Topic: Electrolytic Cell
Do now: p.19 in packet, cross out
# 19 and do # 20 and #21. must
label anode/cathode 
• Chemical rxns can produce electricity
= galvanic (voltaic) cell
OR
• Electrical energy used to carry out chemical
reactions
= electrolytic cell
Electrolytic Cell need electrical energy so
NONSPONTANEOUS
Chemical
Potential
Energy
Galvanic Cell
Electrolytic Cell
Electrical
Potential
Energy
Galvanic cell is a battery
Electrolytic cell needs a battery
Electrolytic Cells
•
•
•
Nonspontaneous
Need battery or power supply
Consumes energy = endothermic
What’s the difference?
Battery in one.
Electrons in galvanic flowing from – to +
Electrons in electrylic flowing from + to e-  e-  e-
anode
Electrolytic Cell
a Fat Red Cat ate an Ox
Use Table J, but opposite
More active metal = cathode = negative
Less active metal = anode = positive
catode
Galvanic Cell
A Fat Red Cat ate an Ox
Use Table J
More active metal = anode = negative
Less active metal = cathode = positive
NONSPONTANEOUS
SPONTANEOUS
e- flow Anode to Cathode
e- flow Anode to Cathode
But from + to –
from – to +
(opposite then we’d think)
(just like we’d think)
That’s why we use the battery That’s why it’s spontaneous
 e-  e-  e-
A POX on Electrolytic Cells
• Anode – Positive – Oxidation
A pox = a disease
And electrolytic
cell behave
differently like
they are
diseased?!
Various types of electrolytic cells
1. Fused Salt Cells – used to purify metals
(Fused means melted = molten salt cell)
• Add NaCl (s) and melt it
• Now NaCl (l)
• Why melt it?! Molten b/c need ions
• Why add CaCl2(s)??!
Lowers MP – don’t need as much heat
• Na+1 is reduce to Na(l)
• Na(l) is less dense then NaCl(l)
so it floats on top
• 20,000 tons of Na are produce
this way in the US every year
Fused Salt Cell (Molten salt cell)
+
-
e-  e-  e-  e-
lose electron
So oxidized
So anode
2Cl- +  Cl 2+ 12 e-
Gain electron
So reduced
So cathode
Na+
(l)
Cl-
Na+ + 1e-  Na
Na+
Cl-
BUT WAIT SOMETHING IS WRONG WITH OUR ANODE
Various types of electrolytic cells
2. Electroplating
A layer of a second metal is deposited on the
metal electrode that acts as the cathode
• Used to enhance the appearance of metal
objects and protect them from corrosion.
Various types of electrolytic cells
2. Electroplating
• cathode = object to be
plated
• anode - made of metal
want to plate on object
• solution: contains ions of
plating metal
+
e-  e-  e-  e-
lose electron
So oxidized
So anode
Ag  Ag+ + 1e-
Gain electron
So reduced
So cathode
Ag+ + 1e-  Ag
NO3-
NO3-
3. Electrolysis 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?
What do every one of these have in
common?