Carbon Dioxide
Overview
Carbon dioxide (KAR-bun dye-OK-side) is a colorless, odorless, tasteless, non-combustible gas that can also exist under pressure as a clear, colorless, odorless, tasteless liquid and as a white, snow-like solid commonly known as dry ice. When dry ice is warmed it sublimes (passes directly from the solid to the gaseous state without first melting) at −78.4°C (−109°F).
Key Facts
Other Names:
Carbonic anhydride; carbonic acid gas
Formula:
CO2
Elements:
Carbon, oxygen
Compound Type:
Nonmetallic oxide
State:
Gas
Molecular Weight:
44.01 g/mol
Melting Point:
Not applicable; liquefies under pressure at −56.56°C (−69.81°F)
Boiling Point:
Sublimes at −78.4°C (−109°F)
Solubility:
Soluble in water; slightly soluble in alcohol and some other organic solvents
The true nature of carbon dioxide was discovered over an extended period of time beginning with the research of the Flemish physician and chemist Jan Baptista van Helmont (1580–1635?). In about 1603, van Helmont isolated a gas produced during the combustion of wood and proved that it was distinct from air. At the time, air was generally regarded as an element that could not be divided into separate components. Van Helmont called the gas gas sylvestre ("wood gas"), a substance we now know to be carbon dioxide. Credit for understanding the true nature of carbon dioxide also goes to the Scottish chemist Joseph Black (1728–1799) who produced carbon dioxide by heating calcium carbonate (CaCO3). Black called the gas fixed air and conducted the first extensive studies of its properties.
The first practical use for carbon dioxide was discovered in the mid-eighteenth century by the English chemist Joseph Priestley (1733–1804). Priestley found that passing carbon dioxide into water produced a sparkling, refreshing drink that he predicted would one day become a great commercial success. He was, of course, correct, since water containing carbon dioxide is the basic component of which all soda drinks are made.
How It Is Made
Carbon dioxide is produced in nature by a number of reactions. Among the most common is the combustion (burning) of the fossil fuels (coal, oil, and natural gas). The gas is also produced during the decay of organic material, the fermentation of carbohydrates by yeast, and the respiration of animals. In the laboratory, the simplest and most direct method of preparation is to treat a carbonate, such as calcium carbonate, with an acid, such as hydrochloric acid (HCl).
Carbon dioxide is obtained commercially as the by-product of a number of industrial reactions. For example, when calcium carbonate is heated to produce lime (CaO), carbon dioxide is released and captured as a by-product. The steam reforming (refining) of petroleum results in the production of a mixture of gases known as synthesis gas, consisting of carbon dioxide, carbon monoxide, hydrogen, and nitrogen. Carbon dioxide can be separated from the other components of synthesis gas for commercial uses. Carbon dioxide also produces as a by-product of the manufacture of ammonia (NH3) by the Haber-Bosch process.
Common Uses and Potential Hazards
Carbon dioxide plays an essential role in most biological processes that take place on Earth's surface. Plants use carbon dioxide as a raw material to make the carbohydrates on which their structures are based. When animals eat plants, those carbohydrates are then used to build and maintain their body structures.
Interesting Facts
- Carbon dioxide is the fourth most abundant gas in the atmosphere (after nitrogen, oxygen, and argon) with a concentration of about 0.036 percent. Researchers have found that the concentration of carbon dioxide in the atmosphere has been increasing at a regular rate for at least the last forty years. They believe that the reason for this increase is the escalating use of fossil fuels by humans to heat homes and offices; drive cars, trucks, trains, and airplanes; and to power industrial operations. They further suspect that an increase in the amount of carbon dioxide in the atmosphere may have significant long-term effects on the planet's climate.
- Scientists have become very interested in a form of carbon dioxide known as supercritical carbon dioxide (SCCO2 or SC-CO2). Under the proper conditions of temperature and pressure, carbon dioxide (as SCCO2) behaves as both a liquid and a gas at the same time. This property has proved to be very valuable in using SCCO2 as a highly efficient solvent that has no environmental disadvantages.
In addition to its role in natural processes, carbon dioxide has many commercial and industrial applications. One of the most important uses is in the carbonation of beverages. Although beers and sparkling wines contain carbon dioxide from natural sources (the fermentation of sugars by yeasts), nearly all carbonated beverages have their carbon dioxide added artificially. The carbon dioxide adds a zesty taste to the beverage and helps to preserve it.
Carbon dioxide is also used as a fire extinguishing agent. Its use for this purpose is based on the facts that it does not burn itself and is heavier than air. Thus, when sprayed on a fire, carbon dioxide settles down on top of the flames and prevents oxygen from reaching the burning material. The carbon dioxide can be supplied in a variety of ways in a fire extinguisher. In some devices, carbon dioxide gas is produced as the result of a chemical reaction that occurs within the fire extinguisher. In other devices, liquid carbon dioxide is released from the extinguisher.
Carbon dioxide is also used in gaseous, liquid, or solid form as a refrigerant. As a gas, it is used as the "working fluid" in refrigerators, the fluid that circulates through the refrigerator changing back and forth from gas to liquid, absorbing heat in the process. In the form of dry ice, carbon dioxide is a very efficient and convenient method for cooling objects to very low temperatures (close to the sublimation point of carbon dioxide, about −78.4°C (−109°F).
Words to Know
Changing of states from solid to gas without becoming liquid first. 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.
Some other uses of carbon dioxide include the following:
- As an aerosol propellant;
- To provide an oxygen-free atmosphere in which to conduct welding and other operations with flammable materials;
- In the industrial manufacture of carbonates;
- For cloud seeding to promote modifications in the weather (increases or decreases in rain fall);
- In the fumigation of rice to preserve the product for extended periods of time;
- As an artificial smoke in theater productions;
- As a moderator to slow down the speed of neutrons traveling in a nuclear power plant;
- In the frozen food industry;
- To enrich the air in a greenhouse, providing additional carbon dioxide to promote plant growth; and
- For the hardening of foundry molds and cores.
In general, carbon dioxide poses little or not threat to humans in concentrations to which one is normally exposed. Dry ice may pose a hazard if not handled carefully as its very low temperature can cause damage to the skin.
For Further Information
"Carbon Dioxide (CO2) Applications and Uses." Universal Industrial Gases, Inc. http://www.uigi.com/carbondioxide.html (accessed on September 29, 2005).
"Carbon Dioxide, Oxygen, and the Air." Skool.ie. http://www.skoool.ie/skoool/examcentre_jc.asp?id=1980 (accessed on September 29, 2005).
"Chemical of the Week: Carbon Dioxide." http://scifun.chem.wisc.edu/chemweek/CO2/CO2.html (accessed on September 29, 2005).
See Also
Calcium Carbonate; Calcium Oxide
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