chemical rxns can produce electricity = galvanic (voltaic) cell or
DESCRIPTION
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 . - PowerPoint PPT PresentationTRANSCRIPT
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Topic: Electrolytic Cell
Do now: p.19 in packet, cross out # 19 and do # 20 and #21. must
label anode/cathode
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• 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
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Chemical Potential
Energy
ElectricalPotentialEnergy
Galvanic Cell
Electrolytic Cell
Galvanic cell is a battery
Electrolytic cell needs a battery
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Electrolytic Cells• Nonspontaneous• Need battery or power supply• Consumes energy = endothermic
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What’s the difference?
anode catode
Battery in one.Electrons in galvanic flowing from – to +Electrons in electrylic flowing from + to -
Electrolytic Cella Fat Red Cat ate an Ox
Use Table J, but oppositeMore active metal = cathode = negative
Less active metal = anode = positive
Galvanic CellA Fat Red Cat ate an Ox
Use Table J More active metal = anode = negativeLess active metal = cathode = positive
e- e- e-
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NONSPONTANEOUS e- flow Anode to Cathode
But from + to –(opposite then we’d think)
That’s why we use the battery
SPONTANEOUS e- flow Anode to Cathode
from – to + (just like we’d think)
That’s why it’s spontaneous
e- e- e-
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A POX on Electrolytic Cells
• Anode – Positive – Oxidation
A pox = a diseaseAnd electrolytic
cell behave differently like
they are diseased?!
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Various types of electrolytic cells1. 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?!
• Why add CaCl2(s)??!
• 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
Molten b/c need ions
Lowers MP – don’t need as much heat
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Fused Salt Cell (Molten salt cell)
(l)
+
Na+
Cl-
Na+
Cl-
-
Na+ + 1e- NaCl- + Cl + 1 e-
Gain electronSo reduced So cathodelose electron
So oxidizedSo anode
BUT WAIT SOMETHING IS WRONG WITH OUR ANODE
22 2
e- e- e- e-
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Various types of electrolytic cells2. 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.
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Various types of electrolytic cells2. Electroplating • cathode = object to be
plated• anode - made of metal
want to plate on object• solution: contains ions of
plating metal
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NO3-
NO3-
+-
Ag+ + 1e- Ag
Gain electronSo reduced So cathode
Ag Ag+ + 1e-
lose electronSo oxidizedSo anode
e- e- e- e-
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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?
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What do every one of these have in common?