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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 (see Atom).

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.

Uses

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 and rockets.