Standard potentials of silver-silver bromide electrode and related thermodynamic quantities in (5, 10 and 15 wt-%) 2-butanol-water mixtures

The standard potentials of silver-silver bromide electrode in 5, 10 and 15 wt.-% 2-butanol have been determined from e.m.f. measurements of a cell of the type: Pt(or Pd), H₂(g)|HBr(m), 2-butanol-water mixtures| AgBr, Ag at temperatures 15°, 25° and 35°C and in the molality range of HBr from 0.003 to 0.1 mol kg^?1. Standard potentials were utilized to calculate: (1) the standard thermodynamic quantities for the cell reaction and for the reaction of HBr formation, (2) the mean activity coefficients of HBr, and (3) the standard thermodynamic quantities for transfer of HBr from water to 2-butanol-water mixtures. The thermodynamic functions for the transfer process have been interpreted in regard to the acid-base properties and structure of the solvents.     

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 IV. Silver-silver chloride electrode in glycerol-water mixtures

Standard potentials of the silver-silver chloride electrode in eighteen glycerol-water mixtures containing up to 90% by weight glycerol, have been determined from e.m.f. measurements of cells of the type Pt, H₂ (gas, 1 atm); HCl (m), X% glycerol, Y% water; AgCl, Ag, at nine different temperatures in the range 15 to 55°C. The standard molal potential in the various solvent mixtures has been expressed as a function of temperature. Standard thermodynamic quantities for cell reaction and the primary medium effects of various solvents upon HCl were also calculated. The temperature variation of the standard potential was utilized to calculate the thermodynamic quantities for the transfer of one mole of HCl from water to glycerol-water media. The results have been interpreted in regard to the acid-base properties and the structure of the solvent.     

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.     

Thermodynamic studies of hydriodic acid in ethylene glycol-water mixtures from electromotive force measurements

The standard potentials of the Ag—AgI electrode in twenty ethylene glycol—water mixtures covering the whole range of solvent composition have been determined from the e.m.f. measurements of the cell Pt¦H₂(g, 1 atm)¦HOAc (m ₁), NaOAc (m ₂), KI(m ₃), solvent¦AgI¦Ag at nine different temperatures ranging from 15 to 55°C. The temperature variation of the standard e.m.f. has been utilized to compute the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HI, and the standard thermodynamic quantities for the transfer of HI from the standard state in water to the standard states in the respective solvent media. The chemical effects of solvents on the transfer process have been obtained by subtracting the electrostatic contributions from the total transfer quantities. The results have been discussed in the light of ion—solvent interactions as well as the structural changes of the solvents.     

Standard potentials of the silver,silver bromide electrode and the thermodynamic properties of hydrobromic acid in 1,2-dimethoxyethane and its aqueous mixtures

The standard potentials of the silver, silver bromide electrode have been determined in 1,2-dimethoxyethane (DME) and in nineteenDME + water solvents from the e.m.f. measurements of cells of the type Pt|H₂(g, 1 atm)|HBr (m), solvent|AgBr|Ag at intervals of 5°C from 5 to 45°C. The molality of HBr covered the range from 0.01 to 0.1 mol kg^–1. In solvents of highDME content, where the dielectric constant is small, it was necessary to correct for ion-pair formation. The temperature variation of the standard potential has been used to evaluate the standard thermodynamic functions for the cell reaction, and the standard quantities for the transfer of HBr from water to the respective solvents. The results have been discussed both in relation to the acid-base nature of the solvent mixtures and also their structural effects on the transfer process.

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Standardpotentiale der Silber, Silberbromid-Elektrode und thermodynamische Eigenschaften von H Br in 1,2-Dimethoxyethan und 1,2-Dimethoxyethan—Wasser-Mischungen

Zusammenfassung Die Standardpotentiale der Silber, Silberbromid-Elektrode wurden in 1,2-Dimethoxyethan (DME) und in 19 verschiedenenDME—Wasser-Gemischen aus EMK-Messungen der Zelle Pt|H₂(g,1 atm)|HBr (m), Lsgsm.|AgBr|Ag in Temperaturintervallen von 5°C zwischen 5 und 45°C bestimmt. Die Molalität von HBr deckte den Bereich von 0,01 bis 0,1 mol kg^–1. Bei Lösungen mit höheremDME-Gehalt — und damit niedrigen Dielektrizitätskonstanten —war es nötig, für die Bildung von Ionenpaaren eine Korrektur einzuführen. Über die Temperaturvariation wurden die thermodynamischen Größen für die Zellenreaktion und die Standardgrößen für den Transfer von HBr aus Wasser in das jeweilige Lösungsmittel bestimmt. Die Ergebnisse werden sowohl im Zusammenhang zur Säure-Base-Natur de Lösungsmittelmischungen als auch in bezug auf strukturelle Effekte im Transferprozeß diskutiert.

     

Thermodynamics of the silver—silver thiocyanate electrode in urea—water mixtures

E.m.f. measurements on cells of the type Ag(s), AgCNS(s), KCNS(c)//KCl(c), AgCl(s), Ag(s) in four different composition of urea—water mixtures at seven different temperatures from 5 to 35°C have been made to determine the standard potentials of the silver—silver thiocyanate electrode in these media. These values have been used to evaluate the transfer thermodynamic quantities accompanying the transfer of 1 g ion of CNS^? ion from the standard state in water to the standard state in urea—water mixtures.     

Studies on the Equilibria of α-Phthalic and Phosphoric Acids in Mixed Methanol — Water Mixture (50% w/w)

The secondary dissociation constants of α-phthalic and phosphoric acids have been determined in 50% w/w methanol-water mixture from the e.m.f measurements of the cell of the type: Pt; H₂(1 atm), M₂A(m), MHA(m), MCl, AgCl; Ag at different temperatures (288.15–308.15 K) and at different ionic strengths. The thermodynamic values ΔG°, ΔH°, ΔS° for the respective equilibria are estimated. The possibility of using these acids as basis for some buffer solutions in 50% methanol – water mixture is discussed.     

Determination of the standard molar Gibbs energy of formation of calcium zirconate by a galvanic cell involving calcium-ion conducting solid electrolyte

The standard molar Gibbs energy of formation of CaZrO₃from CaO andZrO₂ has been determined by the e.m.f. measurements of a galvanic cell with calcium-ion conducting solid-state electrolyte in the temperature range 1073 K to 1273 K. The average values of the standard enthalpy and the standard entropy in the temperature range covered by the e.m.f. measurements have also been estimated. The results have been compared with those obtained by other authors.     

Assignment of standard pH values [pH*(s)] to buffers in 50 mass % methanol + water from 288.15 to 308.15 K

The secondary dissociation constants of o-phthalic and phosphoric acids have been determined in methanol + water (50 mass %) from reversible e.m.f. measurements of the cell of the type: Pt, H(2)(1 atm)|M(2)A(m), MHA(m), MCl|AgCl; Ag at different temperatures (288.15-308.15 K) and at different ionic strengths. To minimize the unsteadiness in potential measurements palladium coated platinum electrodes have been used. The large set of such e.m.f. values has been analyzed in terms of a multi-linear regression method recommended in recent IUPAC documents. The thermodynamic values DeltaG degrees , DeltaH degrees and DeltaS degrees , for the respective equilibria, were estimated. Standard pH values [pH*(s)] have been assigned to buffers in methanol + water (50 mass %) at temperatures between 288.15 and 308.15 K.     

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.     

Thermodynamic properties of the silver ion in alcohol + water solvent mixtures from electromotive force measurements and thermodynamic solubility product constants of AgX (X = Cl,Br, I or CNS) at different temperatures

The standard potentials of the silver-silver ion electrode in alcohol+water solvent mixtures containing 10 and 20 wt% methanol, ethanol, 1-propanol and 2-propanol have been determined from the electromotive force measurements of the cell Ag(s), AgCl(s), NaCl(c), NaNO₃(c)// NaNO₃(c), AgNO₃(c), Ag(s) at seven different temperatures in the range 5–35°C. The standard potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the electrode reaction, the primary medium effects of various solvents upon Ag⁺, and the standard thermodynamic quantities for the transfer of 1 g-ion of Ag⁺ from water to the respective alcohol + water media have been evaluated and discussed in the light of ion-solvent interactions as well as the structural changes of the solvents. From the values of the standard potentials of the Ag/Ag⁺ and Ag/AgX, X^? electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide, silver iodide and silver thiocyanate have been determined in alcohol + water solvent mixtures at different temperatures.     

The standard Gibbs free energy of formation of calcium chromium (III) oxide in the temperature range (1073 to 1273) K

The standard molar Gibbs free energy of formation of CaCr₂O₄ from CaO and Cr₂O₃ has been determined by the e.m.f. measurement of galvanic cells involving a single crystal CaF₂ and a polycrystalline CaZrO₃ solid-state electrolytes in the temperature range (1073 to 1273) K. Reproducible e.m.f. values were obtained. The average values of the standard molar enthalpy and the standard molar entropy in the temperature range covered by the e.m.f. measurements have been also estimated. The results have been compared with those obtained by other authors.     

Determination of the standard Gibbs free energies of formation of barium zirconates in the temperature range (1073 to 1273) K

The standard molar Gibbs free energies of formation of BaZrO₃, and Ba₂ZrO₄ have been determined by solid-state galvanic cells involving a single crystal CaF₂ as a solid-state electrolyte. The e.m.f. measurements were performed in the temperature range (1073 to 1273) K. The average values of the standard molar enthalpy and the standard molar entropy of formation in the temperature range covered by the e.m.f. measurements have been also estimated. The results have been compared with those obtained by other authors.     

Osmotic coefficients and activity coefficients of aqueous hydrobromic acid solutions at 25°C

The osmotic coefficients ? and activity coefficients γ_± of aqueous solutions of HBr depend largely on emf measurements utilizing the silver-silver bromide electrode. There is evidence, however, that side reactions between AgBr and bromide ion render this electrode unreliable when the HBr molality (m) exceeds 2 mol-kg^?1. It is shown, however, that the isopiestic vapor-pressure technique is capable of yielding data for HBr at higher molalities. New emf measurements of cells with hydrogen and AgBr/Ag electrodes at 25°C have been combined with literature data to recommend values for the activity coefficients of HBr in the dilute range. These have been supplemented by isopiestic measurements vs. NaCl and CaCl₂ reference solutions in the range of HBr molalities from 0.7 to 6.2m. A table of ? and γ_± at 25°C at round molalities from 0.005 to 6.0 is presented.     

Thermodynamics of hydrochloric acid in (1-propanol+water) from electromotive-force measurements

The standard electromotive force of the cell: PtH₂(g)|HCl(m) in solvent |AgCl|Ag has been determined at 9 different temperatures ranging from 288.15 to 328.15 K in 20 (propan-1-ol+water) mixtures covering the whole range of solvent composition, by an extrapolation method making use of the extended terms of the Debye-Hückel theory. In solvents of high alcohol content, where the dielectric constant is small, it was necessary to correct for ion-pair formation. The temperature variation of the standard e.m.f. was used to calculate the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HCl, and the standard quantities for the transfer of HCl from the standard state in water to the standard states in each other solvent. The significance of the transfer functions is discussed in relation to the acid-base strength, as well as the structural features of the solvents.     

Bildung siliciumorganischer Verbindungen. XXXIII. Reaktion des 1,1,3,3-Tetramethyl-1,3-disila-4-trimethylsilyl-cyclopentens mit HBr

The ring system of (a), defined in “Inhaltsübersicht”, is cleaved by one mole of HBr already at ?78°C, forming mainly (b) besides (c) and (d). At 80°C (b) reacts by β-elimination completely to (e), (f), (g) and (h). As one of the products by the reaction of (a) with 4 moles of HBr (i) is formed by cleavage of (b) with HBr. The course of the reaction at —78°C is determined by ring cleavage and following HBr addition. With increasing temperature β-elimination of the addition products becomes the preferred reaction. To explain the reaction course the intermediate product (c) has been synthetized and its decomposition with HBr has been investigated. The reaction products have been identified by n.m.r. spectra.     

Selective separation of gold from iron ore samples using ion exchange resin

Gold in iron ore samples is separated from iron (major matrix cation), antimony and vanadium using anion exchange resin in (0.2 M) HBr, potassium peroxodisulfate and acetone:water:nitric acid media. The exchangeable anion Cl⁻ of the ion exchanger Dowex 1X 4 is replaced by Br⁻ using (6 M) HBr solution. Certified reference material DGP-M1, spiked ferric magnetic oxide, gold radioactive tracer ¹⁹⁸Au and gold standard solutions are used to study the adsorption efficiency and the yield recovery of tetrabromoaurate AuBr₄⁻ from the resin. Ten eluents have been tried to elute gold from the column, and it has been found that a 10 ml potassium peroxodisulfate and 240 ml acetone:water:nitric acid [125:5:5] solution fulfills the objective. The set up of the separation procedure allows quantitative adsorption of gold by the resin, while the major matrix cation (Fe) and others (Cd, Ag, Cu, V, Sb, Ti) have been passed through the column with the feeding solution (0.2 M) HBr. The resin selectivity coefficient (K) of separating Au from Fe has been found to be K_Fe^Au≈6.4×10¹¹. The eluted Au is treated with K₂S₂O₈ and H₂O₂ for spectrophotometric determination as rhodamine-B complex at 555.6 nm. The linearity, detection limit, precision, and accuracy of the determination method have been found to be up to 2.0 μg g⁻¹, 0.018 μg g⁻¹, 0.009 μg g⁻¹ and 3%, respectively.     

Standard pH values for phosphate buffer reference solutions in acetonitrile-water mixtures up to 50% (m/m)

Reference pH_ps values for 0.025 mol/kg potassium dihydrogen phosphate + 0.025 mol/kg disodium hydrogen phosphate primary standard buffer solutions in 10, 30, 40 and 50% (m/m) acetonitrile-water mixtures at 298.15 K have been determined from reversible e.m.f. measurements of the cell Pt/Ag/AgCl/primary standard buffer + KCl in acetonitrile-water/glass electrode. The consistency of the results is confirmed by multilinear regression analysis of the pH_ps values obtained for each solution composition. Considering the high number of possible acetonitrile-water mixtures, the methodology of linear solvation energy relationships (LSER) was applied and pH_ps data have been correlated with the Kamlet-Taft solvatochromic parameters of the acetonitrile-water mixtures over the whole of the experimental range.     

Absolute electrode potential and thermodynamics of single ions

A new method, relating the electrode potential to the radius of the solvated ion on whose activity the potential depends, has been developed for the determination of absolute electrode potentials and the thermodynamics of single ions in solution. It is successfully applied to the cells: Pt|H₂(g, 1 atm)|HX, solvent |AgX|Ag, and M|MX, solvent|AgX|Ag, in aqueous, partially aqueous, and non-aqueous solvents. The absolute electrode potentials have been computed in aqueous and methanol+water solvents. The single ion activities, activity coefficients, the radii of solvated cations, and their solvation extent have been calculated. The temperature variation of the standard absolute potential has been utilized to evaluate the standard thermodynamic functions for the electrode reactions, and the standard transfer thermodynamic quantities of single ions from water to methanolic solvents. The results are interpreted in terms of ion—solvent interactions as well as the structural features and the acid—base properties of these solvents.