1. Electrolytic Processes
C3.3
Love, Heba 

2. Electrolysis – Basic Facts
you need to know.
Remember: Molten = Melted ( liquid)
Aqueous = Dissolved in solution
Key points :
• The ions in the electrolyte MUST be free so they can move towards an
electrode
• Electrolysis uses electricity to decompose a compound
• The Cathode ( -ve) attracts cations ( +ve) , and the anode ( +ve) attracts
anions ( -ve)
• Electricity is supplied from a DC
• For an electric circuit to be complete , there must be a flow of electrons.
Positive Anode – Electrons are taken away from ion
Negative Cathode - Electrons which are taken away are given to other ions.

3. Molten NaCl
Electrolysis of Molten
Substances.
_
_
_
_
_
_
+
+
+
+
+
+
Cathode
-ve
Anode
+ve
+
+
-
-
𝐶𝑙2Sodium
Is
produced
at the
Cathode
Chlorine is
Produced
at the
Anode

4. Details…
You need to know electrolysis of : Sodium Chloride
𝑁𝑎+ 𝐶𝑙−
Reduced at Cathode
( gains electron)
𝑁𝑎
Oxidised at Anode
( loses electron)
Joins with another Cl atom
( remember its diatomic )
𝐶𝑙2
OIL RIG = OXIDATION IS LOSS
REDUCTION IS GAIN
𝑁𝑎+ + 𝑒− → Na
2𝐶𝑙− → 𝐶𝑙2 + 2𝑒−

5. Sodium…
Collected and used as/in:
Street lamps
Coolant in some nuclear reactors!

6. Molten Lead Bromide
𝑃𝑏2+
𝐵𝑟−
Goes to: Cathode
Reduction: Gains two
electrons
Becomes: Pb
Goes to: Anode
Oxidation : loses electron
Joins with another Br- ,
overall two electrons lost
Becomes: 𝐵𝑟2
𝑃𝑏2+
+ 2𝑒−
→ 𝑃𝑏 2𝐵𝑟−
→ 𝐵𝑟2 + 2𝑒−

7. Electrolysis of Solutions

8. Before starting , you need to know that when salts are dissolved in
water, there is also Hydrogen and (OH) ions floating about.
Just remember that:
At Cathode
if the metal is less
reactive than
hydrogen – it will
discharge to the
cathode
( go to ) , but if
there is metal that
is more reactive
than hydrogen,
hydrogen will go to
the cathode.
At Anode
“the simplest” ion
will go to the
anode. E.g
Chlorine will be
discharged rather
than Hydroxide.
And Hydroxide
would discharge
instead of (SO4)

9. Electrolysis: Concentrated Sodium
Chloride
_
_
_
_
_
_
+
+
+
+
+
+
Cathode
-ve
Anode
+veKey points:
• Hydrogen is less
reactive than Sodium
• Chlorine is more
simple than (OH)
• Sodium hydroxide is
left in the bottom.
• Hydrogen is collected
at the cathode
• Chlorine is collected
at the anode.
𝐶𝑎𝑡ℎ𝑜𝑑𝑒 ∶ 2𝐻+
+ 2𝑒−
→ 𝐻2
𝐴𝑛𝑜𝑑𝑒: 2𝐶𝑙−
→ 𝐶𝑙2 + 2𝑒−
𝐻+
𝐻+ 𝐶𝑙−
𝐶𝑙−
𝑂𝐻−
𝑂𝐻−
𝑁𝑎+
𝑁𝑎+

10. Electrolysis of other
Compounds you need to know
Electrolyte Half equations At the
Cathode
At the
Anode
𝐶𝑢𝐶𝑙2 Cathode: 𝐶𝑢2+
+ 2𝑒−
→ 𝐶𝑢
Anode: 2𝐶𝑙− → 𝐶𝐿2 + 2𝑒−
Copper Chlorine
𝐶𝑢𝑆𝑂4 Cathode: 𝐶𝑢2+
+ 2𝑒−
→ 𝐶𝑢
Anode: 4𝑂𝐻−
→ 2𝐻20 + 𝑂2 + 4𝑒−
Copper Oxygen
𝑁𝑎2 𝑆𝑂4 Cathode: 2𝐻+
+ 2𝑒−
→ 𝐻2
Anode: 4𝑂𝐻−
→ 2𝐻20 + 𝑂2 + 4𝑒−
Hydrogen Oxygen
NaCl Cathode: 2𝐻+
+ 2𝑒−
→ 𝐻2
Anode: 2𝐶𝑙− → 𝐶𝐿2 + 2𝑒−
Hydrogen Chlorine

11. Electrolysis using copper
Electrodes.

12. Before we start:
• Pure copper is the cathode (-ve)
• Impure copper – Copper (II) Sulphate is the anode ( +ve)
• The main purpose for this is:
Copper can be extracted from its ore using carbon (
heating it up with carbon) , but you do not obtain the finest,
purest copper – so electrolysis is required.
• Remember , just like any electrolysis process :
GAIN ELECTRONS = REDUCTION = AT CATHODE
LOSS OF ELECTRONS = OXIDATION = AT ANODE

13. The process…
1) You start off with a big fat chunk of imputer copper (II) Sulfate as the
anode
and a tiny bit of pure copper as the cathode.
2) The anode contains Cu ions ( Cu+2) we want to obtain this – How?
3) Supplying electricity provides cathode with electrons
4) These electrons in the cathode attract the Cu ions from the impure
Copper
5) The impurities fall in the base of the container called “sludge”
6) Cu is oxidised in the anode as it loses electrons
7) Cu is reduced in the cathode as it gains electrons to become a Cu atom
𝐴𝑛𝑜𝑑𝑒: 𝐶𝑢 + 𝐶𝑢2+
→ 2𝑒−
Copper atoms been oxidised
𝐶𝑎𝑡ℎ𝑜𝑑𝑒: 𝐶𝑢2+
+ 2𝑒−
→ 𝐶𝑢
Copper ions been reduced into
Pure copper atoms.

14. Mass of Anode and Cathode
Obviously the mass of the Anode will decrease and the mass
of the Cathode will increase… To test this:
1) Weigh the anode and cathode before electrolysis
2) Place the electrodes in the copper Sulfate solution
3) Connect to DC
4) After 5 minutes remove the electrodes from electricity
source and dry them
5) Weigh the anode and cathode again.

15. Electroplating

16. Basics…
Electroplating is coating the surface if a metal with
another metal using electricity!
Remember:
- The cathode: The metal that will be plated
- The anode- the bar of metal used for plating
The ions from the solution ( electrolyte ) moves
towards the metal cathode. The Anode keeps the ions
in the solution “topped up”

17. Coating with Silver
• Electrolyte could be : silver nitrate or silver
sulfate!
• Anode: Silver block ( to top up the electrolyte
with ions)
• Cathode: E.g Brass
𝐶𝑎𝑡ℎ𝑜𝑑𝑒: 𝐴𝑔+ + 𝑒− → 𝐴𝑔
𝐴𝑛𝑜𝑑𝑒 ∶ 𝐴𝑔 → 𝐴𝑔+ +𝑒−

18. Electroplating uses:
Use 1 – Decoration – e.g Jewellery is plated with silver or
gold this makes their appearance much better and makes it
more shiny and attractive
Use 2 – Prevention of corrosion– Some metals corrode e.g
Iron ( due to oxygen) – some household objects like cutlery
are coated with an unreactive metal to stop it from
corroding e.g Nickel or chromium