Demonstration 1: Voltaic Cells


Demonstration 2: Fruit and Vegetable Batteries

Demonstration 3: Electrolysis of Water in Color

Demonstration 4: Electrolysis of Potassium Iodide

Demonstration 5: Electroplating Copper

Demonstration 6: Making a Simple Battery: The Gerber Cell

Group and Discussion Activities

Key Questions

1. What is the role of electrons in oxidation-reduction reactions? [Electrons are the exchange particles of oxidation-reduction, moving from the oxidized to reduced species.]

2. How can chemical reactions be used to produce electricity? [If the half cells of a redox reaction are physically separated but connected by a salt bridge (to complete the internal circuit), electrons will flow through an external circuit of wire. The anion and electron movements are in opposite directions.]

3. How can electricity be used to drive a chemical reaction? [If a source of electric potential (such as a battery) is attached to electrodes in a solution or ionic melt, the applied potential forces electrons through the system. The electrode connected to the negative terminal holds an excess of electrons, attracts cations, and reduces them. This electrode is the cathode. Simultaneously, oxidation is driven at the anode as anions are attracted, lose their excess electrons to the electrode, and complete the electrical circuit. Electrolysis and electroplating processes rely on such reactions.]

4. How do materials compare in their relative ability to accept or donate electrons? [Materials tend to be classified as electron donors if they are metallic and receivers if they are nonmetallic. However, any particular reaction depends on the relative tendencies of the materials. Thus we rank materials according to their reduction potential. Even though hydrogen in contact with hydrogen ions is assigned a half-cell potential of zero volts, it (like other half cells) can either involve oxidation or reduction. The process observed depends on the nature of the other reactant. If it has a higher reduction potential, hydrogen molecules will be oxidized; if not, hydrogen ions will be reduced.]

5. How are electrochemical processes used in business and industry? [As sources of energy (electrochemical cells) and to drive chemical processes (electrolytic cells).]

6. How are electrochemical devices used in everyday life? [Applications of electrochemical cells and batteries (groups of cells in series) are myriad. Some examples include flashlights, portable appliances, pacemakers, automobile cranking systems, and submarine propulsion units.]

Counterintuitive Examples/Discrepant Events

Analogies and Metaphors

Figure 5. Electron transport/ water analogies.

3. Imagine that the quantity of work that can be performed by a galvanic cell is similar to the work obtainable from a water wheel powered by falling water.

The height of the waterfall is analogous to the cell potential. The higher the waterfall, the more potential energy it has. In the case of a voltaic cell, the higher the cell potential, the more the "driving force" for an electron. The quantity of water flowing over the waterfall is analogous to the current generated by the voltaic cell. The quantity of work that can be performed by a water wheel (equivalent to the voltaic cell) depends on both how much water flows each second (equivalent to current) and the height that water falls (equivalent to the electric potential.)

Figure 6. Water wheel analogy.height


Memory Aids: Mnemonics, etc.

1. Use a cat picture with + signs for eyes to remember Cation is positive. Or use cat paw with + sign in the pad print to remind students that cations are "pawsitive."

2. LEO the lion says GER. LEO = Loss of Electrons is Oxidation. GER = Gain of Electrons is Reduction.

3. Cathode and Reduction both start with consonants; Anode and Oxidation both start with vowels.

4. "An Ox and Red Cat" (ANode involves OXidation and REDuction involves CAThode)

5. OIL RIG = Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons)