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hydrogen peroxide (H2O2)
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Hydrogen peroxide can act as a powerful oxidizing agent (E0 acid solution +1.77 volts) when converted to water and as a reducing agent (E0 +0.68 volts) when converted to oxygen (for example by potassium permanganate, KMnO4). Concentrations of H2O2 are expressed in terms of the volume of oxygen that can be liberated: 6% = 20 vol.
Hydrogen peroxide is the parent compound of peroxides. It forms adducts, perhydrates, with some salts.
H2O2 is used as a bleach, disinfectant, and deodorizer. It is prepared by electrolytic oxidation of sulfuric acid and by methods involving reduction. In the atmosphere it is probably one of the oxidizers for sulfur dioxide in cloud water droplets that produces sulfuric acid, a major component in acid rain.
| Density (liquid) | 1.4 g/dm3 |
| Melting point | -11 °C (262.15 K) |
| Boiling point | 150.2 °C (423.35 K) |
| Molar mass | 34.0147 g/mol |
Use of hydrogen peroxide in rockets
Hydrogen peroxide was also used as an oxidizer in some early liquid-propellant rocket engines, including those of the German Messerschmitt 163 aircraft and the British Black Knight missile. Hydrogen peroxide has not been used since for this purpose on a large scale because it is dangerous to handle and easily decomposes, making it difficult to store. However, it has been used as a monopropellant in some small thrusters that provide attitude control on satellites.
Hydrogen peroxide and life on Mars
It has been claimed (see Oyama's hypothesis, about the active nature of the Martian soil) that the presence of hydrogen peroxide on the surface of Mars would explain some of the the results of the Viking biological experiments in terms of purely inorganic chemical reactions. However, although hydrogen peroxide is known to form constantly on the surface of the moon Europa as a result of the bombardment of charged particles moving in Jupiter's powerful magnetic field, it does not appear to exist on Mars in anything like the concentration needed to account for the Viking data abiologically.
According to a very different scenario, put forward by Dirk Schulze-Makuch at Washington State University, microbes may exist near the surface of Mars that use a mixture of hydrogen peroxide and water in their cells. Purely water-based life may have originated on Mars when the planet was much wetter than it is today but as the planet cooled and dried out, the martian organisms may have adapted to their new conditions by taking in hydrogen peroxide. This would have lowered the freezing point of their intracellular solvent, enable the creatures to continue metabolizing at much lower temperatures, and would also have allowed them to harvest the small amounts of water vapor in the atmosphere, since hydrogen peroxide has a strong affinity for water. In a paper to be published in the International Journal of Astrobiology Schulze-Makuch points to an energy-capturing process similar to photosynthesis that produces hydrogen peroxide as a by-product instead of water.
The presence of microbes on Mars containing hydrogen peroxide would neatly explain the Viking biology results. For example, the oxygen and carbon dioxide that was observed in the Viking labeled release experiment would be the products of water in the LR experiment causing H2O2-rich cells to pop and, at the same time, oxidize the cells' organic material.
Related categories
• INORGANIC CHEMISTRY
• PROPELLANTS
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