18 3 balancing equations using half reactions in acidic or basic environments
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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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18.3 Balancing equations using Half-reactions in acidic or basic environments

Read pages 730-750


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


SAMPLE PROBLEM 1

  • IO3-(aq)+ Al (s) → I2 (s) + Al 3+(aq)

    Find half reactions:

    IO3-(aq) → I2 (s)

    Al (s) → Al 3+(aq)


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-


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)


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).


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.


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)


Homework

  • Page732 # 17-20

  • Page 734 # 21-24


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