Copper can combine with oxygen to form two compounds: copper(I) oxide and copper(II) oxide. Copper(I) oxide is red and used in agriculture, antifouling paints, and as a semiconductor. Copper(II) oxide is black and used in pigments, rayon production, and as an abrasive. Both compounds can be toxic in large doses.
Oxygen can combine with copper can combine in different ways to form two types of compounds: copper(I) oxide, which is normally a reddish powder, and copper(II) oxide, which is usually a black powder. They occur naturally as minerals in crystalline form. Both forms of copper oxide are used in the production of pigments, but have a number of other different uses.
There are two oxides of copper because it can bond with non-metals by donating one or two electrons. Oxygen forms compounds with metals by gaining two electrons, so it can accept one electron from each of two copper atoms – forming copper(I) oxide – or two electrons from one atom – forming copper(II) oxide. The numbers “I” and “II” represent the number of electrons that the metal has provided; this is known as the oxidation number. The chemical formulas of these compounds are Cu2O and CuO, respectively.
Copper(I) oxide
Event and production
This compound, also known as cuprous oxide, occurs naturally in some parts of the world as the mineral cuprite. Most of the compound in industrial use, however, has been manufactured. It can be produced industrially by heating metallic copper to a high temperature, by electrolysis of salt solutions using copper electrodes, and by mixing some other copper compounds with a reducing agent. Some sugars, such as glucose, act as reducing agents, and this reaction, in which Cu2O forms as a bright red powder, is a very sensitive laboratory test for these types of sugars.
Property
Cu2O is a red powder or crystalline material that melts at 2250°F (1232°C). Tends to oxidize slowly to copper(II) oxide in moist air. Although it does not dissolve in water or organic solvents, it does react with strong acids such as hydrochloric, nitric and sulfuric acids to form salts. It will also react with strong alkalis, such as sodium and potassium hydroxide, to form compounds known as cuprates.
it is used
This compound was one of the first semiconductors to be discovered. It also demonstrates the photoelectric effect, where exposure to light causes an electric current to flow. For this reason it is used in photocells and light detectors. A ceramic material composed of it acts as a superconductor at relatively high temperatures. Superconductors that don’t require extreme cooling to function are still an active area of research.
One of the major uses of copper(I) oxide is in agriculture. It is an ingredient in many fungicides used to protect a wide variety of crop plants from fungal diseases. The compound is also the active component of many antifouling paints, used to protect ships and underwater structures from fouling by marine plants and animals. It is also used as a pigment in the manufacture of some types of glass and in ceramic glazes, giving them a red colour, and as a catalyst in some chemical processes.
Environmental effects
The pesticide use of Cu2O has raised concerns about its effects on the environment. Soluble copper compounds derived from these products are toxic to some aquatic life. This is thought to be more of a problem in freshwater, where the compounds can build up from fungicides washed off the plants. The presence of salt in water tends to reduce the uptake of metals by marine life.
Copper(II) oxide
Event, production and ownership
This compound, also known as cupric oxide (CuO), occurs naturally as the black or gray mineral tenorite. Like Cu2O, it can be made by heating copper, but at a lower temperature. This method gives an impure form, however, and is best prepared by heating some oxygen-containing compound of copper, such as carbonate, hydroxide, or nitrate. It is a black solid that melts above 2192°F (1200°C). At this temperature it loses some oxygen, leaving small amounts of copper(I) oxide. Like the other form, copper(II) oxide is insoluble in most solvents, but does react with acids, forming salts.
it is used
CuO is sometimes added to clay glazes as a pigment. Different colors, including red, blue, and green, can be derived from it, depending on how it is used. It is a precursor in the production of cuprammonium hydroxide, which is used in the production of rayon. Sometimes, the compound is added in small amounts to animal feed to protect against copper deficiency. It is also used as an abrasive to polish lenses and other optical components.
Health effects
Although copper is an essential element for mammals, many of its compounds, including both forms of copper oxide, are toxic in all but small doses. If inhaled, copper(I) oxide can cause shortness of breath, cough and damage to the respiratory tract. Ingestion of this compound may cause gastrointestinal tract irritation, vomiting, stomach pain, and diarrhea. Copper(II) oxide can cause similar symptoms if ingested, as well as vision problems and skin discoloration. Both compounds can cause metal fume fever, a condition that produces flu-like symptoms and is a hazard in occupations that involve severe heating of copper wire or structures.
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