Question

How is rust formed?

Answer 1

Hint: You must have seen in your daily life, when you leave some iron or steel article out in the open for a long time a reddish-brown layer starts appearing on it. Have you ever wondered what causes it? Let’s know about it.

Complete step by step solution:
If given a sufficient amount of time any iron or steel mass, in the presence of oxygen and water can completely turn into rust.
Complex of oxides and hydroxides of Iron is also called rust. Over time oxygen reacts with iron metal and forms compounds which are collectively called rust.
The main reason or the catalyst present behind the process of rusting is water or moisture. Iron or steel structures might appear to be solid and tough, but water molecules can easily penetrate in the cracks of any exposed metal.
The hydrogen atoms present in the water molecules react or combine with other elements to form acids which will eventually cause the metal to be more exposed. And if chloride ions are present, as in the case of salt water, the corrosion is likely to occur more quickly.
During this process, oxygen combines with metallic atoms to form destructive oxide compounds which weakens the metal, making the structure brittle and crumbly. The chemical reaction involved here is:
\[4Fe\,+\,3{{O}_{2}}\,\to \,2F{{e}_{2}}{{O}_{3}}\]
Iron can also rust if the pH of the environment surrounding the metal is acidic. The rusting process is quickened when exposed to acidic rains. Higher pH inhibits corrosion or rusting.
Rusting is also caused when the metal is impure, pure iron rusts slowly as compared to a mixture of metals.

Note: This situation can be avoided by keeping silica gel packets, as it is a good absorbent of moisture or you can just wipe off the water from the articles and keep them in a dry place or painting the metal with a protective coat which will prevent the surface of metal from reacting with moisture.