Mechanistic study of cerium(IV)oxidation of antimony(III)in aqueous sulphuric acid in the presence of micro amounts of manganese(II)by stopped flow technique

摘要

The oxidation of antimony(III)by cerium(IV)has been studied spectrometrically(stopped flow technique)in aqueous sulphuric acid medium.A minute amount of manganese(II)(10~5 mol dm-3)is sufficient to enhance the slow reaction between antimony(III)and cer-ium(IV).The stoichiometry is 1:2,i.e.one mole of antimony(III)requires two moles of cerium(IV).The reaction is first order in both cerium(IV)and manganese(II)concentrations.The order with respect to antimony(IH)concentration is less than unity(ca 0.3).Increase in sulphuric acid concentration decreases the reaction rate.The added sulphate and bisulphate decreases the rate of reaction.The added products cerium(III)and antimony(V)did not have any significant effect on the reaction rate.The active species of oxidant,substrate and catalyst are Ce(SO4)2,[Sb(OH)(HSO4)]~+and[Mn(H2O)4]~(2+),respectively.The activation parameters were determined with respect to the slow step.Possible mechanisms are proposed and reaction constants involved have been determined.