Acidity in water-alcohol mixtures

Abstract

Absorption spectra of D. Y. and B. C. G. were measured in various methanol-water mixtures containing a definite volume of acid or base, and absorbances of its absorption spectra were plotted against methanol volume %. The lines came down with methanol concentration, but a minimum point appeared in every case at about 90% and the lines went up again with much increasing methanol concentration.
The similar behaviour also appeared in mixture with ethanol or iso-propanol in place of methanol.
The term, log [(BH⁺)/(B)], represented as H^* in this report, is in proportion to the proton activity. H^* values were calculated from absorption spectra and plotted against organic solvent concentrations.
Then, observed pH values and activity coefficients of hydrogen ion were calculated from these H^* values in methanol-water mixtures.
For instance, activity coefficients in the solution of 0.012 N sulfuric acid were as follows; 1.00(methanol 10%), 0.39(30%), 0.13(50%), 0.04(70%), 0.03(90%) and 0.12(100%).