Electrolysis
Electrolysis describes what happens in an electrolytic cell and
means to use electricity to make chemicals.
Pb
Na
H2
I2
Al
K
Cl2
O2
Zn
Li
F2
are all made by electrolysis
When metals are made by electrolysis it is sometimes called
electrowinning as the metal is won from the ion as it is reduced.
2e-
→
Pb(s)
Pb2+
+
2Cl-
→ Cl2(g) + 2e-
Electrolysis of Aluminum
Alcan
Kitimat B.C.
Al2O3
+
Name of the Ore used:
Bauxite
Al2O3.3H2O
Heating drives off the water
Al2O3.3H2O + Heat
→
Melting point of Bauxite is 2045 0C
This is too hot!
Cryolite is added
Lowers the melting point to 1000 0C
3H2O
DC Power
+
C
C
Al2O3(l)
DC Power
+
C
C
Al3+
O2-
Al2O3(l)
DC Power
+
C
-
reduction
C
Al3+
O2-
Al2O3(l)
DC Power
+
C
-
Reduction
C
Al3+
O2-
Al2O3(l)
+
Oxidation
DC Power
+
C
-
Reduction
C
Al3+
O2-
Cathode
+
Oxidation
Anode
Al2O3(l)
DC Power
+
C
-
Reduction
C
Al3+
O2-
Cathode
+
Oxidation
Anode
Al2O3(l)
DC Power
+
C
-
Reduction
C
Al3+
O2-
Cathode
+
Oxidation
Anode
Al3+ + 3e- → Al(s)
Al2O3(l)
DC Power
+
C
-
Reduction
C
Al3+
O2-
+
Oxidation
Cathode
Anode
Al3+ + 3e- → Al(s)
2O2- → O2 + 4eAl2O3(l)
Liquid Al
floats to the
top and is
removed.
C
-
Reduction
DC Power
+
C
Al3+
O2-
+
Oxidation
Cathode
Anode
Al3+ + 3e- → Al(s)
2O2- → O2 + 4eAl2O3(l)
Liquid Al
floats to the
top and is
removed.
C
-
Reduction
DC Power
+
Oxygen gas
C
Al3+
O2-
+
Oxidation
Cathode
Anode
Al3+ + 3e- → Al(s)
2O2- → O2 + 4eAl2O3(l)
Non-Inert Electrodes
You must understand that a non-inert Anode might oxidize.
DC Power
-
+
Cu
Cu
K2SO4(aq)
Non-Inert Electrodes
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
K2SO4(aq)
Non-Inert Electrodes
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
2K+
SO42H2O
K2SO4(aq)
Non-Inert Electrodes
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
Cathode
Reduction
2K+
SO42-
H2 O
K2SO4(aq)
Non-Inert Electrodes
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
-
2K+
Cathode
SO42-
Reduction
H2O
2H2O + 2e-→H2 +2OH-0.41 v
K2SO4(aq)
Non-Inert Electrodes
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
Cathode
Reduction
2H2O +
-0.41 v
2e-
→H2
+2OH-
2K+
+
SO42-
Anode
H2O
K2SO4(aq)
Oxidation
You must look at the possible oxidation of:
H2O
SO42Cu
Check out the reduction chart!
S2O82-
+ 2e- →
2SO42-
2.01 v
1/2O2 + 2H+(10-7M) → H20
Cu+ +
1e- →
Cu2+ + 2e- →
0.82 v
Cu(s)
0.52 v
Cu(s)*
0.34 v
*
Strongest Reducing Agent
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
-
+
Cathode
2K+
Reduction
SO42-
2H2O +
-0.41 v
2e-
→H2
Anode
Oxidation
Cu(s) → Cu2++2e-
+2OHK2SO4(aq)
-0.34 v
You must understand that a non-inert Anode might oxidize.
The Cathode will stay inert because it already is reduced.
DC Power
-
+
Cu
Cu
-
+
Cathode
2K+
Reduction
SO42-
2H2O +2e→H2(g)
-0.41 v
Anode
Oxidation
Cu(s) → Cu2++2e-
+2OHK2SO4(aq)
2H2O + Cu(s) → Cu2++ H2 +2OH-
-0.34 v
E0 = -0.75 v
MTV = +0.75 v
Analyze This Cell
0.76 v
Voltmeter
Cu
Zn
HCl(aq)
Analyze This Cell
Or it might look like this
0.76 v
Voltmeter
Cu
Zn
Pourous membrane
HCl(aq)
Analyze This Cell
0.76 v
Voltmeter
Cu
Zn
H+
H2O
Cl-
HCl(aq)
Analyze This Cell
0.76 v
Voltmeter
Cu
Zn
H+
H2O
Cl-
HCl(aq)
Is this cell electrolytic or electrochemical?
Analyze This Cell
0.76 v
Voltmeter
Cu
Zn
H+
H2O
Cl-
HCl(aq)
Electrochemical-
There is no power supply
Cu is higher and the cathode
Zn is lower and the anode.
Analyze This Cell
0.76 v
Voltmeter
Cu
Cathode
Reduction
No Cu2+ to reduce!
Zn
H+
H2O
Cl-
HCl(aq)
Electrochemical-
Cu is higher and the cathode
Zn is lower and the anode.
Analyze This Cell
0.76 v
Voltmeter
Cu
Cathode
Reduction
2H+ + 2e- → H2(g)
0.00 v
Zn
H+
H2O
Cl-
HCl(aq)
Electrochemical-
Cu is higher and the cathode
Zn is lower and the anode.
Analyze This Cell
0.76 v
Voltmeter
Cu
Cathode
Reduction
2H+ + 2e- → H2(g)
0.00 v
Zn
H+
H2O
Cl-
HCl(aq)
Electrochemical-
Anode
Oxidation
What oxidizes?
Zn
H2O
Cl-
Cu is higher and the cathode
Zn is lower and the anode.
Analyze This Cell
0.76 v
Voltmeter
Cu
Cathode
Reduction
2H+ + 2e- → H2(g)
0.00 v
Zn
H+
H2O
Cl-
Anode
Oxidation
Zn → Zn2+ + 2e0.76 v
HCl(aq)
Electrochemical-
Cu is higher and the cathode
Zn is lower and the anode.
Analyze This Cell
0.76 v
Voltmeter
Cu
Cathode
Reduction
2H+ + 2e- → H2(g)
0.00 v
Zn
H+
H2O
Cl-
Anode
Oxidation
Zn(s) → Zn2+ + 2e0.76 v
HCl(aq)
2H+ + Zn(s) → Zn2+ + H2(g)
E0 = 0.76 v
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
Anode:
Cathode:
Electrolyte:
DC Power
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
Anode:
Cathode:
Electrolyte:
Ni
DC Power
Ni
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
Anode:
Ni
Cathode:
Cu
DC Power
Ni
Electrolyte:
C
u
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
Anode:
Ni
Cathode:
Cu
Electrolyte:
Ni(NO3)2
DC Power
Ni
C
u
Ni2+
NO3-
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
Anode:
Ni
Cathode:
Cu
Electrolyte:
Ni(NO3)2
DC Power
+
Ni
C
u
Ni2+
NO3-
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
Anode:
Ni
Cathode:
Cu
Electrolyte:
Ni(NO3)2
DC Power
+
Ni
Reduction
Cathode
C
u
Ni2+
NO3-
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Must be negative!
Must contain the ion of the metal that plates
Electrolyte:
Ni plating a Cu penny
Anode:
Ni
Cathode:
Cu
Electrolyte:
Ni(NO3)2
Reduction
Cathode
Ni2+ + 2e- → Ni(s)
DC Power
+
Ni
C
u
Ni2+
NO3-
Electroplating
Electroplating is the process of reducing a metal on to the surface of another.
Anode:
Metal to be plated on top the other metal
Cathode:
The other metal to be covered with the new metal
Electrolyte:
Must contain the ion of the metal that plates
Ni plating a Cu penny
eAnode:
Ni
Cathode:
Cu
Electrolyte:
Ni(NO3)2
Reduction
Cathode
Ni2+ + 2e- → Ni(s)
DC Power
+
Ni
C
u
Ni2+
NO3-
+
Oxidation
Anode
Ni(s) → Ni2+ + 2e-
Silver plating a Loonie
Anode:
Cathode:
DC Power
Electrolyte:
$
1
Silver plating a Loonie
Anode:
Ag
Cathode:
DC Power
Electrolyte:
Ag
$
1
Silver plating a Loonie
Anode:
Ag
Cathode:
Loonie
-
Electrolyte:
DC Power
+
Ag
Loonie
$
1
Silver plating a Loonie
Anode:
Ag
Cathode:
Loonie
Electrolyte:
-
AgNO3
DC Power
+
Ag
Loonie
$
1
Ag+
NO3-
Silver plating a Loonie
Anode:
Ag
Cathode:
Loonie
Electrolyte:
e-
e-
AgNO3
DC Power
+
Ag
Loonie
Reduction
Cathode
Ag+ + 1e- → Ag(s)
$
1
Ag+
NO3-
+
Oxidation
Anode
Ag(s) → Ag+ + 1e-
Electrorefining
Electrorefining is the process of purifying a metal by electrolysis.
Impure metal is oxidized at the anode and pure metal is reduced at the cathode.
This is the same as electroplating.
The Electrorefinning of Lead
Cominco Trail, B.C.
DC Power
+
Cathode:
Anode:
Electrolyte:
Electrorefining
Electrorefining is the process of purifying a metal by electrolysis.
Impure metal is oxidized at the anode and pure metal is reduced at the cathode.
This is the same as electroplating.
The Electrorefinning of Lead
Cominco Trail, B.C.
DC Power
+
Cathode: Pure Pb
Anode:
Electrolyte:
Electrorefining
Electrorefining is the process of purifying a metal by electrolysis.
Impure metal is oxidized at the anode and pure metal is reduced at the cathode.
This is the same as electroplating.
The Electrorefinning of Lead
Cominco Trail, B.C.
DC Power
+
Cathode: Pure Pb
Anode: Impure Pb
Electrolyte:
Electrorefining
Electrorefining is the process of purifying a metal by electrolysis.
Impure metal is oxidized at the anode and pure metal is reduced at the cathode.
This is the same as electroplating.
The Electrorefinning of Lead
Cominco Trail, B.C.
DC Power
+
Cathode: Pure Pb
Anode: Impure Pb
Pb2+
NO3Electrolyte: Pb(NO3)2
Electrorefining
Electrorefining is the process of purifying a metal by electrolysis.
Impure metal is oxidized at the anode and pure metal is reduced at the cathode.
This is the same as electroplating.
The Electrorefinning of Lead
Cominco Trail, B.C.
DC Power
+
Cathode: Pure Pb
Reduction
Cathode
Pb2+ + 2e- → Pb(s)
Anode: Impure Pb
Pb2+
NO3Electrolyte: Pb(NO3)2
Electrorefining
Electrorefining is the process of purifying a metal by electrolysis.
Impure metal is oxidized at the anode and pure metal is reduced at the cathode.
This is the same as electroplating.
The Electrorefinning of Lead
Cominco Trail, B.C.
DC Power
+
Cathode: Pure Pb
Reduction
Cathode
Pb2+ + 2e- → Pb(s)
Anode: Impure Pb
Zn2+
Pb2+
NO3
-
Au Cu
Electrolyte: Pb(NO3)2
+
Oxidation
Anode
Pb(s) → Pb2+ + 2e-