Oxidation-Reduction Reaction

Probably the earliest human use of oxidation-reduction reactions occurred 7,500-4,500 years ago in the Copper/Bronze Age. Copper ores were heated in the presence of carbon to produce copper metal. In this process, the copper in the ore was reduced to copper metal and the carbon was oxidized to carbon dioxide. This same process was applied to iron ores during the Iron Age, which occurred 4,500-3,500 years ago.

The use of oxidation-reduction reactions has long been a part of pottery making. Differences in color in the clay or glaze can be produced when firing pottery under oxidizing conditions when lots of oxygen is present or under low oxygen reducing conditions, such as with a partially closed kiln or a fire with green leaves on it. Clay containing iron will be orange-red if fired under oxidizing conditions due to the presence of red iron oxide and black in reducing conditions when black iron oxide-in which the iron has a lower oxidation number-forms. Among the people who have historically used oxidizing and reducing fire conditions are the Native Americans in the southwestern United States and the Greeks in the Early Bronze Age.

Another historic use of oxidation-reduction reactions is in explosives, substances that burn-are oxidized-so rapidly that they cause huge amounts of pressure. Gunpowder, thought to be the first explosive used, originated in China as early as A.D. 960. It appeared in Europe around the thirteenth century. Eighteen forty-six was a banner year for explosives-nitrocellulose and nitroglycerin were both developed that year. TNT (trinitrotolmene) saw widespread use in World War I. Since 1955, a commonly used cheap and powerful explosive has been a mixture of ammonium nitrate and fuel oil. This was used to bomb the Federal Building in Oklahoma City in 1995, and its use may be curtailed in the future.

Fireworks, a colorful and bright form of oxidationreduction reactions, are believed to have first been used in China in the sixth century.

An important step in the understanding of oxidationreduction reactions was the discovery of oxygen. Joseph Priestley (1733-1804) was the first scientist on record to prepare oxygen in the laboratory. This historic reaction was also an oxidation-reduction reaction. Priestley heated mercury oxide and formed elemental mercury and oxygen. In this reaction, mercury was reduced and the oxide ion was oxidized. Antoine Lavoisier (1743-1794) recognized that when substances are burned, they combine with oxygen. He even figured out that our bodies burn food and give off carbon dioxide as we produce energy. Tragically, the life of this great chemist was ended prematurely when he was beheaded during the French Revolution.