Question

What is corrosion? Give two examples.

Answer 1

Hint: Most metallic substances are exposed to various chemicals like acids, moisture or even air that can cause significant physical and chemical changes to the metal. One such chemical change is corrosion and its examples are present in everyday life.

Complete answer:
Corrosion is a type of chemical reaction involving the oxidation of metals that leads to their degradation.
There are a lot of appliances and objects around us that are made up of metals. These metallic surfaces are exposed to the atmosphere around them and are sensitive to undergo certain chemical changes by reacting with the chemical substances present in the atmosphere.
Oxygen and water vapour (moisture present in the atmosphere) are the two most important weapons of metallic degradation through corrosion. A corroded metal loses its characteristic physical property of being lustrous. Apart from the colour change associated with corrosion, metals also lose their strength making the objects weak and old.
During the process of corrosion, the metal gets acted upon by moisture and oxygen present in air and gets converted into its oxide. Hence, corrosion brings physical as well as chemical changes to the metal it attacks.
Some well-known examples of corrosion are as follows:
-The rusting of iron leads to the development of a reddish-brown deposition on the iron surface making it lower in volume. This is due to corrosion. The moisture and oxygen present in air consumes the metal to form its oxide.
 $ 4Fe + x{H_2}O + 3{O_2} \to 2F{e_2}{O_3}.x{H_2}O $
-The tarnishing of silver utensils and silver ornaments is also a consequence of corrosion. The atmospheric sulphur reacts with silver metal making it lose its shine and luster and turn black in colour.
 $ Ag(s) + S(atm) \to A{g_2}S(black) $ .

Note:
Corrosion is not only limited to oxidation and can be caused by the action of corrosive acids and bases on metals. Painting the surfaces or the process of galvanization are the methods to protect metals from getting corroded.