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