Disproportionation Reactions in Chemistry

Aug 14, 2024

Disproportionation Reactions in Redox Chemistry

Key Concepts

  • Redox Reactions: Involve oxidation (loss of electrons) and reduction (gain of electrons).
  • Disproportionation Reactions: A single substance is both oxidized and reduced in the same reaction.

Example: Decomposition of Hydrogen Peroxide

  • Reaction: Hydrogen Peroxide (H₂O₂) decomposing into Water (H₂O) and Oxygen (O₂) with a catalyst like Potassium Iodide.
  • Chemical Equation: H₂O₂ → H₂O + O₂

Assigning Oxidation States

  • Methods:
    • Memorization of rules (found in chemistry textbooks).
    • Calculating through dot structures and electronegativity.

Oxidation State Assignment

  1. Water (H₂O) Oxidation State

    • Oxygen in water: -2
    • Calculation:
      • Oxygen is more electronegative than hydrogen, hence attracts electrons.
      • Oxygen has 6 valence electrons, surrounded by 8 (6 - 8 = -2).
  2. Oxygen (O₂) Molecule Oxidation State

    • Oxygen in O₂: 0
    • Calculation:
      • Bonded to another oxygen with equal electronegativity, electrons are shared equally.
      • Normal 6 electrons, surrounded by 6 (6 - 6 = 0).
  3. Hydrogen Peroxide (H₂O₂) Oxidation State

    • Oxygen in H₂O₂: -1
    • Calculation:
      • In O-H bonds, oxygen attracts electrons due to higher electronegativity.
      • In O-O, electrons are shared equally.
      • Oxygen surrounded by 7 electrons instead of 6 (6 - 7 = -1).

Analysis of the Reaction

  • Oxidation:

    • Oxygen is oxidized from -1 in H₂O₂ to 0 in O₂.
    • Increase in oxidation state indicates oxidation.
  • Reduction:

    • Oxygen is reduced from -1 in H₂O₂ to -2 in H₂O.
    • Decrease in oxidation state indicates reduction.
  • Conclusion: The reaction is a disproportionation reaction, where oxygen is both oxidized and reduced.

Conclusion

  • Understanding oxidation states helps in analyzing redox reactions, especially disproportionation where a single substance can undergo both oxidation and reduction simultaneously.