Why is it not possible for hydroxide ion \(\left( {{\bf{O}}{{\bf{H}}^ - }} \right)\)to appear in either of the half-reactions or the overall equationwhen balancing oxidation-reduction reactions in basic solution?

• The oxidation-reduction reaction is also known as a redox reaction. In this reaction, one reactant is oxidized and other is reduced. In balancing an oxidation-reduction reaction, they must be first divided into two half reactions: one is oxidation reaction and other is reduction reaction.
• The balancing of redox reaction is complicated as compared to simple balancing. It is necessary to determine the half reactions of reactants undergoing oxidation and reduction. On adding the two halfreactions, net total equation can be obtained. This method of balancing redox reaction is known as half equation method.

In a basic solution, the concentration of hydroxide ion is more than \(1 \times {10^{ - 7}}\) which is more than the concentration of hydrogen ion. The hydrogen ion does not appear in reactant side as its concentration is approximately zero. If hydrogen ion is produced it immediately reacts with the excess hydroxide ion to produce water. Therefore, in the basic solution, hydrogen ion is not there in the reactant as well as the product side.

Thus, the hydrogen ion does not appear in the reaction because it gets neutralize with the excess hydroxide ion present in the solution.