Activity pubs.acs.org/jchemeduc
Student Fabrication and Use of Simple, Low-Cost, Paper-Based Galvanic Cells To Investigate Electrochemistry Anchalee Chatmontree,† Sanoe Chairam,*,‡ Saksri Supasorn,‡ Maliwan Amatatongchai,‡ Purim Jarujamrus,‡ Suparb Tamuang,‡ and Ekasith Somsook§ †
Program of Science Education, Faculty of Science, Ubon Ratchathani University, Warin Chamrap, Ubon Ratchathani 34190, Thailand ‡ Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University, Warin Chamrap, Ubon Ratchathani 34190, Thailand § NANOCAST Laboratory, Center for Catalysis, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, 272 Rama VI Road. Rachathewi, Bangkok 10400, Thailand S Supporting Information *
ABSTRACT: The stated purpose of this article is to provide teachers an inexpensive model for laboratory activity and demonstration of galvanic cells using a paper-based device. Metal strips, metal solutions, and KNO3 solution serve as electrodes, metal ions, and electrolyte, respectively. A paper-based device is not only a support for reactions, but also a salt bridge for electrolyte. This activity ought to be interesting to all levels of chemistry from middle school classes through potential applications in upper division college classes. Furthermore, teachers may design and fabricate a paper-based device for their classes in chemistry and also related fields.
KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Upper-Division Undergraduate, Analytical Chemistry, Hands-On Learning/Manipulatives, Electrochemistry, Reactions, Oxidation/Reduction, Electrolytic/Galvanic Cells/Potentials
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INTRODUCTION Chemical reaction is a process to transform reactants to products involving the formation and breaking of chemical bonds without the change of nucleon in nuclei.1−3 Oxidation− reduction or redox reaction is a chemical reaction involving the transfer of electrons between species in the reactants leading to the different oxidation states of products.4,5 The electrons gained in the reduction process must be equal to the electrons lost in the oxidation process. A galvanic (sometimes called voltaic) cell is a device that produces an electric current by means of a redox reaction.6,7 The overall cell potential for galvanic cells is regarded as the sum of the two half-cell reduction potentials and also can be calculated from the following equation: E 0 cell = E 0 cathode − E 0 anode
This cell has been often reported in several introductory chemistry textbooks,10−12 because of its cheaper and simpler varieties for adapting in both qualitative and quantitative analysis. The lemon battery also is a simple type that can be commonly made for school science projects because it illustrates main components of battery.13,14 Two strips of metal (called electrodes), typically zinc and copper, are inserted into a lemon. The juice of the lemon acts as the electrolyte. In analytical chemistry, a paper-based device shows several advantages, such as low cost, and easy and fast fabrication.15,16 Although some reports have demonstrated various devices for the construction of galvanic cells,6,7 the fabrication of galvanic cells employing a paper-based device has not been reported. Therefore, this article aims to demonstrate how to fabricate simple and low-cost galvanic cells using a paper-based device, because paper is abundant, inexpensive, flexible, and disposable. The paper-based galvanic cells can be quickly made by students using a piece of filter paper, wax, and small pieces of metal strips. Each half-cell can be constructed by placing metal strip electrodes on paper-based galvanic cells, and the electrolyte solution is added to the center of a device to connect all the
(1)
where the E0cell is the overall cell potential measured in the unit of volt (V). The values of E0cathode and E0anode are the standard reduction potentials for the reactions at the cathode and anode, respectively. A simple example of galvanic cells is commonly presented in the form of the Daniell cell, Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s).8,9 © XXXX American Chemical Society and Division of Chemical Education, Inc.
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DOI: 10.1021/acs.jchemed.5b00117 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 1. Equipment and materials needed for the fabrication of galvanic cells.
Figure 2. Schematic illustration for fabricating paper-based galvanic cells. Note: metal strips should be polished with emery paper before use.
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half-cells. A paper-based device is not only a support for reactions, but also a salt bridge for electrolyte. The paper-based device developed here is well suited for teaching electrochemistry in any classroom activity, classroom demonstration, or laboratory experiment within a short period of time.
CONSTRUCTION OF PAPER-BASED GALVANIC CELLS
The fabrication of a paper-based device using the filter paper was adopted according to Cai and co-workers.17 The template and a lead pencil are used to draw the six distribution channels onto the filter paper. After that, the filter paper is then patterned using wax by hand drawing technique. The waxpainted filter paper then is also put over a hot plate
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EQUIPMENT AND MATERIALS Equipment and materials needed for the fabrication of paperbased galvanic cells are listed in Figure 1. B
DOI: 10.1021/acs.jchemed.5b00117 J. Chem. Educ. XXXX, XXX, XXX−XXX
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(approximately 135−140 °C) for 30−45 s, causing wax to melt and penetrate into the filter paper to form the wax barrier. According to the literature,18 two small slits are cut in the middle of each distribution channel, and these slits should be apart at 5 mm (±1 mm). Finally, each metal strip is placed by embedding in the slits in its corresponding channel. The schematic illustration for fabricating paper-based galvanic cells is shown in Figure 2.
Zn(s) + Cu 2 +(aq) → Zn 2 +(aq) + Cu(s)
(2)
On the basis of the values for the standard reduction potentials (see Supporting Information), the theoretical cell potentials, Ecell (theor), for the galvanic cell for the cell Zn(s)| Zn2+(aq)||Cu2+(aq)|Cu(s) is 1.10 V, while the observed cell potentials, Ecell (obsd) was 1.00 V. In general, the Ecell (obsd) is slightly different from the Ecell (theor) as shown in Table 1.
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Table 1. Comparison between Ecell (Obsd) and Ecell (Theor)
EXPERIMENTAL PROCEDURE Each circle zone of the six distribution channels is added with a solution of metal ion corresponding to the metal strip (e.g., CuSO4 solution on Cu strip, etc.). In case that some metal strips are rusted (i.e., Al, Mg and Fe), emery paper must be applied to remove all rust or stain to obtain more precise results. Then, the center of the paper-based galvanic cells is dropped in 1.0 M KNO3 solution to serve as an electrolyte, also called salt bridge, on a filter paper connecting the half-cells. Finally, the cell potentials are measured using a multi-meter (see Figure 3).
Cell 2+
2+
Zn(s)/Zn (aq)//Cu (aq)/Cu(s) Sn(s)/Sn2+(aq)//Cu2+(aq)/Cu(s) Fe(s)/Fe2+(aq)//Cu2+(aq)/Cu(s) Pb(s)/Pb2+(aq)//Cu2+(aq)/Cu(s) Cu(s)/Cu 2+(aq)//Ag+(aq)/Ag(s) Sn(s)/Sn2+(aq)//Pb2+(aq)/Pb(s) Fe(s)/Fe2+(aq)//Pb2+(aq)/Pb(s) Zn(s)/Zn2+(aq)//Pb2+(aq)/Pb(s) Pb (s)/ Pb2+(aq)//Ag+(aq)/Ag(s) Fe(s)/Fe2+(aq)//Sn2+(aq)/Sn(s) Zn(s)/Zn2+(aq)//Sn2+(aq)/Sn(s) Sn (s)/ Sn2+(aq)//Ag+(aq)/Ag(s) Zn(s)/Zn2+(aq)//Fe2+(aq)/Fe(s) Fe (s)/ Fe 2+(aq)//Ag+(aq)/Ag(s) Zn (s)/ Zn 2+(aq)//Ag+(aq)/Ag(s) a
Ecell (obsd)/Va
Ecell (theor)/V
1.00 0.45 0.45 0.40 0.40 -b 0.20 0.60 0.90 0.20 0.50 0.90 0.30 1.20 1.50
1.10 0.48 0.78 0.47 0.46 0.01 0.31 0.63 0.93 0.30 0.62 0.94 0.32 1.25 1.56
Ecell (obsd) is measured at 25 °C (298 K). bNot detectable
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DISCUSSION In this study, individual half-cell reactions take place at the surface of electrodes on metal strips. The electrode at which the oxidation occurs is called the anode, while the electrode at which the reduction occurs is called the cathode. Electrons can flow spontaneously from the anode (oxidation and marked as negative, −) to the cathode (the reduction and marked as positive, +), while the two half-cells are neutralized by means of the flow of ions from one cell to the other to balance the transfer of electrons and production of ions. To illustrate chemical concepts, like redox reactions, students should be engaged with the three levels of representation: macroscopic, submicroscopic, and symbolic. 23−25 Considering Zn(s)| Zn2+(aq)||Cu2+(aq)|Cu(s), the Zn metal that is oxidized is the reducing agent. Since the reducing agent loses electrons, so it becomes oxidized during the process. In contrast, the Cu2+ ion that is reduced by accepting electrons transferred from Zn metal is the oxidizing agent (see Figure 4). During a hands-on activity, explaining chemistry concepts using three levels of representation could help students to relate what is happened at a submicroscopic level between the Zn metal and Cu2+ ion when they observed some changes in a macroscopic level (i.e., change in color of Cu2+ solution). They then can represent the change in a symbolic level (chemical equation). This supports students to obtain a deep conceptual understanding of electrochemistry.26 However, student’s problems in understanding the relationship between three levels of representation may be attributed to such a lack of experiences with macroscopic, submicroscopic, or symbolic types. In this work, the more active metal is able to reduce the less active metal cation. According to the results obtained in this work, the reducing ability of the metals is given as the following series: Zn, Fe, Sn ≈ Pb, Cu and Ag. In fact, the standard
Figure 3. Measuring the overall cell potentials by a multi-meter.
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HAZARDS Hazards arising from the use of metal ion solutions are minimal. KNO3 is a strong oxidant; there is explosion risk when heated or in contact with organic substances. However, the explosion risk does not seem likely unless students are given solid KNO3 with which to make the electrolyte solution. If they are given the relatively dilute electrolyte solution to begin with, it seems that the explosion risk is largely mitigated.19 Pb(NO3)2 and SnCl2 are toxic by ingestion; a skin irritant and corrosive.20,21 CuSO4, FeSO4, and ZnSO4 are slightly toxic and a skin irritant.22 Mg ribbon is a flammable solid; avoid contact with flames and heat. Metal strips may have sharp edges, especially Mg, Zn, and Al, and students should handle with care. Wearing laboratory coats and protective goggles is always desirable; avoid direct contact of all chemicals without chemical-resistant gloves. When done, rinse the metal strips thoroughly with distilled water and dry them on paper towels.
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RESULTS By nature, the cell potential, Ecell, for the spontaneous chemical reactions is always a positive value. For example, in the Daniell cell, Zn(s)| Zn2+(aq)||Cu2+(aq)|Cu(s), the overall cell reaction is C
DOI: 10.1021/acs.jchemed.5b00117 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 4. Illustration of the overall cell reaction for Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s).
could design and modify a paper-based device for their teaching laboratories in various fields, such as biochemistry, forensic chemistry, and environmental chemistry.
reduction potential of Sn is lower than that of Pb (see Supporting Information). However, the Ecell (obsd) of Sn(s)| Sn2+(aq)||Pb2+(aq)|Pb(s) is not detectable. This might be that their half-cell reactions are similar in voltage (see Supporting Information Table S1). Thus, this is a limitation of galvanic cells. However, a different metal could be substituted for Sn or Pb. The intent appears to be to assert that aluminum oxide or magnesium oxide formed when either of these metals is used as electrode, and therefore, the expected half reaction is inhibited, giving “poor results”.27 Although several microscale and simplified techniques for building galvanic cells have been described in existing publications, this is a novel idea that is both very simple and cost-effective for fabricating galvanic cells. This activity is suitable for either a laboratory class or an active learning “lecture” or “discussion” situation. The teachers may design and fabricate a paper-based device for their classes in chemistry and also related fields, e.g., biochemistry, forensic chemistry, and environmental chemistry.
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ASSOCIATED CONTENT
S Supporting Information *
Detailed descriptions of the instructor notes and student notes. 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 authors declare no competing financial interest.
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ACKNOWLEDGMENTS The financial supports from the Thailand Research Fund (TRF, TRG5680049), the Center of Excellent for Innovation in Chemistry (PERCH−CIC), the Institute for the Promotion of Teaching Science and Technology (IPST), the Office of the Higher Education Commission, Ministry of Education, and the Faculty of Science, Ubon Ratchathani University (UBU) are gratefully acknowledged.
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ADAPTATION POSSIBILITIES This activity is readily adaptable to several different combinations of metals and ions for making a large number of galvanic cells. Ag and Au give a high accuracy and precision of Ecell (obsd), but their bulk metals and chemicals are expensive. Either NaNO3 or KNO3 could be served as electrolyte in this experiment. NaCl or KCl must be avoided when Ag is used as one of the metals being tested, due to the formation of AgCl precipitate.
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REFERENCES
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CONCLUSION We have demonstrated a simple activity for fabricating the galvanic cell using a paper-based device. This device is easy-tomake and easy-to-use and appropriate for the use in the high school laboratory as a model to introduce the students to electrochemistry. This activity can be used as an active learning approach in the first-year, general and upper-division undergraduate courses of analytical chemistry. Furthermore, teachers D
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DOI: 10.1021/acs.jchemed.5b00117 J. Chem. Educ. XXXX, XXX, XXX−XXX
