Oxidation, Reduction, Redox reactions

• Oxidation is the loss of electrons
• Reduction is the gain of electrons
• Oxidation and reduction occur simultaneously in a reaction, known as redox reactions (reduction - oxidation)
• 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 assigning oxidation states:

  • Element has an oxidation state of zero
  • Oxidation states in a neutral compound add up to zero
  • Oxidation states in a charged compound add up to the total 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
• Oxidising agent accepts electrons from the species being oxidised, gains electrons, and is reduced
• Reducing agent donates electrons to the species being reduced, loses electrons, and is oxidised
• Half equations are used to show separate oxidation and reduction reactions in a redox reaction
• Method for balancing half equations:

  1. Balance all species excluding oxygen and hydrogen

  2. Balance oxygen using H2O

  3. Balance hydrogen using H+ ions

  4. Balance charges using e- (electrons)
• Half equations can be combined to determine the overall redox reaction