Advanced Redox Balancing Challenge

Master Redox Balancing

20 Advanced Practice Problems | Acidic & Basic Medium

Instructions: Try to balance these equations on paper first. When you are ready, click the "Submit & Show Detailed Solutions" button at the bottom to reveal the step-by-step answers.

Part I: Acidic Medium

Acidic

1. Permanganate and Oxalate ion

MnO₄^- + C₂O₄^2- → Mn²⁺ + CO₂

Detailed Solution

1. Oxidation: C₂O₄^2- → 2CO₂ + 2e^-

2. Reduction: MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O

3. Balance Electrons: Multiply Oxidation by 5 and Reduction by 2.

Final: 2MnO₄^- + 5C₂O₄^2- + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O

Acidic

2. Dichromate and Iron(II)

Cr₂O₇^2- + Fe²⁺ → Cr³⁺ + Fe³⁺

Detailed Solution

1. Oxidation: Fe²⁺ → Fe³⁺ + 1e^-

2. Reduction: Cr₂O₇^2- + 14H⁺ + 6e^- → 2Cr³⁺ + 7H₂O

3. Balance Electrons: Multiply Oxidation by 6.

Final: Cr₂O₇^2- + 6Fe²⁺ + 14H⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H₂O

Acidic

3. Arsenic Sulfide and Nitrate (Challenging)

As₂S₃ + NO₃^- → H₃AsO₄ + SO₄^2- + NO

Detailed Solution

1. Oxidation: As₂S₃ + 20H₂O → 2H₃AsO₄ + 3SO₄^2- + 34H⁺ + 28e^-

2. Reduction: NO₃^- + 4H⁺ + 3e^- → NO + 2H₂O

3. Balance Electrons: Multiply Oxidation by 3 and Reduction by 28.

Final: 3As₂S₃ + 28NO₃^- + 4H₂O + 10H⁺ → 6H₃AsO₄ + 9SO₄^2- + 28NO

Acidic

4. Copper and Nitrate

Cu + NO₃^- → Cu²⁺ + NO

Detailed Solution

1. Oxidation: Cu → Cu²⁺ + 2e^-

2. Reduction: NO₃^- + 4H⁺ + 3e^- → NO + 2H₂O

3. Balance Electrons: Multiply Oxidation by 3 and Reduction by 2.

Final: 3Cu + 2NO₃^- + 8H⁺ → 3Cu²⁺ + 2NO + 4H₂O

Acidic

5. Iodate and Iodide (Comproportionation)

IO₃^- + I^- → I₃^-

Detailed Solution

1. Oxidation: 3I^- → I₃^- + 2e^-

2. Reduction: 3IO₃^- + 18H⁺ + 16e^- → I₃^- + 9H₂O

3. Balance Electrons: Multiply Oxidation by 8.

Final: IO₃^- + 8I^- + 6H⁺ → 3I₃^- + 3H₂O

Acidic

6. Zinc and Nitrate (Formation of Ammonium)

Zn + NO₃^- → Zn²⁺ + NH₄⁺

Detailed Solution

1. Oxidation: Zn → Zn²⁺ + 2e^-

2. Reduction: NO₃^- + 10H⁺ + 8e^- → NH₄⁺ + 3H₂O

3. Balance Electrons: Multiply Oxidation by 4.

Final: 4Zn + NO₃^- + 10H⁺ → 4Zn²⁺ + NH₄⁺ + 3H₂O

Acidic

7. Thiosulfate and Iodine

S₂O₃^2- + I₂ → S₄O₆^2- + I^-

Detailed Solution

1. Oxidation: 2S₂O₃^2- → S₄O₆^2- + 2e^-

2. Reduction: I₂ + 2e^- → 2I^-

3. Balance Electrons: Electrons already balanced (2e-).

Final: 2S₂O₃^2- + I₂ → S₄O₆^2- + 2I^-

Acidic

8. Sulfite and Permanganate

SO₃^2- + MnO₄^- → SO₄^2- + Mn²⁺

Detailed Solution

1. Oxidation: SO₃^2- + H₂O → SO₄^2- + 2H⁺ + 2e^-

2. Reduction: MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O

3. Balance Electrons: Multiply Oxidation by 5 and Reduction by 2.

Final: 5SO₃^2- + 2MnO₄^- + 6H⁺ → 5SO₄^2- + 2Mn²⁺ + 3H₂O

Acidic

9. Chlorate and Sulfur Dioxide

ClO₃^- + SO₂ → Cl^- + SO₄^2-

Detailed Solution

1. Oxidation: SO₂ + 2H₂O → SO₄^2- + 4H⁺ + 2e^-

2. Reduction: ClO₃^- + 6H⁺ + 6e^- → Cl^- + 3H₂O

3. Balance Electrons: Multiply Oxidation by 3.

Final: ClO₃^- + 3SO₂ + 3H₂O → Cl^- + 3SO₄^2- + 6H⁺

Acidic

10. Hydrogen Peroxide and Dichromate

H₂O₂ + Cr₂O₇^2- → O₂ + Cr³⁺

Detailed Solution

1. Oxidation: H₂O₂ → O₂ + 2H⁺ + 2e^-

2. Reduction: Cr₂O₇^2- + 14H⁺ + 6e^- → 2Cr³⁺ + 7H₂O

3. Balance Electrons: Multiply Oxidation by 3.

Final: 3H₂O₂ + Cr₂O₇^2- + 8H⁺ → 3O₂ + 2Cr³⁺ + 7H₂O

Part II: Basic Medium

Basic

11. Phosphorus Disproportionation (Classic)

P₄ → PH₃ + H₂PO₂^-

Detailed Solution

1. Oxidation: P₄ + 8OH^- → 4H₂PO₂^- + 4e^-

2. Reduction: P₄ + 12H₂O + 12e^- → 4PH₃ + 12OH^-

3. Balance Electrons: Multiply Oxidation by 3.

Final: P₄ + 3OH^- + 3H₂O → PH₃ + 3H₂PO₂^-

Basic

12. Chlorine Disproportionation

Cl₂ → Cl^- + ClO₃^-

Detailed Solution

1. Oxidation: Cl₂ + 12OH^- → 2ClO₃^- + 6H₂O + 10e^-

2. Reduction: Cl₂ + 2e^- → 2Cl^-

3. Balance Electrons: Multiply Reduction by 5.

Final: 3Cl₂ + 6OH^- → 5Cl^- + ClO₃^- + 3H₂O

Basic

13. Aluminum and Nitrite

Al + NO₂^- → AlO₂^- + NH₃

Detailed Solution

1. Oxidation: Al + 4OH^- → AlO₂^- + 2H₂O + 3e^-

2. Reduction: NO₂^- + 5H₂O + 6e^- → NH₃ + 7OH^-

3. Balance Electrons: Multiply Oxidation by 2.

Final: 2Al + NO₂^- + OH^- + H₂O → 2AlO₂^- + NH₃

Basic

14. Chromite and Hypochlorite

Cr(OH)₃ + ClO^- → CrO₄^2- + Cl^-

Detailed Solution

1. Oxidation: Cr(OH)₃ + 5OH^- → CrO₄^2- + 4H₂O + 3e^-

2. Reduction: ClO^- + H₂O + 2e^- → Cl^- + 2OH^-

3. Balance Electrons: Multiply Oxidation by 2 and Reduction by 3.

Final: 2Cr(OH)₃ + 3ClO^- + 4OH^- → 2CrO₄^2- + 3Cl^- + 5H₂O

Basic

15. Permanganate and Cyanide

MnO₄^- + CN^- → MnO₂ + CNO^-

Detailed Solution

1. Oxidation: CN^- + 2OH^- → CNO^- + H₂O + 2e^-

2. Reduction: MnO₄^- + 2H₂O + 3e^- → MnO₂ + 4OH^-

3. Balance Electrons: Multiply Oxidation by 3 and Reduction by 2.

Final: 2MnO₄^- + 3CN^- + H₂O → 2MnO₂ + 3CNO^- + 2OH^-

Basic

16. Hydrazine and Chlorate

N₂H₄ + ClO₃^- → NO + Cl^-

Detailed Solution

1. Oxidation: N₂H₄ + 4OH^- → 2NO + 4H₂O + 8e^-

2. Reduction: ClO₃^- + 3H₂O + 6e^- → Cl^- + 6OH^-

3. Balance Electrons: Multiply Oxidation by 3 and Reduction by 4.

Final: 3N₂H₄ + 4ClO₃^- → 6NO + 4Cl^- + 6H₂O

Basic

17. Zinc and Nitrate (Zincate formation)

Zn + NO₃^- → Zn(OH)₄^2- + NH₃

Detailed Solution

1. Oxidation: Zn + 4OH^- → Zn(OH)₄^2- + 2e^-

2. Reduction: NO₃^- + 6H₂O + 8e^- → NH₃ + 9OH^-

3. Balance Electrons: Multiply Oxidation by 4.

Final: 4Zn + NO₃^- + 7OH^- + 6H₂O → 4Zn(OH)₄^2- + NH₃

Basic

18. Bismuth Hydroxide and Stannite

Bi(OH)₃ + SnO₂^2- → SnO₃^2- + Bi

Detailed Solution

1. Oxidation: SnO₂^2- + 2OH^- → SnO₃^2- + H₂O + 2e^-

2. Reduction: Bi(OH)₃ + 3e^- → Bi + 3OH^-

3. Balance Electrons: Multiply Oxidation by 3 and Reduction by 2.

Final: 2Bi(OH)₃ + 3SnO₂^2- → 3SnO₃^2- + 2Bi + 3H₂O

Basic

19. Ferrate production

Fe(OH)₃ + ClO^- → FeO₄^2- + Cl^-

Detailed Solution

1. Oxidation: Fe(OH)₃ + 5OH^- → FeO₄^2- + 4H₂O + 3e^-

2. Reduction: ClO^- + H₂O + 2e^- → Cl^- + 2OH^-

3. Balance Electrons: Multiply Oxidation by 2 and Reduction by 3.

Final: 2Fe(OH)₃ + 3ClO^- + 4OH^- → 2FeO₄^2- + 3Cl^- + 5H₂O

Basic

20. Cobalt(II) and Peroxide

Co(OH)₂ + H₂O₂ → Co(OH)₃

Detailed Solution

1. Oxidation: Co(OH)₂ + OH^- → Co(OH)₃ + e^-

2. Reduction: H₂O₂ + 2e^- → 2OH^-

3. Balance Electrons: Multiply Oxidation by 2.

Final: 2Co(OH)₂ + H₂O₂ → 2Co(OH)₃

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Redox Reactions Balancing Practice

Master Redox Balancing

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