Lecture on Oxidation and Reduction

Chemistry Class Review

• Oxidation

  • Oxidation is losing electrons (OIL: Oxidation Is Losing)
  • Not necessarily losing electrons outright, sometimes 'hogging' them

• Reduction

  • Reduction is gaining electrons (RIG: Reduction Is Gaining)
  • Gaining electrons reduces the notional charge

• Oxidizing Agents

  • Tend to lose electrons to more electronegative atoms like oxygen

Example of Combustion Reaction

• Hydrogen and Oxygen Reaction

  • Combustion of H2 with O2 produces H2O and heat
  • Molecular hydrogen (H2) and oxygen (O2) have neutral oxidative states

• Oxidation and Reduction in Reaction

  • Hydrogen loses electrons to oxygen, thus oxidized
  • Oxygen gains electrons from hydrogen, thus reduced

Oxidation States in Water

• Electronegativity Concept

  • Oxygen is more electronegative than hydrogen
  • Electrons spend more time around oxygen in water

• Oxidation States Explained

  • Oxygen gains two electrons (2-) from hydrogen
  • Hydrogen each loses one electron (1+)

Half Reactions

• Hydrogen Half Reaction

  • H2 → 2H⁺ + 2e⁻
  • Loss of electrons indicates oxidation

• Oxygen Half Reaction

  • O2 + 4e⁻ → 2O²⁻
  • Gain of electrons indicates reduction

Biological Perspective

• Alternative Definitions

  • Oxidation: Losing hydrogen atoms
  • Reduction: Gaining hydrogen atoms

• Relation to Chemistry Definitions

  • In biological systems, hydrogen often bonds with more electronegative elements
  • Losing hydrogen often equates to losing electrons, consistent with chemistry definitions

• Examples in Biological Context

  • Carbon losing hydrogen to oxygen involves electron transfer
  • Terms used in cellular respiration: NAD is reduced when it gains hydrogen, oxidized when it loses hydrogen

Conclusion

• Definitions in biology and chemistry around oxidation and reduction are consistent
• Understanding helps in applying concepts to cellular respiration and other biological processes