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A bleach is a chemical that removes colors or whitens, often via oxidation. Common chemical bleaches include household chlorine bleach, a solution of approximately 3–6% sodium hypochlorite (NaClO), and oxygen bleach, which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate, sodium percarbonate, sodium persulfate, tetrasodium pyrophosphate, or urea peroxide together with catalysts and activators, e.g., tetraacetylethylenediamine and/or sodium nonanoyloxybenzenesulfonate.

The process of bleaching can be summarized in the following set of chemical reactions:

Cl2(aq) + H2O(l)
H+(aq) + Cl-(aq) + HClO(aq)

The H+ ion of the hypochlorous acid then dissolves into solution, and so the final result is effectively:

Cl2(aq) + H2O(l)
2H+(aq) + Cl-(aq) + ClO-(aq)

Hypochlorite tends to decompose into chloride and a highly reactive form of oxygen:

2Cl- + O2

Mechanism of bleach action

Color in most dyes and pigments are produced by molecules, such as beta carotene, which contain chromophores. Chemical bleaches work in one of two ways:

  1. 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.

  2. 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.[10]

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. Extended exposure often leads to massive discoloration usually reducing the colors to white and typically very faded blue spectrums.[11]

Sodium hypochlorite's anti-bacterial mechanism works by causing proteins to aggregate.[12][13]

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