Cuprous Compounds

Compounds in which the copper appears as monovalent are numerous, although the corresponding monovalent cuprion, Cu^•, is scarcely known. In other words, compounds belonging to such a monovalent series are known in the solid state, but not, in a state of purity, in solution.

In the oxidation of heated copper in the air, a red oxide is first formed, the composition of which is Cu₂O, and which is therefore called cuprous oxide. On being further heated in the air, it is converted into black cupric oxide; on removing this black coating, however, from a piece of oxidised copper, it is found to be generally red coloured on the side next the metal, i.e. to consist of cuprous oxide.

The corresponding cuprous hydroxide, Cu₂(OH)₂, or Cu(OH), is obtained as a brick-red powder by the decomposition of cuprous chloride, to be presently mentioned, with caustic potash or soda.

In nature cuprous oxide occurs as red copper ore, and is a very highly valued ore on account of its richness in copper; it can readily be converted into metallic copper by reduction with charcoal.

Cuprous oxide is also formed as the product of reduction of Fehling's solution with grape-sugar and similar substances, and can be prepared in this way. In moist air it is oxidised to cupric oxide or to basic carbonate.

On treating cupric oxide or hydroxide with acids, not the corresponding cuprous, but the cupric salts are generally formed, and half of the copper is deposited in the metallic state as a blackish-red powder. With sulphuric acid, for example, the reaction takes place according to the equation Cu₂O + H₂SO₄ = Cu + CuSO₄ + H₂O. On considering the ions the process can be interpreted as taking place in such a way that cuprous sulphate is first formed, the monocuprion of which, however, immediately undergoes transformation into dicuprion and metallic copper: 2Cu^• = Cu^•• + Cu. The solution contains dicuprion to a preponderating extent, but it is in accordance with the general relations to assume that it is a case of chemical equilibrium between the two ions and the metallic copper, in which a large concentration of dicuprion is opposed by a very slight concentration of monocuprion.

If instead of sulphuric acid a halogen hydracid, thiocyanic acid, or some other acid which can form a very sparingly soluble cuprous salt, is taken, the above decomposition does not take place, and the respective cuprous compounds are formed. This is explained by the fact that monocuprion is present only in a negligibly small amount in the solution produced, since, of course, the salts are sparingly soluble. The decomposition of monocuprion into dicuprion and metal can therefore take place only to an inappreciably slight extent.

Cuprous hydride, CuH
Cuprous fluoride, CuF
Cuprous chloride, CuCl
Cuprous bromide, CuBr
Cuprous iodide, CuI
Cuprous oxide, Cu₂O
Cuprous hydroxide, CuOH
Cuprous sulphide, Cu₂S
Cuprous sulphite, Cu₂SO₃
Cuprous sulphate, Cu₂SO₄
Cuprous selenide, Cu₂Se
Cuprous telluride, Cu₂Te
Cuprous nitride, Cu₃N
Cuprous phosphide, Cu₃P
Cuprous arsenides
Cuprous carbide Cu₂C₂
Cuprous acetylide, Cu₂C₂
Cuprous carbonate Cu₂CO₃
Cuprous cyanide, CuCN
Cuprous thiocyanate, CuCNS
Cuprous silicide, Cu₄Si
Cuprous silicofluoride, Cu₂SiF₆
Carbonyl cuprous sulphate, (CuCO)₂SO₄
Ammonio-cuprous Derivatives