Sulfur Dioxide
Overview
Sulfur dioxide (SUL-fur dye-OK-side) is a colorless gas with a sharp, harsh odor similar to that of a burning match. It can act as both an oxidizing agent and a reducing agent. An oxidizing agent is a substance that provides oxygen to other substances or provides electrons to them. A reducing agent removes oxygen from other substances or removes electrons from them. Sulfur dioxide dissolves readily in water, forming sulfurous acid (H2SO3), which is readily converted to sulfuric acid (H2SO4).
Key Facts
Other Names:
Sulfurous oxide; sulfurous anhydride
Formula:
SO2
Elements:
Sulfur, oxygen
Compound Type:
Nonmetallic oxide (inorganic)
State:
Gas
Molecular Weight:
64.06 g/mol
Melting Point:
−75.5°C (−104°F)
Boiling Point:
−10.05°C (−13.91°F)
Solubility:
Soluble in water, ethyl alcohol, ether, and chloroform
Sulfur dioxide is a natural component of air. It is produced when trees, brush, and other organic matter burn, and it is present in volcanic gases. It is also released during the normal metabolic reactions of some living organisms, especially marine plankton and bacteria. The compound is also produced in large amounts by human activities. All fossil fuels (coal, oil, and natural gas) contain small amounts of sulfur as impurities. When those fuels burn, the sulfur they contain is converted to sulfur dioxide, which becomes a component of air pollution.
How It Is Made
Sulfur dioxide can be prepared by several methods, the most common of which is the combustion of sulfur or pyrites (FeS2). A variety of furnaces have been developed for carrying out this reaction. Each type of furnace produces sulfur dioxide of different purities. After production, the sulfur dioxide is normally cooled and compressed to convert it to liquid form. Liquid sulfur dioxide is more easily stored and transported than the gaseous form. Sulfur dioxide is also obtained as the byproduct of a number of industrial operations, especially the smelting of metallic ores. Smelting is the process by which a metal is extracted from its ore by heating in air. Since many ores are sulfides, this process often results in the formation of sulfur dioxide, which can be captured as a byproduct of the operation. Finally, sulfur dioxide can be produced by the direct combustion of sulfur itself:
S + O2 → SO2
Common Uses and Potential Hazards
About 45 percent of all the sulfur dioxide produced in the United States is used in the manufacture of other chemical compounds, the most important of which is sodium bisulfite (NaHSO3). Other compounds made from sulfur dioxide include sulfuric acid (H2SO4), chlorine dioxide (ClO2), sodium dithionate (Na2S2O6·2H2O), and sodium thiosulfate (Na2S2O3·5H2O). Sulfur dioxide is also used as a bleaching agent for a number of products, including pulp and paper, textile fibers, straw, glue, gelatin, starches, grains, and various oils. The compound
Interesting Facts
- Sulfur dioxide was first studied in detail by the English physicist and chemist Joseph Priestley (1733–1804), who invented a method for collecting gases over water.
- The ancient Greeks and Romans fumigated their homes by burning sulfur. The sulfur dioxide formed destroyed microorganisms that cause disease and rot.
- The concentration of sulfur dioxide in clean air above the continents is less than one part per billion. Volcanic eruptions account for about half of all the gas produced by natural sources.
has a number of agricultural uses, especially in the treatment of soybeans and corn to destroy molds and preserve the product from decay. It is also used in the processing and refining of metal ores and petroleum. For example, it is added to some petroleum products to remove dissolved oxygen that would cause rust of pipes through which the products are distributed. Some other applications of the compound include:
- As a preservative for certain dried fruits and vegetables, such as cherries and apricots;
- As an additive in beers to prevent the formation of harmful products known as nitrosamines;
- As an additive in wines to prevent the growth of undesirable molds and other fungi;
- In the production of high-fructose corn syrups (HFCS) used as sweeteners in commercial food and drink products;
- As an antichlor in water purification systems;
- In the refining of sugar;
- In the manufacture of certain clay products to counteract the presence of compounds or iron and other metals that would impart color to the final product;
- In the molding and casting of magnesium parts and products; and
- In the sulfonation of oils, an important chemical process by which a sulfate group (−SO3) is added to a compound.
Sulfur dioxide is a very toxic gas that can be an irritant to the eyes, the respiratory system, and, in some cases, the skin. At concentrations normally found in ambient air (the typical atmospheric environment surrounding us), these effects are annoying, but not particularly dangerous. Such is not the case for individuals with respiratory disorders, the young, or the elderly. Such individuals may experience more serious breathing problems that require medical attention. Higher concentrations of the gas may cause more serious problems, such as coughing, headache, dizziness, feelings of suffocation, and nausea. These conditions are most likely to occur in areas where air pollution is a problem, as in urban or industrial areas. People who are constantly exposed to relatively high concentrations of sulfur dioxide (such as smelter workers) may experience more serious long-term health problems, such as asthma, chronic bronchitis, lung disease, or emphysema.
The health effects of sulfur dioxide are serious enough that the compound is not allowed as a food additive in meats and other food products that contain vitamin B1. The reason is that sulfur dioxide reacts with and destroys the vitamin. The U.S. Environmental Protection Agency (EPA) has determined that humans should not be exposed to a concentration of more than 0.030 parts per million on average throughout the year, or more than 0.14 parts per million over any one 24-hour period.
In addition to its health effects on humans, sulfur dioxide has some important consequences for the physical and biological environment. Those effects occur because sulfur dioxide released to the atmosphere from electricity-generating plants and factories combines with moisture in the air to form sulfuric acid. Sulfuric acid then falls to earth in the form of acid rain, acid snow, or some other form of acid precipitation where it damages buildings and other structures, trees and other plant life, and fish and other aquatic organisms. Since 1995, the EPA has sponsored a variety of control programs designed to reduce the release of sulfur dioxide into the atmosphere to prevent such problems.
Words to Know
A chemical that reacts with excess chlorine used for purification, disinfecting, or some other purpose. All of the chemical reactions that occur in cells by which fats, carbohydrates, and other compounds are broken down to produce energy and the compounds needed to build new cells and tissues.For Further Information
"Acid Rain Program." U.S. Environmental Protection Agency. http://www.epa.gov/airmarkets/arp/ (accessed on November 15, 2005).
"SO2—How Sulfur Dioxide Affects the Way We Live & Breathe." Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency. November 2000. Also available online at http://www.epa.gov/air/urbanair/so2. (accessed on November 15, 2005).
"Sulfur Dioxide." Air Liquide. http://www.airliquide.com/en/business/products/gases/gasdata/index.asp?GasID=27 (accessed on November 15, 2005).
"Sulfur Dioxide." New Jersey Department of Health and Senior Services. http://www.state.nj.us/health/eoh/rtkweb/1759.pdf (accessed on November 15, 2005).
"ToxFAQs for Sulfur Dioxide." Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/tfacts116.html (accessed on November 15, 2005).
See Also
Sodium Sulfite; Sulfuric Acid
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