All about Oxygen
Oxygen which has a symbol O is a colourless, odourless,
tasteless, slightly magnetic gaseous element. On Earth oxygen is
more abundant element. Oxygen was discovered in 1774 by the British
chemist Joseph Priestley and, independently, by the Swedish chemist
Carl Wilhelm Scheele; it was shown to be an elemental gas by the
French chemist Antoine Laurent Lavoisier in his classic experiments
Properties and Occurrence
Gaseous oxygen can be condensed to a blue liquid which is strongly
magnetic. Pale blue solid oxygen is produced by compressing the
liquid. The atomic weight of oxygen is 15.9994; at atmospheric pressure,
the element boils at -182.96° C (-297.33° F), melts at -218.4°
C (-361.1° F), and has a density of 1.429 g per litre at 0°
C (32° F).
Oxygen composes 21 per cent by volume, or 23.15 per cent by weight
of the atmosphere; 85.8 per cent by weight of the oceans it means
that 88.8 per cent of pure water is oxygen; and even as a constituent
of most rocks and minerals, 46.7 per cent by weight of the solid
crust of the Earth. Oxygen comprises 60 per cent of the human body.
It is a constituent of all living tissues in almost all plants and
animals, including all humans, require oxygen, in the free or combined
state, to maintain life. See Respiration.
There are three structural forms of oxygen are known: ordinary
oxygen which contain two atoms per molecule having formula O2; ozone,
containing three atoms per molecule having formula O3; and a pale
blue, non-magnetic form having formula O4, containing four atoms
per molecule which readily breaks down into ordinary oxygen. Three
stable isotopes of oxygen are known; oxygen-16 (atomic mass 16)
is the most abundant. It comprises 99.76 per cent of ordinary oxygen
and was used in the determination of atomic weights until the 1960s
Oxygen is prepared in the laboratory from salts such as potassium
chlorate, barium peroxide, and sodium peroxide. The most important
industrial methods for the preparation of oxygen are the electrolysis
of water and the fractional distillation of liquid air. In the latter
method, air is liquefied and allowed to evaporate. The nitrogen
present in the liquid air is more volatile and boils off first,
leaving the oxygen behind. Oxygen is stored and shipped in either
liquid or gaseous form.
Oxygen is a basic component of many organic and inorganic compounds.
It forms compounds called oxides with almost all the elements even
including some of the noble gases. A chemical reaction in which
an oxide forms is called oxidation. The rate of the reaction varies
with different elements. During ordinary combustion, or burning,
is a very rapid form of oxidation. In spontaneous combustion the
heat evolved by the oxidation reaction is sufficiently great to
raise the temperature of the substance to the point that flames
result. For example, phosphorus combines so vigorously with oxygen
that the heat liberated in the reaction causes the phosphorus to
melt and burn. Some very finely divided powders present so much
surface area to the air that they burst into flame by spontaneous
combustion such substances are called pyrophoric substances. Sulphur,
hydrogen, sodium, and magnesium combine with oxygen less energetically
and burn only after the ignition temperature is acieved. Some elements,
such as copper and mercury, form oxides slowly, even when heated.
Inactive metals, such as platinum, iridium, and gold, form oxides
only through indirect methods.
Large amounts of oxygen are used in high-temperature welding torches
which contain a mixture of oxygen and another gas produces a flame
of much higher temperature than is obtained by burning gases in
air. Oxygen is administered to patients whose breathing is impaired
and also to people in aircraft flying at high altitudes, where the
poor oxygen concentration cannot support normal respiration. Oxygen-enriched
air is used in open-hearth furnaces for steel manufacture.
High-purity oxygen is used in the metal-fabrication industries.
It is of great importance as a liquid propellant for guided missiles
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