question_answer

With labelled diagrams describe an activity to find out the conditions under which iron rusts.  

Answer:

Activity to show that air and water are necessary for rusting. Case I In an absolutely clean and dry test tube [Fig. (a)] place about 2 g of anhydrous calcium chloride and then a shining nail. Put stopper on the mouth test tube and place it aside for a week. The anhydrous calcium chloride is used to absorb moisture from the enclosed air. It is seen that the nail does not rust. Thus, we can conclude that dry air does not cause rusting. Case II Fill 3/4 of another test cube with water [Fig. (b)], which is already boiled, so that it does not contain any dissolved air. Over the water, pour 1 cc of any oil so as to cut off the atmospheric air. In the water, place a shining nail and put stopper on the mouth of test tube. After a week, it is seen that the nail does not rust. Thus, we conclude that pure water does not cause rusting. Case III Place a shining nail in a third test tube [Fig. (c)] and half fill it with tap water. Put stopper on the mouth of test rube. After a week, it is seen that the nail rusts. Thus, we can conclude that air and water (moist air) is necessary for rusting.                     (2)