Video: A catalyst in action

The cobalt species are useful catalysts. In this case, the oxidation of the tartrate (2,3-dihydroxybutanedioate) ion is accomplished using hydrogen peroxide with cobalt(II) as a catalyst.
C4O6H42-aq) ® 2 CO2(g) + 2 HCO2-(aq) + 2 H+(aq) + 2 e-
H2O2(aq) + 2 H+(aq) + 2 e- ® 2 H2O(l)
The green intermediate is believed to be a superoxo-bridged dimeric species. Most accounts claim that the final state of the cobalt is cobalt(II) but it is much more likely to be a cobalt(III) species.