Thermodynamics of self-ionization of propylene glycol-water mixtures at different temperatures

The autoprotolysis constants (Ks) of propylene glycol (PH)-water mixtures with compositions of 20, 40, 75, and 90 wt % propylene glycol have been determined In the temperature range 15-45 °C by using the cell Pt, H2 (g, 1 atm)|NaS, MBr, propylene glycol-water|AgBr-Ag where NaS Is the sodium lyate of the solvent and M Is Na or K. The experimental results have been expressed as a function of temperature In the form pKs = A/T-D + CT proposed by Named and Robinson and the coefficients A, D, and C have been obtained by the method of least squares. The variation of pKs with solvent composition has been discussed In terms of the properties of the mixed solvents. Thermodynamic quantities such as ΔG°, ΔH°, and ΔS° for the self-lonlzation process have been evaluated at 25 °C and discussed In terms of the structural aspects of the mixed solvents. © 1984, American Chemical Society. All rights reserved.