Question

Articles made of copper develop a green coating when kept open in air for a long time. Name the cause of it. Write two methods to prevent this phenomena​

Answer 1

Explanation:

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Answer 2

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Answer Explanation:

Copper forms a green deposit on its surface when exposed to air which is usually a mixture of copper carbonate and copper hydroxide due to its reaction with CO2 Present in the air. Hence, the corroded coating of green color is copper carbonate which is basic in nature.  

The chemical reaction is

2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3

The cause of it is corrosion. Corrosion is usually defined as the degradation of metals due to an electrochemical process.

Two methods to prevent this phenomenon are as follows:-

• One way to prevent, or slow, corrosion is by coating the metal. Coating prevents water and oxygen from contacting the metal. Paint or other coatings will slow corrosion, but they are not effective once scratched. Zinc-plated or galvanized iron exploits the fact that zinc is more likely to oxidize than iron. As long as the coating remains, even if scratched, the zinc will oxidize before the iron.
• Another method for protecting metals is cathodic protection. In this method, an easily oxidized and inexpensive metal, often zinc or magnesium (the sacrificial anode), is electrically connected to the metal that must be protected. The more active metal is the sacrificial anode, and is the anode in a galvanic cell. The “protected” metal is the cathode, and remains unoxidized. One advantage of cathodic protection is that the sacrificial anode can be monitored and replaced if needed.