studied corrosion and its effects in chapter 1. When iron exposed to moist air for a long time acquires a coating of a brown flaky substance called rust. Let us find out the condition under which iron rust?
Activity: Take three test tubes label as A, B and C put three iron nails in each of them. Pour some water in test tube ‘A’ and cork it. Pour boiled distilled water in test tube ‘B’ add some oil and cork it. The oil will float on water and prevent the air from dissolving in the water. Put some anhydrous calcium chloride in test tube ‘C’ and cork it. Anhydrous calcium chloride will absorb the moisture. Leave these test tubes for a few days and then observe?
You can observe that iron nails rust in test tube ‘A’ but they do not rust in test tube ‘B’ and ‘C’. In the test tube ‘A’ the nails are exposed to both air and water. In the test tube ‘B’ the nails are exposed to only water and the nails in test tube ‘C’ are exposed to dry air.
Finally you can understand the iron articles rust under the condition of air and water.
Prevention of corrosion: The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys. Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. Alloying is a very good method of improving the properties of a metal. An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. If one of the metals is mercury, then the alloy is known as an amalgam. The electrical conductivity and melting point of an alloy is less than that of pure metals.

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