Question

What is "rusting"? Describe with a labelled diagram an activity to investigate the conditions under which iron rusts.

Answer 1

When iron is exposed to moist air for a long time, it acquires a coating of a brown flaky substance called rust. This process is known as rusting. 

To investigate the conditions under which iron rust, the following activity can be performed:

• Take three test tubes and place clean iron in each of them.                                         
• Label these test tubes  A, B and C. Pour some water in test tube A and cork it.
• Pour boiled distilled water in test tube B, add about 1 ml of oil and cork it.                   
• Put some anhydrous calcium chloride in test tube C and cork it.

On leaving these test tubes for a few days, it will be observed that iron nails rust in test tube A but they do not rust in test tubes B and C.
In the test tube A, the nails are exposed to both air and water.
In the test tube B, the nails are exposed to only water because the oil will float on water and prevent the air from dissolving in the water. 
In the test tube C, the nails are exposed to dry air because anhydrous calcium chloride will absorb the moisture from the air. 

Hence, air and water both are essential conditions for rusting.