Autoprotolysis constants determination of water-methanol mixtures and solvent effect

The autoprotolysis constants (pKap) of water-methanol mixtures were determined at 25°C over the composition range of 0 to 90 vol. % methanol using potentiometric method with a glass electrode. The electromotive forces (emf) values and titration data of both acidic and basic range for all mixtures were obtained by combined pH electrode that its aqueous KCl solution was replaced with 1M KCl in appropriate mixed solvent saturated with AgCl. In all titrations the ionic strength of each mixture was maintained at 0.1M by appropriate concentration of NaClO4 solution. The pKap values were calculated by titration data for each medium studied at 25°C and under nitrogen atmosphere. The solvent effect and variation of solvent composition on pKap values was perused by different methods.