What are the Functions of Sodium Metabisulfite?
Sodium metabisulfite, also called sodium pyrosulfite or disodium, is an inorganic compound. This compound has many chemical properties that make it useful for a variety of industrial purposes. However, there are many dangers of working with or ingesting this compound, which make some of its uses---especially that of a food preservative---a topic of research and controversy.
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Description
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Sodium metabisulfite is a crystalline powder that is white to yellow in color. It is soluble in water. When dissolved, it releases sulfur dioxide gas, which is unpleasant smelling. The chemical formula is Na2S2O5, and the molecular structure is shown in the illustration. Sodium metabisulfite reacts with oxygen when left exposed to air, changing it to a sulfate.
Chemical Properties
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Sodium metabisulfite functions in many chemical reactions. It can purify or isolate aldehydes, which are highly reactive organic compounds commonly used in making resins or dyes. It can also purify or isolate ketones, which are organic compounds resulting from the breakdown of fats. It is a reducer, meaning it can decrease the amount of oxygen in a substance. It also has the ability to sulfonate, meaning it can react with sulfuric acid.
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Industrial Uses
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The many chemical properties of sodium metabisulfite make it a versatile compound useful in many applications. It can eliminate dissolved oxygen in waste water and in pipes. It functions as a bleaching agent, which is useful in making paper pulp, cotton and wool. It is used in water treatment plants to remove excess chlorine. In beer and wine manufacturing, it is often used to sterilize the equipment.
Food Preservative
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Sodium metabisulfite is used as a food preservative and is usually noted as E223. Sodium metabisulfite acts as an antimicrobial, inhibiting the growth of fungi and bacteria, thereby keeping food fresh and safe. However, this use is controversial because it can cause allergic reactions, especially in those with sensitivities to sulfites or those who suffer from asthma. It is commonly found in fruit juices, vinegars, pickles and dried fruits.
Dangers
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Sodium metabisulfite is a dangerous compound, and care should be taken when using it. When it comes into contact with skin, it can cause a severe allergic reaction, and repeated contact can cause dermatitis. If inhaled, it can cause respiratory irritation, and for those with asthma, it may cause a severe reaction. It is also an eye irritant, so if it makes contact with the eyes, immediately flush them with water. Do not swallow sodium metabisulfite; it can cause gastrointestinal irritation, including nausea, vomiting and diarrhea.
Storage and Handling
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Since sodium metabisulfite breaks down when exposed to air, it should be stored in a tightly closed container. It should be kept in a cool and dry area and be protected from moisture. The generation and accumulation of dust should be minimized to avoid inhalation or contact with skin or eyes.
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