Electrolytic Cells

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Electrolytic Cells
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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.

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Galvanic Cell
Chemical Potential Energy
Electrical Potential Energy
Electrolytic Cell
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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?
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Reversing a Galvanic Cell
This time Zn is reduced Cu is oxidized.
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Two kinds of electrolytic cells

• Fused Salt Cells Preparation of pure metals
  (Fused means melted!)
• Plating Cells Designing surface to have
  specific properties

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Electroplating
Move desired coating from anode onto object to be
plated. Solution contains ions of element to be
plated.
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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.

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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.

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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.

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Anode Oxidation Cu ? Cu2 2e-
Battery

Cathode Object to be Plated Reduction Cu2
2e- ? Cu
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Loses mass
Gains mass
Element to be plated.
Notice Net reaction is just moving Cu around.
Cu2 and SO4-2
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Plating
Cathode object to be plated. Anode is made of
metal that you want to plate on object. Solution
contains ions of plating metal.
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Fused Salt Cells

• Used to purify metals from their ores.

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Schematic of fused salt cell
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Ox 2Cl- ? Cl2 2e-
Red Na 1e- ? Na
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• 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?

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