Electrolysis and restoration

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Electrolysis and restoration
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ELECTROLYSIS
Copper chloride does not of its own accord fall
apart into copper and chlorine. However if we
pass an electric current through an aqueous
solution of copper chloride using inert
electrodes (graphite or platinum) as in Figure
8.1, copper deposits on the negative electrode
and chlorine gas evolves from the
positive electrode. Copper chloride is decomposed
by electrolysis. What happens during electrolysis
is this. The voltage source (commonly a battery)
is an electron pump. It pushes electrons out of
its negative terminal into the electrode attached
to it (the left-hand one in Figure 8.1). The
positive copper ions are attracted to this
negative electrode and they take electrons from
it and deposit on the surface as neutral copper
atoms
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384 CHEMISTRY IN USE
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forms neutral Cl atoms which quickly combine to
form Cl2 molecules which come out of solution as
gas 2Cl(aq) ? Cl2( g) 2e The overall process
is the sum of these two electrode processes (half
reactions) CuCl2(aq) (or Cu2 2Cl) ? Cu(s)
Cl2( g) Electrolysis has reversed the normal
spontaneous reaction. The essential features of
electrolysis are shown in generalised form in
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A cell in which electrolysis occurs is called an
electrolytic cell, in contrast to a galvanic cell
which produces electricity. Sometimes we use the
term, electrochemical cell, to cover both types
of cell, galvanic and electroytic
In energy terms A galvanic cell is a device that
uses a spontaneous chemical reaction to
generate electricity that is, it converts
chemical energy into electrical energy. An
electrolytic cell is a device that uses an
electric current to bring about a chemical
reaction that does not occur spontaneously that
is, it converts electrical energy into chemical
energy
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ELECTROLYSIS OF MOLTEN IONIC COMPOUNDS
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