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Today
Electrochemistry in the WorldBatteriesFuel CellsCorrosion
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This is the most impractical 1.1 V battery
volt meter
X
1.1 V
How can we get rid of the beaker and salt bridge?
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Issue to deal with
Beakers keep the oxidation and reduction
reactions physically
separated from one another
Salt bridge connect the circuits by allowing ions to flow between the two regions
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No Beakers is easy. Put chemical into a porous medium
Water and ions can flow in and outSolids can't
Many manytiny
holes
Pb PbO2
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How to connect them?
Use a common electrolyteSame chemical is common to both the
oxidation and reduction
Pb PbO2
HSO4-
H+
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Lead Acid Battery
Anode
Cathode
E° = -0.356Vreduction potential
E°cell = 1.685 - (-.356) = 2.041 V
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Total Reaction
Pb(s) + PbO2(s) + 2HSO4- + 2H3O+ 2PbSO4(s) + 4H2O(l)
Imagine starting with 1M HSO4- and H+ (1 M H2SO4)
E = E° = 2.04 V
What is the voltage when 9/10 of the acid has reacted?
work out on doc cam
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Lead Acid Battery was invented in 1859
Why is it still used in cars today?
A. It provides a lot of voltageB. It provides a lot of currentC. Its fun to drive around with sulfuric acid in the carD. It is infinitely rechargable
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Current is Charge per time
To get a lot of current you need a fast reaction.
This is very hard to accomplish without a liquid battery
The lead battery is among the best at providing high current
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You car needs 12V not 2V
How does it do this with a Lead/Acid Battery
It uses six batteries all tied together
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Something everyone should know
Don't "overcharge" your car batteryOr use too high a voltage!
E°cell = -2.06 V This is very close to the reverse of what you
need to charge the lead reaction.
So if you "over charge" you will generate H2 and O2 in your battery
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Batteries without liquids
Dry Cell
The KeySolid Electrolyte
PasteNH4+, NH3, H2O
Carbon makes electrical connection
Very slow reaction. Constant V. Very low current
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Fuel Cells
Anode Cathodeoxidation reduction
2H2
4H+ + 4e-
O2 + 4e- + 2H2O
4OH-
4e-
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Fuel Cells
2H2
4H+ + 4e-
O2 + 4e- + 2H2O
4OH-
4e-
We need a salt Bridge!
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Fuel Cells
2H2
4H+ + 4e-
O2 + 4e- + 2H2O
4OH-
4e-
H+
Proton Transport Membrane
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