1. Ch. 17 Electrochemistry

2. Electrochemistry Terminology #1
Oxidation – A process in which an element attains a more positive oxidation state
Na(s)  Na+ + e-
Reduction – A process in which an element attains a more negative oxidation state
Cl2 + 2e-  2Cl-

3. Electrochemistry Terminology #2
An old memory device for oxidation and reduction goes like this…
LEO says GER
Lose Electrons = Oxidation
Gain Electrons = Reduction

4. Electrochemistry Terminology #3
Oxidizing agent
The substance that is reduced is the oxidizing agent
Reducing agent
The substance that is oxidized is the reducing agent

5. Electrochemistry Terminology #4
Anode
The electrode where oxidation occurs
Cathode
The electrode where reduction occurs
Memory device:
Reduction
at the
Cathode

6. Table of Reduction Potentials
Measured against the Standard Hydrogen Electrode

7. Measuring Standard Electrode Potential
Potentials are measured against a hydrogen ion reduction reaction, which is arbitrarily assigned a potential of zero volts.

8. Galvanic (Electrochemical) Cells
Spontaneous redox processes have:
A positive
cell potential, E0
A negative free energy change, (-G)

9. Zn - Cu Galvanic Cell From a table of reduction potentials:
Zn2+ + 2e-  Zn E = -0.76V
Cu2+ + 2e-  Cu E = +0.34V

10. Zn - Cu Galvanic Cell Zn  Zn2+ + 2e- E = +0.76V
The less positive, or more negative reduction potential becomes the oxidation…
Cu2+ + 2e-  Cu E = +0.34V
Zn  Zn2+ + 2e E = +0.76V
Zn + Cu2+  Zn2+ + Cu E0 = V

11. Line Notation Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s) | || |
An abbreviated representation of an electrochemical cell
Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
Anode
material
Anode
solution
Cathode
solution
Cathode
material | || |

12. Agenda Catalyst Galvanic cells/Electrochemical cells Multiple Choice
HW: read p

13. Consider the reduction potential chart p
Consider the reduction potential chart p.829 Find and copy the reduction equations for Ag+  Ag and Pb2+  Pb. Be sure to include their reduction potentials (in volts).
1. Which metal ion has the greater reduction potential? 2. If these two metals (and their solutions) were used to create a galvanic cell, which metal would be the anode? 3. Write the reaction at the anode: 4. Write the reaction at the cathode:

14. 5. What is the overall reaction?
6. What would be the voltage of the standard electrochemical cell?
7. If the concentration of Ag+ was increased, will the overall voltage increase or decrease? What if [Pb2+] was increased?
8. Sketch the cell:
9. Write the cell notation for the cell: ______|________||________|_____

15. Calculating G0 for a Cell
G0 = -nFE0
n = moles of electrons in balanced redox equation
F = Faraday constant = 96,485 coulombs/mol e-
Zn + Cu2+  Zn2+ + Cu E0 = V

16. Both sides have the same components but at different concentrations.
???
Concentration Cell
Both sides have the same components but at different concentrations.
Step 1: Determine which side undergoes oxidation, and which side undergoes reduction.

17. Both sides have the same components but at different concentrations.
???
Concentration Cell
Both sides have the same components but at different concentrations.
Anode
Cathode
The 1.0 M Zn2+ must decrease in concentration, and the 0.10 M Zn2+ must increase in concentration
Zn2+ (1.0M) + 2e-  Zn (reduction)
Zn  Zn2+ (0.10M) + 2e- (oxidation)
Zn2+ (1.0M)  Zn2+ (0.10M)

18. CW: Multiple Choice and FRQ a
Given 3 or more half-cells, how can you find the cell potential of a cell?
HW: Read p

19. Electrolytic Processes
Electrolytic processes are NOT spontaneous. They have:
A negative
cell potential, (-E0)
A positive free energy change, (+G)

20. Electrolysis of Water In acidic solution Anode rxn: Cathode rxn:
-1.23 V
Cathode rxn:
-0.83 V
-2.06 V

21. Electroplating of Silver
Anode reaction:
Ag  Ag+ + e-
Cathode reaction:
Ag+ + e-  Ag
Electroplating requirements:
1. Solution of the plating metal
2. Anode made of the plating metal
3. Cathode with the object to be plated
4. Source of current

22. Solving an Electroplating Problem
Q: How many seconds will it take to plate out 5.0 grams of silver from a solution of AgNO3 using a 20.0 Ampere current?
Ag+ + e-  Ag
5.0 g
1 mol Ag
1 mol e- C
1 s
1 mol e-
20.0 C g
1 mol Ag
= 2.2 x 102 s

23. CW: FRQ and p.866 #89b-c & 91