Sodium hypochlorite is a chemical compound with the formula NaOCl. Sodium hypochlorite solution, commonly known as bleach, is frequently used as a disinfectant or a bleaching agent.

Production

Hypochlorite was first produced in 1789 by Claude Louis Berthollet in his laboratory on the quay Javel in Paris, France, by passing chlorine gas through a solution of sodium carbonate. The resulting liquid, known as "Eau de Javel" ("Javel water"), was a weak solution of sodium hypochlorite. However, this process was not very efficient and alternate production methods were sought. One such method involved the extraction of chlorinated lime (known as bleaching powder) with sodium carbonate to yield low levels of available chlorine. This method was commonly used to produce hypochlorite solutions for use as a hospital antiseptic which was sold under the trade names "Eusol" and "Dakin's solution".

Near the end of the nineteenth century, E. S. Smith patented a method of hypochlorite production involving hydrolysis of brine to produce caustic soda and chlorine gas which then mixed to form hypochlorite. Both electric power and brine solution were in cheap supply at this time, and various enterprising marketers took advantage of this situation to satisfy the market's demand for hypochlorite. Bottled solutions of hypochlorite were sold under numerous trade names; one such early brand produced by this method was called Parozone.

Today, an improved version of this method, known as the Hooker process, is the only large scale industrial method of sodium hypochlorite production. In this process sodium hypochlorite (NaOCl) and sodium chloride (NaCl) are formed when chlorine is passed into cold and dilute sodium hydroxide solution. It is prepared industrially by electrolysis with minimal separation between the anode and the cathode. The solution must be kept below 40 °C (by cooling coils) to prevent the undesired formation of sodium chlorate.

Cl₂ + 2 NaOH → NaCl + NaOCl + H₂O

Sodium hydroxide and chlorine are commercially produced by the chloralkali process, and there is no need to isolate them to prepare sodium hypochlorite.

Hence, chlorine is simultaneously reduced and oxidized; this process is known as disproportionation.

The commercial solutions always contain significant amounts of sodium chloride (common salt) as the main by-product, as seen in the equation above.

Sodium hypochlorite can be also made by electrolyzing saturated sodium chloride solution and the product can be tested by dropping hydrochloric acid to determine if it is successfully synthesized.

Packaging and sale

Household bleach sold for use in laundering clothes is a 3-6% solution of sodium hypochlorite at the time of manufacture. Strength varies from one formulation to another and gradually decreases with long storage.

A 12% solution is widely [http://www.awwa.org/publications/AWWAJournalArticle.cfm?itemnumber=40152&showLogin=N] used in waterworks for the chlorination of water and a 15% solution is more commonly used for disinfection of waste water in treatment plants. High-test hypochlorite (HTH) is sold for chlorination of swimming pools and contains approximately 30% calcium hypochlorite. The crystalline salt is also sold for the same use; this salt usually contains less than 50% of calcium hypochlorite. However, the level of active chlorine may be much higher.

It can also be found on store shelves in Daily Sanitizing Sprays, as the sole active ingredient at 0.0095%.

Reactions

Sodium hypochlorite reacts with metals gradually, such as zinc, to produce the metal oxide or hydroxide:

NaOCl + Zn → ZnO + NaCl

It reacts with hydrochloric acid to release chlorine gas:

NaOCl + 2 HCl → Cl₂ + H₂O + NaCl

It reacts with other acids, such as acetic acid, to release hypochlorous acid:

NaOCl + CH₃COOH → HClO + CH₃COONa

It decomposes when heated or evaporated to form sodium chlorate and sodium chloride:

3 NaOCl → NaClO₃ + 2 NaCl

In reaction with hydrogen peroxide it gives off molecular oxygen:

NaOCl + H₂O₂→ H₂O + NaCl + O₂↑

Uses

Bleaching

In household form, sodium hypochlorite is used for removal of stains from laundry. It is particularly effective on cotton fiber, which stains easily but bleaches well. Usually 50 to 250 mL of bleach per load is recommended for a standard-size washer. The properties of household bleach that make it effective for removing stains also result in cumulative damage to organic fibers such as cotton, and the useful lifespan of these materials will be shortened with regular bleaching. The sodium hydroxide (NaOH) that is also found in household bleach (as noted later) causes fiber degradation as well. It is not volatile, and residual amounts of NaOH not rinsed out will continue slowly degrading organic fibers in the presence of humidity. For these reasons, if stains are localized, spot treatments should be considered whenever possible. With safety precautions, post-treatment with vinegar (or another weak acid) will neutralize the NaOH, and volatilize the chlorine from residual hypochlorite. Old t-shirts and cotton sheets that rip easily demonstrate the costs of laundering with household bleach. Hot water increases the activity of the bleach, owing to the increased kinetic energy of the molecules.

Disinfection

A weak solution of 1% household bleach in warm water is used to sanitize smooth surfaces prior to brewing of beer or wine. Surfaces must be rinsed to avoid imparting flavors to the brew; these chlorinated byproducts of sanitizing surfaces are also harmful.

US Government regulations (21 CFR Part 178) allow food processing equipment and food contact surfaces to be sanitized with solutions containing bleach, provided that the solution is allowed to drain adequately before contact with food, and that the solutions do not exceed 200 parts per million

Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula NaHCO 3. Sodium bicarbonate is a white solid that is crystal line but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda ( sodium carbonate). It is

Sulfurous acid (British English: sulphurous acid) is the chemical compound with the formula H₂SO₃. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase. The conjugate bases of this elusive acid are, however, common anions, bisulfite (or hydrogensulfite) and sulfite.

Raman spectra of solutions of sulfur dioxide in water show only signals due to the SO₂ molecule and the bisulfite ion, HSO₃^−. The intensities of the signals are consistent with the following equilibrium:

SO₂ + H₂O HSO₃^− + H⁺

K_a = 1.54; pK_a = 1.81.

Aqueous solutions of sulfur dioxide, which sometimes are referred to as sulfurous acid are used as reducing agents and as disinfectants, as are solutions of bisulfite and sulfite salts. They are also mild bleaches, and are used for materials which may be damaged by chlorine-containing bleaches.

This industry classification includes establishments engaged in manufacturing alkalies and chlorine. Examples of products include compressed or liquefied chlorine, sodium or potassium hydroxide, sodium bicarbonate, and soda ash (not produced at mines). Alkalies produced by mining are classified in SIC 1474: Potash, Soda, and Borate Minerals. 325181 (Alkalies and Chlorine Manufacturing) The two primary commodities offered by the alkalies and chlorine industry are chlorine and sodium hydroxide (caustic soda), together representing about 82 percent of all shipments. Soda ash, an alkali product used in glassmaking, water treatment, pulp bleaching, and detergent manufacturing, accounts for only 14 percent of shipments. Other products account for the remaining 4 percent. Chlorine and caustic soda have consistently appeared on lists of the top 10 U.S. chemicals according to production weight. They are co-products of the same chemical process. This means that they are created at the same time and that the production of one results in the production of the other. Although there are several modern procedures used to produce chlorine and caustic soda, most rely on a technique called electrolysis. As electricity is passed through brine (a salt water solution), the brine's components, salt (sodium chloride) and water (made up of hydrogen and oxygen), recombine to form chlorine and sodium hydroxide (caustic soda) in approximately equal amounts. Some hydrogen gas also results from the process. Organic chemical manufacturers are the primary chlorine users in the United States. Some examples of chemicals produced with chlorine are ethylene dichloride, carbon tetrachloride, and methylene chloride. These and other chlorinated organic chemicals are used to make many products, including flame retardants, herbicides, solvents, refrigerants, polyvinylchloride (PVC) pipe, and pigments. The second-largest chlorine user is the pulp and paper industry, which uses chlorine as a bleaching agent. Chlorine products are also used as raw ingredients in household and commercial bleaches, scouring powders, and automatic dishwashing compounds. Other chlorine uses include water treatment, sewage treatment, sanitizing, and metal extracting. Caustic soda has a wide range of industrial applications. It is used in petroleum exploration and by water treatment facilities, tanneries, and the textile industry. It also plays a role in food processing, metal fabrication, and chemical manufacturing. Caustic soda is also used in industrial complexes to remove boiler scale. According to U.S. Department of Commerce statistics, shipments within the alkalies and chlorine industry totaled $2.3 billion in 2001, down from $2.5 billion in 1997. Despite the recent downward trend, the industry more than doubled between 1987 and 1997. The industry became volatile during the early 2001 as the U.S. economy became sluggish, and demand for chlorine and alkalies fell off. By 2003, the industry was beginning to show signs of recovery. Conditions within the chlorine segment of the industry affected other products. Because caustic soda is a co-product of chlorine, cuts in chlorine production lead to shortages and higher prices within the caustic soda market. Caustic soda, following an upward trend in natural gas prices, was priced between $190 to $220 per ton in April 2003. Although soda ash has been manufactured synthetically from the evaporation of brines, it is primarily produced from trona, a mined product. The last synthetic soda ash facility in the United States closed in 1986, idling 700,000 tons of capacity. Operators closed the plant because it could not produce soda ash at prices low enough to compete with the trona-reliant process. Almost half of the domestic production of soda ash is used by glassmakers. Approximately 99 percent of the chlorine and alkali chemical manufacturers in the United States and Canada belong to the Chlorine Institute, a group founded by 10 industry leaders in 1924. Although its original purpose was to further the demand for chlorine, its focus shifted to providing the industry with supervision and direction following a destructive hurricane in 1926 that wrought havoc on Florida's water treatment facilities. Thousands of chlorine cylinders were shipped to the state to aid in restoring safe water supplies, but many could not be used because the industry had no previously adopted standardized fittings. The emergency chlorine supply sat idle until adapters and valves could be obtained. As a result of this experience, the group initiated a study of valve and fitting designs and recommended a standard that was voluntarily adopted by producers. Federal officials later relied on information from the Chlorine Institute in establishing standards for all compressed gases. The Chlorine Institute also began working on programs to improve the safety record of the industry. In the 1930s an informal policy was established for responding to emergencies. Later the institute developed a formal program called CHLOREP (Chlorine Emergency Plan). CHLOREP consisted of volunteer teams available to respond to chlorine emergencies 24 hours a day, seven days a week. By 1991 the Chlorine Institute had trained 250 CHLOREP teams composed of members from more than 40 companies, and they were placed at more than 100 locations throughout the United States and Canada. In addition to establishing standards and emergency response programs, the Chlorine Institute has published a wide range of manuals, pamphlets, and audiovisual materials to provide technical and safety information. The group has also worked on behalf of its members with the government agencies responsible for regulating various aspects of chemical production and shipment such as the Department of Transportation (DOT), the Interstate Commerce Commission (ICC), the Coast Guard, and the Occupational Safety and Health Administration (OSHA). The use of chlorine compounds in chemical processes dates back to at least 77 A.D., but the isolated element itself was not produced until 1774. Although chlorine is a common element, in nature it exists only in compounds because it reacts readily with other substances, both organic and inorganic. For example, ordinary table salt, or sodium chloride, consists of chlorine and sodium. A Swedish chemist, Carl Wilhelm Scheele (1742-1786), is acknowledged as the first person to create and identify chlorine. Scheele (who also co-discovered oxygen) generated a greenish-yellow gas during experiments with sea water. He called it "dephlogisticated marine acid air." The word "dephlogisticated" referred to the fact that it was not susceptible to combustion. The phrase "marine acid air" identified the new gaseous material produced from the acid obtained from marine brine. In 1810, when Sir Humphry Davy (1778-1829) used electricity to prove that the gas was an element, he coined the word "chlorine" from chloros, the Greek word for greenish yellow. The bleaching effects of chlorine were first put to commercial use by textile makers in France near the end of the eighteenth century. Natural cottons and linens were light brown and required bleaching before they could be dyed with light or bright colors. Traditionally this had been accomplished by spreading the fabrics out and exposing them to the sun. Bleaching fabrics in this manner took as long as three months for cotton and as long as six months for linen. Chlorine bleaching compounds enabled textile manufacturers to keep up with the increasing speed of production that followed improvements in spinning and weaving methods. Chlorine products were greatly improved by technology during the late eighteenth and early nineteenth centuries. In 1792 a process for bleaching rags used in paper making was developed. Bleaching powder, or calcium hypochlorite, was first introduced in 1799. The ability to transport chlorine to markets distant from manufacturing plants was achieved through the formation of potassium hypochlorite, a liquid product created with chlorine and caustic potash. The development of chlorine production based on electrolysis lowered chlorine prices and increased