Redox equations

• OILRIG

  Oxidation is the loss of electrons

  Reduction is the gain of electrons
• Oxidation number

  The oxidation number / state of an atom in a compound is the charge that atom would have if the compound consist only of separate ions
• You work out oxidation number by using their charge number e.g O2 is -2 oxidation number

  
• Rules for assigning oxidation number

  • An element on its own has an oxidation number of 0 e.g. Br2
  • For a simple ion the oxidation number is the charge of the ion e.g. O2 = -2
  • Fluorine is always -1
  • Hydrogen has an oxidation state of +1 except in metal hydrides is -1
• Rules for assigning oxidation number pt2

  • Chlorine is always -1 in compounds except in compound involving oxygen and fluorine
  • In a compound the sum of the oxidation states is 0 e.g. H2S = 0 bcs H = +1 and S = -2 so +2-2 = 0
• Disproportionation reaction is where the same element is being oxidised and reduced
• Oxidising agents

  • Oxidises other substances
  • Accepts electrons
  • Are themselves reduced
• Reducing agents

  • Reduces other substances
  • Donates electrons
  • Are themselves oxidised
• Half equations with water

  
  

  The H+ are always on the left side of the equation

  The electrons (e-) are also on the left side of the equation

  The water would be on the right side of the equation

  E.g.

  Cr2O7^2- ---> 2Cr^3+ + H20

  
  

  1st Balance equation

  Cr2O7^2- ---> 2Cr^3+ + 7H20

  
  

  2nd Add the hydrogen ions

  Cr2O7^2- + 14H+ ---> 2Cr^3+ + 7H20

  
  

  3rd Calculate balance charges (the oxidation state)

  So left hand side would be 12+ and the right hand side is 6+ so there's 6e- on the left side

  Final equation

  Cr2O7^2- + 6e- + 14H+ ----> 2Cr^3+ + 7H2O