ELECTROLYSIS
Electrolysis is a process of decomposing a substance using electrical energy.
.i.e Some ions are Discharged during electrolysis.
To Discharge-is to remove charge..ie. Ions change into atoms.
.e.g Cu2+ + 2e- Cu (s) (reduction)
4OH- 2H2O + O2 + 4e- (oxidation)
Substance / materials which conduct electricity are;
✓ Metals-Conduct by movement of free/delocalized electrons (metallic bonding).
✓ Graphite (which is carbon)-It has delocalized electrons which carry electric current.
✓ Ionic compounds- conduct by movement of ions. They can only conduct in molten
state (liquid) or when dissolved in water (aqueous) because ions are free to move.
NB; ionic compounds do not conduct in solid state unlike metals and graphite
because their ions are strongly attracted to each other in a giant lattice structure.
An electrolytic cell is used to demonstrate conduction by electrolytes.
An Electrolytic cell.
+ - Cell
Bulb
Anode Cathode
--------------------
Electrolyte
Electrodes
1
LSS CHEM DEPT
,PARTS OF ELECTROLYSIS CELL
✓ An electrolyte is a compound in solution or molten state which can conduct an
electric current.
✓ Electrodes are electric conducting materials like copper, platinum and carbon rods.
They are classified as;
Anode-it is connected to the positive terminal of a cell/battery.
It attracts anions during electrolysis.
Cathode- It is connected to the negative terminal of a cell/battery.
It attracts cations during electrolysis.
Types of electrodes
i) Inert electrodes-they are unreactive. .eg. Carbon and Platinum electrodes.
ii)Active/reactive electrodes-They react or are corroded during electrolysis. .eg.
Copper metal electrodes ionize during electrolysis forming Copper (ii) ions in
solution. This causes copper anode to reduce in size.
.e.g. Cu (s) Cu2+ + 2e-
ELECTROLYSIS OF MOLTEN LEAD BROMIDE,PbBr2(l)
It is a liquid hence during electrolysis the following occurs;
Lead ions (Pb2+) migrate to the cathode. They are discharged forming lead atoms.
Bromide ions (Br-) migrate to the anode. They are discharged forming bromine
atoms/ (diatomic hence forms bromine gas)
IONS IN LIQUID LEAD (II) BROMIDE
PbBr2 (s) Pb2+( ) + 2Br-( )
Cathode and Anode reactions
a) At the cathode (-ve)
Pb2+ ions are attracted and discharged;
Pb2+ + 2e- Pb (s) [Reduction]
2
LSS CHEM DEPT
, b) At the anode (+ve)
Br- ions are attracted and discharged.
2Br- Br2 + 2e- [oxidation]
OBSERVATIONS
Bubbles are produced and a brown gas is seen at the anode because bromine gas is
produced.
OVERALL ELECTROLYSIS EQUATION
Redox reaction; reduction + oxidation
[Cathode + Anode]
Pb2+ + 2e- Pb(s)
Br- Br2 + 2e-
______________________________________________________
．．．． ． ．．． ．． ．
．． ．．．
．
．
Pb2+ + 2Br- Pb(s) + Br2
Question
Show the ions in liquid, reaction at the cathode and anode for electrolysis of
molten (liquid) sodium chloride.
Soln
a. At the anode (+ve )
Cl- ions are attracted and discharged.
2Cl- Cl2 + 2e- [oxidation]
b. At the cathode (-ve)
Na+ ions are attracted and discharged.
Na+ + 1e- Na(s) [reduction]
3
LSS CHEM DEPT
Electrolysis is a process of decomposing a substance using electrical energy.
.i.e Some ions are Discharged during electrolysis.
To Discharge-is to remove charge..ie. Ions change into atoms.
.e.g Cu2+ + 2e- Cu (s) (reduction)
4OH- 2H2O + O2 + 4e- (oxidation)
Substance / materials which conduct electricity are;
✓ Metals-Conduct by movement of free/delocalized electrons (metallic bonding).
✓ Graphite (which is carbon)-It has delocalized electrons which carry electric current.
✓ Ionic compounds- conduct by movement of ions. They can only conduct in molten
state (liquid) or when dissolved in water (aqueous) because ions are free to move.
NB; ionic compounds do not conduct in solid state unlike metals and graphite
because their ions are strongly attracted to each other in a giant lattice structure.
An electrolytic cell is used to demonstrate conduction by electrolytes.
An Electrolytic cell.
+ - Cell
Bulb
Anode Cathode
--------------------
Electrolyte
Electrodes
1
LSS CHEM DEPT
,PARTS OF ELECTROLYSIS CELL
✓ An electrolyte is a compound in solution or molten state which can conduct an
electric current.
✓ Electrodes are electric conducting materials like copper, platinum and carbon rods.
They are classified as;
Anode-it is connected to the positive terminal of a cell/battery.
It attracts anions during electrolysis.
Cathode- It is connected to the negative terminal of a cell/battery.
It attracts cations during electrolysis.
Types of electrodes
i) Inert electrodes-they are unreactive. .eg. Carbon and Platinum electrodes.
ii)Active/reactive electrodes-They react or are corroded during electrolysis. .eg.
Copper metal electrodes ionize during electrolysis forming Copper (ii) ions in
solution. This causes copper anode to reduce in size.
.e.g. Cu (s) Cu2+ + 2e-
ELECTROLYSIS OF MOLTEN LEAD BROMIDE,PbBr2(l)
It is a liquid hence during electrolysis the following occurs;
Lead ions (Pb2+) migrate to the cathode. They are discharged forming lead atoms.
Bromide ions (Br-) migrate to the anode. They are discharged forming bromine
atoms/ (diatomic hence forms bromine gas)
IONS IN LIQUID LEAD (II) BROMIDE
PbBr2 (s) Pb2+( ) + 2Br-( )
Cathode and Anode reactions
a) At the cathode (-ve)
Pb2+ ions are attracted and discharged;
Pb2+ + 2e- Pb (s) [Reduction]
2
LSS CHEM DEPT
, b) At the anode (+ve)
Br- ions are attracted and discharged.
2Br- Br2 + 2e- [oxidation]
OBSERVATIONS
Bubbles are produced and a brown gas is seen at the anode because bromine gas is
produced.
OVERALL ELECTROLYSIS EQUATION
Redox reaction; reduction + oxidation
[Cathode + Anode]
Pb2+ + 2e- Pb(s)
Br- Br2 + 2e-
______________________________________________________
．．．． ． ．．． ．． ．
．． ．．．
．
．
Pb2+ + 2Br- Pb(s) + Br2
Question
Show the ions in liquid, reaction at the cathode and anode for electrolysis of
molten (liquid) sodium chloride.
Soln
a. At the anode (+ve )
Cl- ions are attracted and discharged.
2Cl- Cl2 + 2e- [oxidation]
b. At the cathode (-ve)
Na+ ions are attracted and discharged.
Na+ + 1e- Na(s) [reduction]
3
LSS CHEM DEPT
