Studies on the acidity function H-of solutions of KOH and NaOH in ethanol water-mixtures using m-aminophenol dimer and o-aminophenol polymer as indicators

ABSTRACT

Attempts are made to calculate the value of H- from the spectrophotometrically determined molar extinction coefficients epsilon, epsilon A- and epsilon HA of m-aminophenol polymer and p- aminophenol dimer in solutions of KOH and NaOH in ethanol-water mixtures. The value of these coefficients are then used for the computation of the indicator ratios I of the different indicators in the various solutions. In addition, the pKa, values of the indicators in questions are obtained from [log I-log CoH] plots. The relating H- with medium composition disclose several maxima and minima, the locations of which depends on alkali concentration and identity. The basic strength in water and pure ethanol increases according to the order KOH > NaOH, whereas in ethanol-water mixtures it is a composite function of alkali concentration and medium composition