Electrochemical determination of acidity level and dissociation of formic acid/water mixtures as solvent

The autoprotolysis constant KHS of formic acid/water mixtures as solvent has been calculated from acid–base potentiometric titration curves. A correlation of the acidity scale pKHS of each medium versus pure water has been implemented owing to the Strehlow R0(H+) electrochemical redox function. The results show that formic acid/water mixtures are much more dissociated than pure water; such media are sufficiently dissociated to allow electrochemical measures without addition of an electrolyte. It has also been shown that for a same H+ concentration the activity of protons increases with formic acid concentration. For more than 80 wt.% of formic acid the acidity is sufficiently increased to locate the whole acidity scale pKHS in the super acid medium of the generalized acidity scale pHH2OpHH2O.