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18.3 Balancing equations using Half-reactions in acidic or basic environments

18.3 Balancing equations using Half-reactions in acidic or basic environments. Read pages 730-750. METHOD 1 – USING THE TABLE OF STANDARD REDUCTION POTENTIALS. identify reactants and products for possible half reactions. Find half reaction equations from page 11 (data booklet) that match

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18.3 Balancing equations using Half-reactions in acidic or basic environments

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  1. 18.3 Balancing equations using Half-reactions in acidic or basic environments Read pages 730-750

  2. METHOD 1 – USING THE TABLE OF STANDARDREDUCTION POTENTIALS • identify reactants and products for possible half reactions. • Find half reaction equations from page 11 (data booklet) that match • Look for a reduction half reaction and an oxidation half reaction. • Make the number of electrons lost equal the number of electrons gained. (multiply the reactions) • Add the oxidation and reduction half reactions. Electrons will cancel out and equation is balanced NOTE: • number of atoms and total charge on both sides must balance out. • If it takes place in acidic environment add H+, if basic environment add OH- to help balance out charges and atoms

  3. SAMPLE PROBLEM 1 • IO3-(aq)+ Al (s) → I2 (s) + Al 3+(aq) Find half reactions: IO3-(aq) → I2 (s) Al (s) → Al 3+(aq)

  4. try to find a reduction and an oxidation half reaction that matches on page 11 Reduction: 2IO3-(aq)+ 12H+ (aq) + 10 e-→ I2 (s) + 6H2O (aq) Oxidation: Al (s) → Al 3+(aq) + 3 e-

  5. Multiply by 3 6IO3-(aq)+ 36H+ (aq) + 30 e-→ 3I2 (s) + 18H2O (aq) Multiply by 10 10Al (s) → 10Al 3+(aq) + 30 e- Finally, add them together and inspect. 6IO3-(aq)+ 36H+ (aq) + 10Al (s) → 3I2 (s) + 18H2O (aq) +10Al 3+(aq)

  6. SAMPLE PROBLEM 2 • Use half reactions found on page 11to write a balanced redox equation for the reduction of acidic MnO4-(aq) solution to Mn 2+(aq) by Ni (s).

  7. SAMPLE PROBLEM 3 • Use the half reactions found on page 11to write a balanced redox equation for the oxidation of NO (g) by an acidic Cr2O72-(aq) solution.

  8. PRACTICE: Write the balanced oxidation-reduction equation for: • the reduction of acidic MnO4- (aq) solution to Mn 2+ (aq) by Fe 2+ (aq). • the reduction of acidic MnO4- (aq) solution to MnO2(s) by Pb (s). • Al + Fe 3+ → Al 3+ + Fe 2+ • the oxidation of Cl- (aq) by acidic H2O2(aq)

  9. Homework • Page732 # 17-20 • Page 734 # 21-24

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