In the Laboratory
What Happens When Chemical Compounds Are Added to Water? An Introduction to the Model–Observe–Reflect–Explain (MORE) Thinking Frame
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Adam C. Mattox and Barbara A. Reisner* Department of Chemistry, James Madison University, Harrisonburg, VA 22807; *
[email protected] Dawn Rickey Department of Chemistry, Colorado State University, Fort Collins, CO 80523
In this article, we present a laboratory module that is designed to help students understand how different compounds behave when they are dissolved in water. Using the laboratory activities in conjunction with an instructional tool called the Model–Observe–Reflect–Explain (MORE) Thinking Frame, students refine their ideas about the behavior of electrolytes and nonelectrolytes in aqueous solutions. The MORE Thinking Frame is an instructional tool that guides students’ thinking in the laboratory. Using the MORE Thinking Frame, students bring their initial understanding of a system to the lab (model), conduct experiments to test their model (observe), consider the implications of their observations, and use these to refine their initial ideas (reflect and explain). Students are also explicitly encouraged to make connections between macroscopic observations and their understanding of the behavior of particles at the molecular level. The MORE Thinking Frame encourages students to begin with their own ideas and, through successive refinements, reconcile their ideas with experimental evidence. In this way, students’ understanding typically progresses toward the accepted scientific understanding. For further details regarding the use of the MORE Thinking Frame, see the description provided by Tien, Rickey, and Stacy (1). Studies of students participating in laboratory courses that employ the MORE Thinking Frame have shown that using MORE confers significant benefits for students in both the laboratory and lecture portions of their courses. The MORE Thinking Frame is one of the first instructional tools that has been shown to improve students’ lecture course performance based solely on laboratory activities (2). Compared with students in control groups that employed traditional laboratory experiments, MORE students exhibited significantly enhanced propensity to engage in reflection and metacognition, ability to solve lecture-related examination problems and understanding of fundamental chemistry ideas (2). Originally, multiweek laboratory modules that incorporated the MORE Thinking Frame were developed.1 However, subsequent implementations of the MORE Thinking Frame indicate that it can also be used successfully by superimposing it onto existing laboratory experiments and providing appropriate pre- and postlab assignments. We have designed a two-week laboratory module entitled “What Happens When Chemical Compounds Are Added to Water?” to serve as an introduction to the MORE Thinking Frame. The module helps students understand and use the components of MORE so that the thinking frame can be effectively employed throughout the rest of the semester (with traditional laboratory experiments or with other MORE labo622
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ratory modules). The experiments can also be used in a classroom that is not using the MORE instructional method.2 Using the MORE Thinking Frame The topic of dissolution was chosen as a vehicle for introducing the MORE Thinking Frame to students, in part because students have extensive experience with dissolving things from their everyday-life experiences (e.g., dissolving sugar in beverages). At the macroscopic level, it is easy for students to make correct predictions. However, what occurs at the molecular level is not as obvious to them. In fact, it has been well documented that many students have difficulty understanding chemical phenomena at the molecular level, including the process of dissolution (3–11). Most students realize that solids will break into smaller units upon dissolution, but the nature of these units is not clear to students (see examples of initial models in the Supplemental MaterialW). Without a probe other than visual observation, it is not possible to develop a complete understanding of what happens to compounds at the molecular level. Measuring conductivity is an excellent way to explore the molecular-level behavior because it reveals that substances either remain as neutral species or break apart into charged particles. Since the systems employed in these laboratory experiments are simple and accessible, students can easily make connections between their macroscopic observations and molecular-level explanations so that they can revise their initial understandings to more closely approximate scientifically accepted ideas. These experiments also introduce a number of laboratory skills, including proper techniques for determining mass and the preparation of solutions using volumetric flasks. The laboratory module introduced here is divided into four major sections: Part I. What happens when you put chemical compounds in water?; Part II. Use your refined model to predict how new systems will behave.; Part III. Using the MORE Thinking Frame independently!; and Part IV. Why does your source of water matter? During each of these parts, one or more iterations of the MORE Thinking Frame are employed, with students revising their models in each iteration. Since this experience is designed to be the first time that students encounter the MORE Thinking Frame, numerous prompts regarding explicating a personal model, observing, reflecting, explaining, and refining are initially given. Over the course of the laboratory module, these supports are gradually removed and students begin to use the MORE Thinking Frame more independently. The laboratory activities include periods of experimental measurement and small-
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In the Laboratory
group discussion interspersed with whole-class discussions about observations and model refinements. The integration of the MORE Thinking Frame with the experimental portion of the laboratory is described in depth for the first part of the experiment.
Prelaboratory Assignment The week before the laboratory module begins, students are given a description of the MORE Thinking Frame. They are also given a prelaboratory assignment in which they are asked to develop their initial model of the system by describing their current understanding of what happens when sugar and salt are added to water. In their initial model assignment, students are asked to describe and represent both a macroscopic model (what they expect to observe) and a molecularlevel model (what they believe the molecules, atoms, or ions are doing that is responsible for their observations). Because this is the first time that students have constructed a model, they are asked explicit questions that guide them in constructing their model. These supports are particularly important the first time that students construct models because students often have difficulty differentiating between the macroscopic and molecular levels. The initial model assignment as well as examples of student models are provided in the Supplemental Material.W Model Before any experimental work is conducted, students are assigned to lab groups and are asked to verbally describe and draw pictures of their initial models for the rest of their group. During this time, instructors visit with groups to discover students’ ideas about dissolution. These initial discussions serve to help students to confront their initial ideas and defend them to their group. They also show group members that their peers have different explanations for their observations. Once students have shared their initial ideas, the instructor leads a discussion on students’ ideas, the difference between macroscopic- and molecular-level models and elements of a good model. To facilitate this discussion, several student groups with different models are asked to present their ideas to the class. Models are discussed to illustrate the range of ideas and are assessed based on completeness, not correctness. Students are asked to identify model components as macroscopic or molecular level and to add any of their own ideas that were not presented. Observe During this portion of the experiment, students conduct their laboratory work. Before lab work begins, students are introduced to appropriate laboratory techniques. The conductivity meter is briefly described. It is also important for the instructor to emphasize that students should use their senses (e.g., vision, hearing) to obtain additional information regarding what happens when compounds are added to water. Reflect Students are asked to reflect on their observations by looking for trends or patterns in conductivity. To help students reconcile their initial models with their observations and refine their initial models if necessary, students are asked to anwww.JCE.DivCHED.org
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swer a series of questions that will help them think about the connections between the macroscopic and molecular levels.
Explain During each part of this laboratory module, students are asked to share their data with the class. As a class, students develop “rules” that can help them predict whether a solution of a compound will conduct electricity. Using their own data as well as that of others in the class, students are asked to reflect upon the experimental evidence and how it relates to their initial models and to make any model refinements that are necessary to explain the data. Students then use the MORE Thinking Frame to guide further inquiry regarding aqueous solutions of ionic compounds with formulas that do not have 1:1 ratios of cations and anions, polyatomic ions and electrolytes that do not contain metal ions. In each case, students predict the behavior of solutions based on their current model and then test their model using a conductivity meter. As a postlaboratory assignment, students are asked to construct a final model that is consistent with all of their laboratory observations. They are asked to explain how salt and sugar behave when dissolved in water as well as to generalize their model to describe what happens when any compound is added to water. Experimental Procedure The first laboratory activity involves differentiating between compounds that behave as electrolytes and nonelectrolytes in aqueous solution. Students measure the conductivity of various aqueous solutions using handheld conductivity testers with LED displays (12). By counting the number of LEDs illuminated, students can differentiate between electrolytes and nonelectrolytes and approximate the relative numbers of ions in solution. Students dissolve 2 g of selected compounds in 20 g of deionized water in beakers. We have used NaCl, CaCl2 (anhydrous), CuCl2⭈2H2O, glucose, isopropanol, and sucrose. 3 Anhydrous CaCl2 and CuCl2⭈2H2O were chosen to demonstrate that changes other than dissolution can occur when chemical compounds are added to water. The dissolution of CaCl2 evolves heat while the dissolution of CuCl2⭈2H2O changes the color of the solution. At these concentrations, all electrolytes produce the maximum reading on the conductivity meters used. Once students are able to differentiate between electrolytes and nonelectrolytes, they investigate how ionic compounds break apart in solution. Students begin by investigating whether there is a relationship between the mass of the compound added to water and conductivity by quantitatively preparing solutions of NaCl and NaI in volumetric flasks (0.100 g salt per 100-mL solution).4 Students discover that these solutions do not light up the same number of LEDs; the NaCl solution lights up six LEDs and the NaI solution lights up two LEDs. After a whole-class discussion in which the mole concept is recognized to be a key factor, students are asked to prepare a NaI solution that will light up the same number of LEDs as their original NaCl solution. This provides evidence for the relationship between moles and conductivity or concentration of ions. During the final parts of the module, students make predictions regarding and investigate the behavior of ionic com-
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In the Laboratory
pounds with formulas that do not have 1:1 ratios of cations and anions (CaCl2⭈2H2O), polyatomic ions (NaNO3 and Na2SO4) and electrolytes that do not contain metal cations (NH4Cl). In each case, students are asked to predict how these compounds will dissociate when added to solution and prepare a solution that will produce the same number of ions as the original sodium chloride solution. Once students have successfully completed these activities, they investigate the conductivity of tap water to learn why deionized water must be used in the preceding laboratory experiments. Hazards The chemicals used in this experiment pose no unusual hazards. Inorganic compounds used in this experiment contain cations and anions that do not present a significant hazard (13–14). Small amounts of these compounds may be flushed to the sewer with plenty of water; consult local regulations. Implementation This laboratory module has been tested in various general chemistry laboratory courses (including regular, honors, and chemistry majors' sections) at a research university, a primarily undergraduate institution, a community college, and a high school. Comments from all instructors who implemented the module were positive. Results of the effectiveness of the laboratory module in prompting students to revise their molecular-level ideas regarding chemical compounds dissolved in water will be published in a companion paper (15). We recommend that this laboratory module be conducted during two lab periods of 2–3 hours each. During the first lab period, students should complete Parts I and II; the remainder should be conducted during the second lab period. The laboratory module could be shortened to fit into a single laboratory period by omitting Part III (compounds with stoichiometries other than 1:1 or containing polyatomic ions) or by having the instructor provide that data (e.g., via demonstration of conductivity measurements on previously prepared solutions). Summary This laboratory module both introduces students to the MORE Thinking Frame and improves students’ conceptual understanding of the behavior of compounds dissolved in water. Although the experiment is deceptively simple, it promotes student reflection as well as group discussion about these phenomena (15, 16). The coverage and depth of the treatment of concepts examined during the experiment can be adjusted by the instructor through the selection of the parts of the experiment to be conducted by students. Although this lab module has been designed for a curriculum that is implementing the MORE Thinking Frame, it can also be used in classes that have not adopted MORE. W
Supplemental Material
Student handouts for a college-level general chemistry course, required supplies, sample results, instructor notes, 624
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examples of student work, and suggestions for grading are available in this issue of JCE Online. Acknowledgments This work was supported by the National Science Foundation Research on Learning and Education (EHR-0208029) and REU (CHE-0097448) programs. We acknowledge and thank the instructors who have tested this lab module in their courses and who have given us helpful feedback. Thanks are also extended to Melonie Teichert for valuable conversations and comments. Notes 1. The original MORE curriculum was used in a one-semester comprehensive general chemistry course taught at the University of California at Berkeley. 2. A version of the laboratory module without the explicit use of the MORE Thinking Frame, originally implemented at Monroe Community College, is available upon request. 3. Relative to the other compounds employed, sucrose dissolves slowly. Fructose can be substituted for sucrose; it dissolves much more rapidly. However, sucrose is what students think of when they hear “sugar”. 4. Prior to making conductivity measurements, students are asked to predict which solution will light up the greatest number of LEDs: NaCl, NaI, or neither. We were surprised that approximately one-third of each class selected each possibility.
Literature Cited 1. Tien, Lydia T.; Rickey, Dawn; Stacy, Angelica M. J. Coll. Sci. Teach. 1999, 28, 318–324. 2. Rickey, Dawn. The Effects of Laboratory Curriculum and Instruction on Undergraduate Students’ Understanding of Chemistry. Ph.D. Thesis, University of California, Berkeley, CA, 1999. 3. Nurrenbern, Susan C.; Pickering, Miles. J. Chem. Educ. 1987, 64, 508–510. 4. Lythcott, Jean. J. Chem. Educ. 1990, 67, 248–252. 5. Nakhleh, Mary B. J. Chem. Educ. 1992, 69, 191–196. 6. Smith, Kimberly Jo.; Metz, Patricia A. J. Chem. Educ. 1996, 73, 233–235. 7. Ebenezer, Jazlin V.; Erickson, Gaalen L. Sci. Educ. 1996, 80, 181–200. 8. Lee, Kam-Wah Lucille. J. Chem. Educ. 1999, 76, 1008–1012. 9. Sanger, Michael J. J. Chem. Educ. 2000, 77, 762–766. 10. Raviolo, Andrés. J. Chem. Educ. 2001, 78, 629–631. 11. Pinarbasi, Tacettin; Canpolat, Nurtaç. J. Chem. Educ. 2003, 80, 1328–1332. 12. Ganong, Barry R. J. Chem. Educ. 2000, 77, 1606–1608. 13. National Academies Press: Prudent Practices in the Laboratory. http://www.nap.edu/books/0309052297/html/ (accessed Jan 2006). 14. National Research Council. Prudent Practices in the Laboratory; National Academy Press: Washington, DC, 1995; p 166. 15. Tien, Lydia T.; Teichert, Melonie A.; Rickey, Dawn. J. Chem. Educ., in press. 16. Teichert, Melonie A.; Tien, Lydia T.; Rickey, Dawn. manuscript in preparation.
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