Acid-Base Equilibria in Glacial Acetic Acid. V. The Effect of Water on Potentiometric and Indicator End-Points in Acid-Base Titrations in Acetic Acid

The effect of water on acid-base equilibria in acetic acid can be calculated quantitatively for titrations carried out potentiometrically or with indicators. The equations governing the shape of potentiometric titration lines of bases in acetic acid as a function of water concentration have been derived and experimentally verified. These relationships have been used to calculate the change in e.m.f. in the vicinity of, at and after the equivalence point for bases of different concentration and strength. They predict that titration to an equivalence potential, which is independent of concentration of base, will be an accurate procedure. The relationships determining the ratio of acid to basic color of an indicator base over the titration range in water containing acetic acid also have been established and tested and used to predict the color change of p-naphtholbenzein (PNB) in a sodium perchlorate solution.