Electrolysis of an aqueous solution and electrodes may react

1
Type III Electrolytic Cell

• Electrolysis of an aqueous solution and
  electrodes may react

eg CuSO4
Substances present Cu2, SO42-, Fe, Cu, H2O

• Reduction (Cathode)

Cu2 2e- ? Cu
E? 0.34V
2H2O 2e- ? H2 2OH-
E? -0.41V

• Oxidation (Anode)

2SO42- ? S2O82- 2e-
E? -2.05V
Why not Fe?
Cu ? Cu2 2e-
E? -0.34V
H2O ? ½O2 2H 2e-
E? -0.82V
2
Note

• Net voltage is 0V.

• Fe does not react because of its position.

• No net reaction occurs.

• This process is used for electroplating

3

• Industrial Applications of Electrolytic Cells

• Production of Cl2 (N. Vancouver)

Inert electrodes
Brine (solution of NaCl)
Anode
2Cl- ? Cl2(g) 2e-
Cathode
2H2O 2e- ? H2 2OH-
Products
Cl2
Bleach
H2
NH3 (ammonia)
NaOH
Soap
4

• Electrorefining

eg Production of pure copper.
Impure Copper (Copper Ore)
Pure Copper
Anode
Cu(s) ? Cu2 2e-
Impure
Cathode
Cu2 2e- ? Cu(s)
Pure
5

• Production of Aluminum

Heat
Al2O33H2O ? Al2O3 3H2O
Bauxite
Aluminum Oxide

• Al2O3 has a very high melting point 2045?C

• Instead of melting it, it is dissolved in
  cryolite (Na3AlF6) at 1000?C

• The Al2O3 dissociates into Al3 and O2-

Carbon electrode
Al Core
Anode
C(s) 2O2- ? CO2(s) 4e-
Cathode
Al3 3e- ? Al(l)
Pure molten aluminum