Demonstration pubs.acs.org/jchemeduc
Music Generated by a Zn/Cu Electrochemical Cell, a Lemon Cell, and a Solar Cell: A Demonstration for General Chemistry Susan G. Cady* P.O. Box 262 Clover, Virginia 24534-0262, United States S Supporting Information *
ABSTRACT: The circuit board found in a commercial musical greeting card is used to supply music for electrochemical cell demonstrations. Similar to a voltmeter, the “modified” musical device is connected to a chemical reaction that produces electricity. The commercial 1 V battery inside the greeting card circuit board can be replaced with an external power source such as a zinc and copper(II) electrochemical cell, a lemon battery or other zinc/proton cell variations, or a commercial solar cell. Directions are given to modify the musical circuit board, to make two types of homemade batteries, and to connect the “modified” musical device to an external power source to create a musical electrical circuit. Unlike a buzzer or flashing light, noticeable variations in music can warn the user of a gradual impending power failure. Students, including the visually impaired and blind, can relate the low volume and the slow tempo of a familiar song with weak or dying batteries and the lack of sufficient power. KEYWORDS: General Public, Elementary/Middle School Science, High School/Introductory Chemistry, First-Year Undergraduate/General, Demonstration, Hands-On Learning/Manipulatives, Humor/Puzzles/Games, Inquiry-Based/Discovery Learning, Electrolytic/Galvanic Cells/Potentials, Green Chemistry
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Imagine sitting in a preschool or kindergarten class. Today the teacher will use a battery demonstration to illustrate the three phases of matter. A glass jar is filled with a clear liquid. The teacher swishes the liquid to show it changes shape as it moves. Then the teacher shows two different colored strips of solid metals. The solids do not easily change shape and can be used to stir the liquid. When the solids are placed in the liquid, bubbles appear. The teacher explains these gas bubbles are the result of the liquid “eating” or corroding one of the solids. The teacher then connects the solid metal strips with a double clipped wire, explains this zinc/citric acid setup is a primitive battery, and shows it can play music, to the delight of the children, when connected to a 1 V music generator. In an elementary class, the teacher may use a battery demo as a mathematical problem exercise. A glass jar contains a blue liquid and a separate glass jar contains a clear liquid. The jars are connected with a draped piece of wet salty paper. The teacher places a shiny brown copper metal strip in the blue jar and a gray zinc metal strip in the clear liquid. The two solid metal strips are connected with a clipped wire. Then a compass is placed near the wire to show something flowing between the metals (current) is creating a (magnetic) force to deflect the compass needle. If available, a voltmeter can be inserted into the circuit to measure ∼1 V. The teacher can explain that this setup acts like a 1 V dry cell battery to provide power. The teacher can then hold up various sizes of dry cell batteries and ask the students how many “1 V jar liquid metal setups” are
nstead of discarding a musical greeting card, the circuit board chip in the greeting card can be used to create musical electrochemical cell demonstrations. The musical circuit board can be added into a pre-existing circuit as an additional resistor or a power-requiring load. But it is more challenging to use chemical reactions that produce electricity, that is, to build an electrochemical cell, to run the “modified” musical device. This is the first known report where the power provided by a Zn/ Cu(II) electrochemical cell, a solar panel, and the lemon Zn/ weak acid proton battery is used to generate music. Although lights and buzzers capture the students’ attention more than a deflecting compass, these demonstrations can be difficult to observe in large classrooms without use of audiovisual equipment. Creating music provides an added dimension to electrochemical demonstrations. Today’s students are musically influenced or “in tune”. A lower volume and slower, even dragging tempo, are easier to detect and measure than a light bulb or monotone buzzer. Audio output allows the visually impaired and blind to participate. The hearing impaired and deaf students could measure the volume differences with audio conversion to visual and tactile devices. Adding music to an electrical demonstration can be entertaining. If the song is familiar (i.e., Happy Birthday), the audience can be encouraged to sing along. Many skeptical, inquisitive smiles have appeared on the faces of students after they heard a lemon “sing”. This musical demonstration can be used with all age groups to introduce the components of a simple battery and then show that the “homemade” battery can do useful work or be entertaining. © XXXX American Chemical Society and Division of Chemical Education, Inc.
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needed to replace the given dry cell battery. For example, a 9 V battery would require about nine setups. The 1.5 V AA and AAA batteries would require two setups because you cannot create half an electrochemical cell. After the math exercise, the Zn/Cu(II) setup is connected to a “modified” 1 V musical device to show the students it will play music. Scientific educational standards can be followed for each school grade level to introduce more electrochemistry concepts and terminology. Senior high and college students will use the table of standard reduction potentials to calculate the overall cell potential or the electromotive force (emf) between two redox reactions. They may routinely do the calculations by applying numbers seen in the table without much attention given to the chemistry. The students may see that the above two electrochemical cells use the same metal electrodes and think they are the same chemical reaction. The citrate derivative of the lemon battery is not a zinc/copper(II) (Zn/Cu2+) battery but a zinc/proton (Zn/H+) battery. It may be helpful to build an electrochemical cell during the lecture to illustrate that two chemical reactions can create electricity and then show what that amount of generated power can do, for example, play music. Still after many years of studying the workings of a battery, there is always something new to learn. Circuits have been miniaturized. Low voltage requiring devices can be run by different lemon cell setups. (A summary is in the Supporting Information.) Wet batteries can be replaced by rechargeable solar dry cell batteries. Solar batteries labeled with the same 1.2 V voltage, are manufactured to produce different currents and power levels 500, 350, or 150 mA h.
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Figure 1. Using two wires with clips at both ends, one wire is attached to the bendable upper leaf of the “on/off switch” while the other wire is connected to the bottom of the leaf clamp. The other end of each wire is attached to the appropriate electrode. A diagram and more details are available in the Supporting Information section.
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ELECTROCHEMICAL CELL BASED ON COPPER AND ZINC REDOX REACTIONS A strip of copper is placed in a 80 mL beaker filled with ∼50 mL of 1 M copper(II) sulfate. A similar sized strip of zinc metal is placed in a separate beaker containing 1 M zinc sulfate. The beakers are placed side by side (Figure 2). Then a salt bridge,
MATERIALS
The following materials are needed: musical greeting card containing a 1 V battery, 4 smooth needle nose micro clips or alligator clips and 2 wires, small folded piece of aluminum foil, thin rectangular strips of zinc and copper (about 2.5 cm × 10 cm × 1 mm thick), and an external power source described below. Although you can construct your own musical circuit board,1 it is quicker to purchase one that is inside a musical greeting card. Greeting cards contain a musical device1 consisting of a rectangular thin plastic circuit board holding an encapsulated musical tune generator microchip, flat button cell battery, and a leaf pinch clamp (“on/off switch”). Extending from this circuit board unit are two delicate wires leading to a large round piezoelectric speaker. The commercial 1 V battery in the circuit board is removed, and the physical gap is bridged with conductive material. A wire with clips at each end is used to attach the upper leaf of the pinch clamp to one metal strip. The second wired clip is attached over the edge of the circuit board so the clip touches the metal area on the circuit board below the bendable leaf (Figure 1). The two clips attached to the leaf clamp should not touch or current will not flow through the musical chip. Then the “modified” musical device is connected to a chemical reaction that produces enough current and voltage to play the musical tune. (Detailed instructions are provided in the Supporting Information.) The external power source can be a commercial battery (the one removed from the card), a solar panel, a homemade Zn/Cu(II) cell, or variations of the Zn/proton lemon battery.
Figure 2. “Modified” musical circuit board is powered by a Zn/Cu(II) electrochemical cell.
consisting of a narrow strip of filter paper presoaked in a solution of sodium chloride (NaCl) or potassium chloride (KCl), is draped over the sides of the adjacent beakers so the end of each paper rests below the surface of each solution. (Details and chemical reaction are provided in the Supporting Information.) Two wires with clips at each end are used to connect the copper and zinc strips to the appropriate leaf clamp “on/off switch” position of the “modified” musical device. With fresh 1 M2 (and even 0.5 M3) solutions of copper(II) sulfate and zinc sulfate, this cell is a dependable source of about 1 V. The original solutions can be used many times. When the volume of the music is too low to hear, both solutions should be replaced.
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LEMON BATTERY: AN ELECTROCHEMICAL CELL BASED ON WEAK ACIDS DISSOLVING ZINC METAL Unlike the Zn/Cu(II) cell, which should be disposed of as hazardous waste, the lemon battery and its food variations promote green or environmentally friendly chemistry. Simply B
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compost it! About 0.6 V is produced when copper and zinc metal strips are inserted into whole (Figure 3) or pieces of
Figure 4. Outdoor solar light is disassembled to attach wires to its empty battery terminals and the “modified” musical circuit board. Figure 3. “Modified” musical circuit board is powered by a lemon electrochemical cell.
connections, an alternative attachment of electrode wires to intermediate posts on a sturdy platform is suggested in the Supporting Information.
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various fruits and vegetables or their juices. Alternatively, the hydrogen gas bubbles generated by this cell can be seen when a weak acid solution such as ascorbic acid (vitamin C), citric acid, acetic acid (vinegar), or an electrolyte replenishing drink is placed in a beaker. (Supply sources and chemical reaction are provided in the Supporting Information.) The metal strips should be close together but not touching. The metals stuck in the fruit or liquids are connected, using wires with clips at each end, to the “modified” musical device and the music begins to play.
HAZARDS Eye protection is always encouraged when handling solutions. Voltage and current levels are low and not dangerous. The levels of hydrogen gas generated should be safe with adequate ventilation and absence of flames. Use extreme care if soldering is used to join clips to the ends of a wire. Zinc and copper are heavy metals. Copper(II) sulfate is a biocide. These solutions should be treated as hazardous waste and disposed of properly. Do not flush them down the drain.
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SOLAR CELL Photons from sunlight can be converted directly to electricity via redox reactions (photovoltaic effect) that occur in light capturing devices called solar cells that are grouped together to make solar arrays or panels.4 Although solar panels can be made in the lab,5−7 they are now readily available in solar calculators, outside lights, toys, and artistic decorations. The popular 1.2 V 350 mA h solar light that is used to illuminate sidewalks or the driveway can be connected to and run “modified” musical devices that originally contained one, two, and three 1 V batteries. Two wires with an alligator or needle nose clip attached to each end are needed. A screwdriver is used to remove the screws holding the decorative cover to expose the battery holder under the solar panel containing cap. The rechargeable battery is removed. This battery serves both as a power source when sun is not present and as a storage unit that becomes recharged by sunlight. Then, the clipped wires are connected with the correct polarity, to the springy (−) and smooth (+) terminals of the battery holder and the “on/off switch” leaf clamp (Figure 4). The solar panel is propped up so light can reach it and music will play. If indoors, use a flashlight or small desk lamp to directly illuminate the solar panel. When the light is too dim, the tune will drag or the volume will be too low to hear. This musical demonstration powered by a solar cell requires no chemical clean up and is inexpensive so it can be used in science outreach and hands-on activities. The “on/off switch” leaf clamp and wires connected to the circuit board in the greeting card are easy to twist and break, especially while moving about to capture direct sunlight. To stabilize the “modified” musical device and to allow quick and easy wire
CONCLUSION The next time students buy a battery for a watch, a calculator, or their social media device, or recharge a digital camera, they might wonder how many lemons are required. If a cell phone is dead, they might wonder if a lemon or a solar light could provide enough power in an emergency8 to make it work. The next time students sing “Happy Birthday”, they may recall and discuss the musical lemon demo that they saw in class or during a chemical show. If so, the ideas inspired, discoveries made,9 and memories created by these electrochemical demos are worth the time to show this demonstration in class.
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ASSOCIATED CONTENT
S Supporting Information *
Detailed instructions to modify the musical device; details to create a platform for the musical device; details about the chemical reactions; variations for the lemon cell. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The author declares no competing financial interest.
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ACKNOWLEDGMENTS Dedicated in memory of Thomas and Catherine Harrington for sharing their interests in science with children. Catherine was very excited about the musical lemon battery. Sadly, at age 94, she passed away before hearing the musical lemon or reading C
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this publication. The cartoon was drawn by Jeff Hibbert. The wooden platform with intermediate posts was suggested and designed by Jack Lancaster of the North Carolina State University College of Design’s Materials Laboratory. The paper salt bridge idea for the zinc/copper(II) electrochemical cell was contributed by unknown chemistry faculty members (prior to the year 2000) teaching at North Carolina State University.
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REFERENCES
(1) Musical Greeting Card. http://www.instructables.com/id/ Musical-Greeting-Card/ by Neelandon (accessed May 2014). (2) Shakhashiri, B. Chemical Demonstrations: A Sourcebook for Teachers of Chemistry, Vol. 4; University of Wisconsin Press: Madison, WI, 1992; p 101. (3) Demo-029 Making a Copper-Zinc Battery. University of Arizona, Chemistry Department. http://www.quiz2.chem.arizona.edu/ preproom/Demo%20Files/cu-zn_battery.htm (accessed May 2014). (4) (a) J. Chem. Educ. Staff. The Solar Resource. J. Chem. Educ. 1979, 56 (4), 264−266. (b) Mickey, C. D. Solar Photovoltaic Cells. J. Chem. Educ. 1981, 58 (5), 418−423. (c) Meyer, G. Efficient Light-toElectrical Energy Conversion: Nanocrystalline TiO2 Films Modified with Inorganic Sensitizers. J. Chem. Educ. 1997, 74 (6), 652−656. (5) Boudreau, S. M.; Rauh, R. D.; Boudreau, R. A. A Photoelectrochemical Solar Cell. An Undergraduate Experiment. J. Chem. Educ. 1983, 60 (6), 498−499. (6) McDevitt, J. T. Photoelectrochemical Solar Cells. J. Chem. Educ. 1984, 61 (3), 217−221. (7) Smestad, G. P.; Gratzel, M. Demonstrating Electron Transfer and Nanotechnology: A Natural Dye−Sensitized Nanocrystalline Energy Converter. J. Chem. Educ. 1998, 75 (6), 752−756. (8) Hunt, V.; Sorey, T.; Balandova, E.; Palmquist, B. Juan’s Dilemma: A new twist on the old lemon battery. Sci. Teach. 2010, 52−56. (9) Ritter, S. Silver Solos In Lemon Circuit: Materials Chemistry: Electrochemical cell based on same-metal electrodes is a first. Chem. Eng. News 2011, 89 (29), 11.
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