Bleach

Bleach is the name given to a group of chemicals, which are used industrially and domestically to whiten clothes, lighten hair color and remove stains. Many bleaches have broad spectrum bactericidal properties, making them useful for disinfecting and sterilizing and are used in swimming pool sanitation to control bacteria, viruses, and algae and in many places where sterile conditions are required. They are also used in many industrial processes, notably in the bleaching of wood pulp. Bleach is also used for removing mildew, killing weeds, and increasing the longevity of cut flowers.

The bleaching process has been known for millennia, but the chemicals currently used for bleaching resulted from the work of several 18th century scientists. Chlorine is the basis for the most common bleaches: for example, the solution of sodium hypochlorite, which is so ubiquitous that most simply call it "bleach", and calcium hypochlorite, the active compound in "bleaching powder". Oxidizing bleaching agents that do not contain chlorine are usually based on peroxides such as hydrogen peroxide, sodium percarbonate, and sodium perborate. While most bleaches are oxidizing agents, some are reducing agents such as sodium dithionite and sodium borohydride.

Bleach ingestion can cause damage to the esophagus and stomach, possibly leading to death. When left on skin, it will cause irritation, drying, and potentially burns. Inhalation of bleach fumes can damage the lungs. Bleach splashed in the eyes will also cause damage.

The earliest form of bleaching involved spreading fabrics and cloth out in a bleachfield to be whitened by the action of the sun and water. Modern bleaches resulted from the work of 18th century scientists including Swedish chemist Carl Wilhelm Scheele, who discovered chlorine, French scientists Claude Berthollet, who recognized that chlorine could be used to bleach fabrics and who first made sodium hypochlorite (Eau de Javel, or Javel water, named after a quarter in Paris where it was produced) and Antoine Germain Labarraque, who discovered the disinfecting ability of hypochlorites. Scottish chemist and industrialist Charles Tennant first produced a solution of calcium hypochlorite, then solid calcium hypochlorite (bleaching powder).

Louis Jacques Thénard first produced hydrogen peroxide in 1818 by reacting barium peroxide with nitric acid. Hydrogen peroxide was first used for bleaching in 1882, but did not become commercially important until after 1930. Sodium perborate as a laundry bleach had been used in Europe since the early twentieth century, but did not become popular in North America until the 1980s.

Colors typically arise from organic dye and pigments, such as beta carotene. Chemical bleaches work in one of two ways:

This page was last edited on 25 January 2018, at 16:52.
Reference: https://en.wikipedia.org/wiki/Bleach under CC BY-SA license.

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