Electrolytic Cells
Electrolytic Cells
• Use electricity to force a nonspontaneous
reaction to occur. Endothermic.
• Electrolytic cells can be identified by the
presence of a battery or a power supply.
• There are many kinds of electrolytic cells.
Galvanic Cell
Chemical
Potential
Energy
Electrolytic Cell
Electrical
Potential
Energy
Electrolytic Decomposition of H2O
H2 is produced at one
electrode, O2 at the other.
2H2O + energy 2H2 + O2
Can you tell from the picture
which electrode is
producing H2?
Reversing a Galvanic Cell
This time: Zn
is reduced &
Cu is
oxidized.
Two kinds of electrolytic cells
• Fused Salt Cells – Preparation of pure
metals (Fused means melted!)
• Plating Cells – Designing surface to have
specific properties
Electroplating
Move desired
coating from anode
onto object to be
plated.
Solution contains
ions of element to
be plated.
Electroplating: Cu onto Al
• Al is above Cu in Table J.
• This reaction will not happen spontaneously.
• Use an external energy source – a power
supply or a battery – to force reaction to
occur.
An Ox ate a Fat Red Cat
• Anode is still electrode at which oxidation
occurs.
• Cathode is still electrode at which
reduction occurs.
• Polarity of electrodes is different!
– Anode is positive.
– Cathode is negative.
A POX on Electrolytic Cells.
• Anode – Positive – Oxidation
• In an electrolytic cell, the polarity is
determined by the outside power supply.
• The anode is hooked up to the positive
terminal and the cathode is hooked up to
the negative terminal.
• Look at drawings in Regents questions.
+
Battery
+
-
Loses
mass
Anode = Oxidation
Cu  Cu+2 + 2eCathode = Object to
be Plated = Reduction
Cu+2 + 2e-  Cu
Gains mass
Element to
be plated.
Cu+2 and SO4-2
Notice: Net
reaction is just
moving Cu around.
Cathode = object to be plated.
Plating
Anode is made of metal that you want to
plate on object.
Solution contains ions of plating metal.
Fused Salt Cells
• Used to purify metals from their ores.
Schematic of fused salt cell
+
+
Ox: 2Cl-  Cl2 + 2e-
-
Red: Na+ + 1e-  Na
• Why does the NaCl have to be molten?
• Which electrode will the Na+ ions be
attracted to?
• Which electrode will the Cl- ions be
attracted to?