Question

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 equation when balancing oxidation-reduction reactions in acidic solution?

Short answer

In an acidic solution, hydroxide ion is not present in the reactant or the product side.

Step-by-step solution

Define oxidation and reduction

• The oxidation-reduction reaction is also known as a redox reaction. In this reaction, one reactant is oxidized and the other is reduced. In balancing an oxidation-reduction reaction, they must be first divided into two half reactions: one is the oxidation reaction and other is the reduction reaction.
• The balancing of a 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 half reactions, the net total equation can be obtained. This method of balancing a redox reaction is known as the half equation method.

Determine the balanced reaction for each pair of half reactions in an acidic solution.

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