Copper(II) oxide or copper oxide is an inorganic compound with the chemical formula CuO. Black solid, one of two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral it is called tenorite. It is a product of copper mining and a precursor to many other copper-containing products and compounds. [

It is produced on a large scale through pyrometallurgy as a stage in the extraction of copper from ore. The ore is treated with an aqueous mixture of ammonium carbonate, ammonia, and oxygen to yield copper(I) and copper(II) ammonium complexes, which are then extracted from the solid. These complexes were decomposed with steam to give CuO.

It can be formed by heating copper in air at around 300–800°C:

2 copper + O2 → 2 copper

For laboratory use, pure copper(II) oxide is better prepared by heating copper(II) nitrate, copper(II hydroxide) or basic copper(II carbonate):[4]

2 Cu(NO3)2(s) → 2 CuO(s) + 4 NO2(g) + O2(g) (180°C)

Cu2(OH)2CO3(s) → 2 CuO(s) + CO2(g) + H2O(g)

Cu(OH)2(s) → CuO(s) + H2O(g) [5]

Copper(II) oxide is dissolved in inorganic acids such as hydrochloric acid, sulfuric acid or nitric acid to form the corresponding copper(II) salt:

Cuprous oxide belongs to the monoclinic crystal system. The copper atoms are coordinated by 4 oxygen atoms in an approximately square planar configuration.

An important product of copper mining, copper dioxide is the starting point for the production of other copper salts. For example, many wood preservatives are made from copper oxide.