Bleach

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To bleach something is to remove or lighten its colour, sometimes as a preliminary step in the process of dyeing; a bleach is a chemical that produces these effects, often via oxidation. Common chemical bleaches include "chlorine bleach", a solution of sodium hypochlorite (NaClO), and "oxygen bleach", which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate or sodium percarbonate. Bleaching powder is calcium hypochlorite.

Contents 1 Types of bleach 2 Hazards 3 History 4 See also 5 References 6 External links

[edit] Types of bleach

Household or chlorine bleach, a dilute solution of sodium hypochlorite (NaClO), has a pH level of 11 and is used in the home for whitening clothes, removing stains, and disinfecting. Sodium hypochlorite yields chlorine radicals, which are oxidizing agents and readily react with many substances. Note in particular, that mixing cleansers containing bleach and ammonia, or using bleach to clean up urine can result in the formation of many harmful byproducts including toxic chloramine gases including the unstable nitrogen trichloride.

Chlorine bleach is often used with laundry detergents and is also commonly used as a disinfectant. Many clothing dyes are not chlorine bleach safe, and bleaching them will genenerally result in a yellow-orange hue. In addition many materials such as spandex may be damaged by bleach, resulting in the loss of elasticity or discoloration.^[1] Seemingly dingy white cottons which are older or have been excessively bleached may instead need to be treated with bluing.

Hair bleach contains H₂O₂ (hydrogen peroxide).

Various other peroxide yielding chemicals are used as bleaching additives. Sodium perborate, sodium percarbonate, sodium persulfate, sodium perphosphate, sodium persilicate, 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. This can result in formation of dioxins, and the paper industry has begun to user peroxides instead.

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 an oxidizing nature. Sodium dithionite is used as a powerful reducing agent in some bleaching formulas.

[edit] Hazards

A problem with chlorine is that it reacts with organic material to form trihalomethanes like chloroform, which is a well known carcinogen. There is debate over whether any risk from the chloroform in treated drinking water is worth the benefits. However, the use of elemental chlorine in industrial processes such as paper bleaching, with its attendant production of organochlorine-persistent organic pollutants (including dioxins), does not have any benefits. As a consequence over 80 % of the woodpulp is nowadays bleached with chlorine dioxide, reducing the dioxin generation under detectable levels.

Chlorine is a respiratory irritant. It also attacks mucous membranes and burns the skin. As little as 3.5 ppm can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. Exposure to chlorine should not exceed 0.5 ppm (8-hour time-weighted average - 40 hour week).^{[citation needed]}

Another hazard is the formation of acrid chloramine fumes when hypochlorite bleach comes into contact with ammonia or urine, which, though not nearly as dangerous as chlorine, can cause severe respiratory distress.

For these reasons, some consumers prefer the use of natural cleaning products as an alternative to bleach.

[edit] History

Chlorine was first characterized by the Swedish chemist Carl Wilhelm Scheele in 1774. (As an adherent of the Phlogiston theory, he called it "dephlogisticated marine acid".) French chemist Claude Louis Berthollet, noting the bleaching properties of chlorine, invented hypochlorite bleach in 1789. In French, bleach is known as Eau de Javel, after the village where it was manufactured.

Several alternatives to bleach have recently appeared in industrialized countries. These substances are touted as being less toxic, and the use of bleach as a stain remover has become less popular in the United States. However, due to the recent upsurge of illness due to methicillin-resistant Staphylococcus aureus (known as MRSA) and other bacterial pathogens susceptible to bleach, the bleach industry has recovered somewhat, and the use of bleach as a disinfectant is increasing in a variety of industrial and commercial, as well as household settings.

[edit] See also

Household chemicals

[edit] References

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[edit] External links

• Washington Post's A Sanitary History Of Household Bleach