Estudi cromàtic d'indicadors en solvents no aquosos. Aplicacions volumètriques

Abstract

This paper is a contribution to assess the present state of chemical and chromatic studies of chemical indicators both in aqueous and the mainnonaqueoussolvents. It deals with the theoretical approach and practical procedure to characterize the transition ranges,pH of maximum colour change,optimum concentration for the titration and quality of colour change,as well as the determination of pKa values.Equations defining the transition straight line in complementary chromaticitydiagram and conditions defining the bests creened indicator to be prepared from a given pure acid-base indicator and dyes are also given. The developped parameters and indexes have been applied to the study of indicators in tert-buty land isopropyl alcohols,acetonitrile and anhydrous acetic acid,which are the mainly used solvents to titrate acids and bases or their mixtures.In each of them, aseries of commercial indicators has been stablished that covers the whole useful acidity range.From it, it is possible to select the best indicator for the problemat hand.