Oxidation-Reduction Reactions
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„
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Electrons can be neither created
out of nothing nor destroyed
In any redox reaction there is an element
being reduced and an element being oxidized
The total increase in the oxidation numbers must
equal the total decrease in the oxidation numbers
If an element is reduced
If an element is oxidized
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It gains electrons
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It loses electrons
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Oxidation number decreases
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Oxidation number increases
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The substance is classified
as an oxidizing agent
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The substance is classified
as a reducing agent
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Balancing Redox Reactions
1. Determine oxidation numbers for all elements
in each compound involved in the reaction
2. Separate the oxidation and reduction
processes and write them as half-reactions
3. Balance each half-reaction by inspection and
add the necessary number of electrons to
balance the charge
4. Multiply the half-reactions by integer
numbers to equalize the numbers of
electrons gained and lost in each
5. Add the half-reactions and cancel any
common terms to get the balanced equation
2
Example 1
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Balance the following redox reaction. Determine the
oxidizing and reducing agents and write the net
ionic equation.
KMnO4 + KCl + H2SO4 → MnSO4 + K2SO4 + H2O + Cl2
3
Example 2
„
Balance the following redox reaction. Determine the
oxidizing and reducing agents and write the net
ionic equation.
HNO3 + H2S → NO + S + H2O
4
Example 3
„
Balance the following redox reaction. Determine the
oxidizing and reducing agents and write the net
ionic equation.
Zn + NaNO3 + NaOH + H2O → Na2[Zn(OH)4] + NH3
5
Example 4
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Balance the following redox reaction. Determine the
oxidizing and reducing agents and write the net
ionic equation.
NaHSO4 + Al + NaOH + H2O → Na2S + Na[Al(OH)4]
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Example 5
„
Balance the following redox reaction. Determine the
oxidizing and reducing agents and write the net
ionic equation.
CoCl2 + Na2O2 + NaOH + H2O → Co(OH)3 + NaCl
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Example 6
„
Balance the following redox reaction. Determine the
oxidizing and reducing agents and write the net
ionic equation.
K2Cr2O7 + HCl → CrCl3 + Cl2 + H2O + KCl
8
Example 7
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The citrate ion, C2O4–, is oxidized by the
permanganate ion, MnO4–, in the sulfuric acid
solution, forming carbon dioxide and Mn2+ ion.
Write and balance the net ionic equation, and then
derive the formula unit equation for this reaction.
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Example 8
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525 mL of iodine solution was titrated with
7.28 mL of 0.2 M nitric acid solution producing
iodic acid and nitrogen(IV) oxide. What is the
concentration of the iodine solution?
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Example 9
„
What mass of N2H4 can be oxidized
to N2 by 24.0 g K2CrO4, which is
reduced to Cr(OH)4– in basic solution?
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Assignments & Reminders
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Read Chapter 11 completely
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Read Section 4-7 of Chapter 4
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Review Session – 5:30 to 7:00 pm
TODAY in 107 Heldenfels
Review Session – 5:00 to 7:00 pm
TOMORROW in 105 Heldenfels
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