(481) Unit 4.9 - Oxidation-Reduction (REDOX) Reactions

Introduction to Redox Reactions

• Definition of Redox Reactions: Reactions that involve the transfer of electrons, where one element loses electrons (oxidation) and another gains electrons (reduction).

• Oxidation States: Assigned to each element to track changes in electron count from reactants to products.

Chapter 1: Assigning Oxidation States

• Example: Zinc (Zn) is by itself with an oxidation state of zero.

• Zinc Oxidation:

  • Zinc's oxidation state changes from 0 to +2 (oxidation).

  • Iron (Fe): Reduction occurs as its oxidation state decreases.

• Identifying Oxidation and Reduction: Determine which element is oxidized (electron loss) or reduced (electron gain) based on changes in oxidation state.

Chapter 2: Balancing a Redox Reaction

• Balancing Method: Unlike regular reactions, redox reactions require balancing for charge, not just for mass.

• Half-Reactions: Write separate half-reactions for oxidation and reduction.

  • Example: Separate reactions are created for zinc oxidation and iron reduction.

Chapter 3: Charge Balancing

• Balancing Half-Reactions for Charge:

  • Zinc Reaction:

    • Initial charge: 0 (left) to +2 (right).

    • Add 2 electrons to the right to balance.

  • Iron Reaction:

    • Initial charge: +3 (left) to +2 (right).

    • Add 1 electron to the left to balance.

Chapter 4: Adding Electrons

• Important Note on Electron Placement: Ensure that electrons are on opposite sides in the half-reactions.

• Equalizing Electron Count: If the number of electrons differs, multiply the entire half-reaction to equalize (e.g., multiply iron's reaction by 2).

Chapter 5: Combining Half-Reactions

• Final Steps:

  • Combine the two balanced half-reactions by canceling common species (like electrons).

  • Check that both sides have the same number of elements and charge.

  • Example: Confirm that both sides of the final reaction yield charge balance of +6.

Chapter 6: Additional Practice Example

• Oxidation and Reduction:

  • Identify oxidation states (e.g., chromium goes from 0 to +3; oxidized).

  • Silver goes from +1 to 0; reduced.

• Balanced Net Ionic Equation:

  • Confirm half-reactions have written electrons on opposite sides; ensure equal electron counts.

  • Example of modification: For a hypothetical silver ion with +3 charge, adjust coefficients accordingly to cancel electrons (e.g., cobalt's equation multiplied by 3).

Conclusion

• Review of Redox Balancing Steps:

  • Write half-reactions.

  • Balance charges with electrons.

  • Equalize electron counts.

  • Combine and ensure balance of elements and charges.

• Final Note: Understanding how to balance reactions prepares for potential variations and more complex reactions in future studies.