Lecture Notes: Redox Reactions and Oxidation States

1. Introduction to Redox Reactions

• Redox Reaction: Combination of Reduction and Oxidation occurring simultaneously.
• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.

2. Understanding Oxidation States

• Octet Rule: Atoms bond to achieve a full outer electron shell (8 electrons).
• Oxidation State: Charge on a single atom due to loss or gain of electrons.
  • Example:
    • Oxygen (O) gains 2 electrons → Oxidation state = -2.
    • Magnesium (Mg) loses 2 electrons → Oxidation state = +2.

3. Key Concepts

3.1. Oxidation Number

• Represents the charge on a single atom in a compound.
• Determined during bond formation.
• Can be positive or negative based on electron transfer.

3.2. N Factor

• Represents the number of moles of electrons transferred per mole of substance.
• N Factor Calculation:
  • Example: If one mole of a substance transfers 2 moles of electrons, N factor = 2.

4. Balancing Redox Reactions

• Balancing Steps:
  1. Determine oxidation states.
  2. Identify which species are oxidized and reduced.
  3. Use N factor to balance electron transfer.
  4. Adjust coefficients to balance atoms on both sides.

4.1. Example Reaction Balancing

• Reaction: FeO + V2O5 → Fe2O3 + VO
  • Identify N factors and adjust coefficients.
• Example Reaction: HNO3 + H2S →
  • Find oxidation states, calculate N factors, and balance using equivalent weight.

5. Oxidizing and Reducing Agents

5.1. Oxidizing Agent

• A substance that oxidizes others while being reduced itself.
  • Example: KMnO4 oxidizing oxalic acid.

5.2. Reducing Agent

• A substance that reduces others while being oxidized itself.
  • Example: Sodium thiosulfate reduces iodine.

6. Special Redox Reactions

6.1. Disproportionation Reactions

• A type of redox reaction where the same element is oxidized and reduced.
  • Example: Cu+ → Cu2+ and Cu0.

7. Equivalent Weight Calculation

• Formula: Equivalent Weight = Molecular Weight / N Factor.
  • For example, calculate equivalent weight of V2O5 based on its N factor derived from oxidation states.

8. Conclusion

• Understanding redox reactions, oxidation states, and balancing is crucial for physical chemistry.
• Always remember the principles of electron transfer and oxidation states while solving problems.

9. Important Tips

• Use shortcuts for N factor calculation and balancing reactions.
• Regular practice of balancing redox reactions is essential for NEET preparation.