Cobalt(II,III) oxide

Cobalt(II,III) oxide is a chemical compound. It contains some (1 atom) cobalt in the +2 oxidation state and some (2 atoms) in the +3 oxidation state. Its chemical formula is Co3O4. It contains cobalt and oxide ions.
Properties.
It is a black solid. It reacts with hydrochloric acid to make chlorine and cobalt(II) chloride.
Preparation.
It is made when cobalt(II) oxide is heated to . When it is heated to , it turns back into cobalt(II) oxide.
Uses.
It has been used in research for making hydrogen.
Safety.
It is irritating to the skin. It can cause harm if swallowed. It dissolves in the stomach acid.