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Question
What is meant by 'rusting of iron'? With the help of labelled diagrams, describe an activity to find out the conditions under which iron rusts.
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Solution
Iron objects, kept in moist air for a long period of time, react with moist air to form a reddish brown crumbling substance called rust (hydrated iron (III) oxide, Fe2O3. X H2O, where X is the number of moles of water that differs). This corrosion of iron metal by reacting with moist air is called the rusting of iron.
Conditions essential for the rusting of iron:
1. Presence of air (oxygen)
2. Presence of water (moisture)
Let us do an activity to prove that moist air is necessary for the rusting of iron.
Experiment: Take three test tubes and place a dirt-free iron nail in each of these test tubes (refer to the figure below). In the first test tube, anhydrous calcium chloride is added and the test tube is closed. In the second test tube, distilled water and a layer of oil is added and the test tube is closed with a cork. In the third test tube, tap water is added. The nail is dipped into water in such a way that a part of it is exposed to the damp air present inside the test tube.
Observation:
(i) The nails in the first and the second test tube do not rust.
ii) The nail present in the third test tube rusts.
Conclusion:
Hence, we can conclude that both air and water are necessary for the rusting of iron.
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