Since it is available commercially, copper sulfate is usually purchased and not prepared in the laboratory. It can be made by the action of sulfuric acid on a variety of copper(II) compounds, for examplecopper(II) oxide; this oxide can be generated with the addition of hydrogen peroxide to the acid. It may also be prepared by electrolyzing sulfuric acid, using copper electrodes. It can also be prepared by electrolysis of magnesium sulfate [Epsom salts] solution at moderate voltage with a copper anode: this reaction produces hydrogen, copper sulfate solution, and magnesium hydroxide precipitate:
- MgSO4(aq) + 2 H2O + Cu(s) → H2(g) + Mg(OH)2(s) + CuSO4(aq)
- 2 Cu + O2 → 2 CuO
- 2 Cu(NO3)2 → 2 CuO + 4 NO2 + O2
- Cu(OH)2 (s) → CuO (s) + H2O (l)
- CuCO3 → CuO + CO2
- CuO + 2 HNO3 → Cu(NO3)2 + H2O
- CuO + 2 HCl → CuCl2 + H2O
- CuO + H2SO4 → CuSO4 + H2O
It reacts with concentrated alkali to form the corresponding cuprate salts:
- 2 XOH + CuO + H2O → X2[Cu(OH)4]
- CuO + H2 → Cu + H2O
- CuO + CO → Cu + CO2
A laboratory method for preparing copper II oxide would be to electrolyze water containing sodium bicarbonate at a moderate voltage with a copper anode, collect the mixture of copper hydroxide, basic copper carbonate, and copper carbonate produced, and heat it.
Cupric oxide is used as a pigment in ceramics to produce blue, red, and green (and sometimes gray, pink, or black) glazes. It is also used to produce cuprammonium hydroxide solutions, used to makerayon. It is also occasionally used as a dietary supplement in animals, against copper deficiency.Copper(II) oxide has application as a p-type semiconductor, because it has a narrow band gap of 1.2 eV. It is an abrasive used to polish optical equipment. Cupric oxide can be used to produce dry cell batteries. It has also been used in wet cell batteries as the cathode, with lithium as an anode, and dioxalane mixed with lithium perchlorate as the electrolyte. Copper(II) oxide can be used to produce other copper salts. It is also used when welding with copper alloys.
Another use for cupric oxide is as a substitute for iron oxide in thermite. This can turn the thermite from an incendiary to a low explosive.
Copper(I) oxide may be produced by several methods.Most straightforwardly, it arises via the oxidation of copper metal:
- 4 Cu + O2 → 2 Cu2O
Additives such as water and acids affect the rate of this process as well as the further oxidation to copper(II) oxides. It is also produced commercially by reduction of copper(II) solutions with sulfur dioxide. Aqueous cuprous chloride solutions react with base to give the same material. In all cases, the color is highly sensitive to the procedural details.
Formation of copper(I) oxide is the basis of the Fehling's test and Benedict's test for reducing sugars. These sugars reduce an alkaline solution of a copper(II) salt, giving a bright red precipitate of Cu2O.
Cuprous oxide is commonly used as a pigment, a fungicide, and an antifouling agent for marine paints.Rectifier diodes based on this material have been used industrially as early as 1924,long before siliconbecame the standard.