Hydrogen peroxide
|
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 | Hazardous Chemical Database |
SI units were used where possible. Unless otherwise stated, standard conditions were used. | |
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 strong concentrations) as an oxidizer or monopropellant in rockets.
It is commonly used (in very low concentrations, such as 5%) to bleach human hair, hence the phrases "peroxide blonde" and "bottle blonde". It burns if it comes into contact with the skin in sufficient concentration. In lesser concentrations, it is used medically for cleaning wounds and removing dead tissue.
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 most things, 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 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 aluminum (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. Its use in torpedoes has been discontinued by most navies due to safety considerations. A hydrogen peroxide leak was blamed for the sinkings of HMS Sidon and the Russian submarine Kursk.
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 supercool, or cool below its freezing point without freezing. One way to avoid this is to drop a seed crystal of already-frozen peroxide into the supercooled solution to cause it to freeze.
Exact data on the purification of hydrogen peroxide is hard to come by, since most people with experience with this chemical know how hazardous it can be, and are afraid of getting sued if an amateur follows their instructions and winds up injured or dead, or deliberately uses the purified hydrogen peroxide as a bomb. They prefer that these amateurs calculate the numbers themselves from the basic properties, such as the freezing point of peroxide and the freezing point of water. Similar circumstances often require those who would try these experiments to lie about their intentions to the 70% hydrogen peroxide suppliers, since these companies do not wish to be seen as officially supporting hydrogen peroxide rocketry experiments.
35% hydrogen peroxide has been marketed under names such as "oxywater" to be diluted and used for "hyper-oxygenation therapy" to cure everything ranging from AIDS to stupidity, with claims that information about such "beneficial" uses of peroxide have been suppressed by the scientific community. The US Food and Drug administration has published a warning against the use of 35% peroxide in the home for any purpose. Accidental consumption of peroxide at the full 35% concentration being marketed has caused deaths and serious injuries, usually to children. "This concentration is not approved by FDA for any therapeutic purpose," FDA Commissioner Frank E. Young, M.D., Ph.D., said. "Indeed, no one has come forward with any evidence this substance taken internally has any medical value. Buyers are being cheated and subjected to significant risks and family members are being injured."