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Sodium hypochlorite


 
 
Sodium hypochlorite is a chemical compoundChemical compound

A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a ...
 with the formulaChemical formula

A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compoun...
 NaClO. Sodium hypochlorite solution, commonly known as bleachBleach

To bleach something is to remove or lighten its color; a "bleach" is a chemical that can produce these effects, often via ox...
, is frequently used as a disinfectant and as a bleaching agent.
ProductionSodium hypochlorite may be prepared by absorbing chlorineChlorine

Chlorine , is the chemical element with atomic number 17 and symbol Cl....
 gas in cold sodium hydroxideSodium hydroxide

Sodium hydroxide , also known as lye or caustic soda, is a caustic metallic base....
 solution:

2NaOH + Cl2 ? NaCl + NaClO + H2O


Sodium hydroxide and chlorine are commercially produced by the chloralkali processChloralkali process

A chloralkali process is any which produces chlorine or a related oxidizer, such as bleaching powder and an alkaline salt su...
, and there is no need to isolate them to prepare sodium hypochlorite. Hence NaClO is prepared industrially by the electrolysisFacts About Electrolysis

In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric ...
 of sodium chlorideSodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula NaCl....
 solution with minimal separation between the anodeAnode

An anode is the electrode in a device that electrons flow out of to return to the circuit....
 and the cathodeCathode

A cathode is the electrode at which electrons go into a cell, tube or diode, whether driven externally or internally....
. The solution must be kept below 40 °C (by cooling coils) to prevent the formation of sodium chlorateSodium chlorate

Sodium chlorate is an oxidizing agent....
.

The commercial solutions always contain significant amounts of sodium chloride (common salt) as the main byproduct, as seen in the equation above.
Packaging and saleHousehold bleach sold for use in laundering clothes is a 3-6% solutionPercentage solution

In biology percentage solutions are often preferred to molar ones....
 of sodium hypochlorite at the time of manufacture.






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Sodium hypochlorite is a chemical compoundChemical compound

A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a ...
 with the formulaChemical formula

A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compoun...
 NaClO. Sodium hypochlorite solution, commonly known as bleachBleach

To bleach something is to remove or lighten its color; a "bleach" is a chemical that can produce these effects, often via ox...
, is frequently used as a disinfectant and as a bleaching agent.

Production

Sodium hypochlorite may be prepared by absorbing chlorineChlorine

Chlorine , is the chemical element with atomic number 17 and symbol Cl....
 gas in cold sodium hydroxideSodium hydroxide

Sodium hydroxide , also known as lye or caustic soda, is a caustic metallic base....
 solution:

2NaOH + Cl2 ? NaCl + NaClO + H2O


Sodium hydroxide and chlorine are commercially produced by the chloralkali processChloralkali process

A chloralkali process is any which produces chlorine or a related oxidizer, such as bleaching powder and an alkaline salt su...
, and there is no need to isolate them to prepare sodium hypochlorite. Hence NaClO is prepared industrially by the electrolysisFacts About Electrolysis

In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric ...
 of sodium chlorideSodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula NaCl....
 solution with minimal separation between the anodeAnode

An anode is the electrode in a device that electrons flow out of to return to the circuit....
 and the cathodeCathode

A cathode is the electrode at which electrons go into a cell, tube or diode, whether driven externally or internally....
. The solution must be kept below 40 °C (by cooling coils) to prevent the formation of sodium chlorateSodium chlorate

Sodium chlorate is an oxidizing agent....
.

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

Packaging and sale

Household bleach sold for use in laundering clothes is a 3-6% solutionPercentage solution

In biology percentage solutions are often preferred to molar ones....
 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 chlorinationChlorination

Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for hum...
 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%.

Uses

Bleaching

In household bleachBleach

To bleach something is to remove or lighten its color; a "bleach" is a chemical that can produce these effects, often via ox...
 form, sodium hypochlorite is used for removal of stains from laundry. It is particularly effective on cotton fiber, which stains easily but bleaches well. 50 to 250 ml per load is usually 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 weak organic acids such as acetic (vinegar) 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 thermal decomposition of hypochlorite which ultimately generates environmentally-undesirable chlorate.

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 the solution is allowed to drain adequately before contact with food, and 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 virusVirus

A virus is a microscopic particle that can infect the cells of a biological organism....
es, and is often the disinfectant of choice in cleaning surfaces in hospitals (Primarily in the United States). The solution is corrosiveCorrosion

Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment....
, and needs to be thoroughly removed afterwards, so the bleach disinfection is sometimes followed by an ethanolEthanol

This article is about the chemical compound....
 disinfection.

Water treatment

For shock chlorinationShock chlorination

Shock chlorination is a process used in many swimming pools, water wells, springs, and other water sources to reduce the bac...
 of wells or water systems, a 2% solution of household bleach is used. For larger systems, HTH 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 AgencyUnited States Environmental Protection Agency

The Environmental Protection Agency is an agency of the federal government of the United States charged with protecting hum...
 recommends the use of 2 drops of 5%ac household bleach per quart of water. If the treated water doesn't smell of bleach, 2 more drops are to be added.

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 chloroformChloroform

Chloroform, also known as trichloromethane and methyl trichloride, is a chemical compound with formula CHCl3....
.

Endodontics

Sodium hypochlorite is now used in endodonticsEndodontics Summary

Endodontics is a specialty of dentistry, that deals with the tooth pulp and tissues surrounding the root of a tooth....
 during root canal treatments. It is the medicament of choice due to its efficacy against pathogenic organisms and pulp digestion. Historically, Henry Drysdale DakinHenry Drysdale Dakin

Henry Drysdale Dakin was an English chemist....
'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 clinical effectiveness does not increase conclusively for concentrations higher than 1% .

Wastewater treatment

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 in the form of household bleach is often used to oxidize foul-smelling thiolThiol

In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom...
 wastes generated in a chemistry laboratory.

Oxidation

Household bleach, with a phase-transfer catalyst, has been reported to oxidize alcohols to the corresponding carbonyl compound.

Mechanism of action

See Hypochlorous acidHypochlorous acid

Hypochlorous acid is a weak acid with the chemical formula HOCl....
.

Safety

Sodium hypochlorite is a strong oxidizer. Products of the oxidation reactions are corrosive. Solutions burn skin and cause eye damage, particularly 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 defattingFacts About Defatting

Defatting is a food preparation technique intended to reduce the fat content of a meal....
 and saponificationSaponification

Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of the acid....
 of skin oils and destruction of tissue. The slippery feel of bleach on skin is due to this process.

Sodium thiosulfateSodium thiosulfate Overview

Sodium thiosulfate is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O35H2O, an effloresce...
 (hypo) is an effective chlorine neutralizer. Rinsing with a 5mg/L solution, followed by washing with soap and water, quickly removes chlorine odor from the hands.

Chlorination of drinking water can oxidize organic contaminants, producing trihalomethaneFacts About Trihalomethane

Trihalomethanes are chemical compounds in which three of the four hydrogen atoms of methane are replaced by halogen atoms....
s (also called haloforms), which are carcinogenic. The extent of the hazard thus created is a subject of disagreement.

Mixing bleach with some household cleaners can be hazardous. For example, mixing an acidAcid

An acid is traditionally considered any chemical compound that when dissolved in water, gives a solution with a pH of less ...
 cleaner with sodium hypochlorite bleach generates chlorineChlorine

Chlorine , is the chemical element with atomic number 17 and symbol Cl....
 gas. Mixing with ammoniaAmmonia

Ammonia is a compound of nitrogen and hydrogen with the formula NH3....
 solutions (including urineUrine

}Urine is liquid produced by an animal's kidney, collected in the bladder and excreted through the urethra....
) produces chloramineChloramine

Chloramine is chemical compound with the formula NH2Cl....
s. Both chlorine gas and chloramine gas are toxic. Bleach can react violently with hydrogen peroxideHydrogen peroxide

Hydrogen peroxide is a very pale blue liquid which appears clear in a dilute solution, slightly more viscous than water....
 and produce oxygen gas:

H2O2 (aqueous) + NaClO(aqueous) ? NaCl(aqueous) + H2O(liquid) + O2 (gas)


It is estimated that there are about 3300 accidents needing hospital treatment caused by sodium hypochlorite solutions each year in British homes (RoSPA, 2002).

A number of commonly used household cleaning products (bleaches, mildew stain removers, toilet cleaners, cleaning sprays, gels, and scouring powders) contain sodium hypochlorite that is often accompanied by many other chemicals (e.g., surfactants and fragrances). Mixing bleach with ammonia-based cleaners results in formation of chloramines while mixing it with an acid-based cleaner will cause chlorine gas release. Therefore, the main concern associated with the use of chlorine-bleach-containing cleaning-products has been mixing them with other cleaning products that can generate hazardous fumes.

A recent study indicated for the first time that sodium hypochlorite and organic chemicals (e.g., surfactants, fragrances) contained in several household cleaning products react to generate chlorinated volatile organic compounds (VOCs). These chlorinated compounds are emitted during cleaning applications and most of them 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) 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 household bleach use is a newly identified source that could be important in terms of inhalation exposure to these compounds . Preliminary risk assessment suggested that using these cleaning products may significantly increase the cancer risk. Further studies are also needed for a detailed investigation of the health risks associated with the use of these products and other possible exposure routes (i.e., dermal). However, these are not the only adverse environmental effects of the released VOCs, they are also ozone depleting compounds and powerful greenhouse gases.

Bibliography

  • Institut National de Recherche et de Sécurité. (2004). "Eaux et extraits de Javel. Hypochlorite de sodium en solution". Fiche toxicologique n° 157, Paris.

External links

  • (solutions<10% active Cl)
  • (solutions >10% active Cl)
  • (in French)
  • (UK RoSPA)
  • (US NIH)
  • (Oklahoma State University)