Electrolysis
What is electrolysis?• Electrolysis means
• “breaking up a compound with electricity”
• From the Greek• Electro – electricity• Lysis – breaking up
• Electrolysis keywords
• Anode – positive electrode• Cathode – negative electrode• Ion - charged particle• Electrolyte – substance that can be electrolysed
• Anion – ion that goes to the anode• Cation – ion that goes to the cathode
What is electrolysis?
• Electrolysis only works on substances made of ions.
• These are mostly the compounds of metals.
• The products of electrolysis are vital for our industry.
What is electrolysis?• Electrolysis will only
work if the ions in the substances are free to move.
• In solids the ions are fixed in place, so electrolysis will not work on solids
• But
• Electrolysis works on liquids and molten compounds
• Electrolysis works on solutions.
Melting
When ionic crystals melt
the ions are free to move
Dissolving
When an ionic substance dissolves
the ions spread out and are free to move
1
Electrodes NegativeCathode
PositiveAnode
D.C.current
Sodium ChlorideSolution
+ -
A little revision
Name the following
23 4
5
When Salt Dissolves
• The sodium ions and the chloride ions split up.
• This gives us• Na+ ions• and• Cl- ions
• Some water molecules also split up
• This gives us• H+ ions• and• OH- ions
NegativeCathode
PositiveAnode
D.C.current
+ -
Na+
Na+Cl-
Cl-H+
H+
OH-
OH-
Where will the ions go?
NegativeCathode
PositiveAnode
D.C.current
+ -
Na+
Na+Cl-
Cl-H+
H+
OH-
OH-
At the anode
Cl2There are lots of chloride ions in brine.They are attracted to the anode first
The chloride ions lose electrons and become chlorine gas
2Cl- Cl2 + 2e-
OXIDATION
The hydroxide ions get left behind in solution. There aren’t enough to discharge.
2e-
NegativeCathode
PositiveAnode
D.C.current
+ -
Na+
Na+Cl-
Cl-H+
H+
OH-
OH-
At the cathode2e-
The electrons get pumped into the cathode.
Positive ions are attracted to it.
Hydrogen ions get to the cathode before the sodium ions.
Hydrogen gas is discharged.
2H+ + 2e- H2Reduction
Sodium ions are left behind in solution.
H2
NegativeCathode
PositiveAnode
D.C.current
+ -
Na+
Na+Cl-
Cl-H+
H+
OH-
OH-
Where will the ions go?
H2Cl22e-
Products
• The three main products are:
• Hydrogen gas
• Chlorine gas
• Sodium hydroxide solution
Cl2
H2
Na+ OH-
NegativeCathode
PositiveAnode
D.C.current
+ -
Na+
Na+Cl-
Cl-H+
H+
OH-
OH-
In the Diaphragm Cell
H2Cl22e-
Cl-
Cl-Cl2
