Sodium hypochlorite is a chemical compound with the formula NaOCl or NaClO, which consists of sodium cations ( Na
) and hypochlorite anions ( ClO - or OCL -
). It can also be seen as a sodium salt of hypochlorite acid.
Sodium hypochlorite is most often encountered as a greenish-yellow aqueous solution commonly known as bleaching fluid or just bleaching, household chemicals that are widely used (since the 18th century) as disinfectant or whitening agent.
Anhydrous compounds are unstable and can be decomposed explosively. These can be crystallized as pentahydrate NaOCl Ã, Â · 5 H
2 O, an unexplained and stable pale yellow-green solid if stored in the refrigerator. The compound in the solution freely decomposes liberating chlorine, which is the active principle of the product. Indeed, sodium hypochlorite is the oldest and most important chlorine-based bleach.
Although sodium hypochlorite is not toxic properly, its general availability, corrosive properties, and reaction products make it a significant safety risk. In particular, mixing the bleach liquid with other cleaning products, such as acids or ammonia, can produce toxic fumes.
Video Sodium hypochlorite
Chemistry
Solid stability
Anhydrous sodium hypochlorite can be prepared; However, like many hypochlorites, it is extremely unstable and decomposes explosively on heating or friction. Decomposition is accelerated by carbon dioxide at atmospheric levels. It is a white solid with orthorhombic crystal structure.
Sodium hypochlorite can also be obtained as a pentahydrate of crystals NaOCl Ã, Â · 5 H
2 O , which is not explosive and much more stable than anhydrous compounds. This formula is sometimes given as 2 NaOCl Ã, Â · 10 H
2 O . The orthorhombic crystal is transparent greenish yellow containing 44% heavy NaOCl and melt at 25-27 ° C. The compound decomposes rapidly at room temperature, so it should be stored under cooling. At lower temperatures, however, it is quite stable: reportedly only 1% decomposition after 360 days at 7 ° C.
United States Patent 1966 claims that sodium hypochlorite dihydrate is stable NaOCl Ã, Â · 2 H
2 O can be obtained with care not including chloride ions ( Cl - ), which is present in the general manufacturing process output and is said to catalyze the decomposition of hypochlorite into chlorate ( ClO < span> -
3 ) and chloride. In one test, the dihydrate is expressed only showing a 6% decomposition after 13.5 months storage at -25 ° C. This patent also claims that the dihydrate can be reduced to anhydrous form by vacuum drying at about 50 ° C, producing solids that do not show decomposition after 64 hours at -25 ° C for 64 hours.
The equilibrium and stability of the solution
At typical ambient temperatures, sodium hypochlorite is more stable in aqueous solutions, which contain Na
and OCL - > ion. The density of the solution is 1.093 g/mL at a concentration of 5%, and 1.21 g/mL at 14%, 20 deg C. The stoichiometric solution is fairly basic, with a pH of 11 or more due to hypochlorite acid is a weak acid:
- OCl - H
2 O ? HOCl OH -
Seperti pada kebanyakan larutan hipoklorit, spesies dan equilibria berikut hadir dalam larutan NaOCl :
- HOCl? H
OCl -
- 2 HOCl? Cl
2 H
2 O
The second equilibrium equation above will shift to the right if chlorine Cl
2 is allowed to pass as a gas. Ratio Cl
2 , HOCl, and OCl -
in solution also depends on pH. At pH below 2, most of the chlorine in the solution is in the form of solute element Cl
2 . At a pH greater than 7.4, the majority is in the form of hypochlorite acid HClO . Equilibrium can be shifted by adding acid (such as hydrochloric acid) or base (such as sodium hydroxide) to solution:
- ClO - (aq) 2 HCl (aq) -> Cl
2 (g) H
2 O (aq) Cl -
(aq) - Cl
2 ( g) 2 OH - -> ClO - aq) Cl - ( aq) H
2 O (aq)
At a pH of about 4, as obtained by addition of a weak acid such as acetic acid, the undistributed (unionized) HOCl amount is the highest. The reactions can be written as:
- ClO - (aq) CH
3 COOH (aq) -> HClO CH
3 COO
-> Cl
2 (g) 2 Na
(aq)
At pH & gt; 8, chlorine is practically all in the form of anion hypochlorite ( OCl - ). The solution is quite stable at pH 11-12. However, one report claims that the conventional 13% NaOl reagent solution loses 17% of its strength after being stored for 360 days at 7 ° C. For this reason, in some applications one can use more stable chlorine-releasing compounds such as calcium hypochlorite < span> Ca (ClO)
2 trichloroisocyanuric (CNClO)
3 .
Sodium hypochlorite anhydrode is soluble in methanol, and the solution is stable.
Decomposition into chlorate or oxygen
Dalam larutan, dalam kondisi tertentu, anion hipoklorit mungkin juga tidak proporsional (teroksidasi) terhadap klorida dan klorat:
- 3 clO -
H
-> ClO -
3 } 2 Cl -
In particular, this reaction occurs in a solution of sodium hypochlorite at a temperature, forming sodium chlorate and sodium chloride: Naocl (aq) NaClO 3 (aq)
This reaction is exploited in industrial production of sodium chlorate.
Penguraian alternatif hipoklorit menghasilkan oksigen sebagai gantinya:
- 2 OCl -
-> 2 Cl -
O
2
In hot sodium hypochlorite solution, this reaction competes with chlorate formation, producing sodium chloride and oxygen gas:
- 2 NaOCl (aq) -> 2 NaCl (aq) O
2 (g)
The two decomposition reactions of the NaClO solution are maximized at a pH of about 6. Chlorine-producing reactions predominate at a pH above 6, while oxygen becomes significantly below it. For example, at 80 ° C, with NaOCl and NaCl concentrations of 80 mM, and pH 6-6.5, chlorates are produced at ~ 95% efficiency. The oxygen pathway predominates at pH 10. This decomposition is influenced by light ion catalysts and metals such as copper, nickel, cobalt, and iridium. Catalysts like sodium dichromate Na
2 Cr
2 O
7 and sodium molybdate Na
2 MoO
4 may be added industrially to reduce oxygen pathways, but reports claim that only the latter is effective.
Titration
Titration of the hypochlorite solution is often accomplished by adding a measured sample to a number of excess potassium iodide ( KI ) solutions and then liberated iodine titration ( I
2 ) with standard sodium thiosulfate or phenyl arsine oxide solution, using starch as indicator until blue disappeared.
According to one US patent, the stability of sodium hypochlorite content of a solid or solution can be determined by monitoring the infrared absorption due to the O-Cl bond. The characteristic wavelength is given as 140.25? M for aqueous solution, 140.05 for NaOClÃ,2,2 solid H
2 O , and 139.08? m for anhydrous mixed salt Na
2 (OCl) (OH) .
Oxidation of organic compounds
Oxidation of starch by sodium hypochlorite, which adds carbonyl and carboxyl groups, is relevant to the production of modified starch products.
In the presence of a phase transfer catalyst, the alcohol is oxidized to the corresponding carbonyl compound (aldehyde or ketone). Sodium hypochlorite may also oxidize organic sulfides to sulfoxides or sulfonates, disulfides or thiols to sulfonyl chloride or bromide, the imine being oxaziridine. It can also de-aromatize phenols.
Metal and complex oxidation
Heterogeneous sodium hypochlorite and metals such as zinc are slow to produce metal oxide or hydroxide:
- NaClO Zn -> ZnO NaCl
The homogeneous reaction with metal coordination complexes runs somewhat faster. This has been exploited in the epoxidation of Jacobsen.
Other reactions
If not stored properly in an airtight container, sodium hypochlorite reacts with carbon dioxide to form sodium carbonate:
- 2 NaOCl (aq) CO 2 (g) -> Na
2 CO
3 (aq) Cl
2 (g)
Sodium hypochlorite reacts with most of the nitrogen compounds to form volatile chlorine, dichlorine, and trichloride nitrogen:
- NH
3 NaClO -> NH
2 Cl NaOH - NH
2 Cl NaClO -> NHCl
2 NaOH - NHCl
2 NaClO -> NCl
3 NaOH
Neutralization
Sodium thiosulfate is an effective chlorine neutralizer. Rinsing with 5 mg/L solution, followed by washing with soap and water, will remove chlorine from the hand.
Maps Sodium hypochlorite
Production
Chlorination soda
Potassium hypochlorite was first produced in 1789 by Claude Louis Berthollet in his laboratory at Quai de Javel in Paris, France, by passing chlorine gas through a solution of potassium carbonate. The resulting liquid, known as " Eau de Javel " ("Javel water"), is a weak solution of potassium hypochlorite. Antoine Labarraque replaces potash lye with cheaper soda lye, thus obtaining sodium hypochlorite ( Eau de Labarraque ). (aq) H 2 O (aq) 2 <
Therefore, chlorine is simultaneously reduced and oxidized; this process is known as disproportion.
This process is also used to prepare pentahydrate NaOCl Ã, Â · 5 H
2 O for industrial and laboratory use. In a typical process, chlorine gas is added to a 45-48% NaOH solution. Some sodium chloride presiditates are removed by filtration, and pentahydrate is then obtained by cooling the filtrate to 12 ° C.
Of calcium hypochlorite
Metode lain yang melibatkan reaksi natrium karbonat ("soda pencuci") dengan kapur yang diklorinasi ("bubuk pemutih"), campuran kalsium hipoklorit Ca (OCl)
2 , kalsium klorida CaCl
2 , dan kalsium hydroxide Ca (OH)
2 :
- Na
2 CO
3 (aq) Ca (OCl)
2 (aq) -> CaCO
3 ( s) 2 NaOCl (aq) - Na
2 CO
3 (aq) CaCl
2 (aq) -> CaCO
3 (s) 2 NaCl (aq) - Na
2 CO
3 (aq) Ca (OH )
2 (aq) -> < span> CaCO
3 (s) 2 NaOH (aq)
This method is typically used to produce hypochlorite solutions for use as hospital antiseptics sold after World War I under the name "Eusol", the abbreviation for Edinburgh University Solution Of Lime (Chlorinated) - a reference to the university's pathology department, where it was developed.
Saltwater electrolysis
Toward the end of the nineteenth century, E. S. Smith patented the chloralkali process: a method of producing sodium hypochlorite involving saltwater electrolysis to produce sodium hydroxide and chlorine gas, which is then mixed to form sodium hypochlorite. The key reactions are:
2 O 2 -> H
2 2 HO - /span> (in the cathode)
Both electric power and salt water solutions are inexpensive supply at the time, and various enterprising marketers take advantage of the situation to meet market demand for sodium hypochlorite. The bottle of sodium hypochlorite solution is sold under various trade names.
Today, an improved version of this method, known as the Hooker process (named after Hooker Chemicals, acquired by Occidental Petroleum), is the only method of large-scale industrial production of sodium hypochlorite production. In the process, sodium hypochlorite (NaClO) and sodium chloride (NaCl) are formed when chlorine is passed into a cold dilute sodium hydroxide solution. Chlorine is prepared industrially with electrolysis with minimal separation between anode and cathode. The solution should be kept below 40 Ã, Â ° C (with cooling coil) to prevent unwanted sodium chlorate formation.
Commercial solutions always contain large amounts of sodium chloride (ordinary salt) as a major by-product, as seen in the above equation.
From hypochlorous acid and soda
Patent 1966 describes the production of stable solids of dihydrate NaOCl Ã, Â · 2 H
2 by reacting a solution of chloride-free hypochlorite acid HClO (as prepared from chlorine monoxide ClO and water) , with concentrated sodium hydroxide solution. In a typical preparation, 255 mL of a solution with 118 g/L HClO is slowly added with stirring into a solution of 40 g of NaOH in water 0 Â ° C. Some sodium chloride precipitates and is removed by fitration. The solution is vacuum evaporated at 40-50 Â ° C and 1-2 mmHg until the dyhydrate crystallizes out. The crystals are vacuum dried to produce a free flowing crystalline powder.
The same principle was used in another patent of 1991 to produce a slurry of NaClO Ã, Â · 5 H
2 O . Typically, a 35% (by weight) HClO solution is combined with sodium hydroxide at or below 25 ° C. The resulting slurry contains about 35% NaClO, and is relatively stable due to low chloride concentrations.
From ozone and salt
Sodium hypochlorite can be readily produced for research purposes by reacting ozone with salt.
- NaCl O 3 -> NaClO O 2
This reaction occurs at room temperature and can help to oxidize alcohol.
Packaging and sales
Household bleach sold for use in washing clothes is a 3-8% sodium hypochlorite solution at the time of manufacture. Strength varies from one formulation to another and gradually decreases with old storage. Sodium hydroxide is usually added in small amounts to household bleach to slow the decomposition of NaClO.
The 10-25% sodium hypochlorite solution, according to the Univar safety sheet, is supplied with a synonym or whitening trademark, Hypo, Everchlor, Chloros, Hispec, Bridos, Bleacol, or Vo-redox 9110.
A 12% solution is widely used in irrigation for water chlorination, and a 15% solution is more commonly used for disinfection of wastewater in treatment plants. Sodium hypochlorite can also be used for disinfection of drinking water at certain points.
Aqueous solutions (50 ppm to 1.5%) were found in spray disinfectants and tissues used on hard surfaces.
Usage
Bleaching
Household bleach is, in general, a solution containing 3-8% sodium hypochlorite, by weight, and 0.01-0.05% sodium hydroxide; sodium hydroxide is used to slow the decomposition of sodium hypochlorite into sodium chloride and sodium chlorate.
Clean
Sodium hypochlorite has destaining properties. Among other applications, it can be used to remove mold stains, tooth stains caused by fluorosis, and stains on the equipment, especially those caused by tannins in tea. It has also been used in detergents and as a surface cleaner.
The effects of bleaching, cleansing, deodorizing and caustic are caused by oxidation and hydrolysis (saponification). Organic waste affected by hypochlorite becomes water soluble and non-volatile, which reduces the odor and facilitates its removal.
Disinfection
Sodium hypochlorite in the solution exhibits broad spectrum anti-microbial activity and is widely used in health care facilities in a variety of settings. It is usually dissolved in water depending on the intended use. The "strong chlorine solution" is a 0.5% hypochlorite solution (containing about 5000 ppm of free chlorine) used to disinfect areas contaminated with body fluids, including large blood spills (this area is first cleaned with detergent before it is disinfected). This can be done by diluting the household bleach properly (usually 1 part of bleach to 9 parts water). The solution has been shown to disable both C. difficile and HPV. The "weak chlorine solution" is a 0.05% hypochlorite solution used for hand washing, but is usually prepared with calcium hypochlorite granules.
The "Dakin solution" is a disinfectant solution containing low concentrations of sodium hypochlorite and some boric acid or sodium bicarbonate to stabilize the pH. It has been found to be effective with a concentration of NaOCl as low as 0.025%.
US government regulations allow food processing equipment and food contact surfaces to be cleaned with a bleach-containing solution, provided that the solution is allowed to flow sufficiently before contact with food, and that the solution does not exceed 200 parts per million (ppm) of chlorine available (eg, one tablespoon of bleach typical households containing 5.25% sodium hypochlorite, per gallon of water). If higher concentrations are used, the surface should be rinsed with drinking water after cleaning.
The same concentration of bleach in warm water is used to clean the surface before brewing beer or wine. The surface should be rinsed with sterilized water to avoid flavoring the drink; Chlorinated byproducts from the cleaning surfaces are also dangerous. The mode of action of sodium hypochlorite disinfectant is similar to that of hypochlorite acid.
Solutions containing more than 500 ppm of chlorine are available corrosive to some metals, alloys and many thermoplastics (such as acetal resins) and should be completely removed thereafter, so bleaching disinfection is sometimes followed by disinfecting ethanol. The sodium hypochlorite-containing liquid as the main active component is also used for household cleaning and disinfection, for example toilet cleaners. Some cleansers are formulated so that the thickness does not dry quickly from the vertical surface, such as the inside of the toilet bowl.
Nonionized (nonionized) hypochlorite acids are believed to react with and inactivate bacterial and viral enzymes.
Neutrophils of the human immune system produce small amounts of hypochlorite in the phagosome, which digest bacteria and viruses.
Eliminate odor
Sodium hypochlorite has a deodorizing properties, which go hand in hand with its cleaning properties.
Wastewater treatment
Sodium hypochlorite solutions have been used to treat dilute cyanide water, such as electroplating wastes. In batch processing operations, sodium hypochlorite has been used to treat more concentrated cyanide waste, such as silver cyanide coating solution. Toxic cyanides are oxidized to non-toxic (OCN - ) cyanide, idealized as follows:
- CN - OCl - -> OCN - Cl -
Sodium hypochlorite is generally used as a biocide in industrial applications to control mucus and bacterial formation in water systems used in power plants, pulp and paper mills, etc., in solutions typically 10-15% by weight.
Endodontics
Sodium hypochlorite is the drug of choice because of its efficacy against pathogenic organisms and pulp digestion in endodontic therapy. The concentration of use varies from 0.5% to 5.25%. At low concentrations dissolve especially necrotic tissue; at higher concentrations it also dissolves vital tissues and additional bacterial species. One study has shown that Enterococcus faecalis is still present in the dentin after 40 minutes of exposure 1.3% and 2.5% sodium hypochlorite, while 40 min at 5.25% concentration is effective in E. faecalis deletion. In addition to higher sodium hypochlorite concentrations, longer time exposure and heating solutions also increase their effectiveness in removing soft tissues and bacteria in the root canal space. 2% is a general concentration because there is less risk of iatrogenic hypochlorite incidence. The occurrence of hypochlorite is a direct reaction of severe pain, followed by edema, hematoma, and ecchymoses as a consequence of a solution that comes out of the teeth boundaries and enters the periapical space. This may be due to binding or excessive pressure on the syringe, or may occur if the tooth has a very large apical foramen.
Neutralization of nerve agents
In various neural agents (chemical nerve gas fuel) destruction facilities across the United States, 50% of sodium hypochlorite is used to remove all traces of nerve agents or blister agents from Personal Protection Equipment after entries are made by personnel to the toxic area. 50% sodium hypochlorite is also used to neutralize any unintentional nerve agent release in the toxic area. The lower concentrations of sodium hypochlorite are used in the same way in the Pollution Reduction System to ensure that no nerve agents are released in the flue gases.
Skin damage reduction
Bathing whitened baths have been used for decades to treat moderate to severe eczema in humans, but it is unclear why they work. According to a study published by researchers at Stanford University School of Medicine in November 2013, a very dilute sodium hypochlorite solution (0.005%) in water successfully treated skin damage with inflammatory components caused by radiation therapy, excessive sun exposure or aging. in lab rats. Mice with radiation dermatitis given daily bath 30 minutes in bleach solution suffered more severe skin damage and better healing and hair regrowth than animals bathed in water. A molecule called a chain-enhancing kappa nuclear factor of activated B cell (NF-B) is known to play an important role in inflammation, aging, and radiation response. The researchers found that if NF-B activity was blocked in older rats by bathing them in a bleach solution, animal skin began to look younger, changing from aging and brittle to thicker, with increased cell proliferation. The effect is reduced after the shower is stopped, suggesting that regular exposure is necessary to maintain skin thickness.
Security
An estimated 3300 accidents require hospitalization caused by sodium hypochlorite solution each year in British homes (RoSPA, 2002).
Oxidation and corrosion
Sodium hypochlorite is a powerful oxidizing agent. The oxidation reaction is corrosive. Solutions burn the skin and cause eye damage, especially when used in concentrated form. However, as recognized by NFPA, only solutions containing more than 40% sodium hypochlorite by weight are considered to be harmful oxidizers. Solutions less than 40% are classified as moderate oxidizing hazards (NFPA 430, 2000).
Household bleach and pool chlorinator solutions are usually stabilized by significant concentrations of alkali solutions (caustic soda, NaOH) as part of the manufacturing reaction. This additive will in itself cause caustic irritation or burns due to defatting and saponification of skin oil and tissue destruction. The slippery taste of bleach on the skin is due to this process.
Hazard storage
Contact of sodium hypochlorite solution with metals may give rise to flammable hydrogen gas. The container may explode when heated due to the release of chlorine gas.
Hypochlorite solutions are corrosive to common contaner materials such as stainless steels and aluminum. Some compatible metals include titanium (which is however not compatible with dry chlorine) and tantalum. Safe glass container. Some plastics and rubber are also affected; safe options include polyethylene (PE), high density polyethylene (HDPE, PE-HD), polypropylene (PP), some chlorine and fluorinated polymers such as polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF); as well as ethylene propylene rubber, and Viton.
The container should allow oxygen ventilation generated by decomposition over time, otherwise they will explode.
Reactions with other common products
Mixing bleach with some household cleaners can be dangerous.
Sodium hypochlorite solutions, such as bleach, can release toxic chlorine gas when heated above 35 ° C or mixing acids, such as muriatic acid or vinegar.
A 2008 study showed that sodium hypochlorite and organic chemicals (eg, surfactants, fragrances) contained in some household cleaning products can react to produce chlorinated volatile organic compounds (VOCs). This chlorinated compound is emitted during cleaning applications, some of which are toxic and possible human carcinogens. This study showed that indoor air concentrations increased significantly (8-52 times for chloroform and 1-1170 times for carbon tetrachloride, respectively, above the baseline quantity in the household) during use of bleach-containing products. Increased concentrations of chlorinated volatile organic compounds are the lowest for plain bleach and the highest for products in the form of "thick liquid and gel." Significant improvements observed in indoor air concentrations of some chlorinated VOCs (especially carbon tetrachloride and chloroform) suggest that the use of bleach may be a potentially important source of inhalation exposure to these compounds. The authors suggest that using these cleaning products may increase cancer risk significantly.
In particular, mixing hypochlorite bleach with amines (eg, cleaning products containing or releasing ammonia), ammonium salts, urea, or related compounds and biological materials such as urine) produces chloramine and nitrogen trichloride. These gas products can cause acute lung injury. Chronic exposure, for example, from the air in the pool where chlorine is used as a disinfectant, can lead to the development of atopic asthma.
Bleach can react violently with hydrogen peroxide and produce oxygen gas: (aq) H 2 O (aq) 2 (aq) Na < O 2 (g)
Explosive reactions or byproducts may also occur in industrial and laboratory settings when sodium hypochlorite is mixed with formic acid, phenylacetonitrile, aziridine, and methanol.-- & gt;
Restrictions on health care
The National Institute for Excellence Health and Nursing UK in October 2008 recommended that the Dakin solution should not be used in routine wound care.
Environmental impact
In spite of strong biocidal action, sodium hypochlorite per se has limited environmental impact, as rapidly hypochlorite ions are degraded before they can be absorbed by living things.
However, one of the main concerns arising from the use of sodium hypochlorite is that it tends to form persistent chlorinated organic compounds, including known carcinogens, which can be absorbed by organisms and enter the food chain. These compounds may be formed during storage and use of households as well during industrial use. For example, when household bleach and wastewater are mixed, 1-2% of the available chlorine is observed to form organic compounds. In 1994, not all byproducts have been identified, but the identified compounds include chloroform and carbon tetrachloride. Estimates of exposure to these chemicals from use are thought to be within the limits of occupational exposure.
See also
- Calcium hypochlorite Ca (OCl)
2 ("whitener powder") - Potassium hypochlorite KOCl ("original Javel water")
- Lithium hypochlorite NaOCl
References
Bibliography
-
Jones, F.-L. (1972). "Chlorine poisoning from mixing household cleaners". J. Me. Med. Assoc . 222 (10): 1312. doi: 10.1001/jama.222.10.1312.
- National Institute de Recherche et de Sà © à © curitÃÆ' ©. (2004). "Eaux et extraits de Javel, Hypochlorite de sodium en solution." Toxicological Toxic n  ° 157, Paris.
External links
- International Chemical Safety Card 0482 (solution & lt; 10% active Cl)
- International Chemical Safety Card 1119 (solution & gt; 10% active Cl)
- The national institute de recherche et de sÃÆ' Â © curitÃÆ'Â © ( in French )
- Home and Accident Statistics 2002 (UK RoSPA)
- Emergency Disinfection from Drinking Water (United States Environmental Protection Agency)
- Alcoholic Beverages (IARC Monograph)
- NTP Study Report TR-392: Chlorinated & amp; Water Chloraminated (US NIH)
- Guidelines for the Use of Chlorine Bleach as Sanitizers in Food Processing Operations (Oklahoma State University)
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