Introduction
Redox equations must be balanced not only for mass (atoms) but also for charge, since electrons are transferred in the process. A properly balanced redox reaction is essential in both theory and NECTA practical exams, especially in titrations and electrolysis.

Key Concepts

There are two major methods of balancing redox reactions:

1. Oxidation Number Method

2. Ion-Electron (Half-Reaction) Method

This lesson focuses on the Ion-Electron method, which is most used in aqueous (acidic or basic) solutions.

🔹 Steps for Balancing Redox Equations Using the Half-Reaction Method

🧪 Worked Example 1:

Balance the redox reaction below in acidic solution:

Step 1: Write two half-reactions

Oxidation (Fe²⁺ is oxidized):

Reduction (MnO₄⁻ is reduced):

Step 2: Balance all elements except H and O

Already balanced.

Step 3: Balance oxygen by adding H₂O

MnO₄⁻ has 4 oxygen atoms, so we add 4 H₂O to the right:

Step 4: Balance hydrogen by adding H⁺

There are 8 H atoms in 4H₂O, so add 8 H⁺ to the left:

Step 5: Balance charge by adding electrons

Left side charge: +8 (H⁺) + (-1) = +7
Right side charge: +2 (Mn²⁺)
Add 5 electrons to the left to equalize charge:

Fe²⁺ → Fe³⁺ is already balanced for atoms; add 1 electron to the right:

Step 6: Equalize electrons transferred

Multiply Fe reaction by 5:

Now, both half-reactions involve 5 electrons.

Step 7: Add the half-reactions

✅ Final balanced redox equation.

🔹 Worked Example 2:

Balance this redox reaction in acidic solution:

Step 1: Half-reactions
Oxidation:

Reduction:

Balance O:

Balance H:

Balance charge:
Total charge left = +14 + (-2) = +12
Right = +6 → Add 6e⁻ to left:

Now multiply I⁻ reaction by 3:

Final redox equation:

🔹 Oxidation Number Method (Summary)

Steps:

1. Assign oxidation numbers to all elements

2. Identify which ones increase (oxidation) or decrease (reduction)

3. Calculate total electrons lost and gained

4. Balance them

5. Balance all atoms and charges

💡 NECTA Tips:

• Always show oxidation numbers above each element when asked

• State clearly which element is oxidized or reduced

• Indicate oxidizing and reducing agents

🧪 Real-Life Applications

• Redox titrations (e.g. KMnO₄ vs Fe²⁺)

• Industrial electrolysis

• Battery reactions

✅ Summary

• Redox equations must be balanced for both mass and charge

• Use half-reactions to organize the process

• Always balance O using H₂O, H using H⁺ (in acidic medium)

• Equalize electrons and combine the two halves