1. Type I Electrolytic Cell:
Electrolytic Cells:
Non-spontaneous, endothermic redox reactions can be made to occur by applying an external voltage (in an electrolytic cell).
Type I Electrolytic Cell:
Electrolysis of a molten substance (ionic compound)
eg: molten NaCl
External voltage +
NaCl
800C -
Inert electrodes (carbon)
Substances present: Na+, Cl-
Cathode:
Na+ + e-  Na(s)
E = V
Anode:
2Cl-  Cl2(g) + 2e-
E = V
Ecell = V

2. This is how Na(s) and Cl2(g) are produced industrially.
At least 4.07V are required to force reaction to occur. (In practice more than this is required)
This is how Na(s) and Cl2(g) are produced industrially.
Type II Electrolytic Cell:
Electrolysis of an aqueous solution of an ionic compound.
eg: NaI +
NaI(aq) -
Inert electrodes (platnum or carbon)
Substances present: Na+, I- , H2O
Must determine which reactions take place.

3. Two choices for reduction:a)
Na+ + e-  Na
E = V b)
2H2O + 2e-  H OH-
E = V
b) will occur because it requires the least voltage.
Two choices for oxidation: a)
2I-  I e-
E = V b)
H2O  ½O H e-
E = V
a) will occur because it requires the least voltage.
Anode:
2I-  I e-
Ecell = V
Cathode:
2H2O + 2e-  H OH-
This electrolytic cell requires at least 0.94V
The products are H2(g) & I2(s). (also NaOH)

4. Overpotential effect:
In practice, the actual voltage required to power an electrolytic cell is always greater than the calculated voltage.
The difference between the calculated voltage and the voltage actually required is called the “overpotential”.
This overpotential is higher for reactions involving the oxidation or reduction of water.
Compounds included in the “overpotential effect” at the top of the SRP table are more easily oxidized than water.
Compounds included in the “overpotential effect” at the bottom of the SRP table are more easily reduced than water.
(Br- and Cl- always oxidize before H2O due to overpotential effect)

5. Practice:
Predict anode and cathode half reactions during electrolysis of these 1.0M solutions. KI
HCl
NaF
NaBr HF
Calculate the minimum amount of voltage required to power each of the above. (Ecell)
Draw a labeled diagram of 1a).