C7 redox

• a redox reaction involves reduction and oxidation
• oxidation means loss of electrons

  reduction means gain of electrons
• oxidising agents oxidise other species, so they themselves are reduced, they are electron acceptors
• reducing agents reduce other species, so they themselves are oxidised, they are electron donors
• oxidation states are numbers which represent the extent to which an element has been oxidised or reduced as part of a compound
• the overall oxidation state of a compound is the sum of the individual oxidation states, it should add up to 0 as all compounds are neutral
• a negative oxidation state shows the element has gained electrons so has been reduced
• a positive oxidation state shows the element has lost electrons so has been oxidised
• general rules for oxidation states:

  • uncombined elements = 0
  • hydrogen = +1
  • group 1 = +1
  • group 2 = +2
  • aluminium = +3
  • oxygen = -2
  • group 7 = -1
• half equations are used to show the separate oxidation and reduction reactions that happen as part of a redox reaction, they need to be balanced in terms of elements and charges
• the process to write balanced half equations:

  • balance everything except oxygen and hydrogen
  • balance oxygen by adding H2O
  • balance hydrogen by adding H+ ions
  • balance charges by adding e-
• half equations can be combined to determine the overall redox reaction
• to combine half equations, multiply one or both half equations by a factor so they have the same number of electrons, then combine and cancel the electrons