Chemistry Everyday for Everyone edited by
Chemistry for Kids
John T. Moore Stephen F. Austin State University Nacogdoches, TX 75962
David Tolar R. C Fisher School Athens, TX 75751
Introductory Electrochemistry for Kids — Food for Thought, and Human Potential1 Gary G. Stroebel and Stephanie A. Myers Department of Chemistry and Physics, Augusta State University, Augusta, GA 30904-2200 Modern-day children literally grow up with batteries, which power many of their toys, games, and various other forms of portable entertainment. However, a basic understanding of how electricity is “stored”, released, and distributed is not normally achieved until rather late in their formal education (1). We wish to report the development of simple, inexpensive, and portable activities that invite active participation and aid in linking chemistry and electricity for young children (grades 2–6). Prior understanding of atoms, ions, electrons, or redox processes by the participants is not necessary, and careful guidance promotes discovery through experimentation with familiar materials.
probes are inserted into any one of them. However, when one of these probes is replaced by a steel (consisting mostly of the element iron) wire and both are inserted once again (Fig. 1), the voltmeter indicates that something interesting is happening. At this point participants are asked to predict which cell might produce the greatest potential, and each is tested in turn. During these tests it is suggested that the measured potential is a result of reactions between chemicals3 inside each cell and the different metal electrodes. Thus, these electrochemical cells, like all others, don’t store electricity; they store chemicals!
Procedure We begin our explorations with ordinary D-cells and the device typically included with their purchase, which tests their charge, or potential to produce electricity. We then show how a voltmeter equipped with alligator clips2 connected to short lengths of stiff copper wire to serve as probes can provide better information about the potential available from cells to be tested. Electricity is then explained as the flow of small invisible particles called electrons through a circuit (often consisting of wires), and voltage is a measure of the force with which cells pump (2, 3), by pushing and pulling, electrons through the wires in a complete circuit. Series connections are then made between opposite poles (+ to –) of 2 or more D-cells using additional lengths of copper wire to produce a battery (more than one cell in a circuit). The larger number shown on the voltmeter clearly shows how the cells connected in this way are “working together” to increase the voltage in a series circuit. We next introduce some rather unusual electrochemical cells: an “A cell” (an apple), a “B cell” (a banana), and an “O cell” (an orange). Participants typically indicate strong skepticism about the likely usefulness of these cells, and this seems to be confirmed when the copper voltmeter
Figure 1. A B-cell circuit. Even the youngest participants often refer to the specific metals by their correct elemental symbols based on appearance of the metal.
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Chemistry Everyday for Everyone Reactions of these chemicals result in a “push” on electrons at the iron electrode, and a “pull” on electrons at the copper electrode. This cannot happen when both electrodes are made of the same metal, since the same chemical reactions will happen at each (and therefore equal “pushing” or “pulling” forces act on each). At this point, observation usually has been replaced by involvement as participants are encouraged to suggest their own ideas for further experimentation—and where possible, even to construct their own circuits with different combinations of other metal electrodes. A galvanized nail is a common form of zinc metal, and samples of lead, silver, and aluminum are usually readily available; more exotic metals such as magnesium may be obtained through schools. Voltages resulting from different pairs of metal probes inserted into the cells demonstrate clearly that combinations of different metals, and not the nature of the fruit, are the most important factor in determining individual cell potentials. In a classroom setting, a matrix chart can be constructed on the chalkboard, and students can record voltages achieved with various electrode-pair combinations (3). Discoloration of some of the electrodes during these tests confirms that something chemical is indeed happening, and this corrosion accounts for much of the voltage fluctuations observed. Steel wool should be available for occasional cleaning of the electrodes. Additional insight is gained by suggesting that pieces be cut off of the “B” cell while the iron and copper electrodes are inserted (voltage does not change), then cutting the cell between the two electrodes, at which point cell voltage falls to zero.4 Invariably, an insightful participant will successfully repair the cell by sticking the two pieces back together to reestablish chemical/electrical contact. The same “repair” can be accomplished by connecting the two pieces with a short piece of copper wire, to complete the circuit again. Iron–copper couples (constructed by soldering together short lengths of steel and copper wire) are now used to connect individual pieces of “B cell”, which have one electrode inserted in each. When each cell is connected within the circuit by the different metals, the voltmeter indicates that these connectors result in an overall voltage roughly equal to the sum of the voltages of each cell. By now it is apparent that different chemical reactions at each electrode are generating more pushes and pulls, and the cells are working together to increase the total pumping force acting on the electrons. When the connecting couple is reversed (each cell with electrodes of like metals inserted), total voltage falls to near zero (pushes now cancel pulls). By this time, participants have their own ideas for experiments that they wish to perform, and subtle guidance by the leader produces a “fruit salad battery” (Fig. 2) consisting of different types of cells in a series circuit. Finally, when our budding electrochemists begin to run out of ideas for further experimentation, the leader announces that there is one additional cell to be tested–an “H (for human) cell”. This test consists of merely grasping the copper electrode in one hand and the iron electrode in the other, producing a potential at least comparable to that of the average orange! Once reassured that they won’t receive a shock, most participants want to be tested as well, and by this time they conclude that chemical reactions occurring at the electrodes are responsible for this “human potential”. Iron–copper couples are then used to connect a number of “H-cells” into a people battery! Because each cell is chemically connected to electrodes of different composition, humans are more than salt bridges (4, 5) in this experiment. It is important to point out the difference between voltage and amperage (6), lest anyone conclude that the various batteries
Figure 2. Fruit-salad battery, with metal electrodes alternating in the circuit.
that have been constructed are viable sources of electrical power. On the other hand, previous articles have described how vegetable and fruit batteries can be used to fire a flash cube (7) and power a digital clock (8).5 Results Because of the low cost, easy portability, and benign nature of the materials and equipment, we have conducted these activities in a variety of venues, including classrooms (grades 2–6) and even busy retail stores at which shoppers (preschoolers through adults) stopped, observed, and actively participated. Genuine interest results when all members of a group can actively participate. Even with the aid of video projection equipment, merely demonstrating these experiments before a large audience (approximately 200) failed to produce the level of excitement generated in smaller groups. This observation suggests to us that participation by everyone present accounts for the special appeal of these experiments. It appears that no one wants to be left out of the circuits. Conclusions Our experiences with this activity strongly support the notion that material-centered experiments (9) are quite effective for the early development of a basic understanding of many abstract concepts of electrochemistry. Furthermore, these activities have broad appeal and are therefore ideally suited for outreach efforts. Although the experiments are simple, results can be interpreted with a level of sophistication appropriate to the audience. Our experiences indicate that young children have in fact developed experientially based familiarity with concepts that include electrochemical cells, batteries, electrodes, circuits, series connection, and voltage/potential. For example, we frequently observe that even the youngest of participants effectively troubleshoot problems in these circuits when potential decreases to 0.0 V. For older children and adults, these activities help expand the notion of what is “chemical” and establish the principle that chemical reactions of common and even edible materials can provide sources of electrical energy. Finally, teachers of grades 2–6 who have participated in this activity have reported that this is a valuable learning experience for them and their students.
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Chemistry Everyday for Everyone Acknowledgments We wish to thank Paul Stroebel for assistance in developing the explanations for voltage and for suggesting construction of the fruit salad battery.
4. Voltages as high as 0.2 V are occasionally observed after the pieces are separated, if both pieces are touching the work surface. When either is lifted clear, the resulting potential is 0.0 V. 5. Two “H-cells” connected in a series circuit through zinc– copper couples can successfully power the “Two-Potato Clock” manufactured by Skilcraft and available in many popular toy stores.
Notes 1. Presented as a workshop for elementary school teachers at the 1996 Georgia Science Teachers Association annual convention, Augusta, GA, February 9, 1996. 2. The clips are convenient for investigating the properties of other metal samples, which can be labeled with colored tape bearing the appropriate elemental symbol. See Figures 1 and 2. 3. The attention of even younger children is clearly focused on the cells at this point, and the voltmeter itself is not a significant distraction.
Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.
Chambers, J. Q. J. Chem. Educ. 1983, 60, 259. Faulkner, L. R. J. Chem. Educ. 1983, 60, 262–264. Fortman, J. J.; Battino, R. J. Chem. Educ. 1993, 70, 939–940. Silverman, P. L; Bunn, B. B. J. Chem. Educ. 1992, 69, 309–310. Scharlin, P.; Battino, R. J. Chem. Educ. 1990, 67, 156–157. Kissinger, P. T. Curr. Separations 1985, 6, 62–64. Worley, J. D.; Fournier, J. J. Chem. Educ. 1988, 65, 158. Letcher, T.; Sonemann, A. W. J. Chem. Educ. 1992, 69, 157–159. Whitmer, J. C. J. Chem. Educ. 1974, 51, 170.
A Note from John T. Moore and David Tolar, Editors of Chemistry for Kids We are excited by the opportunity to edit the Chemistry for Kids feature. The science education of the young child is extremely important and should be presented with a liberal dose of enthusiasm and hands-on activities. However, many times someone might be interested in making a contribution, but they’re unsure of what to do. We hope that the Chemistry for Kids feature will provide both ideas and motivation for the readers. We intend to highlight educational resources, such as the ACS Office of Pre-High School Education, in future issues. We encourage all of you to become involved in your local elementary and middle school science programs. Give a chemistry presentation, judge a science fair, give a tour of your lab, mentor a public school teacher—the list is endless. We are always available to help you and to provide resource information via email, phone, or letter, so don’t hesitate to contact us. We look forward to sharing your experiences with others through this Journal. John T. Moore earned his Bachelor’s degree form the University of North Carolina– Asheville and his Masters from Furman University. He began teaching in the chemistry department at Stephen F. Austin State University, Nacogdoches, Texas, in 1971. While teaching, he earned his Doctorate from Texas A&M University and spent almost five years as a part-time medical laboratory technician. In addition to his teaching duties, Moore is active in civic affairs, including volunteering his services as Lab Director at local community health center for the last seven years. Although trained as an analytical chemist, Moore has been involved in chemical education and curriculum development for over ten years. He has developed several courses for students wishing to teach in the public schools, including one on laboratory and stockroom management and another for elementary education majors. He is a member of several professional organizations, including the American Chemical Society and the National Science Teachers Association. David Tolar has experienced a wide variety of life’s offerings. From truck farmer and orchardist to housekeeper and cook to teacher of 6th grade mathematics, he has followed his interests with intensity. Born and reared in Texas, Tolar attended Stephen F. Austin State University where he earned a Bachelor’s Degree with a double major in Mathematics and English, a degree reflecting his diverse enthusiasms. In the course of his studies, Tolar pursued his interest in science by taking courses in geology, physics, and chemistry as electives. After graduation he worked for a few years with his father to establish a 900 tree peach orchard, an employment which gave him experience with practical chemistry. He returned to SFASU to obtain his teaching certificate. While fulfilling the requirements of certification, he and another student worked with John T. Moore searching the literature for chemistry experiments and demonstrations suitable for the pre-high school classroom, rewriting them as needed for clarity, and classifying them by appropriate grade-level. At present, Tolar teaches 6th grade mathematics in a rural school district in East Texas. He has chosen to work in the lower grades because of his belief that the love of learning must be instilled as early as possible to be most effective. He looks forward to the opportunities Chemistry for Kids will provide to extend and fulfill his mission of education. John T. Moore • Stephen F. Austin State University, Box 13006 SFA Station, Nacogdoches, TX 75751 • phone 409/468-3606 • fax 409/468-1266 • email:
[email protected] David Tolar • R. C. Fisher 6th Grade, 404 Martin Luther King Blvd., Athens, TX 75751 • phone: 903/489-3426
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