Activity pubs.acs.org/jchemeduc
JCE Classroom Activity #111: Redox Reactions in Three Representations Edgardo L. Ortiz Nieves,† Reizelie Barreto,‡ and Zuleika Medina*,§ †
Department of Physics and §Materials Research Science and Engineering Center, The Pennsylvania State University, University Park, Pennsylvania 16802, United States ‡ Department of Physics, Astronomy, and Geosciences, Towson University, Towson, Maryland 21252, United States S Supporting Information *
ABSTRACT: This activity introduces students to the concept of reduction− oxidation (redox) reactions. To help students obtain a thorough understanding of redox reactions, the concept is explored at three levels: macroscopic, submicroscopic, and symbolic. In this activity, students perform hands-on investigations of the three levels as they work at different stations that support examination and discovery of the general ideas in redox reactions, including oxidizing and reducing agents, and the stoichiometry of a reaction.
KEYWORDS: High School/Introductory Chemistry, Hands-On Learning/Manipulatives, Problem Solving/Decision Making, Oxidation State, Oxidation/Reduction, Reactions FEATURE: JCE Classroom Activity
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zinc reaction, Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s), by performing hands-on exploration as they work at three different stations, each incorporating a different representation. During the reaction, zinc solid is oxidized to zinc(II) ion by transferring two electrons to copper(II) ion, reducing the latter to copper solid, as shown in eq 1.
BACKGROUND A reduction−oxidation (redox) reaction involves transfer of electrons among the chemical species in the reaction. Examples of redox reactions include corrosion of metals1,2 and combustion of fuels.3,4 In addition, biological processes such as cellular respiration5,6 involve oxidation of glucose to carbon dioxide and reduction of oxygen to water. To obtain a deep understanding of a chemical concept, like redox, students should be exposed to the three levels of representation in chemistry:7−10 macroscopic, submicroscopic, and symbolic. The macroscopic representation deals with phenomena as experienced with the senses, such as changes in color, and formation of precipitates in chemical reactions. The submicroscopic representation provides descriptions at the particulate level, such as atoms and molecules. The symbolic representation involves chemical symbols, drawings, and mathematical expressions used to represent chemical situations. Students generally memorize, repeat chemical equations, and solve problems in an algorithmic fashion without conceptually comprehending or connecting the macroscopic, submicroscopic, and symbolic levels.11−15 Learning scientific concepts using multiple representations could help students become better in transferring between different levels16 and improve their reasoning and problem-solving skills. Although the use of the threefold representation has been implemented before in the classroom,17 more activities are needed in different topics. In this Activity, students investigate the copper(II) sulfate and © 2012 American Chemical Society and Division of Chemical Education, Inc.
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INTEGRATING THE ACTIVITY INTO THE CURRICULUM This Activity serves to provide connections between three levels of representation in chemical reactions. It can be used as a hands-on reinforcement after the redox concept has been taught. For students to perform the activity successfully, prior knowledge of reduction and oxidation, ionic compounds, nomenclature, and stoichiometry is recommended. This Activity can be used as an introduction to other activities, such as building a battery18 and electroplating.19 Published: February 3, 2012 643
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Activity
adhesive white and black hook-and-loop fastener dots.20 The balls and fasteners can be obtained in most sporting goods stores and fabric stores, respectively. The instructor should make the setup ahead of time. (See Figure 2.) Using the
ABOUT THE ACTIVITY Each group (2−4 students) is initially assigned to one of three stations labeled macroscopic, submicroscopic, and symbolic. After all groups complete the task in the first station, they move to the next station in the sequence and so forth, until all groups have participated in all three stations. Students will need approximately 10 min to complete the tasks at each station. The instructor should prepare multiple stations of each level to accommodate varying class sizes. The chemistry involved in the copper(II) sulfate and zinc solid redox reaction is not explained in the Student Activity because the main purpose of this activity is for the students to describe the reaction using the information gathered from participating in the activities of all three stations. Macroscopic
At this station, students are given two pieces of zinc solid and 5 mL of 1 M copper(II) sulfate solution in a 10 mL glass vial or glass test tube. (See Figure 1.) The 1 M copper(II) sulfate
Figure 2. Submicroscopic station setup.
marker, label the white balls as “Zn” and the orange balls as “Cu”. Apply two of the white hook fasteners to opposite sides of each orange ball. (See Figure 3, left.) Repeat this procedure
Figure 1. (Left) Macroscopic station setup. Vial with copper(II) sulfate solution and two pieces of zinc shot. (Right) Formation of copper on the surface of the shot after several minutes.
solution (#C0246) is available from Flinn Scientific. The cost of 500 mL is ∼$7.00, sufficient for 100 iterations of the station’s activity. Alternatively, a 1 M CuSO4·5H2O solution can be prepared in advance: Dissolve 50 g of copper(II) sulfate pentahydrate in 200 mL of distilled water. Copper(II) sulfate pentahydrate, CuSO4·5H2O (#C0102) is available from Flinn Scientific, at a cost of ∼$8.50 for 100 g. This makes 400 mL of solution, sufficient for 80 iterations of the station’s activity. Also, copper(II) sulfate pentahydrate can be found in hardware stores as root killer. The zinc solid (zinc metal shot, #Z0021) can be ordered from Flinn Scientific at ∼$16.00 for 100 g, sufficient for approximately 500−1000 iterations of the station’s activity (depending on the size of the shots). Students will observe the solution (blue color and liquid) and the metal (gray color and solid) and record their observations. Students will place two zinc solids in the copper(II) sulfate solution and record their observations. The reaction results in the formation of copper solid. (See Figure 1, right.) After the activity, instructors should collect all the solutions and solids separately in glass bottles, label them accordingly, and dispose according to local regulations.
Figure 3. Ping-pong balls prepared for the submicroscopic station with hook-and-loop fasteners. (Left) Copper, represented by orange balls with white fasteners. (Right) Zinc, represented by white balls with black fasteners.
with the black hook fasteners and the white balls. Connect the black loops to the black hooks on the white balls. (See Figure 3, right.) To avoid having the sticky part of the loops exposed, the instructor can apply the loops to a piece of paper and cut them. Place the balls inside the beaker using the same number of white and orange balls to ensure the stoichiometry of the reaction (1:1). Instructors can use 2 or 3 ping-pong balls of each color per station. The orange and white balls represent copper(II) ion and zinc solid, respectively. The two hook-andloop fasteners on the white balls correspond to the two valence electrons in zinc, and the two hook fasteners in the orange balls represent two available energy sublevels in copper(II) ion. Students will remove the loop fasteners (two electrons) from the white balls and attach these to hook fasteners on the orange balls. The transfer of the two loop fasteners on the white balls to the orange balls corresponds to the two electrons lost by zinc and gained by copper(II) ion. Students will use their observations to explain that two electrons are transferred from Zn to Cu2+.
Submicroscopic
In this station, students will work on a model to explore the redox reaction at the submicroscopic level. For the setup, the instructor will need a beaker (400 mL or larger) or a container, white and orange ping-pong balls, a permanent marker, and 644
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Symbolic
(6) Baines, A. T.; McVey, M.; Rybarczyk, B.; Thompson, J. T.; Wilkins, H. R. Mystery of the Toxic Flea Dip: An Interactive Approach to Teaching Aerobic Cellular Respiration. Cell Biol. Educ. 2004, 3, 62− 68. (7) Chandrasegaran, A. L.; Treagust, D. F.; Mocerino, M. Emphasizing Multiple Levels of Representation To Enhance Students’ Understandings of the Changes Occurring during Chemical Reactions. J. Chem. Educ. 2009, 86, 1433−1436. (8) Johnstone, A. H. Macro- and Microchemistry. School Sci. Rev. 1982, 64, 377−379. (9) Johnstone, A. H. Thinking about Thinking. Int. Newsletter Chem. Educ. 1991, 36, 7−10. (10) Johnstone, A. H. Why Is Science Difficult To Learn? Things Are Seldom What They Seem. J.Comput. Assist. Learn. 1991, 7, 75−83. (11) Ben-Zvi, R.; Eylon, B.; Silberstein, J. Students’ Visualization of a Chemical Reaction. Education in Chemistry 1987, 24, 117−120. (12) Nakhleh, M. B. Why Some Students Don’t Learn Chemistry. J. Chem. Educ. 1992, 69, 191−196. (13) Hinton, M. E.; Nakhleh, M. B. Students’ Microscopic, Macroscopic, and Symbolic Representations of Chemical Reactions. Chemical Educator 1999, 4, 158−167. (14) Mulford, D. R.; Robinson, W. R. An Inventory for Alternate Conceptions among First- Semester General Chemistry Students. J. Chem. Educ. 2002, 79, 739−744. (15) Bunce, D. M.; Gabel, D. L.; Samuel, K. B. Enhancing Chemistry Problem-Solving Achievement Using Problem Categorization. J. Res. Sci. Teach. 1991, 28, 505−521. (16) Chandrasegaran, A. L.; Treagust, D. F.; Mocerino, M. An Evaluation of a Teaching Intervention To Promote Students’ Ability To Use Multiple Levels of Representation When Describing and Explaining Chemical Reactions. Res. Sci. Educ. 2008, 38, 237−248. (17) Rodriguez, E.; Vicente, M. A. A Copper-Sulfate-Based Inorganic Chemistry Laboratory for First-Year University Students That Teaches Basic Operations and Concepts. J. Chem. Educ. 2002, 79, 486−488. (18) Tamez, M.; Yu, J. H. Aluminum−Air Battery. J. Chem. Educ. 2007, 84, 1936A−1936B. (19) Bentley, A. K.; Farhoud, M.; Ellis, A. B.; Lisensky, G. C.; Nickel, A. L.; Crone, W. C. Template Synthesis and Magnetic Manipulation of Nickel Nanowires. J. Chem. Educ. 2005, 82, 765−768. (20) ApeTape Web Site. http://www.apetape.co.uk/ecom-catshow/ hookandloopdots.html (accessed Jan 2012).
In this station, students will read and discuss the half ionic and molecular redox equations provided on a card or paper. (A template for this is available to instructors in the online Supporting Information.) Students will use the information on the card (Figure 4) to explain the chemical equation. After
Figure 4. Symbolic station material: card printed with the half ionic and molecular redox equations.
observations are made in the three stations, students will apply the information gathered in each station to explain the copper(II) sulfate and zinc redox reaction by interconnecting the macroscopic properties observed with the transfer of electrons at the submicroscopic level, and will learn how to write the chemical equation using symbols.
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ASSOCIATED CONTENT
S Supporting Information *
Student activity worksheet; answers to questions for students; template of the half ionic and molecular redox equations for the symbolic station. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected].
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ACKNOWLEDGMENTS We thank the Department of Materials Science and Engineering at The Pennsylvania State University, and especially Allen Kimmel for teaching the activity at the 2009 Exploring Renewable Energy Technologies and the Materials That Make It Happen Residential Camp. In addition, we thank Jenneth Layaou for her assistance in recruiting participants for the research project associated with this activity. This work was supported by The Pennsylvania State University Materials Research Science and Engineering Centers (MRSEC) under NSF grant DMR-0820404.
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REFERENCES
(1) Wright, S. W.; Folger, M. R.; Quinn, R. P. The Oxidation of Iron in a Gel Using Consumer Chemicals. J. Chem. Educ. 2005, 82, 1633− 1635. (2) Wright, S. W. Trusty or Rusty? Oxidation Rate of Nails. J. Chem. Educ. 2005, 82, 1648A−1648B. (3) Combustion. http://sciencenetlinks.com/esheets/combustionof-fossil-fuels/ (accessed Jan 2012). (4) Chemistry of Petroleum 2: What Happens to Hydrocarbons When They Burn? http://sciencenetlinks.com/lessons/chemistry-ofpetroleum-2/ (accessed Jan 2012). (5) Briggs, B.; Mitton, T.; Smith, R.; Magnuson, T. Teaching Cellular Respiration and Alternate Energy Sources with a Laboratory Exercise Developed by a Scientist−Teacher Partnership. Am. Biol. Teacher 2009, 71 (3), 164−167. 645
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