Balancing Redox Reactions in Basic Solutions

Introduction

• Balancing redox reactions in basic solutions is more challenging than in acidic solutions.
• Similar approach as acidic solutions, with additional steps to neutralize protons with hydroxide ions.

Step-by-step Process

Step 1: Identify Oxidation States

• Hypochlorite anion (ClO⁻):
  • Oxygen: -2
  • Total charge: -1
  • Chlorine: +1 (since +1 and -2 = -1)
• Chromium compound (Cr(OH)₄⁻):
  • Hydroxide: -1 (4 * -1 = -4)
  • Total charge: -1
  • Chromium: +3 (since +3 and -4 = -1)
• Chromate anion (CrO₄²⁻):
  • Oxygen: -2 (4 * -2 = -8)
  • Total charge: -2
  • Chromium: +6 (since +6 and -8 = -2)
• Chloride anion (Cl⁻):
  • Charge: -1
  • Oxidation state: -1

Step 2: Identify Oxidation and Reduction

• Oxidation:
  • Chromium: +3 to +6
  • Chromium is oxidized.
• Reduction:
  • Chlorine: +1 to -1
  • Chlorine is reduced.

Step 3: Writing Half Reactions

• Reduction Half Reaction:
  • ClO⁻ → Cl⁻
• Oxidation Half Reaction:
  • Cr(OH)₄⁻ → CrO₄²⁻

Step 4: Balance Atoms (other than O and H)

• Chlorine and Chromium are already balanced.

Step 5: Balance Oxygen by Adding Water

• Reduction:
  • Add H₂O to the product side.
• Oxidation:
  • Already balanced.

Step 6: Balance Hydrogen by Adding Protons

• Reduction:
  • Add protons (H⁺) to the reactant side.
• Oxidation:
  • Add protons (H⁺) to the product side.

Step 7: Balance Charge by Adding Electrons

• Reduction:
  • Add electrons to the reactant side.
• Oxidation:
  • Add electrons to the product side.

Step 8: Equalize Electrons in Half Reactions

• Multiply half reactions to have the same number of electrons.
• Use Lowest Common Denominator (LCD).

Step 9: Add Half Reactions

• Combine to cancel electrons and simplify.

Step 10: Adjust for Basic Solution (Add Hydroxide)

• Neutralize protons with hydroxide ions (OH⁻).
• Add OH⁻ to both sides of the equation.

Final Reaction

• Ensure atoms and charges are balanced.
• Final simplified balanced equation:
  • 3ClO⁻ + 2Cr(OH)₄⁻ + 2OH⁻ → 3Cl⁻ + 5H₂O + 2CrO₄²⁻

Conclusion

• Verify by checking balance of atoms and charges.
• Method ensures proper balancing of redox reactions in basic solutions.