Abstract

Justine Gabriel K. Rodrigo and Voltaire G. Organo*

DOI : http://dx.doi.org/10.13005/ojc/360312

A simple colorimetric approach using a universal pH indicator to differentiate inorganic anions according to their relative acidity or basicity is presented. Anions caused changes in the pH of the solution, producing various colors of the universal indicator. Among halides, F- was differentiated from Cl-, Br- and I-. The indicator was also used on conjugate acid-base pair anions to distinguish HCO3- from CO32-, HSO4- from SO42-, HSO3- from SO32-, and various phosphate species. Oxyanions SO32-, HSO3-, ClO-, ClO2- and NO2- can be differentiated from oxyanions with more oxygens attached, namely, SO42-, HSO4-, ClO3-, and NO3-, respectively. Results can be correlated with the acid ionization constant K_a and/or base hydrolysis constant K_b of the anion.

Anion Differentiation; Colorimetric; Ionization Constants; pH; Universal pH Indicator

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