Balancing Redox Reaction

The redox reaction can be balanced by any of the following methods:

  1. Oxidation Number Method
  2. Ion Electron Method

Oxidation Number Method

The steps involved in balancing redox reactions by this method are as follows:

  1. Write the skeletal equation of reaction - chemical equation without the stoichiometric coefficient.
  2. Write the oxidation number of each atom above its symbol in the equation.
  3. Identify the atoms undergoing change in oxidation number.
  4. Calculate the increase or decrease in oxidation number per atom for the atom undergoing a change in oxidation number. If more than one atom is involved, multiply the increase or decrease in number with the number of atoms undergoing the change to determine the total change in oxidation number.
  5. Equate the increase and decrease in oxidation number on the reactant side by multiplying the formula of the oxidizing and reducing agents suitably.
  6. Balance the equation with respect to all the atoms except hydrogen and oxygen.
  7. Finally balance H and O also.
  8. If the reaction is taking place in acidic medium balance the O atoms by adding required number of H2O molecule on the side where O atoms are less in number. Balance the H atoms by adding H+ to the side deficient in H atoms.
  9. In the basic medium add required number of negative charges by adding required number of OH– ions to the side deficient in the magnitude of charges, then add H2O molecules to balance OH– ions.

Ion Electron Method

This method is based on the principle that electrons lost during oxidation half reaction is equal to the electrons gained in the reduction half reaction. The steps involved are:

  1. Write the skeleton equation.
  2. Write the oxidation number of all the atoms above their symbols in the skeletal equation.
  3. Find the atoms undergoing change in Oxidation Number. Find out the species getting oxidized and reduced respectively.
  4. Split the whole (net) equation into two half reactions - oxidation half reaction and reduction half reaction.
  5. Balance the atoms, undergoing change in oxidation number in each half reaction.
  6. Calculate the total change in oxidation number in each half reaction which is equal to total number of electron transfer.
  7. Add total number of electron transfer as calculated above on the reactant side in reduction half and on the right hand side on the oxidation half reaction.
  8. Balance the charges by adding H+ (for reactions in acidic medium) or OH– (reactions basic medium) either on left or right of equation.
  9. Finally, balance H and O by adding H2O on the required side of the reaction.
  10. Add the two half reactions such that total number of electrons cancel out on both sides. To do so, half reactions may be required to multiplied by some numbers to make the number of electrons equal on both sides.