Catalytic effects of monolayers of metals deposited at underpotentials: Oxidation of formic acid on platinum

An independent potentiometric method is developed for the determination of autoprotolysis constants of nonaqueous amphiprotic solvents. The data of potentiometric titrations of a weak protolyte (base or acid) with a strong one are used for calculation of both autoprotolysis constant of the solvent and acid—base constant of the protolyte. The calculations are based on the method of least-squares in combination with the “pit-mapping” procedure developed by Sillén. The validity of the method was proved by the determination of the autoprotolysis constant of water. The method has no restriction concerning the strength of the weak protolyte, the latter being its main advantage. The autoprotolysis constants of methanol and ethylene glycol were determined by means of the proposed method too. The obtained values of pK_MeOH=17.00 and pK_EG=15.91 are in a good agreement with some recent data.