Bleach

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.

Household bleach, also known as chlorine bleach, sodium hypochlorite (NaClO), 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 readily reacting 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.

Chlorine bleach is often used with laundry detergents and is also commonly used as a disinfectant. Mixing bleach and cleaners containing ammonia, or using bleach to clean up urine can create toxic chloramine gases and an explosive called nitrogen trichloride.

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.

Color in most dyes and pigments is 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.

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.