Almost all living organisms need O2 to live (typically give plants during photosynthesis but more O2 from than they consume). You see him mostly by breathing in air, or by absorption of water (dissolved oxygen). In high concentrations, however, it is toxic to most living things.The metastable, high-energy and reactive allotrope of three O2 atoms (O3) is called ozone. Atomic oxygen, ie O2 in form of free, single O2 atoms, is stable before only under extreme conditions, such as in vacuum of space or in hot stellar atmospheres. However, it has a significant meaning as a reactive intermediate in many reactions of atmospheric chemistry.
Some oxygen-rich inorganic compounds such as potassium permanganate, potassium nitrate (saltpeter), potassium chlorate and potassium chromate enter upon heating or reaction with reducing agents from oxygen. A further possibility of producing O2 in laboratory, is the decomposition of hydrogen peroxide on platinum-plated nickel foil. Pure O2 can be obtained by electrolysis of 30% potassium hydroxide solution of nickel electrodes. It Hydrogen and O2 are separated.
This promoted the combustion gas and Scheele called it "fire air" or the origin. He found that air consists of O2 and this "foul air". Completely independent, was two years later produced by heating mercuric oxide O2 gas, the Englishman Joseph Priestley. The Briton published his findings in 1774, Scheele published his book Chemical Observations of air and the fire but only in 1777.
Most white dwarfs, which are the final state of 97% of all stars in prior theory, exist side by helium and carbon to a large extent of oxygen. Technically O2 is today almost exclusively obtained by rectification of air. The method in 1902, first developed by Carl von Linde (Linde process) and designed by Georges Claude economically viable. Small amounts arising as a by-product in production of hydrogen by electrolysis of water.
For O2 recovery after Claude process air by means of compressors to 5-6 bar is compressed, cooled and then removed by first filter of carbon dioxide, humidity, and other gases. The compressed air is cooled by flowing past gases from the process to a temperature near the boiling point. It is then expanded in turbines. A portion of energy used for compression can again be recovered. This is the method -. In contrast to Linde process, in which no energy is recovered - a lot more efficient.
O2 is the most abundant and widespread element on earth. It occurs both in atmosphere and in lithosphere, hydrosphere and biosphere. O2 has a mass fraction of 50.5% of earth's crust (up to 16 km depth, including hydro and atmosphere). In air, his mass fraction is 23,16% (by volume: 20.95%), the water 88.8% (the sea water but only 86%, since there large amounts salts, eg. As sodium chloride are dissolved).
The most common stable oxygen isotope 16O (99.76%), in addition still comes 18O (0.20%) and 17O (0.037%) before. In addition to the stable oxygen isotopes are still a total of 13 unstable, radioactive nuclides from 12O to 28O are known which are artificially produced. Their half lives often are only milliseconds to seconds, with two minutes 15O this case has the longest half-life, and is frequently used in positron emission tomography.
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