A red insoluble solid, Cu2O; r.d. 6.0; m.p. 1235°C. It is obtained by reduction of an alkaline solution of copper(II) sulphate. Since the addition of alkalis to a solution of copper(II) salt results in the precipitation of copper(II) hydroxide the copper(II) ions are complexed with tartrate ions; under such conditions the concentration of copper(II) ions is so low that the solubility product of copper(II) hydroxide is not exceeded.
When copper(I) oxide reacts with dilute sulphuric acid a solution of copper(II) sulphate and a deposit of copper results, i.e. disproportionation occurs.Cu2O+2H+ → Cu2++Cu+H2OWhen dissolved in concentrated hydrochloric acid the [CuCl2]− complex ion is formed. Copper(I) oxide is used in the manufacture of rectifiers and the production of red glass.
Cu2O+2H+ → Cu2++Cu+H2O