Cobalt (III) oxide
Cobalt (III) oxide is a compound of cobalt (III) with a formula of Co2O3. It greatly resembles manganese dioxide in its properties, and an inexperienced chemist couldn't even tell them apart without knowing which is which beforehand.
Cobalt (III) oxide is a black powder which is insoluble in water.
It is a somewhat effective oxidizer, it reacts with reducing agents. It does not react with acids or alkalis in aqueous solutions. Again, its properties are almost the same as manganese dioxide. It even has the exact same reaction with hydrogen peroxide.
Cobalt (III) oxide is a component in some types of hopcalites (used in gas masks to protect against carbon monoxide).
It can be made by oxidizing cobalt (II) compounds. Aurora Nikolaeva (Sciencemadness user ave369) prepared it by oxidizing cobalt (II) hydroxide (freshly precipitated) by sodium hypochlorite alkalinized by potassium hydroxide. It precipitates as a fine black powder.
- Make percobaltates
You should treat this compound with the same level of respect as any other heavy metal oxide.
It should be stored in glass containers.
Not much is known about this oxide's danger to the environment, but such danger is likely to exist.