CBSE Class 10 Answered
Corrosion is the chemical degradation of metals when they come into contact with air, water (or moisture) in the atmosphere over time.
Basically conditions required for corrosion and rusting are “presence of Air and Moisture”.
Rusting refers to the corrosion of iron metal. When iron oxidises by reacting with oxygen in the air coupled with water (or moisture), it produces hydrated ferric (III) oxide, often known as rust.
4Fe + 3O2 + 2xH2O → 2Fe2O3.xH2O
Rusting of iron occurs in the presence of air (oxygen) and water (or moisture).
Let us now conduct an experiment to demonstrate the circumstances required for iron rusting. Mark three clean test tubes with the letters I, II, and III.
Half-fill test tube I with tap water and insert a nail. Seal the test tube with cork.
Add some boiled, cooled pure distilled water to the second test tube (test tube II) (boiling the distilled water for a minute eliminates any dissolved oxygen present). Place the nail in it and seal the surface of the water with oil to avoid contact with air. Seal the test tube with cork.
Then take three rust-free clean nails. Place a few bits of calcium chloride in the test tube III and cork it.
Close the test tube with a cork after placing a nail on the calcium chloride since it is a good absorbing agent that absorbs any water or moisture present in the test tube. Keep the three test tubes aside.
Observe the three test tubes in this manner for a few days. The nails in test tubes II and III are rust-free, however the nail in test tube I is rusted. This experiment demonstrates that both air (oxygen) and water (or moisture) are required for iron rusting.