Determination of dissociation parameters of weak acids in different media according to the isohydric method

The isohydricity (pH constancy) principle is referred to the pair of solutions: weak acid (HL, C0 mol/L) and strong acid (HB, C mol/L) when mixed e.g., according to titrimetric mode. Such a case takes place if the relation C0 = C + C2 × 10pK1 is valid, where pK1 = −log K1, K1 – dissociation constant for a weak monoprotic acid HL. This principle, outlined and formulated in earlier paper (Michałowski et al., Talanta 82 (2010) 1965), is the basis for a sensitive method of pK1 determination, confirmed for a series of weak acids in presence of basal electrolytes or in water + organic solvent (dimethyl sulphoxide, methanol, isopropanol) media. The results of titrations were elaborated according to principles of regression analysis, with use of least squares method. A new criterion for precision of the results obtained according to this method is formulated. The pK1 values obtained are comparable with ones found in literature.