Water, Composition Of
Water (H2O)is a fluid compound composed of two hydrogen atoms and one oxygen atom.
Scientists have long known that water is essential to the existence of life on our planet. In fact, the ancient Greeks believed that water, air, fire, and earth, were the four basic elements from which all matter was derived. It was not until the 1600s and 1700s that scientists began to explore the composition of water. Even as late as the 1700s it was generally accepted that solid materials could be made by heating water in a sealed flask. People observed that after several days of heating a solid sediment would appear in the flask, and they assumed that the water in the container had been changed into that sedimentary substance. In 1768 French chemist Antoine-Laurent Lavoisier dispelled this ancient notion in an experiment where he carefully weighed the container and the water before and after heating. His test proved that the sediment was made up of material that had been eaten away from the container during heating and was not from the water itself.
Additional information on the composition of water was provided by Henry Cavendish. Cavendish had isolated hydrogen gas, which he called inflammable air, in 1766 and studied its properties for several years. In some of his most important experiments, completed in 1784 and 1785, Cavendish found that when hydrogen is combined with air and sparked, the mixture explodes and creates water. Cavendish even anticipated the development of water's modern chemical formula when he calculated approximately how much hydrogen and air combine to produce the compound. Cavendish thus proved that water is made of at least two distinct gases and is not in itself an element. However, he was unaware that only the oxygen in the air combines with hydrogen to form water.
The actual chemical formula of water was finally determined by Italian chemist and physicist Amedeo Avogadro, who showed that each molecule of water contains two hydrogen atoms and one oxygen atom. French chemist Joseph Gay-Lussac had observed that all gases expand by the same amount with the same rise in temperature. To explain this phenomenon, Avogadro suggested (in 1811) that equal volumes of gases contain equal numbers of molecules at a given temperature. Avogadro's hypothesis also explained why gases always combine in simple volumetric proportions and accounted for experiments in which water molecules were split apart by electrolysis, thereby producing two volumes of hydrogen for every volume of oxygen.
Water rarely exists in its pure form; instead it is usually found with trace amounts of dissolved minerals and other materials. Key components typically include positively charged ions such as calcium, magnesium, and potassium as well as negatively charged ones such as chloride, bicarbonate, sulfate, fluoride, and nitrate. In addition other uncharged components such as silica (SIO2) may be present. Measurement of these materials in water is collectively referred to as water hardness. In addition to these minerals water may contain a significant number microorganisms some of which may be harmful if ingested.
Extraneous materials may be removed from water using a variety of purification processes including filtration, deionization, distillation, ozonation, and chlorination. Such techniques can remove undesirable elements from the water to more suitable for use in scientific experiments or to make it taste better. Interesting, there is a strong trend in the United States in the late 1990s toward bottled drinking water. This water is typically collected from natural springs, filtered, bottled, and sold at a considerable upcharge. In 1997 sales of bottled water in the U.S. exceeded $4.5 billion.
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