Copper(II) oxide
chemical compound
Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite, or sometimes black copper. It is a product of copper mining and the precursor to many other copper-containing products and chemical compounds.
Structure and physical properties
Copper(II) oxide belongs to the monoclinic crystal system. The copper atom is coordinated by 4 oxygen atoms in an approximately square planar configuration.
The work function of bulk CuO is 5.3 eV.
Production
It is produced on a large scale by pyrometallurgy, as one stage in extracting copper from its ores. The ores are treated with an aqueous mixture of ammonium carbonate, ammonia, and oxygen to ultimately give copper(II) ammine complex carbonates, such as [Cu(NH3)4]CO3. After extraction from the residues and after separation from iron, lead, etc. impurities, the carbonate salt is decomposed with steam to give CuO.
It can be formed by heating copper in air at around 300–800 °C:
2 Cu + O2 → 2 CuO
For laboratory uses, copper(II) oxide is conveniently prepared by pyrolysis of copper(II) nitrate or basic copper(II) carbonate:
2 Cu(NO3)2 → 2 CuO + 4 NO2 + O2 (180°C)
Cu2(OH)2CO3 → 2 CuO + CO2 + H2O
Dehydration of cupric hydroxide has also been demonstrated:
Cu(OH)2 → CuO + H2O
Copper(II) oxide can also be produced, at industrial scales, by chemical precipitation of copper(II) sulfate (CuSO4) with sodium hydroxide (NaOH) to form copper(II) hydroxide, which is then heated at around 250°C to produce CuO.
Uses
As a significant product of copper mining, copper(II) oxide is the starting point for the production of many other copper salts. For example, many wood preservatives are produced from copper oxide.
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