This document provides definitions and explanations related to electrolysis. It defines key terms like electrolyte, electrode, anode, and cathode. It explains that electrolysis involves the decomposition of ionic compounds through the movement of ions when a current is passed. Molten salts and those dissolved in solutions conduct electricity because the ions are free to move. Simple experiments are described to demonstrate electrolysis, including the electrolysis of molten lead(II) bromide. Equations are given for the reactions at the anode and cathode.

1. Introduction to Electrolysis
Definitions and Terminology

2. Examination Requirements
i) Electrolysis
1.39 understand an electric current as a flow of
electrons or ions
1.40 understand why covalent compounds do not
conduct electricity
1.41 understand why ionic compounds conduct
electricity only when molten or in solution
1.42 describe simple experiments to distinguish
between electrolytes and non-electrolytes

3. Examination Requirements
1.43 recall that electrolysis involves the formation
of new substances when ionic compounds
conduct electricity
1.44 describe simple experiments for the
electrolysis, using inert electrodes, of molten
salts such as lead(II) bromide
1.45 write ionic half-equations representing the
reactions at the electrodes during electrolysis.

4. Definitions
Electric current - a flow of electrons through
a wire, or a flow of electrical charge through
a conducting material.
Electrode - a device for putting current into
or taking current out of a conductor.
Electrolysis - a process in which a compound is
decomposed by an electric current.

5. Definitions (continued)
Cathode - a negative electrode. An electrode
with a surplus of electrons.
Anode - a positive electrode. An electrode
deficient in electrons.
Electrolyte - a substance which, when
liquid(molten) or in solution, conducts
electricity and is decomposed by the current.

6. Definitions (continued)
Ion - an atom, or group of atoms, with an
electric charge. Metal ions are positively
charged. Non‑metal ions are negatively
charged.
Anion - a negative ion which flows towards the
anode during electrolysis.
Cation - a positive ion which flows towards the
cathode during electrolysis.

7. Electrolytes
To be an electrolyte, the compound must contain ions
to carry the electric current through the compound.
The ions must be free to move so that they are
attracted to the electrode of opposite charge. The
ions are free to move in molten(melted) compounds
or when the compound is dissolved in water.
Electrolytes are;
a) Ionic compounds (metal/non-metal compounds).
b) Acids or alkalis.
c) Salts.

8. Electrolysis of Lead(II) Bromide
The electrode connected
to the positive side of
the battery is the anode.
The electrode connected
to the negative side of
the battery is the
cathode.
+ve -ve
graphite
anode
graphite
cathode
lead(II)
bromide

9. Electrolysis of Lead(II) Bromide
The battery is an
‘electric pump’ which
provides the energy
needed to push the
electrons around the
external circuit.

10. Electrolysis of Lead(II) Bromide
Inside the electrolyte,
ions are carrying the
electric current.
Electrons are gained at
the cathode and
electrons are removed at
the anode. Effectively
electrons move from the
cathode to the anode.
movement
of anions
movement
of cations

11. Electrolysis of Lead(II) Bromide
Inside the electrolyte,
ions are carrying the
electric current.
Electrons are gained at
the cathode and
electrons are removed at
the anode. Effectively
electrons move from the
cathode to the anode.
movement
of anions
movement
of cations

12. Movement of Ions
During electrolysis, ions move through the molten
electrolyte.
The negative ions, anions, flow towards the anode.
The positive ions, cations, flow towards the cathode.
The bulb only lights when a current is flowing. If the
electrolyte is solid, there are no free ions, so the
charge (electric current) cannot be carried through
the electrolyte.

13. Questions 1-3
1. What could be used instead of the bulb to
show an electric current is flowing through
the electrolyte?
2. Why is electrolysis classed as a
decomposition reaction?
3. Is electrolysis exothermic or
endothermic? Give a reason for your
answer.

14. Ions at the Cathode
When the positive ions arrive
at the cathode, they gain
electrons.
Atoms are formed on the
surface.
M+
(l) + e-
→ M(s)
Metals and hydrogen are
formed at the cathode.

15. Ions at the Anode
When the negative ions
arrive at the anode, they lose
electrons.
Atoms are formed on the
surface.
2X-
(l) - 2e-
→ X2(g)
Non-metals are formed at
the anode, usually as
molecules.

16. Equations for Lead(II) Bromide
Reaction at cathode
Pb2+
(l) + 2e-
→ Pb(l)
Reaction at anode
2Br-
(l) - 2e-
→ Br2(l)

17. Questions 4-5
4. What are the products for the electrolysis of
the following compounds? For each compound,
write the equations for the reactions at the
anode and cathode.
a) Sodium chloride,
b) Magnesium oxide,
c) Calcium fluoride,
d) Iron(III) bromide.
5. What would be the products if a mixture of
potassium fluoride and lead(II) iodide were
electrolysed?

18. Metal Extraction
Metals low down in the Reactivity Series can
be extracted from solutions by electrolysis.
This method is more often used for the
purification of the metal, rather than the
extraction of the metal from its ore.