Case Study: How Oxidation and Reduction were Utilized 2200 Years Ago

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oxidation, reduction, chemical metal plating

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Oxidation and reduction, also called chemical metal plating, was first developed by the Andean cultures of South America. The earliest form of chemical metal plating was primarily used on artwork. Although chemical metal plating was practiced in many cities during many time periods, the Moche metal smiths of Peru during the years 800-400 BC were the most sophisticated artisans. Much of Moche art consists of copper on the inside covered by a uniform gold film ranging in thickness from 0.5-2 mm. When doing chemical metal plating, Moche metal smiths dissolved gold in corrosive minerals which were common in the Peruvian desert. They then heated a piece of copper and placed it in the gold solution. A gold film formed on the copper object according to the following single replacement equation: Chemical metal plating occurs when a "base" metal such as copper which is at the end of the electromotive series is placed in an electrolyte that contains ions of a "noble" metal, one that is at the positive end of the electromotive series such as gold. The chemical metal plating mechanism is identical to that of a simple oxidation and reduction cell. In an oxidation and reduction cell, the oxidizing agent looses electrons to the reducing agent. In the case of Moche chemical metal plating, copper acts as the oxidizing agent loosing electrons to the reducing agent, gold ions. oxidation: reduction:

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Author:
Dave Goodman
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