What is the chemical formula and color of copper after corrosion?

Expert Answers
gsenviro eNotes educator| Certified Educator

Corrosion is commonly defined as the slow eating away of metals. The most commonly encountered corrosion is that of iron, which is also known as rusting. Copper also corrodes in presence of oxygen. When this happens, the following chemical reaction takes place:

`4Cu + O_2 -> 2Cu_2O`

In this reaction, copper metal reacts with oxygen to form copper (I) oxide. This oxide is red in color. Over time, other reactions take place and ultimately a green colored layer would be obtained. This green colored layer is also known as the patina. 

Copper artifacts covered with patina are commonly used for decoration and are made by accelerating the process of copper corrosion.

Corrosion of iron or rusting, in comparison, is a harmful process and we try to prevent it by coating the iron surface with paint or zinc, etc.

Hope this helps. 

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