User:Vyshnab/sandbox

RUSTING OF IRON
When a piece of iron is left in open for some time, it acquires a brown layer over it. This layer is called rust and the process is called rusting. Rusting causes degradation of iron. Since iron is used in industries for manufacturing of articles, to construct buildings the economic loss due to rusting is very large. Rusting is a chemical change. Let us understand the process of rusting. If we leave a piece of iron untouched in open for some time, the water vapour or moisture and air in the atmosphere comes in contact with the iron article to form the layer of rust. What exactly is rust? Are both water and air essential to form rust? Let us explore and find through an activity. Take three test tubes and dip one nail in each test tube. Label the test tubes as one, two and three. Add water to test tube one. To the second, add boiled water and a few drops of oil to make a layer on water. To the third, put dry slaked lime. The three test tubes are kept undisturbed by covering the mouth for few days. Then we see the nail in test tube one rusted since it was in contact with both air and water, whereas nails in test tubes two and three do not rust. In test tube two, nail gets water but not air. In test tube three, nail gets only dry air, but not water because the slaked lime absorbs all the water vapours inside the test tube. From this activity, it is clear that both oxygen and water are essential for rusting. More the moisture, faster will be rusting. If salt is present, for example sea water, iron tends to get rusted quickly. Now, do you understand why the iron rods inside the bricks are not getting rusted? The process of rusting can be expressed as follows: Fe + O2 + H2O > Fe2O3 Where Fe2O3, ferrous oxide is rust. Rusting of iron is a redox reaction in which oxidation and reduction occurs simultaneously. Here, oxygen gains electrons and acts as oxidising agent and iron losses electrons and acts as reducing agent.