Carbon Monoxide
Overview
Carbon monoxide is a colorless, odorless, tasteless, toxic gas. It is one of the most common poisons in the environment and is responsible for thousands of deaths and hospital emergency room visits each year in the United States. Carbon monoxide is produced from fuel-burning appliances, such as space heaters, furnaces, stoves, and vehicles. It is also a component of cigarette smoke. Carbon monoxide is flammable and capable of forming an explosive mixture with air.
Key Facts
Other Names:
None
Formula:
CO
Elements:
Carbon, oxygen
Compound Type:
Nonmetallic oxide
State:
Gas
Molecular Weight:
28.01 g/mol
Melting Point:
−205.02°C (−337.04°F)
Boiling Point:
−191.5°C (−312.7°F)
Solubility:
Slightly soluble in water; soluble in alcohol and chloroform
Under ideal circumstances, a carbon-containing fuel such as charcoal, natural gas, or wood burns in air to form carbon dioxide and water. Lacking an adequate supply of oxygen, at low temperatures, or under certain other conditions, incomplete combustion occurs. Incomplete combustion is a process in which a fuel is not completed oxidized. In such instances, carbon monoxide is produced along with carbon dioxide and water. An inadequate supply of oxygen can occur in enclosed, poorly vented spaces, such as the interior of houses, garages, and cars.
The discovery of carbon monoxide is usually credited to the English chemist Joseph Priestley (1733–1804). Between 1772 and 1799, Priestley investigated the properties of carbon monoxide and recognized the difference between carbon monoxide and carbon dioxide. The gas was first prepared synthetically by the French chemist Joseph Marie François de Lassone (1717–1788) in 1776, although he mistakenly identified it as hydrogen. The correct chemical formula for carbon monoxide was first identified by the English chemist William Cruikshank (1745–1800) in 1800.
How It Is Made
A number of methods are available for the commercial production of carbon monoxide. In one procedure, air is passed over hot coke, graphite, or anthracite coal to make producer gas, a mixture of carbon dioxide, carbon monoxide, hydrogen, and water vapor. In a similar procedure, steam is passed over hot coke or graphite to make water gas, a mixture of carbon monoxide, carbon dioxide, hydrogen, and nitrogen. In a third procedure, steam is mixed with natural gas to form synthesis gas, consisting of carbon dioxide, carbon monoxide, and hydrogen. In all three procedures, the carbon monoxide component of the gas mixture produced in the reaction can be separated out from the other gases.
Yet a fourth method for making carbon monoxide involves the partial oxidation of hydrocarbon gases obtained from natural gas or petroleum. These gases consist of carbon-hydrogen compounds which, when oxidized, are converted to carbon monoxide, carbon dioxide, and water. By controlling the amount of reactants used and the conditions of the reaction (temperature and pressure), the portion of carbon monoxide produced can be increased.
Common Uses and Potential Hazards
Carbon monoxide has three major industrial uses. The first is in the synthesis of a large variety of organic compounds. For example, it takes part in a group of reactions known as the Fischer-Tropsch reactions in which carbon monoxide is first reduced with hydrogen gas and then converted to any number of organic compounds that contain oxygen. The gas is also used to make acetic acid, a major industrial chemical used in the synthesis of polymers and other organic products.
Interesting Facts
- Some authorities believe that the American writer Edgar Allan Poe (1809–1849) owed his wild imagination and early death to chronic carbon monoxide poisoning, caused by the gas lighting used in his home.
- Public health authorities estimate that the number of suicides resulting from the inhalation of carbon monoxide fumes from automobiles has decreased by about 80 percent since the introduction of catalytic converters in cars. Catalytic converters reduce the amount of carbon monoxide released in a car's exhaust.
- Carbon monoxide bonds to hemoglobin in the blood stream 200 times as efficiently as does oxygen. This ability to exclude oxygen from the blood is responsible for the toxic effects caused by carbon monoxide in the body.
A second application of carbon monoxide, either by itself or in conjunction with other gases, is as an industrial fuel. The gas burns very efficiently with the release of large amounts of heat and relatively few undesirable by-products (the most important being carbon dioxide).
A third industrial use for carbon monoxide is in the refining of metals. Most metal ores exist in the form of oxides or sulfides when extracted from the earth. For example, the two most important ores of iron are magnetite (Fe3O4) and hematite (Fe2O3). After an ore has been mined, it is treated to remove the oxygen or sulfur in the ore to obtain a pure metal. Carbon monoxide is often used for this purpose with oxide ores because it combines with oxygen from the ore to form carbon dioxide, leaving the metal behind: Metal oxide + CO → Metal + CO2.
Carbon monoxide is a highly toxic gas that has noticeable health effects even in relatively small concentrations. When the concentration of carbon monoxide reaches levels of about 100 ppm (parts per million), an individual is likely to experience mild headaches, fatigue, shortness of breath, and errors in judgment. As the concentration of carbon monoxide increases, these symptoms become more pronounced. Exposure to a concentration of more than 400 ppm for more than three hours is likely to put a person at serious health risk. He or she may begin to lose consciousness and experience serious disorientation. At concentrations of more than 1,500 ppm, death is likely in less than an hour. These symptoms vary somewhat depending on a person's age and overall health.
Words to Know
A compound consisting of very large molecules made of one or two small repeated units called monomers. Chemical reaction in which oxygen is removed from a substance or electrons are added to a substance. A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants. A mixture of several gases, such as carbon dioxide and hydrogen, used to produce compounds such as methanol and ammonia that can be separated out from the synthesis gas.Most governmental agencies have set a recommended limit of 35 ppm for periods of up to eight hours. For purposes of comparison, the normal concentration of carbon monoxide in the atmosphere in an open area tends to be less than 1 ppm. But in urban areas or other locations with many vehicles, gas heaters, wood burning stoves, or other sources of carbon monoxide, carbon monoxide levels can be much higher. Someone traveling inside a car on a busy freeway, for example, may be exposed to carbon monoxide levels of up to 25 ppm. Concentrations of up to 100 ppm have been measured in the center of busy downtown urban areas.
For Further Information
"Carbon Monoxide." Chemical Fact Sheet. Plastics and Chemicals Industries Association. http://www.pacia.org.au/_uploaditems/docs/3.carbon_monoxide.pdf (accessed on October 2, 2005).
"Carbon Monoxide Questions and Answers." Consumer Product Safety Commission. CPSC Document #466. http://www.cpsc.gov/cpscpub/pubs/466.html (accessed on October 3, 2005).
Dwyer, Bob, et al. Carbon Monoxide: A Clear and Present Danger. Mount Prospect, Ill.: ESCO Press, 2004.
Patnaik, Pradyot. Handbook of Inorganic Chemicals. New York: McGraw-Hill, 2003, 1887–191.
See Also
Acetic Acid; Carbon Dioxide
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