Peroxide
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Peroxide has three distinct meanings:
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Colloquial meaning
In common usage, peroxide is an aqueous solution of hydrogen peroxide (HOOH or H2O2) sold for use as a disinfectant or mild bleach. The usual peroxide used in commercial applications is a dilute solution containing traces of stabilisers, and is sold in either brown glass or opaque polyethylene bottles to minimise the rate of decomposition. The concentrations sold are generally either 3% w/v or 6% w/v; these are sometimes described as "10 volume" and "20 volume", respectively. This refers to the relative volume of oxygen gas produced, at STP, from the complete decomposition of the peroxide. 20 volume peroxide is strong enough to bleach skin it touches, causing unnaturally white blotches.
Due to the presence of catalase in blood, peroxide is only marginally effective in disinfecting open wounds, but excellent for bleaching blood stains. It is also often used as a disinfectant in the dairy industry because after application it leaves absolutely no harmful residues.
Organic chemistry
In organic chemistry, peroxide is a specific functional group or a molecule containing that functional group.
- ROOR'
Organic peroxides tend to decompose easily to free radicals of the form:
- RO·
This makes them useful as catalysts for some types of polymerisation, such as the epoxy resins used in glass-reinforced plastics. MEKP (methyl ethyl ketone peroxide) is commonly used for this purpose.
However, the same property also means that organic peroxides can accidentally initiate explosive polymerisation in materials with unsaturated chemical bonds. Since peroxides can form spontaneously in some materials, some caution must be exercised with such "peroxide forming materials". In addition, many liquid ethers in the presence of air, light, and metal slowly (over a period of months) form ether peroxides (e.g. diethyl ether peroxide) which are extremely unstable. Consequently it is recommended that ether be stored over potassium hydroxide, which not only destroys peroxides but also acts as a powerful drying agent. Extreme care must be taken with samples showing signs of crystal growth or precipitates.
Inorganic chemistry
In inorganic chemistry, peroxide is the anion O22-, usually formed by burning alkali metals or alkaline earth metals in air or oxygen. It is a powerful oxidiser, and usually fairly unstable. The oxides, peroxides and superoxides are closely related, forming a chain of oxygen ions of progressively higher oxidation number.
Barium peroxide is used in pyrotechnics and tracer ammunition, and was once used in the manufacture of hydrogen peroxide. Sodium peroxide is used as a carbon dioxide absorber and oxygen regenerator (e.g. in some submarines), through the reaction:
- 2Na2O2 + 2CO2 → 2Na2CO3 + O2
See also
External links
- Shangyuchem, a commercial supplier of inorganic peroxides (http://www.chem-world.com)