Download UNIT 17 - OXIDATION-REDUCTION (“REDOX”) REACTIONS

UNIT 17 - OXIDATION-REDUCTION (“REDOX”) REACTIONS
REDOX REACTION:
I. Assigning Oxidation Numbers
A.
Review from Unit 7
B.
Example: Determine the oxidation number of each element in Li2SO4.
1. Answer: Lithium is in Group 1, so its oxidation number is +1.
2. Oxygen's oxidation number is almost always -2.
3. Find oxidation number of sulfur.
Let x = sulfur's oxidation number.
There are 2 Li, and each one is +1. There are 4 O, and each one is -2.
There is 1 S, and its oxidation number is x.
Add these up and set the equation equal to zero.
So...
2 (+1) + 1 (x) + 4 (-2) = 0
lithium
sulfur
oxygen
+2 + x -8 = 0 
x-6=0

x=6
II.
Oxidation:
Duncan
A. (A decrease / an increase) in oxidation number means that the atom or ion has
lost electrons.
B. A species that loses electrons is said to be "oxidized" or to "undergo oxidation".
III.
Reduction:
A. (A decrease / an increase) is oxidation number means that the atom or ion has
gained electrons.
B. A species that gains electrons is said to be "reduced" or to "undergo reduction".
**Hint for remembering the terms "oxidation" and "reduction"**
LEO the lion says GER
(LEO = Lose Electrons = Oxidation)
(GER = Gain Electrons = Reduction)
IV.
Half Reactions - Overall Redox reaction:
A. Oxidation half-reaction:
K + LiNO3 --> Li + KNO3
B. Reduction half-reaction:
V.
Oxidizing Agent
A. Substance with the potential to cause another substance to be oxidized.
B. Substance that undergoes reduction.
VI.
Reducing Agent
A. Substance with the potential to cause another substance to be reduced.
B. Substance that undergoes oxidation.
Unit 15 - Oxidation - Reduction ("Redox") Reactions
REDOX REACTIONS WORKSHEET
Write the half-reactions for oxidation and reduction for each of these overall equations. Identify
the species oxidized and the species reduced. Then, identify the oxidizing agent and the
reducing agent.
EXAMPLE:
oxidized
Mg
+
reducing
agent
Fe
+
Zn+2
MgBr2
Mg0 --> Mg+2 + 2 e2 e- + Br20 --> 2 Br-1
oxidation half-reaction:
reduction half-reaction:
1.
reduced
Br2
-->
oxidizing
agent
-->
Fe+2
+
Zn
Oxidation half-reaction:
Duncan
Reduction half-reaction:
Oxidizing agent:
2.
2 Al
+
3 Fe+2
Reducing agent:
-->
2 Al+3
+
3 Fe
Oxidation half-reaction:
Reduction half-reaction:
Oxidizing agent:
3.
Reducing agent:
Zn+2 + Mg --> Mg+2 + Zn
Oxidation half-reaction:
Reduction half-reaction:
Oxidizing agent:
4.
2 H2 + O2 --> 2 H2O
Oxidation half-reaction:
Reduction half-reaction:
Reducing agent:
UNIT 17 - OXIDATION-REDUCTION (“REDOX”) REACTIONS
Oxidizing agent:
UNIT 15 NOTES (CONT’D)
VII.
Reducing agent:
Electrochemistry:
Duncan
A. Applications:
B. Electrochemical Cell
1. Anode:
2. Cathode:
3. Electrons flow from the anode to the cathode!
Unit 15 - Oxidation - Reduction ("Redox") Reactions
THE ELECTROCHEMICAL CELL WORKSHEET
Al3+ + 3e- --> Al
Pb2+ + 2e- --> Pb
-1.66 V
-0.13 V
Answer the questions below referring to the electrochemical cell above and the information
given from the Standard Reduction Table.
1. Which is more easily oxidized, aluminum or lead?
2. What is the balanced equation showing the spontaneous reaction that will occur?
Duncan
3. What is the maximum voltage that this cell can produce?
4. What is the direction of electron flow in the wire?
5. Which electrode is decreasing in size? Increasing in size?
6. What is happening to the concentration of aluminum ions? Lead ions?
7. What is the voltage in this cell when the reaction reaches equilibrium?
8. Which is the anode?
9. Which is the cathode?