3.1.7 Oxidation, Reduction, and Redox

• What is oxidation?

  • The loss of electrons
  • OR Gain of Oxygen (or any electronegative element)
  • OR Loss of Hydrogen (or any electropositive element)
• Reduction: The process of electron gain / decrease in oxidation number
• Define oxidation state. A number which represents the number of electrons lost or gained by an atom of that element in the compound
• Oxidising agent: A reagent that oxidises (removes electrons from) from another species.
• Reducing agent: a species that reduces another element (electron donors)
• What is reduction?

  • The gain of electrons
  • OR Loss of Oxygen (or any electronegative element)
  • OR Gain of Hydrogen (or any electropositive element)
• What are the half equations for SnO + Zn → ZnO + Sn?

  
  

  Half Equations:

  • Sn2+ + 2e- → Sn
  • Zn → Zn2+ + 2e
• What is the oxidation state of oxygen in OF2 ? [O] = +2
• What is the oxidation state of hydrogen in KH ? [H] = -1
• What is the oxidation state of chlorine in NaClO ?

  [Cl] = +1
• Disproportionation: Where in a redox reaction, the oxidation states of atoms of the same element, increase for some atoms, whereas decrease for some atoms.
• What is the oxidation state of phosphorus in PCl5 ? [P] = +5
• What is the oxidation state of nitrogen in ammonia? [N] = -3
• What is the oxidation state of arsenic in AsO4 -3 ?

  [As] = +5
• What happens in a redox reaction:

  • Electrons are transferred from one species (element) to another.
  • One element is oxidised whilst another is reduced.
• Why is, 2CrO4 2- + 2H+ → Cr2O7 2- + H2O, not a redox reaction?

  
  

  Chromium is oxidised whereas hydrogen remains the same oxidation state (no element is reduced).