Analysis of post-secondary instructors’ pedagogical content knowledge of organic acid–base chemistry using content representations
J. R.
Boothe
a,
E. K.
Zotos
b and
G. V.
Shultz
*b
aUniversity of Pittsburgh at Greensburg, 150 Finoli Drive, Greensburg, Pennsylvania 15601, USA. E-mail: jrb270@pitt.edu
bUniversity of Michigan, Department of Chemistry, 930 North University Avenue, Ann Arbor, Michigan 48109, USA. E-mail: gshultz@umich.edu
First published on 6th January 2023
Abstract
Acid–base chemistry is a foundational concept for organic chemistry, and the complexities in teaching and learning acid–base chemistry are well documented. This study aimed to investigate post-secondary instructors' pedagogical content knowledge (PCK) for teaching acid–base chemistry in an organic chemistry context. Two groups of three graduate teaching assistants and one group of three faculty instructors constructed content representations (CoRes). The three CoRes generated by these groups were qualitatively analyzed and organized into a summary compiled CoRe. Analysis of the compiled CoRe revealed eight major concepts of organic acid–base chemistry as defined by these instructors. Three major concepts were identified as foundational definitions, and five were identified as concepts that build upon these definitions. We arranged all eight concepts into a progression. Analysis of the compiled CoRe also revealed that instructors primarily leverage students’ prior knowledge when teaching acid–base chemistry. Our results serve as a reference for organic chemistry instructors and may inform further research on the instruction of organic chemistry.
Introduction
The chemistry of acids and bases forms the foundation upon which much of the content in introductory organic chemistry is built. Prior studies investigating acid–base chemistry in organic contexts underscore its importance in the development of mechanistic reasoning and the understanding of rational reaction intermediates and products (Bhattacharyya and Bodner, 2005; Ferguson and Bodner, 2008; Grove et al., 2012a, 2012b). Despite the importance of this topic, students often struggle with the key concepts (e.g., Lewis acid–base theory, estimation of pKa, etc.) and with using their knowledge of acid–base chemistry in critical thinking and problem-solving contexts (Cros et al., 1986; Shaffer, 2006; Orgill and Sutherland, 2008; Cooper et al., 2016; Flynn and Amellal, 2016).To date, studies of knowledge for teaching have focused mainly on high school teachers and demonstrate that teachers also struggle with chemistry content (Quílez-Pardo and Solaz-Portolés, 1995; Bradley and Mosimege, 1998; Bannerjee, 2007; Damanhuri et al., 2016), which may in turn impact student learning in a way that persists through undergraduate courses. This impact may present additional challenges to these students (Demerouti et al., 2004; Shaffer, 2006; Watters and Watters, 2006; Bannerjee, 2007; Anderson and Bodner, 2008; Orgill and Sutherland, 2008; Bhattacharyya, 2014) and their post-secondary instructors. Compounding the issues associated with an undergraduate-level understanding of subject matter is the inherent limitation of student-professor interactions in many large-enrollment courses at doctoral-granting institutions. Large-enrollment courses, such as introductory organic chemistry, often involve a central lecture course (typically led by a professor or post-doctoral instructor) with additional course time spent in discussion or office hours with a graduate student teaching assistant. Graduate teaching assistants often have more face time with undergraduates and thus play an important role in undergraduate education (Lawrenz et al., 1992). Relatively few studies have investigated the chemistry teaching knowledge of faculty members (Carr, 1984; Nakhleh and Krajcik, 1994; Maeyer and Talanquer, 2010; McClary and Talanquer, 2011a, 2011b; Bretz and McClary, 2015; Gibbons et al., 2018) and even fewer have involved graduate students (Bond-Robinson, 2005; Hale et al., 2016; Connor and Shultz, 2018; Zotos et al., 2020). None of these studies have explicitly focused on organic acid–base chemistry.
A better understanding of faculty members’ and graduate teaching assistants’ knowledge for teaching is critical for improving undergraduate instruction (Luft et al., 2004; Bhattacharyya, 2006; Baumgartner, 2007; Reeves et al., 2016; Wheeler et al., 2017). In this study, we investigated post-secondary instructors’ pedagogical content knowledge (PCK) of organic acid–base chemistry by having groups of instructors construct content representations (CoRes) on this topic (Berry et al., 2009; Bertram and Loughran, 2012; Chordnork and Yuenyong, 2014).
This study was guided by two research questions about the PCK of chemistry faculty and graduate teaching assistants:
1. What do post-secondary instructors perceive to be the important topics in acid–base chemistry for first-semester organic chemistry students to learn?
2. What aspects of PCK are revealed as post-secondary instructors assemble content representations for organic acid–base chemistry?
We answer these questions using a qualitative analysis of CoRes generated by groups of post-secondary instructors and characterize the critical topics to inform studies on student learning and the design of pedagogical tools and learning environments supporting learning in organic chemistry. We also characterize the PCK portrayed by participants to build on our understanding of knowledge for teaching postsecondary chemistry.
Background
Acid-base chemistry in an organic context
The chemistry of acids and bases forms the groundwork for understanding much of organic chemistry. A working knowledge of acid–base chemistry is essential for a range of skills including predicting of reaction products and the diagnostic mindset required to solve complex mechanistic problems (Bhattacharyya and Bodner, 2005; Anderson and Bodner, 2008; Ferguson and Bodner, 2008; Grove et al., 2012a, 2012b; Bhattacharyya, 2013; Bhattacharyya, 2014). According to the ACS guidelines, three of the eleven conceptual topics of organic chemistry are directly related to acid–base chemistry, including concepts of (a) Lewis and Brønsted–Lowry acid–base chemistry, (b) methods of activation—including Lewis and Brønsted–Lowry acid–base chemistry, free radical chemistry, organometallic chemistry—and (c) addition, elimination, substitution, and rearrangement mechanisms—classes of reactions that are frequently discussed in the context of acidity and basicity (American Chemical Society, 2015). The same report found the acidity and basicity of organic compounds to be one of eight topics essential to constructing one-semester foundational courses. Although an understanding of acids and bases is viewed as a foundational concept for learning chemistry—alongside contributing substantially to organic chemistry reasoning skills (Graulich, 2015)—reports demonstrate that students and teachers at multiple levels have difficulty with learning and teaching acid–base chemistry. acid–base chemistry is generally considered challenging due to many complex factors, ranging from those related to molecular structure (e.g., steric hindrance, resonance, and inductive effects) to distinct environmental factors (e.g., solvent and presence or absence of catalysts). As a result, efforts by the chemistry education community to better understand student and instructor perspectives on this topic are ongoing and numerous (Carr, 1984; Hand, 1989; Ross and Munby, 1991; Demerouti et al., 2004; McClary and Talanquer, 2011a).Various curricular paths leading up to college-level organic chemistry may contribute to the difficulty of teaching and learning acid–base concepts within an organic chemistry course. As an illustrative example, Paik (2015) reported that instruction of acids and bases at the secondary level often involves three definitions: Arrhenius, Brønsted–Lowry, and Lewis. When taught sequentially, students often rely on the earliest acid–base definition learned to inform subsequent definitions, which can lead to confusion, misconceptions, and conflict with the emphasis of these models presented within textbooks—ultimately increasing the difficulty of instructing this topic (Tobin et al., 1994; Dreschler and Schmidt, 2005).
While some students attend institutions that provide organic-first instruction (Coppola et al., 1997; Ege et al., 1997; Reingold, 2001; Reingold, 2005; Malinak et al., 2014), many students at the post-secondary level enroll in general or analytical chemistry courses as prerequisites for organic chemistry. Prerequisite courses often emphasize the calculations surrounding acid–base chemistry (e.g., pH, buffer, and titration calculations) and move away from conceptual approaches to acid–base models (Shaffer, 2006; Watters and Watters, 2006; Orgill and Sutherland, 2008). An increased emphasis on calculations and shifting between three acid–base models introduces difficulties for students throughout their time in chemistry classrooms. The confluence of these difficulties—alongside a simultaneous decrease in conceptual understanding—is thought to give rise to many alternative student conceptions (Carr, 1984; Cros et al., 1986; Nakhleh and Krajcik, 1994; Maeyer and Talanquer, 2010).
Once students matriculate to organic chemistry, acid–base chemistry is often re-taught (and re-learned) to suppress the influence of any alternative conceptions students may have, thus re-orienting them to the Lewis and Brønsted–Lowry definitions of acid–base chemistry that form a foundation for understanding organic reactions. The ACS Examinations Institute devised a concept map of ten anchoring concepts taught throughout second-year organic chemistry courses based on an analysis of previous ACS exams. The ten anchoring concepts are categorized by: (1) atoms, (2) bonding, (3) structure and function, (4) intermolecular reactions, (5) chemical reactions, (6) energy and thermodynamics, (7) kinetics, (8) equilibrium, (9) experiments, measurement, and data, and (10) visualization. The concept map was created to support instructors in identifying “how test items measure specific content in terms of students' knowledge and do so in a way that can assist in the development of models for student learning across time” (Raker et al., 2013a, 2013b, p. 1444). While the Anchoring Concepts Concept Map spans the organic chemistry curriculum, many of these concepts include acid–base chemistry knowledge.
Stoyanovich et al. (2015) analyzed organic chemistry textbooks and complex reactions to identify the most important learning outcomes related to introductory organic acid–base chemistry. They describe 25 intended learning outcomes and categorize them into six categories: definitions, mechanism-related, most/least acidic proton or most/least basic atom, equilibrium concepts, using pKas, and “other.” As described by Stoyanovich et al., these intended learning outcomes can inform the teaching and assessment of organic acid–base chemistry taught in introductory organic chemistry courses.
From a student learning perspective, conceptual reasoning in organic acid–base chemistry is an area of great interest in the chemistry education community (Flynn and Amellal, 2016; Cooper et al., 2016). Chi et al. consider conceptual change from ‘matter’ to ‘process’ (i.e., shifting between discrete ontological categories) a particularly challenging learning process (Chi et al., 1994). Difficulties with the alternative conceptions of acid–base chemistry in different courses exacerbate this already challenging process, and research into organic chemistry students’ conceptions of acid–base chemistry remains prevalent in the literature (Cartrette and Mayo, 2011; McClary and Talanquer, 2011b; Bretz and McClary, 2015; Stoyanovich et al., 2015; Cooper et al., 2016; Dood et al., 2018; Schmidt-McCormack et al., 2019; Petterson et al., 2020). Given the challenges inherent to learning organic acid–base chemistry, alongside the challenges of instruction, we sought to interview graduate students and faculty to determine their PCK of this material.
Pedagogical content knowledge
Instructors possess a unique form of knowledge for teaching described by a model called pedagogical content knowledge (PCK). As described in Shulman's (1986) seminal work Those Who Understand: Knowledge Growth in Teaching, instructor knowledge is differentiated among three categories: subject matter knowledge, PCK, and curricular knowledge, where PCK includes knowledge of strategies to represent and communicate content so that it is most understandable to learners. Since its first conceptualization by Shulman (1986, 1987), active research in PCK has led to evolving definitions and conceptions, including several in the field of science education (Magnusson et al., 1999; Park and Oliver, 2008) and comprehensive reviews (Chan and Hume, 2019). A unifying feature of PCK studies is that PCK goes beyond content knowledge (i.e., subject matter knowledge) and is specific to a topic and a grade level (Wilson et al., 2002). Instructors need not only expertise about the subject being taught, but also teaching knowledge including knowledge of student understanding, instructional strategies, and representations that assist in student learning.Knowledge of student understanding requires an awareness of students’ prior knowledge of a topic (i.e., what they come to class knowing already), common student difficulties in the topic, and various ways students think about a topic (Ball et al., 2008; Magnusson et al., 1999; Park and Oliver, 2008). Instructional strategies and representations include visual representations, analogies, as well as activities or other approaches that facilitate student learning (Depaepe et al., 2013). Additionally, chemistry instructors that are aware of students’ prior knowledge of the Arrhenius definitions often recognize both the strengths and limitations of this approach, and help students to adjust to the Brønsted–Lowry and/or Lewis acid–base definitions instead.
A recent summit on PCK (Hume et al., 2019) expanded on PCK by defining three realms of PCK: enacted PCK (the knowledge and skills used by an instructor while teaching), personal PCK (an individual teacher's set of PCK and skills that are drawn upon while teaching), and collective PCK (cPCK; PCK that is shared among a group of professionals). As stated by Carlson and Daehler (2019), collective PCK “represents a continuum of knowledge held by a group that extends beyond what is in the literature and recognizes that knowledge about science teaching is also developed within school districts, school sites, departments, grade-level teacher teams, and professional learning communities” (p. 89).
In our investigations, we became interested in the cPCK conceptions of instructors at doctoral-granting institutions to gain greater insight into how this topic may be taught in this institutional context. Several studies have focused on PCK for specific instructional topics to improve teacher resources at the primary and secondary levels (Cochran, 1993; Rollnick et al., 2008; Mavungha, 2014; Rollnick and Mavungha, 2015). However, only more recently are investigations into the topic-specific PCK of post-secondary instructors gaining traction (Bond-Robinson, 2005; Wagner et al., 2007; Padilla et al., 2008; Padilla and Van Driel, 2011; Padilla and Van Driel. 2012; Maries and Singh, 2013; Hale et al., 2016; Connor and Shultz, 2018; Schultz et al., 2018; Lawrie et al., 2019; Lutter et al., 2019; Zotos et al., 2020; Zotos et al., 2021).
Post-secondary instructors’ topic-specific knowledge
Early experiences of teaching in graduate school tend to inform future faculty members’ instruction (Brownell and Tanner, 2012). Graduate students at research-intensive institutions wear many hats throughout their post-secondary degree programs, including researcher, instructor, and student. Professional development programs are not universally offered at the graduate level (Luft et al., 2004; Baumgartner, 2007; Oleson and Hora, 2014; Reeves et al., 2016; Wheeler et al., 2017), despite reports demonstrating that 52% of science-related doctorate recipients report a desire to pursue careers in academia (DeHaan, 2005; National Science Foundation, 2017; Woolston, 2017).Like graduate students, faculty members face multiple responsibilities beyond instruction, including outreach, grant writing, and committee service responsibilities. Faculty may not fully utilize professional development programs at the post-secondary level. These offerings vary widely depending on the institution. Because faculty members were once graduate students themselves, the systemic disconnect between the development of research skills and the development of pedagogical skills persists—in some cases, throughout entire careers (Wright, 2005).
Owing to the relative dearth of instructional professional development programs for these groups, many faculty, and graduate students must rely on their content knowledge and their own prior experiences as students to lead their lecture or laboratory sections (Zotos et al., 2020). While some studies show that instructors with higher levels of content knowledge have greater classroom adaptability, corresponding with greater overall PCK (Davis and Petish, 2005; Rollnick et al., 2008; Abdo and Taber, 2014), other studies indicate that content knowledge does not guarantee PCK (Hale et al., 2016; Connor and Shultz, 2018). Furthermore, graduate students are reported to struggle with content knowledge of introductory chemistry topics such as acid–base chemistry (Bhattacharyya and Bodner, 2005; Bhattacharyya, 2006). It follows that this may cause additional struggles with performing their teaching duties, ultimately leading to downstream effects on undergraduate conceptions of acid–base chemistry. Undergraduate STEM instructors have been called upon to alter their pedagogical approach (Freeman et al., 2014), requiring expertise (Andrews et al., 2011) alongside knowledge of instructors’ current conceptions to enact this change effectively. Due to the importance of maintaining integrity in the factual correctness of our instructors at this level, we focused on the topic-specific PCK of post-secondary instructors’ acid–base chemistry in organic contexts.
Theoretical framework
We rely on the PCK framework put forth by Park and Oliver (2008), because it is well-aligned with the Content Representation categories completed by participants in this study. While the refined consensus model provides a current and comprehensive framework for pedagogical content knowledge (Hume et al., 2019), the analysis reinforced the connection between Park and Oliver's (2008) framework and the themes present in our collected data.Park and Oliver acknowledged the difficulties with defining PCK, especially when considering various instructional factors—like student characteristics and context—that increase the specificity of instructors’ PCK. The authors argue that instructors within specific groups of educational stakeholders, researchers, teacher educators, or others may interpret PCK differently and thus construct different meanings of PCK (Park and Oliver, 2008). Upon re-examination of constructs of PCK with instructors, the authors further refine collective PCK for science instruction as being a set of interwoven characteristics that both influence and are influenced by the instructors’ reflection-in-action and reflection-on-action (Park and Oliver, 2008). Five components of science teacher PCK described by Park and Oliver—(1) orientation to teaching science, (2) knowledge of instructional strategies and reform, (3) knowledge of students, (4) knowledge of curriculum, and (5) knowledge of assessment—are also influenced by and influence the sixth component: teacher efficacy (i.e., teacher confidence in their ability to instruct successfully). Using this framework, we sought to investigate faculty and graduate student PCK of acid–base chemistry within organic contexts.
Methods
Content representations (CoRes)
Loughran et al. (2006) previously investigated instructor PCK through the generation and analysis of one or more components of a Resource Folio consisting of CoRes and Pedagogical and Professional-experience Repertoires (PaP-eRs). CoRes provide a wealth of detailed information regarding instructor knowledge and beliefs about the big ideas and concepts that comprise a given topic, as well as instructor knowledge and beliefs about student understanding of these concepts, how to assess these topics, and how to incorporate specific teaching strategies to promote student learning of these topics—a key component of PCK (Magnusson et al., 1999).PaP-eRs provide an account of one's practice and offer deeper understanding of the information provided by the CoRe (Loughran et al., 2006). As further outlined by Loughran et al.:
A Resource Folio for a given content area contains CoRe(s) and the associated PaP-eRs, which together create complementary representations of successful teachers’ PCK about teaching a particular subject matter of a specific group of students in a particular way for important pedagogical reasons (Loughran et al., 2006, p. 20).
Instructors create CoRes from a template provided by the researcher(s), which is then subsequently completed to the best of the instructors’ capabilities; an example of this framework is presented in Table 1. The researcher provides the first column, but the remaining columns are left open (Loughran et al., 2006; Kind, 2009; Lehane and Bertram, 2016). Each CoRe affords the instructor(s) freedom to determine the number and type of big ideas (which comprise the top row) and fill in the aspects of each big idea. It is not necessary to fill in all the cells of the table. Once each item from column one is filled in as thoroughly as possible for each big idea in the topic chosen, the CoRe is considered complete.
| Question row | Question | Participant-generated major concepts based on overarching topic | |||
|---|---|---|---|---|---|
| Concept A | Concept B | Concept C | Etc.…a | ||
| a Participants choose the overall number of major concepts based on how many major concepts participants determine will best describe the overarching topic; the number of concept columns—as well as their labels—will vary by individual or group. | |||||
| 1 | Q1: What did you intend the students to learn about this idea? | ||||
| 2 | Q2: Why is it important for students to know this? | ||||
| 3 | Q3: What else you know about this idea (that you do not intend students to know yet)? | ||||
| 4 | Q4: Difficulties/limitations connected with teaching this idea. | ||||
| 5 | Q5: Knowledge about students’ thinking that influences your teaching of this idea. | ||||
| 6 | Q6: Other factors that influence your teaching of this idea. | ||||
| 7 | Q7: Teaching procedures you use (and the particular reasons for using these to engage with the content). | ||||
| 8 | Q8: Specific ways of ascertaining students’ understanding or confusion around this idea (please include any likely ranges of responses). | ||||
CoRes have been employed to survey a variety of educational settings, including several examples from science education (Padilla et al., 2008; Berry et al., 2009; Bertram and Loughran, 2012; Chordnork and Yuenyong, 2014; Schultz et al., 2018; Lawrie et al., 2019). A recent review by Lehane and Bertram (2016) highlights several publications that discuss the use of CoRes to capture chemistry-centric PCK from a variety of instructors, ranging from pre-service K-12 science teachers (Adadan and Oner, 2014; Alvarado et al., 2015) through university professors (Davidowitz and Rollnick, 2011; Padilla and Garritz, 2014). We sought to better understand both post-secondary instructors’ topic-specific PCK of acid–base chemistry and instructors’ cPCK by having small groups of instructors work on CoRes collaboratively.
Data collection and study context
This report details the summative results of CoRes developed by two groups of three graduate students (data collected in Fall 2017) and one group of three faculty members (data collected in Summer 2018). All participants were recruited from a single, large research university in the Midwest, United States of America. At this university, students may enroll in organic chemistry during their first semester of college. Consequently, participants were asked to consider acid–base chemistry in the specific context of a first-semester organic chemistry course during the construction of the CoRe.Graduate students and faculty members who taught (or were teaching) organic chemistry were invited to participate via email, and participants that agreed to participate were recruited based on their level of teaching experience. CoRe groups were formed according to participants’ teaching experience (see Table 2). In this way, purposeful sampling was used to maximize the variation in teaching experience between groups. Lunch was purchased for all participants as an incentive for participation. Audiovisual data were collected in a conference room equipped with a projector and audiovisual recording equipment. Each 1–2 hour session began with background on how to complete the CoRe using a sample CoRe from Loughran et al. (2006) projected on a smart board (Chapter 4: Particle Theory, pp. 32–37). Participant groups were then given a blank CoRe spreadsheet in the program Google Sheets to generate their major components for the topic. Participants worked in their group of three to fill out the CoRe during the time remaining.
| CoRe group | Participant | Chemistry field | Context of organic acid/base instruction | Year in graduate school | Course instruction experience (semesters) | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| General chemistry | Organic chemistry I | Organic chemistry II | ||||||||
| Lecture | Lab | Lecture | Lab | Lecture | Lab | |||||
| GS = graduate school teaching experience; UG = undergraduate teaching experience; 2 year = two-year college instructional experience; 4 year = four-year college/university instructional experience. | ||||||||||
| I | Sandor | Physical | None | First | 0 | 1 | 0 | 0 | 0 | 0 |
| I | Cersei | Organic | GS | Second | 0 | 0 | 0 | 0 | 2 | 0 |
| II | Margaery | Organic | GS | Second | 0 | 0 | 2 | 1 | 0 | 1 |
| II | Brienne | Organic | UG/GS | Second | 0 | 0 | 1 | 0 | 4 | 1 |
| I | Tyrion | Materials | UG/GS | Fourth | 0 | 1 | 0 | 1 | 0 | 1 |
| II | Arya | Organic | GS | Fifth | 0 | 0 | 0 | 2 | 0 | 1 |
| III | Davos | Organic | GS/2 year/4 year | Faculty | 0 | 0 | 1 | 4 | 2 | 2 |
| III | Olenna | Chemical Biology | GS/4 year | Faculty | 5 | 0 | 0 | 0 | 0 | 1 |
| III | Daenerys | Biochemistry | GS/4 year | Faculty | 0 | 0 | 20+ | 20+ | 0 | 1 |
Participants were monitored from an observation room with the researcher available to provide additional clarification on the process of filling out the CoRe when needed (e.g., “Do we need to fill out all cells?”). Finally, follow-up emails were sent to participants to gather information about the emphasis of their graduate degree (e.g., organic, inorganic, analytical, etc.), the contexts in which they had instructed acid–base chemistry, the courses they have taught, and how often, and their year in graduate school or experience as a lecturer (Table 2). Group I (Tyrion, Cersei, and Sandor) collectively possessed the least combined teaching experience, Group II (Arya, Brienne, and Margaery) represented an intermediate level of teaching experience, and Group III (Daenerys, Olenna, and Davos) collectively had the greatest amount of teaching experience.
Data analysis
Resultant data were qualitatively analyzed to parse patterns and explore our research questions. Individual groups’ CoRes were ultimately organized into a compiled CoRe that captured the results across all three groups.First, the tabulated CoRe results from each group (Groups I–III) were open coded to identify which concepts were overlapping and which concepts were distinct between each group. Similar ideas in each category were combined and edited for spelling errors and phrasing. For example, Group I determined Identifying Functional Groups and Used pKaTables to Estimate Acidity as major concepts, Group II identified Using/Interpreting a pKaChart as a major concept, and Group III identified Evaluating Acid Strength (Estimating a pKa) and Understanding Its Correlation with Base Strength as a major concept. Based on similarities in what participants intended students learn about these concepts (from both written CoRes and recordings of CoRe construction), these were combined to form Concept E: Evaluating and Approximating pKa Using a pKa Table. As an important note, the pKa table used at this institution is from Ege et al. (2004).
Additionally, discrete ideas were sorted into the best fit category of the compiled CoRe and remain as written. For example, Group I originally had Definitions of Acid/Base as a separate category from Determining Lewis Acids and Bases. Compared with the other CoRe categories generated by Groups II & III, these categories were parsed into Concepts A–C of the compiled CoRe based on how they were discussed in the recordings of CoRe construction.
From this initial round of coding, the eight distinct concepts that arose from across the individual CoRes of Groups I–III became Concepts A–H of the compiled CoRe (Table 3 & Appendix I). Subsequently, the columns of the compiled Core were filled in using each individual group's CoRes. Audiovisual recordings were then coded in NVivo 11 for each compiled CoRe concept to identify when each group discussed each concept during their CoRe construction. These codes were used to corroborate findings from the written CoRes, to provide some insight into the decisions made during participant construction of their CoRe, and to clarify any ambiguous responses. Collected audio data were transcribed verbatim using an offsite transcription service and used as a further corroborating data source to back up findings from the constructed CoRes.
| CoRe group | Concept A: Lewis acids and bases | Concept B: Brønsted–Lowry acids and bases | Concept C: differentiate Lewis vs. Brønsted acid–base | Concept D: definition of pKa and relationship to pH | Concept E: evaluating and approximating pKa using a pKa table | Concept F: predicting the major species in solution | Concept G: evaluating the likelihood of individual proton transfer reactions (Keq) | Concept H: acid–base chemistry as it pertains to drawing reaction mechanisms |
|---|---|---|---|---|---|---|---|---|
| “X” = group provided this concept in the construction of their CoRe; “—“ = group did not provide this as a major concept in the construction of their CoRe. | ||||||||
| I | X | X | — | — | X | X | X | — |
| II | — | X | — | X | X | — | X | X |
| III | X | — | X | X | X | X | — | — |
Using the science teacher PCK framework proposed by Park and Oliver (2008), we further analyzed the compiled CoRe to identify and describe our participants’ PCK of organic acid–base chemistry. To answer our research questions, units of analysis were the cells of the compiled CoRe. Individual CoRes were used to identify any PCK differences across groups, and those differences were noted. Audiovisual data were examined for any instances in which participants mentioned a topic that was not explicitly connected to their written CoRe, providing additional context for the presence or absence of a topic. For example, if a group verbally mentioned the importance of acid–base chemistry to organic mechanisms, this provided information that the group considered and discussed this topic—even if they did not write it in the final version of their group CoRes. After initial analysis, we noticed that participants’ orientations to science teaching were largely absent from our data. This is likely due to the design of the CoRe; CoRe questions do not specifically probe this aspect of PCK. Thus, we focused on describing the other five components of PCK: (1) knowledge of science curriculum, (2) knowledge of students’ understanding in science, (3) knowledge of instructional strategies for teaching science, (4) knowledge of assessment of science learning, and (5) teacher efficacy (Park and Oliver, 2008).
The first author performed all audiovisual and CoRe coding and constructed the compiled CoRe. The results were then discussed with two other chemistry education researchers until consensus agreement was reached. Consider this passage from Group III's CoRe:
The idea that for every Brønsted–Lowry acid you have a conjugate base, and for every base you have a conjugate acid. The notion that if you have a strong base, the conjugate acid will be a weak acid (and vice versa).
Initially, this was categorized under Concept E: evaluating and approximating pKa using a pKa table in the original compiled CoRe, but was determined after discussion with the other researchers to be more in line with Concept B: Brønsted–Lowry Acids and Bases. Any changes were noted—as in the illustrative example above—and the compiled CoRe was adjusted to reflect the consensus interpretation of the results.
Results and discussion
Construction of the compiled CoRe (Appendix I) revealed several trends that inform our understanding of graduate student and faculty instructors’ knowledge for teaching organic acid–base chemistry. Patterns that surfaced during the analysis process are outlined in the following sections alongside relevant discussion of results.Research question 1: what do post-secondary instructors perceive to be the important topics in acid–base chemistry for first-semester organic chemistry students to learn?
Individual CoRe results were organized into the compiled CoRe, yielding eight major concepts of organic acid–base chemistry: (A) the definition and identification of Lewis acids and bases, (B) the definition and identification of Brønsted–Lowry acids and bases, (C) the ability to differentiate between acid–base definitions, (D) understanding the definition of pKa and its relationship to pH, (E) estimating and evaluating acidity through the use of a pKa table or molecular features, (F) the ability to identify major species in solution, (G) being able to evaluate the likelihood of individual proton transfers (Keq), and (H) understanding acid–base chemistry in the context of organic mechanisms. A summary of major components, and the CoRe groups that provided them, is found in Table 3. An overview of each major concept is included in this section, while Appendix I consists of a more detailed account of participants’ responses.Participants in all three groups noted that students should be able to define and identify Lewis and Brønsted–Lowry acids and bases (Concepts A and B) and should be able to differentiate between these and other definitions of acids and bases (Concept C). Participants mentioned that a firm grasp of Lewis and Brønsted–Lowry acids and bases is foundational knowledge and is essential for predicting molecular reactivity. As participants noted, differentiation between acid–base definitions is important because the mode of action is different for each (e.g., complexation vs. proton transfer) and is something that students and teachers have been shown to struggle with (Cros et al., 1986; Bannerjee, 2007). Concepts A, B, and C are perhaps the most foundational concepts necessary to understand more complex organic acid–base chemistry.
While only Groups II and III explicitly listed understanding the connection between pH and pKa as being a discrete key concept (Concept D), all groups noted that understanding this relationship is an important precursor to predicting reactivity and has laboratory implications (e.g., choosing an acid or base for a reaction). Another key concept was evaluating acid–base strength using the trends provided in a pKa table (Concept E), which all groups mentioned as a skill needed to predict the outcome of acid–base reactions. Researchers have shown that students struggle with making inferences from pKa tables because it requires linking symbols and data (e.g., the information in a pKa table) with chemical meaning (Flynn and Amellal, 2016).
Taking the understanding of pH and pKa one step further, all three groups included predicting the major species in a solution at a given pH as a major concept (Concept F). Participants stated that it is important that students can determine where equilibrium lies and, in turn, predict reaction outcomes.
CoRe Groups I and II explicitly wrote about the importance of being able to evaluate the likelihood of a proton transfer reaction (Keq; equilibrium). Participants noted that students should (1) be able to estimate Keq based on the reactants and products and (2) conceptualize the connection between Keq and the pKa values of the reactants and products. Participants indicated that understanding pKa differences in the context of Keq can lead to a better understanding of other acid–base concepts.
The final concept—acid–base chemistry as it pertains to drawing reaction mechanisms (Concept H)—was only explicitly written about by Group I. However, all groups mentioned the importance of understanding acid–base chemistry to predict and explain reactions throughout the construction of their CoRes—often in the second question row (Q2): Why is it important for students to know this? In other words, participants recognized that Concepts A–G were important precursors to understanding reaction mechanisms. Participants note that understanding individual steps of a reaction—especially acid–base steps—can help their understanding of a mechanism overall.
Concepts A–G reveal what post-secondary instructors consider as the most important organic acid–base concepts for introductory organic chemistry students to learn. Many of these major concepts align with the literature on the importance of acid–base chemistry in an organic context (Raker et al., 2013a, 2013b; American Chemical Society, 2015; Stoyanovich et al., 2015). Compiled CoRe Concepts A–C echo both the American Chemical Society guidelines (2015) and the intended learning outcomes of organic acid–base chemistry, which state that students should understand Lewis and Brønsted–Lowry acid–base chemistry, including identifying and drawing acids and bases, identifying the most acidic or basic atom in a molecule, and identifying and drawing conjugate acids and bases (Stoyanovich et al., 2015). Once students can understand the definitions of these concepts, they can build on them: compiled CoRe Concepts D–G emphasize a deeper understanding of Brønsted–Lowry acid–base chemistry that relates to relative states of protonation and likelihood of proton transfer in solution, all of which play a major role in the diagnostic approach of methods of activation in solution (Bhattacharyya and Bodner, 2005; Anderson and Bodner, 2008; Ferguson and Bodner, 2008; Grove et al., 2012a, 2012b; Bhattacharyya, 2013; Bhattacharyya, 2014)—another important aspect of the ACS guidelines (American Chemical Society, 2015). Concepts D–G align with many of the components of the eighth anchoring concept of organic chemistry—equilibrium—as defined by Raker et al. (2013a, 2013b). Concepts D–G also align with intended learning outcomes (e.g., identifying the predominant form of a compound at a given pH and predicting the direction of an acid–base equilibrium using relative base stabilities) from Stoyanovich et al. (2015). While the correct use of a pKa table is not explicitly listed as an intended learning outcome in work by Stoyanovich et al. (2015), many of the other intended learning outcomes rely on understanding pKa trends. It is possible that at the particular university where this study was conducted, the introductory organic chemistry course emphasized using pKa tables as resources when compared to other institutions. Concept H focuses on the importance of acid–base chemistry as it relates to drawing mechanisms in organic chemistry, a common theme of introductory organic chemistry courses, an intended learning outcome of organic chemistry, and the fifth anchoring concept of introductory organic chemistry classes (Raker et al., 2013a, 2013b; Graulich, 2015; Stoyanovich et al., 2015).
 | ||
| Fig. 1 The visual arrangement of eight major compiled CoRe concepts. Arrows indicate knowledge flow. Foundational concepts (start of arrow) are required to understand the concept in question (arrow terminus). Mechanistic understanding requires all concepts. Orange concepts are definitional. Blue concepts build on these definitions. | ||
Research question 2: what aspects of PCK are revealed as post-secondary instructors assemble content representations for organic acid–base chemistry?
A CoRe is intended to elicit PCK, and the compiled CoRe—alongside each group's constructed CoRe—provides detailed, concept-specific insight into the aspects of PCK exhibited by the instructors that participated in this process. In addition to these concept-specific responses, some patterns emerged in how participants viewed the instruction of this topic. In this section, we have presented these patterns as both emergent themes and (when applicable) in the context of the aspects of science teacher PCK (Park and Oliver, 2008).Our participants recognized that students have difficulty remembering and applying mathematical knowledge from prior courses. Participants from all three groups expressed the importance of reminding students how to interpret and manipulate logarithmic scales, which Olenna (Group III) described as a challenge to work through “the whole power thing” and “struggles with algebra.” More specifically, instructors reported student difficulty with the idea that the more negative your pKa, the stronger your acid (or, the more acidic your solution) is. Instructors described the magnitude of a logarithmic scale as a major roadblock to students’ learning of pKa, pH, and Keq. Difficulties with mathematics also translate to the broader notion of equilibrium; instructors reported that students have difficulty grasping that Keq is never negative or equal to zero.
One related mathematics education study indicated that students can perform logarithmic transformations required to get a correct answer, but have difficulty with conceptual questions related to these concepts (Liang and Wood, 2005). These results are consistent with findings in the chemistry education literature (Watters and Watters, 2006; Potgieter et al., 2007), and the nature of the negative logarithmic scale has been said to provide pitfalls to student understanding of pH and pKa (Kolb, 1978; Kolb, 1979). Several chemistry education studies demonstrate that even students that can perform the numerical calculations correctly may not possess a working conceptual understanding of the magnitude of the scale (Nurrenbern and Pickering, 1987; Lythcott, 1990; Sawrey, 1990; Sheppard, 2006).
Participants in all three groups noted that students have a more robust understanding of Brønsted–Lowry acids and bases than Lewis acids and bases. This finding was observed in another study of undergraduate organic chemistry majors (Cartrette and Mayo, 2011). Some attributed this to high school curricula, in which they assumed Brønsted–Lowry acids and bases are covered more in-depth. Groups I and II (graduate students) noted that they believe students are more familiar with and are more likely to grasp the concept of Brønsted–Lowry acids and bases. As instructors they build upon that knowledge when defining and discussing Lewis acids and bases. This assumption could be problematic because, as Cartrette and Mayo (2011) demonstrated, undergraduate organic chemistry students who explained Lewis acids and bases using Brønsted–Lowry principles may also exhibit limited problem-solving abilities. Participants ascribed difficulty teaching Lewis acid–base chemistry to poor student understanding of the “octet rule”, molecular orbitals, and hybridization. Our participants said that while students often feel comfortable with the concept of electron pair donation (as lone pairs are often signified in Lewis structures and easily identifiable), the idea of an “open-shelled atom” seemed to violate student conceptions of the “octet rule”. This perceived violation generates conceptual friction between the idea of the “octet rule” and Lewis acid–base concepts. Instructors in our study suggested that a thorough understanding of molecular orbital theory and hybridization provides an enhanced foundation for teaching Lewis acid–base theory. It is worth noting that we have preserved the “octet rule” mention in our CoRe to provide an accurate representation of what our participants discussed, despite mounting literature that “octet rule” discussions should be instead reframed to maximize understanding (Taber, 2002).
Participants also noted that students gravitate toward more rigid, cut-and-dry methods of reasoning and shy away from conceptualizing organic acid–base chemistry in a relative manner. Most prevalent were participants’ mentions of students struggling with (1) identifying acids and bases that do not fall under the Brønsted–Lowry definition and (2) identifying molecules that can act as both acids and bases in different pH conditions. Participants believe that while students are more comfortable with Brønsted–Lowry definitions than with Lewis definitions, they may struggle with less traditional Brønsted–Lowry pairings (e.g., acetic acid and hydrochloric acid). Additionally, working definitions of compounds as either acids or bases in organic contexts are more fluid than students are used to working with; instructors mentioned student discomfort with this definitional fluidity as being a common difficulty for this topic. This type of reasoning corresponds to the literature on heuristic reasoning, under the heuristic of rigidity (Talanquer, 2006; Talanquer, 2009; McClary and Talanquer, 2011b; Maeyer and Talanquer, 2013). Under this heuristic, students try “using knowledge that has worked in the past and [fail] to consider other approaches” (Connor et al., 2019, p. 531).
The instructors’ perception of students’ desire for a strict ruleset permeates several other topics beyond molecular definitions of acids and bases. This perception was present in discussions of topics such as greater specificity of the pKa table (e.g., “I see benzoic acid on the pKa table but not 4-methyl benzoic acid…what's the pKa of that?”), and relative acid–base strength (e.g., “tert-butoxide is always a strong base”). Similar to a study by Flynn and Amellal (2016), our participants noted that students find it difficult when there are structural differences between their molecule of interest and the molecules on their given pKa table. Flynn and Amellal (2016) recommended that teachers scaffold instruction to include: (a) selecting sources of information to determine a pKa value, (b) navigating between the levels of representation (macroscopic, submicroscopic, and symbolic) to connect pKa values to structural drawings (symbols) and chemical meaning; and (c) predicting results when the exact information is not available (Flynn and Amellal, 2016).
Frequently, participants mentioned that students want to categorize compounds as acids or bases without recognizing that in certain circumstances, a compound may act as an acid, while in other cases it will act as a base. For example, Margaery (Group II) mentioned that it's important for her students to learn that “it's…a scale, it's not just like something is only a strong acid.” This concern is echoed by Tyrion in Group I, who said, “when I look at ammonia and ammonium…it's easy for us to look at it and see this as an acid-conjugate base.” He reported that students have difficulty visualizing that even though ammonia itself is usually viewed as a base, it also is a conjugate acid that “can lose another proton and it's, like, a crazy base” (i.e., NH2−). According to these instructors, students have a desire to categorize a given compound as always being an acid or always acting as a base. In reality, any proton transfer or Lewis acid–base interaction depends upon the nature of both compounds involved.
Another example of students tending toward rigid reasoning methods involves the pH scale. Margaery (Group II) described how instruction from previous classes focused on aqueous pH or pKa scales as being definite and constrained on a range of 0–14, with a pH of 7 representing neutral—significantly different from some of the pKa values used in organic chemistry problem-solving. Additionally, multiple instructors including Cersei (Group I) expressed their experiences with students’ desire to “look for the H+ and OH−” rather than visualize other acids and bases present in solution. The emergence of these topics reflects student difficulties with acid–base chemistry described previously in the literature, which suggests that students’ prior understanding of topics may lead to conflict as they progress to new material (Tobin et al., 1994; Paik, 2015).
In addition to helping students to adjust to new conceptions of the pKa and pH scales, instructors also detailed the challenges in students remembering concepts about equilibrium from prior classes. Le Chatelier's principle was reported to be challenging to remember and consider when problem-solving. Moreover, conceptions of Keq remain limited: instructors related that students often forget that Keq cannot be zero or less than zero and have trouble visualizing how Le Chatelier's principle connects with Keq. This emergent notion aligns with several studies in the literature, which report that students (and some teachers) have difficulty calculating and applying chemical equilibrium (Quílez-Pardo and Solaz-Portolés, 1995; Bradley and Mosimege, 1998; Kousathana and Tsaparlis, 2002; Bannerjee, 2007). In particular, Quílez-Pardo and Solaz-Portolés (1995) identified that “one of the greatest and most challenging aspects has been students’ proper use of Le Chatelier's principle.” (p. 941).
The fifth major theme of participants’ knowledge of students’ understanding was that students tend to have a great degree of difficulty seeing reaction systems as dynamic and consisting of more than one set of molecules. This sentiment echoes results from studies focused on investigating students’ mechanistic reasoning—students often struggle to consider multiple components of a reaction at once (Bhattacharyya and Bodner, 2005; Bhattacharyya, 2014). Group III emphasized how students’ “difficulty with Avogadro's number and equivalence, in general, leads to many reminders that quantity matters.” Chemical equations used in class to teach organic reactions are representations of (often) trillions upon trillions of molecules; as such, the conceptual understanding of equivalence is difficult for many students. This difficulty may be ascribed to student difficulties with bridging the symbolic representation that a chemical equation or mechanism on paper is representative of a massive population at the molecular scale (Johnstone, 1991; Taber, 2013).
Throughout CoRe construction, instructors frequently mentioned the ties between acid–base chemistry and constructing mechanistic explanations, and often framed their conversation this way. For example, when asked by Tyrion (Group I) the importance of understanding how to estimate acidity using a pKa table, Sandor immediately responded, “so we can predict the mechanism of that reaction.” Cersei responded that “being able to estimate relative pKa…is important to do when you’re trying to evaluate the outcome of a reaction or design a reaction,” going further to mention how investing time in understanding pKa “really helped” with understanding reactivity. In Group III, Davos mentions that Brønsted–Lowry acid–base chemistry is “one of the fastest reactions there is in chemistry,” which Daenerys elaborates makes it “easy to overlook proton transfers that will occur before other reactions” in the context of mechanism-based exam problems later in the term. Of note: This statement from Davos in Group III represented the only instance during CoRe collection when participants discussed more than thermodynamic stability and addressed kinetics and rate of reaction.
The notion of acid–base chemistry as fundamental to the understanding of mechanisms is also reflected within the chemistry education literature (Bhattacharyya and Harris, 2017; Flynn and Featherstone, 2017; Weinrich and Sevian, 2017; Caspari et al., 2018). Additionally, those working on curriculum development find this concept of interest, because determining the order of when to teach certain topics is a major factor of curricular design (Stoyanovich et al., 2015; Flynn and Amellal, 2016; Webber and Flynn, 2018).
The use of examples remained a mainstay of instructional strategies across experience levels. Participants mentioned that they would present examples of molecules and spend time as a class (1) identifying which are acids and which are bases (Concepts A–C), (2) ranking the acidity of the molecules (Concept E), (3) determining the Keq for a given reaction (Concept F), and (4) reasoning through the reaction mechanism for a certain acid–base pair (Concept G). Participants also discussed using models and demonstrations to support student learning of various acid–base concepts. For example, using 3D orbital diagrams when discussing Lewis acid–base chemistry and using colorimetric indicators and titration curves when discussing pKa and its relationship to pH. Instructors’ desires to tap into students' prior knowledge of acid–base chemistry also remained key, with many instructors reporting using Brønsted–Lowry examples to help situate student learning and showing the mathematics of logarithms to understand why the pH and pKa scales exist the way they do.
More experienced CoRe groups (II and III) emphasized forming connections to students’ experiences outside of class. Participants in these groups mentioned using battery acid and orange juice as an example of two compounds that appear to have very similar pKa values, but in reality are very different to demonstrate the logarithmic magnitude of the pKa scale, which was frequently reported as a difficulty for students. Connecting content to the real world was a major goal in another study focused on chemistry graduate teaching assistants’ teacher knowledge, stating that many graduate students wanted to demonstrate how chemistry content is relevant to students’ daily lives (Zotos et al., 2020). Group I did not mention any connections to everyday life during CoRe construction. By introducing out-of-class examples, instructors may be attempting to increase student representational competence—the process by which students make meaning, communicate and think about a topic by utilizing multiple representations of the concepts that topic covers (Kozma and Russell, 1997; Daniel et al., 2018; Popova and Bretz, 2018).
Although this discussion did not appear in all CoRe groups, word choice for how to understand and conceptualize various acids and bases tended to vary broadly. Group I favored the use of “electron source” and “electron sink,” while Group III favored the definition of “lone pair donor” and “lone pair acceptor”. This may be reflective of their identities as instructors and their fluidity with those terms in the context of chemistry's words, syntax, and symbolic language (Taskin and Bernholt, 2014; Flynn and Featherstone, 2017; Galloway et al., 2017). Group II did not specifically use either of these phrasings but suggested that as students are likely to be more familiar with Brønsted–Lowry, they begin with Brønsted–Lowry definitions and use those to compare to Lewis definitions.
Groups of instructors also mentioned that asking students to verbally provide rationales for their thinking is a method to ascertain student conceptions of the topic and to determine any current limits of student understanding. In a previous study, chemistry graduate teaching assistants were reported to have used the same method for assessing students (Zotos et al., 2020), and similar methods to elicit thinking are commonly used in research studies (Ericsson and Simon, 1980). Our graduate student participants mentioned this strategy as worthwhile in the context of laboratory, discussion, or office hours, where fewer students are present. Faculty, on the other hand, did not specify the conditions under which they suggested thinking aloud. This strategy was viewed as particularly useful when asking students difficult questions. Instructors suggested that alternative conceptions tend to surface more easily when they ask students to walk their peers through acid–base identification, determination of pKa, determination of Keq, product prediction, and mechanisms. By teaching their peers, students are better able to learn the material themselves as well.
Participants demonstrated a desire to increase problem difficulty over time. Instructors focused on beginning with elementary problems and steadily building to more challenging problems until students feel comfortable identifying and solving all problems of various difficulties. This is a common teaching strategy across many disciplines, stemming from Vygotsky's Zone of Proximal Development (Vygotsky, 1978).
Despite in-depth descriptions of the types of problems students would be asked on exams or homework assignments; instructors did not offer alternative methods of assessing student understanding. Participants appeared to be pigeon-holed into classical methods of assessing student understanding. This finding aligns with prior studies reporting that many instructors have limited exposure to knowledge of different assessment terminology (Bretz, 2012; Emenike et al., 2013; Raker et al., 2013a, 2013b; Raker and Holme, 2014).
These emergent instructor beliefs regarding self-reflection of their own effectiveness with teaching and how this is translated to student learning aligns with literature on teacher efficacy (Gibbs and Powell, 2012; Zotos et al., 2020). Results from this CoRe also align with previous studies in chemistry which reported that graduate students struggle with the content relevant to introductory chemistry courses (Bhattacharyya and Bodner, 2005; Zotos et al., 2020), which can, in turn, impact undergraduate student learning. Interestingly, instructor efficacy did not factor into the faculty instructor group's discussion.
Limitations
While this manuscript offers insight into the PCK of our graduate student instructors and professors, all participants were from a single, research-intensive institution. Thus, further investigation into the PCK of instructors at other types of institutions (e.g., community colleges, primarily undergraduate institutions) is needed as it may reveal different (or similar) results. Additionally, any comparisons between CoRe Groups do not necessarily represent the broader views of novice vs. experienced instructors due to our small population size.Although CoRes reveal and deconstruct an instructor's PCK, the identities and skill level of our graduate students and faculty participants must be considered. While the institution studied herein involves instruction conducted by graduate students at different years of their programs, other institutions may possess different teaching structures for their students and different populations of instructors. From an institutional perspective, graduate students may leave or return to instructional positions throughout their masters or doctoral studies depending upon research funding, fellowship opportunities, and general interest in teaching. Accordingly, reasonably high levels of turnover may be observed year-to-year. Although efforts were made to sample a variety of graduate students, participants in this study may not be wholly representative of the graduate student instructor population over time.
Furthermore, the participants in this study all agreed to participate; as such, volunteering may have introduced a self-selection bias. Participants were neither screened nor assessed for subject matter knowledge before CoRe generation. Participants were not tested or assessed on content outside of CoRe generation, nor were they interviewed or asked to reflect upon the experience of generating a CoRe. Moreover, no record of participants engaging in classroom practices was made. Although an instructor may possess the content knowledge to construct their CoRe, they may not have well-developed in-class pedagogical skills to assist in the translation of this topical knowledge to their students.
As described in the introduction of this manuscript, a Resource Folio for a specific content area is a collection of CoRes and PaP-eRs, which together provide a complete picture of topic-specific PCK. Although CoRe generation provides valuable insight into instructional practices of graduate students and faculty is often used as a standalone research project, guidelines from Loughran et al. (2006) suggest this is an incomplete Resource Folio, which may lend itself to future study and further probing with the construction of PaP-eRs.
Conclusions and implications
We sought to gain a deeper understanding of the knowledge possessed by graduate students and faculty members for teaching acid–base chemistry in an organic context. To do so, two groups of graduate students and one group of faculty developed content representations (CoRes) on the topic. The products of these CoRes were then organized into a compiled CoRe, which allowed us to ascertain (1) what graduate students and faculty viewed as the major components of organic acid–base chemistry introductory courses, and (2) what aspects of PCK were revealed as these instructors assembled their CoRes.CoRe construction by these instructors revealed eight major components of organic acid–base chemistry. Three of these components emphasized definitions (Lewis acid–base, Brønsted–Lowry acid–base, pKa) and are considered foundational for the topic. The remaining five components (acid–base definition differentiation, ability to identify major species in solution, estimating and evaluating acidity using a pKa table, evaluating Keq, and understanding acid–base chemistry in the context of reaction mechanisms) build upon these definitions. The concepts revealed in the study presented herein align with ACS guidelines (American Chemical Society, 2015), the acid–base chemistry intended learning outcomes identified by Stoyanovich et al. (2015), and the anchoring concepts of organic chemistry (Raker et al., 2013a, 2013b).
The components of organic acid–base chemistry emerged by the CoRe were arranged in a manner to demonstrate how the concepts inform and interact with other concepts from the CoRe. While the arrangement of the CoRe concepts in Fig. 1 suggests a possible organic acid–base learning progression, additional research on this topic is needed. Considering that acid–base chemistry is foundational, a learning progression on this topic could be beneficial for the field in considering student learning, instruction, and assessment on the topic.
Concerning instructor PCK, several major themes surfaced from CoRe analysis. CoRe construction revealed students' prior knowledge as a major theme that contributed to the instruction of organic acid–base chemistry. Namely, instructors noted that (1) students struggle with remembering and applying mathematical concepts from previous courses, (2) students are more familiar with the Brønsted–Lowry theory of acids and bases than the Lewis theory, (3) students prefer rigid, cut-and-dry answers, (4) students have trouble understanding the relationship between Keq and Le Chatelier's principle, and (5) students have difficulty understanding that reaction systems are dynamic. Instructors noted that, because students have a firm grasp on Brønsted–Lowry definitions, they explain Lewis acid–base theory in terms of Brønsted–Lowry. This conflation could be problematic for student understanding. As reinforced in another study, it was shown that undergraduate organic chemistry majors did the same thing—they explained the behaviors of Lewis acids and bases in terms of Brønsted–Lowry principles (Cartrette and Mayo, 2011). Students were often unsuccessful when using this approach, indicating that students need additional support in developing their understanding of Lewis acids and bases and how they differ from Brønsted–Lowry acids and bases. Further research, perhaps through observations of instructors, is needed to determine how Lewis acid–base chemistry is taught in classes to inform our understanding of how students develop their knowledge of Lewis acid–base theory.
The instructors’ context was an emergent theme of instructor PCK. Both faculty and graduate students reflected upon student attitudes toward teaching and learning, and the context of transitioning to the university level. Student understanding of acid–base chemistry in terms of relative reactivity presents an instructional hurdle. Instructors note that students tend to consider a single molecule to always be acid or always a base, rather than determining reactivity by viewing each molecule within a given environment or context. Instructors also viewed acid–base chemistry as a gateway to understanding and conceptualizing reactivity and mechanistic reasoning.
Analysis of participants’ knowledge of instructional strategies revealed that instructors most often taught organic acid–base chemistry by working through example problems, using models and demonstrations, and discussing chemistry relevance in broader contexts. An interesting component of instruction was revealed in this section: participants had inconsistent word choice when discussing acid–base chemistry. One group most often used the terms “electron source” and “electron sink,” while another favored the terms “lone pair donor” and “lone pair acceptor”, aligning with notions that inherent challenges of learning chemistry can come from understanding that these terms are often used interchangeably and that instructors must be wary that new students are not as familiar with the language of chemistry (Taskin and Bernholt, 2014; Flynn and Featherstone, 2017; Galloway et al., 2017). Notably, the terms “electrophile” and “nucleophile” were largely absent from the discussion. This omission could indicate that instructors rarely use the terms “electrophile” and “nucleophile” while teaching acid–base chemistry, but further research on this topic is needed. Other studies have revealed that students struggle with the proper use of these terms (Kraft et al., 2010; Cartrette and Mayo, 2011), which can lead to incorrect problem solving (Kraft et al., 2010). We echo these studies and call instructors to model their problem-solving techniques using the appropriate chemical language.
Participants’ knowledge of assessments of science was limited to the use of problem-solving questions for both formative and summative assessments, and asking students to explain their reasoning out loud as a second formative assessment. While these methods can be useful in gauging student understanding, participants lacked variation in how they would assess different topics and levels of competency. This is unsurprising given that other studies have found university instructors possess limited knowledge of assessment (Bretz, 2012). As these studies have indicated, additional assessment training for university instructors is needed.
This study sheds light on post-secondary instructor PCK and may serve as a reference for new organic chemistry instructors, or for programs seeking to provide professional development for organic chemistry instructors. Additionally, we see implications for future study in not only organic chemistry but general chemistry and mathematics as well: our instructors reported perceived student difficulties with the concepts of logarithm, equilibrium, pH scale, and the notions of acids and bases. The compiled CoRe—alongside the emergent patterns presented here—may be used for instructor training, evaluation, and curriculum development in not only chemistry but mathematics courses as well.
Conflicts of interest
There are no conflicts to declare.Appendices
Appendix I
Appendix I contains the compiled CoRe in its entirety, which was constructed based upon the CoRes generated by instructor groups (Table 4).| Concept | Concept A: Lewis acids and bases | Concept B: Brønsted–Lowry acids and bases |
|---|---|---|
| What did you intend the students to learn about this idea? | • Identify Lewis acids and Lewis bases | • Identify Brønsted–Lowry acids and bases |
| • Predict product of a Lewis acid–base reaction | • Predict product(s) of a Brønsted acid–base reaction | |
| • Understand that for every Brønsted–Lowry acid you have a conjugate base (and vice versa) and that if you have a strong base, the conjugate acid will be a weak acid (and vice versa) | ||
| Why is it important for students to know this? | To identify reactive sites in molecules. It is also an important part of many larger, more complicated transformations, making a firm understanding essential for predicting reactivity | To identify reactive sites in molecules. It is a fundamental reaction, either as a single transformation or as part of many other organic reactions, making a firm understanding essential for predicting reactivity. |
| What else do you know about this idea (that you do not intend students to know yet)? | The application of more structurally complicated Lewis acids/bases. The concept of hard and soft acids/bases. In-depth MO theory, including how electron charge is derived. Why hybridization causes changes in relative acidity. The acidity of metal hydrides and d-orbital effects on acidity. | Everything from the left cell and: The ubiquity of this reaction can be overwhelming, as the reaction is frequently employed in problem-solving and laboratory courses. |
| Difficulties and limitations connected with teaching this idea. | The concept of an open shelled atom existing in a starting material seems to defy the idea of being a legitimate representation of a Lewis structure (octet rule). Even as an intermediate, the perception is that open-shell atoms do not form. It is confusing to see a Lewis Base “attacking” (and often becoming charged) without another group leaving for “balance.” | The meaning of “proton” may be confusing for students who have a limited understanding of atomic composition. The use of “H+” as shorthand for hydronium adds to the confusion. It is easy to overlook proton transfers that will occur before other reactions. Previous Brønsted–Lowry acid–base knowledge is focused on pH, not pKa. Students have difficulty understanding that two forms exist around “H+” (HA, A−), and how to utilize the concept of conjugate acid–base chemistry. The relative nature of acid–base chemistry is new; a given molecule can be acid in one context and a base in another – it is a spectrum. |
| Knowledge about students’ thinking that influences your teaching of this idea. | Students struggle with distinguishing reactivity (Lewis acid–base theory) from structural organization (Lewis dot structures) perceive that charged molecules lack stability, and forget how resonance, conjugation, and inductive effects contribute to acidity. | Keeping in mind the common confusions, it is important to remind (by example and by problem-solving) them of the opportunity for proton transfer. |
| Other factors that influence your teaching of this idea. | Students lack exposure to Lewis acids and bases in organic I & II, so they struggle with those problems. Assumptions about previous knowledge from high school or general chemistry. Personal background. | Previous exposure to acid–base chemistry in other contexts, such as high school or general chemistry. |
| Teaching procedures you use (and the particular reasons for using these to engage with the content). | Introducing the students to the use of 3D orbital drawings is essential for understanding the “open shell”. Lewis structures to visualize where the charge is located. Using formal charges. Using pKa tables to approximate relative strength of Lewis bases. Electron sources and electron sinks. Providing sample Lewis acids and bases, with subsequent class/small group practice identification problems. Drawing reactions using conjugate acids and bases to give the “reverse” of what students typically encounter | Connect in-class concepts to out of class, real-world contexts, e.g., apply the pH scale to household items, food chemistry, and pH indicators. Draw upon prior knowledge about where “H+” comes from. Include comparisons/contrasts to Lewis acid–base chemistry. Use demonstrations and diagrams such as titration curves, or draw multiple molecules and ‘cancel-out’ acid–base products. Use mathematics (i.e., Henderson-Hasselbalch equation) to prove certain concepts and to reach students who learn through different means. |
| Specific ways of ascertaining students’ understanding or confusion around this idea (please include any likely ranges of responses). | Proper drawing of starting materials and product(s), with proper assessment of changes in hybridization and geometry due to the reaction. Having students explain their reasoning behind answers and their thought processes. Ask pointed questions. | Proper drawing of starting materials and products, with proper assessment of any changes in hybridization and geometry due to the reaction. Have students explain their reasoning behind answers and their thought processes. Ask pointed questions. |
| Concept | Concept C: differentiate Lewis vs. Brønsted acid–base | Concept D: definition of pKa and relationship to pH |
|---|---|---|
| What did you intend the students to learn about this idea? | • Differentiate between Lewis and Brønsted–Lowry acids and bases, including identification and differences in reactivity | • Understand that pKa is a ranking system established on a negative-logarithmic scale, which derives from the acid dissociation constant (Ka) at equilibrium after removal of the constant water, derived from Henderson–Hasselbalch. |
| • Use this definition and connect to pH and acid strength | ||
| Why is it important for students to know this? | As the mode of action is different for each (complexation or proton transfer), students must be able to discuss chemistry or read about it knowing basic definitions. Definitions help to establish foundational knowledge. | Relating pH to pKa allows differentiation between protonated and deprotonated forms of compounds, which have different properties. pKa is a more inclusive measure for predicting reactivity than pH. |
| What else do you know about this idea (that you do not intend students to know yet)? | The application of more structurally complicated Lewis acids and bases. The concept of hard and soft acids/bases. In-depth MO theory, including how electron charge is derived. Why hybridization causes changes in relative acidity. The acidity of metal hydrides and d-orbital effects on acidity. | pKa shifts’ dependence on environmental factors (such as reaction solvent). |
| Difficulties and limitations connected with teaching this idea. | Identification of Brønsted–Lowry acids or bases is easier for students to identify, due to ubiquity and previous exposure. In contrast, Lewis acids and bases are less frequent. When students do see Lewis acids and base, the mode of action is not always explicitly identified as a complexation. Good examples to illustrate each definition can be difficult to describe. | Numerical analysis and returning to logs and powers are challenging to explain and understand. As pKa and pH are on a negative logarithmic scale, instructional challenges abound; students have difficulty visualizing that a difference of 1 unit of pKa translates to a ten-fold difference in acidity, and the notion that the smaller a pKa value is, the more acidic it is (this seems counter-intuitive). |
| Knowledge about students’ thinking that influences your teaching of this idea. | Students tend to understand Brønsted–Lowry better, so we define Lewis acid–base chemistry in terms of analogy to Brønsted–Lowry. As students have difficulty with Lewis, examples are often avoided (intentionally or unintentionally). Previously, acid–base chemistry is taught based on pH, which is not fully applicable to Lewis definitions. | Some students struggle with algebra, so the derivation is minimized, and a more qualitative and intuitive approach is used. The confusion surrounding a negative-logarithmic scale is non-intuitive (that a smaller value is a stronger acid may seem backward at first glance). Different protons on a molecule have different pKas |
| Other factors that influence your teaching of this idea. | Students lack exposure to Lewis acids and bases in organic I & II, so they struggle with those problems. Assumptions about previous knowledge from high school or general chemistry. Personal background. | Previous exposure to acid/base chemistry in other contexts, such as high school or general chemistry. |
| Teaching procedures you use (and the particular reasons for using these to engage with the content). | Show examples in the context of a reaction mechanism, arrow-pushing to demonstrate lone pair movement and bond breaking/forming events. Begin with hydronium and hydroxide, then move to more inclusive definitions. Explain why a molecule may be a Lewis (or Brønsted–Lowry) acid (or base). Provide examples of molecules that fall into each definition, perhaps using electron source (−) and electron sink (+) nomenclature. | Demonstrations utilizing indicators (perhaps including titrations) – visuals help students to see the transformation. Connect prior knowledge of mathematics to current trends. Use everyday examples that use two compounds that appear to have very similar pKas, but in actuality are very different (such as battery acid vs. an orange juice). |
| Specific ways of ascertaining students’ understanding or confusion around this idea (please include any likely ranges of responses). | Provide students a Brønsted–Lowry acid-catalyzed epoxide opening problem; then assign a homework problem with the same substrate paired with a Lewis acid. Ascertain if students figure out the mechanism on their own. Classify molecules within Lewis vs. Brønsted–Lowry, acid vs. base. Gear problems toward classification AND supporting evidence (students may find it challenging to explain their answers to others). Vary difficulty in examples, provide scaffolding to demonstrate how to work through difficult examples | Being able to predict what form predominates at a given pH in an aqueous environment. Ask students how the molecule's acidity changes based on small changes on the molecule; for example, two carboxylic acids that differ by having possessing either an electron-withdrawing or electron-donating group. Ask students to draw molecules in different solutions of varying pH (particularly if the molecule has multiple acidic protons such as amino acids). |
| Concept | Concept E: evaluating and approximating pKa Using a pKa table | Concept F: predicting the major species in solution |
|---|---|---|
| What did you intend the students to learn about this idea? | • Use a pKa table to estimate pKa of a given compound | • Predict major species in a solution of a given pH |
| • Understand trends (e.g., connectivity, formal charge, resonance, electronegativity, inductive effects) and how they influence the pKa of a given proton | • Determine what form(s) predominate in a given aqueous setting (and how to manipulate that form) | |
| • Estimate pKa without relying on a pKa table | ||
| Why is it important for students to know this? | To understand how and when a proton will be removed in systems with more than one acidic proton, and to choose a reagent strong enough for a reaction to “work.” To predict structural influences on acidity and estimate pKa for predicting the outcome of a reaction. Predict reaction likelihood and mechanism. Develop an efficient use of a pKa table to save time. | To determine where equilibrium lies depending on what is in solution or the pH, and in turn, predict reaction outcomes and understand overall what is happening in a reaction. Knowing the protonation state also allows one to design an experiment. Laboratory applications are common (LLE), and biochemical implications (drug binding, solubility, conformational change) are profound. |
| What else do you know about this idea (that you do not intend students to know yet)? | pKa shifts’ dependence on the environment (such as reaction solvent). It is impossible to take everything into account using a simple estimation. The acidity of molecules which contain metals. | Multi-variable adjustment for calculating pH of buffers. How a conjugate acid (or base) may affect the solution pH. |
| Difficulties and limitations connected with teaching this idea. | Comparison to pKa table representatives is difficult because students struggle to identify molecular similarities and can get too reliant on the pKa table's given compounds. Students desire cut-and-dry rules rather than considering multiple factors (resonance, charge, sterics, hyperconjugation, etc.), have difficulty identifying the strength of a base from a pKa table and lose sight of the orders of magnitude on a logarithmic scale. | Students want to draw all Lewis structures in their neutral form, even though that doesn't make sense in terms of pKa (for example, they don't like drawing the zwitterionic form of amino acids). When two acids (or bases) are close in pKa, there is some ambiguity as to what is acting as the acid (or base), and the students sometimes want a more cut-and-dry answer instead of multiple reasonable answers. Equilibrium is dynamic. |
| Knowledge about students’ thinking that influences your teaching of this idea. | Students must be reminded of the connection between a value and a structural component. Students want cut-and-dry. Previous knowledge of functional groups (or lack thereof) and how to name and identify them. | Knowing students want a cut-and-dry answer drives a desire to emphasize the ambiguity of acid–base chemistry sometimes, but it is easier to use “the same” acid or base in many examples. Students may not be familiar with equilibrium and the notion of multiple species existing in solution simultaneously. |
| Other factors that influence your teaching of this idea. | Previous exposure to acid–base chemistry, Keq, and Le Chatelier's principle. Student misunderstandings are difficult to remedy in later material. How students learn and retain knowledge of functional groups and molecular similarity. | An understanding of students' prior knowledge and background in chemistry. pH and how it relates to the deprotonation or protonation of species. Knowledge of functional groups. Additionally, their year in college/education level. |
| Teaching procedures you use (and the particular reasons for using these to engage with the content). | Provide examples of molecules not listed on pKa tables to get them used to comparison. Show how pKa changes with slight changes to a molecule (e.g., adding different functional groups). Explain when to choose one functional group comparison on the table vs. another (e.g., alcohols vs. phenols). Use examples with multiple functional groups: which is the most acidic/basic? Assign pKa of all groups in one molecule. | Consider conjugate acid–base chemistry and how this may affect equilibrium. Identify all functional groups in a molecule and determine protonated or deprotonated sites individually. Amino acids are good examples because they contain acidic and basic functional groups at various pH. |
| Specific ways of ascertaining students’ understanding or confusion around this idea (please include any likely ranges of responses). | Ask students to estimate pKas. Give a quiz that has functional groups not on the pKa table and ask them to find the group on the table that is most similar. Be explicit about identifying the pKa for a specific proton rather than the whole molecule. Determine where in the process students are struggling when using the table. Ask students to explain their reasoning for picking a certain pKa from the table. Ask pointed questions. | Provide an acid/base pairing without the conjugate base/acid, and students draw equilibrium arrows. Assign increasingly difficult problems to judge problem-solving abilities. Assign problems with a buffer. Use amino acid examples that contain different functional groups. Ask the protonation state of the same molecule in different pH conditions. How does adding or removing functional groups change a major species? Explain reasoning and thought processes. Ask probing questions. |
| Concept | Concept G: evaluating the likelihood of individual proton transfer reactions (Keq) | Concept H: acid–base chemistry as it pertains to drawing reaction mechanisms |
|---|---|---|
| What did you intend the students to learn about this idea? | • Estimate the favourability of any proton transfer based on the pKa of the proton in reactants/products | • Draw a reasonable mechanism that they haven't been shown in class before, using their previous understanding of acid–base mechanisms |
| • Conceptualize the connection between Keq and the pKa values of reactants/products | ||
| • Understand the concept of acid–base equilibrium for a given acid and its conjugate base, or between multiple acids and bases in solution | ||
| Why is it important for students to know this? | Brønsted–Lowry proton transfers are the only reactions in the course that can be quantitatively assessed on structural elements. Understanding how to evaluate pKa differences in the context of Keq can lead to a better grasp of other acid–base concepts. | Students struggle with mechanisms they do not reproduce from in-class examples. Understanding acid–base reactions help students visualize individual steps, leading to a greater understanding of the larger picture. |
| What else do you know about this idea (that you do not intend students to know yet)? | — | Sometimes we skip proton transfers or condense steps to make drawing a mechanism faster, or we skip drawing certain reaction arrows. |
| Difficulties and limitations connected with teaching this idea. | The extent of a reaction is based on relative strengths (pKas), and students forget how that translates to Keq. The ideas of equivalence, that a Keq can only be estimated for a single proton movement, and that favourability can be in either reaction direction are challenging. They forget that Keq is a ratio whose power can be negative or positive. Remembering that conversion from the negative logarithmic scales of pKa to the power scale of Keq (e.g., a difference of 5 pKa units means a difference of 105 in Keq). | Students prefer to memorize and repeat steps or rules rather than determine a reasonable mechanism themselves. Although directions will often provide reaction conditions (e.g., acidic or basic), students will often use improper acid–base forms (e.g., use of OH− in an acid-catalyzed electrophilic addition reaction). pH of solution affects nucleophilicity or electrophilicity of an atom/molecule. Students often don't know what a “workup” is. Conservation of charge throughout the mechanism is often forgotten. |
| Knowledge about students’ thinking that influences your teaching of this idea. | Students’ difficulty with Avogadro's number (and equivalence in general) leads to many reminders that quantity matters. pKa viewed from a relativist perspective is a new concept that needs to be related to general chemistry knowledge of acid–base. Additionally, assumptions about previous knowledge of acid–base concepts students have. | Students want step-by-step instructions. They want to make broad, sweeping “rules or patterns” when they shouldn't. |
| Other factors that influence your teaching of this idea. | Math skills and stoichiometry. The anticipated high level of difficulty with this concept and the student attitude/emotional response. | Acid–base chemistry gets forgotten later in the term, especially when students get to more complex mechanisms that involve more than just acid–base steps. |
| Teaching procedures you use (and the particular reasons for using these to engage with the content). | Use many diverse examples, especially some with Keq < 1. Remind students that pH tells us the current state of the solution, while pKa tells us about the molecule and reactivity. Concentrate on framing questions carefully to be difficult but still understandable. Use full, balanced equations, have students assign pKa, and predict Keq based on this information. | Lots of practice. As an instructor, explain your thoughts and rationale aloud along the way. Use diverse examples, such as starting at the end and working backward. |
| Specific ways of ascertaining students’ understanding or confusion around this idea (please include any likely ranges of responses). | Have students determine the Keq for proton transfers. Ask questions that focus on the notion that pH and pKa are complimentary, but do not provide the same data. Ask questions of the type: “If we change ‘X’, how does that affect this equilibrium?” | Have students explain and talk through each arrow and charge, probing why they did what they did. Talking through the problems aloud helps others to understand the mechanism, and shows where gaps in their knowledge may be. Ask students which steps they aren't sure about, and ask why they aren't sure about it. |
Acknowledgements
JRB would like to acknowledge the participants of this study for their time and insight into how they conceptualize teaching acid–base chemistry in an organic context. Authors would also like to thank Megan Connor and Field Watts for their assistance in checking reliability and Jeff Spencer for feedback throughout the study. This project was approved by the Institutional Review Board under HUM00104007.Notes and references
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