Effectiveness of a MORE Laboratory Module in ... - ACS Publications

Research: Science and Education edited by

Chemical Education Research

Diane M. Bunce

Effectiveness of a MORE Laboratory Module in Prompting Students To Revise Their Molecular-Level Ideas about Solutions

The Catholic University of America Washington, D.C. 20064

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Lydia T. Tien Department of Chemistry and Geosciences, Monroe Community College, Rochester, NY 14623 Melonie A. Teichert and Dawn Rickey* Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872; *[email protected]

Numerous studies have documented that learning that results from conventional, didactic instruction (i.e., lectures and laboratory courses in which students follow cookbook procedures and perform algorithmic calculations on the data they collect) is often shallow and that many students continue to hold misconceptions following courses that rely on these instructional methods (1–7). In addition, studies have documented student difficulties in understanding phenomena from a molecular-level (also called a particulate or microscopic) perspective (6–13). Some common misrepresentations that reveal misconceptions regarding chemical compounds dissolved in water include: separating molecular compounds into individual atoms or ions, not separating ionic species, improperly dissociating polyatomic ions as separate species, misinterpreting subscripts or coefficients, and misrepresenting diatomic species (e.g., Cl2 in solution vs. Cl᎑) (7, 11–12). Various instructional methods, such as computer animations and emphasis on molecular-level representations in the lecture, have been implemented with the goal of improving students’ understanding of phenomena from a molecular-level perspective (14–18). A recent article in this Journal (19) describes a laboratory module (What Happens When Chemical Compounds Are Added to Water?), that was designed to probe and develop students’ molecular-level understandings of aqueous solutions. Unlike methods that emphasize instructors presenting molecular-level representations to students, this laboratory module focuses on students’ ideas and their individual ways of representing what happens at the molecular level. The pedagogical approach of this lab module embeds the Model– Observe–Reflect–Explain (MORE) Thinking Frame, an instructional tool that guides students’ thinking and encourages students to reflect upon their ideas and how these ideas fit with experimental evidence (20–23). Developing deep and robust understandings of science concepts requires students to construct their own personal understandings in the social setting of the classroom or laboratory (24). The MORE Thinking Frame encourages this personal meaning-making for students. Using the MORE Thinking Frame, students describe their current understanding of an experimental system as part of the pre-laboratory preparation (Model), carry out experiments to explore the experimental system (Observe), think about the implications of their observations and use the experimental evidence as a basis for refining their ideas (Reflect and Explain). As part of their reflections, students www.JCE.DivCHED.org

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make connections between their macroscopic observations and their understanding of the behavior of particles at the molecular level. Laboratory experiments incorporating the MORE framework prompt students to refine their models to be consistent with evidence, which often leads to revision to scientifically correct ideas, or at least progression toward more scientifically correct ideas. Thus, prior to beginning this laboratory module, students are asked to describe their understanding of what happens when salt (NaCl) and sugar (C12H22O11) are added to water. As part of the initial model assignment, students are explicitly asked what they expect to observe at the macroscopic level and to then connect this to what they think is happening at the molecular level. (See Figure 1 for an abbreviated version of the initial model assignment. The full assignment and details of the module can be found in ref 19.) Students begin their laboratory investigations by testing the conductivity of deionized water and observing the conductivities of various solutions to distinguish electrolytes and nonelectrolytes. Students then measure conductivities semi-quantitatively using

Initial Model Describe your understanding of what happens to chemical compounds when they are added to water. For your initial model, consider two solids that can be found in any kitchen cupboard: salt (NaCl) and sugar (C12H22O11). Describe what you expect to observe (see, hear, feel, smell) before and after you have added these solids to water; this is your initial macroscopic model. Then, explain what you think the molecules, atoms, and/or ions are doing that results in your observations; this is your initial molecular-level model. Refined Model Develop a refined model for what happens to chemical compounds when they are added to water. For your refined model, consider two solids that can be found in any kitchen cupboard: salt (NaCl) and sugar (C 12H22O11). Then, generalize your macroscopic and molecular-level models so that they can be used to predict what will happen when other chemical compounds are added to water. Figure 1. Abbreviated assignment instructions for the initial model and refined model of the laboratory module entitled, What Happens When Chemical Compounds Are Added to Water?

Vol. 84 No. 1 January 2007

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Journal of Chemical Education

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hand-held conductivity test instruments with 10-bar LED displays (25, 26). The MORE Thinking Frame is an essential part of the module and explicitly encourages reflection and metacognition. It provides a structure to make students aware of their ideas prior to conducting experiments, and prompts students to reflect upon those ideas in light of experimental evidence and to refine their ideas to be consistent with their observations. As shown in Figure 1, the initial model assignment asks students to articulate their ideas about expected macroscopic observations and molecular-level behaviors for the dissolution of salt and sugar. Before students collect data, the instructor facilitates a discussion of the initial models, giving students the opportunity to present their ideas and to hear the ideas of their peers. At this point, the instructor accepts all ideas without judging their correctness; instead, the instructor creates a learning environment in which students are open to considering and evaluating different views in light of experimental observations. In the first part of the laboratory module, students observe the dissolution process and measure the conductivities of various aqueous solutions. After the instructor provides the chemical formulas of the compounds investigated, the students work in groups to identify patterns that help to distinguish between electrolytes and nonelectrolytes. After small-group and whole-class discussions, the students individually evaluate and revise their models. Subsequent parts of the laboratory module provide opportunities for further model refinement. The research reported in this paper investigates the effectiveness of the first implementations of this introductory MORE laboratory module in prompting three different populations of general chemistry students to revise their molecular-level ideas regarding chemical compounds dissolved in water. We also examine the correctness of the student models. An expanded version of this article, including analyses of the progression of student ideas toward more scientifically accurate ideas, students’ perceptions of the lab module, and all institutional data is available in the Supplemental Material.W Method

Participants and Instructional Contexts The general chemistry students who consented to participate in this study (N ⫽ 84) were recruited from three different institutions, as follows: 1. Honors general chemistry laboratory course at a research university (RU, N ⫽ 24) 2. General chemistry laboratory course for chemistry majors at a primarily undergraduate institution (PUI, N ⫽ 32) 3. Introductory chemistry course at a community college (CC, N ⫽ 28)

Only students who completed the pre-laboratory and post-laboratory assignments for the module, attended the associated laboratory sessions, and completed their lab course are included in the study. Of the 83 students who completed pre-course surveys, all but one reported taking a high school chemistry course. The student who had not taken high school chemistry com176


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pleted a preparatory chemistry course at the community college. Furthermore, 46% of the RU students, 81% of the PUI students, and 11% of the CC students reported taking a high school chemistry course with a designation of honors, advanced, advanced placement (AP), or international baccalaureate (IB). Half of the CC students (and none of the RU or PUI students) reported taking a previous college chemistry course, most often a preparatory chemistry course. This paper reports on the results of the first implementations of the module at each institution. Faculty members who had used the MORE method previously taught the laboratory courses at the community college and undergraduate institution, while a graduate student instructor who had not used the MORE method before taught the lab course at the research university. At the undergraduate institution and research university, students completed the experiments comprising the first two parts of the laboratory module (19) in one laboratory period during the second week of the semester. At the community college, students carried out the experiments for all four parts of the laboratory module over a two-week span during the third and fourth weeks of the semester. At all three institutions, the corresponding general chemistry lecture instructor had discussed differences between ionic and molecular compounds—but had not distinguished electrolytes and nonelectrolytes—prior to students’ first day working on the module.

Data Sources and Analyses To assess the effectiveness of the introductory MORE laboratory module at prompting students to revise their molecular-level ideas regarding chemical compounds dissolved in water, we analyzed the initial models (pre-laboratory assignments) and final refined models that students submitted for the module. (See Figure 1.) Two researchers reviewed the models to identify categories describing the students’ various molecular-level ideas. These emergent categories were expanded into a coding scheme. All student ideas expressed in the models, both words and pictures, were considered in coding; thus, one student’s model was often assigned multiple codes. All codes assigned to a particular student’s models were considered when evaluating the student’s ideas for consistency with experimental evidence and correctness. The criteria for considering a molecular-level model to be fully correct were strict. For example, if a student described in words that NaCl broke apart into ions, but drew a picture of NaCl broken into neutral Na and Cl atoms, the model was not considered correct. Both of the researchers coded 16% of the initial and refined models and obtained an interrater reliability of 88%. After resolving the differences, one researcher coded the remaining student models. The two researchers discussed and reached consensus on models for which the coding was found to be ambiguous by the primary coder. Results and Discussion

Students’ Initial Models In their initial models, most students provided accurate descriptions of what they would observe macroscopically upon adding salt and sugar to water. However, first-semester general chemistry students typically have little, if any, experience with describing and illustrating their molecular-level


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understandings, particularly early in the semester. Thus, it is interesting that the majority of students at all institutions were also able to provide molecular-level initial models, even though this was the first time in the semester that they were asked to do so. All students submitted molecular-level models for aqueous salt solutions, and 88% of students submitted molecular-level models for aqueous sugar solutions. The community college students appeared to have the most difficulty constructing molecular-level models for sugar solutions (21% did not present molecular-level ideas), probably due to weaker chemistry backgrounds or longer time elapsed between chemistry courses compared with the other student populations. Students’ initial molecular-level models contained a range of ideas; some of these ideas were consistent with scientifically accepted views of salt and sugar dissolved in water, but the majority were not, as indicated in Table 1. While the chemical systems are relatively simple and all students had taken at least one previous chemistry course, only 15% of students expressed scientifically accurate molecular-level initial ideas for both the dissolution of salt and the dissolution of sugar. Overall, 35% of the students presented a correct molecular-level initial model for aqueous NaCl and 32% presented a correct molecular-level initial model for aqueous C12H22O11. The proportions of students who submitted correct molecular-level initial models were not significantly different among institutions. Although the relevant concepts may seem straightforward, they are clearly problematic for college-level general chemistry students prior to instruction, even if the students have strong chemistry backgrounds (e.g., the chemistry majors at the PUI). Some common misconceptions found in the initial models include salt existing as “NaCl molecules” in solution, salt breaking up into neutral atoms, sugar molecules dissociating into atoms or ions, salt and/or sugar forming chemical bonds with water (distinct from hydrogen bonding or other intermolecular attractions), and salt and/or sugar undergoing other reactions (e.g., metathesis) with water. Table 1 summarizes students’ molecular-level views of the dissolution of salt and sugar. Figures 2 and 3 present excerpts from the models submitted by students. Student RU-26’s models (Figure 2) illustrate two common misconceptions and provide an example of how a student revised her ideas over the course of the laboratory module. Initially, student RU-26 pictured dissolved NaCl as molecular units; in her refined model, she revised her ideas to show that NaCl breaks apart into ions. Additionally, her initial model suggests a chemical reaction with water, but in her refined model she corrects this idea. Student RU-32’s refined model (Figure 3) illustrates ions bonding with water; the student uses the same representation (solid line) to depict both the interactions between atoms within the water molecules and the interactions between ions and the atoms of a water molecule. While some of the student misconceptions revealed in this study have been reported previously (7, 11–12), others appear to be new to the literature, specifically salt and sugar forming chemical bonds with water, salt and sugar reacting with water upon dissolution, and sugar molecules (disaccharides) breaking apart into monosaccharides. One study of high school students reported conceptions of sugar particles “joining with” water when sugar dissolves (11), but the nature of this attachment was nonspecific. In our study, some students www.JCE.DivCHED.org

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Table 1. Students’ Molecular-Level Ideas about the Dissolution of Salt and Sugar in Initial and Refined Models Students’ Molecular-Level Ideas about Salt and Sugar Dissolution

MMNOverall Incidence a MMMInitialMMMRefined

Correct Ideas Correct molecular-level model MMof salt dissolution.

35%

80%

Correct molecular-level model MMof sugar dissolution.

32%

52%

18%

00%

14%

02%

Sugar molecules dissociate MMinto atoms.

05%

02%

Sugar molecules dissociate MMinto ions.

07%

05%

Salt forms chemical bonds MMwith water.c

21%

10%

Sugar forms chemical bonds MMwith water.

15%

05%

Salt undergoes a metathesis MMreaction with water.

07%

01%

Sugar molecules (disaccharides) MMbreak apart into MMmonosaccharides.

05%

05%

Other misconceptions (salt and MMsugar).

05%

02%

No molecular-level model given MMfor sugar.

12%

10%

Incorrect Ideas Salt exists as NaCl molecular units. Salt breaks up into neutral atoms.

b

a N ⫽ 84; bThe CC students expressed this idea in their initial models less frequently than the PUI and RU students (Fisher’s exact tests, p ⫽ 0.026 and p ⫽ 0.016, respectively); cThe PUI students expressed this idea in their initial models less frequently than the RU students (Fisher’s exact test, p ⫽ 0.0057).

were explicit about how they thought salt and/or sugar formed bonds with water, with 20% of students drawing molecularlevel pictures indicating chemical bonding of a solute to water (e.g., student RU-32’s refined model in Figure 3). Students’ lack of experience with describing and representing phenomena at the molecular level may account for some of the inconsistencies observed in their initial models. For instance, three students said that NaCl dissociated into individual ions, but drew Na and Cl as uncharged species. In addition, three students stated that water molecules surround the sugar molecules or salt ions, but drew representations that implied that the water molecules bonded to the molecules or ions. Thus, students who implied that sugar forms chemical bonds with water may have meant to indicate hydrogen bonding, while students who denoted salt forming chemical bonds with water may have been trying to represent ion–dipole


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Initial Model of Student RU-26 “An atomic view of each solution would show the separate molecules mixed together. Although both solutions are homogeneous mixtures, I can see what would happen if the salt were to chemically react with the water. If NaCl split into its ions in

the water, each would be attracted to opposite sides of the polar water molecule. The chemical formula would then be as such: 2 H2O ⫹ 2 NaCl → 2 NaOH ⫹ Cl2 ⫹ H2. I don’t, however, know how sugar would react with water.”

Refined Model of Student RU-26 “Microscopically, when the NaCl is dissolved in water, the ionic bonds between the sodium and the chlorine break apart so that there are ions of Na+ and Cl- mixed in the water molecules. The sugar, however, is made up of covalent bonds since it is an organic molecule. Therefore the molecule of C12H22O 11 doesn’t break apart in the water, but just disperses itself throughout. Also, because the NaCl solution ionizes, it conducts electricity, whereas the C12H22O11 solution will not be conductive.”

“In my initial model, I discussed how if NaCl split up, it would be attracted to the poles of the water molecule and form a new compound. This would only happen if there were a chemical reaction. However, in dissolving, the NaCl does break into its ions Na⫹ and Cl᎑, but since this is a physical change, the ions will come back together to form salt if the water is boiled off.”

Figure 2. Excerpts from student RU-26’s initial and refined models for dissolution of salt and sugar in water. (The student’s written descriptions were typed verbatim; the student’s drawings were scanned directly from the student’s laboratory reports.)

Refined Model of Student RU-32 “The formula NaCl ⫹ H2O (l) → Na⫹ ⫹ Cl᎑ shows table salt dissolving into its ions in water. Solutions containing ions conduct an electric current. The ions in a solution can move about and carry a charge.”

Figure 3. An example of a student misconception found in both initial and refined models. (The student’s written descriptions were typed verbatim; the student’s drawing was scanned directly from the student’s laboratory report.)

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Table 2. Consistency of Students’ Molecular-Level Ideas with Experimental Evidence and Correctness of Students’ Ideas in Refined Models of Aqueous Salt and Sugar Solutions Category

Refined Models of Salt Solutions (N = 84) Overall, %

RU, %

PUI, %

CC, %

Refined Models of Sugar Solutions (N = 84) Overall, %

RU, %

PUI, %

CC, %

MConsistent with data, not revised

40

42

47

32

46

46

56b

36b

MConsistent with data, revised

49

46

44

57

37

42

41b

29b

MNot consistent with data

05

08

03

04

05

00

00b

14b

MVague

02

00

03

04

02

00

00b

07b

MDid not answer

04

04

03

04

10

13

03b

14b

MCorrect, not revised

35

29

44

29

32

33

38b

25b

MCorrect, revised

45

42

41

54

20

13

25b

21b

MIncomplete

02

00

03

04

20

21

31a

07a

MIncorrect

14

25

09

11

18

21

03b

32b

MDid not answer

04

04

03

04

10

13

03b

14b

a Compared with the PUI students, the CC students presented a lower proportion of refined models of sugar solutions that were incomplete (Fisher’s exact test, p = 0.025). b Compared with the PUI students, the CC students presented a higher proportion of refined models of sugar solutions that were incorrect (Fisher’s exact test, p = 0.004).

interactions. As part of the refined model assignments, students were asked to be explicit with respect to the evidence that supported their initial ideas or that compelled them to make changes to their initial models. Students were also encouraged to pay attention to detail and language in presenting their molecular-level ideas. Thus, students learned to represent their molecular-level views more accurately.

Students’ Refined Models— Consistency with Experimental Evidence The MORE framework encourages students to reflect upon the experimental evidence they collect and to reconcile their observations and data with their ideas. Thus, after completing each part of the laboratory module, students are asked to refine their previous models based on their empirical observations and data. Because the conductivity evidence collected by students during this laboratory module differentiates between electrolytes and nonelectrolytes, we expected that students would revise (if necessary) their molecular-level models to reflect how salt and sugar behave differently when added to water. Note that it is possible for a student’s refined model to be fully consistent with the experimental evidence collected during the laboratory module, yet not fully correct. The conductivity data obtained by students during the laboratory module indicate that aqueous sugar solutions do not contain charged particles; some students used this evidence to support such molecular-level ideas as sugar breaking up into neutral atoms or forming other neutral species when dis-

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solved in water. For instance, student RU-16 explained why an aqueous sugar solution is not conductive: C12H22O11 doesn’t break down into cations and anions. It might break down into two smaller sugars, but the net charge of that molecule is 0, so there is nothing to attract or repel the electricity.

Such students used their empirical observations to support their models, an important aspect of using the MORE Thinking Frame successfully. Because the data collected in the laboratory module do not completely address the molecular-level behavior of sugar solutions, students were not necessarily compelled to revise their initial ideas to obtain a model that was in full agreement with the scientifically accepted view. Refined models were first evaluated based on their consistency with the empirical observations and data collected by the students throughout the laboratory module. Each student’s refined model for each substance was assigned to one of five categories: 1. Consistent with data, not revised (i.e., the initial model was consistent with the evidence) 2. Consistent with data, revised 3. Not consistent with data 4. Vague (such that it could not be determined whether or not the model was fully consistent with the data) 5. Did not answer

Table 2 summarizes the results of this analysis.


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Overall, 89% of all students articulated refined molecular-level models of salt solutions that were fully consistent with the data collected, and 83% of students articulated refined molecular-level models of sugar solutions that were fully consistent with the data. Of the students whose initial models were not consistent with the experimental evidence, 82% revised their ideas about the dissolution of salt and 69% revised their ideas about sugar to be fully consistent with the data. There were no statistically significant differences among institutions in terms of the consistency of students’ refined molecular-level models of aqueous salt solutions with the experimental evidence. For refined models of aqueous sugar solutions, there was one difference. Compared with the CC students, a significantly larger percentage of the PUI students had refined molecular-level models for aqueous sugar solutions that were consistent with the experimental evidence (Fisher’s exact test, p ⫽ 0.0017). In particular, while none of the RU or PUI students expressed the idea that “sugar molecules dissociate into ions” in their refined models, 14% of the CC students expressed this idea despite observing that aqueous sugar solutions did not conduct electricity. The CC students’ difficulties with refining their molecular-level sugar models for consistency may be related to the instructional conditions under which the lab module was implemented at the CC in Spring 2004. Unlike the students at the RU and the PUI, the CC students carried out the two-week version of the laboratory module. In addition, the CC students were not required to submit a formal model refinement between the first and second weeks of the laboratory module. Because the second week focuses exclusively on solutions of soluble ionic compounds (19), by the time the students submitted their final refined models, it is likely that some CC students forgot to consider the data regarding solutions of nonelectrolytes that they collected during the first week and that some mistakenly believed that all solutes behaved similar to the soluble ionic compounds that they studied during the second week. Based on the analyses presented in this paper as well as initial analyses of data collected during later implementations of the laboratory module, we observe that despite clear final refined model guidelines that indicate that aqueous sugar solutions should be addressed (see Figure 1), approximately 15– 25% of students may neglect to include discussions of aqueous sugar solutions in their final refined models when the twoweek version of the module is implemented. Requiring students to submit formal intermediate refined models appears to improve the situation because students are much more likely to discuss solutions of nonelectrolytes in a refined model that immediately follows the experiments involving them. For this reason, when implementing the two-week version of the laboratory module, we recommend that students be required to submit and discuss intermediate refined models between the first and second weeks. Design-based research exploring methods of improving students’ attention to solutions of nonelectrolytes in their final refined models is currently underway.

Students’ Refined Models—Correctness of Ideas Students’ refined models were also evaluated based on their correctness or agreement with the scientifically accepted views of salt and sugar dissolution. In implementing the MORE Thinking Frame, instructors never simply present the correct ideas to the students. The role of the instructor is to 180


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facilitate student thinking and discussion of ideas. Thus, student model refinements leading to correct molecular-level models are not due to instructor presentation of the correct ideas. Table 2 summarizes the correctness of students’ molecular-level refined models of NaCl and sugar dissolved in water. Students who were categorized as having “incomplete” ideas lacked specificity in their molecular-level descriptions. For instance, if a student said that “sugar does not separate”, the student might have meant that the individual sugar molecules do not dissociate or that sugar molecules do not separate from each other. As stated above, 35% of students had correct initial molecular-level models of NaCl dissolved in water, 32% of students had correct initial models of sugar dissolved in water, and 15% of students had correct initial models for both salt and sugar. In their refined models, 80% of the students articulated scientifically accurate molecular-level models of NaCl dissolution, 52% described sugar dissolution accurately, and 46% of students had correct refined models for both salt and sugar. A significantly greater proportion of students had correct refined molecular-level models compared with the proportion who had correct initial models for salt dissolution (χ2 ⫽ 37.1 [1, N ⫽ 168]; p ⬍ 0.0001) and for sugar dissolution (χ2 ⫽ 7.05 [1, N ⫽ 168]; p ⬍ 0.01). There were no statistically significant differences among institutions in the correctness of students’ refined molecularlevel models of aqueous salt solutions. By the end of the laboratory module, most students at each institution recognized that NaCl dissociated into individual ions in solution, and correctly represented their molecular-level models. In addition, most of the students (10 of 12) who were classified as possessing incorrect ideas recognized that NaCl broke up into Na⫹ and Cl᎑ ions, but also included inaccurate ideas (e.g., the ions bonding to water or ions represented as neutral species). In the refined models of aqueous sugar solutions, 52% of all students articulated correct molecular-level ideas. There were some differences in the correctness of students’ models among the different student populations as noted in Table 2. In addition, one common response in the refined models of the PUI students was that sucrose does not completely dissolve in water. This was an isolated problem observed in the PUI population during the Fall 2003 semester; in the Fall 2004 implementation, no PUI student claimed that sucrose did not dissolve. This illustrates that it is helpful for instructors to be aware that sucrose takes longer to dissolve than other compounds used during the module. If an instructor notices that students are not allowing enough time to observe that sucrose dissolves in water, the instructor can initiate discussions with students regarding how they can reliably determine whether or not a substance is soluble, and can ask students to relate their laboratory experiences to their everyday experiences of adding sugar to beverages. The relatively low incidence (52%) of students possessing correct molecular-level ideas regarding the dissolution of sugar in their refined models is not entirely discouraging given that the correct ideas were not presented to the students. Of the students who expressed incorrect molecular-level ideas in their refined models of aqueous sugar solutions, 60% of them articulated ideas that were fully consistent with the experimental evidence.


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Conclusions

Acknowledgments

Understanding what happens at the molecular level when ionic and molecular compounds dissolve in water is a foundational topic in general chemistry, yet only 15% of the firstsemester general chemistry students who participated in this study (all of whom had taken at least one previous chemistry course and many of whom had strong chemistry backgrounds) presented correct initial ideas regarding both salt and sugar dissolved in water. Thus, it is important to employ instructional methods that facilitate students’ development of robust understandings of these ideas. This work investigated the effectiveness of the first implementations of an introductory MORE laboratory module in prompting three different populations of general chemistry students to revise their molecular-level ideas regarding chemical compounds dissolved in water. MORE instruction emphasizes student reflection upon and revision of personal models to be consistent with experimental evidence. Ideally, consideration of the experimental evidence promotes student model revisions to progressively more correct ideas so that students’ final refined models are both consistent with the data and in line with scientifically accepted views. The module was particularly effective for encouraging students to revise their ideas about aqueous salt solutions such that the ideas were both consistent with experimental data (89%) and scientifically correct (80%). Participation in the MORE laboratory module also prompted students to make significant productive revisions to their ideas about aqueous sugar solutions (83% consistent, 52% correct). The analyses presented in this paper summarize the evolution of students’ molecular-level ideas from the beginning to the end of the laboratory module as expressed in their written models. In addition to providing information about students’ ideas and the effectiveness of the laboratory module in the three contexts in which it was initially implemented, these analyses highlight specific instructional conditions that are important for the module’s effectiveness. In particular, for two-week versions of the module, students should be required to submit and discuss intermediate refined models. Additionally, instructors should be aware that sucrose takes longer to dissolve than the other compounds that students work with during the module. W

Supplemental Material

An expanded version of this article, including analyses of the progression of student ideas toward more scientifically accurate ideas, students’ perceptions of the lab module, and all institutional data, is available in this issue of JCE Online.

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