Balancing Oxidation Reduction Equations

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Balancing Oxidation Reduction Equations
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Oxidation and Reduction

• Oxidation the atom loses electrons
• The charge becomes more positive
• Reduction the atom gains electrons
• The charge becomes more negative
• Mass and charge must be conserved for all
  chemical equations.

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Steps for Balancing Redox reactions

• Acidic Solutions
• Step 1 Write the half reactions for the
  oxidation and reduction.
• MnO4- H2SO3? SO42- Mn2 H2O
• (Mn goes from Mn7 to Mn2 so this is reduction)
• MnO4- ? Mn2

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Steps for Balancing Redox reactions

• S goes from S4 to S6, so this is oxidation
• H2SO3 ? SO42-
• Step 2 Balance the half rxns for atoms other
  than H and O.
• Already balanced for the example.
• Step 3 Balance the Os by adding H2O.
• MnO4- ? Mn2 4H2O
• H2O H2SO3 ? SO42-

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Steps for Balancing Redox Reactions

• Step 4 Balance H atoms with H
• MnO4- 8H ? Mn2 4H2O
• H2O H2SO3 ? SO42- 4H
• Step 5 Balance the charge on each side by
  adding electrons.
• MnO4- 8H ? Mn2 4H2O
• total charge 7 ? total charge 2
• So, add 5e- to the reactants side to balance the
  charge.

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Steps for Balancing Redox Reactions

• 5 e- MnO4- 8H ? Mn2 4H2O
• H2O H2SO3 ? SO42- 4H
• charge 0 charge 2
• So,
• H2O H2SO3 ? SO42- 4H 2e-
• Electrons must be added to opposite sides for
  each half reaction.

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Steps for Balancing Redox Reactions

• Step 6 Balance the electrons between both half
  reactions.
• (5 e- MnO4- 8H ? Mn2 4H2O) x 2
• 10 e- 2MnO4- 16H ? 2Mn2 8H2O
• (H2O H2SO3 ? SO42- 4H 2e-) x 5
• 5H2O 5H2SO3 ? 5SO42- 20H 10e-
• Now the electrons will cancel out

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Steps for Balancing Redox Reactions

• Step 7 Cross cancel the electrons and other
  substances.
• 10 e- 2MnO4- 16H ? 2Mn2 8H2O
• 5H2O 5H2SO3 ? 5SO42- 20H 10e-
• Step 8 Add the half reactions together
• 5H2SO4 2MnO4- ? 2Mn2 3H2O
• 5SO42- 4H

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Basic Solutions

• Follow the same steps as for acidic solutions,
  and add the following steps.
• Step 9 Add OH- to both sides to equal the H
• 5H2SO3 2MnO4- ? 2Mn2 3H2O
• 5SO42- 4H
• 4 OH- ? 4OH-

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Basic Solutions

• Step 10 Combine the H and OH- to make water.
• 4 OH- 5H2SO3 2MnO4- ? 2Mn2 3H2O
  5SO42- 4H2O
• Step 11 Cancel the H2O if they are on both
  sides.
• 4 OH- 5H2SO3 2MnO4- ? 2Mn2 7H2O
  5SO42-