Thermodynamics of Hydrogen Chloride in Propylene Glycol-Water Mixtures from Electromotive Force Measurements

The standard potentials of Ag-AgCI electrodes In propylene glycol (PG)-water mixtures In the composition range 20-90 wt % propylene glycol have been determined from 15 to 45 °C by emf measurements using the cell Pt,H2(g, 1 atm)/HCI(m),propylene glycol(x)-water(y)|AgCI-Ag. The primary medium effects and the mean molal activity coefficients, In the concentration range 0.005-0.05 mol kg”1 at 25 °C, have been evaluated. The standard molal potential tEm o has been expressed as a function of temperature. The thermodynamic parameters for transfer of HCI from water to propylene glycol-water mixtures have been calculated from emf data at 25 °C on the mole fraction scale. The transfer energies of hydrogen and chloride Ions have also been determined by employing the ferrocene reference method. The significance of the various thermodynamic quantities associated with the transfer process has been discussed. From the slope of the linear plot between ΔGtoc and log øw (øw = volume fraction of water), In the various solvent mixtures, n, the number of water molecules coordinated to HCI, was evaluated. © 1983, American Chemical Society. All rights reserved.