## Ion-Electron Method

The balancing of a chemical equation by ion-electron method (using half reactions) is done acccording to the following steps:

• Find the elements whose oxidation numbers are changed. Choose the substance, which acts as an oxidizing agent and one that acts as a reducing agent.
• Separate the complete equation into two half reactions, one for the change undergone by the oxidizing agent and the other for the change undergone by the reducing agent.
• Balance half equations by the following steps:

a) Balance all atoms other than H and O.

b) Calculate the oxidation number on both sides of the equation and add electrons to whichever side is necessary, to make up the difference.

c) Balance the half equation so that both sides get the same charge.

d) Add water molecules to complete the balancing of the equation.
• Add two balanced half equations. Multiply one or both half equations by suitable numbers so that on adding the two equations, the electrons are balanced.
Redox reactions take place in all the three media acidic or basic or neutral. If H+ ions appear on either side of the equation, the reaction takes place in acidic medium. If OH- ions appear on either side of the equation, the solution is basic. If neither H+ nor OH- ions are present, the reaction occurs in neutral solution. For balancing redox reactions involving acidic and basic media, the method has to be modified slightly.