1. Chemistry 21.3

2. Electrolytic Cells
21.3
DVDs have made it possible to store large amounts of data in a very small space. A laser is used to transfer data to the master DVD. You will read about electrochemical processes that require (rather than produce) electrical energy.

3. Electrolytic vs. Voltaic Cells
21.3
Electrolytic vs. Voltaic Cells
Electrolytic vs. Voltaic Cells
How do voltaic and electrolytic cells differ?

4. Electrolytic vs. Voltaic Cells
21.3
Electrolytic vs. Voltaic Cells
An electrolytic cell is an electrochemical cell used to cause a chemical change through the application of electrical energy.
The process in which electrical energy is used to bring about such a chemical change is called electrolysis.

5. Electrolytic vs. Voltaic Cells
21.3
Electrolytic vs. Voltaic Cells
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 pushed by an outside power source, such as a battery.

6. Electrolytic vs. Voltaic Cells
21.3
Electrolytic vs. Voltaic Cells
Electrochemical cells can be classified as voltaic or electrolytic. a) In a voltaic cell, energy is released from a spontaneous redox reaction. The system (cell) does work on the surroundings (lightbulb). b) In an electrolytic cell, energy is absorbed to drive a non-spontaneous reaction. The surroundings (battery or power supply) do work on the system (cell). Comparing and Contrasting How are voltaic and electrolytic cells similar? How are they different?

7. Electrolytic vs. Voltaic Cells
21.3
Electrolytic vs. Voltaic Cells
Electrochemical cells can be classified as voltaic or electrolytic. a) In a voltaic cell, energy is released from a spontaneous redox reaction. The system (cell) does work on the surroundings (lightbulb). b) In an electrolytic cell, energy is absorbed to drive a non-spontaneous reaction. The surroundings (battery or power supply) do work on the system (cell). Comparing and Contrasting How are voltaic and electrolytic cells similar? How are they different?

8. Electrolytic vs. Voltaic Cells
21.3
Electrolytic vs. Voltaic Cells
Electrochemical cells can be classified as voltaic or electrolytic. a) In a voltaic cell, energy is released from a spontaneous redox reaction. The system (cell) does work on the surroundings (lightbulb). b) In an electrolytic cell, energy is absorbed to drive a non-spontaneous reaction. The surroundings (battery or power supply) do work on the system (cell). Comparing and Contrasting How are voltaic and electrolytic cells similar? How are they different?

9. 21.3
Electrolysis of Water
Electrolysis of Water
What products are formed by the electrolysis of water?

10. 21.3
Electrolysis of Water
The products of the electrolysis of water are hydrogen gas and oxygen gas.

11. 21.3
Electrolysis of Water
When an electric current is passed through water, the water decomposes into oxygen gas and hydrogen gas. Interpreting Photographs Which electrode in the photograph is the cathode? The anode?

12. Balancing the Equation
21.3
Electrolysis of Water
Balancing the Equation

13. 21.3
Electrolysis of Brine
Electrolysis of Brine
What oxidation and reduction reactions occur during the electrolysis of brine?

14. 21.3
Electrolysis of Brine
During electrolysis of brine, chloride ions are oxidized to produce chlorine gas at the anode. Water is reduced to produce hydrogen gas at the cathode.

15. Balancing the Equation
21.3
Electrolysis of Brine
Balancing the Equation

16. 21.3 > Electrolytic Cells Electrolysis of Brine Battery
The electrolytic cell used for the electrolysis of brine. Interpreting Diagrams Which substances are produced by oxidation? By reduction?

17. 21.3
Electrolysis of Brine
To produce chlorine and sodium hydroxide in electrolytic cells, electricity is passed through brine, a sodium chloride solution.
To produce chlorine and sodium hydroxide in electrolytic cells, electricity is passed through brine, a sodium chloride solution. The products have many uses, such as disinfecting swimming pools, cleaning drains, manufacturing soap, and producing paper pulp.

18. Using Electrolysis in Metal Processing
21.3
Using Electrolysis in Metal Processing
Using Electrolysis in Metal Processing
How are electrolytic cells used in metal processing?

19. Using Electrolysis in Metal Processing
21.3
Using Electrolysis in Metal Processing
Electrolytic cells are commonly used in the plating, purifying, and refining of metals.

20. Using Electrolysis in Metal Processing
21.3
Using Electrolysis in Metal Processing
Electroplating and Electroforming
Electroplating is the deposition of a thin layer of a metal on an object in an electrolytic cell.
Electroforming is a process in which an object is reproduced by making a metal mold of it at the cathode of a cell.

21. Using Electrolysis in Metal Processing
21.3
Using Electrolysis in Metal Processing
The cathode is the object to be plated. The anode is the plating metal.
Electroplating In an electrolytic cell used for plating, the object to be plated (a bracelet) is the cathode. The anode is the plating metal, in this case, a piece of silver. At the anode, silver is oxidized to silver ions. Silver ions in the electrolyte solution reduce to silver metal. The silver metal forms a thin coating on the cathode, producing a plated bracelet.

22. Using Electrolysis in Metal Processing
Animation 27
Take an atomic-level look at how electricity can bring about a chemical change.

23. Using Electrolysis in Metal Processing
21.3
Using Electrolysis in Metal Processing
Electrowinning
In electrowinning, impure metals are purified in an electrolytic cell. Aluminum is produced from alumina at the cathode of an electrowinning cell.

24. Using Electrolysis in Metal Processing
21.3
Using Electrolysis in Metal Processing
Electrorefining
In the process electrorefining, a piece of impure metal is made the anode of the cell. It is oxidized to the cation and then reduced to the pure metal at the cathode.

25. 21.3 Section Quiz.
21.3.

26. 21.3 Section Quiz.
1. In electrolysis, an electric current is used to
cause a chemical change.
produce a battery.
generate heat.
run a motor

27. 21.3 Section Quiz.
2. During the electrolysis of water, the region around the anode
changes color.
turns basic.
turns acidic.
remains neutral.

28. 21.3 Section Quiz.
3. Choose the correct words for the spaces. In the net reaction for the electrolysis of water, __________ is/are produced at the cathode and ___________ is/are produced at the anode.
hydrogen, oxygen
oxygen, hydrogen
hydrogen ions, hydroxide ions
hydroxide ions, hydrogen ions

29. 21.3 Section Quiz.
4. In the process of electroplating, the metal is deposited by
reduction at the anode.
reduction at the cathode.
oxidation at the anode.
oxidation at the cathode.

30. 21.3 Section Quiz.
5. Which of the following processes does NOT use the principles behind an electrolytic cell?
electroforming
electrowinning
electrorefining
electrochemical energy production

31. Solve the Concept Map with the help of an interactive guided tutorial.

32. END OF SHOW