Abstract
The kinetics of the reaction 2Mn(III) + H202 — 2Mn(II) + 02 + 2H+ has been studied spectrophotometrieally with a stopped-flow apparatus at 25° in 1.00-3.70 M perchloric acid solutions of ionic strength between 2.23 and 4.90 M. The stoichiometry was determined by measuring the difference in the concentration of one of the reactants before and after reac- tion and by direct analysis of the oxygen produced. For conditions where the initial excess of peroxide was fivefold or less, the ratio of riianganese(III) consumed to hydrogen peroxide consumed had the value of 1.97 ± 0.09; i.e., [ ( )] /
[ 202] = 2, within experimental error. Deviations from this stoichiometry were observed at very high excesses of H202
by direct oxygen analysis (relative error in an individual determination = ±3%). The reciprocal of the observed second-
order rate constant is dependent on [Mn2+]/[Mn(III)]0 and [H202]o/[Mn(III)]o. The rate is independent of ionic strength. The proposed mechanism involves the over-all rate-determining steps
Mn3+ + H202
MnOH2+ + H202
kl
k -j kl'
k -l'
Mn«+ + H202+
Mn2+ + H02 + H20