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created Jun 11th, 13:55 by sandhya shrivatri



549 words
36 completed
Oxygen is a non metallic chemical element of the periodic table. Oxygen is colourless and odourless. It is a tasteless gas essential to living organisms. Animals convert it to carbon dioxide and plants in turn utilize carbon dioxide as a source of carbon and return the oxygen to the atmosphere. Oxygen forms compounds by reaction with practically any other element as well as by reactions that displace elements from their combinations with each other. In many cases these processes are accompanied by the evolution of heat and light and in such cases are called combustions. Its most important compound is water. Oxygen was discovered by a Swedish chemist Carl Wilhelm Scheele who obtained it by heating potassium nitrate and mercuric oxide along with many other substances. An English chemist Joseph Priestley independently discovered oxygen in by the thermal decomposition of mercuric oxide and published his findings the same year which was three years before Scheele published. French chemist Antoine with remarkable insight interpreted the role of oxygen in respiration as well as combustion discarding the earlier theory which had been accepted up to that time. He noted its tendency to form acids by combining with many different substances and accordingly named the element oxygen from the Greek words for acid former. Oxygen is the most plentiful element in Earth crust. The proportion of oxygen by volume in the atmosphere is one third and by weight in seawater is nine tenth. In rocks it is combined with metals and non metals in the form of oxides that are acidic or basic and as salt like compounds that may be regarded as formed from the acidic and basic oxides such as sulphates and carbonates or aluminates and phosphates. Plentiful as they are these solid compounds are not useful as sources of oxygen because separation of the element from its tight combinations with the metal atoms is too expensive. During respiration animals and some bacteria take oxygen from the atmosphere and return carbon dioxide to it whereas by photosynthesis green plants assimilate carbon dioxide in the presence of sunlight and evolve free oxygen. Almost all the free oxygen in the atmosphere is due to photosynthesis. Dissolved oxygen is essential for the respiration of fish and other marine life. Oxygen has two allotropic forms which are diatomic and triatomic. The properties of the diatomic form account for the paramagnetism of oxygen. The three atoms in the ozone molecule do not lie along a straight line. When required in tonnage quantities oxygen is prepared by the fractional distillation of liquid air. Of the main components of air oxygen has the highest boiling point and therefore is less volatile than nitrogen and argon. The process takes advantage of the fact that a compressed gas cools when it is allowed to expand. The steel
industry is the largest consumer of pure oxygen. It is used in blowing high carbon steel that is volatilizing carbon dioxide and other non metal impurities in a more rapid as well as easily controlled process than if air were used. The treatment of sewage by oxygen holds promise for more efficient treatment of liquid effluents rather than other chemical processes. Incineration of wastes in closed systems using pure oxygen has become important. Pure oxygen is used in submarines and diving bells.

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