Rusting of iron is an example of a redox reaction. During rusting, iron combines with oxygen in the presence of water. This is an oxidation reaction where oxygen acts as an oxidising agent. Since oxygen also combines with the metal iron, this is a reduction reaction, where the metal iron acts as a reducing agent.
What is rust?
The formation of rust, that is a mixture of iron oxides, on the surface of iron objects or structures. The rust is formed by the redox reaction between oxygen and iron in an environment containing water such as air containing high levels of moisture.
The reaction taking place in the formation of rust is given below
Oxygen is a highly active oxidizing agent whereas iron is a reducing agent. Therefore, the iron atom immediately gives up electrons when exposed to oxygen.
The chemical reaction takes place as follows
Fe → Fe2+ + 2e–
The oxidation state of iron is further increased by the oxygen atom when water is present in the atmosphere
4Fe2+ + O2 → 4Fe3+ + 2O2-
The listed below acid-base reactions occur between the iron cations and the water molecules.
Fe2+ + 2H2O ⇌ Fe(OH)2 + 2H+
Fe3+ + 3H2O ⇌ Fe(OH)3 + 3H+
The hydroxides of iron are also formed from the direct interaction and reaction between the iron cations and hydroxide ions.
O2 + H2O + 4e– → 4OH–
Fe2+ + 2OH– → Fe(OH)2
Fe3+ + 3OH– → Fe(OH)3
How to avoid rusting of iron?
We can avoid rusting of iron to some extent. Listed below are the few ways to avoid rusting of iron articles
- Cathodic protection
- Usage of alloys mixed with iron
The iron articles get rusted due to the oxygen and moisture content present in the atmosphere and it is a common phenomenon in each and every place. These above ways help to reduce the rusting of iron articles.
Check out the video below for more information on the corrosion of metals