Development of the Enthalpy and Entropy in Dissolution and

Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Development of the Enthalpy and Entropy in Dissolution and Precipitation Inventory Timothy N. Abell and Stacey Lowery Bretz*

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Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States ABSTRACT: The Enthalpy and Entropy in Dissolution and Precipitation Inventory (E2DPI) has been developed to measure student understanding of the dissolution of ionic solutes, aqueous precipitation reactions, and the enthalpy and entropy changes that accompany these processes. The E2DPI was designed using a mixed-methods protocol, such that the questions on the instrument were grounded in the reasoning and explanations offered during the semi-structured interviews with general chemistry and physical chemistry students. The concept inventory was administered to general chemistry (n = 383), physical chemistry (n = 10), and biophysical chemistry students (n = 43) at one institution. The inventory was also administered at a second institution to students in a postorganic General Chemistry II course (n = 160). The validity and reliability of the data generated from the E2DPI were assessed using both qualitative and quantitative data. Some of the misconceptions assessed by the instrument and data indicating the prevalence of these ideas are presented. KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Upper-Division Undergraduate, Chemical Education Research, Physical Chemistry, Misconceptions/Discrepant Events, Testing/Assessment, Aqueous Solution Chemistry, Precipitation/Solubility, Thermodynamics FEATURE: Chemical Education Research

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INTRODUCTION Aqueous solutions are ubiquitous in the undergraduate chemistry curriculum. However, several studies have reported students’ struggles with explaining the formation of these solutions.1−11 Students think that reactions occur between ionic salts and water1−3,7,11 and that ionic molecular pairs exist in solution.5 Research studies have also reported students’ misconceptions related to the driving forces behind the dissolution and precipitation processes, enthalpy,10,12−14 and entropy.15−23 Students attribute enthalpy changes during bond breaking and formation to the fact that energy is stored in bonds.10,12−14 Meanwhile, students’ reasoning about entropy is largely limited to the analogy of disorder, focusing on surface features in chemical equations such as phase changes or counting the number of moles of reactants and products to describe changes in entropy.15−20,22 In addition to the abstract nature of these concepts, the representations used to depict chemistry are essential for students to learn in order to make connections among three different levels of representation: macroscopic, particulate, and symbolic.24,25 Experts can fluently use the “language” of chemistry and these representations, whereas novices struggle to do so.26 The research studies cited above were conducted using interviews with small sample sizes. Measuring the prevalence of these ideas among much larger samples of students requires a different form of assessment. The National Research Council27 (NRC) has called for assessments to be developed that are grounded in the findings of qualitative interviews with students (e.g., to create multiple choice measures with item distractors © XXXX American Chemical Society and Division of Chemical Education, Inc.

faithful to the language and thinking of the students who were interviewed). This is one approach to developing concept inventories.28 Other methods to develop concept inventories include using expert-generated items and distractors29 or gathering student ideas for distractors through open-ended questions.30 Regardless of the approach taken to developing an assessment, a researcher must be able to demonstrate that a concept inventory generates valid and reliable data for the population for which it was designed.31 Four concept inventories have been published that assess student knowledge about thermochemistry.32−35 The Thermal and Transport Science Concept Inventory35 and the Heat and Energy Concept Inventory32 were designed for engineering students and, therefore, do not align well with chemistry content. Both the Thermochemistry Concept Inventory34 and Thermal Concepts in Everyday Context33 assess student knowledge about the transfer of thermal energy but do not assess the additional thermodynamic concepts of entropy or spontaneity. No assessment tool exists to assess student understanding of the dissolution and precipitation processes (what) and the thermodynamic driving forces behind these processes (why). Received: March 1, 2019 Revised: July 17, 2019

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DOI: 10.1021/acs.jchemed.9b00186 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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Figure 1. Five phases of the interviews and the tasks students performed during each phase. Reprinted from ref 3. Copyright 2018 American Chemical Society and the Division of Chemical Education.

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The interview consisted of five phases (Figure 1). The first phase of the interview explored students’ prior knowledge through general questions about dissolution, precipitation, enthalpy, entropy, and spontaneity. Demonstrations were conducted with the students for the remaining four phases of the interview. Phases 2 and 4 asked the students to observe and explain the exothermic dissolution of magnesium chloride and the endothermic dissolution of silver nitrate in water, respectively. In phase 5, students combined the two solutions made in phases 2 and 4, resulting in the exothermic formation of a precipitate (silver chloride). Students attended to both visible and tactile changes in phases 2, 4, and 5. The demonstration in phase 3 asked students to add silver chloride solid to water but did not result in a noticeable visible or tactile change. During each phase of the interview, students were asked to explain their observations as well as answer questions regarding the spontaneity of each demonstration and any accompanying changes in enthalpy and entropy. Detailed findings from these interviews have been reported previously in this Journal.3,22

RESEARCH QUESTIONS In order to measure student understanding of dissolution and precipitation and the enthalpy and entropy changes that accompany these processes, a study was designed to answer three research questions: 1. How do students explain what happens when a. an ionic salt dissolves in water? b. an ionic compound does not visibly dissolve in water? c. a precipitate forms from the mixing of two aqueous solutions? 2. How do students reason about enthalpy, entropy, and spontaneity when explaining these phenomena? 3. What evidence exists for the validity and reliability of the data generated by the E2DPI? The findings for Research Questions 1 and 2 have been previously reported in this Journal.3,22 This manuscript reports the development of an assessment to measure student reasoning, along with evidence for the validity and reliability of the data generated by the measure, in order to answer Research Question 3.

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Limitations

The items on the E2DPI were created from interview tasks that focused on endothermic and exothermic dissolution of ionic solutes, a sparingly soluble ionic compound, and a precipitation reaction with two aqueous solutions of ionic solutes. The interviews did not examine student thinking with molecular solutes (e.g., sucrose), nor did they explore sparingly soluble equilibria via Ksp. Therefore, the E2DPI does not contain items that examine the thermodynamics of dissolution and precipitation with molecular solutes nor those that explore the extent of solubility via Ksp. The interviews did not address PV work with regard to enthalpy but instead focused on ΔH = qp. The interview guide did not intentionally explore the symbolic representation of the free energy equation, ΔG = ΔH − TΔS, although some students certainly invoked mathematics to try to reason through the tasks.22 Therefore, the E2DPI does not contain items that directly probe students’ mathematical reasoning regarding dissolution, precipitation, enthalpy, entropy, and spontaneity.

METHODS

Interview Sample

Students from General Chemistry (GC, n = 19) and two upperdivision courses, Physical Chemistry (PC, n = 7) and Biophysical Chemistry (BPC, n = 6) were interviewed after being taught and tested on the relevant material. GC students were interviewed during the second-semester of the first-year chemistry course. All students were enrolled at a medium-sized, midwestern university. Data collection was approved by an Institutional Review Board, and all participants were informed of their human subject rights. Students were compensated for their time with a nominal gift card. Interviews

Semi-structured interviews were conducted to better understand how students think about dissolution, precipitation, and the changes in enthalpy and entropy that accompany those processes. An interview guide was constructed to investigate connections between students’ macroscopic observations, both visual and tactile (temperature change), and their mental models of the particulate world.22 During the interview, students were provided with paper and a LiveScribe pen36 in order to generate representations as part of their explanations. All interviews were video and audio recorded, transcribed verbatim, and analyzed using a constant comparative method.37 The data was managed using NVivo11.38

Inventory Development

The students’ reasoning and understandings that were identified during the analysis of the interviews were used to develop questions and distractors for the Enthalpy and Entropy in Dissolution and Precipitation Inventory (E2DPI). The NRC’s suggestion of developing concept inventories grounded in student interview data was followed to ensure the face validity of the distractors developed for each item.27 Questions were written to focus upon (1) the mechanisms of both dissolution and precipitation and (2) the underlying thermodynamic driving forces (i.e., changes in enthalpy and entropy). For B



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Figure 2. Question from the E2DPI focusing on entropy changes, with the confidence scale.

example, Figure 2 depicts Question 15, which focuses on student understanding of how an entropy change occurs during a precipitation reaction. Each of the distractors (options A, B, and D) were developed from responses given by students in the interviews: Henry, BPC: I would probably say... [laughs] umm... one likely candidate would be water which could go from liquid to ions. Umm that could possibly be one thing. Jana, PC: [The surroundings are] becoming more random and disordered. Umm... it’s equal and opposite of the system [laughs]... whatever [entropy] was lost from the system went to the surroundings. Ryan, GC: But umm in the solution umm dumping in more particles umm that increases in the entropy because then there’s more things bouncing around in umm a space, in a small space. Students were asked to indicate their confidence in each answer by placing an “X” on a scale that followed each item (Figure 2). The scale ranged from 0% (just guessing) to 100% (absolutely certain, Figures 2 and 3). The confidence scale provides the instructor with information about the strength of the ideas held by the students. This scale was used over a Likert type scale in order to provide continuous data to be analyzed.39−41 Previous literature has referred to the confidence scale as a second tier to each item.42,43 However, the word “tier” in this manuscript refers to a pair of two items (including their confidence scales), not to one item and its confidence scale.

Figure 3. E2DPI item assessing student knowledge of the particulate representation of the products of a precipitation reaction.

E2DPI Administration

semesters of organic chemistry and then finally by one semester of General Chemistry II.44 Students responded to the inventory using paper and pencil by circling their answers and marking an “X” on each confidence scale. In all administrations, students answered the questions on the E2DPI after they had been taught and tested on dissolution, precipitation, and thermodynamics. The inventory required 15−20 min to complete.

The 28-question E2DPI was administered through three data collection opportunities at a medium-sized midwestern university (Institution 1) and a large, research intensive midwestern university (Institution 2). The inventory was first administered to students at Institution 1 who were enrolled in either physical chemistry (PC, n = 10) or biophysical chemistry (BPC, n = 43) at the beginning of the Spring 2018 semester. At the end of the Spring 2018 semester, the E2DPI was administered to second-semester general chemistry (GC II, n = 383) students at Institution 1. The E2DPI was also administered in Fall 2018 to students in a postorganic General Chemistry II course (PO-GC II, n = 160) at Institution 2, where the curriculum consisted of a 1:2:1 course sequence in which one semester of general chemistry was followed by two

Response Process Interviews

Response process interviews were conducted at Institution 1 with seven PC/BPC students approximately 2−3 weeks after administration. The purpose of these interviews was to ensure that students were properly interpreting the questions and that they were selecting the right answer for the right reasons.45 If one or both of these conditions were not met, then the item was C



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Table 1. Descriptive Statistics for the E2DPI GC II (n = 383)

PO-GC II (n = 160)

PC/BPC (n = 53)

Parameter

Items

Confidence (%)

Items

Confidence (%)

Items

Confidence (%)

Mean SD Median Minimum score Maximum score Cronbach α Ferguson δ

11.9 4.5 11 3 26 0.73 0.96

59.4 16.9 60.4 12.0 99.5

16.1 4.5 16 5 26 0.72 0.98

64.3 16.6 64.4 0.0 96.7

16.2 5.0 16 6 27 0.79 0.93

71.9 12.5 72.1 45.3 99.5

Figure 4. Total score distribution for GC II (blue), PO-GC II (red), and PC/BPC (gray). Note the differences in scale due to the large differences in sample sizes.

Classical test theory (CTT) was used to evaluate the data generated by the assessment. When using CTT historically, five statistical analyses were evaluated:46 (1) item difficulty (2) item discrimination (3) point biserial (4) reliability index (often Cronbach’s α) (5) Ferguson’s δ However, the literature has also suggested that these tests, namely, Cronbach’s α47 and Ferguson’s δ,48 be interpreted with caution because they presume an internal structure focused on one or more identifiable constructs. The construction of items using student thinking as distractors can pose a threat to the underlying assumptions of these tests.40,45 The distributions of scores for each of the three samples are shown in Figure 4. In order to assess the normality of each distribution, the Kolmogorov−Smirnov (K−S) test (Table 2)

revised on the basis of feedback from the students during the interviews with regard to how they interpreted the item stem and distractors. For example, option F was added to Question 14 (Figure 3) after the response process interviews because several students indicated that they were picking the correct answer only on the basis of the representation of the aqueous solution while ignoring the representation of the solid. Revising Question 14 to include option F required students to consider the representations of both the aqueous solution and the solid, thereby improving the validity of the conclusions drawn by the research team when analyzing students’ answer choices. The E2DPI was revised on the basis of interviews with the PC/BPC students and then administered to the GC II students at Institution 1 at the end of the semester. Nine more response process interviews were conducted with GC II students at Institution 1, but no further revisions were found to be necessary.

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Table 2. Kolmogorov−Smirnov Test Statistics

RESULTS AND DISCUSSION

Descriptive Statistics

The final version of the E2DPI had 28 items, including four twotiered answer-reason items.29 The E2DPI was scored from 0 to 28 (“1” for correct and “0” for incorrect). Each tier was scored separately, as each question had its own associated confidence (i.e., students’ confidence ratings regarding each item in a twotiered pair need not be necessarily equal). Table 1 shows the descriptive statistics for the GC II students, PO-GC II students, and PC/BPC students. The PC (m̅ = 14.6, SD = 5.15) and BPC (m̅ = 16.6, SD = 4.93) student data were combined because a two-tailed independent samples t-test suggested that the samples were not significantly different (t(51) = −1.14, p = 0.262).

Sample

K−S Statistic

df

p-Value

GC II PO-GC II PC/BPC

0.122 0.069 0.060

383 160 53

0.00 0.124 0.200

was conducted.49 The null hypothesis for the K−S test is that the distribution of interest is equivalent to a normal distribution; therefore, a p-value greater than 0.05 indicates that the distribution is not significantly different than a normal distribution. The PO-GC II and PC/BPC data were normally distributed, whereas the GC II data were not. The GC II score distribution was right skewed, meaning the inventory was difficult for the majority of students, although many students achieved higher scores. This demonstrates that the assessment is D



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Figure 5. Comparisons of total scores and average confidences for GC II (blue), PO-GC II (red), and PC/BPC (gray). Lines are placed at the halfway point on each scale.

Figure 6. Difficulty and discrimination of each item for the GC II, PO-GC II, and PC/BPC samples.

not too difficult for the target population. Ferguson’s δ was calculated (Table 1) to assess the discriminatory ability of the instrument.50 A Ferguson’s δ > 0.9 denotes a large distribution of scores across the range of total possible scores. All three samples of students had satisfactorily large δ values, meaning that the students earned a range of multiple scores among the possible scores. It is important to note that Ferguson’s δ does not differentiate between differences due to student performance and differences due to measurement error.48 Comparing students’ scores to their average confidences (Figure 5) showed that 47% of GC II students, 20% of PO-GC II students, and 28% of PC/BPC students overestimated their knowledge. Each sample had students that averaged above 50% confidence on the assessment yet answered fewer than half of the items correctly. Overconfidence about one’s own knowledge, known as the Dunning−Kruger effect,51 has been previously reported in other research regarding chemistry students.52,53 Our data suggest that as students have more experience with chemistry they are better able to gauge their understanding of chemistry content, with 26% of GC II students, 64% of PO-GC II students, and 66% of PC/BPC students averaging more than 50% confidence and answering at least 14 items correctly. Few students in each of the samples (3% GC II, 6% PO-GC II, and 4% PC/BPC) reported confidence below 50% while scoring above 50% on the assessment. Cronbach α values were calculated to examine the internal consistencies of the scores for the three samples. A Cronbach α > 0.7 is typically interpreted to mean that the assessment items are internally consistent.54 For all three samples, the calculated α was greater than 0.7 (Table 1), suggesting evidence for the internal consistency of student responses to this instrument. For

instruments like the E2DPI, however, the α value should be interpreted with caution because the instrument is designed to measure students’ misconceptions, meaning that students may not be using coherent ideas when responding to each item.40,45,47 Concurrent Validity

The total scores of the GC II and PC/BPC students were compared to examine the extent to which the E2DPI can differentiate between these two groups of students (concurrent validity).55 Concurrent validity was assessed because, theoretically, it would be expected that students with more instruction regarding the chemistry content as measured by the E2DPI (namely, the PC/BPC students) ought to perform better when compared with students with less instruction (i.e., the GC II students). The comparison was made only between the two samples from Institution 1 because the PC/BPC students were presumed to have had course sequences and GC II instruction similar to those of the GC II sample. This cross-sectional comparison has been used before in other studies to compare general chemistry and organic chemistry students from the same institution.17,56 The mean total score for the PC/BPC students (16.2 ± 5.0) was significantly higher than the mean for the GC II students (11.9 ± 4.5), as determined by a two-tailed independent samples Mann−Whitney U test [U = 5158.5, p < 0.001 with η2 = 0.078 indicating a small effect size]. This result suggests that the E2DPI can distinguish between theoretically different groups of students, providing concurrent validity to the results. E



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E2DPI Item Function

spontaneity (Figure 7). The performances of the three student samples on each category of items can be found in Table 3. Two

The items on the E2DPI were analyzed using classical test theory by calculating item difficulty, discrimination, and point biserial correlations. Item difficulty and discrimination are depicted in Figure 6. Item difficulty (p) is the proportion of students who answered an item correctly, meaning that a higher difficulty value indicates an easier item. Acceptable values are typically 0.3 < p < 0.8.46 As can be seen in Figure 6, a wide range of item difficulties were calculated across all samples of students. A few items were easy (p > 0.8) for the PO-GC II students and for the PC/BPC students. However, none of the items were easy for the GC II students, and quite a few were difficult (p < 0.3). This analysis is consistent with the students’ overall performance on the assessment. Figure 6 also indicates how well each item discriminates between the top and bottom performing students.45,46 Discrimination (D) is determined by calculating the difference between the percentage of items answered correctly by the top 33% of students and the percentage answered correctly by the bottom 33% of students.57 The top and bottom performing students are determined on the basis of their overall scores on the inventory. Discrimination values can range from −1 to 1, where a positive number indicates that the top third of students answered a question correctly more often than the bottom third of students. Values of D > 0.3 are considered highly discriminating.45,46 Items that are considered difficult (p < 0.3) or easy (p > 0.8) are likely to have low D-values because almost all students answered the items incorrectly or correctly, respectively. Item 24, for example, was difficult for both the GC II and PC/BPC samples but not for the PO-GC II sample. Item 24 asked students to select the best definition of entropy, and 62.4, 54.7, and 47.5% of the GC II, PC/BPC, and PO-GC II students selected the response “disorder”, respectively. Only 17% of GCII students, 30.2% of PC/BPC students, and 48.1% of PO-GCII students chose the correct answer pertaining to microstates. Inspection of Figure 6 reveals that a few items for each sample were neither hard nor difficult, yet these items did not discriminate well because higher performing students hold misconceptions that are detected by those items. Such items are particularly important for an instructor in order to know which misconceptions are strongly held by even the top performing students. Item reliability was calculated using point biserial correlations (ρbis) between an item’s score (correct = 1, incorrect = 0) and the overall score on the instrument. Typically, ρbis ≥ 0.2 are acceptable.46 The majority of the items met or exceeded this threshold for all three samples. The few items that did not meet the acceptable correlation were those items with lower discriminatory power for each sample. The low ρbis values for such items can be explained by the fact that even higher performing students were attracted to the incorrect distractors for those items.

Figure 7. Question assessing student knowledge of the relative strengths of hydrogen bonds and covalent bonds.

items assess student understanding of particulate representations, and six items provide students with tactile, macroscopic information (hot vs cold) that they are asked to explain at a particulate level. Cutting across each of these categories of questions (dissolution, precipitation, and no context) are questions about changes in enthalpy, changes in entropy, and spontaneity. Six of the dissolution and seven of the precipitation items specifically focus on changes in enthalpy and changes in entropy that occur (Figure 2). Five items assess student understanding of enthalpy, entropy, and spontaneity without any specific context. This includes items like defining entropy and determining the changes in enthalpy and entropy that are required for a process to be spontaneous at all temperatures. The performances of the three samples on the items related to enthalpy, entropy, and spontaneity can be found in Table 4. The items that were not in the context of dissolution or precipitation, the easiest category of items for each sample, had the highest percentage of students getting all of the items correct (Table 3). For the items that addressed enthalpy, entropy, and spontaneity, a quarter of the PO-GC II students answered all five items correctly (Table 4), outperforming both the GC II and PC/BPC samples. An example of an item from this category is Question 23 (Figure 7), which asks students about the relative strengths of covalent bonds and hydrogen bonds. The distribution of all three sample’s responses to Question 23 can be found in Figure 8. Fifty-eight percent of GC II students, 71% of PO-GC II students, and 87% of PC/BPC students selected the correct answer (option A). The PC/BPC students did not appear to hold the misconception measured by this question, whereas 22% of GC II students and 15% of PO-GC II students thought that hydrogen bonds between water molecules were stronger than the covalent bonds within a water molecule (option B). For the precipitation items, the mode for GC II was 3, with none of the students getting all nine items correct. PO-GC II had a mode of 5, and PC/BPC had a mode of 4, with 1.9% of both samples correctly answering all nine items that were set in the context of precipitation reactions. A larger percentage of both GC II and PO-GC II students answered all items correctly when

Misconceptions Measured by the E2DPI

The 28 items for the E2DPI examine student knowledge about enthalpy, entropy, and spontaneity either (1) within the context of dissolution (12 items) or precipitation (9 items) or (2) absent any specific context (7 items). For example, the dissolution items and precipitation items assess student knowledge about what attractions are broken and formed during these processes and how to best represent the particles present in the solution (Figure 3). The remaining seven items are conceptual questions related to intermolecular forces, enthalpy, entropy, and F



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Table 3. Categories of Items and Descriptive Statistics for All Samples GC II (n = 383) Category (Number of Items) Dissolution (12) Precipitation (9) Concepts without context (7)

PO-GC II (n = 160)

Mode

Students Answering All Items Correctly (%)

3 3 3

1.6 0.0 3.4

PC/BPC (n = 53)

Mode


Mode


6 5 5

0.6 1.9 21.3

6 4 4

7.5 1.9 11.3

Table 4. Enthalpy, Entropy, and Spontaneity Items by Category and Descriptive Statistics for All Samples GC (n = 383)

PO-GC II (n = 160)

PC/BPC (n = 53)

Subcategory (Number of Items Per Category)

Mode


Mode


Mode


Enthalpy, entropy, and spontaneity within the context of dissolution (6) Enthalpy, entropy, and spontaneity within the context of precipitation (7) Enthalpy, entropy, and spontaneity without context (5)

2

3.7

2

8.8

2

13.2

3

1.0

3

7.5

3

1.9

2

5.5

4

25.6

2

11.3

increase in the percentage of students answering all items correctly for the items related to spontaneity or changes in enthalpy or entropy means that some students in each sample struggled with the items related to the dissolution process, but they were able to correctly answer the items related to thermodynamics of the dissolution process. An example of an incorrect idea held by all three samples related to the dissolution process can be seen in the students’ responses to Question 1 (Figure 10). Responses to Question 1 (Figure 11) indicate that 62% of GC II, 36% of PC/BPC, and 21% of PO-GC II students thought that hydrochloric acid and magnesium hydroxide (or magnesium oxide) were formed in a reaction between magnesium chloride and water (Figure 10). The PO-GC II students were better able to recognize the symbolic representation of the dissolution process than the other two student samples, but almost a quarter of the PO-GC II students still thought that a reaction had occurred.

Figure 8. Distribution of student responses to Question 23 for all three samples.

the items that did not ask about spontaneity or changes in enthalpy or entropy were removed (Table 4). However, there were no PC/BPC students who correctly answered the seven items dealing with spontaneity or changes in enthalpy and entropy and did not also answer all nine precipitation items correctly. This means that the precipitation process items were just as challenging as the thermodynamic items in the context of precipitation for the PC/BPC students. The precipitation item that all three samples struggled with the most was Question 15 (Figure 2). When asked to explain how the entropy of the surroundings increased during a precipitation reaction, almost 40% of the GC II students and 30% of the PO-GC II students thought that entropy could be transferred, and even after a full semester of thermodynamics, 30% of the PC/BPC students still held this idea (Figure 9). These responses indicate that many chemistry students do not understand the nature of entropy nor the connection between entropy and energy. For all of the dissolution items, both the PO-GC II sample and the PC/BPC sample had modes of 6, whereas the mode for the GC II sample was only 3. The PC/BPC sample had the highest proportion of students answering all 12 items correctly. The

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CONCLUSIONS AND IMPLICATIONS FOR TEACHING This article describes the development of an assessment to measure students’ misconceptions about the dissolution and precipitation processes, the enthalpy and entropy changes that accompany these processes, and the concept of spontaneity in the context of these processes. The instrument was developed using students’ reasoning and explanations from semistructured interviews. The E2DPI generated valid and reliable data for both GC II and PC/BPC students at a single institution and can detect misconceptions in both samples. The instrument also generated valid and reliable data from a second institution (POGC II) with a different course sequence than Institution 1, thereby adding to the reliability of the data generated by this instrument. The absence of a ceiling effect (numerous perfect scores) or floor effect (numerous scores of zero) across the three samples indicated that the items were collectively neither too easy nor too difficult for these students. The E2DPI can be used by instructors as a formative assessment and only requires 15−20 min to administer. For example, faculty who teach general chemistry might administer the instrument to measure the prior knowledge that students bring from high school regarding dissolution and precipitation and the thermodynamics underlying these processes. Likewise,

Figure 9. Distribution of student responses to Question 15 for all three samples. G



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Figure 10. Question assessing student knowledge on the symbolic representation of dissolving magnesium chloride.

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ACKNOWLEDGMENTS This material is based in part upon work supported by the National Science Foundation under award number 1432466. We thank the students and faculty who volunteered to participate in this study.

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Figure 11. Distribution of student responses to Question 1 for all three samples.

(1) Naah, B. M.; Sanger, M. J. Investigating Students’ Understanding of the Dissolving Process. J. Sci. Educ. Technol. 2013, 22 (2), 103−112. (2) Smith, K. C.; Nakhleh, M. B. University Students’ Conceptions of Bonding in Melting and Dissolving Phenomena. Chem. Educ. Res. Pract. 2011, 12, 398−408. (3) Abell, T. N.; Bretz, S. L. Dissolving Salts in Water: Students’ Particulate Explanations of Temperature Changes. J. Chem. Educ. 2018, 95 (4), 504−511. (4) Kelly, R. M.; Jones, L. L. Exploring How Different Features of Animations of Sodium Chloride Dissolution Affect Students’ Explanations. J. Sci. Educ. Technol. 2007, 16 (5), 413−429. (5) Kelly, R. M.; Jones, L. L. Investigating Students’ Ability To Transfer Ideas Learned from Molecular Animations of the Dissolution Process. J. Chem. Educ. 2008, 85 (2), 303−309. (6) Kelly, R. M.; Barrera, J. H.; Mohamed, S. C. An Analysis of Undergraduate General Chemistry Students’ Misconceptions of the Submicroscopic Level of Precipitation Reactions. J. Chem. Educ. 2010, 87 (1), 113−118. (7) Ebenezer, J. V.; Erickson, G. L. Chemistry Students’ Conceptions of Solubility: A Phenomenography. Sci. Educ. 1996, 80 (2), 181−201. (8) Teichert, M. A.; Tien, L. T.; Anthony, S.; Rickey, D. Effects of Context on Students’ Molecular-Level Ideas. Int. J. Sci. Educ. 2008, 30 (8), 1095−1114. (9) Smith, K. J.; Metz, P. A. Evaluating Student Understanding of Solution Chemistry through Microscopic Representations. J. Chem. Educ. 1996, 73 (3), 233−235. (10) Ebenezer, J. V.; Fraser, D. M. First Year Chemical Engineering Students’ Conceptions of Energy in Solution Processes: Phenomenographic Categories for Common Knowledge Construction. Sci. Educ. 2001, 85 (5), 509−535. (11) Valanides, N. Primary Student Teachers’ Understanding of the Particulate Nature of Matter and Its Transformations During Dissolving. Chem. Educ. Res. Pract. 2000, 1 (2), 249−262. (12) Boo, H. K. Students’ Understandings of Chemical Bonds and the Energetics of Chemical Reactions. J. Res. Sci. Teach. 1998, 35 (5), 569− 581. (13) Galley, W. C. Exothermic Bond Breaking: A Persistent Misconception. J. Chem. Educ. 2004, 81 (4), 523−525. (14) Teichert, M. A.; Stacy, A. M. Promoting Understanding of Chemical Bonding and Spontaneity through Student Explanation and Integration of Ideas. J. Res. Sci. Teach. 2002, 39 (6), 464−496. (15) Carson, E. M.; Watson, J. R. Undergraduate Students’ Understandings of Entropy and Gibbs Free Energy. Univ. Chem. Educ. 2002, 6, 4−12.

faculty who teach physical chemistry might do the same to see what prior knowledge their students bring forward from their first two years of undergraduate chemistry. The instrument could also be administered postinstruction to characterize learning and what material students still struggle with after instruction. The data gathered can help teachers iterate on how to improve instruction. Data from this instrument, in aggregate with our previously published, rich descriptions of students’ explanations of their observations about dissolution, insolubility, and precipitation,3,22 suggest that students would benefit from additional opportunities to connect sensory information with representations in the particulate domain of dissolution and precipitation. This instrument was administered to students from only two institutions. Further research with a larger sample of students from multiple institutions should be conducted. Although the data from this instrument were shown to be valid and reliable for the samples of students to whom it was administered, this may not be true for all samples of students. The validity and reliability of the data should be assessed with each administration of the instrument.31 Any colleague interested in a copy of the E2DPI for use in their classroom or for research purposes should contact the corresponding author.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Stacey Lowery Bretz: 0000-0001-5503-8987 Notes

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