Sodium Sulfite
Sodium Sulfite
OVERVIEW
Sodium sulfite (SO-dee-um SUL-fite) is a white powder or crystalline solid with no odor but a slightly salty taste. The compound is stable in dry air, but tends to decompose in moist air to produce sulfur dioxide (SO2) and sodium hydroxide (NaOH). The compound has a variety of uses as a food preservative and in the paper and pulp industry.
HOW IT IS MADE
Sodium sulfite can be prepared by reacting sulfur dioxide, soda ash (sodium carbonate; Na2CO3), and water. The product of this reaction is sodium bisulfite (NaHSO3), which is then treated with excess soda ash to obtain sodium sulfite. The compound can also be obtained as a byproduct in the preparation of phenol (C6H5OH).
KEY FACTS
OTHER NAMES:
Disodium sulfite
FORMULA:
Na2SO3
ELEMENTS:
Sodium, sulfur, oxygen
COMPOUND TYPE:
Salt (inorganic)
STATE:
Solid
MOLECULAR WEIGHT:
126.04 g/mol
MELTING POINT:
Not applicable; decomposes
BOILING POINT:
Not applicable
SOLUBILITY:
Soluble in water; slightly soluble in ethyl alcohol
COMMON USES AND POTENTIAL HAZARDS
Sodium sulfite is an essential chemical in the pulp and paper industry. Just over half of all the sodium sulfite made in the United States is used by the pulp and paper industry. The compound acts as a pulping agent for wood, rags, and straw. A pulping agent is a substance that breaks down raw materials and converts them into the pulp from which paper is made. Sodium sulfite is also used to remove excess chlorine used to bleach wood pulp and other raw materials needed in the production of paper.
The second largest application of sodium sulfite is in water and wastewater treatment plants, where it is used to react with and neutralize excess chlorine used in the water and wastewater treatment processes. The third most important application of sodium sulfite is in photography. The compound is used in the developing process, and it acts as a preservative for the final picture produced. Sodium sulfite is still used as a food preservative also, although the conditions under which it can be added are somewhat limited. In addition to its hazards among individual with allergies, sodium sulfite destroys both vitamins B1 and E, meaning that it cannot be added to foods that contain these vitamins. It is still widely used, however, in the wine-making industry for the control of bacteria involved in the wine-making process.
As noted above, a significant number of people are allergic to sodium sulfite. In addition to this health hazard, the compound can be an irritant to the skin, eyes, and respiratory tract. It can cause inflammation of the skin and eyes, irritation of the nose and throat, problems with breathing, and stomach upset. With the level at which most people come into contact with the compound, however, it poses little threat to a person's health.
Interesting Facts
- Sodium sulfite has been used as a food preservative for many years. However, in 1986 the U.S. Food and Drug Administration (FDA) banned the use of sodium sulfites for certain types of food. The agency had discovered that about one in a hundred people are sensitive to sodium sulfite. Thirteen deaths and more than 500 allergic reactions resulting from exposure to sodium sulfite had been reported to the FDA. The agency now prohibits the use of sodium sulfite as a preservative on raw fruits and vegetables. Processed foods that contain sodium sulfite must include a notice to that effect on the food label.
FOR FURTHER INFORMATION
"Sodium Sulfite." Esseco General Chemical. http://www.genchemcorp.com/pdf/msds/Sodium%20Sulfite,%20EGC%20-%204-03.pdf (accessed on November 12, 2005).
"Sodium Sulfite." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/s5066.htm (accessed on November 12, 2005).
"Sodium Sulfite." Solvay Chemicals. http://www.solvaychemicals.us/pdf/Sodium_Sulfite/SODSULF.pdf (accessed on November 12, 2005).
"Sodium Sulfite Photographic Grade." Center for Advanced Microstructures and Devices, Louisiana State University. http://www.camd.lsu.edu/msds/s/sodium_sulfite.htm (accessed on November 12, 2005).
See AlsoSulfur Dioxide