1. Ch. 20: Electrochemistry
Lecture 4:
Electrolytic Cells & Faraday’s Law

2. Electrolytic Processes
Electrolytic processes are NOT spontaneous.
An external power source is required for the cell to work. They have:
A negative
cell potential, (-E0)
A positive free energy change, (+G)

6. Electrolysis of Water
Anode rxn:
-1.23 V
Cathode rxn:
-0.83 V
-2.06 V

7. Electroplating of Silver
Anode reaction:
Ag(s)  Ag+ + e-
Cathode reaction:
Ag+ + e-  Ag(s)
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

8. Current, I I = q/t Current: flow of charge. e– through wire, and
Ions through solutions and salt bridge
I = q/t

9. Relating I, q, and t
I = q/t
I = current (amperes or amp or coulombs/seconds, C/s)
q = charge (coulombs, C) = n*F
t = time (seconds, s)

10. Relating I, q, and t I = q/t Zn(s)+ Cu2+  Zn2+ + Cu(s) E0 = + 1.10 V
Calculate the mass of copper deposited on the copper electrode in a galvanic cell in 30 seconds if the current, I, is 30 amperes (C/s).
Calculate q:
b) Use Faraday’s constant, 96,485 coulombs/mol e-, determine number of moles of electrons: q = nF
c) Calculate the mass of copper deposited:
q = I * t = (30 C/s) * (30 s) = 900 C

11. Solving a Faraday’s Law 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?
I = 20.0 C/s
Ag+ + e-  Ag
I = q/t
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

12. I = q/t Problem 1 on HW I = current (amperes or coulombs/seconds, C/s)
q = charge (coulombs, C) = nxF
t = time (seconds, s)