Application of Electrolytic Cells Lesson 11

Electrolysis describes what happens in an electrolytic cell and means to use electricity to make chemicals. Many elements are made by electrolysis Pb Al Zn Na K Li H2 Cl2 F2 I2 O2 Pb2+ + 2e- → Pb(s) 2Cl- → Cl2(g) + 2e- This is sometimes called electrowinning- the element is won from its ion

Making Aluminum by Electrolysis Alcan (70,000 employees in 55 countries) Kitimat B.C. 2.7 MT 7 % world production

Aluminum

Aluminum Production by Electrolysis Name of the Ore imported from (Guinea and Brazil) Bauxite Al2O3.3H2O Heating drives off the water Al2O3.3H2O + Heat → Al2O3 + 3H2O   Melting point of Bauxite is 2045 0C This is too hot! Cryolite is added Lowers the melting point to 1000 0C

Reduction of water You cannot reduce Aluminum in water! It must be molten!

Liquid Al floats to the top and is removed DC Power - + Oxygen gas C C - Reduction Cathode Al3+ + 3e- → Al(s) + Oxidation Anode O2- → 1/2O2(g) + 2e- Al3+ O2- Al2O3(l) Cation Cathode Reduction Anion Anode Oxidation

Electroplating e- - Reduction Au Cathode Au+ + e- → Au(s) + Au+   Au plating a Cu penny Electroplating is the process of reducing a metal on to the surface of another Electrolyte: Must contain the ion of the metal that plates Cathode: The metal to be covered with a new metal Anode: Metal to be plated on top the other metal DC Power - + e- - Reduction Cathode Au+ + e- → Au(s) Au + Oxidation Anode Au(s) → Au+ + 1e- Au+ CN- Cu Cu

+ve -ve stainless steel or Au AuCN

Au plated

Copper Ring Gold Plated

Tanya’s Ring Gold Plated

Electroplating e- - Reduction Ag Cathode Ag+ + e- → Ag(s) + Ag+   Ag plating a Loonie DC Power - + e- - Reduction Cathode Ag+ + e- → Ag(s) Ag + Oxidation Anode Ag(s) → Ag+ + 1e- Ag+ NO3- $1 $1

Electrorefinning Lead Trail, B.C. Teck 16 mines in BC Major World Producer of Zn, Cu, Pb, and Coal

Lead Refinery-Trail

The Electrorefinning of Lead Electrorefining is the process of purifying a metal by electrolysis. The electrolyte must contain Pb Impure metal is oxidized at the anode and pure metal is reduced at the cathode. This is the same as electroplating.   DC Power - + Cathode: Pure Pb Anode: Impure Pb - Reduction Cathode Pb2+ + 2e- → Pb(s) Pb2+ NO3-

The impurities in Pb are: Au Ag Zn

At the Anode Au does not oxidize The voltage is controlled so that: Ag does not oxidize Pb oxidizes Zn oxidizes

At the Cathode The voltage is controlled so that: Pb2+ reduces Zn2+ does not reduce

The Electrorefinning of Lead Electrorefining is the process of purifying a metal by electrolysis. The electrolyte must contain Pb Impure metal is oxidized at the anode and pure metal is reduced at the cathode. This is the same as electroplating.   DC Power - + Cathode: Pure Pb Anode: Impure Pb - Reduction Cathode Pb2+ + 2e- → Pb(s) + Oxidation Anode Zn(s) → Zn2+ + 2e- Pb(s) → Pb2+ + 2e- Pb2+ NO3- Zn2+ Au Ag Solid Au and Cu are released from the anode and fall to the bottom

Video of the thermite reaction used to make Iron The Thermite reaction is very exothermic and produces white hot molten iron. Fe2O3 + 2Al(s) → Al2O3(s) + 2Fe(l) + energy