Amy Williams, age 15, of Glendale, Ariz., for her question:
WHERE IS SODIUM FOUND?
Sodium is a silvery white metallic element that has many important uses. It is the sixth most common chemical element in the earth's crust. It makes up about 2.8 percent of the crust. Sodium is never found pure that is, as a separate element. In nature it always combines with many other elements, forming compounds.
To obtain pure sodium, the metal must be extracted or removed from its compounds.
One of the most familiar sodium compounds is sodium chloride, which is common table salt. Sodium chloride can be found in dry lake beds, underground and in seawater. Countries with large deposits of sodium chloride include China, France, Great Britain, India, Russia, the United States and West Germany.
Many plants and the bodies of animals contain small amounts of sodium salts. The human body must have a certain amount of sodium for the cells to live and work.
Sodium compounds have many uses in industry, medicine, agriculture and photography.
Pure sodium also has industrial uses. Some nuclear power plants use it in liquid form to cool atomic reactors. A few electric power cables have been made of pure sodium metal. Special insulation around the sodium keeps it from combining with air, water or other substances.
An English chemist named Sir Humphrey Davy in 1807 became the first man to obtain pure sodium. He used electricity to extract the metal from sodium hydroxide. Manufacturers still use electricity to obtain sodium. The process is called electrolysis.
With electrolysis, an electric current is passed through a molten sodium compound, such as sodium chloride. The current separates the compound into chlorine gas and sodium metal.
Pure sodium is extremely active chemically. Sodium immediately combines with oxygen when it is exposed to air.
Because sodium immediately combines with oxygen when it hits air, the element loses its shiny appearance and becomes dull. Sodium's bright surface can be seen only after it has been newly cut or extracted.
Sodium weighs less than water. It decomposes or breaks up in water, producing hydrogen gas and sodium hydroxide. This chemical reaction is very violent. It produces heat that often causes the hydrogen to burst into flame.
The element also reacts quickly with such other nonmetals as chlorine and fluorine, and it forms alloys with many metals.
Sodium must be handled and stored with extreme care. In laboratories, small amounts are stored under kerosene in airtight bottles. The kerosene prevents air or moisture from reaching the metal.
Large amounts of sodium in brick form are stored and shipped in air tight, moisture free barrels. Sodium is also shipped in sealed tank cars. The metal is melted and poured into the tanks. The sodium hardens during shipping and must be melted again before it can be removed.