-pyridinium: cobalt in the foam was determined and found to be 2.0–2.7 for CoCl₂ plus KCN solution and 3.0–3.3 for K₃[Co(CN)₆] solution. Spectroscopic measurements of the former anion show that mainly [Co(CN)₅H₂O]²- anions were floated. The [Co(CN)₆]^3- flotation was established in the presence of Cl^?, Br^?, I^?, CN^?, NO₃^? and SO₄^2- anions. The accelerating influence of the ion flotation produced by the presence of Cl^?, Br^?, I^?, CN^?, NO₃^? and SO₄^2- increased as their partial molal volume increased. The solvent sublation of [Co(CN)₆]^3- anions was established in the presence of these anions.     

Evaluation and origins of the difference between double-layer capacitance behaviour at Au-metal and oxidized Au surfaces

In studies of processes at oxidized compared with unoxidized electrode surfaces by transient methods corrections for double-layer charging are usually required and have often been made by extrapolation of double-layer capacitance (C_dl) data for the metallic surface, e.g. at Au or Pt, into the potential region of oxide-film formation. Voltammetry and impedance spectroscopy provide direct information on C_dl values determined at unoxidized, i.e. metallic, Au surfaces compared with those of anodic oxide films generated potentiostatically to various extents that are stable in time, and characterized by reductive linear-sweep voltammetry. C_dl is derived from constant-phase element (CPE) values and the CPE parameter, ?, which is near unity for most conditions. At oxidized Au surfaces C_dl depends on potential for various extents of oxide formation; it increases from 15 (±1) μF cm⁻² at 1.75 V (RHE) to 25 (±1) μF cm⁻² at 1.45 V (RHE) and is independent of added Cl⁻ or Br⁻ for concentrations 0-10⁻³ M of both anions, while, at unoxidized Au electrodes in the absence of halide anions, C_dl has a maximum value of 60 (±2) μF cm⁻² at 0.80 V (RHE) and is now dependent on concentration of added Cl⁻ or Br⁻ ion. These major differences of C_dl for the oxidized and unoxidized Au surfaces indicate that double-layer charging corrections cannot be made simply by extrapolation of C_dl data for unoxidized Au metal surfaces into the potential region for oxide formation.     

Influence of bromide,chloride and thiourea additions on the reduction of Pb(II) from molten Ca(NO)3)2.4H2O at the mercury electrode

Electrochemical reduction of Pb(II) ion in the presence and absence of bromide, chloride and thiourea(TU) have been studied in molten Ca(NO₃)₂.4H₂O at 60°C. The overall and step-wise stability constants of the bromo, chloro and thiourea complexes have been evaluated from polarographic parameters using a computer analysis.Adsorption of complexes of Pb(II) in the melt induced by coadsorption of ligands (Br^? and TU) is also inferred and surface excesses are calculated from the results of lsv and chronopotentiometry are discussed.     

Selectivity Coefficients for Divalent Oxyanions from the Continuous Foam Fractionation of a Quaternary Ammonium Surfactant

Abstract

An experimental investigation is presented of the continuous, single equilibrium stage foam fractionation of chromate (CrO₄ ^2-) and of thiosulfate (S₂O₃ ^2-) from 0.4 to 3.0 × 10–⁴ M aqueous solutions. The cationic surfactant, ethyl-hexadecyldimethylammonium bromide (EHDA-Br), is modeled as a soluble ion exchanger, considering the exchange of CrO₄ ^2- and S₂O₃ ^2- or EHDA-CrO₄ ^? and EHDA-S₂O₂ ^? for Br^?. The data indicate that EHDA-CrO₄ ^? or EHDA- S₂O₃ ^? is exchanged with Br^?. The selectivity coefficient for chromate is 3.90 and that for thiosulfate is 16.8.