Standard potentials of the silver—silver bromide electrode in dioxane—water mixtures and related thermodynamic functions

The standard potentials of AgAgBr electrode in eighteen dioxane + water solvent mixtures containing up to 90 wt % dioxane, have been evaluated from the emf measurements of the cell Pt, H₂ (g, 1 atm); HBr (m), X % dioxane, Y % water: AgBr, Ag at nine different temperatures in the range 15–55°C. 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 HBr and the standard thermodynamic quantities for the transfer of one mole of HBr from water to the respective dioxane + water media have been computed and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents.     

Thermodynamic properties of hydrobromic acid in 5 wt% 1-butanol-water,and 5 wt% 2-methyl-1-propanol-water-mixture from emf measurements

From the electromotive force measurements of the cell Pt (or Pd), H₂(g)|HBr(m), 5 wt% alcohol-water mixture|AgBrAg for different m in the temperature range from 288.15 to 308.15 K, the standard potential of AgAgBr electrode has been determined in the mixture where alcohol was 1-butanol and 2-methyl-1-propanol. The standard thermodynamic quantities for cell reaction and for HBr formation, the activity coefficients of HBr, and the standard thermodynamic quantities for the transfer of HBr from water to mixed solvents have been evaluated. The transfer functions were compared with those for water mixtures of other isomeric butanols as well as for the mixture with small proportions of other alcohols.     

Thermodynamic studies of sodium bromide in 2-propanol—water mixtures (10, 30 and 50 wt.%) from electromotive force measurements

The emf of the cell: Pt|Na(Hg)|NaBr(m), w wt.% 2-propanol—water mixture|AgBr, Ag has been measured with w = 10, 30 and 50 at temperatures of 293.15, 303.15 and 313.15 K in the molality range of NaBr from 0.04 to 0.18 mol kg^?1. From these data the standard emf of the cell has been obtained and by utilizing data from the literature for the E⁰ of Ag/AgBr electrode the standard potential of sodium amalgam electrode has been determined. Mean activity coefficients of NaBr and thermodynamic functions ΔG⁰_t, ΔH⁰_t and ΔS⁰_t for transfer of NaBr from water to 2-propanol—water mixtures have also been calculated. Thermodynamic quantities of transfer have been compared to those for the HBr electrolyte.     

Thermodynamic studies of Hydrobromic acid in acetonewater mixtures (10, 30 and 50 wt-%) from electromotive force measurements

The emf of the cell: Pd,H₂(g)/HBr(m), x wt-% acetonewater mixture/AgBr,Ag was measured with x = 10, 30 and 50 at temperatures 15, 25 and 35°C in the molality range for HBr from 0.003 to 0.1 mol kg^?1. From these data the standard potentials for Ag|AgBr electrode are obtained, and used in calculations of: (a) the standard thermodynamic quantities for the cell reaction and the reaction of HBr formation, (b) the mean activity coefficients of HBr, (c) the primary medium effect, and (d) the standard thermodynamic quantities for transfer of HBr from water to the acetonewater mixed solvents. On the basis of the values obtained under (d), the spontaneity of transfer the process for HBr is discussed, the acid—base properties of mixed solvents and their structure.     

Thermodynamic properties of hydrobromic acid in ethanol + water solvent mixtures from electromotive force measurements at 15–55°C

From the electromotive force measurements of cells of the type: Pt, H₂ (gas, 1 atm); HBr (m), ethanol + water solvent mixtures; AgBr, Ag, at nine different temperatures in the range 15–55°C and in the molality range of HBr from 0.005 to 0.1 mol kg^?1, the standard potentials of silver—silver bromide electrode have been determined in twenty ethanol + water solvent mixtures covering the whole range of solvent composition. The temperature variation of the standard potential was utilized to calculate the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr, and the standard quantities for the transfer of HBr from the standard state in water to the standard states in the respective solvent media. The results have been interpreted in regard to the acid-base properties and structure of the solvents.     

Thermodynamics of hydrochloric acid in tetrahydrofuran-water mixtures

From the emf measurements of the cell Pt, H₂ (g, 1 atm):HCl (m), X% tetrahydrofuran, Y% water: AgCl, Ag the standard potentials of AgAgCl electrode have been determined in eighteen tetrahydrofuran-water mixtures at nine different temperatures in the range 15–55°C. The temperature variation of the standard emf was utilized to calculate the standard thermodynamic functions for the cell reaction and the standard thermodynamic quantities for the transfer of one mole of HCl from water to tetrahydrofuran-water media. The primary medium effects of various solvents upon HCl were also calculated. The results have been interpreted in regard to the acid-base properties and the structure of the solvent.     

Thermodynamics of the silver—silver chromate electrode in water + 10, + 20, + 30 and + 40 mass percent of dioxane at different temperatures

The emf of the cell: Ag, AgCl, NaCl(m)?Na₂CrO₄(m/2), Ag₂CrO₄, Ag in water + 10, + 20, + 30, and + 40 mass percent of dioxane has been measured at 5°C intervals over the temperature range 15–45°C. The values of the standard potentials of the silver—silver chromate electrode have been determined in these mixed solvent media at these temperatures. The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reaction in water + dioxane mixtures have been evaluated at these temperatures. The results are discussed in terms of the preferential solvation of the ions.     

Thermodynamic properties of copper sulphate in urea + water mixtures from EMF measurements

Electromotive force measurements of the cell, Cu-Hg/CuSO₄(m), urea + water mixtures/Hg₂SO₄(s)/Hg have been done in four different compositions of urea + water mixtures at 303, 308, 313 and 318 K. These have been utilized to evaluate the standard potentials of the cell, the mean activity coefficient of copper sulphate (molal scale) and transfer energetics (ΔG⁰_t, ΔS⁰_t and ΔH⁰_t) of copper sulphate from water to the respective urea + water mixtures (11.52, 20.31, 29.64 and 36.83 wt. % of urea). The transfer energetics have been explained in the light of ion-solvent interactions and structural contributions of solvents.     

Standard potentials of the silver/silver-iodide electrode in aqueous mixtures of ethylene glycol at different temperatures and the thermodynamics of transfer of hydrogen halides from water to glycolic media

The standard potentials (E°) of the silver/silver-iodide electrode in aqueous mixtures of ethylene glycol (containing 10, 30, 50, 70 and 90 wt-% glycol) have been determined from emf measurements of the cell Pt, H₂(g, 1 atm)/HOAc(m₁), NaOAc(m₂), Kl(m₃), solvent/AgI/Ag at nine temperatures ranging from 5 to 45°C. These E° values have been utilized to compute free energy (Δt_t°), entropy (ΔS_t°) and enthalpy (ΔH_t°) changes accompanying the transfer of HI from water to each of the solvents. These values as well as those for HCl and HBr and obtained earlier have also been utilized to evaluate ΔS_t°(i) for individual ions by a method of ‘simultaneous extrapolation,’ which in turn furnished the values of ΔH_t°(i) for these ions. These quantities and also the ‘chemical’ contributions for the halide ions as obtained by subtracting the ‘electrostatic’ contribution computed with the Born equation, have been examined in the light of ion—solvent interactions as well as the structural changes of the solvents. The observed results conform with what is expected from the competitive effects of the preferential solvating capacities of water towards halide ions and that of other solvents towards hydrogen ions, and also of the effects arising from the structural changes of the solvents that are likely to occur in the over-all transfer process.     

Excess molar enthalpies of ternary and constituent binary systems {1,2-dichloropropane+2-propanol+2-butanol} at T=298.15 K

Ternary excess molar enthalpies at T=298.15 K and P=101.3 kPa for the system of {1,2-dichloropropane+2-propanol+2-butanol} and their constituent binary systems {1,2-DCP+2-propanol}, {1,2-DCP+2-butanol}, and {2-propanol+2-butanol} have been measured over the whole composition range using an isothermal micro-calorimeter with flow-mixing cell. All of the binary and ternary systems, including three pseudobinary systems, show endothermic behavior except for the binary mixture {2-propanol+2-butanol}, which shows small exothermicity. The Redlich-Kister equation was used to correlate the binary H _{m, ij} ^E data, and the Morris equation to correlate the ternary H _{m, 123} ^E data. Comparisons between the Morris and Radojkovi equations for the prediction of H _m,123 ^E have been also made. The experimental results have been qualitatively discussed in terms of self-association, isomeric effect and chain length among molecules.     

Ion—solvent interactions in acetonitrile + water mixtures

Standard Gibbs energies of transfer, ΔG°_t of alkali metal chlorides (M = Li, Na, K, Rb and Cs) and potassium bromide and iodide from water to the aqueous mixtures of 20, 40, 60 and 80 mass per cents of acetonitrile (ACN) have been determined at 25°C from emf measurements performed on the double cell comprising AgAg X and M (Hg) electrodes. The individual ionic contributions to ΔG°_t have also been evaluated using the reference electrolyte (RE = Ph₄AsBPh₄) method, the required ΔG°_t's of the RE being obtained from the measured solubilities of salts viz. Ph₄AsPic, KBPh₄ and KPic (Pic = picrate and Ph = phenyl). The observed increasing ΔG°_t values of the halide ions X^? and their order Cl^? ? Br^? ? I^? furnish the thermodynamic evvidence for the effect of the well known decreased H-bonding and the anion destabilizing propensities of dipolar aprotic cosolvent ACN. But the observed shallow minima in ΔG°_t-composition profiles for M⁺ and H⁺ are indicative of the result of the oppositg effects of water structure breaking propensities and the protophobic character of ACN and their relative order is the combined effects of acid—base, Born-type and soft—soft interactions. Moreover, while the distinctly pronounced stabilization of large tetraphenyl ionshas been ascribed as the combined effects of dispersion and cavity-forming interactions, the less pronounced solvation of Pic^? has been attributed to the combined effects of increased dispersion interactions of benzene nucleus and of decreased H-bonding interactions of O-atoms of the substituents. These contentions have been further substantiated by comparing ΔG°_t(i) values of some selected ions in ethylene glycol—water mixtures.     

Solutions of iodic acid in formamide. Thermodynamic properties from electromotive force measurements

Electromotive force measurements on cells without liquid junction have been used to determine pK_a of iodic acid and the standard electrode potentials (E°) of the silver-silver iodate electrode in formamide at 9 temperatures from 5–45°C. The pK_a was evaluated by using the Debye-Huckel theory with an ion-size parameter of 5.5 A°. The change in the standard electrode potentials is given as a function of temperature, t°C by the equation E°_t = 0.2786 - 8.125 x 10^?4(t - 25) - 6.385 x 10^?6(t - 25)² The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reactions have been evaluated for different temperatures.     

Thermodynamics of hydrochloric acid in dioxane—water mixtures

From the emf measurements of the cell H₂¦Cl¦AgCl¦Ag the standard potentials (IUPAC convention) of AgAgCl electrode have been determined in 10, 30, 40 and 60 wt% of dioxanewater media at 25, 30, 40 and 45°C, together with the activity coefficients of HCl in the same media. The relevant thermodynamic functions for hydrochloric acid in the same media were also calculated.     

Solution of hydrochloric acid in formamide—V. Thermodynamic properties from EMF of the cell Pt,H2|HCl(m)|Hg2Cl2, Hg over a temperature range 5–55°C (278.15–328.15 K)

The emf of cells (A) Pt, H₂|HCl(m)|Hg₂Cl₂, Hg and (C). AgAgCl|HCl(m)|Hg₂Cl₂, Hg have been measured at intervals of 5°C over the temperature range 5–55°C (278.15–328.15 K) using formamide as the solvent. The molal standard potentials of Hg, Hg₂Cl₂ electrode, determined on the basis of emf data of cell (A), agree well with those derived from the emf of cell (C) using known values of E⁰_Ag-AgCl reported earlier. Based on emf data of these cells, the standard thermodynamic changes ΔG⁰, ΔH⁰ and ΔS⁰ for the cell reactions as well as the mean molal activity coefficients of HCl at rounded molalities have been determined.     

Standard pH values for potassium hydrogenphthalate reference buffer solutions in acetonitrile—water mixtures up to 70 wt% at various temperatures

Reference value standards, pHs, for 0.05 mol kg⁻¹ potassium hydrogenphthalate (KHPh) reference buffer solutions in 30, 50 and 70 wt% acetonitrile—water mixed solvents at temperatures from 288.15 to 308.15 K have been determined from emf measurements of the reversible cell Pt|Ag|AgCl|KHPh + KCl|Quinhydrone|Pt, in which the H⁺-reversible quinhydrone electrode replaces the ill-behaving hydrogen electrode. Values of the first ionization constant of the o-phthalic acid (H₂Ph; benzene-1,2 dicarboxylic acid) in these mixed solvents have also been determined from analogous measurements. The consistency of the present results with the previously determined pHs values in 5, 15 and 30 wt% acetonitrile—water mixtures is analysed by multilinear regression of pHs as a function of both solution composition and temperature. These smoothed standard pHs values are used to optimize the parameters of an equation predicting pHs values in different aqueous organic solvents.     

Ionic solvation—I. Free energies of transfer of copper(II) ion from water to alcohols and to their mixtures with water

The emf of the cell: Cu|Cu²⁺ in water||Cu²⁺ in water + alcohol|Cu for different alcohols (methanol, ethanol, 1-propanol, 2-propanol, t-butanol, ethylene glycol, propylene glycol and glycerol) and their mixtures with water have been measured at 25°C. These data were used for calculation of Gibbs free energies of transfer of copper(II) ion from water to nonaqueous alcohols and to their mixtures with water, with the help of negligible liquid junction potential assumption. Determined free energies of transfer are positive for all solvents studied, which may be simply interpreted assuming that copper(II)ion interacts more strongly with water molecules than with alcohol molecules, without reference to any special structural properties of these solvents.     

Studies in isodielectric media Part—I. Standard potentials of the silver—silver chloride electrode in dimethyl formamide + ethylene glycol mixtures at 25°C

Standard potentials (_sE^s) of the silver—silver chloride electrode have been determined at 25°C in some approximately isodielectric media containing ethylene glycol (EG) and 10, 30 and 50% by weight of N-N-dimethyl formamide (DMF) from emf measurements performed on the cell: H₂ (g, 1 atm)/HCl (m). solvent/AgClAg. From these values the activity coefficients (^s_sγ) of HCl at several concentration in each of the mixed solvents and the standard Gibbs energies of transfer (ΔG⁰_t) of HCl from EG to the mixed solvents have been computed. Comparison of the observed ΔG⁰_t (HCl)-composition profile with those for three other related solvent systems studied earlier, reveals that the observed profile results from the opposing effects of the larger proton-accepting and the pronounced anion-desolvating propensities of DMF and its glycolic mixtures compared to pure EG and that the increased stabilization of proton is superseded by the increased desolvation of Cl^? at higher proportions of DMF.     

Mercury-mercurous propionate electrode: standard potentials at different temperatures and related thermodynamic quantities in dioxan-water media

The standard molal potentials (E°_m/V) of the Hg/Hg₂(OPr)₂, OPr^? electrode at 15, 20, 25, 30 and 35°C have been determined in dioxan-water media. The values of E°_m as a function of the Celsius temperature, t, in different solvent composition may be represented by the following equations:

The related thermodynamic quantities have been calculated. The dependence of the standard potentials at 25°C on the dielectric constant of the media (in the light of the Born equation), the volume fraction (Φ_w) and the mole fraction (N_w) of water (based on Feakins-French relationship) have been examined. The variation of the thermodynamic quantities ΔG°, ΔS° and ΔH° with various parameters associated with solvent media have also been examined. The observations are similar to those reported in our previous work on mercury-mercurous acetate electrode in the same media. ΔC°_p for the cell reaction has been calculated.     

Thermodynamic studies with silver—silver thiocyanate electrodes: transfer of (H+ SCN−) from aqueous to dioxane—water solutions

Electromotive force measurements of the cell:

have been made at 15, 25, 35 and 45°C for solvent compositions X = 10, 20, 30 and 40% (w/w) of dioxane. These have been used to evaluate the standard potentials of the cell and various thermodynamic functions for the transfer of (H⁺ SCN^?) from water to the respective dioxane—water media. The standard free energy of transfer values along with those for halogen acids are briefly discussed in relation to ion solvation.     

Thermodynamic studies of zinc chloride in mixed aqueous solvents from electromotive force measurements—II. Dioxan,acetone and acetic acid mixtures with water

From the emf measurements of the cell Pt/Zn(Hg)/ZnCl₂, H₂O, organic co-solvent/AgCl/Ag the standard emf of the cell have been determined for dioxan (10,20 and 30 wt%), acetone (10, 20 and 30 wt%) and acetic acid (10, 20, 30, 50, 70 and 90 wt%) mixtures with water at 298 K. These data were used in calculations of: (a) the mean activity coefficients of zinc chloride (b) the primary medium effect (c) the standard Gibbs energies of transfer of zinc chloride from water to mixed solvents. The standard Gibbs energies for the transfer process have been interpreted in regard to the acid-base (in Lewis meaning) properties of the water molecules in mixed solvents.