Question

Describe an experiment to show the conditions necessary for rusting of iron.

Answer 1

Corrosion is the chemical destruction of metals, when they come in contact with air, water (or moisture) present in the atmosphere over a period of time. The corrosion of iron metal is called rusting. When iron undergoes oxidation by reacting with oxygen present in the air along with water (or moisture), it forms hydrated ferric (III) oxide, which is called rust.
$4\mathrm{Fe}+3{\mathrm{O}}_2+2{\mathrm{xH}}_2\mathrm{O}\to 2{\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}$

Rusting of iron takes place in the presence of air (oxygen) along with water (or moisture).

Let us now perform an experiment which shows the necessary conditions required for rusting of iron. Take three clean test tubes and mark them as X, Y, Z. Then take three clean rust-free nails. Add a few pieces of calcium chloride in the test tube X and place some cotton over it. Now place a nail on the cotton (calcium chloride is a good absorbing agent which absorbs any water or moisture present in the test tube) and close the test tube with a cork. In the second test tube (test tube Y), add some boiled, cooled pure distilled water (boiling the distilled water for a minute removes any dissolved oxygen present in the distilled water). Place the nail in it and, to avoid contact of air, seal the surface of water by adding a layer of oil. Close the test tube with a cork. Fill half of the test tube Z with tap water and place a nail in it. Close the mouth of the test tube with a cork. Leave the three test tubes in this way for a few days and observe them. You will see that nails in test tubes X and Y are rust-free, whereas the nail in the test tube Z contains rust. This experiment shows that air (oxygen) and water (or moisture) both are required for rusting of iron.