Hydrogen peroxide

Properties

General
Name	Hydrogen peroxide
Chemical formula	H2O2
Appearance	Colourless liquid
Physical
Formula weight	34.0 amu
Melting point	272.6 K (-0.4 °C)
Boiling point	423 K (150 °C)
Density	1.4 ×103 kg/m3
Solubility	miscible
Thermochemistry
ΔfH0gas	-136.11 kJ/mol
ΔfH0liquid	-188 kJ/mol
ΔfH0solid	-200 kJ/mol
S0gas, 1 bar	232.95 J/mol·K
S0liquid, 1 bar	110 J/mol·K
S0solid	? J/mol·K
Safety
Ingestion	Serious injury, death possible.
Inhalation	Severe irritation, death possible.
Skin	Causes bleaching—flush immediately.
Eyes	Dangerous.
More info
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

The chemical compound hydrogen peroxide (H₂O₂) is a viscous liquid that has strong oxidizing properties and is therefore a powerful bleaching agent that has found use as a disinfectant and (in high concentrations) as an oxidizer or monopropellant in rockets.

Use

It is commonly used (in very low concentrations, typically around 5%) to bleach human hair, hence the phrases "peroxide blonde" and "bottle blonde". It burns the skin upon contact in sufficient concentration. In lower concentrations (3%), it is used medically for cleaning wounds and removing dead tissue. Combined with urea as carbamide peroxide, it is used for whitening teeth.

It is also used intravenously in extremely low (less than one percent) concentrations for hydrogen peroxide therapy - a controversial alternative medical treatment for cancer. However according to the American Cancer Society, "there is no scientific evidence that hydrogen peroxide is a safe, effective or useful cancer treatment". They advise cancer patients to "remain in the care of qualified doctors who use proven methods of treatment and approved clinical trials of promising new treatments."

Decomposition

Hydrogen peroxide tends to decompose exothermically into water and oxygen gas. The rate of decomposition is dependent on the temperature and concentration of the peroxide, as well as the presence of impurities and stabilizers. The ability of peroxide to coexist with a substance is called compatibility. Peroxide is incompatible with many substances, including most of the transition metals (i.e. iron, copper, silver, cobalt, etc.) and their compounds, many organic compounds, dirt, human beings, etc. Spilling high concentration peroxide on a flammable substance can cause an immediate fire.

The use of a catalyst (such as manganese dioxide, silver, or the enzyme catalase) vastly increases the rate of decomposition of hydrogen peroxide. High strength peroxide (also called high-test peroxide, or HTP) must be stored in a vented container to prevent the buildup of pressure leading to the eventual rupture of the container. Any container must be made of a compatible material such as polyethylene or aluminium (not stainless steel) and be cleaned of all impurities (a process sometimes referred to as passivation) prior to the introduction of peroxide.

Hydrogen peroxide has also been used as a propellant. In the 1930s and 40s, Hellmuth Walter pioneered methods of harnessing the rapid decomposition of hydrogen peroxide in gas turbines and rocket engines. However its use in torpedoes has been discontinued by most navies for safety reasons. Hydrogen peroxide leaks were blamed for the sinkings of HMS Sidon and the Russian submarine Kursk.

Concentration

Hydrogen peroxide works best as a propellant in extremely high concentrations. However, there are very few suppliers of high purity hydrogen peroxide, and they are averse to selling to any but the largest institutions. As a result, amateurs wishing to use this for rocket fuel usually have to purchase 70% or lower purity (most of the remaining 30% is water, and sometimes there are traces of stabilizing materials, such as tin, to reduce the decomposition rate), and increase its concentration themselves, since 70% makes for extremely poor propellant compared to 90% or better. Many try distillation, but this is extremely dangerous with hydrogen peroxide.

A safer approach is sparging, possibly followed by fractional freezing. Sparging takes advantage of the fact that warm (not hot) air will preferentially evaporate water.

In high concentrations (above 62%), hydrogen peroxide in solution with water will freeze before the water. Below 62%, the water will freeze first, until the liquid solution reaches 62%. Hydrogen peroxide tends to AIDS, cancer, and many other conditions. Some have claimed that information about these "beneficial" uses of peroxide have been suppressed by the scientific community. The US Food and Drug administration has published a against the use of 35% peroxide in the home for any purpose. At least one death, and several serious injuries, have occurred as a result of ingesting this treatment. People who use 35% hydrogen peroxide "water it down" to whatever concentration is needed for the specific situation. Storing 35% makes it convenient to keep enough on hand, which is why people buy it this way. For example, use of 1 cup of 35% H2O2 in a warm bath is simple (and cheap), where use of 3% H2O2 would be less convenient (about 11 cups) and more expensive.

A little known but practical use for peroxide

Commercial peroxide, as bought at the drugstore in a 3% solution, can be used to remove bloodstains from carpets and clothing. Pour a few tablespoons of peroxide onto the stain and it will bubble up in the area of the blood. Wait a few minutes, then wipe up the excess liquid with a cloth or paper towel.