Solvent effect on standard electrode potential: Part III. Silver-silver chloride electrode in methanol-water mixtures

From measurements of the electromotive force of the Pt, H₂ (gas, 1 atm); HCl (m), X% methanol, Y% water; AgCl, Ag cells at nine temperatures from 15 to 55°C at 5° intervals, the standard potential of the silver-silver chloride electrode has been determined over a broad range of methanol concentrations (0–90 wt. % methanol). The standard molal potential in the various solvent mixtures has been expressed as a function of temperature. The primary medium effects of various media on hydrochloric acid, and the standard thermodynamic quantities accompanying the transfer of HCl from water to the respective solvent media have been computed. The results have been discussed both in terms of the acid-base behaviour of the solvent mixtures and also their structural effects on the transfer process.     

Solvent effect on standard electrode potential: Part I. Silver-silver iodide electrode in methanol-water mixtures

The standard potentials of the Pt, H₂ (1 atm); HI (m), X % CH₃OH, Y % H₂O; AgI, Ag cell have been determined in nineteen methanol-water solutions (0–90 wt. % methanol) at eight different temperatures from 20 to 55° C at five intervals. The primary medium effect on hydriodic acid and the thermodynamic functions of the cell have been calculated and discussed in terms of solvation effects.     

Solvent effect on standard electrode potential: Part V. Silver-silver chloride electrode in tert-butyl alcohol + water mixtures

The electromotive force measurements of the cell Pt, H₂ (gas, 1 atm); HCl (m), X % Bu ^tOH, Y% H₂O; AgCl, Ag, at nine different temperatures ranging from 15 to 55°C at 5° intervals, have been used to determine the standard potentials of the silver-silver chloride electrode in eighteen tert-butyl alcohol+water solvent mixtures containing up to 90 wt. % alcohol. The standard molal potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HCl, and the standard thermodynamic quantities for the transfer of one mole of HCl from water to tert-butyl alcohol+water media have been evaluated. The results have been discussed in the light of ion-solvent interactions as well as the structural changes of the solvents.     

Solvent effect on standard electrode potential: Part II. Silver-silver bromide electrode in methanol-water mixtures

The standard potentials of the silver-silver bromide electrode have been determined over a broad range of methanol concentrations from e.m.f. measurements of the cell Pt, H₂(g, 1 atm); HBr(m), X% methanol, Y% water; AgBr, Ag at eight temperatures ranging from 20 to 55°C. The standard e.m.f. has been expressed as a function of temperature. Thermodynamic functions of cell process, the primary medium effect of various media on hydrobromic acid, and thermodynamics of transfer of HBr from water to methanolic media have been computed and discussed in the light of ion-solvent interactions as well as the structural changes of the solvents.     

Relaxation dynamics in glycerol-water mixtures: I. Glycerol-rich mixtures

We discuss the relaxation dynamics of glycerol-water mixtures, as studied by dielectric spectroscopy in the frequency range from 1 Hz to 250 MHz and at temperatures between 173 and 323 K. The experimental results obtained for the glycerol-rich mixtures suggest that the main dielectric relaxation process, as well as the so-called high-frequency "excess wing" (EW) and dc conductivity, follow the same temperature dependence. This result indicates that all of these processes are induced by the same molecular origin. A new phenomenological function is proposed to describe the whole dielectric spectrum in the covered frequency range, and some possible mechanisms of dielectric behaviors through the dc conductivity, the main relaxation process, and the EW are discussed.     

Relaxation dynamics in glycerol-water mixtures. 2. Mesoscopic feature in water rich mixtures

The relaxation dynamics of water-rich glycerol-water mixtures is studied by broadband dielectric spectroscopy (BDS) at 173-323 K and differential scanning calorimetry (DSC) at 138-313 K. These data indicate the existence of the critical concentration of 40 mol % glycerol. In the studied temperature range for water-rich glycerol mixtures, the two states of water (ice and interfacial water) are observed in addition to water in the mesoscopic 40 mol % glycerol-water domains. The possible kinetics of water exchange between different water states is discussed in order to explain the mechanism of the broad melting behavior observed by DSC.     

The standard electrode potential of the silver-silver chloride electrode in 5 wt. % tetramethylurea-water mixture at 30°C

Electromotive force measurements were made at 30°C with the cell $$H_2 (g)|Pt(s)|HCl(m){\text{ }}TMU(x){\text{ }}H_2 O(100 - x)|AgCl(s)|Ag(s)$$ wherex=5 wt. % tetramethylurea (TMU). The standard electrode potential of the silver-silver chloride electrode, the mean molal activity coefficient of hydrogen chloride, the primary medium effect, and the free energy of transfer of hydrogen chloride from the aqueous standard state to the standard state in the mixed solvent were derived from the measurements. The acquisition of data was limited to this single composition and temperature because of the difficulty of preparing hydrogen electrodes for this solvent medium. The results obtained for hydrogen chloride in 5 wt. % tetramethylurea-water mixture are discussed, relative to other organic-aqueous mixtures of the same composition, in terms of structural effects and hydrogen bonding.     

Non-linear perturbation functions in the study of electrode kinetics: Part IV. Instrumentation

The construction of a digital function generator with the capability of generating voltage-time functions of the form E=E₀t^?1/2 is described. Some applications of such a device for fast chronopotentiometric measurements employed for the study of the mechanism of electrode reactions and superimposed non-faradaic charging processes are suggested.     

Convolution potential sweep voltammetry: Part IV. Homogeneous follow-up chemical reactions

The application of Convolution Potential Sweep Voltammetry to mechanism analysis and rate determination in electrochemical processes involving homogeneous chemical reaction is discussed. The formal analysis of the transition between pure diffusion control and pure kinetic condition is treated in the case of a first order follow-up reaction. The practical applicability of the method is then tested on the reductive pinacolization of acetophenone in acetonitrile using as operational parameters the sweep rate, the initial concentration and the water content of the medium.     

Thermal degradation of polymer-fire retardant mixtures: Part IV—Mechanism of fire retardancy in polypropylene-chlorinated paraffin mixtures

From oxygen and nitrous oxide indices of polypropylene-chlorinated paraffin mixtures it can be deduced that, in addition to the flame poisoning effect of HCl eliminated by the chloroparaffin, the lower flammability of the volatile products formed by thermal degradation of polypropylene heated in the presence of this additive seems to contribute to its fire retardance activity.     

Hydrodynamic voltammetry at channel electrodes: Part IV. Theory of chronopotentiometry for reversible electrode reactions

The theory of chronopotentiometric measurements at channel electrodes is developed for reversible electrode reactions, by rigorously solving the corresponding time-dependent boundary value problem, where the non-uniform accessibility of the channel electrode surface is taken into consideration. The theoretical equations of the transition time and the potential-time curve are derived as functions of (I_d/I), where I denotes the applied current intensity and I_d the limiting diffusion current obtained at steady-state. Finally, the time variation of the current density distribution at the electrode surface is given.     

Solvent effect on the redox potential of quinone-semiquinone systems

Polarographic reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone and 9,10-anthraquinone was studied in pyridine, acetone, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide and propylene carbonate. The variation of the E_1/2-values proper for the first electron transfer step (measured against oxidation potential of ferrocene) with the properties of solvent is analyzed in terms of the donor-acceptor concept. Linear correlations of E_1/2 vs. acceptor number are observed; the slopes of corresponding lines correlate with the spin densities at oxygen atoms of semiquinones.     

Solvent hydrogen bonding and structural effects on nucleophilic substitution reactions: Part 3. Reaction of benzenesulfonyl chloride with anilines in benzene/propan‐2‐ol mixtures

Substitution reactions of 13 para‐ and meta‐substituted anilines with benzenesulfonyl chloride in varying mole fractions of benzene in propan‐2‐ol have been investigated conductometrically. The second‐order rate constants correlate well with pK_a values of anilines and with the Hammett's equation. The negative Hammett reaction constant indicates the formation of an electron‐deficient transition state. The rate data correlate satisfactorily with macroscopic solvent parameters such as relative permittivity, ε_r, and polarity, E_T^N. Correlation of rate data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that both the specific and nonspecific solute–solvent interactions influence the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 657–663, 2007     

Tensammetry with accumulation on the hanging mercury drop electrode : Part 5. The behaviour of mixtures of oxyethylated alcohols

The behaviour of the following mixtures of polydispersed oxyethylated alcohols having a well-defined n-alkyl radical was investigated: 18-14/6-14, 18-14/10-14, 18-14/18-10, 18-14/18-6, 18-6/18-10, 6-14/10-14 and 18-6/18-10/18-14 (the first number denotes the number of carbon atoms in the n-alkyl chain, and the second is the number of oxyethylene subunits). The influence of preconcentration potential in the range more negative than - 1.0 V vs. SCE is described in detail. The results are compared with the behaviour of model mixtures of poly(ethylene glycols). The surfactant mixtures 18-14/6-14 and 18-14/10-14 behave similarly to a model mixture of components having sufficiently different properties. Separate peaks for both components appear on the tensammetric curves of the mixtures, but only at certain preconcentration potentials are the peak heights similar to the peak heights for the individual components alone. The behaviour of the 18-14, 18-10 and 18-6 mixtures, in alt combinations, depends strongly on whether premicellar (associated) forms are present in the solution. These premicellar forms are indicated by a common very narrow peak on the tensammetric curves. If the monomeric forms predominate (i.e., at low-total surfactant concentrations) the peak heights for the mixtures are approximately additive after preconcentration at a suitable potential. If premicellar forms predominate (as at total concentrations > 0.1 mg l^?1), the behaviour of the mixtures is a result of competition between the monomeric and premicellar forms in the adsorption process. This behaviour approximates the behaviour of a mixture consisting of sufficiently different components; monomeric forms behave like the first component, and premicellar forms like the second component of the model mixture. For the surfactant mixture 18-14/18-10, which behaves additively under certain conditions, it is possible to determine the total concentration within the range 10-35μgl^?1. The 6-14/10-14 mixture forms a single nonadditive peak.     

Cyclodextrin derivatives in the GC separation of racemic mixtures of volatile compounds: Part IV

This paper reports the chromatographic performance of columns coated with 2,3,6-trimethyl-α-, β-, and γ-cyclodextrins (2,3,6-TriMe-α,- β-, and γ-CD) and their derivatives 2,6-dimethyl-3-trifluoroacetyl-α-, β-, and γ-cyclodextrins (2,6-DiMe-3-TFA-α-, β-, and γ-CD), all six diluted in polysiloxane, for the separation of the enantiomers of volatile compounds. The influence of column length and film thickness on separation is reported. Phenomena related to reproducibility and consistency, over a period of time, of columns prepared with these CD derivatives are also discussed, and a possible solution to some drawbacks reported here is proposed.     

Solubility studies in formamide: II. Solubility product of silver iodate and standard electrode potential of silver—silver iodate electrode in formamide

The solubility and solubility product of silver iodate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. The solubilities in pure formamide are found to be 2.169 × 10^?4, 2.488 × 10^?4, and 2.943 × 10^?4 mole I^?1, respectively, at these temperatures, and the corresponding solubility products are 4.609 × 10^?8, 6.053 × 10^?8, and 8.448 × 10^?8 mole² 1^?2. The standard potential of the Ag_(s)/AgIO_3(s)/IO₃^? electrode has been calculated and found to be 0.2562 V at 25°C. The mean activity coefficients of silver iodate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgIO_3(s)åAg⁺ (solvated) + IO₃^? (solvated) have been calculated at these three temperatures.     

Thermal reactions of lead(IV) chloride complexes in the solid state. Part IV. Thermolysis of alkali metal hexachloroplumbates

Alkali metal hexachloroplumbates of general formula M₂(I)PbCl₆, with M(I) = K, Rb, Cs, undergo thermal decomposition on heating to 700 K. The thermal processes in the solid state have been studied by differential thermal analysis (DTA) and thermogravimetry (TG) with a derivatograph. The thermolysis occurs in one step M₂(I)PbCl₆→2M(I)Cl_(s)+PbCl_2(s)+Cl_2(g) The experimental TG and DTG curves were used to estimate the enthalpy of thermal dissociation. Based on these curves the kinetic parameters of thermolysis have been evaluated. In the linearization procedure of the kinetic equation.

the methods of Freeman and Carroll, Coats and Redfern, Horowitz and Metzger and Gorbachev were applied. Sixteen f(α) functions which describe the primary mechanism of thermal decomposition of solid substances—nucleation, growth of nuclei, phase boundary reactions and diffusion processes—were used in the least squares error analysis. The dehydration of calcium oxalate monohydrate was performed to confirm the validity of the analytical and computational procedures. The differences in values of the kinetic and thermodynamic parameters for hexachloroplumbates thermolyses have been discussed. It was found that K₂PbCl₆ showed atypical thermal properties. This is probably caused by the different crystal structure of K₂PbCl₆ as compared with those of Rb₂PbCl₆ and Cs₂PbCl₆, as well as the abnormal course of its thermolysis. The thermal properties of alkali metal hexachloroplumbates have been compared with those for analogous compounds of the type M₂(I)M(IV)X₆ (M(IV) = Pt, Te, Tc; X = Cl, Br).     

Solubility studies in formamide: III. Solubility product of silver bromate and standard electrode potential of silver—silver bromate electrode in formamide

The solubility and solubility product of silver bromate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. At these temperatures, the solubilities in pure formamide are found to be 1.837 × 10^?2, 1.967 × 10^?2, and 2.092 × 10^?2 moll^?1, respectively, and the corresponding solubility products are 3.375 × 10^?4, 3.869 × 10^?4, and 4.377 × 10^?4 mol² l^?2. The standard potentials of the Ag(s)/AgBrO₃(s)/BrO^?₃ electrode have been calculated and found to be 0.4997, 0.4948, and 0.4892 V, at 25, 30, and 35°C, respectively. The mean activity coefficients of silver bromate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgBrO₃(s) → Ag⁺(solvated) + BrO^?₃(solvated) have been calculated at these three temperatures and compared with those for the process AgIO₃(s) → Ag⁺(solvated) + IO^?₃(solvated) in formamide.     

Solvent extraction study on the hydrolysis of tracer concentration of Po(IV) in chloride solutions

The hydrolysis and chlorocomplex formation of Po(IV) was investigated through solvent extraction with dithizone-carbon tetrachloride solutions. In a 1.0 M (H,Na)Cl solution, a tracer concentration of Po(IV) (about 10⁻¹² M) was found to exist as; Po(OH)₂Cl₄²⁻, Po(OH)₂Cl_3.7^1.7−, Po(OH)₂Cl_3.5^1.5−, Po(OH)_2.1Cl_2.0⁻ and Po(OH)₄ for −log[H⁺] = 0, 1, 2, 3 and 6, respectively. The constants of successive hydrolysis, β₁ = [Po(OH)₃Cl_n¹⁻ⁿ][Po(OH₄]⁻¹[H⁺]⁻¹[Cl⁻¹]⁻ⁿ and β₂ = [Po(OH)₂Cl_n²⁻ⁿ][Po(OH)₄]⁻¹[H⁺]⁻²[Cl⁻]⁻ⁿ were calculated from the distribution ratios obtained, giving the results; log β₁ = 4.6 ± 0.3 and log β₂ = 8.7 ± 0.3. The chemical composition of extracted species was probably PoCl₂(HDz)₂, Po(OH)Cl(HDz)₂ and Po(OH)₂(HDz)₂.     

Solvent effect on the kinetics of oxidation of ferrocyanide by lodate in water-methanol mixtures

Summary The kinetics of oxidation of ferrocyanide by iodate ion in water-methanol solvent mixtures have been studied spectro-photometrically in the range 0.0 to 54wt% methanol, at five different temperatures ranging from 10 °C to 30 °C. The rate of reaction is increased with increasing of the methanol content in the mixture. Thermodynamic activation parameters have been calculated. An appropriate mechanism, consistent with the kinetic results, is suggested.