Copper(I) oxide

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Copper(I) oxide
IUPAC name
Copper(I) oxide
Other names
Cuprous oxide
Dicopper oxide
Red copper oxide
3D model (JSmol)
ECHA InfoCard 100.013.883
EC Number 215-270-7
PubChem CID
RTECS number GL8050000
Molar mass 143.09 g/mol
Appearancebrownish-red solid
Density 6.0 g/cm3
Melting point 1,232 °C (2,250 °F; 1,505 K)
Boiling point 1,800 °C (3,270 °F; 2,070 K)
Solubility in acidSoluble
Band gap 2.137  eV
-20·10−6 cm3/mol
93 J·mol−1·K−1
−170 kJ·mol−1
Safety data sheet
Harmful (Xn)
Dangerous for the environment (N)
R-phrases (outdated) R22, R50/53
S-phrases (outdated) (S2), S22, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calciumSpecial hazards (white): no codeCopper%28I%29 oxide
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 1 mg/m3 (as Cu) [1]
REL (Recommended)
TWA 1 mg/m3 (as Cu) [1]
IDLH (Immediate danger)
TWA 100 mg/m3 (as Cu) [1]
Related compounds
Other anions
Copper(I) sulfide
Copper(II) sulfide
Copper(I) selenide
Other cations
Copper(II) oxide
Silver(I) oxide
Nickel(II) oxide
Zinc oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Copper(I) oxide or cuprous oxide is the inorganic compound with the formula Cu2O. It is one of the principal oxides of copper, the other being CuO or cupric oxide. This red-coloured solid is a component of some antifouling paints. The compound can appear either yellow or red, depending on the size of the particles. [2] Copper(I) oxide is found as the reddish mineral cuprite.

An inorganic compound is typically a chemical compound that lacks C-H bonds, that is, a compound that is not an organic compound, but the distinction is not defined or even of particular interest.

Oxide chemical compound with at least one oxygen atom

An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– atom. Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 (called a passivation layer) that protects the foil from further corrosion. Individual elements can often form multiple oxides, each containing different amounts of the element and oxygen. In some cases these are distinguished by specifying the number of atoms as in carbon monoxide and carbon dioxide, and in other cases by specifying the element's oxidation number, as in iron(II) oxide and iron(III) oxide. Certain elements can form many different oxides, such as those of nitrogen.

Copper Chemical element with atomic number 29

Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.



Copper(I) oxide may be produced by several methods. [3] 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.

Sulfur dioxide chemical compound

Sulfur dioxide is the chemical compound with the formula SO
. It is a toxic gas with a burnt match smell. It is released naturally by volcanic activity and is produced as a by-product of the burning of fossil fuels contaminated with sulfur compounds and copper extraction.

Pourbaix diagram for copper in uncomplexed media (anions other than OH not considered). Ion concentration 0.001 m (mol/kg water). Temperature 25degC. Cu-pourbaix-diagram.svg
Pourbaix diagram for copper in uncomplexed media (anions other than OH not considered). Ion concentration 0.001 m (mol/kg water). Temperature 25°C.

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.

Fehlings solution

Fehling's solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone functional groups, and as a test for reducing sugars and non-reducing sugars, supplementary to the Tollens' reagent test. The test was developed by German chemist Hermann von Fehling in 1849.

Benedict's reagent is a chemical reagent named after American chemist Stanley Rossiter Benedict.

Sugar generic name for sweet-tasting, soluble carbohydrates

Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. The various types of sugar are derived from different sources. Simple sugars are called monosaccharides and include glucose, fructose, and galactose. "Table sugar" or "granulated sugar" refers to sucrose, a disaccharide of glucose and fructose. In the body, sucrose is hydrolysed into fructose and glucose.

It forms on silver-plated copper parts exposed to moisture when the silver layer is porous or damaged. This kind of corrosion is known as red plague.

Silver Chemical element with atomic number 47

Silver is a chemical element with symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is found in the Earth's crust in the pure, free elemental form, as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining.

Corrosion Gradual destruction of materials by chemical reaction with its environment

Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion.

Red plague is an accelerated corrosion of copper when plated with silver. After storage or use in high-humidity environment, cuprous oxide forms on the surface of the parts. The corrosion is identifiable by presence of patches of brown-red powder deposit on the exposed copper.

Little evidence exists for cuprous hydroxide, which is expected to rapidly undergo dehydration. A similar situation applies to the hydroxides of gold(I) and silver(I).


The solid is diamagnetic. In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are tetrahedral. The structure thus resembles in some sense the main polymorphs of SiO2, and both structures feature interpenetrated lattices.

Copper(I) oxide dissolves in concentrated ammonia solution to form the colourless complex [Cu(NH3)2]+, which is easily oxidized in air to the blue [Cu(NH3)4(H2O)2]2+. It dissolves in hydrochloric acid to give solutions of CuCl2. Dilute sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively. [4]

Cu2O degrades to copper(II) oxide in moist air.


Cu2O crystallizes in a cubic structure with a lattice constant al=4.2696 Å. The Cu atoms arrange in a fcc sublattice, the O atoms in a bcc sublattice. One sublattice is shifted by a quarter of the body diagonal. The space group is , which includes the point group with full octahedral symmetry.

Semiconducting properties

In the history of semiconductor physics, Cu2O is one of the most studied materials, and many experimental obser and semiconductor applications have been demonstrated first in this material:

The lowest excitons in Cu2O are extremely long lived; absorption lineshapes have been demonstrated with neV linewidths, which is the narrowest bulk exciton resonance ever observed. [8] The associated quadrupole polaritons have low group velocity approaching the speed of sound. Thus, light moves almost as slowly as sound in this medium, which results in high polariton densities. Another unusual feature of the ground state excitons is that all primary scattering mechanisms are known quantitatively. [9] Cu2O was the first substance where an entirely parameter-free model of absorption linewidth broadening by temperature could be established, allowing the corresponding absorption coefficient to be deduced. It can be shown using Cu2O that the Kramers–Kronig relations do not apply to polaritons. [10]


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 silicon became the standard. Copper(I) oxide is also responsible for the pink color in a positive Benedict's test.

See also

Related Research Articles

Hydroxide anion

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.


In physics, polaritons are quasiparticles resulting from strong coupling of electromagnetic waves with an electric or magnetic dipole-carrying excitation. They are an expression of the common quantum phenomenon known as level repulsion, also known as the avoided crossing principle. Polaritons describe the crossing of the dispersion of light with any interacting resonance. To this extent polaritons can also be thought as the new normal modes of a given material or structure arising from the strong coupling of the bare modes, which are the photon and the dipolar oscillation. The polariton is a bosonic quasiparticle, and should not be confused with the polaron, which is an electron plus an attached phonon cloud.

Copper oxide is a compound from the two elements copper and oxygen.


A polaron is a quasiparticle used in condensed matter physics to understand the interactions between electrons and atoms in a solid material. The polaron concept was first proposed by Lev Landau in 1933 to describe an electron moving in a dielectric crystal where the atoms move from their equilibrium positions to effectively screen the charge of an electron, known as a phonon cloud. This lowers the electron mobility and increases the electron's effective mass.

Copper(II) oxide chemical compound

Copper(II) oxide or cupric oxide is the inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or cuprous oxide. As a mineral, it is known as tenorite. It is a product of copper mining and the precursor to many other copper-containing products and chemical compounds.

Copper(I) chloride chemical compound

Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid. Impure samples appear green due to the presence of copper(II) chloride (CuCl2).

Copper(II) chloride chemical compound

Copper(II) chloride is the chemical compound with the chemical formula CuCl2. This is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate. The copper(II) chlorides are some of the most common copper(II) compounds, after copper sulfate.

Copper(II) hydroxide chemical compound

Copper(II) hydroxide is the hydroxide of copper with the chemical formula of Cu(OH)2. It is a pale greenish blue or bluish green solid. Some forms of copper(II) hydroxide are sold as "stabilized" copper hydroxide, although they likely consist of a mixture of copper(II) carbonate and hydroxide. Copper hydroxide is a weak base.

Copper(I) acetylide, or cuprous acetylide, is a chemical compound with the formula Cu2C2. Although never characterized by X-ray crystallography, the material has been claimed at least since 1856. One form is claimed to be a monohydrate with formula Cu
). It is a reddish solid, that easily explodes when dry.

Copper(I) fluoride chemical compound

Copper(I) fluoride or cuprous fluoride is an inorganic compound with the chemical formula CuF. Its existence is uncertain. It was reported in 1933 to have a sphalerite-type crystal structure. Modern textbooks state that CuF is not known, since fluorine is so electronegative that it will always oxidise copper to its +2 oxidation state. Complexes of CuF such as [(Ph3P)3CuF] are, however, known and well characterised.

Tetrakis(acetonitrile)copper(I) hexafluorophosphate chemical compound

Tetrakis(acetonitrile)copper(I) hexafluorophosphate is a coordination compound with the formula [Cu(CH3CN)4]PF6. It is a colourless solid that is used in the synthesis of other copper complexes. It is a well-known example of a transition metal nitrile complex.

Alexey Kavokin Physics professor

Alexey V. Kavokin is a Russian and French theoretical physicist and writer.

Delafossite oxide mineral

Delafossite is a copper iron oxide mineral with formula CuFeO2 or Cu1+Fe3+O2. It is a member of the delafossite mineral group, which has the general formula ABO2, a group characterized by sheets of linearly coordinated A cations stacked between edge-shared octahedral layers (BO6). Delafossite, along with other minerals of the ABO2 group, is known for its wide range of electrical properties, its conductivity varying from insulating to metallic. Delafossite is usually a secondary mineral that crystallizes in association with oxidized copper and rarely occurs as a primary mineral.

Copper(I) sulfate, also known as cuprous sulfate and dicopper sulfate, is the chemical compound with the chemical formula Cu2SO4 and a molar mass of 223.15 g mol−1. It is an unstable compound as copper(I) compounds are generally unstable and is more commonly found in the CuSO4 state. It is light green in color at room temperature and is water-soluble. Due to the low-stability of the compound there are currently not many applications to date.

Terahertz spectroscopy detects and controls properties of matter with electromagnetic fields that are in the frequency range between a few hundred gigahertz and several terahertz. In many-body systems, several of the relevant states have an energy difference that matches with the energy of a THz photon. Therefore, THz spectroscopy provides a particularly powerful method in resolving and controlling individual transitions between different many-body states. By doing this, one gains new insights about many-body quantum kinetics and how that can be utilized in developing new technologies that are optimized up to the elementary quantum level.

Bose–Einstein condensation can occur in quasiparticles, particles that are effective descriptions of collective excitations in materials. Some have integer spins and can be expected to obey Bose–Einstein statistics like traditional particles. Conditions for condensation of various quasiparticles have been predicted and observed. The topic continues to be an active field of study.

Copper(I) thiocyanate chemical compound

Copper(I) thiocyanate is a coordination polymer with formula CuSCN. It is an air-stable, white solid used as a precursor for the preparation of other thiocyanate salts.

Bose–Einstein condensation of polaritons is a growing field in semiconductor optics research, which exhibits spontaneous coherence similar to a laser, but through a different mechanism. A continuous transition from polariton condensation to lasing can be made similar to that of the crossover from a Bose–Einstein condensate to a BCS state in the context of Fermi gases. Polariton condensation is sometimes called “lasing without inversion”.

A quantum dot single-photon source is based on a single quantum dot placed in an optical microcavity. It is an on-demand single photon source. A pulsed laser can excite a pair of carriers known as an exciton in the quantum dot. Due to the discrete energy levels, only one exciton can exist in the quantum dot at a given time. The decay of the exciton due to spontaneous emission leads to the emission of a single photon. It is a nonclassical light source that shows photon antibunching. The emission of single photons can be proven by measuring the second order intensity correlation function. The linewidth of the emitted photons can be reduced by using distributed Bragg reflectors (DBR’s). Additionally, DBR's lead to an emission in a well-defined direction.

Chevreul's salt (Copper(I,II) Sulfite Dihydrate, Cu2SO3•CuSO3•2H2O (Cu3(SO3)2•2H2O)), is a copper salt which was prepared for the first time by a French chemist Michel Eugène Chevreul in 1812. Its unique property is that it contains copper in both of its common oxidation states. It is insoluble in water and stable in air. What was known as Rogojski's salt is a mixture of Chevreul's salt and metallic copper.


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