Redox reactions are those in which oxidation and reduction takes place at the same time. In these reactions, one substance is reduced while the other is oxidised.
Activity: 6Take a china dish and add a small amount of copper powder and heat it. What happens to the copper powder? The surface of copper powder has changed to black colour. This is because oxygen has combined with copper and copper oxide is formed.
2Cu + O2 2CuO
If hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse takes place and again copper is obtained.
Cupric oxide (CuO) changes into copper (Cu). Oxygen is, thus, removed from cupric oxide. Since removal of oxygen is reduction, cupric oxide is reduced to copper. Hydrogen removes this oxygen from cupric oxide. Hence hydrogen is the reducing agent.
Thus, oxidation and reduction occur simultaneously.
For example, sodium gets oxidised when it changes to Na+.
Na Na+ + e-
- Oxidation is defined as the gain of oxygen or loss of hydrogen or loss of electrons by a substance.
- Reduction is defined as the gain of hydrogen or loss of oxygen or gain of electrons by a substance.
Zinc gets oxidised to Zn2+, when a zinc rod is dipped in a copper sulphate solution.
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)
In this reaction, zinc has lost two electrons to become Zn2+. Thus, zinc gets oxidised.
Zn(s) Zn2+(aq) + 2e-
On the other hand Cu2+ gets reduced as it accepts two electrons (released by Zn) to become Cu.
Cu2+(aq) + 2e- Cu(s).