Sodium Hypochlorite KEY FAC T S. Na + O OVERVIEW

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1 Na + O Cl OTHER NAMES: Sodium oxychloride; hypochlorite; bleach; chlorine bleach FORMULA: NaClO ELEMENTS: Sodium, chlorine, oxygen COMPOUND TYPE: Oxy salt (inorganic) STATE: Solid or aqueous solution; See Overview MOLECULAR WEIGHT: g/mol MELTING POINT: Solid NaClO explodes on heating. The pentahydrate (NaClO5H 2 O) is more stable; its melting point is 18 C(64 F) BOILING POINT: Not applicable; decomposes SOLUBILITY: Soluble in water KEY FAC T S Sodium Hypochlorite OVERVIEW Sodium hypochlorite (SO-dee-um hye-po-klor-ite) is the active ingredient in liquid chlorine bleaches, used in the home and many industries to whiten fabric and other materials and to disinfect surfaces and water. The anhydrous compound is very unstable and explodes readily. The pentahydrate is a palegreen crystalline solid that is relatively stable. The compound is usually made available as an aqueous solution that contains anywhere from 3 to 6 percent sodium hypochlorite (for household use) to as high as 30 percent (for industrial applications). In solution form, sodium hypochlorite is quite stable and can be stored for long periods of time out of sunlight. Sodium hypochlorite decomposes by two mechanisms. In one case, it breaks down to form sodium chloride and sodium chlorate: 3NaOCl! 2NaCl + NaClO 3 In the second case, it breaks down to form sodium chloride and nascent (free single atoms) oxygen: CHEMICAL COMPOUNDS 759

2 Sodium hypochlorite. Red atom is oxygen; green atom is chlorine; and turquoise atom is sodium. PUBLISHERS RESOURCE GROUP NaOCl! NaCl + (O) Nascent oxygen is a very active form of oxygen that is responsible for the bleaching and disinfectant properties of sodium hypochlorite. Humans have long made efforts to bleach fabrics. Neither cotton nor linen, two very popular fabrics, are naturally very white, so efforts were made to find ways to convert them to white materials. Those efforts were not very successful until the discovery of chlorine by the Swedish chemist Karl Wilhelm Scheele ( ) in the 1770s. The powerful oxidizing powers of chlorine made it a likely candidate for use as a bleach (although chemists at the time did not understand how bleaching occurred). The first person to take advantage of chlorine s bleaching powers was the French chemist Claude Louis Berthollet ( ), who lived in Javelle, France. Berthollet produced a weak solution of sodium hypochlorite by passing chlorine gas through sodium carbonate. The product had excellent bleaching powers, and it became known by the name of eau de Javelle or eau de Berthollet. Berthollet s invention came at just the right time. The Industrial Revolution was just getting under way, and the invention of machines like the spinning jenny and the power loom mechanized the commercial production of cotton and linen cloth and rapidly increased the demand for bleaching agents. HOW IT IS MADE Sodium hypochlorite is made commercially by passing chlorine gas (Cl 2 ) through a cold aqueous solution of sodium hydroxide (NaOH): 760 CHEMICAL COMPOUNDS

3 Cl 2 + 2NaOH! NaClO + NaCl + H 2 O The pentahydrate then can be extracted by crystallization. COMMON USES AND POTENTIAL HAZARDS Sodium hypochlorite is used almost exclusively for one of two purposes: bleaching or purification. The compound is available commercially for household use under a number of trade names, including Antiformin Ò, B-K Liquid Ò, Clorox Ò, Dakin s Solution Ò, Dazzle Ò, Hychlorite Ò, Javelle water, Piochlor Ò, Purex Ò, and Saniton Toothbrush Sanitizer Ò. About two-thirds of the sodium hypochlorite made in the United States is used as a laundry bleach and sanitizer, in restaurants and institutional kitchens for bleaching and sanitation, and for water purification in residential pools and spas. Some examples of the ways in which sodium hypochlorite is used include: For the sterilization of milking equipment and containers at dairy farms; For the cleaning and sterilization of work surfaces by amateur and professional beer and wine makers; As an ingredient in home cleaning agents, such as toilet bowl sanitizers, mold removers, and drain cleaners; and As a disinfectant in private water wells to prevent the growth of microorganisms. About half of all the sodium hypochlorite used for industrial purposes is consumed in municipal and water treatment systems. About a third of the compound production goes to the sterilization of municipal and commercial swimming pools. The remaining sodium hypochlorite is used in commercial, municipal, and industrial cleaning and bleaching operations. Sodium hypochlorite is a fire and health hazard. It reacts strongly with metals and organic materials. The rate of reaction increases with the concentration of sodium hypochlorite in solution, so industrial and municipal formulations present a greater environmental threat than do household products. One combination of special concern to consumers is the reaction between sodium hypochlorite and compounds that contain ammonia. For example, the combination of household bleach and household ammonia can produce an explosive or flam- CHEMICAL COMPOUNDS 761

4 Interesting Facts Until the discovery of chlorine, cloth was usually bleached by soaking it in sour milk or buttermilk and letting it sit in the sun. The process often took up to eight weeks and required large bleaching fields on which the cloth could be laid out. The first attempt to apply chemical principles to the practice of bleaching was documented in a book on the subject by the Scottish physician Francis Home, published in Home suggested using a weak solution of sulfuric acid for bleaching, a practice that reduced bleaching time to about 12 hours. mable mixture. The fumes from this combination can also be harmful, even deadly. Similarly, household bleach should not be use to clean spills that contain urine since urine itself contains ammonia. Sodium hypochlorite is also incompatible with hydrogen peroxide and acidic products. Sodium hypochlorite is an irritant to the skin, eyes, and respiratory system. It can produce inflammation, burning, and blistering of the skin; burning of the eyes, with subsequent damage to one s vision; and irritation of the gastrointestinal system that can result in stomach pain, nausea, vomiting, coughing, and ulceration of the digestive tract. Words to Know ANHYDROUS Lacking water of hydration. AQUEOUS SOLUTION A solution that consists of some material dissolved in water. OXIDATION A chemical reaction in which oxygen reacts with some other substance or, alternatively, in which some substance loses electrons to another substance, the oxidizing agent. PENTAHYDRATE A form of a crystalline compound that occurs with five molecules of water. 762 CHEMICAL COMPOUNDS

5 FOR FURTHER INFORMATION Chalmers, Louis. Household and Industrial Chemical Specialties. Vol. 1. New York: Chemical Publishing Co., Inc., Fletcher, John, and Don Ciancone. Why Life s a Bleach (The Sodium Hypochlorite Story). Environmental Science & Engineering. May Also available online at (accessed on November 8, 2005). Medical Management Guidelines (MMGs) for Calcium Hypochlorite (CaCl 2 O 2 ) Sodium Hypochlorite (NaOCl). Agency for Toxic Substances and Disease Registry. (accessed on January 12, 2006). Sodium Hypochlorite. Hill Brothers Chemical Co. (accessed on November 8, 2005). Sodium Hypochlorite. Medline Plus htm (accessed on November 8, 2005). CHEMICAL COMPOUNDS 763