bleach

=__**Bleach**__= Bleach is made up of several chemicals including: Bleach is used to remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach (a solution of approximately 3–6% sodium hypochlorite, NaClO), lye, oxygen bleach (which contains either hydrogen peroxide or a peroxide-releasing compound), and bleaching powder (calcium hypochlorite). The bleaching process was known to most ancient civilizations and has been around for thousands of years. Modern bleaches resulted from the work of 18th century scientists including Swedish chemist Carl Wilhelm Scheele, French scientists Claude Berthollet and Antoine Germain Labarraque, and Scottish chemist Charles Tennant.
 * Purpose:**
 * History:**

Household chlorine bleach is created in two ways: by separating sodium hypochlorite from sea water or brine using electrolysis or by adding chlorine gas to sodium hydroxide which produces sodium hypochlorite, water and sodium chloride. The active ingredient in bleach, hypochlorite ion, is produced by the following set of chemical reactions: Cl 2 (aq) + H 2 O(l) H+(aq) + Cl-(aq) + HOCl(aq)
 * Process:**
 * Chemistry:**

The H+ ion of the hypochlorous acid then dissolves into solution, and so the final result is effectively: Cl 2 (aq) + H 2 O(l) 2H+(aq) + Cl-(aq) + ClO-(aq)

Hypochlorite tends to decompose into chloride and a highly reactive form of oxygen: 2ClO- 2Cl- + O 2

Hypochlorite and chlorine are in equilibrium in water; the position of the equilibrium is pH dependent and low pH (acidic) favors chlorine
 * Additional chemical reactions:**

Cl 2 + H 2 O H+ + Cl- + HClO

Chlorine is a respiratory irritant that attacks mucous membranes and burns the skin. As little as 3.53 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine has been limited to 0.5 ppm (8-hour time-weighted average—38 hour week) by OSHA in the U.S.

Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed. The main reaction is chlorination of ammonia, first giving chloramine (NH 2 Cl), then dichloramine (NHCl 2 ) and finally nitrogen trichloride (NCl 3 ). These materials are very irritating to the eyes and lungs and are toxic above certain concentrations.

NH 3 + NaOCl → NaOH + NH 2 Cl NH 2 Cl + NaOCl → NaOH + NHCl 2 NHCl 2 + NaOCl → NaOH + NCl 3

Industrial bleaching agents can also be sources of concern. For example, the use of elemental chlorine in the bleaching of wood pulp produces organochlorines and persistent organic pollutants, including dioxins. According to an industry group, the use of chlorine dioxide in these processes has reduced the dioxin generation to under detectable levels. [|[9]] However, respiratory risk from chlorine and highly toxic chlorinated byproducts still exists.

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Chlorine dioxide is used for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, skin, and in a number of other industries

Sodium thiosulfate also called sodium hyposulfite, sometimes shortened to thio or hypo, is used in pH testing of bleach substance. If one first adds sodium thiosulfate to the bleach solution, it will neutralize the color-removing effects of bleach and allow one to test the pH of bleach solution with liquid indicator.

In the food industry, some organic peroxides (benzoyl peroxide, etc.) and other agents (e.g., bromates) are used as flour bleaching and maturing agents.

Peracetic acid and ozone are used in the manufacture of paper products, especially newsprint and white Kraft paper

Two-part bleaches are utilized in the whitening of wood, especially oak.

Color safe bleach uses hydrogen peroxide as the active ingredient



=**Hair Bleach:**= Washington, Mar 25 : Japanese scientists have created what could be world''s first `green' hair bleach, an environmentally friendly preparation for lightening the colour of hair on the head and other parts of the body without the unwanted effects of the bleaches used by millions every year. Kenzo Koike, a chemist with Kao Corporation ''s Beauty Research Centre in Tokyo, has isolated an enzyme from a strain of Basidiomycete ceriporiopsis, a type of `white-rot' fungus that has also shown potential to degrade and clean up pollutants in soil. Traditional hair bleaches rely on hydrogen peroxide. But the bleaching usually has to be repeated. Plus, hydrogen peroxide is a harsh material, whose repeated use can leave hair brittle and lifeless, with almost no sheen. It also can irritate the scalp and other parts of the body. Those unwanted effects have set scientists on a quest for milder bleaching agents. Koike said that his new "green" hair treatment might be the long-awaited solution. The enzyme has the added benefit of combating the effects of free radicals, highly reactive agents produced by hydrogen peroxide responsible for making hair brittle, dull, and difficult to manage. The researchers said that the enzyme could be added to traditional hair bleaches to prevent hair damage, leading to haircare products that use less hydrogen peroxide. The research has been presented at the 237th National Meeting of the American Chemical Society.