A proposal for an experiment in instrumental analytical chemistry: Spectrophotometric determination of the ionization constant of alizarin red in micellar media

Abstract

Two methods were used to determine the conditional ionization constant of the alizarin red indicator S in different micellar solutions at 25 ^oC, at constant ionic strength. The first method used was the derivation of the maximum absorbance curve of each spectrum as a function of the pH of the various solutions. In the second method, Handesson-Hasselbach linearization was used, in which the maximum absorbance of each spectrum as a function of the pH of the various solutions is also used. The results of both methods show that the ionization constant of this indicator is influenced by the presence of neutral surfactants Triton X-100, cationic SDS and anionic CTAB. The potentiometric and spectrophotometric techniques commonly used in instrumental analytical chemistry, combined with mathematical methods, proved to be efficient in determining parameters in systems in acid-base equilibrium.