Electrochemistry with Simple Materials to Create Designs and Write

Apr 18, 2019 - An activity is described in which items found around the home are used in electrochemical experiments to create messages and artistic d...
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Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

Electrochemistry with Simple Materials to Create Designs and Write Messages Thomas S. Kuntzleman* Department of Chemistry, Spring Arbor University, 106 East Main Street, Spring Arbor, Michigan 49283, United States

J. Chem. Educ. Downloaded from pubs.acs.org by VOLUNTEER STATE COMMUNITY COLG on 04/18/19. For personal use only.

S Supporting Information *

ABSTRACT: An activity is described in which items found around the home are used in electrochemical experiments to create messages and artistic designs. To do so, a battery is connected to wires fashioned out of aluminum foil. When these wire electrodes are touched to a paper towel soaked in fluids obtained from household cleaners or disinfectants, the resultant redox reactions cause color changes on the paper towel. For example, the reduction of water at a cathode can cause a blue color to develop on a paper towel soaked in foam cleaner that contains thymolphthalein, and oxidation of iodide ions at an anode can produce a black color on a paper towel soaked in decolorized iodine. The experiments are very simple to set up and carry out; produce striking visual results; and relate to concepts in electrochemistry, acid−base chemistry, and thermodynamics. As such, the activity may be tailored for use in settings that range from outreach events to general- and analytical-chemistry courses. KEYWORDS: General Public, Elementary/Middle School Science, High School/Introductory Chemistry, First-Year Undergraduate/General, Demonstrations, Hands-On Learning/Manipulatives, Consumer Chemistry, Electrochemistry, Oxidation/Reduction, Thermodynamics

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INTRODUCTION

H 2O →

The use of electrochemical reactions to write messages is a classic experiment that has found much use in the chemistry classroom.1−5 In such experiments, a battery or other external power source is used to drive nonspontaneous chemical reactions that result in color changes, and these color changes are used to write notes and messages. For example, a metal wire acting as a cathode can reduce water, generating a hydroxide ion: H 2O + e− →

1 H 2 + OH− 2

(2)

Therefore, an anode that is touching and carefully moved over the surface of an indicator-soaked piece of wet paper can also produce messages and designs.4 A metal wire acting as an anode can also oxidize colorless iodide ions to iodine, which is yellow-brown in color:2 2I− → I 2 + 2e−

(3)

Thus, when a metal anode is touched to paper soaked in a solution of iodide, a colored spot develops at the point of contact between the paper and the metal. Because paper contains starch, the colored spot that is formed may darken over time because of the formation of the starch−iodine complex, which is black in color:9

(1)

Thus, when connected to an appropriate source of power, a metal cathode touched to a wet piece of paper can generate hydroxide ions. If the paper contains an acid−base indicator, the hydroxide ions formed at the paper−cathode interface can cause a visible color change in the acid−base indicator. The color change allows notes and letters to be produced by purposefully moving the cathode over the paper surface (Figure 1). The experiments discussed in this activity use color-changing foam cleaners as a source of thymolphthalein, an acid−base indicator that is colorless in acid and blue in base.6−8 Furthermore, a metal wire acting as an anode can oxidize water, producing protons: © XXXX American Chemical Society and Division of Chemical Education, Inc.

1 O2 + 2H+ + 2e− 2

starch + I 2 → starch−I 2 (blue‐black)

(4)

Presented herein are approachable and artistic extensions to the traditional electrochemical writing experiment. Using decorative items such as metal pendants and cookie cutters as electrodes in this experiment allows for a fun and artistic Received: January 5, 2019 Revised: February 28, 2019

A

DOI: 10.1021/acs.jchemed.9b00012 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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reduction of water (eq 1). The hydroxide ions thusly formed cause the thymolphthalein to turn blue, allowing for messages to be written. The messages slowly fade in color over time as carbon dioxide from the atmosphere dissolves into the paper towel (eq 5). Therefore, care should be taken not to exhale onto the paper towel when writing messages because the relatively high concentration of carbon dioxide in exhaled breath can cause the messages to disappear more quickly. Interestingly, the messages may also be caused to quickly disappear by rubbing a gloved hand in a circular motion over the images produced (Figure 2). The rubbing motion causes

Figure 1. Conversion of water into hydroxide ions on the surface of a paper towel with a wire fashioned out of aluminum foil as the cathode. The paper towel is soaked with a cleaner that contains thymolphthalein, which turns blue in the presence of excess hydroxide ions.

variation of this classic electrochemical experiment. These extensions also involve the use of familiar and easily obtainable items, making the experiment accessible to a larger audience of teachers and students. The user-friendly nature of these modifications has provided a vehicle to showcase concepts in electrochemistry for students that span a wide range of scientific sophistication, from science camps through analytical-chemistry courses.

Figure 2. Rubbing causing concomitant neutralization of electrochemically generated hydroxide and rapid disappearance of messages.

protons formed on the back of the paper towel (at the surface of the square foil, eq 2) to migrate to the top of the paper towel. Protons that reach the top surface of the paper towel neutralize the hydroxide ions, causing disappearance of the blue-colored image:

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PERFORMING THE EXPERIMENT WITH FOAM CLEANER Enough color-changing foam cleaner is sprayed onto a disposable plate to cover the bottom; then, 5−10 mL of water and 1 g of table salt (as the supporting electrolyte) are added. These foams contain thymolphthalein,6,7 an acid−base indicator that is colorless in acid and blue in base (pKa ∼ 10).8 When the foam is initially sprayed into the plate, it has a blue color. Over time the blue color fades to white as carbon dioxide from the atmosphere dissolves into the cleaner to form carbonic acid: H 2O + CO2 → H 2CO3 (5)

H+ + OH− → H 2O

(6)

Conducting this experiment allows for discussion that the square foil acts as an anode, with protons produced as water is oxidized at its surface (eq 2). It could also be the case that rubbing messages in this manner causes carbon dioxide from the atmosphere (and exhaled breath) to dissolve into the paper towel at an increased rate, causing the messages to disappear more rapidly than they do when left undisturbed. Observers find it interesting that several repeated cycles of message creation and erasure can be performed. In addition, any developed blue color can be erased by repeating the experiment with the polarity reversed such that the foil square acts as the cathode and the “writing” wire as the anode. When the anode is touched to blue color on the paper towel, protons forming at the anode neutralize hydroxide ions, lowering the pH and causing the blue color to disappear.

The buildup of carbonic acid in the foam lowers the pH, causing the thymolphthalein to shift from blue to colorless. A 10 × 10 cm sheet of paper towel is completely soaked with the water/foam mixture. After blotting off of excess foam, the paper towel is placed on a 12 × 12 cm piece of aluminum foil. A wire (it is convenient to simply fashion aluminum foil into a make-shift wire) is used to connect the square piece of foil to the positive terminal of a battery. Experience shows that 6 V lantern batteries are most convenient for this activity, but 1.5 and 9 V batteries also work in this case. A second wire (again, aluminum foil works well) is attached to the negative terminal of the battery. When this second wire is touched to the surface of the wet paper towel, the circuit is completed and messages can be written (Figure 1). Under these conditions, the “writing” wire acts as a cathode, producing hydroxide ions via

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PERFORMING THE EXPERIMENT WITH IODIDES TINCTURE Messages can also be produced at an anode via the oxidation of iodide ions (eq 3). To do so, decolorized iodine, which can be found in the pharmacy sections of grocery and retail stores, may be used as an easily obtained source of iodide ions. Decolorized iodine is also called iodides tincture, and it contains potassium iodide, ammonium hydroxide, and alcohol in water. It is important to note that tincture of iodine, which is B

DOI: 10.1021/acs.jchemed.9b00012 J. Chem. Educ. XXXX, XXX, XXX−XXX

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dark brown in color, will not work in this experiment. Enough decolorized iodine is poured onto a disposable plate to cover the bottom. Some slight yellowing of the decolorized iodine may be observed because of trace amounts of iodine. Two sheets of 10 × 10 cm paper towel are stacked on top of each other and dipped into the decolorized iodine/water mixture. After soaking the paper towels, they are held above the plate until no more liquid drips from them. The towels are then placed on a 12 × 12 cm piece of aluminum foil. In this case the square foil serves as the cathode; thus, it is attached to the negative terminal of a battery. In this experiment only the 9 and 6 V batteries are observed to consistently work. When the circuit is closed, the half reaction described by eq 1 occurs at the interface between the square foil and soaked paper towel. A second wire, which serves as the anode, is attached to the positive terminal of the battery. In this case, when the tip of this second wire is touched to the top layer of the paper towel soaked with iodide ions, the half reaction described by eq 3 occurs. The iodine thusly formed at the tip of the anode can be used to write messages on the surface of the paper towel (see Supporting Information). Over time, the messages darken because of the reaction between iodine and starch in the paper towel (eq 4). In contrast to the experiment done with the foam cleaner, the dark-colored designs cannot be erased by reversing the polarity and repeating the experiment. This indicates that the starch−iodine complex forms on the paper towel in this experiment in an irreversible manner. In addition to writing messages, ornamental pieces of metal may be used as electrodes to produce artistic images on the paper towel. For example, a decorative metal pendant is placed on top of a paper towel soaked in tincture of iodides and placed on a square sheet of aluminum foil as described above. The square foil is attached with a wire to the negative terminal of a battery and a second wire is attached to the positive terminal. The wire attached to the positive terminal is briefly touched to the metal trinket (Figure 3, left). At the same time,

Figure 4. Reduction at decorative-metal cathodes forming blue images on paper towels soaked with foam cleaner that contains thymolphthalein. (Left) Metal cookie cutter used as a cathode. (Right) Cross-shaped charm used as a cathode.

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PERFORMING THE EXPERIMENT WITH TRADITIONAL REAGENTS If desired, this activity may be also be performed using traditional reagents, as described previously.1,2 To produce blue designs, the same experiment is conducted by touching a foil wire acting as a cathode onto a paper towel soaked in a mixture of 0.8 g of NaNO3, 20 mL of water, and 5 mL of thymolphthalein indicator solution.1,2 To produce the dark images, a foil wire acting as an anode is touched onto a paper towel soaked in a mixture of 1.6 g of KI, 5 mL of 1.0 wt % starch solution, and 20 mL of water.1,2

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HAZARDS Goggles and gloves should be worn at all times during this experiment. Iodides tincture contains alcohol; keep it away from flame. Because both decolorized iodide and foam cleaner give off substantial odor, soaking paper towels should be conducted in the hood or well-ventilated area. Cookie cutters used as electrodes should not be used for cooking and should be labeled as such. Because the current achieved in this experiment has consistently been measured to be less than 1.5 A DC, and electric potentials of 9 V or less from household batteries are used, this experiment is not expected to pose an electric-shock hazard. However, under some circumstances wires and electrodes can become hot to the touch. Use of batteries with lower potentials avoids this situation. Used batteries should be collected for recycling.

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INTEGRATING THE EXPERIMENT INTO THE CURRICULUM This activity can be used with elementary and middle-school aged students to show how certain chemical reactions require energy in order to proceed, and that some chemical reactions can be powered by electrical energy. This activity may also be used in introductory chemistry classes to introduce the topic of redox reactions to students. Furthermore, this activity connects with a wide variety of more advanced topics in electrochemistry, thermodynamics, and chemical equilibria. For example, in the experiment with iodide ions, the half reactions that occur at the cathode (eq 1) and anode (eq 3) can be combined to give the standard cell potential and equation for the overall reaction driven by the battery.

Figure 3. (Left) Make-shift wire connected to the positive terminal of a battery and touched to a decorative metal pendant, which acts as an anode for the oxidation of iodide. (Right) Produced iodine forming a pattern where the decorative pendant touches the paper towel.

a brown color develops on the paper towel in the shape of the ornament used as the cathode. Upon removal of the piece of metal, a pattern is seen to have formed on the surface of the paper towel (Figure 3, right). Blue-colored images may be developed by soaking paper towels in foam cleaner as described previously and using a decorative metal piece, such as a cookie cutter, as the cathode (Figure 4).

2H 2O + 2e− → H 2 + 2OH−

E 0 = − 0.83 V

I 2 + 2e− → 2I−

E 0 = 0.54 V

2H 2O + 2I− → H 2 + I 2 + 2OH− E 0 = − 1.37 V C

(7)

DOI: 10.1021/acs.jchemed.9b00012 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Notes

Using the standard cell potential (−1.37 V), the standard Gibbs energy of the overall process described by eq 7 can be calculated: ΔG 0 = −nFE 0

The author declares no competing financial interest.

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ACKNOWLEDGMENTS I wish to thank Julienn C. Williams for testing this demonstration. I would also like to thank the reviewers of this manuscript, whose insight, comments, and suggestions for additional experiments greatly improved this work.

(8)

where ΔG0 is the standard Gibbs energy, n is the number of moles of electrons transferred in the reaction, and F is Faraday’s constant (96,485 coulombs per mole of electrons). For eq 7, E0 = −1.37 V, so ΔG0 = +264 kJ mol−1. Students can also use the following to calculate the equilibrium constant for eq 7 under standard conditions (R = 8.314 J mol−1 K−1 and T is the absolute temperature): ΔG = −RT ln Keq

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(9)

Using eq 9 and the value of ΔG0 calculated using eq 8, students can calculate that Keq = 4.8 × 10−47 under standard conditions. The negative cell potential, positive Gibbs energy, and small equilibrium constant all remind students that eq 7 is not spontaneous, which is why a battery is required to conduct this experiment.

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DISCUSSION The experiments described herein provide ways to explore electrochemical processes using everyday items. Using familiar materials in chemical experimentation is advantageous for a number of reasons. Convenient acquisition of materials is advantageous in preparing experiments and planning the logistics of lessons. The substitution of readily available materials for more standard reagents allows for a wider audience to prepare, present, and carry out traditional chemistry experiments. Furthermore, the study and use of ordinary items also connects to everyday experiences, which tends to increase student interest. In addition, the experiments reported here also describe creative and aesthetic ways to explore many concepts: electrochemistry, acid−base chemistry, thermodynamics, and chemical equilibria. Several authors have described the benefits of interfacing artistic expression into chemistry lessons,10−13 and it is therefore no surprise that many activities have been produced toward this end.14−18 As stated by John Moore, a former editor of this Journal, “In teaching science we need to remember that communication always benefits from imagination and aesthetic sense.”10 It is hoped that the experiments reported here provide another means to allow students and teachers to use their imaginations as they study chemistry.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.9b00012.

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REFERENCES

(1) Gilbert, E. C. Oxidation and Reduction of Ions at Electrodes. In Tested Demonstrations in Chemistry; Alyea, H. N., Dutton, F. B., Eds.; Division of Chemical Education of the American Chemical Society: Easton, PA, 1965; p 145. (2) Harris, D. Quantitative Chemical Analysis, 8th ed.; W. H. Freeman and Company: New York, 2010. (3) Goldenrod Electrochemistry Kit. Educational Innovations, Inc. https://www.teachersource.com/product/goldenrodelectrochemistry-kit/ (accessed Jan 2019). (4) Beyer, T. Goldenrod Paper Does What?!, 2016. Educational Innovations, Inc. http://blog.teachersource.com/2016/03/04/ goldenrod-paper-electrochemistry/ (accessed Jan 2019). (5) Valetaud, M.; Loget, G.; Roche, J.; Hüsken, N.; Fattah, Z.; Badets, V.; Fontaine, O.; Zigah, D. The EChemPen: A Guiding Hand To Learn Electrochemical Surface Modifications. J. Chem. Educ. 2015, 92, 1700−1704. (6) Kuntzleman, T. Wash Your Blues Away - With Chemistry! ChemEd X, Sept 3, 2015. https://www.chemedx.org/blog/wash-yourblues-away-chemistry (accessed Jan 2019). (7) Kuntzleman, T. Solution to Chemical Mystery #13: Bye Bye Blue! ChemEd X, Nov 22, 2018. https://www.chemedx.org/blog/ solution-chemical-mystery-13-bye-bye-blue (accessed Jan 2019). (8) Kooser, A. S.; Jenkins, J. L.; Welch, L. E. Acid Base Indicators: A New Look at an Old Topic. J. Chem. Educ. 2001, 78, 1504. (9) The chemistry involved in the formation of the starch-iodine complex is multifaceted. For more information, see Harris, D. Quantitative Chemical Analysis, 8th ed.; W. H. Freeman and Company: New York, 2010; pp 347−351. (10) Moore, J. W. Science and Art. J. Chem. Educ. 2001, 78, 1295. (11) Danipog, D. L.; Ferido, M. B. Using Art-Based Chemistry Activities To Improve Students’ Conceptual Understanding in Chemistry. J. Chem. Educ. 2011, 88, 1610−1615. (12) Bent, H. A. A Dialogue Concerning the Two Chief World Systems: Art and Science. J. Chem. Educ. 1981, 58, 331−333. (13) Hemraj-Benny, T.; Beckford, I. Cooperative and Inquiry-Based Learning Utilizing Art-Related Topics: Teaching Chemistry to Community College Nonscience Majors. J. Chem. Educ. 2014, 91, 1618−1622. (14) Jacobsen, E. K. JCE Resources for Chemistry and Art. J. Chem. Educ. 2001, 78, 1316−1321. and references therein. (15) Gaquere-Parker, A. C.; Doles, N. A.; Parker, C. D. Chemistry and Art in a Bag: An Easy-To-Implement Outreach Activity Making and Painting with a Copper-Based Pigment. J. Chem. Educ. 2016, 93, 152−153. (16) Wiggins, M. B.; Heath, E.; Alcántara-García, J. Multidisciplinary Learning: Redox Chemistry and Pigment History. J. Chem. Educ. 2019, 96, 317. (17) Esson, J. M.; Scott, R.; Hayes, C. J. Chemistry and Art: Removal of Graffiti Ink from Paints Grounded in a Real-Life Scenario. J. Chem. Educ. 2018, 95, 400−402. (18) Blatti, J. L. Colorful and creative chemistry: Making Simple Sustainable Paints with Natural Pigments and Binders. J. Chem. Educ. 2017, 94, 211−215.

Information regarding the foam cleaners and iodides tincture, helpful tips, and student laboratory sheet (PDF, DOCX)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Thomas S. Kuntzleman: 0000-0002-2691-288X D

DOI: 10.1021/acs.jchemed.9b00012 J. Chem. Educ. XXXX, XXX, XXX−XXX