1. Voltaic or
Galvanic Cells
D8 c34
Electrochemical Cell

2. Electrolytic vs. Voltaic Cells
How do voltaic and electrolytic cells differ?
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3. Electrolytic vs. Voltaic Cells
The process in which electrical energy is used to bring about a chemical change is called electrolysis.
You are already familiar with some results of electrolysis, such as gold-plated jewelry, chrome-plated automobile parts, and silver-plated dishes.
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4. The apparatus in which electrolysis is carried out is an electrolytic cell.
An electrolytic cell uses electrical energy (direct current) to make a non-spontaneous redox reaction proceed to completion.
An electrolytic cell is an electrochemical cell used to cause a chemical change through the application of electrical energy.
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5. Electrolysis Using electrical energy to produce chemical change.
Sn2+(aq) + 2 Cl-(aq) ---> Sn(s) + Cl2(g)
SnCl2(aq)
Cl2 Sn

6. Electrolytic vs. Voltaic Cells
Anode (oxidation)
Cathode (reduction)
Energy
Battery
Voltaic Cell
Electrolytic Cell e–
In both voltaic and electrolytic cells, electrons flow from the anode to the cathode in the external circuit.
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7. Electrolytic vs. Voltaic Cells
Anode (oxidation)
Cathode (reduction)
Energy
Battery
Voltaic Cell
Electrolytic Cell e–
The key difference between voltaic and electrolytic cells is that in a voltaic cell, the flow of electrons is the result of a spontaneous redox reaction, whereas in an electrolytic cell, electrons are caused to flow by an outside power source, such as a battery.
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8. Electrolytic vs. Voltaic Cells
Anode (oxidation)
Cathode (reduction)
Energy
Battery
Voltaic Cell
Electrolytic Cell e–
In a voltaic cell, the anode is the negative electrode and the cathode is the positive electrode.
In an electrolytic cell, the cathode is considered the negative electrode.
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9. In electrolysis, an electric current is used to do which of the following?
A. Cause a chemical change
B. Produce a battery
C. Generate heat
D. Run a motor
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10. In electrolysis, an electric current is used to do which of the following?
A. Cause a chemical change
B. Produce a battery
C. Generate heat
D. Run a motor
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11. Driving Nonspontaneous Processes
What are some applications that use electrolytic cells?
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12. Driving Nonspontaneous Processes
Electrolysis of a solution or of a melted, or molten, ionic compound can result in the separation of elements from compounds.
Electrolytic cells are also commonly used in the plating, purifying, and refining of metals.
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13. Electrolysis of water Anode (+) 2 H2O ---> O2(g) + 4 H+ + 4e-
Cathode (-)
4 H2O + 4e- --->
2H2 + 4 OH-

14. Electrolysis of Water
The overall cell reaction is obtained by adding the half-reactions (after doubling the reduction half-reaction equation to balance electrons).
Oxidation: 2H2O(l) → O2(g) + 4H+(aq) + 4e–
Reduction: 2 [2H2O(l) + 2e– → H2(g) + 2OH–(aq)]
6H2O(l) → 2H2(g) + O2(g) + 4H+(aq) + 4OH–(aq)
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15. Driving Nonspontaneous Processes
Electrolysis of Molten Sodium Chloride
The electrolytic cell in which this commercial process is carried out is called the Downs cell.
The cell operates at a temperature of 801°C so that the sodium chloride is maintained in the molten state.
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16. Electrolysis of Molten Sodium Chloride
Sodium and chlorine are produced through the electrolysis of pure molten sodium chloride, rather than an aqueous solution of NaCl.
Chlorine gas is produced at the anode.
Molten sodium collects at the cathode.
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17. Electrolysis of Molten Sodium Chloride
The overall equation is the sum of the two half-reactions:
Reduction: 2Na+(l) + 2e– → 2Na(l)
2NaCl(l) → 2Na(l) + Cl2(g)
Oxidation: 2Cl–(l) → Cl2(g) + 2e–
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18. Electroplating
Electroplating is the deposition of a thin layer of a metal on an object in an electrolytic cell.
An object that is to be silver-plated is made the cathode in an electrolytic cell.
The anode is the metallic silver that is to be deposited.
The electrolyte is a solution of a silver salt, such as silver cyanide.
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19. Electroplating
When direct current is applied, silver ions move from the anode to the object to be plated.
Reduction: Ag+(aq) + e– → Ag(s) (at cathode)
This figure shows statuettes that were electroplated with copper, nickel, and 24-carat gold.
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20. This technique is used to obtain ultrapure silver, lead, and copper.
Electrorefining
In the process of electrorefining, a piece of impure metal is made into the anode of the cell.
It is oxidized to the cation and then reduced to the pure metal at the cathode.
This technique is used to obtain ultrapure silver, lead, and copper.
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21. Electrowinning
In a process called electrowinning, impure metals can be purified in electrolytic cells.
The cations of molten salts or aqueous solutions are reduced at the cathode to give very pure metals.
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22. Producing Aluminum 2 Al2O3 + 3 C ---> 4 Al + 3 CO2
Charles Hall ( ) developed electrolysis process. Founded Alcoa.

23. Key Concepts
The key difference between voltaic and electrolytic cells is that in a voltaic cell, the flow of electrons is the result of a spontaneous redox reaction, whereas in an electrolytic cell, electrons are caused to flow by an outside power source, such as a battery.
Electrolysis of a solution or of a melted, or molten, ionic compound can result in the separation of elements from compounds. Electrolytic cells are also commonly used in the plating, purifying, and refining of metals.
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24. Glossary Terms
electrolysis: a process in which electrical energy is used to bring about a chemical change; the electrolysis of water produces hydrogen and oxygen
electrolytic cell: an electrochemical cell used to cause a chemical change through the application of electrical energy
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25. BIG IDEA
Matter and Energy
The two types of electrochemical cells are voltaic cells and electrolytic cells.
In an electrolytic cell, a nonspontaneous redox reaction is driven by the application of electrical energy.
Electrolytic cells are used to produce commercially important chemicals and to plate, purify, and refine metals.
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26. Quantitative Aspects of Electrochemistry
electrolysis of aqueous silver ion.
Ag+ (aq) + e- ---> Ag(s)
1 mol e- ---> 1 mol Ag
If measure the moles of e-, can know the quantity of Ag formed.
But how to measure moles of e-?

27. Quantitative Aspects of Electrochemistry
Measure the electrical current
Units

28. Quantitative Aspects of Electrochemistry
But how is charge related to moles of electrons?
= 96,500 C/mol e- = 1 Faraday

29. Michael Faraday
Originated the terms anode, cathode, anion, cation, electrode.
Discoverer of
electrolysis
magnetic props. of matter
electromagnetic induction
benzene and other organic chemicals

32. Quantitative Aspects of Electrochemistry
1.50 A flow thru a Ag+(aq) solution for 15.0 min. What mass of Ag metal is deposited?
Solution: Calc. charge
Charge (C) = current (A) x time (t)
= (1.5 A)(15.0 min)(60 s/min)
= C

33. Quantitative Aspects of Electrochemistry
Charge = 1350 C
NEXT: Calculate moles of e- used
(c) Calc. quantity of Ag

34. Pb(s) + HSO4-(aq) ---> PbSO4(s) + H+(aq) + 2e-
If a battery delivers 1.50 A, and you have 454 g of Pb, how long will the battery last?
Solution
a) 454 g Pb = mol Pb
b) Calculate moles of e-
c) Calculate charge
4.38 mol e- • 96,500 C/mol e- = 423,000 C

35. NEXT:
Use Charge = 423,000 C
d) Calculate time
About 78 hours