Copper(I) Oxide

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Copper(I) Oxide


Copper(I) oxide (KOPP-er one OK-side) is also known as cuprous oxide, red copper oxide, copper protoxide, copper hemioxide, and copper suboxide. It is a yellowish, red, or brown crystalline substance, depending on its method of preparation. It does not burn and is stable in dry air. In moist air, it slowly changes to copper(II) oxide (CuO). The compound has been used by humans for thousands of years, first as a pigment in glazes, and later in fungicides, electronic components, and industrial reactions.

In 1883, copper(I) oxide was the first substance found to have semiconducting properties. A semiconductor conducts an electric current, although not nearly as efficiently as a conductor like copper, gold, or silver. Semiconductor components are now widely used in computer chips, although they are now made from silicon rather than copper(I) oxide.



See Overview.




Copper, oxygen


Metallic oxide




143.09 g/mol


1235°C (2255°F)


Decomposes at 1800°C (3300°F)


Insoluble in water; soluble in inorganic acids, such as hydrochloric, sulfuric, and nitric acids


Copper(I) oxide occurs naturally as the mineral cuprite. It forms when native copper (copper as an element) is exposed to the air, although the process occurs very slowly. Copper(I) oxide can also be made synthetically by exposing copper metal to a high concentration of oxygen at an elevated temperature. Care must be taken, however to prevent the copper from oxidizing completely to form copper(II) oxide. A number of other industrial methods are also available for the synthesis of copper(I) oxide. For example, electrolysis of a solution of sodium chloride using copper electrodes results in the formation of copper(I) oxide.


Copper(I) oxide is used as a pigment in porcelain glazes and stained glass. In opaque glass, it provides a bright brick-red color if large enough crystals are used. Smaller crystals give a yellowish color. The use of copper(I) oxide as a pigment in glazes dates back to the time of ancient Egypt.

Many antifouling marine paints contain copper(I) oxide. Antifouling paints are paints that prevent the formation of barnacles and other organisms on the bottom of a boat. The compound is also used as an antifungal agent, a substance that kills mildew, rust, and other types of fungus. Fungicides based on copper(I) oxide are commonly used on a variety of crops susceptible to attack by such organisms. Copper(I) oxide acts by inhibiting the growth of fungal spores (from which new plants develop) rather than killing mature fungi.

Copper(I) oxide is used in photoelectric cells, which are cells that generate an electric current when exposed to light. Photoelectric materials are usually semiconductors. Copper(I) oxide photoelectric cells do not generate much power, but they react rapidly to changes in light levels. This property makes them useful as light detectors, which have many applications from cameras with automatic adjustment settings to automatic door openers and burglar alarms.

In the 1980s, a ceramic form of copper(I) oxide was found to have superconducting properties at temperatures higher than previously known superconductors. Superconductors have the ability to carry an electric current virtually without resistance. Once a current is initiated in a superconductor, it continues to travel through the material essentially forever. Superconductor research may lead to new technologies, from cheaper electrical power to magnetically levitated high-speed trains.

Interesting Facts

  • Copper metal is sometimes used for roofing on notable buildings, such as art museums or state capitols. Over time, the copper metal develops a patina, a thin layer of color that adds to the elegance of the roof. The patina consists primarily of copper(I) oxide.
  • In 1904, the German physicist Wilhelm Hallwachs (1859–1922) discovered that a combination of copper metal and copper(I) oxide displays the photoelectric effect, in which a beam of light causes electricity to flow through a material.

Exposure to moderate amounts of copper(I) oxide can be irritating to the skin, eyes, and respiratory system. If heated, it gives off copper fumes that can cause symptoms similar to the common cold and may discolor the skin and hair. If swallowed, copper(I) oxide has a metallic taste and may induce vomiting, nausea, and stomach pain. In the most severe cases, copper(I) oxide may cause black or tarry stools, jaundice, and bloody vomiting, with long-term damage to the liver. In the environment, copper(I) oxide is very toxic to fish and crustaceans.

Words to Know

Process in which an electric current is used to bring about chemical changes.
To combine with oxygen.
A device that generates electricity when exposed to light.
A substance that allows electricity to flow through it at a lesser rate than a conductor, though more than a non-conductive substance.
A substance that allows electricity to flow through it with very little resistance.
Chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.


"Cuprite." Dale Minerals International. (accessed on October 3, 2005).

"Cuprous oxide." Hummel Croton, Inc. (accessed on October 3, 2005).

Patnaik, Pradyot. Handbook of Inorganic Chemicals. New York: McGraw-Hil, 2003, 271-273.

Richardson, H. W., ed. Handbook of Copper Compounds and Applications. New York: Marcel Dekker, 1997.

See AlsoCopper(II) Oxide