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oxidation-reduction reactions - oxidation states change

  • oxidation - increasing oxidation number, losing electrons
  • reduction - decreasing oxidation number, gaining electrons
  • reduction always accompanies oxidation (and vice versa)
  • oxidizing agent (oxidant) - makes it possible for another substance to get oxidized
    • gets reduced
  • reducing agent (reductant) - makes it possible for another substance to get reduced
    • gets oxidized
  • half-reactions - show either oxidation or reduction alone
    • electrons cancel each other out when combined into single equation

For the following equations, determine the oxidizing agent and reducing agent.  

  • remember, oxidizing agent gets reduced, reducing agent gets oxidized
  • I2O5 + 5CO >> I2 + 5CO2
    • I+5 >> I0, gets reduced - oxidizing agent
    • C+2 >> C+4, gets oxidized - reducing agent
  • H2O2 + C2H4 >> H2O + C2H4O
    • C-2 >> C-1, gets oxidized - reducing agent
    • O-1 >> O-2, gets reduced - oxidizing agent

steps for balancing a redox reaction

  • divide equation into 2 half-reactions
  • balance each half-reaction
    • balance all elements other than H and O
    • balance O atoms by adding H2O
    • balance H atoms by adding H+
  • multiply each half-reaction by integer so that # of electrons lost equals # of electrons gained
    • add together half-reactions, cancel out all spectator substances
  • check
  • if in basic solution, add OH- to both sides in order to cancel H+ ions

Balancing MnO4-1 + Fe+2 >> Mn+2 + Fe+3  

  • Mn+7 >> Mn+2
    • MnO4-1 >> Mn+2 + 4H2O
    • MnO4-1 + 8H+ >> Mn+2 + 4H2O
    • oxidation number of Mn -5
  • Fe+2 >> Fe+3
    • no need to balance
    • oxidation number of Fe +1
  • 5Fe+2 + MnO4-1 + 8H+ >> 5Fe+3 + Mn+2 + 4H2O
Subject X2: 

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