Oxidation, reduction and redox

• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Oxidation and reduction occur simultaneously in a reaction because one species loses electrons which are then donated and gained by the other species
• Redox reactions


  Reduction-oxidation reactions
• The redox rule is remembered using the acronym OILRIG (oxidation is loss, reduction is gain)
• Oxidation number


  Gives the oxidation state of an element or ionic substance

  
• Rules for allocation of oxidation state

  • Oxidation state of an element is zero
  • Oxidation states in a neutral compound add up to zero
  • Oxidation states in a charged compound add up to total the charge
  • Hydrogen has an oxidation state of +1
  • Oxygen has an oxidation state of -2
  • All halogens have an oxidation state of -1
  • Group I metals have an oxidation state of +1

  
• These rules can be used to work out the oxidation number of species or elements in a reaction
• Determining oxidation number of Sulfur

  • 2 - 8 + x = 0
  • -6 + x = 0
  • X = 6

  
• Oxidising agent


  Accepts electrons from the species that is being oxidised, therefore it gains electrons and is reduced
• Reducing agent


  Donates electrons to the species being reduced, therefore it loses electrons and is oxidised
• Half equations


  Used to show the separate oxidation and reduction reactions that occur in a redox reaction

  
• Steps to write balanced half equations

  1. Balance all species excluding oxygen and hydrogen

  2. Balance oxygen using H2O

  3. Balance hydrogen using H+ ions

  4. Balance changes using e- (electrons)
• Half equations can be combined in order to determine the overall redox reaction, the number of electrons must be the same for both half equations