the principle of Bleaches

When chlorine gas is bubbled through a cylinder of tomato juice, the [URL=]chlorine[/URL]/tomato juice mixture turns almost completely white within five minutes. This spectacular change is a result of the chemical action of chlorine, acting as an oxidizing bleaching agent, on the pigments in tomato juice. When old newspaper clippings, discolored through aging and exposure to light, are treated with 1 percent aqueous[URL=]sodium borohydride[/URL] solution, the paper is dramatically whitened within twenty minutes. In this instance, the paper has been restored to its original white color by the action of sodium borohydride acting as a reducing bleaching agent.
A bleaching agent is a substance that can whiten or decolorize other substances. Colored substances generally contain groups of atoms, called chromophores, that can absorb visible light having specific, characteristic wavelengths, and reflect or transmit the part of light that is not absorbed. For example, if a chromophore absorbs blue light, it will reflect light of the complementary color, and the chromophore-containing substance will appear yellow. Bleaching agents essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of these absorbing groups. Thus, bleaches can be classified as either oxidizing agents or reducing agents.
Some of the use of bleaching agents are:

The bleaching of textiles and fabrics
The bleaching of wood pulp
The removal of stains
Commercial and household laundering and cleaning
As ingredients in scouring cleansers and dishwashing products
The bleaching of hair


WebElements: the periodic table on the WWW []

Copyright 1993-20010 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.