Cobalt(III) oxide
Cobalt oxide is the inorganic compound with the formula of Co2O3. Although only two oxides of cobalt are well characterized, CoO and Co3O4, procedures claiming to give Co2O3 have been described. The treatment of Co salts such as cobalt(II) sulfate with an aqueous solution of sodium hypochlorite gives a black solid:
Some formulations of the catalyst hopcalite contain "Co2O3".
Some studies have been unable to synthesize the compound, and report that it is theoretically unstable.
It is soluble in cold diluted sulfuric acid and produces Co23, which is blue in aqueous solution.
Cobalt ion is a strong
oxidizer in acidic solution, its standard electrode potential is +1.84V in this situation.