Electrolytes are substances that can conduct electricity in the molten or liquid state and undergo chemical changes. Electrolysis is a process where electrolytes are broken down into their constituent elements by passing electricity through them. During electrolysis, ions migrate to the oppositely charged electrodes. At the anode, ions lose electrons and form gases or dissolve. At the cathode, ions gain electrons and form solid elements. Examples of electrolysis of molten lead(II) bromide and lead(II) oxide are described through their half reactions at the anode and cathode and overall reactions.

1. Electrolysis

2. Electrolysis of Molten
substances

3. Ionic
compound
Positive ion Negative ion
Sodium
Chloride
NaCl
Lead (ll)
Oxide
PbO
Magnesium
Chloride
MgCl2
Zinc Bromide
ZnBr2

4. Ionic
compound
Positive ion Negative ion
Sodium
Chloride
NaCl
Na+ Cl-
Lead (ll)
Oxide
PbO2
Pb2+ O2-
Magnesium
Chloride
MgCl2
Mg2+ Cl-
Zinc Bromide
ZnBr2 Zn2+ Br-

5. Which is electrolyte and non-
electrolyte?
• Sodium Chloride
• Lead (ll) Oxide
• Magnesium Chloride
• Zinc Bromide
These ionic compounds are electrolytes

6. The term electrolysis
was introduced by
Michael Faraday.
• ‘Lysis’ means loosening
in Greek.
• Thus electrolysis means
‘loosening by
electricity’.

7. Electrolysis
Electrolysis is a process occurs
when electricity is pass
through a solution
(electrolyte) and cause it to
decompose into its
constituent elements.

8. Electrolytes are substances able to conduct
electricity in [ ] state or [ ]
state and undergo [ ] change.
Electrolysis is a process where the [ ]
are broken down into its [ ]
elements by passing [ ] through it.
electrolytes molten chemical
liquid electricity constituent

9. Electrolytes are substances able to
conduct electricity in [molten] state or
[liquid] state and undergo [chemical]
change.
Electrolysis is a process where the
[electrolytes] are broken down into its
[constituent] elements by passing
[electricity] through it.

10. Electrolytic Cell
The electrolytic cell is the set of
apparatus needed to conduct
electrolysis.

11. Electrolytic cell consists
of
•a battery connected to
a switch in series with
•2 metal plates called
electrodes. Electrodes
will carry electricity to
the electrolyte.

12. Electrolytic Cell
Battery
Electrolyte
Metal Plates
(Electrodes)
ammeter

13. a)Electrode connected to
the positive terminal of
an electric source is
called anode.
b)Electrode connected to
the negative terminal of
an electric source is
called cathode.

14. Anode (+) Cathode (-)

15. • When electric current is allowed
to pass through, the electrolytes
which are ionic compound will
split up into positive (+) and
negative (-)ions.
• Example:
NaCl Na+ + Cl-
Ionic compound +ve ion -ve ion

16. • Ions will migrate to the oppositely
charged electrodes.
• Negatively charged (-) ions will
move to the positively charged
anode (+).
Therefore called anions.
• Positively charged (+) ions will
move to the negatively charged
cathode (-) and are called cations.

17. • At the anode, the negative ions
will lose their electrons to the
anode.
• Anode will readily accepts
electrons because it is positively
charged.
ANODE

18. CATHODE
• At the cathode, the positively
charged cations will accept
electrons from the cathode.
• This discharging of ions at the
electrode results in chemical
decomposition of the
electrolyte.
• The movement of ions allows
electricity to be conducted.

19. When describing
electrolysis, state:
• The ions present in the
electrolyte
• The movement of ions to
the anode and cathode
• Half equation at the anode
and cathode

20. Electrolysis of Molten
Lead (ll) Bromide
PbBr2

21. • Lead (ll) bromide is an ionic
compound electrolyte.
• PbBr2 consist of lead (ll)
cations, Pb2+ and bromide
anions, Br-.
• In solid lead (ll) bromide,
these ions do not move freely
but are held in fixed positions
in lattice.

22. • It can only can conduct
electricity when dissolved in
water or in molten state.

23. Molten
lead (ll)
bromide
Crucible
Electrolysis of molten lead (ll) bromide

24. • A bulb is connected to the circuit to
show when the electricity is
flowing.
• Carbon electrodes are used
because it will not react with the
products formed.
• When a current is passed through
the molten lead bromide, lead (ll)
cations, Pb2+ and bromide
anions, Br- are formed.

25. •Bromide anions which are negatively charged
are attracted to the positive anode.
•Lead (ll) cations which are positively charged
are attracted to the negative cathode.

26. ANODE
•Bromide ions will
move towards anode.
•At anode, each
bromide ion will
release an electron to
form a neutral bromine
atom.
•Two bromine atoms
combine to form
bromine gas.
•Thus, bromine gas
evolves at the anode.

27. • Lead (ll) cations
attracted to
cathode.
• At the cathode,
each lead (ll) ion
accept 2
electrons to form
lead atom.
• Hence, silvery
lead globule
deposited.
CATHODE

28. Pb2+, Br-
Br-
Pb2+
release accept
1 2
bromine gas
evolves
silvery grey
globule

29. Half Equation
Half equation is equation
used to show the reaction
occur at the anode or
cathode.

30. • Bromide ion, Br- releases an
electron to form a bromine atom,
Br.
Br- Br + e-
• Two bromine atoms combine to
form a bromine gas, Br2 molecule.
Br + Br Br2
Half equation:
2 Br- (l) Br2 (g) + 2e-
ANODE

31. • lead (ll) ion, Pb2+ accept 2
electrons to form lead atom.
Half equation:
Pb2+ (l) + 2e- Pb (s)
CATHODE

32. Combining the two half equations,
we get the overall equation that
represent the electrolysis of molten
lead (ll) bromide
Anode: 2 Br-(l) Br2 (g) + 2e-
Cathode: Pb2+ (l) + 2e- Pb (s)
Pb2+ (l) + 2 Br- (l) Pb (s) + Br2 (g)

33. Electrolysis of Molten
Lead (ll) Oxide
PbO

34. Pb2+, O2-
O2-
Pb2+
release accept
2 2
oxygen gas
evolves
silvery grey
globule

35. • The Pb2+ ions move towards the
cathode
• The O2- ions move towards the
anode
• At cathode,
 a lead (ll) ion accepts two electrons
to form a lead atom.
• At anode,
 an oxide ion releases two electrons
to form an oxygen atom.
 Two oxygen atoms combine to
form one molecule of oxygen gas.

36. Half Equation
ANODE
Anode: 2 O-(l) O2 (g) + 2e-
CATHODE
Cathode: Pb2+ (l) + 2e- Pb (s)
Pb2+ (l) + 2 O- (l) Pb (s) + O2 (g)
Overall Equation

37. Web Link
• You can find out more about electrolysis
of molten compound.
TRY THESE:
• http://www.mcwdn.org/chemist/pccha
nge.html