The sewer valves in the picture above are made of iron, a very common and useful metal. However, these iron valves have been exposed to air and water for a long time and have begun to undergo a chemical reaction commonly known as rusting. You know that when an iron tool or other object turns to rust, it eventually stops functioning and becomes useless. What is going on in the rusting process? Can anything be done to keep it from happening? Rusting is just one specific example of a chemical process called corrosion. Corrosion occurs to many metals besides iron, such as copper, silver, and zinc. The chemical reaction responsible for corrosion is one in which electrons are transferred from one substance to another. When metallic iron forms rust (iron(III) oxide), its identity is changed due to a transfer of electrons. In this chapter, you will learn about oxidation and reduction, the general terms given to processes in which electrons are lost or gained by the reacting substances.
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