Application ofElectrolytic Cells

Lesson 11

Electrolysis describes what happens in an electrolytic cell andmeans 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 ElectrolysisAlcan (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 waterAl2O3

.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!

CC

DC Power

- +

Al3+

O2-

-

Reduction

Cathode

Al3+ + 3e- → Al(s)

+

Oxidation

Anode

O2- → 1/2O2(g) + 2e-

Liquid Al floats to the top and is removed

Oxygen gas

Al2O3(l)

Cation Cathode Reduction Anion Anode Oxidation

Au+

CN-

Au+

CN-

Electroplating

Au plating a Cu pennyElectroplating is the process of reducing a metal on to the surface of anotherElectrolyte: Must contain the ion of the metal that platesCathode: The metal to be covered with a new metalAnode: Metal to be plated on top the other metal

DC Power- +

DC Power- +

Au

+OxidationAnodeAu(s) → Au+ + 1e-

e--ReductionCathodeAu+ + e- → Au(s)

CuCu

AuCN

-ve+ve

stainless steel or Au

Au plated

Copper Ring Gold Plated

Tanya’s Ring Gold Plated

Ag+

NO3-

Electroplating

Ag plating a Loonie

DC Power- +

DC Power- +

Ag

+OxidationAnodeAg(s) → Ag+ + 1e-

e--ReductionCathodeAg+ + e- → Ag(s)

$1

Electrorefinning Lead Trail, B.C.Teck 16 mines in BCMajor 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 PbImpure metal is oxidized at the anode and pure metal is reduced at the cathode.This is the same as electroplating.

DC Power- +

DC Power- +

Pb2+

NO3-

-ReductionCathode

Pb2+ + 2e- → Pb(s)

Cathode: Pure Pb

Anode: Impure Pb

The impurities in Pb are:AuAgZn

Zn oxidizes

Ag does not oxidize

Pb oxidizes

Au does not oxidizeAt the Anode

The voltage is controlled so that:

Pb2+ reduces

At the Cathode

Zn2+ does not reduce

The voltage is controlled so that:

The Electrorefinning of Lead Electrorefining is the process of purifying a metal by electrolysis.The electrolyte must contain PbImpure metal is oxidized at the anode and pure metal is reduced at the cathode.This is the same as electroplating.

DC Power- +

DC Power- +

Pb2+

NO3-

-ReductionCathode

Pb2+ + 2e- → Pb(s)

Cathode: Pure Pb Anode: Impure Pb

+OxidationAnodeZn(s) → Zn2+ + 2e-

Pb(s) → Pb2+ + 2e-

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