Question

Take some clean iron nails and place them in three test tubes prepared as under:
Test tube A: Contains boiled water and a thin layer of oil
Test tube B: Contains a small cloth bag containing soda lime
Test tube C: Contains ordinary water. Some nails are kept underwater and some more are suspended above the water surface
All the test tubes are tightly closed after placing nails. After some time what will you observe?
A. Nail A rusts
B. Nail B rusts
C. Nail C rusts
D. Nail A does not rust

Answer 1

Hint: Nails are generally made of steel and can also be prepared from iron, copper, and aluminium. The oil and boiled water do not contain dissolved oxygen. Soda-lime is a mixture of sodium hydroxide and calcium hydroxide chemicals. Soda-lime also does not contain oxygen (\[{{O}_{2}}\]). Normal water contains some dissolved amount of oxygen in it.

Complete step by step solution:
-In the question, it is given that iron nails are kept in three test tubes named as A, B and C.
-Test tube A contains boiled water and a thin layer of oil on the surface of the boiled water.
-Test tube B contains a small cloth bag containing soda lime.
-Test tube C contains ordinary water.
- We have to observe the three test tubes carefully.
-Out of the three test tubes, in test tube C some amount of oxygen is dissolved in normal water.
-Nails won’t get rust if we are going to keep them in test tube A. Because in boiled water there is no oxygen and a thin oil layer separates the nails from atmospheric oxygen. Then nails in the test tube A do not get rust.
-Nails in test tube B also do not get rust because soda-lime removes the rust if the nails contain rust. Then the nails in test tube B are safe.
-Nails in test tube C will get rust because the ordinary water contains dissolved oxygen in it. Then the dissolved oxygen reacts with iron present in nails. Then the nails in test tube C will get rust.

Therefore option (C) is correct, Nail C rusts.

Note: The molecular formula of rust is\[F{{e}_{2}}{{O}_{3}}.3{{H}_{2}}O\]. Due to rust, the nails slowly start to decay called corrosion and we will lose the nails slowly. The reaction of iron in nails with oxygen (formation of rust) is as follows.
\[4Fe+3{{O}_{2}}+3{{H}_{2}}O\to 2\underset{Rust}{\mathop{F{{e}_{2}}{{O}_{3}}.3{{H}_{2}}O}}\,\]