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Hydrogen peroxide

From Academic Kids

Hydrogen peroxide
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Image:Hydrogen_peroxide.png
Hydrogen peroxide

General
Systematic name  ?
Other names  ?
Molecular formula H2O2
Molar mass 34.01 g/mol
Appearance viscous liquid
CAS number [7722-84-1]
EINECS number 231-765-0
Properties
Density and phase 1.4 g/cm3, liquid
Solubility in water miscible
Melting point −11°C
Boiling point 141°C
Acidity (pKa)  ?
Basicity (pKb)  ?
Viscosity  ? cP at ? C
Structure
Molecular shape  ?
Dipole moment  ? D
Thermodynamic data
Standard enthalpy
of formation
ΔfHsolid
 ? kJ/mol
Standard molar entropy
Ssolid
 ? J.K1.mol1
Safety data
EU classification Oxidant (O)
Corrosive (C)
R-phrases R5, R8, R20/22, R35
S-phrases S1/2, S17, S26
S28, S36/37/39, S45
PEL-TWA (OSHA) 1 ppm (1.4 mg/m3)
IDLH (NIOSH) 75 ppm
Flash point non flammable
RTECS number MX0900000
Supplementary data page
Structure & properties n, εr, etc.
Thermodynamic data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other cations Sodium peroxide
Related compounds  ?
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

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 high test peroxide) as an oxidizer or monopropellant in rockets. Hydrogen peroxide is manufactured commercially by several processes. Inorganic processes employ the electrolysis of an aqueous solution of sulphuric acid or acidic ammonium bisulphate (NH4HSO4), followed by hydrolysis of the peroxydisulfate ((SO4)2) which is formed. Organic processing methods have become important in the production of hydrogen peroxide. These include (1) the autoxidation of hydroquinone(C6H4(OH)2) or one of its homologues in a suitable solvent system and (2) the partial gas-phase oxidation of hydrocarbons.

Contents

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. However, recent studies have indicated that hydrogen peroxide is toxic to new cells and is therefore not recommended for wound care.

Some gardeners and hydroponics implementers have professed the value of hydrogen peroxide in their watering solutions. They claim its spontaneous decomposition releases oxygen to the plant which can enhance root development and also help treat root rot, which is root cellular death due to lack of oxygen.

Combined with urea as carbamide peroxide, it is used for whitening teeth. It reacts with acetone to form Acetone peroxide and it interacts with ozone to form Hydrogen trioxide.

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."

As a propellant it is pumped into a reaction chamber where usually a metal (esp. silver or platinum) catalyst triggers decomposition, the oxygen-water steam that is produced is either used directly or mixed with a fuel to burn. As a monopropellant (not mix with fuel) it produces a maximum Isp of 161 s (1.6 kN]s/kg) which makes it a low performance monopropellant. Compared to hydrazine (a more powerful monopropellant) peroxide is much less toxic. When decomposed to burn a fuel as an oxidizer, specific impulses as high as 350 s (3.5 kNs/kg) can be achieved depending on the fuel. The famous Bell rocket belt used hydrogen peroxide monopropellant. Hydrogen peroxide as oxidizer was experimented with in the 1940's and 50's in the Walter turbine for submarines to use while submerged; it was found to be too noisy and maintenance demanding compared to the conventional diesel-electric power system. Some torpedoes, though, used hydrogen peroxide as oxidizer or propellant.

Decomposition

Hydrogen peroxide often decomposes exothermically into water and oxygen gas spontaneously:

2H2O2 -> 2H2O + O2 + Energy

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, and their compounds, such as organic compounds, which catalyse the decomposition of hydrogen peroxide. The same reaction is catalysed by the enzyme catalase, whose main function in the body is the removal of toxic byproducts of metabolism and the reduction of oxidative stress. Spilling high concentration peroxide on a flammable substance can cause an immediate fire fueled by the oxygen released by the decomposing hydrogen peroxide.

The use of a catalyst (such as manganese dioxide, potassium permanganate, 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 from natural spontaneous decomposition 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.

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. While its application as a monopropellant for large engines has waned, small thrusters for attitude control which run on hydrogen peroxide are still in use on some satellites and provide benefits on the spacecraft, making it easier to throttle and safer loading and handling of fuel before launch (as compared to Hydrazine monopropellant). However Hydrazine is a more popular monopropellent in spacecraft because of its higher specific impulse and lower rate of decomposition.

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 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. They prefer that 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.

According to http://www.astronautix.com/props/h2o2.htm, the situation was different back in 1959, when the approximate United States total production (based on 100% hydrogen peroxide) was 50,000 short tons (45,000 metric tons). In large quantities, 95 per cent hydrogen peroxide then cost approximately $1.00 per kg, while in small drum lots, 98 per cent solutions cost $2.00 per kg, both in 1959 dollars. Some amateur groups have expressed interest in manufacturing their own peroxide, for their use and for sale in small quantities to others.

Claimed therapeutic value

"35 percent Food Grade Hydrogen Peroxide", which is 35% pure hydrogen peroxide, has been marketed under names such as "Oxywater" or "H2O2", with claims of medicinal or therapeutic value as Hydrogen Peroxide therapy. According to peddlers of the product, it can be diluted and used for "hyper-oxygenation therapy" to cure 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 warning (http://www.fda.gov/bbs/topics/NEWS/NEW00122.html) 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.

Recently, alternative medical practitioners have been administering doses of hydrogen peroxide intravenously. Suffice to say, this has been a little controversial.

External links

de:Wasserstoffperoxid es:Perxido de hidrgeno fr:Peroxyde d'hydrogne he:מימן על-חמצני nl:Waterstofperoxide ja:過酸化水素 pl:Nadtlenek wodoru zh-cn:过氧化氢

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