Bromide mediated oxidation of antimony(III) by cerium(IV) in aqueous sulphuric acid medium

Abstract

The micro amount (10⁻³ mol dm⁻³) of bromide mediated oxidation of antimony(III) by cerium(IV) in an aqueous sulphuric acid medium has been studied spectrophotometrically at 25ºC and I = 3.10 mol dm⁻³. In the presence of bromide, one mole of antimony(III) requires two moles of cerium(IV). The reaction is first order with respect to [cerium(IV)] and [bromide], whereas the order with respect to [antimony(III)] is less than unity. Increase in [sulphuric acid] accelerates the reaction rate. The order with respect to [H⁺ ion] is less than unity. Added products, cerium(III) and antimony(V) do not have any significant effect on the rate of reaction. The active species of oxidant is identified as H₃Ce(SO₄)₄⁻, whereas that of reductant as SbBr₂⁺. The possible reaction mechanism is proposed and the activation parameters determined and discussed.