GALVANIC CELLS
Learning Objectives
By the end of this lesson, students will:
· Define oxidation and reduction in terms of loss or gain of electrons.
· Describe the operation of a galvanic cell (using such terms as anode, cathode, electron flow, salt bridge, and ions).
· Build simple galvanic cells and measure cell potential.
· Describe, write, and balance anode and cathode half reactions.
· Define oxidation and reduction in terms of loss or gain of electrons.
· Describe the operation of a galvanic cell (using such terms as anode, cathode, electron flow, salt bridge, and ions).
· Build simple galvanic cells and measure cell potential.
· Describe, write, and balance anode and cathode half reactions.
Lesson Approaches and Overview (Specific Expectations: F2.1, F2.2, F2.4, F2.5, F3.1, F3.2, F3.3)
· As an introductory activity or hook, have students watch the following video:
After the video, ask students: “name one thing you have used to today that depends on batteries.” Have them name objects in a quick manner, almost as if it were a “lightning” round. Thorough this discussion, emphasize the importance of batteries, electrochemistry, in their everyday lives.
· Bring to class a “dead” dissected galvanic cell. This is an effective way to illustrate some of the features of cell and battery technology. To show students the structure of a cell, bring a cut out in half (vertically) D dry cell so that the actual construction can be shown. Use pliers to peel back the outer steel jacket of a 9-V battery and show the 6 cells in series. This can also be done with a 6-V “lantern” battery, which contains 4 cells in series.
· Exercise caution, as these chemicals are caustic. Use plastic gloves and put the dissected battery in a sealable bag).
· Bring to class a “dead” dissected galvanic cell. This is an effective way to illustrate some of the features of cell and battery technology. To show students the structure of a cell, bring a cut out in half (vertically) D dry cell so that the actual construction can be shown. Use pliers to peel back the outer steel jacket of a 9-V battery and show the 6 cells in series. This can also be done with a 6-V “lantern” battery, which contains 4 cells in series.
· Exercise caution, as these chemicals are caustic. Use plastic gloves and put the dissected battery in a sealable bag).
· For a PowerPoint presentation about galvanic cells, go to the following link:
· Remind students that during a redox reaction, one substance loses electrons while another substance gains electrons. As this occurs, electrons are transferred from the substance that is oxidized to the substance that is reduced. When this reaction occurs spontaneously, there is a small release of energy. When the different ions are in direct contact, the chemical energy of the transferred electrons cannot be directly harnessed. Instead, it is released to the environment as thermal energy. The key to harnessing the energy is to separate the oxidizing agent from the reducing agent in a way that forces electron transfer to occur trough a wire. When electrons flow through a wire, electric current is produced.
· Introduce the concepts of half-cells, electrodes, and a cell.
· Explain the operation of galvanic cells as a transfer of energy when the strongest oxidizing agent reacts at the cathode and the strongest reducing agent reacts at the anode. The components of a galvanic cell are cleverly arranged so that the exchange of electrons takes place through an external conductor.
· Explain to the students that salt bridges are a good way to connect the two half-cells in a galvanic cell. Explain that the function of the salt bridge is to maintain the electrical neutrality of each half-cell by promoting the migration of ion through it. A useful analogy for a porous barrier (the salt bridge) is an ordinary sponge, which holds water until squeezed. Similarly, ions don’t move through a porous material very rapidly by diffusion, but do move relatively easily when squeezed by electrical forces caused by a potential difference.
· For the characteristics of a galvanic cell, the following videos are helpful:
· Introduce the concepts of half-cells, electrodes, and a cell.
· Explain the operation of galvanic cells as a transfer of energy when the strongest oxidizing agent reacts at the cathode and the strongest reducing agent reacts at the anode. The components of a galvanic cell are cleverly arranged so that the exchange of electrons takes place through an external conductor.
· Explain to the students that salt bridges are a good way to connect the two half-cells in a galvanic cell. Explain that the function of the salt bridge is to maintain the electrical neutrality of each half-cell by promoting the migration of ion through it. A useful analogy for a porous barrier (the salt bridge) is an ordinary sponge, which holds water until squeezed. Similarly, ions don’t move through a porous material very rapidly by diffusion, but do move relatively easily when squeezed by electrical forces caused by a potential difference.
· For the characteristics of a galvanic cell, the following videos are helpful:
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The following are some effective animations about galvanic cells:
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· Visual and kinesthetic students would benefit from having all students draw and label each component of a galvanic cell. Also, this is a great way to introduce the “line notation of galvanic cells.”
· Remind students that the direction of electron flow in a galvanic cell can be predicted using the table of Standard Reduction Potentials (to be studied on the next lesson). Also, the ion migration cannot be predicted except in a general way: that anions move towards the anode, and cations toward the cathode.
· The following are suggested lab activities for students to construct galvanic cells:
· Remind students that the direction of electron flow in a galvanic cell can be predicted using the table of Standard Reduction Potentials (to be studied on the next lesson). Also, the ion migration cannot be predicted except in a general way: that anions move towards the anode, and cations toward the cathode.
· The following are suggested lab activities for students to construct galvanic cells:
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PLEASE NOTE THAT THE "GALVANIC-LAB-ANSWERS.PPT" FILE ABOVE IS THE ANSWER TO "GALVANIC CELL LAB 4"
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· Remind the students: The strongest oxidizing agent present in the cell always undergoes a reduction at the cathode, while the strongest reducing agent present in the cell always undergoes oxidation at the anode.
· “The Galvanic Cell” game is a really good consolidation activity that I suggest:
- Another consolidation activity can be assigned as homework, or done in class, and consists of an investigation and research of a technological application that is based on the redox reaction that occurs in galvanic cells. The teacher can provide examples such as pacemakers, batteries, electroplating, the practical issue with hydrogen fuel cells, or the reaction that occurs in chargeable and non-rechargeable batteries. This can be a graded project.
References
- Image on top retrieved from: http://www.substech.com/dokuwiki/lib/exe/fetch.php?w=&h=&cache=cache&media=galvanic_cell.png
- Di Guiseppe, M., Haberer, S., Salciccioli, K., Sanader, M, Vavitsas, A. (2012) Chemistry 12. Toronto: Nelson Education Ltd.
- van Kessel, H., Jenkins, F., Davies, L., Plumb, D., Di Guiseppe, M., Lantz, O., Tompkins, D. (2003). Chemistry 12. Toronto: Thomson Canada Limited