1 Electrolytic Cells Mr. Shields Regents Chemistry U14 L04.
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Transcript of 1 Electrolytic Cells Mr. Shields Regents Chemistry U14 L04.
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Electrolytic Cells
Mr. Shields Regents Chemistry U14 L04
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Earlier we said there were two types of Cells:
- Electrochemical (i.e. voltaic/galvanic cell)- Electrolytic cell
Electrochemical cells produce electricity through aSpontaneous Redox reaction.
In an ELECTROLYTIC CELL, electrons (i.e. electricity) areprovided to drive a non-spontaneous Redox reaction
Electrolytic CellsElectrolytic Cells
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Electrolytic cells are typically used to:
- plate metals on other metals- obtain a pure metal from it’s compounds- recharge batteries
Electrolytic Cell Usage
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They need Electricity to force a redox rxn to occur
There is an external power source req’dThey don’t produce electricity
The polarities are reversed (we’ll see why later)
The Anode is positive The Cathode is negative
Electrolytic cell reactions are also different because they usually take place in one solution/one cell
Electrolytic Cells are different from Voltaic Cells because …
Differences between Electrochemical Cells
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Let’s look at the electrical decomposition of water. This isan example Of an electrolytic cell. It’s called ELECTROLYSIS
2H20(l) 2H2(g) + O2(g)
In this exampleA battery suppliesElectrons to driveThe non-spontaneousReaction forward
What If we drew this electrolytic cell,What would it look Like?
Electrolysis
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Notice that oxidation still takes place at the anode andReduction still takes place at the Cathode.
BUT … now theAnode is positiveAnd the cathodeIs negative.
Electrons from anExternal source Flow into theCathode making itNegative.
Electrons flow fromThe anode intoThe external power sourceMaking this electrode positive
O2 H2
Battery feedse- into cell
+ -
2O-2 O2 +4e-
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Remember our phrase for recalling characteristics ofAn electrochemical (Voltaic) cell?
“ An Ox ate a Red Pussy Cat”
Well there’s another one for an electrolytic cell toalso help you remember.
“A POX on Electrolytic cells”
AnodePositive
Oxidation The Cathode is then just the opposite
Cathode / Negative / Reduction
Memory Jogger
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Voltaic CellVoltaic Cell Electrolytic Electrolytic CellCell
AnodeAnode NegativeNegative PositivePositive
CathodeCathode PositivePositive NegativeNegative
AnodeAnode Oxidation Oxidation takes placetakes place
Oxidation Oxidation takes placetakes place
CathodeCathode Reduction Reduction takes placetakes place
Reduction Reduction takes placetakes place
Electrode ComparisonElectrode Comparison
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Other Electrolytic CellsOther Electrolytic CellsRemember we said earlier that Electrolytic cells are typically used to …
- plate metals on other metals- obtain pure elements from compounds- recharge batteries
We’re going to look at two of these processes:
- Production of pure elements - Mainly Group 1 + 2 elements - Downs Cell
- Metal Plating
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ElectroplatingElectroplatingThis is another example of an electrolytic cell. It is usedTo plate one metal over another conducting object.
For example:
To plate Ag overStainless steel
To plate Au over Cu Or Ni
To plate Cr over Fe
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ElectroplatingElectroplatingIn this diagram what is:
The Cathode
The Anode
At what electrodeDoes Ox. Occur
At which electrodeDoes Red. Occur
What are the halfCell reactions?
Chrome electrode
What’s plated+
-
Chrome Electrode
What’s plated
Cr Cr+2 +2e-
Cr+2 +2e- Cr
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+
SimplifiedCell
+
Downs Cell (fused Salt)Downs Cell (fused Salt)
All reactiveGroup 1 +2 metals,F2 & Al Areproduced This way.
If Na is being producedAt the cathode thenNaCl is melted (Fused)(801 deg C)
To produce a differentMetal I need to use afused salt of that metal
+ -
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A manufacturer wants to make Gold forks out ofhis more cheaply made stainless steel (Fe) forks. DrawAn electrolytic cell that he could use to accomplish this Task. Assume Au forms Au+3. Label everything fullyand specify the oxidation and reduction half cellreactions that will take place.
PROBLEM