Notes on Balancing Redox Reactions using Half Reaction Method

Introduction

• Focus on the half-reaction method to balance redox reactions.
• Examples covered for neutral, acidic, and basic solutions.

Balancing Redox Reaction in Neutral Solution

• Example: Aluminum (Al) reacts with Nickel (Ni²⁺) to produce Al³⁺ and Ni.
• Key Steps:
  • Separate the unbalanced reaction into two half-reactions:
    • Oxidation Half Reaction: Al → Al³⁺ + 3e⁻
    • Reduction Half Reaction: Ni²⁺ + 2e⁻ → Ni
  • Balance electrons:
    • Multiply each half-reaction to equalize electrons: LCM of 2 and 3 is 6.
    • 2Al → 2Al³⁺ + 6e⁻
    • 3Ni²⁺ + 6e⁻ → 3Ni
  • Add half-reactions:
    • Electrons cancel each other, ensuring charge balance.
    • Final balanced reaction: 2Al + 3Ni²⁺ → 2Al³⁺ + 3Ni

Balancing Redox Reaction in Acidic Solution

• Example: Zinc (Zn) reacts with Bromate (BrO₃⁻) to produce Zn²⁺ and Br⁻.
• Key Steps:
  • Half-Reactions:
    • Zn → Zn²⁺ + 2e⁻
    • BrO₃⁻ + 6H⁺ + 6e⁻ → Br⁻ + 3H₂O
  • Balance electrons:
    • Multiply the zinc half-reaction by 3 to match electrons:
      • 3Zn → 3Zn²⁺ + 6e⁻
  • Add half-reactions:
    • Electrons cancel out.
    • Final balanced reaction: 3Zn + BrO₃⁻ + 6H⁺ → 3Zn²⁺ + Br⁻ + 3H₂O

Balancing Redox Reaction in Basic Solution

• Example: Aluminum producing a polyatomic ion.
• Key Steps:
  • Balance under acidic conditions first, then adjust for basic.
  • Half-Reactions:
    • Al + 4OH⁻ → Al(OH)₄⁻ + 3e⁻
    • ClO₄⁻ + 8H⁺ + 8e⁻ → Cl⁻ + 4H₂O
  • Adjust acidic reaction to basic by adding OH⁻ ions:
    • ClO₄⁻ + 4H₂O + 8OH⁻ → Cl⁻ + 8OH⁻ + 4H₂O
  • Balance charges:
    • Add electrons where necessary to match charge and atoms.
    • Multiply and add reactions to balance electrons (LCM of 3 and 8 is 24).
    • Final balanced reaction includes reducing hydroxide ions on both sides.

Conclusion

• Ensure balance of mass and charge:
  • Atoms and total charges must be equal on both sides.
• The method can be applied to neutral, acidic, and basic solutions effectively.