Reaction of hydrogen peroxide with hexaaquacobalt(III) perchlorate

The reaction of Co(OH2)63+ with H2O2 in 1.0 M HClO4/LiClO4 was found to be first-order in both reactants and the [H+] dependence of the second-order rate constant is given by k2obs = b/[H+], b at 25 °C is 26.4 ± 0.5 s−1. The rate law shows a simple inverse dependence on [H+] that is consistent with a rapidly maintained equilibrium between Co(OH2)63+ and its hydrolyzed form Co(H2O)5(OH)2+, followed by the rate controlling step, i.e. oxidation of H2O2 by Co(H2O)5(OH)2+.

The reaction of Co(OH2)63+ with H2O2 involves a rapidly maintained equilibrium between Co(OH2)63+ and Co(H2O)5(OH)2+ and oxidation of H2O2 by both of these species, followed by the fast terminating steps. The experimental data follows the second-order rate constant.k2obs=k1+k2Ka[H+]A plot of k2obs versus 1/[H+] gives an intercept of k1 and slope of k2Ka. The absence of an intercept in the figure indicates that the k1 pathway does not make a significant contribution.Figure optionsDownload as PowerPoint slide