Difference between revisions of "Bleach" - New World Encyclopedia
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| − | + | {{two other uses|the chemical substance|the anime/manga|Bleach (manga)}} | |
| − | + | [[Image:Bleach-bottle.jpg|right|thumb|150px|Commercial chlorine bleach]] | |
| − | + | To '''bleach''' something is to remove or lighten its [[color]]; a "bleach" is a [[chemical]] that can produce these effects, often via [[oxidation]]. Common chemical bleaches include a solution of [[sodium hypochlorite]] (NaOCl), or "chlorine bleach," and "oxygen bleach," which contains [[hydrogen peroxide]] or a peroxide-releasing compound such as [[sodium perborate]] or [[sodium percarbonate]]. "Bleaching powder" is [[calcium hypochlorite]]. Bleaching may be a preliminary step in the process of [[dyeing]]. | |
| − | == | + | == Types of bleach == |
| − | + | Household bleach, also known as '''chlorine bleach''', [[sodium hypochlorite]] (NaClO), has a [[pH]] level of 11 and is used in the home for whitening clothes, removing [[stain]]s, and [[disinfect]]ing. This is because sodium hypochlorite yields [[chlorine]] [[radical (chemistry)|radical]]s — [[oxidizing agent]]s readily reacting with many substances. Using chlorine bleach on garments made of wool, nylon, silk, leather or any amount of [[spandex]] will stain the garment yellow which is permanent or very difficult to remove.<ref>http://experts.about.com/q/Cleaning-2305/Yellow-Bleach-Stain.htm</ref> | |
| + | Chlorine bleach is often used with [[laundry detergent]]s and is also commonly used as a [[disinfectant]]. Mixing bleach and cleaners containing [[ammonia]], or using bleach to clean up [[urine]] can create toxic [[chloramine]] gases and an explosive called [[nitrogen trichloride]]. | ||
| − | + | Hair bleach contains H<sub><small>2</small></sub>O<sub><small>2</small></sub> ([[hydrogen peroxide]]), which gives off [[active oxygen|oxygen radicals]] as it decomposes. [[Oxygen]] and chlorine radicals both have comparable bleaching effects. | |
| − | + | Various other peroxide yielding chemicals are used as bleaching additives. [[Sodium perborate]], [[sodium percarbonate]], [[sodium persulfate]], [[sodium perphosphate]], [[sodium persilicate]], their ammonium, potassium and lithium analogs, [[calcium peroxide]], [[zinc peroxide]], [[sodium peroxide]], [[carbamide peroxide]], and others are commonly used in [[detergent]]s, [[toothpaste]]s, and other products. | |
| + | [[Chlorine dioxide]] is used for the bleaching of [[wood pulp]], [[fat]]s and [[oil]]s, [[cellulose]], [[flour]], [[textile]]s, [[beeswax]], and in a number of other industries. | ||
| + | In the food industry, some [[organic peroxide]]s ([[benzoyl peroxide]], etc.) and other agents (e.g. [[bromate]]s) are used as [[flour bleaching agent|flour bleaching]] and [[maturing agent]]s. | ||
| − | + | Not all bleaches have to be of oxidizing nature. [[Sodium dithionite]] is used as a powerful reducing agent in some bleaching formulas. | |
| − | == | + | == How bleaches work == |
| + | {{sectstub}} | ||
| − | + | Color in most [[dye]]s and [[pigment]]s are produced by molecules, such as [[beta carotene]], that contain [[moiety|moieties]] (pieces) known as [[chromophore]]s. Chemical bleaches work in one of two ways: | |
| − | + | *An oxidizing bleach works by breaking the [[chemical bond]]s that make up the chromophore. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb [[visible light]]. | |
| − | == | + | *A reducing bleach works by converting [[double bond]]s in the chromophore into [[single bond]]s. This eliminates the ability of the chromophore to absorb visible light.<ref>{{ cite web|url=http://sci-toys.com/ingredients/bleach.html| title=Ingredients — Bleach| work=Science Toys| year=2006| accessdate=2006-03-02|author=Field, Simon Q}}</ref> |
| − | + | Sunlight acts as a bleach through a process leading to similar results: high energy [[photon]]s of light, often in the [[Violet (color)|violet]] or [[ultraviolet]] range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless.<ref>{{ cite web|url=http://howthingswork.virginia.edu/sunlight.html| title=Sunlight| work=How Things Work Home Page| year=2006| accessdate=2006-03-02|author=Bloomfield, Louis A}}</ref> | |
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== Hazards == | == Hazards == | ||
| − | + | A problem with chlorine is that it reacts with organic material to form [[trihalomethane]]s like [[chloroform]], which is a well known [[carcinogen]]. There is debate over whether any risk from the chloroform in treated [[drinking water]] is worth the benefits. However, the use of elemental chlorine in industrial processes such as paper bleaching, with its attendant production of organochlorine-persistent organic pollutants (including [[dioxins]]), does not have any benefits. As a consequence over 80 % of the woodpulp is nowadays bleached with chlorine dioxide, reducing the dioxin generation under detectable levels. | |
| − | + | Chlorine is a respiratory irritant. It also attacks [[mucous membrane]]s and [[burn (injury)|burns]] the skin. As little as 3.5 [[parts_per_million|ppm]] can be detected as an odor, and 1000 [[parts_per_million|ppm]] is likely to be fatal after a few deep breaths. Exposure to chlorine should not exceed 0.5 [[parts_per_million|ppm]] (8-hour time-weighted average - 40 hour week). | |
| − | + | Another hazard is the formation of acrid [[chloramine]] fumes when hypochlorite bleach comes into contact with [[ammonia]] or [[urine]], which, though not nearly as dangerous as chlorine, can cause severe respiratory distress. | |
| − | + | For these reasons, some consumers prefer the use of [[Natural Cleaning Products|natural cleaning products]] as an alternative to chemical cleaners. | |
| − | |||
| − | == | + | == History == |
| − | + | [[Chlorine]] was first characterized by the [[Sweden|Swedish]] [[chemist]] [[Carl Wilhelm Scheele]] in [[1774]]. (As an adherent of the [[Phlogiston theory]], he called it "dephlogisticated marine acid".) [[Frenchman|French]] [[chemist]] [[Claude Louis Berthollet]], noting the bleaching properties of chlorine, invented hypochlorite bleach in [[1789]]. In [[French language|French]], bleach is known as ''[[Eau de Javel]]'', after the village where it was manufactured. | |
| − | == | + | == References == |
| − | + | <div class="references-small"> | |
| + | * E.R. Trotman. Textile Scouring and Bleaching. London: Charles Griffin & Co., 1968. | ||
| + | * Dr. Bailey Bodkins. Bleach. Philedelphia: Virginia Printing Press 1995. | ||
| + | * http://livre.inventeur.info/book_english/index-section.php3?cat_id=23 | ||
| + | </div> | ||
| + | {{reflist}} | ||
| − | + | == External links == | |
| − | + | * [http://c3.org/chlorine_knowledge_center/070397bleach.html Washington Post's ''A Sanitary History Of Household Bleach''] | |
| − | |||
| − | + | [[Category:Physical sciences]] | |
| − | + | [[Category:Chemistry]] | |
| − | + | {{Credit|99752636}} | |
| − | |||
Revision as of 22:32, 10 January 2007
- This article is about the chemical substance. For the anime/manga, see Bleach (manga). For other uses, see Bleach (disambiguation).
To bleach something is to remove or lighten its color; a "bleach" is a chemical that can produce these effects, often via oxidation. Common chemical bleaches include a solution of sodium hypochlorite (NaOCl), or "chlorine bleach," and "oxygen bleach," which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate or sodium percarbonate. "Bleaching powder" is calcium hypochlorite. Bleaching may be a preliminary step in the process of dyeing.
Types of bleach
Household bleach, also known as chlorine bleach, sodium hypochlorite (NaClO), has a pH level of 11 and is used in the home for whitening clothes, removing stains, and disinfecting. This is because sodium hypochlorite yields chlorine radicals — oxidizing agents readily reacting with many substances. Using chlorine bleach on garments made of wool, nylon, silk, leather or any amount of spandex will stain the garment yellow which is permanent or very difficult to remove.[1]
Chlorine bleach is often used with laundry detergents and is also commonly used as a disinfectant. Mixing bleach and cleaners containing ammonia, or using bleach to clean up urine can create toxic chloramine gases and an explosive called nitrogen trichloride.
Hair bleach contains H2O2 (hydrogen peroxide), which gives off oxygen radicals as it decomposes. Oxygen and chlorine radicals both have comparable bleaching effects.
Various other peroxide yielding chemicals are used as bleaching additives. Sodium perborate, sodium percarbonate, sodium persulfate, sodium perphosphate, sodium persilicate, their ammonium, potassium and lithium analogs, calcium peroxide, zinc peroxide, sodium peroxide, carbamide peroxide, and others are commonly used in detergents, toothpastes, and other products.
Chlorine dioxide is used for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, and in a number of other industries.
In the food industry, some organic peroxides (benzoyl peroxide, etc.) and other agents (e.g. bromates) are used as flour bleaching and maturing agents.
Not all bleaches have to be of oxidizing nature. Sodium dithionite is used as a powerful reducing agent in some bleaching formulas.
How bleaches work
|
This short section requires expansion. |
Color in most dyes and pigments are produced by molecules, such as beta carotene, that contain moieties (pieces) known as chromophores. Chemical bleaches work in one of two ways:
- An oxidizing bleach works by breaking the chemical bonds that make up the chromophore. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb visible light.
- A reducing bleach works by converting double bonds in the chromophore into single bonds. This eliminates the ability of the chromophore to absorb visible light.[2]
Sunlight acts as a bleach through a process leading to similar results: high energy photons of light, often in the violet or ultraviolet range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless.[3]
Hazards
A problem with chlorine is that it reacts with organic material to form trihalomethanes like chloroform, which is a well known carcinogen. There is debate over whether any risk from the chloroform in treated drinking water is worth the benefits. However, the use of elemental chlorine in industrial processes such as paper bleaching, with its attendant production of organochlorine-persistent organic pollutants (including dioxins), does not have any benefits. As a consequence over 80 % of the woodpulp is nowadays bleached with chlorine dioxide, reducing the dioxin generation under detectable levels.
Chlorine is a respiratory irritant. It also attacks mucous membranes and burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine should not exceed 0.5 ppm (8-hour time-weighted average - 40 hour week).
Another hazard is the formation of acrid chloramine fumes when hypochlorite bleach comes into contact with ammonia or urine, which, though not nearly as dangerous as chlorine, can cause severe respiratory distress.
For these reasons, some consumers prefer the use of natural cleaning products as an alternative to chemical cleaners.
History
Chlorine was first characterized by the Swedish chemist Carl Wilhelm Scheele in 1774. (As an adherent of the Phlogiston theory, he called it "dephlogisticated marine acid".) French chemist Claude Louis Berthollet, noting the bleaching properties of chlorine, invented hypochlorite bleach in 1789. In French, bleach is known as Eau de Javel, after the village where it was manufactured.
ReferencesISBN links support NWE through referral fees
- E.R. Trotman. Textile Scouring and Bleaching. London: Charles Griffin & Co., 1968.
- Dr. Bailey Bodkins. Bleach. Philedelphia: Virginia Printing Press 1995.
- http://livre.inventeur.info/book_english/index-section.php3?cat_id=23
- ↑ http://experts.about.com/q/Cleaning-2305/Yellow-Bleach-Stain.htm
- ↑ Field, Simon Q (2006). Ingredients — Bleach. Science Toys. Retrieved 2006-03-02.
- ↑ Bloomfield, Louis A (2006). Sunlight. How Things Work Home Page. Retrieved 2006-03-02.
External links
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