Rusting is a process that happen with many materials like iron, we are all familiar with rusty iron. This process is called corrosion. The definition of corrosion is the disintegration of materials due to a chemical reaction, but the corrosion is not all the time considered bad, for example the corrosion of aluminium metal and copper metal can form a protective barrier.
Corrosion is caused by chemical reactions called oxidation and reduction reactions.
Definition of oxidation and reduction
Oxidation is defined as the loss of one or more electrons by an atom. During this reaction the oxidation number of the reactant increases. The oxidized element is called “Reducing agent”.
The reduction reaction is defined as the gain of one or more electrons by an atom. During this reaction the oxidation number decreases. The reduced element is called “Oxidising agent”.
Oxidation-Reduction reaction or Redox reaction
In a redox reaction oxidation and reduction occurs simultaneously. The oxidation number of at least two elements must change. When the oxidation number of an atom increases, this atom is oxidized. When the oxidation number of an atom decreased, this atom is reduced.
Identify what is being oxidized and reduced in this reaction : 2Na + Br2 → 2NaBr
First step : Determine the oxidation number of atoms in the reactants and the products
Both reactants are the elemental forms of their atoms, so the oxidation number of Na and Br atoms is 0. In the ionic product NaBr, the Na+ ions have an oxidation number of +1, while the Br− ions have an oxidation number of −1.
Second Step: Identify the oxidation and the reduction reactions.
The Oxidation number of Na changes from 0 to +1, so it increase. Na is the reducing agent. This transformation is the oxidation reaction.
The Oxidation number of Br changes from 0 to -1, so it decreases. Br is the oxidizing agent. This transformation is the reduction reaction.
So In this reaction, the oxidation and the reduction occur simultaneously. This is a REDOX reaction.
Prove that rusting iron is a REDOX reaction
As we already mentioned rusting of iron is an example of a redox reaction. During rusting, iron atoms combine with oxygen in the presence of water.
The balanced overall reaction of rusting iron is mentioned below :
2 Fe + O2 + 2 H2O –> 2 Fe(OH)2
The oxidation number of Fe atom change from 0 to +2, this is the oxidation reaction and Fe is the reducing agent. The Oxidation number of O2 change also from 0 to -2, this is the reduction reaction and the oxygen is the oxidizing agent. That’s why rusting iron is considered as a redox reaction.