Research: Science and Education edited by
Diane M. Bunce The Catholic University of America Washington, DC 20064
“Gone” into Solution: Assessing the Effect of Hands-On Activity on Students' Comprehension of Solubility
Vickie M. Williamson Texas A & M University College Station, TX 77823
Laura B. Bruck and Aaron D. Bruck Department of Chemistry, Purdue University, West Lafayette, Indiana 47907 Amy J. Phelps* Department of Chemistry, Middle Tennessee State University, Murfreesboro, Tennessee 37132 *
[email protected] Chemistry, as a whole, is difficult for many students to learn (1-6), and even beginning graduate students can harbor misconceptions in their chemical understandings (7). Some of the challenges students face in chemistry stem from the fact that it has three major forms of representation: symbolic, macroscopic, and microscopic (3). The expert can easily transition from a symbolic representation of a phenomenon to a microscopic representation and then to a macroscopic representation (3). Novices, however, cannot seamlessly make these conversions (3), and beginning students can easily become lost in the complex jargon of chemistry (3). In addition, many chemical education approaches are in direct conflict with the psychological ways in which students learn (8). It was observed in a first-semester general chemistry laboratory that a majority of students in the course struggled with solubility, and many did not seem to grasp the fundamental concept: that a clear, colorless liquid may contain ions that are able to interact with other clear, colorless liquids also containing aqueous species. This observation was consistent with results reported in the literature (6). Thus, in this study, an established general chemistry laboratory experiment (9) was modified as we proposed a new method for teaching and building solubility understanding in the laboratory. Review of Literature A breach exists between students' conceptual knowledge of phenomena and students' ability to solve algorithmic or mathematical problems to describe and explain phenomena (10-14). The chemical education literature reveals that students may be able to compute mathematical and algorithmic problems without having an understanding of the chemical concepts underlying the algebra (10-14). Current literature describes problems faced by chemical educators in today's classrooms and laboratories with regard to teaching solubility. Many innovative methods and advice for teaching solubility and solutions have been published over the past decade (15-25). While all these may be helpful, very few offer data to support the efficacy of these strategies. In addition, the effectiveness of the laboratory as a means of enhancing students' comprehension of concepts is debated throughout the literature (26).
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Bloom (27) describes six cognitive objectives (knowledge, comprehension, application, analysis, synthesis, and evaluation) for classifying teaching and learning. “Comprehension” is the level at which students can both understand a concept broadly and what they are being asked to do with it. At the “synthesis” level, learners are not only expected to combine aspects to create cumulative conclusions but also to take these conclusions and extrapolate them (27). In our study, we anticipated almost all general chemistry students initially being at the “comprehension” level because students had been exposed to the relevant materials in lecture. A recent study concluded that the majority of chemistry laboratory activities in a sample of 229 published chemistry experiments did not include much inquiry and were written such that data analysis is provided to the student (28). We assert that performing data analysis still requires synthesis level abilities on the part of the student, even when the steps for analyzing data are provided, because students must use their prior knowledge of a chemical concept to draw conclusions from the data they have gathered. Thus, we argue that students in laboratory must possess synthesis-level abilities. When provided only a comprehensionlevel content background from lecture, how can students be expected to function at the synthesis level in laboratory? Piaget's theory of cognitive development is comprised of four levels: sensorimotor, preoperational, concrete operational, and formal operational (29). “Concrete operational” (29) learners require the use of tangible, physical objects to solve problems; that is, problem-solving abilities are based on students' manipulation of material objects. As one can deduce, at the “formal operational” (29) stage, students understand abstract ideas and think independently without the aid of manipulatives or corporeal objects. Piaget's theory has been applied to college chemistry students many times and has been discussed in the literature (1, 30, 31). From these ideas about the nature of learning, we hypothesized that students' understanding of solubility could be enhanced by the students' use of physical manipulatives to model, and thus visualize, atomic interactions occurring at the submicroscopic level. Our primary research questions follow: • Can students' conceptual understandings of solubility be enhanced by their participation in a conceptual, hands-on activity involving manipulatives?
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r 2009 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 1 January 2010 10.1021/ed800016f Published on Web 12/18/2009
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Research: Science and Education • Can a multilevel laboratory activity increase students' ability to transition through Johnstone's microscopic, macroscopic, and symbolic forms of chemical representations (3) more proficiently?
Study Demographics Participants were 141 first-semester general chemistry students (70 female, 71 male) at a large, primarily undergraduate institution in Tennessee. Data were collected during 3-h laboratory sessions approximately halfway through the semester after the corresponding material had recently been addressed in lecture. One laboratory section consisting of 37 students (18 female, 19 male) served as the control group, and three laboratory sections with a total of 104 students (52 female, 52 male) comprised the treatment group. Both control and treatment groups completed the same pretest prior to the activity. Students in the control group completed the laboratory entitled Introduction to Chemical Changes (9) and a posttest immediately after the activity, whereas participants in the treatment group completed a heavily modified version of Introduction to Chemical Changes (9) immediately followed by the posttest. The details of the pre- and posttests are described below. Methods Control Group Standard Laboratory After taking a pretest, students in the control group completed the unmodified procedure. Vermillion and White's Introduction to Chemical Changes (9) is a standard general chemistry laboratory activity on solutions in which students are asked to complete a reaction series and identify an unknown solution. In this activity, students witness displacement reactions by mixing known solutions and determining the chemistry that is taking place in their test tubes. Students observe precipitate formation in many of these reactions. At the end of the activity, students are provided an unknown solution and asked to determine its identity by combining it with known solutions used in the reaction series stage of the lab. The solubility of the unknown can be used to identify it, and thus, by comparing the observations of the unknown with known solutions to notes on precipitation during the reaction series, students are able to identify the unknown solution. Introduction to Chemical Changes (9) contains no visualization activities, but it does ask students to write complete and net ionic reaction equations. Treatment Group Laboratory Activities The treatment group was in laboratory the same amount of time as the control group. After the pretest, the treatment group lab activities began with two mini-lectures containing presentations and demonstrations by the first author (L.B.B.). With respect to submicroscopic interactions between water molecules and ions in solution, these mini-lectures moved conceptually from general to specific. The instructor first explained basic terminologies of solutions such as solvent, solute, and solution. Next, an ion-pair model that was made by attaching a wooden ball to a metal-filled Styrofoam ball with sugar “glue” (high concentration sugar solution that was allowed to dry) was shown to the students and then dropped into a 1-L beaker filled with water. With a stir, the sugar “glue” dissolved, and the ion pair 108
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separated. The heavier ball sank, and the lighter one floated. This demonstration was included to illustrate the physical separation of ions in solution. The sugar “glue” demonstration and mini-lecture was immediately followed by an explanation of a poster illustration depicting ions surrounded by water molecules, providing students with more detailed mental images of ions in solution. Students were given questions to answer during instructor demonstrations and were encouraged to complete them before moving to the activity stations, allowing their completed questions to serve as references in the following activities. After the instructor demonstrations and mini-lectures, which took approximately 15 min, the students then moved to stations in the lab to complete activities designed to build concepts of solubility at the macroscopic, microscopic, and symbolic levels. No more than five pairs of students were permitted at each station, and students were given ten minutes at each station. Questions were provided to guide students through station activities and reinforce concepts. Station 1 was developed to visually illustrate solvent effects using color. Two graduated cylinders were displayed: one with copper(II) sulfate, hexane, and water and another with iodine, hexane, and water. Students were provided graduated cylinders, hexane, iodine, water, copper(II) sulfate, and information (name and molecular structure) about each species and were then directed to replicate the models and determine which combinations of solutes and solvents replicated the examples. This station was also designed to illustrate that substances that do not dissolve in a solvent remain visible as solids, whereas soluble substances are not observed as solids. The educational goal of Station 2 aimed to illustrate submicroscopic modeling of solubility, in that water molecules surround ions in solution. Each student pair was given a box and a water molecule modeling kit (32). This kit contained model water molecules, cations, anions, and nonpolar molecules. The water molecules and the ions have magnets positioned inside them such that intermolecular forces can be simulated and the ions attract to the water molecules in the appropriate places. Using these models to represent water, sodium ions, chloride ions, and ethane, students observed water-ion and water-ethane interactions. Students placed the water kit pieces in the corners of a box and, upon shaking the box, were able to observe which molecules were attracted to each other and which were not. Finally, Station 3 taught students the symbolic representations of solubility by providing students the opportunity to practice writing complete and net ionic equations from molecular equations. Students also practiced reading solubility charts. After completion of the stations, treatment-group participants completed a modified version of Introduction to Chemical Changes lab (9), which included precipitation reactions, a reaction series, and identification of an unknown. At the end of the modified (reduced) Introduction to Chemical Changes (9) activity, treatment-group students completed the same posttest as the control group. Data Collection Quantitative data were collected from pre- and posttests completed by students before and after the lab station activities. To further explore students understandings of solubility, qualitative data were collected from free-response questions that
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Research: Science and Education
students were asked on a handout while completing station activities. The quantitative pre- and posttests asked similar questions, but were not identical to each other. Free-response sheets that were used to collect qualitative data also differed from the pre- and posttests, but addressed similar aspects of solubility. In the following section, both qualitative and quantitative data collection strategies will be discussed. Quantitative Data The goal in writing pre- and posttests was to evaluate Johnstone's levels (3) in the context of conceptual and technical skills. Both the pre- and posttests contained three questions, and each was aimed at one of Johnstone's (3) forms of representation. On the pretest, one multiple-choice question addressed Johnstone's microscopic level of representation (3) by asking students to choose which illustration best represented NaCl in water. Another question on the pretest assessed Johnstone's macroscopic level (3), asking students to provide a narrative explanation of a molecule being “in solution”. The last pretest question focused on Johnstone's symbolic level (3) and asked students to write ionic and net ionic equations for a given reaction. The posttest was similar to the pretest. One question asked students to draw how AgNO3 might look in solution, if viewed through a submicroscope, given symbols for Agþ, NO3-, and H2O, and thus addressed Johnstone's microscopic level of representation (3). A second question addressing Johnstone's symbolic level asked students to, again, write ionic and net ionic equations. This question was intentionally designed very similarly to the equation-writing question on the pretest to serve as a mode of direct comparison for gains from pre- to postassessments. Finally, the last posttest question asked students to define a precipitate and to describe how precipitates form, thus addressing Johnstone's macroscopic level (3). Qualitative Data Qualitative data were collected from free-response questions students answered during station activities. Figure 1 lists
the open-ended questions that were asked in the treatment activities. Data Analysis Quantitative Analysis For grading the pre- and posttests, a grading rubric for how partial credit of incorrect answers would be assigned was developed and agreed upon by both researchers. Pre- and posttests were graded exactly from the prespecified grading rubric. All preand posttests were graded by one researcher, and results were then discussed by the research team. Results of pre- and posttest scores of both groups were statistically compared to determine the effectiveness of a handson, concept-building activity on solubility comprehension, and a confidence level of pe0.05 was chosen for analysis by independent samples t-tests using SPSS statistical software. Because the treatment and control students came from a variety of lecture and laboratory instructors, an analysis of covariance was employed using the pretest score as the covariate, and the two groups were found to be comparable (F = 0.030; p = 0.864). Initial results of grading pre- and posttests revealed higher average posttest scores in the treatment group (control: 44.8; treatment: 58.4), and this difference was then shown to be statistically significant (t = 3.738, p = 0.001). The first research goal asked whether students' conceptual understandings of solutions could be enhanced by participation in hands-on activities, and the second research goal aimed to determine whether the treatment activities enhanced students' abilities related to Johnstone's three forms of representing chemical phenomena (3). Thus, question-by-question analysis of the pre- and posttests was conducted. Within both groups, raw scores for points earned on each of the three questions were tabulated and converted to percentages, since the pre- and posttests had different point values. In our design, two groups (treatment and control) took the same pre- and posttests. Because of this, the independent samples t-test was most appropriate. Individual pre- and posttest question scores for the macro,
Figure 1. Open-ended questions asked during treatment station activities.
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Research: Science and Education Table 1. Independent Samples t-Test Results for Control and Treatment Students' Scores at the Micro, Macro, and Symbolic Levels Control Representational level Micro Macro Symbolic
Test
Mean
Treatment SD
Mean
t-Test Valuesa
SD
p Values
Pretest
0.351
0.484
0.365
0.484
-0.152
0.880
Posttest
1.89
1.15
3.62
1.54
-6.210
