This document discusses electrolysis, which is the process of using direct current to cause non-spontaneous chemical reactions. Electrolysis requires an electrolyte containing free ions, a direct current power supply, and two electrodes. During electrolysis, ions are oxidized or reduced at the electrodes through electron transfer. As an example, electrolysis can be used to purify copper by dissolving impure copper and conducting electrolysis, depositing pure copper at the cathode. Electrolysis equations describe the half-reactions that occur at each electrode. The document also provides an example of electrolyzing brine to produce chlorine gas, hydrogen gas, and sodium hydroxide.

1. Electrolysis
the passage of a direct electric current
through an ionic substance that is
either molten or dissolved in a suitable
solvent, resulting in chemical
reactions at electrodes and separation
of materials.
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2. Requirements of electrolysis
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An electrolyte - It is a substance containing
free ions which are the carriers of electric
current in the electrolyte
A direct current (DC) supply - It provides
the electrical energy necessary to create or
discharge the ions in the electrolyte.
Electrical current is carried by electrons in
the external circuit.

3. Requirements of electrolysis
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Two electrodes - Electrode is an electrical
conductor which provides the physical
interface between the electrical circuit
providing the energy and the electrolyte.

4. Requirements of electrolysis
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The following figure
shows the
electrolyte, battery
( power supply) and
electrodes
( cathode and anode )
required for
electrolysis.

5. Electrolysis
If you melt or dissolve an ionic compound (such as
NaCl or CuCl2), then the ions become free to move
around – and carry electrical current.
Molecule of solid
copper chloride
CuCl2 (s)
Molecule of solid
copper chloride after
being dissolved
chloride
ion
Copper
ion
CuCl2 (aq)
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6. Electrolysis
Electrolysis is
used to
separate a
metal from its
compound.
= chloride ion
= copper ion
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7. Purifying Copper
Impure
copper
Solution
containing
copper ions
+
+ Cu
+ Cu
+ Cu
At the anode:
Cu(s)
Cu2+(aq) + 2e-
2+
---
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Pure copper
2+
2+
At the cathode:
Cu2+(aq) + 2e-
Cu(s)

8. Electrolysis equations
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We need to be able to write “half equations” to show what
happens during electrolysis (e.g. for copper chloride):
At the negative electrode the
positive ions GAIN electrons to
become neutral copper ATOMS. The
half equation is:
Cu2+ + 2e-
Cu
At the positive electrode the
negative ions LOSE electrons to
become neutral chlorine
MOLECULES. The half equation is:
2 Cl- - 2e-
Cl2

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Oxidation and Reduction in Electrolysis
At the positive
electrode the
negative ions LOSE
electrons –This is
called Oxidation.
The half equation is:
At the negative
electrode the
positive ions GAIN
electrons – this is
called Reduction.
The half equation is:
2Cl- - 2e-
Cu2+ + 2e-
Cl2
Cu

10. Electrolysis of brine
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Sodium chloride (salt) is made of an alkali metal and a
halogen. When it’s dissolved we call the solution
“brine”, and we can electrolyse it to produce 3
things…
Chlorine gas (Cl2) – used to
kill bacteria and to make
acids, bleach and plastics
Hydrogen gas (H2) – used
to manufacture ammonia
and margarine
Sodium
chloride (brine)
NaCl(aq)
Positive
electrode
Negative
electrode
Sodium hydroxide
(NaOH(aq)). Used to
make soap, paper and
ceramics