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ELECTROCHEMISTRY AND
ELECTROLYSIS
OBJECTIVES:
DEFINITION OF TERMS
WHAT IS ELECTROLYSIS?
USES OF ELECTROLYSIS
WHAT HAPPENS DURING ELECTROLYSIS

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Definition of terms:
▪ Electric current

A flow of charged particles (electrons or ions )
▪ Conductor

A substance that allows electricity to pass through,
for example, all metals, graphite (carbon)
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Definitions contd
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▪ Electrolyte

A molten substance or solution that allows
electricity to pass through causing it to
decompose, for example, molten salts,
aqueous solutions of acids, alkalis and salts
...

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Molten
▪ A substance liquefied by heat
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e
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Electrodes
▪ Points or plates at which current enters or

leaves the electrolyte
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Electrodes (contd
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Examples of inert electrodes are: graphite,
platinum and gold
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Electrodes

(contd
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e
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e
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Anode
▪ The positive electrode
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▪ The anode removes electrons from the

electrolyte
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Cathode
▪ The negative electrode
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▪ It supplies electrons to the electrolyte
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e
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lose electrons

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Electronegative
▪ Electron attracting ability
▪ Is a chemical property that describes the tendency

of an atom to attract electrons towards itself and
thus the tendency to form negative ions
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Metallic conduction (contd
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Metallic conduction (contd
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e
...


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Electrolytic conduction
▪ Involves the movement of free (mobile) ions

through a molten substance or a solution
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What is electrolysis?
▪ Electrolysis is the chemical change occurring

when an electric current is passed through an
electrolyte
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USES OF ELECTROLYSIS
▪ In the extraction of reactive metals from their

ores or compounds
▪ In the extraction of active non-metals

▪ In electroplating and corrosion protection
▪ In the anodizing of aluminium

▪ In electrorefining
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▪ Electrolysis involves the use of electrodes

connected to a battery
▪ The apparatus in which electrolysis is carried

out is known as an electrolytic cell
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e
...

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Diagram of an electrolytic cell

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Theory of electrolysis

Ms
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Smith

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Two main things occur during
electrolysis:
▪ Flow of electrons through wire of the external

circuit and a flow of ions through the
electrolyte
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e
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NB Oxidation therefore occurs at the anode
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i
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Electrons lost at the anode enter the external
circuit and re-enter the electrolytic cell at the
cathode
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Cations (+) are attracted to the cathode (-)
where they gain the electrons from the anode
to form neutral atoms, i
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they are
discharged
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(reduction is gain of electrons-RIG)

Half reaction/equation:

Cn+ + ne- →C
Mg2+ + 2e- →Mg
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An electric current can produce
the following types of chemical
changes:▪ Deposition of metals at the cathode
▪ Evolution of hydrogen at the cathode, apart

from when electrode is active
▪ Discharge of non-metals at the anode
▪ Metal atoms leaving the anode and entering the

solution as metal ions
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Electrolysis of molten electrolytes

Molten electrolytes contain only two types of ion, (one

cation and one anion)
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Ions present: Pb2+ (l), Br- (l)
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Reaction occurring at the anode
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e
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Bromine is a diatomic molecule; therefore
pairs of bromine atoms immediately join to
form bromine molecules:

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Br-(l) – e- →Br

Br-(l) – e- →Br
Overall reaction:

2Br-(l) – 2e- →Br2 (g)

NB At the temperature required to melt lead (II)
bromide, brown bromine vapour is released
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e
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