Difference between revisions of "Bleach" - New World Encyclopedia
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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]]. | 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]]. | ||
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| + | == History == | ||
| + | |||
| + | [[Chlorine]] was first characterized by the [[Sweden|Swedish]] [[chemist]] [[Carl Wilhelm Scheele]] in 1774. As a person who accepted 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. | ||
== Types of bleach == | == Types of bleach == | ||
| − | Household bleach, also known as '''chlorine bleach''', [[sodium hypochlorite]] | + | Household bleach, also known as '''chlorine bleach''', has the chemical name [[sodium hypochlorite]], with the formula NaClO. It 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 that readily react 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 | + | Chlorine bleach is often used with [[laundry detergent]]s and is also a common [[disinfectant]]. |
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. | 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. | ||
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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. | + | 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 an ongoing debate over whether any risk from the chloroform in treated [[drinking water]] is worth the benefits. Yet, the use of elemental chlorine in industrial processes such as paper bleaching, with its attendant production of organic pollutants (such as [[dioxins]]), does not have any benefits. Consequently, over 80 percent of woodpulp is nowadays bleached with chlorine dioxide, reducing the generation dioxin below detectable levels. |
| − | Chlorine is a respiratory irritant. It also attacks [[mucous membrane]]s and [[burn (injury)|burns]] the skin. As little as 3.5 [[ | + | 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 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine should not exceed 0.5 ppm (for an 8-hour time-weighted average, during a 40-hour week). |
| − | + | Chlorine bleach should not be mixed with cleaners containing [[ammonia]] or used to clean up [[urine]]. Such mixtures produce toxic [[chloramine]] fumes and an explosive called [[nitrogen trichloride]]. | |
For these reasons, some consumers prefer the use of [[Natural Cleaning Products|natural cleaning products]] as an alternative to chemical cleaners. | For these reasons, some consumers prefer the use of [[Natural Cleaning Products|natural cleaning products]] as an alternative to chemical cleaners. | ||
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== Footnotes == | == Footnotes == | ||
Revision as of 23:20, 24 February 2007
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.
History
Chlorine was first characterized by the Swedish chemist Carl Wilhelm Scheele in 1774. As a person who accepted 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.
Types of bleach
Household bleach, also known as chlorine bleach, has the chemical name sodium hypochlorite, with the formula NaClO. It 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 that readily react 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 a common disinfectant.
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 an ongoing debate over whether any risk from the chloroform in treated drinking water is worth the benefits. Yet, the use of elemental chlorine in industrial processes such as paper bleaching, with its attendant production of organic pollutants (such as dioxins), does not have any benefits. Consequently, over 80 percent of woodpulp is nowadays bleached with chlorine dioxide, reducing the generation dioxin below detectable levels.
Chlorine is a respiratory irritant. It also attacks mucous membranes and burns the skin. As little as 3.5 parts per million (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 (for an 8-hour time-weighted average, during a 40-hour week).
Chlorine bleach should not be mixed with cleaners containing ammonia or used to clean up urine. Such mixtures produce toxic chloramine fumes and an explosive called nitrogen trichloride.
For these reasons, some consumers prefer the use of natural cleaning products as an alternative to chemical cleaners.
Footnotes
- ↑ 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.
ReferencesISBN links support NWE through referral fees
- Trotman, E.R. 1968. Textile Scouring and Bleaching. London: Charles Griffin & Co., 1968.
- Bodkins, Dr. Bailey, 1995. Bleach. Philedelphia: Virginia Printing Press 1995.
External links
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