Chromium(III)-catalysed oxidation of antimony(III) by alkaline hexacyanoferrate(III) and analysis of chromium(III) in microamounts by a kinetic method

Abstract

The oxidation of antimony(III) by hexacyanoferrate(III) has been studied in alkaline media. A microamount of chromium(III)(10–6 mol dm–3) is sufficient to catalyse the reaction. The active species of catalyst and oxidant in the reaction are understood to be [Cr(OH)4]– and [Fe(CN)6]3–. The autocatalysis exhibited by one of the products, i.e. antimony(V), is attributed to complex formation between antimony(V) and [Fe(CN)6]3–. A composite mechanism and rate law are proposed. The reaction has been utilised for the analysis of chromium(III) in the range 5.2 ng cm–3–1.14 µg cm–3.