Balancing of Redox Reactions

Two methods are used to balance redox reactions:

Method 1: Oxidation Number Method

The change in oxidation number is used to balance electron gain and loss.

Steps (Acidic Medium):

1. Write the skeleton equation; balance all atoms except O and H first
2. Identify which atoms change oxidation number; calculate the net increase and decrease
3. Multiply coefficients to make total increase in oxidation number = total decrease
4. Balance O atoms by adding H₂O to the side with fewer O atoms
5. Balance H atoms by adding H⁺ ions
6. Check that all atoms and charges are balanced

Method 2: Ion Electron Method (Half-Reaction Method)

The reaction is split into two half-reactions (oxidation and reduction) which are balanced separately and then combined.

Steps:

1. Write the redox reaction in ionic form
2. Split into oxidation half-reaction and reduction half-reaction
3. Balance atoms in each half-reaction (except O and H first)
4. Balance O by adding H₂O; balance H by adding H⁺ (acidic) or OH⁻ (basic)
5. Balance charge by adding electrons to the appropriate side
6. Equalise electrons transferred — multiply one or both half-reactions by suitable factors so electrons cancel
7. Add both half-reactions; cancel identical species on both sides
8. Check that all atoms and charges are balanced

For Basic Medium (Ion Electron Method):
After balancing in acidic conditions:

• Add OH⁻ ions to both sides equal to the number of H⁺ ions
• H⁺ + OH⁻ → H₂O (combine)
• Eliminate H₂O molecules appearing on both sides
• Final check: all elements and charges must balance