ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Copper. Sheet of the metallic element copper (Cu). The left half (pink) has been cleaned using citric acid. The right half (orange) has been tarnished by exposure to the air. Reactions with oxygen and water and pollutant gases will slowly form oxides, hydroxides, carbonates and sulphates of copper. A chemical reaction between the citric acid (or any acid) removes this tarnished layer. In the case of copper, the tarnish acts to protect the metal from further corrosion. Copper is a transition metal element. It is used to manufacture coins and also for plumbing. It is also used in metal alloys such as brass, and in dyes and chemical catalysts.
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