Oxidation-Reduction Reactions

1
Oxidation-Reduction Reactions

• 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
• It gains electrons
• Oxidation number decreases
• The substance is classified as an oxidizing agent

• If an element is oxidized
• It loses electrons
• Oxidation number increases
• The substance is classified as a reducing agent

2
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

3
Example 1

• Balance the following redox reaction. Determine
  the oxidizing and reducing agents and write the
  net ionic equation.
• KMnO4 KCl H2SO4 ? MnSO4 K2SO4 H2O Cl2

4
Example 2

• Balance the following redox reaction. Determine
  the oxidizing and reducing agents and write the
  net ionic equation.
• HNO3 H2S ? NO S H2O

5
Example 3

• Balance the following redox reaction. Determine
  the oxidizing and reducing agents and write the
  net ionic equation.
• Zn NaNO3 NaOH H2O ? Na2Zn(OH)4 NH3

6
Example 4

• Balance the following redox reaction. Determine
  the oxidizing and reducing agents and write the
  net ionic equation.
• NaHSO4 Al NaOH H2O ? Na2S NaAl(OH)4

7
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

8
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

9
Example 7

• 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.

10
Example 8

• 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?

11
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?

12
Assignments Reminders

• Read Chapter 11 completely
• Read Section 4-7 of Chapter 4
• Review Session 530 to 700 pm TODAY in 107
  Heldenfels
• Review Session 500 to 700 pm TOMORROW in
  105 Heldenfels