Solution:
Rust is a red-brown flaky material that forms when an iron object is exposed to wet air (or water) for an extended period of time. This is referred to as iron rusting.
- We insert some anhydrous calcium chloride in the first test-tube holding iron nail and cover its mouth with a tight cork. Anhydrous calcium chloride takes moisture from the wet air in the test tube and dries it. The iron nail in the first test tube is maintained dry in this manner (having no water vapour in it).
- We used boiling distilled water in the second test tube holding the iron nail. Water that has been boiled has no dissolved air (or oxygen) in it (this is because the process of boiling removes all the dissolved air from it). To prevent the outside air from mingling with the boiling water in the test tube, a coating of oil is placed over it. The iron nail in the second test-tube is maintained in air-free boiling water in this manner.
- We placed unboiled water in the third test-tube holding an iron nail such that roughly two-thirds of the nail is immersed in water and the rest is exposed to moist air. The iron nail in the third test-tube has been immersed in both air and water in this manner.
All three test tubes’ mouths are sealed with a cork and set away for roughly a week.
One week later, we examine the iron nails in each of the three test jars one by one. In the first test tube, we observe that there is no rust on the surface of an iron nail stored in dry air (water-free air). This indicates that rusting of iron does not occur solely in the presence of air.
(ii) The surface of an iron nail maintained in air-free, boiling water in the second test tube shows no rust. This indicates that rusting of iron does not occur just in water.
(iii) On the surface of an iron nail held in the presence of both air and water in the third test tube, red-brown rust may be detected. This means that rusting of iron occurs when it is exposed to both air and water.