Electrolysis is a process where an electric current is passed through an ionic substance, causing the substance to decompose. During electrolysis, the substance being electrolyzed (called the electrolyte) contains positive and negative ions. Positive ions move to the negative electrode where they gain electrons through reduction reactions. Negative ions move to the positive electrode where they lose electrons through oxidation reactions. This process is used industrially for processes like refining metals and producing chemicals.

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What is electrolysis?
An ionic compound conducts electricity
when it is molten or in solution. The
current causes the ionic compound
to split up and form new substances.
Electrolysis has many uses, including:
 purifying copper
 plating metals with silver and gold
 extracting reactive metals, such as aluminium
 making chlorine, hydrogen and sodium hydroxide.
This process is called electrolysis,
a word which comes from Greek
and means “splitting by electricity”.

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heat
What happens during electrolysis?
In electrolysis, the substance that the current passes through
and splits up is called the electrolyte.
Positive ions move
to the negative electrode
and gain electrons.
This is reduction.
Negative ions move
to the positive electrode
and lose electrons.
This is oxidation.
The electrolyte contains positive and negative ions.
What happens to these ions during electrolysis?

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Electrolysis of molten lead bromide

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What redox processes occur at the
electrodes during the electrolysis
of molten lead bromide (PbBr2)?
Electrolysis of molten PbBr2 – redox equations
What is the overall equation for the electrolysis of molten
lead bromide ?
At the negative electrode:
Pb2+ + 2e-  Pb (reduction)
lead bromide  lead + bromine
PbBr2 (l)  Pb (l) + Br2 (g)
At the positive electrode:
2Br-  Br2 + 2e- (oxidation)

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Electrolysis of molten PbBr2 – summary

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Why and how is aluminium extracted?
Aluminium is one of the most
useful metals in the world.
Aluminium ore (bauxite) has a very high
melting point (2050°C).
Electrolysis is used to extract
aluminium from its ore. Why
is it not possible to extract
aluminium by heating its ore
with carbon?
For electrolysis, the ore is dissolved in
a compound called cryolite (Na3AlF6),
which lowers the melting point to 700°C.
Why is this important economically?

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Extracting aluminium

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What redox processes occur at the
electrodes during the electrolysis
of aluminium oxide (Al2O3)?
Extracting aluminium – redox equations
What is the overall equation for the extraction of aluminium
by electrolysis?
At the negative electrode:
Al3+ + 3e-  Al (reduction)
aluminium oxide  aluminium + oxygen
2Al2O3 (l)  4Al (l) + 3O2 (g)
At the positive electrode:
2O2-  O2 + 4e- (oxidation)

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Extracting aluminium – summary

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What are the products of electrolysis?