Oxygen Essays - Chemical Elements, Industrial Gases,

Oxygen Oxygen is one of the 92 known elements. An element is a substance that cannot be decomposed into a simpler substance by any simple means. Each of the 92 naturally occurring elements are therefore one of the fundamental materials from which everything in the Universe is made. The History of Oxygen On August 1,1774, Joseph Priestley examined the effect of intense heat on mercuric oxide. He noted that an air or gas was readily expelled from the specimen. To his surprise a candle burned in this with a remarkably vigorous flame. He called this new substance dephlogisticated air, in terms of the current chemical theory of combustion. On a visit to Paris in 1775 he related his discovery directly to Antoine Lavoisier. Immediately Lavoisier checked the results by accurate experiments and found that Priestley's dephlogisticated air actually combined with metals and other substances. Since some of the compounds he formed produced acids he regarded the dephlogisticated air as a acidifying principle and called it oxygen, derived from the Greek words for ?sour? and ?I Produce?. From his experiments Lavoisier recognized that air was composed of two main constituents: vital air or oxygen and azote (Greek for lifeless-now called nitrogen) which would not support life or combustion. From these facts Lavoisier developed the modern theory of combustion, and thus laid the foundation of modern chemistry. Forms of Oxygen Oxygen comes in a variety of forms. One of the more deadly forms of Oxygen is Ozone, O3. Ozone (O3), named for the Greek word for smell, is a poisonous, colorless and tasteless gas with a distinctive strong smell. Molecules of ozone are probably the source of the smell that can be detected close to working electrical equipment such as motors and TVs. If a vehicle with a catalytic converter is started cold, ozone can be detected in the exhaust fumes. Most ozone is found high in the atmosphere in a region of the stratosphere called the ozone layer. Here ozone performs a vital life-protecting role, absorbing the ultraviolet rays of the sun that would be harmful to both plant and animal life. Ozone is usually prepared by passing a silent electric discharge through oxygen. Because of its powerful oxidizing properties ozone is widely used for sterilizing water and for air purification. It also is applied in organic chemistry in ozonolysis, which is the reaction of ozone with unsaturated compounds such as the hydrocarbon ethylene. Oxides are a large and important class of chemical compounds in which oxygen is combined with another element. Nearly all the elements form oxides, which vary in properties according to their composition. Metal oxides are crystalline solids that contain a metal cation and the oxide anion, O-2. They typically react with water to form bases or with acids to form salts. Calcium oxide (CaO), for example, reacts with water to form calcium hydroxide [Ca(OH2)], a strong base, and with hydrochloric acid to form calcium carbonate (CaCl2), a salt. Nonmetals oxides are volatile compounds in which the oxygen atoms are linked covalently to the nonmetal atom. They react with water to form acids or with bases to form salts. Thus, sulfur trioxide (SO3) reacts with water to form sulfuric acid (H2SO4), a strong acid, and with sodium hydroxide to form sodium sulfate (Na2SO4), a salt. Amphoteric oxides contain oxygen along with cations such as aluminum, tin, or zinc; they may combine with either acids or bases to form salts. Aluminum oxide (Al2O3), for example, reacts with hydrochloric acid to form aluminum chloride (AlCl3) and with sodium hydroxide to form Sodium Aluminate (NaAlO2). Certain organic compounds react with oxygen or other oxidizing agents to produce substances called oxides. Thus, amines, phosphines, and sulfides form amine oxides, phosphine oxides, and sulfoxides, respectively, in which the oxygen atom is covalently bonded to the nitrogen, phosphorus, or sulfur atom. The so-called olefin oxides are cyclic ethers. Another place where oxygen is found is the atmosphere. The Atmosphere surrounding the earth is a mechanical mixture of gases. The most important of these gases are oxygen, nitrogen, and carbon dioxide. The relative proportions of these gases in the atmosphere are found to be remarkably constant. Oxygen is essential to life. It is odorless, colorless, tasteless, and slightly heavier than air. The