Mixed solvent water AgBr

Electromotive Forces and Thermodynamic Functions of the Cell Pt, H2 HBr(m), X% Alcohol, Y% Water AgBr-Ag in Pure and Mixed Solvents... 

Electromotive force measurements of the cell Pt, H2 HBr(m), X% alcohol, Y% water AgBr-Ag were made at 25°, 35°, and 45°C in the following solvent systems (1) water, (2) water-ethanol (30%, 60%, 90%, 99% ethanol), (3) anhydrous ethanol, (4) water-tert-butanol (30%, 60%, 91% and 99% tert-butanol), and (5) anhydrous tert-butanol. Calculations of standard cell potential were made using the Debye-Huckel theory as extended by Gronwall, LaMer, and Sandved. Gibbs free energy, enthalpy, entropy changes, and mean ionic activity coefficients were calculated for each solvent mixture and temperature. Relationships of the stand-ard potentials and thermodynamic functons with respect to solvent compositions in the two mixed-solvent systems and the pure solvents were discussed. 

The values of E, log y , Mxy> A, and B from Equations 5-10 substituted into Equation 4, make it possible to calculate Em0 at known molalities of hydrobromic acid, solvent compositions, and temperatures. By plotting values of Em° at a given solvent composition and temperature vs. molality, one can find the standard electrode potential E° of the Ag-AgBr electrode at that solvent composition and temperature from the value of Em° extrapolated to infinite dilution. This method has been used successfully in water and in organic solvent-water mixtures of higher dielectric constants, but if the mixed solvents have low dielectric constants, ca. 50 or below, the curvatures of the Em0f vs. m plots are sufficient to prevent accurate determinations of Em0 and hence of E°. 

The method of autoprotolysis constant value determination based on electromotive force measurement in galvanic element composed from Pt,H2(l atm) KOH(m), KBr(m), solvent AgBr,Ag was proposed elsewhere. The method was used for polythermal study of autoprotolysis constant of binary mixed solvent 2-methoxyetanol - water. On the basis of ionization constants, polytherms data, and the autoprotolysis process, thermodynamic data were calculated. 

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