sodium hypochlorite (n.)
1.an unstable salt (NaOCl) used as a bleaching agent and disinfectant
Sodium Hypochlorite (n.)
1.(MeSH)It is used as an oxidizing and bleaching agent and as a disinfectant. (From Grant&Hackh's Chemical Dictionary, 5th ed)
voir la définition de Wikipedia
Sodium Hypochlorite (n.) (MeSH)
sodium hypochlorite (n.)
Inorganic Chemicals - Acids, Noncarboxylic, Noncarboxylic Acids - Oxides - Active Oxygen, Oxygen Radicals, Oxygen Species, Reactive, Pro-Oxidants, Reactive Oxygen Species - Chlorine Compounds, Chlorine Compounds, Inorganic[Hyper.]
Sodium Hypochlorite (n.) [MeSH]
substance du textile (fr)[ClasseParExt.]
produit d'entretien (fr)[ClasseParExt...]
détergent et savon (fr)[Thème]
pureté de la matière (fr)[Thème]
perdre sa (ses) couleur(s) (fr)[termes liés]
bactericidal, disinfectant, germicidal[CeQuiEst~]
substance pour laver (fr)[ClasseParExt.]
eau de javel (fr)[Thème]
pureté de la matière (fr)[termes liés]
sodium hypochlorite (n.)
|Jmol-3D images||Image 1|
|Molar mass||74.442 g/mol|
|Odor||disagreeable and sweetish|
18 °C, 291 K, 64 °F (pentahydrate)
101 °C, 374 K, 214 °F (decomp.)
|Solubility in water||29.3 g/100mL (0 °C)|
|MSDS||ICSC 1119 (solution, >10% active chlorine)
ICSC 0482 (solution, <10% active chlorine)
|EU classification||Corrosive (C)
Dangerous for the environment (N)
|S-phrases||, , , ,|
|Other anions||Sodium chloride
|Other cations||Lithium hypochlorite
|Related compounds||Hypochlorous acid|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Sodium 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 alternative 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 that was sold after World War I under the trade names "Eusol" and "Dakin's solution".
Near the end of the nineteenth century, E. S. Smith patented a method of sodium hypochlorite production involving electrolysis of brine to produce sodium hydroxide and chlorine gas, which then mixed to form sodium hypochlorite. This is known as the chloralkali process. Both electric power and brine solution were in cheap supply at the time, and various enterprising marketers took advantage of the situation to satisfy the market's demand for sodium hypochlorite. Bottled solutions of sodium hypochlorite were sold under numerous trade names.
Today, an improved version of this method, known as the Hooker process, is the only large scale industrial method of sodium hypochlorite production. In the process, sodium hypochlorite (NaClO) 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.
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.
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 used in waterworks for the chlorination of water, and a 15% solution is more commonly used for disinfection of waste water in treatment plants. Sodium hypochlorite can also be used for point-of-use disinfection of drinking water.
Sodium hypochlorite reacts with metals gradually, such as zinc, to produce the metal oxide or hydroxide:
It reacts with hydrochloric acid to release chlorine gas:
It reacts with other acids, such as acetic acid, to release hypochlorous acid:
It decomposes when heated to form sodium chlorate and sodium chloride:
In reaction with hydrogen peroxide it gives off molecular oxygen:
When dissolved in a solution of water, it will slowly decompose, releasing chlorine, oxygen, and sodium hydroxide.
Household bleach is, in general, a solution containing 4-6% sodium hypochlorite and 0.01-0.05% sodium hydroxide; the sodium hydroxide is used to delay the breakdown of sodium hypochlorite into sodium chloride and sodium chlorate.
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 effectiveness of the bleach, owing to the increased reactivity of the molecules.
A weak solution of 2% 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 (ppm) available chlorine (for example, one tablespoon of typical household bleach containing 5.25% sodium hypochlorite, per gallon of water). If higher concentrations are used, the surface must be rinsed with potable water after sanitizing.
A 1-in-5 dilution of household bleach with water (1 part bleach to 4 parts water) is effective against many bacteria and some viruses, and is often the disinfectant of choice in cleaning surfaces in hospitals (primarily in the United States). The solution is corrosive, and needs to be thoroughly removed afterwards, so the bleach disinfection is sometimes followed by an ethanol disinfection. Even "scientific-grade", commercially produced disinfection solutions such as Virocidin-X usually have sodium hypochlorite as their sole active ingredient, though they also contain surfactants (to prevent beading) and fragrances (to conceal the bleach smell).
For shock chlorination of wells or water systems, a 3% solution of household bleach is used. For larger systems, sodium hypochlorite is more practical because lower rates can be used. The alkalinity of the sodium hypochlorite solution also causes the precipitation of minerals such as calcium carbonate, so that the shock chlorination is often accompanied by a clogging effect. The precipitate also preserves bacteria, making this practice somewhat less effective.
Sodium hypochlorite has been used for the disinfection of drinking water. A concentration equivalent to about 1 liter of household bleach per 4000 liters of water is used. The exact amount required depends on the water chemistry, temperature, contact time, and presence or absence of sediment. In large-scale applications, residual chlorine is measured to titrate the proper dosing rate. For emergency disinfection, the United States Environmental Protection Agency recommends the use of 2 drops of 4% to 6% household bleach per litre of water. If the treated water does not smell of bleach, 2 more drops are to be added.
Many who would prefer to store drinking water on a long term basis for emergency use should consider following the same treatment protocol during the storage process (and not when the time comes to access the water); typically using the 'additional' treatment rate of approximately 15 drops per gallon of water (~1 spoon full per 7 gallons of water) unless the water is from a municipality and is known to be free of excessive contaminants and already contains a certain amount of sodium hypochlorite. Note that you should confirm that the water has a bleach scent after sitting for half an hour. Additionally, dumping the water and replacing it every 3~5 years is recommended. Washing out the food grade containers (usually made of polyethylene) during this time is encouraged by using warm soapy water or alternatively a solution of water with heavy concentration of bleach (10x 'additional' rate) followed by rinsing with clean water.
The use of chlorine-based disinfectants in domestic water, although widespread, has led to some controversy due to the formation of small quantities of harmful byproducts such as chloroform.
An alkaline solution (pH 11.0) of sodium hypochlorite is used to treat dilute (< 1 g/L) cyanide wastewater, e.g., rinsewater from an electroplating shop. In batch treatment operations, sodium hypochlorite has been used to treat more concentrated cyanide wastes, such as silver cyanide plating solutions. A well-mixed solution is fully treated when an excess of chlorine is detected.
Sodium hypochlorite is now used in endodontics during root canal treatments. It is the medicament of choice due to its efficacy against pathogenic organisms and pulp digestion. In previous times, Henry Drysdale Dakin's solution (0.5%) had been used. Its concentration for use in endodontics today varies from 0.5% to 5.25%. At low concentrations it will dissolve mainly necrotic tissue; whereas at higher concentrations tissue dissolution is better but it also dissolves vital tissue, a generally undesirable effect. It has been shown that clinical effectiveness does not increase conclusively for concentrations higher than 1%.
At the various nerve agent destruction facilities throughout the United States, 50% sodium hypochlorite is used as a means of removing all traces of nerve agent or blister agent from PPE (Personal Protection Equipment) after an entry is made by personnel into toxic areas. 50% sodium hypochlorite is also used to neutralize any accidental releases of nerve agent in the toxic areas. Lesser concentrations of sodium hypochlorite are used in similar fashion in the PAS (Pollution Abatement System) to ensure that no nerve agent is released in furnace flue gas.
Sodium hypochlorite is a strong oxidizer. Oxidation reactions are corrosive, solutions burn skin and cause eye damage, in particular, when used in concentrated forms. However, as recognized by the NFPA, only solutions containing more than 40% sodium hypochlorite by weight are considered hazardous oxidizers. Solutions less than 40% are classified as a moderate oxidizing hazard (NFPA 430, 2000).
Household bleach and pool chlorinator solutions are typically stabilized by a significant concentration of lye (caustic soda, NaOH) as part of the manufacturing reaction. Skin contact will produce caustic irritation or burns due to defatting and saponification of skin oils and destruction of tissue. The slippery feel of bleach on skin is due to this process. Trichloramine, the gas that is in swimming pools can cause atopic asthma. 
Sodium thiosulfate (thio) is an effective chlorine neutralizer. Rinsing with a 5 mg/L solution, followed by washing with soap and water, quickly removes chlorine odor from the hands.
Mixing bleach with some household cleaners can be hazardous. For example, mixing an acid cleaner with sodium hypochlorite bleach generates chlorine gas. Mixing with ammonia solutions (including urine) produces chloramines. Mixtures of other cleaning agents and or organic matter can result in a gaseous reaction that can cause acute lung injury. 
It is estimated that there are about 3300 accidents needing hospital treatment caused by sodium hypochlorite solutions each year in British homes (RoSPA, 2002).
One major concern arising from sodium hypochlorite use is that it tends to form chlorinated organic compounds; this can occur during household storage and use as well during industrial use. For example, when household bleach and wastewater were mixed, 1-2% of the available chlorine was observed to form organic compounds. As of 1994, not all the byproducts had been identified, but identified compounds include chloroform and carbon tetrachloride. The estimated exposure to these chemicals from use is estimated to be within occupational exposure limits.
A recent European study indicated that sodium hypochlorite and organic chemicals (e.g., surfactants, fragrances) contained in several household cleaning products can react to generate chlorinated volatile organic compounds (VOCs). These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable human carcinogens. The study showed that indoor air concentrations significantly increase (8-52 times for chloroform and 1-1170 times for carbon tetrachloride, respectively, above baseline quantities in the household) during the use of bleach containing products. The increase in chlorinated volatile organic compound concentrations was the lowest for plain bleach and the highest for the products in the form of “thick liquid and gel”. The significant increases observed in indoor air concentrations of several chlorinated VOCs (especially carbon tetrachloride and chloroform) indicate that the bleach use may be a source that could be important in terms of inhalation exposure to these compounds. While the authors suggested that using these cleaning products may significantly increase the cancer risk, this conclusion appears to be hypothetical:
Further studies of the use of these products and other possible exposure routes (i.e., dermal) may reveal other risks. Though the author further cited ozone depletion greenhouse effects for these gases, the very low amount of such gases, generated as prescribed, should minimize their contribution relative to other sources.
A study on housewives showed that exposure to common household cleaning products with sodium hypochlorite can cause Reactive Airway Dysfunction Syndrome (RADS). RADS contains "asthma-like symptoms" and its severity depends on exposure and environmental factors. The long term effects have not been recorded. Due to the onset of RADS, caution should be emphasized when using bleach and other chemicals. 
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