Investigating the influence of pre-service chemistry teachers' understanding of the particle nature of matter on their conceptual understanding of solution chemistry
Emine
Adadan
Department of Secondary School Science and Mathematics Education, Faculty of Education, Bogazici University, 34342, Bebek, Istanbul, Turkey. E-mail: emine.adadan@boun.edu.tr
First published on 31st January 2014
Abstract
This mixed method study mainly explored how the extent of pre-service chemistry teachers' understanding of the particle nature of matter (PNM) affects their understanding of solution chemistry in the context of multirepresentational (MR) instruction. The ultimate goal was to describe the levels of understanding of specific solution chemistry concepts of a group of participants with a high understanding of the PNM and a group with a low understanding of the PNM before and immediately after MR instruction. Data sources included questionnaires about the PNM and interviews on solution chemistry. Data from these sources were coded and analyzed using quantitative and qualitative methods. There was a statistically significant difference between the results obtained for the understanding of solution chemistry before MR instruction for participants with a high understanding of the PNM and those with a low understanding of the PNM. Both groups of participants exhibited substantial progress towards the scientific understanding of solution chemistry from pre- to post-instruction; however, the participants with a high understanding of the PNM still outperformed those with a low understanding of the PNM in terms of developing a more scientific conceptual understanding of the topic after the MR instruction. Moreover, when the participants were provided with an opportunity to view dynamic visual particulate representations of phenomena to support verbal representations, about two-thirds of the participants from both groups were able to develop a scientific understanding of dissolution regardless of the extent of their understanding of the PNM. Yet, the findings suggested that the participants with a high understanding of the PNM were more likely to develop a scientific understanding of a particular concept (e.g., supersaturated solutions) in solution chemistry even without viewing the available visual particulate representations of the phenomenon.
The particle theory of matter is regarded as being central to science, and also to science curriculums worldwide (e.g., Feynman, 1995; NRC, 1996), because the learning of almost every topic in chemistry (e.g., solution chemistry, bonding, etc.) rests greatly on the essential aspects of the particle theory of matter (Harrison and Treagust, 2002; Stevens et al., 2010). Liu and Lesniak (2005) claimed that a comprehensive understanding of the particle nature of matter (PNM) “determines students' understanding of principles and theories of physical and chemical changes” (p. 434). However, very few studies have provided empirical evidence for this idea. For example, Johnson (1998) suggested that the development of the PNM facilitated students' understanding of a gas as being a substance, which eventually opened the way to understanding chemical change. In addition, Othman et al. (2008) found a strong relationship between high school students' conceptions of the PNM and their understanding of chemical bonding, such that students who showed a lack of understanding of the PNM did not employ the essential PNM concepts while responding to questions about chemical bonding.
Research on the role of multiple representations (MRs) in science learning has received considerable attention in science education literature (Kozma, 2003; Ainsworth, 2006; Cheng and Gilbert, 2009). In science teaching, MRs have been considered as being essential for constructing and communicating the understanding of abstract concepts. In particular, visuals that represent unseen natural phenomena at the submicroscopic level allow students to make sense of the interactions occuring between particles and to understand the related chemistry concepts (Kozma, 2003). However, students' ability to interpret and understand such representations seems to be critical for how they construct the associated chemistry content (Kozma and Russell, 1997; Cook et al., 2008).
Research on students' science learning has consistently indicated that students from all grade levels, including pre-service science teachers, sometimes hold diverse alternative conceptions about various natural phenomena (e.g., dissolving; Duit, 2009). However, students' already existing conceptions not only shape their further conceptual understanding of science concepts but also their interpretation of MRs, in particular visual particulate representations used in chemistry teaching (Seufert, 2003; Taber, 2008). Studies have been carried out which have examined how an individual’s prior knowledge of the domain affects their understanding of and interpretation of MRs while learning chemistry (e.g., Kozma and Russell, 1997; Seufert, 2003; Cook et al., 2008). However, given the crucial function of the PNM in science learning, there is a need to look into how the extent of an individual’s understanding of the PNM influences the nature of their understanding of further science concepts (e.g., solution chemistry) in the context of MR instruction.
In addition, previous studies have usually focused on high school students or first-year college students' understanding of solution chemistry (e.g., Ebenezer, 2001; Pinarbasi et al., 2006; Devetak et al., 2009; Tosun and Taskesenligil, 2013). Few studies have explored pre-service science teachers' conceptions of solution chemistry (Pinarbasi and Canpolat, 2003; Çalık et al., 2007; Leite et al., 2007; Pinarbasi et al., 2009). Thus, there seems to be a need to examine pre-service science teachers' conceptions of solution chemistry, which may possibly contribute to the extension of research on learners' science learning.
Purpose of the study
This study mainly explored how the extent of pre-service chemistry teachers' understanding of the PNM affects their understanding of solution chemistry in the context of MR instruction. In particular, the goal was to identify and describe the levels of understanding of specific solution chemistry concepts of two groups of participants who differed in their understanding of the PNM, namely a group with a high understanding of the PNM and a group with a low understanding of the PNM, before and immediately after the MR instruction. For the current study, the levels of understanding were characterized by descriptive categories indicating the degree to which participants conceptually understood specific solution chemistry concepts. The following research questions guided the study:(1a) How do the groups of pre-service chemistry teachers with a high understanding of the PNM and a low understanding of the PNM compare in terms of their understanding of solution chemistry before and after completion of the MR instruction?
(1b) How does the conceptual understanding of solution chemistry differ pre- to post-instruction for the groups of pre-service chemistry teachers with a high understanding of the PNM and a low understanding of the PNM ?
(2) What levels of conceptual understanding of specific solution chemistry concepts, namely the nature of dissolution and types of solutions, are demonstrated by the groups of pre-service chemistry teachers with a high understanding of the PNM and a low understanding of the PNM before and immediately after the MR instruction?
Theoretical framework
The development of conceptual understanding involves the building of a strong well-connected and hierarchically arranged knowledge framework (Stevens et al., 2010). Yet, research has revealed that developing a scientific conceptual understanding is rather difficult due to the resilience of alternative conceptions that are embedded in larger conceptual frameworks, and are often supported by learners' everyday experiences (Treagust and Duit, 2008).Posner et al. (1982) suggested that conceptual change learning involves either the addition of new knowledge into an existing conceptual framework without any conflict (conceptual growth) or the major restructuring of existing knowledge to incorporate new knowledge into the conceptual framework (conceptual change). The conceptual change learning begins when learners become dissatisfied with their own alternative conceptions, and learning continues as they come to view a new conception as more intelligible, plausible, and fruitful (Posner et al., 1982). In addition, for conceptual change, the status of a conception is raised as the relative status of an alternative conception is lowered (Hewson and Thorley, 1989).
Students' and teachers' conceptual difficulties regarding liquid-state phenomena
Predicting or explaining liquid-state phenomena (e.g., dissolution) is closely intertwined with a student’s ability to utilize the particle theory of matter (Selley, 2000; Leite et al., 2007). However, research has persistently shown that learners with varied levels of education develop an idea of matter as continuous and static with macroscopic properties, as opposed to the idea that matter is made up of particles in constant motion and interaction, separated from one another by empty space (Johnson, 1998; Liu and Lesniak, 2005).Learning chemistry with multiple representations
Cheng and Gilbert (2009) pointed to the multimodal nature of science concepts, suggesting the same teaching practices for science classrooms. MRs support student science learning in two ways: (a) MRs provide equally useful but different pieces of information about the domain, (b) MRs promote the integration of information and the construction of comprehensive understanding (Ainsworth, 2006). Although MRs have great potential to facilitate student learning, learners need to be able to construct, analyze, interpret, transform, and coordinate the domain-specific representations in order to develop a complete and coherent science knowledge framework. This particular set of skills has been characterized as representational competence (Kozma and Russell, 1997). Research has revealed a close relation between such representational skills and students' understanding of chemical phenomena (Kozma and Russell, 1997; Stieff, 2011).Professional chemists make sense of the phenomenon as they simultaneously operate with and between the macroscopic (tangible and visible; e.g., table salt in water), the submicroscopic (molecules and ions; e.g., dissolution of table salt into its ions), and the symbolic (chemical equations, formulae; e.g., NaCl(s) → Na(aq)+ + Cl(aq)−) levels of representation (Johnstone, 1993), which is sometimes referred as the chemistry triplet (Talanquer, 2011). However, learners often lack such representational competence, and they focus heavily on the observable surface features of phenomena while building their understanding, because learners have difficulty in understanding the submicroscopic and symbolic levels of representation due to their imperceptible and abstract nature (Kozma and Russell, 1997; Cook et al., 2008).
Talanquer (2011) recently further elaborated on the chemistry triplet by providing more complex, multi-dimensional chemistry knowledge space, which included the different types, levels, dimensions, and approaches of chemical knowledge. He portrayed types of chemistry knowledge as experiences (actual observations), models (underlying theories), and visualizations (static and dynamic visual signs). Talanquer described the knowledge space at six levels/scales, ranging from the macroscopic to subatomic. The dimensions of knowledge space look into chemical substances and processes with respect to their composition/structure, energy, and time. In addition, Talanquer suggested four different approaches for building chemistry knowledge, namely mathematical, conceptual, contextual, and historical. The current study integrated conceptual and contextual approaches in the MR instruction which aimed to help students connect and translate between experiences, models, and visualizations at the different levels while they make sense of the change in the composition/structure of substances and processes as time passes.
Research has shown that students with a high prior knowledge develop a complete, more abstract understanding of the domain, as well as having the ability to map the knowledge from one representation on to that of another, making clear connections across macroscopic and submicroscopic representations (Cook et al., 2008). In fact, it is the stable underlying knowledge base that facilitates the connections across representations. However, such a coordination across representations is quite difficult for students with a low prior knowledge, because they utilize the surface features of a phenomenon thereby constraining their interpretation of submicroscopic representations, leaving them with limited conceptual knowledge and few connections across representations (Cook et al., 2008).
The framework of multi-representational instruction
The MR instruction of solution chemistry was designed intending to foster the (re)construction of the conceptual understanding of science concepts. The MR instruction took 7 class periods and was created to address the participants' frequently observed alternative conceptions of solution chemistry (see Table 1). The targeted concepts of solution chemistry were introduced in a particular sequence considering their prevalence in building the subsequent concepts (see Vosniadou et al., 2001). Thus, although the effect of temperature on the solubility of solids was not the focus of interviews, it was included in the instruction, because this concept provides the basis for constructing the concept of supersaturated solutions.| Targeted concepts | Nature of activities | Instructional approaches |
|---|---|---|
| The nature of dissolution | Observing the melting of ice in water and the dissolution of table salt in water with no stirring. | Observing each phenomenon |
| Recording the observations | ||
| Discussing how each phenomenon occurs within groups | ||
| Student-generated verbal explanations about what happens at the particulate level while each phenomenon occurs | ||
| Student-generated visual particulate representations of the phenomenon | ||
| Whole class discussion, sharing of ideas | ||
| Viewing online animation of dissolution of a solid in water and melting of a solid | ||
| Comparing the pictorial particulate representations to the dynamic particulate representations (animations) of each phenomenon | ||
| Journal writing | ||
| Factors affecting solubility of solids | Exploring the effect of temperature on the solubility of solids. | Designing an experiment to find out the solubility of a solid at different temperatures |
| Collecting and graphically representing data | ||
| Identifying the patterns in the data | ||
| Drawing a conclusion concerning the solubility and temperature relationship | ||
| Student-generated verbal explanations about how the observed phenomenon occurs at the submicroscopic level | ||
| Whole class discussion, sharing of ideas | ||
| Journal writing | ||
| Types of solutions relative to the solubility of a solid | Part A: preparing a saturated solution of a table salt with no undissolved solid, and then heating this solution until it boiled. Thus, half of the solution evaporated, and then the remaining solution, with stirring, was cooled down to room temperature, resulting in a saturated solution at equilibrium with its precipitate. | Predicting the resulting solution for the following case: the saturated solution with no undissolved solid was heated until it boiled, and half of the solution was evaporated and then the remaining solution, with stirring, was cooled down to room temperature |
| Observing the actual phenomenon as described in the prediction phase | ||
| Comparing the predictions and observations | ||
| Identifying the resulting solution | ||
| Student-generated verbal explanations about what happened at the particulate level as the particular phenomenon occurs | ||
| Student-generated visual particulate representations about the initial and the resulting solution | ||
| Whole class discussion, sharing of ideas | ||
| Viewing online animation of a saturated solution at equilibrium with its precipitate | ||
| Journal writing | ||
| Part B: preparing a supersaturated solution of sodium acetate by gently warming up the saturated solution with undissolved solid in a water bath and then slowly cooling it down to room temperature. | Preparing a saturated solution with undissolved solid at room temperature and gently warming up the solution in a water bath (with no boiling), and then slowly cooling it down to room temperature. | |
| Observing and predicting what happens during these sequences of events | ||
| Identifying the resulting solution | ||
| Adding a few crystals of salt to the supersaturated solution, observing what happens | ||
| Student-generated verbal explanations about what happened at the particulate level during these sequences of events | ||
| Whole class discussion, sharing of ideas | ||
| Journal writing | ||
The MR instruction placed particular emphasis on promoting the construction of scientific conceptions in the context of meaningful activities and a collaborative environment (see Table 1; Vosniadou et al., 2001; Taber, 2013). Drawing upon Talanquer's (2011) idea of chemistry knowledge space, during the MR instruction the participants engaged in direct observations (experiences) to collect evidence for each phenomenon (see Table 1). Because verbal representations (language) in the MR learning environments act as “a semantic glue that holds different representations together” (Kozma and Russell, 1997, p. 965), the participants developed verbal explanations (models) for each macroscopically observed phenomenon. They also drew visual particulate representations as well as viewing the particulate animations available online about the observed phenomenon (visualizations). In this context, to promote the participants' conceptual understandings (approach), they communicated their ideas within groups or with the whole class on multiple levels such that they interpreted the macroscopic level evidence in light of their existing knowledge, and predicted the submicroscopic level occurrences of the phenomenon involving solution chemistry (Talanquer, 2011).
Rivard and Straw (2000) found that “writing is an important discursive tool for organizing and consolidating rudimentary ideas into knowledge that is more coherent and well-structured” (p. 586). Accordingly, the participants were provided with activity sheets for each phenomenon. This offered the participants with an opportunity to carefully organize their internal mental models of particular phenomena as they verbally and pictorially (through drawings) represented their own ideas on paper (Rivard and Straw, 2000; Vosniadou et al., 2001). Moreover, they were also able to compare their own representations with the ones offered by their peers during small-group or whole-class discussions, which perhaps promoted their metaconceptual awareness (Vosniadou et al., 2001).
Students need to recognize the existence of alternative conceptions and reconsider their value and scientific accuracy in light of new knowledge for conceptual change (Treagust and Duit, 2008). This can be promoted by having students metacognitively reflect upon their learning. Thus, following each activity, the participants were asked to write a one-page journal entry responding to the following prompt: “How does the knowledge that you currently know differ from what you used to think?”
The researcher, a science teacher educator, was the instructor of the course where this study took place over two sequential years. Each year, the researcher taught the course and also collected the research data, serving as a “participant observer” (Glesne, 1999). Each year, while implementing the MR instruction on solution chemistry, each class period was video recorded. Then, the participant observer viewed video recordings following each class period and took field notes to ensure the fidelity of the implementation of MR instruction. In addition, no data was analyzed until the end of the data collection over a two-year period to prevent researcher bias on the part of the instructor.
Methods
This mixed method study adopted a quasi-experimental comparison group design with a pre- and post-interview, along with qualitative data collection and quantitative and qualitative data analysis procedures (Campbell and Stanley, 1963; Johnson and Onwuegbuzie, 2004).Participants and context of the study
All students who were enrolled in a “Secondary School Chemistry Laboratory Applications” course were invited to participate in this study over two consecutive years. This particular course was offered in the fall semester to third-year pre-service chemistry teachers enrolled in a five-year chemistry teacher education program. A total of 40 of the 47 invited students agreed to participate in the study.More than half of the 40 participants were female (65%). Fourteen of the participants were male (35%). The number of university chemistry course credits that the participants had completed before their involvement in the study ranged from 13 to 30 semester hours, with a mean of 18.9. All of the participants had successfully completed the first year introductory level chemistry courses, and 27 of the 40 participants had also completed their analytical chemistry and inorganic chemistry courses.
While analyzing the data, the 40 participants, who were engaged in the same instruction on solution chemistry, were divided into groups with a high understanding of the PNM and a low understanding of the PNM with respect to their scores on the PNM-DQ, which they had taken before the MR instruction on solution chemistry (described more fully in the data analysis below). The high understanding of the PNM group of 19 participants consisted of 11 female and 8 male students. The low understanding of the PNM group of 21 participants included 15 female and 6 male students.
A Secondary School Chemistry Laboratory Applications course was designed for the pre-service chemistry teachers to address their difficulties with various chemistry topics (e.g., solution chemistry). The participants were involved in different levels of inquiry-based activities throughout the course, so that they had an opportunity to gain first-hand experience in what the inquiry learning environment looks like, as well as developing their scientific understanding of chemistry concepts.
Data collection
Qualitative data were collected from diverse sources (e.g., questionnaires, interviews) involving multiple modes of evidence (e.g., pictorial, verbal). The goal for using qualitative data sources was to provide rich information about the participants' understanding of relevant science concepts, namely the PNM and solution chemistry, without constraining their responses to the preset categories.Each aspect of particle theory was assessed for three states of matter at least twice in different contexts to ensure that the participants' understanding of the PNM was not restricted to the context (Adadan et al., 2010). In addition, research revealed that drawings provide detailed information about students' understanding of abstract concepts (Dove et al., 1999). Therefore, four of the PNM-DQ questions included pictorial representation sections, along with open-ended questions that requested explanations of students' pictorial representations (see Appendix for a PNM-DQ sample question).
| Tasks | Description of the tasks |
|---|---|
| Dissolution (verbal; macroscopic and submicroscopic) | |
| 1 | 15 grams of table salt (NaCl) is placed into 100 mL of water, and it is left on the table for one day without being stirred. The participants were asked to consider “what happens to salt over a day”. If participants came up with the idea of dissolution, they were asked to explain the process of dissolution at the particulate level. If they came up with a different idea (e.g., melting), they were asked to explain how it happens in the given context, and then they were asked to explain “what dissolution is”, and “what happens at the particulate level during dissolution”. |
| Types of solutions (verbal; macroscopic and submicroscopic) | |
| 2 | Given that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature (25 °C) until no more salt is dissolved. The following questions were asked: (a) What type of solution is that? If participants identified that as a saturated solution: (b) How would you observe such a solution at the macroscopic level? (c) How would you imagine such a solution at the particulate level? (d) Could you please compare and contrast the saturated solution with an unsaturated solution, considering your macroscopic level observations and the particulate level image of such solutions? |
| 3 | Given that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature (25 °C) until no more salt is dissolved. Then, the solution is heated on a heater until it boils, and about half of the solution is evaporated off, and then the remaining solution, with stirring, is cooled down to room temperature (25 °C). The participants responded to the following questions: (a) What type of solution would the resulting solution be? (b) Based on participants' responses, how would you observe such a solution? (c) How would you imagine such a solution at the particulate level? |
| 4 | The participants explained the following questions: (a) How would you prepare a supersaturated solution? If participants mentioned that the solution needs to be gently warmed up in a water bath to prepare such a solution, their responses followed up with the question like “what happens to the solution when it is left as it is to cool down to room temperature?” (b) How would you observe a supersaturated solution? (c) How would you imagine such a solution at the particulate level? |
| Types of solutions (visual; macroscopic and submicroscopic) | |
| 5 | Given the particulate representations of the different types of sucrose solutions existing at the same temperature and containing an equal volume of water (see Fig. 1), the participants were asked to identify the type of each given solution, and justify their classification. Then, they were asked to explain what they need to do (a) to obtain solution I beginning with the solution II? (b) to obtain solution II beginning with solution I? (c) to obtain solution III beginning with solution II? |
 | ||
| Fig. 1 Particulate level representations for different types of sucrose solutions. | ||
Research suggested that when engaged in reasoning about a range of natural phenomena, students should be able to navigate between different modes and levels of representation in order to be able to exhibit their conceptual understanding (Kozma, 2003; Cheng and Gilbert, 2009). Consistent with the instructional features of this study, eliciting the participants' understanding of solution chemistry using multiple modes and levels of representation offered evidence of the stability of their understanding across the tasks (see Table 2).
Data analysis
Drawing upon the idea that knowledge is structured through the organization and connection of the related conceptual elements (units) existing within learners' conceptual frameworks (Taber, 2008; Stevens et al., 2010), the participants' responses to each item in the PNM-DQ were divided into conceptual units. A coding sheet was developed to record the numeric points for each unit. While doing so, the participants' responses were compared to the scientific ones established by a panel of the experts who earlier validated the content of the PNM-DQ. One (1) point was assigned to each unit that included elements of the scientific response, and zero (0) points were assigned to all the other responses. However, the relative weights of the questions ranged from two to four points, depending on the number of units existing within each question, and added up to the highest likely total score of 30.Similarly, the participants' responses to each task in the pre- and post-interview on solution chemistry were divided into units and compared to the scientific criteria identified by a panel of experts (see Table 3). If a participant's responses met the scientific criteria in the particular interview task (e.g., dissolution), one (1) point was assigned to each unit. If a participant's response included alternative conceptions or no relevant explanations, zero (0) points were assigned. Then, the pre- and post-interview scores were calculated for each participant. The highest possible total score for the pre- and post-interview was 19.
| Codes | Scientific criteria-verbal | Codes | Scientific criteria-visual |
|---|---|---|---|
| Dissolution | |||
| S-NSS | Nature of the solute and solvent | ||
| S-ESI | Nature of the electrostatic interaction between solute and solvent particles | ||
| S-HS | Formation of an hydration shell around solute particles | ||
| S-CM | The role of constant movement of water molecules in dissolution | ||
| S-UNI | Uniform solution | ||
| Types of solutions-saturated | Types of solutions-saturated | ||
| S-SaC | The concentration of a solution | S-IDSa | Identifying the saturated one among given solutions (see Fig. 1) |
| S-DSa | Describing the submicroscopic view of a solution | S-PAR | Providing an acceptable reason for the identification |
| S-DE | The presence of dynamic equilibrium when there exists undissolved solute (or precipitate) at the bottom of a solution | ||
| Types of solutions-supersaturated | Types of solutions-supersaturated | ||
| S-SuC | The concentration of a solution | S-IDSu | Identifying the supersaturated one among given solutions (see Fig. 1) |
| S-UeRT | Explaining that this is an unstable solution and exists at room temperature | S-PAR | Providing an acceptable reason for the identification |
| S-DSu | Describing the submicroscopic view of a solution | ||
| Types of solutions-unsaturated | Types of solutions-unsaturated | ||
| S-USaC | The concentration of a solution | S-IDUSa | Identifying the unsaturated one among given solutions (see Fig. 1) |
| S-DUSa | Describing the submicroscopic view of a solution | S-PAR | Providing an acceptable reason for the identification |
The pre- and post-interview data were also qualitatively coded and analyzed using the constant comparative method, which was originally developed by Glaser and Strauss (1967) for generating systematic holistic categories (e.g., the levels of understanding categories). Before coding the data, the criteria for a scientific understanding were identified for each aspect of solution chemistry by a panel of experts (see Tables 3 and 4), and earlier studies served to identify the probable alternative conceptions that participants might have (Pinarbasi and Canpolat, 2003; Adadan and Savasci, 2012; Tosun and Taskesenligil, 2013). This information was used to develop a “partial framework” (Glaser and Strauss, 1967, p. 45) for analysis. An initial coding scheme was created based on the partial framework. Table 3 includes the descriptions of the codes for scientific criteria, and the descriptions of the codes for alternative conceptions can be seen in Table 4. Data analysis started with coding participants' responses to each task in the pre- and post-interview. Each time the researcher looked for alignment of the participants' responses to the coding scheme, and the new codes (alternative conceptions) which emerged from the data were recorded. NVivo8®, a qualitative data analysis software (QSR, 2008), was used for managing the data coding. As the coding proceeded, the coding scheme was modified by the addition of new codes. Note that six new codes (alternative conceptions, namely A-TE, A-DSa, A-SaC1, A-SaC2, A-UeRT, A-SuC) solely emerged from the data of the current study (see Table 4).
| Level of understanding | Codes | Criteria |
|---|---|---|
| Scientific understanding | SU | Includes all components of scientific criteria (identified for each aspect of solution chemistry, see Table 3). |
| Partial understanding | PU | Includes a subset of the scientific criteria components, but not all the components. |
| Partial understanding with alternative conceptions | PU/AC | Includes a subset of the scientific coding criteria components along with one or more alternative conceptions (see below). |
| Alternative conceptions | ACs | Includes one or more alternative conceptions without clearly exhibiting any components of scientific criteria. The most common alternative conceptions emerged from the data follows: |
| Dissolution | ||
| A-TE | As the water molecules randomly move and hit salt ions, they give energy to them, thus salt ions start moving fast and dissolve in the water. | |
| A-ST | Solution needs to be stirred in order to dissolve solute into solvent. | |
| A-TLD | Table salt turns into a liquid as it also dissociates into its ions. | |
| Types of solutions | ||
| A-IDSa | A saturated solution containing undissolved solid/or precipitate is a supersaturated solution. | |
| A-DSa | Water molecules and dissolved ions exist as one to one pairs in a saturated solution. | |
| A-SaC1 | A saturated solution consists of an equal number of water molecules and positive and negative ions. | |
| A-SaC2 | Undissolved salt accumulated at the bottom of a saturated solution increases the concentration of a solution. | |
| A-UeRT | Supersaturated solutions only exist above room temperature. As they are cooled down to room temperature, the excess solute immediately precipitates. | |
| A-SuC | Saturated and supersaturated solutions have the same concentration at room temperature. | |
| No understanding | NU | Includes irrelevant or unclear evidence. |
In order to identify an individual participant's level of understanding at each data collection point, the emerged codes for each specific aspect of solution chemistry (dissolution, unsaturated, saturated, and supersaturated solutions) were compared across the tasks that involve different modes and levels of representation for any inconsistency. Then, the emerged codes for each specific aspect of solution chemistry were categorized and compared to the levels of conceptual understanding scheme (see Table 4). Thus, each participant's level of understanding for each specific aspect of solution chemistry in the pre- and post-interview were identified. Notice that the levels of understanding scheme was adopted from previous research, but the labels and descriptions of categories were modified in a way to precisely reflect the data (see Table 4; Abraham et al., 1994).
For research question 1, a median score of 26 was obtained when the participants' PNM-DQ scores were rank ordered. The participants whose PNM-DQ scores were 26 or below were included in the low understanding of the PNM group, and the participants whose PNM-DQ scores were above 26 were assigned to the high understanding of the PNM group. To identify if there was a statistically significant difference across the high understanding of the PNM and the low understanding of the PNM group of participants' conceptual understandings of solution chemistry, the Wilcoxon–Mann–Whitney test was performed on the total scores from the pre- and post-interviews (RQ-1a; Siegel and Castellan, 1988). To test the change in the two groups of participants' conceptual understandings of solution chemistry from pre- to post-interview, the Wilcoxon signed-rank test was conducted by using the participants' pre- and post-interview total scores (RQ-1b; Siegel and Castellan, 1988).
For research question 2, after the participants' levels of understanding of each specific aspect of solution chemistry were classified in the pre- and post-interview, comparisons were performed across the participants within each group and across the groups to identify the change in the level of understanding categories before and after the participants were engaged in the MR instruction. The comparisons conducted at six levels provided evidence for the change in each group of participants' levels of understanding about the specific aspects of solution chemistry (Charmaz, 2000).
Fifty percent of the participants' PNM-DQ responses were selected at random, and the researcher and a graduate student coded this data independently. Inter-rater agreement between the two coders' scores for each unit, determined by Cohen's Kappa, was κ = 0.823, indicating an “excellent” (Altman, 1991, p. 404) level of agreement between the two raters.
Moreover, 15% of data from pre- and post-interviews was selected at random, and the researcher and a graduate student independently coded this data both qualitatively and quantitatively. Agreement of the participants' levels of understanding of each aspect of solution chemistry was calculated at 93%. In addition, the Spearman rank order correlation coefficient was computed to determine the consistency of rankings for the total scores obtained for each participant by the two raters. The ranked total score values of the two raters indicated a strong rank-order correlation of rs = 0.900, p < 0.000.
Findings
Research question 1: (a) How do the high understanding of the PNM and the low understanding of the PNM groups of pre-service chemistry teachers compare in terms of their understanding of solution chemistry before and after completion of the MR instruction? (b) How do the high understanding of the PNM and the low understanding of the PNM groups of pre-service chemistry teachers' conceptual understandings of solution chemistry differ pre- to post-instruction?As shown in Table 5, before the MR instruction, statistics from the analysis of a Wilcoxon–Mann–Whitney test indicated a statistically significant difference between the mean ranks of the two groups (U = 94.500, p < 0.01). That is, the participants with a high understanding of the PNM exhibited a more scientific understanding of solution chemistry than the participants with a low understanding of the PNM did in the pre-interview.
A Wilcoxon signed-rank test of the high understanding of the PNM and low understanding of the PNM group of participants' pre- and post-interview total scores showed statistically significant progress towards the scientific understanding of solution chemistry for both groups of participants (high PNM: Z = 3.862, p < 0.01; low PNM: Z = 3.925, p < 0.01).
Following the MR instruction, Wilcoxon–Mann–Whitney test statistics also resulted in a statistically significant difference between the mean ranks of the two groups (U = 71.000, p < 0.01) (see Table 6). This result showed that even if both groups of participants developed a more scientific understanding of solution chemistry from pre- to post-instruction (see the previous paragraph), engaging in the same MR instruction, the participants with a high understanding of the PNM outperformed those in the low understanding of the PNM group in the extent and frequency of developing a full scientific understanding of solution chemistry immediately after the MR instruction.
Research question 2: What levels of conceptual understanding of specific solution chemistry concepts, namely the nature of dissolution and types of solutions, are demonstrated by the groups of pre-service chemistry teachers with a high understanding of the PNM and a low understanding of the PNM before and immediately after the MR instruction?
Note that the four aspects of solution chemistry (the nature of dissolution, saturated solutions, supersaturated solutions, and unsaturated solutions) were included in data analysis (see Table 3), but more than 75% of participants in both groups already exhibited a scientific understanding of the nature of unsaturated solutions before the instruction, and all the participants in both groups held a scientific understanding of this particular concept following the instruction. Thus, the following sections include discussion of the other three aspects of solution chemistry for which participants frequently showed alternative conceptions.
The nature of dissolution
| Level of understanding | Pre-interview | Post-interview | ||
|---|---|---|---|---|
| High PNM | Low PNM | High PNM | Low PNM | |
| Scientific understanding | 2 (11%) | 0 (0%) | 12 (63%) | 14 (67%) |
| Partial understanding | 10 (52%) | 7 (33%) | 7 (37%) | 3 (14%) |
| Partial understanding with alternative conceptions | 6 (32%) | 3 (14%) | 0 (0%) | 4 (19%) |
| Alternative conceptions | 1 (5%) | 4 (19%) | 0 (0%) | 0 (0%) |
| No understanding | 0 (0%) | 7 (33%) | 0 (0%) | 0 (0%) |
| Total | 19 (100%) | 21 (100%) | 19 (100%) | 21 (100%) |
Following the instruction, no participants showed non-scientific conceptions of the nature of dissolution; thus, 12 of the 19 participants with a high understanding of the PNM indicated a scientific understanding, and 7 of the 19 participants with a high understanding of the PNM exhibited a partial understanding of this concept. Excerpts from a high understanding of the PNM participant's explanations on the pre- and post-interview are presented here as a typical sample of this group of participants' conceptual understanding before and after the instruction. Codes are provided showing how the particular explanation was coded (see Tables 3 and 4 for a key).
Participant 11H, high understanding of the PNM group, pre-interview:
R: “Consider that you have 100 mL of water in a beaker at room temperature. If you put 15 grams of table salt (NaCl) in it and wait a day without stirring, what do you think happens?”
P 11H: “…it highly likely dissolves to a great extent, but there might be some undissolved salt at the bottom…”
R: “How would you explain the phenomenon of dissolving at the particulate level?”
P 11H: “…sodium chloride dissociates into its ions when we put it into water. Chloride is negatively charged, sodium is positively charged. Hydrogen side of water has partial positive charge, and oxygen side has partial negative charge (S-NSS). There will be electrostatic interactions between positive and negative charges (S-ESI). After some time, salt ions will homogenously disperse among water molecules…”
R: “How would homogeneous dispersion happen, when salt dissolves into water?”
P 11H: “…well… it [water] has a positive side and negative side, water has dynamic structure, it does not hold still (S-CM)… Table salt has polar structure…it also dissociates into positive and negative ions. An even distribution would occur as these positive and negative charged particles interact with each other and disperse (S-ESI; S-UNI).”
Participant 11H, high understanding of the PNM group, post-interview:
R: “Consider that you have 100 mL of water in a beaker at room temperature. If you put 15 grams of table salt (NaCl) in it and wait a day without stirring, what do you think happens?”
P 11H: “…It dissolves.”
R: “How does the dissolving of table salt occur?”
P 11H: “…hmm, when we add salt, we know that salt is in solid form, and it exists as ions not molecules. Sodium and chloride ions (S-NSS), they vibrate. …water molecules move, and because their movement is fast [compared to salt ions], they initiate the dissolving process (S-CM). Hmm, water molecules and salt ions interact, and for example, sodium is positively charged, …Its [water] oxygen side is partially negative, its [water] hydrogen side is partially positive (S-NSS). For example, if we consider one sodium ion, hmm, water molecules' partially negative side interact with it and pull it to the solution…(S-ESI) and six water molecules establish a hydration shell around it [sodium ion], and in a similar manner, all other ions also become a part of solution (S-HS). Then, these hydration shells of ions continue to move… hmm… so that we obtain a homogeneous mixture… (S-UNI).”
Before the instruction, participant 11H's conceptual understanding of the nature of dissolution was classified as a partial understanding, because her explanations met 4 of the 5 scientific criteria (S-NSS, S-CM, S-ESI, S-UNI, see Table 3), and she did not provide any evidence in terms of understanding the formation of an hydration shell around the solute particles. Following the instruction, her post-interview explanation of the nature of dissolution included all five scientific criteria, indicating the features of a scientific understanding.
Similar to their peers with a high understanding of the PNM, following the instruction the majority of participants with a low understanding of the PNM indicated no alternative conceptions in their explanations, and their levels of understanding concerning the nature of dissolution were classified as scientific or partial understanding (see Table 7). However, 4 of the 21 participants with a low understanding of the PNM still held alternative conceptions, showing the features of partial understanding with alternative conceptions category in their post-interview explanations of the nature of dissolution. Excerpts from a low understanding of the PNM participant's pre- and post-interview explanations provide evidence of the nature of this group of participants' conceptual understandings before and after the MR instruction (see Tables 3 and 4 for a coding key).
Participant 10L, low understanding of the PNM group, pre-interview:
R: “Consider that you have 100 mL of water in a beaker at room temperature. If you put 15 grams of table salt (NaCl) in it and wait a day without stirring, what do you think happens?”
P 10L: “…well, some dissolves but…some remains undissolved. …because solids only vibrate, some force …dissolves better something like stirring… yet all salt does not dissolve within a-day…(A-ST).”
R: “What happens between salt and water particles during dissolving?”
P 10L: “Hmm… well, water molecules move…, but…well… salt particles exist as solid crystal, and they just vibrate…(S-CM) water molecules may do something like they may transfer their movement energy to salt particles during that interaction, so dissolving may happen…(A-TE)”.
R: “What would you tell about the nature of salt and water? How does dissolving happen?”
P 10L: “…well, it dissolves into ions, and a homogeneous mixture results (S-UNI)…hmm, when salt enters into water, it dissociates into positive and negative ions, …how does something occur?… I started thinking if it is related to polarity. …well, I guess because water is polar, it dissolves polar substances, table salt is polar anyway…(S-NSS).”
Participant 10L, low understanding of the PNM group, post-interview:
R: “Consider that you have 100 mL of water in a beaker at room temperature. If you put 15 grams of table salt (NaCl) in it and wait a day without stirring, what do you think happen?”
P 10L: “It spontaneously dissolves, maybe some remains at the bottom.”
R: “What happens between salt and water, when dissolving occurs?”
P 10L: “Water molecules have mobility, so even if we do not stir…, they interact…(S-CM).”
R: “How does that interaction happen?”
P 10L: “…Since sodium has positive charge, you know, water molecules' oxygen side will become closer to that, of course, not only a single water molecule, something like six of them (S-ESI), then, these molecules' oxygen side surrounds that [sodium ion], because partial negative charge of water molecules attracts the ion, and then they separate that ion…(S-HS, S-NSS). Similarly, water molecules approach to one chloride ion by their partial positive sides, hydrogen side, and pick it up (S-ESI). Then, one chloride ion is surrounded by six water molecules…(S-HS) hmm… each salt ion is taken by water molecules, because ions in water are in motion, they homogeneously disperse… (S-UNI).”
Before the instruction, participant 10L showed evidence of holding two different alternative conceptions (A-ST, A-TE), along with some scientific conceptions of the nature of dissolution (S-CM, S-NSS, S-UNI). Therefore, her pre-instruction level of understanding was categorized to be partial understanding with alternative conceptions. Following the instruction, her level of understanding progressed to a scientific understanding, as she included all five scientific criteria in her explanation.
The nature of saturated solutions
| Level of understanding | Pre-interview | Post-interview | ||
|---|---|---|---|---|
| High PNM | Low PNM | High PNM | Low PNM | |
| Scientific understanding | 3 (16%) | 1 (5%) | 16 (84%) | 11 (52%) |
| Partial understanding | 5 (26%) | 6 (28%) | 2 (11%) | 6 (28%) |
| Partial understanding with alternative conceptions | 11 (58%) | 13 (62%) | 1 (5%) | 4 (20%) |
| Alternative conceptions | 0 (0%) | 1 (5%) | 0 (0%) | 0 (0%) |
| Total | 19 (100%) | 21 (100%) | 19 (100%) | 21 (100%) |
Participant 8H, high understanding of the PNM group, pre-interview:
R: “Imagine that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature until no more salt is dissolved. What do you think about the resulting solution?”
P 8H: “It is a saturated solution (S-IDSa).”
R: “How would you expect to view such a solution at the particulate level?”
P 8H: “…Because there is too much salt dissolved in a saturated solution, salt particles… will be crowded and look close to each other. (S-SaC). Yet, in an unsaturated solution, …salt particles will stay away from each other…”
R: “Consider that the initial solution is heated until it boils, and about half of the solution is evaporated off. Then, this solution, with stirring, is cooled down to room temperature. How would you name the resulting solution?”
P 8H: “Well, …because of evaporation, its solubility will decrease to half so that half of the salt will precipitate to the bottom. We call it a supersaturated solution (A-IDSa).”
R: “If you compare the concentration of initial solution and the resulting one, what would you say?”
P 8H: “…they both have the same concentration; for example, if one dissolves 50 grams of salt in 100 mL of water, the other one dissolves 25 grams in 50 mL of water… (S-SaC).”
R: “[see Fig. 1]. These contain sugar solutions with different concentrations. They exist at room temperature and have equal volumes of water, but water molecules are not shown. How would you name each solution?”
P 8H: “…the second one, supersaturated… [pointing to Picture II] (A-IDSa).”
Participant 8H, high understanding of the PNM group, post-interview:
R: “Imagine that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature until no more salt is dissolved. What do you think about the resulting solution?”
P 8H: “It is a saturated solution (S-IDSa).”
R: “How would you expect to view such a solution at the particulate level?”
P 8H: “…I would see water molecules that created hydration shells around salt ions… and salt ions are homogeneously distributed in water (S-DSa). Well, in a saturated solution, the amount of dissolved salt is more than the unsaturated solution… (S-SaC) ... in an unsaturated one,…there are more water molecules that remain unoccupied [by salt ions].”
R: “Consider that the initial solution is heated until it boils, and about half of the solution is evaporated off. Then, this solution, with stirring, is cooled down to room temperature. How would you name the resulting solution?”
P 8H: “… I obtain a saturated solution again, but the number of water molecules that form hydration shell would decrease… when I cool it down to room temperature, hmm, …compared to the initial solution, the amount of salt in the remaining water would increase. Since it [remained water] cannot dissolve that amount, some salt precipitates to the bottom… (S-DSa).”
R: “If you compare the concentration of initial solution and the resulting one, what would you say?”
P 8H: “Their concentrations are the same, because concentration… is directly related to the solubility of a salt. They both dissolves the maximum amount of salt, but the second one is a saturated solution with its precipitate (S-SaC), solid particles at the bottom are constantly replaced by the dissolved solute particles… (S-DE).”
R: “[see Fig. 1]. These contain sugar solutions with different concentrations. They exist at room temperature and have equal volumes of water, but water molecules are not shown. How would you name each solution?”
P 8H: “This is a saturated solution at equilibrium with its precipitate [pointing to the Picture II] (S-IDSa).”
R: “Why do you think so?”
P 8H: “… I see some precipitates here, … undissolved salt is accumulated, but solution above it should be saturated… hmm, they are in continuous equilibrium… (S-PAR).”
Before the instruction, participant 8H's level of conceptual understanding of the nature of saturated solutions was identified to be partial understanding with alternative conceptions, because her pre-instructional explanation about this concept was rather vague and included alternative conceptions (A-IDSa) along with a few elements of the scientific criteria. Following the instruction, she not only expanded and elaborated her explanation, but also included all five scientific criteria in her explanation without any alternative conceptions, exhibiting a scientific understanding.
Participant 7L, low understanding of the PNM group, pre-interview:
R: “Imagine that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature until no more salt is dissolved. What do you think about the resulting solution?”
P 7L: “It is a saturated solution (S-IDSa).”
R: “How would you expect to view such a solution at the particulate level?”
P 7L: “…salt dissolves into its ions in water…there will be an equal number of water molecules and positive and negative ions (A-SaC1), …I mean, because it is saturated, one ion should be paired with a water molecule… (A-DSa).”
R: “Consider that the initial solution is heated until it boils, and about half of the solution is evaporated off. Then, this solution, with stirring, is cooled down to room temperature. How would you name the resulting solution?”
P 7L: “…While it [water] evaporates, salt starts precipitating, because…water plays a role in ionization of a salt…but its amount is decreased now…so, it is not a homogeneous mixture anymore as it was before… (S-DSa).”
R: “If you compare the concentration of initial solution and the resulting one, what would you say?”
P 7L: “The second one's concentration is higher (A-SaC2), because the amount of water is decreased, there is more solid substance. If we consider the proportion between the amount of existing solute and the amount of water left, the second one has higher concentration.”
R: “[see Fig. 1]. These contain sugar solutions with different concentrations. They exist at room temperature and have equal volumes of water, but water molecules are not shown. How would you name each solution?”
P 7L: “This is a supersaturated solution [pointing to Picture II] (A-IDSa).”
Participant 7L, low understanding of the PNM group, post-interview:
R: “Imagine that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature until no more salt is dissolved. What do you think about the resulting solution?”
P 7L: “A saturated solution (S-IDSa).”
R: “How would you expect to view such a solution at the particulate level?”
P 7L: “…it dissolves the maximum amount that it could dissolve… (S-SaC) ...when we compare it to an unsaturated solution, there are numerous interactions between water molecules, at the same time, there are also interactions between water molecules and solute particles. However, at saturated solution, the number of interactions between water molecules is low…well, because there are a lot of ions, all water molecules interact with ions (S-DSa).”
R: “Consider that the initial solution is heated until it boils, and about half of the initial solution is evaporated off, and then the solution, with stirring, is cooled down to room temperature. What would you say about the resulting solution?”
P 7L: “…we may call it a saturated solution with its precipitate (S-IDSa).”
R: “How would you expect to view this solution at the particulate level?”
P 7L: “Because it is saturated, there are interactions between water molecules and solute particles, but now few water molecules remain compared to the amount of solute, and some solute particles cannot establish an interaction with water molecules. Since these solute particles do not dissociate, they generate a precipitate (S-DSa).”
R: “If you compare the concentration of initial solution and the resulting one, what would you say?”
P 7L: “…The second one is higher, because there is less amount of water in comparison to the amount solute existing in that… (A-SaC2).”
R: “[see Fig. 1]. These contain sugar solutions with different concentrations. They exist at room temperature and have equal volumes of water, but water molecules are not shown. How would you name each solution?”
P 7L: “…This solution is saturated with its precipitate [pointing to Picture II] (S-IDSa).”
Although participant 7L's pre-interview explanation included some pieces of scientific criteria, they were inconsistent when considering her explanations within the entire interview. In addition, she held four different alternative conceptions, two of which were about the concentration of saturated solutions (A-SaC1; A-SaC2) in different forms. The other two involved the description and identification of a saturated solution at the particulate level (A-DSa, A-IDSa). Therefore, her level of pre-instruction conceptual understanding was identified to be alternative conceptions. Following the instruction, although she developed scientific views about some aspects of the nature of saturated solutions (S-SaC, S-DSa, S-IDSa), she was still not aware of the existence of dynamic equilibrium between a solid and a solution (see Table 3). In addition, she was not able to eliminate one of her alternative conceptions (A-SaC2) following the instruction. Therefore, her level of post-instruction understanding was classified as partial understanding with alternative conceptions.
The nature of supersaturated solutions
| Level of understanding | Pre-interview | Post-interview | ||
|---|---|---|---|---|
| High PNM | Low PNM | High PNM | Low PNM | |
| Scientific understanding | 2 (11%) | 1 (4%) | 15 (79%) | 4 (19%) |
| Partial understanding | 0 (0%) | 0 (0%) | 1 (5%) | 5 (24%) |
| Partial understanding with alternative conceptions | 4 (21%) | 10 (48%) | 2 (11%) | 9 (43%) |
| Alternative conceptions | 13 (68%) | 10 (48%) | 1 (5%) | 3 (14%) |
| Total | 19 (100%) | 21 (100%) | 19 (100%) | 21 (100%) |
Participant 10H, high understanding of the PNM group, pre-interview:
R: “Consider that you have a 100 mL of saturated potassium nitrate (KNO3) solution at room temperature. Then, this solution is heated until it boils, and about half of this solution is evaporated off, and then the solution, with stirring, is cooled down to room temperature. How would you name the resulting solution?”
P 10H: “We call it supersaturated, …there appears solid solute at the bottom… (A-IDSa).”
R: “How would you expect to view this solution at the particulate level?”
P 10H: “…the liquid part, it is no different from a saturated one, (A-SuC) …there exists as much solute as it dissolves… Yet, as we go toward the bottom…there are potassium and nitrate ions that are all together…because there is not enough water to keep the ions separate… (A-DSu).”
R: “How would you prepare a supersaturated solution?”
P 10H: “We put 100 mL of water and a lot of salt into a beaker, then we stir it for a while. If some undissolved salt is left at the bottom, this is a supersaturated solution (A-DSu).”
R: “[see Fig. 1]. These contain sugar solutions with different concentrations. They exist at room temperature and have equal volumes of water, but water molecules are not shown. How would you name each solution?”
P 10H: “…this is a supersaturated one [pointing Picture II]… (A-IDSa) ...it is apparent that, this is a supersaturated solution, because there is some solid at the bottom…”
Participant 10H, high understanding of the PNM group, post-interview:
R: “How would you prepare a supersaturated solution?”
P 10H: “We prepare a supersaturated solution by slowly increasing the temperature…as the temperature gradually increases, the movement of water molecules speeds up so…they more frequently interact with solute particles. …at supersaturated ones, all water molecules are absolutely in interaction with the solute particles … (S-DSu)”
R: “How would you imagine this solution at the particulate level?”
P 10H: “…compared to a saturated solution, …the amount of dissolved particles are too much (S-SuC). Well… in so much as something small interferes, solute particles come out of solution… because it is not a stable solution (S-UeRT). In general, the main reason for generation of hydration shells around solute particles [while dissolving] is to keep strongly attracted [oppositely charged] ions away from each other. Yet, here there is virtually one water molecule between solute particles… I mean, there are not too many water molecules…so, water molecules are probably placed around solute particles… For example, as the water molecules' hydrogen sides turn toward the negative ion, their oxygen sides turn toward the positive ion (S-DSu). …but it becomes very sensitive to outside interferences, its equilibrium is quickly disturbed… (S-UeRT).”
R: “You said that the temperature of water needs to be increased while preparing a supersaturated solution. If it is gently cooled down to the room temperature, what do you think happens?”
P 10H: “…nothing happens for a long time (S-UeRT) …but at some point, some solid may start coming out of solution.”
R: “Consider that a crystal of a solute put into this supersaturated solution, what do you think happens?”
P 10H: “…some water molecules try to dissolve that small amount of solid, this disturbs very sensitive equilibrium… so, as water molecules interact with these solid particles, already dissolved ions may become attracted to each other… (S-UeRT).”
R: “[see Fig. 1]. Here are sugar solutions prepared by using equal amount of water, and they exist at the same temperature. Only sugar molecules are seen in the picture. How would you classify each one?”
P 10H: “…clearly this [pointing to Picture I] is a supersaturated one… (S-IDSu) When I look at Picture II, this [Picture I] is certainly supersaturated… because when I compared the densities of particles…[in Picture I and II], here I see that the density of particles is high, but there is not solid substance as it is here… [Picture II] (S-PAR).”
Before the instruction, participant 10H held totally non-scientific views about the nature of supersaturated solutions (A-SuC, A-DSu, A-IDSu); thus, his pre-instruction level of understanding was identified to be alternative conceptions. After the instruction, he extended his explanations, as well as including solid evidence about all five scientific criteria about the nature of supersaturated solutions. He also changed his non-scientific conceptions to scientific ones, developing a scientific understanding.
Participant 21L, low understanding of the PNM group, pre-interview:
R: “Imagine that potassium nitrate salt (KNO3) is added bit by bit with stirring to 100 mL of water at room temperature until no more salt is dissolved. What do you think about the resulting solution?”
P 21L: “This is a supersaturated solution, because water becomes to the state that it cannot dissolve anymore, there will be some salt accumulation at the bottom of beaker…”
R: “How would you expect to view such a solution at the particulate level?”
P 21L: “[compared to a saturated solution] …the number of solute particles will be high… (S-SuC) there will be more salt particles but less water…and some undissolved salt is left at the bottom… (A-DSu).”
R: “If you compare the concentration of saturated and supersaturated solution of a salt, what would you say?”
P 21L: “If it is the same salt, supersaturated one has the higher concentration… (S-SuC).”
R: “[see Fig. 1]. Here are sugar solutions prepared by using equal amount of water, and they exist at the same temperature. Only sugar molecules are shown in the picture. How would you classify each one?”
P 21L: “For Picture I, I would say saturated, and Picture II, it is supersaturated… I just noticed… it appears here that the density of saturated solution is higher than the supersaturated one… In fact, the second one looks as if I thought, well, the molecules at the bottom are very close, at solid state, but I was expecting the upper part to be more dense. However, the first one is more dense in this picture. …well, anyway since there is some solid at the bottom, this should be a supersaturated solution… [pointing to Picture II] (A-IDSa).”
Participant 21L, low understanding of the PNM group, post-interview:
R: “How would you prepare a supersaturated solution?”
P 21L: “…I should know how much it dissolves at room temperature…for example, suppose that 100 mL of water dissolves 20 grams of sugar, I put 30 grams of sugar into 100 mL of water. Twenty grams dissolve, and 10 grams remain at the bottom. Then, I start heating the solution without allowing it to evaporate. As the temperature increases, the water molecules energy will increase, and because they have higher energy, they more frequently interact with sugar molecules at the bottom. They break them apart. Thus, water will be able to dissolve that remaining sugar. This is the way how I can obtain a supersaturated solution (S-DSu).”
R: “How would you expect to view this solution at the particulate level?”
P 21L: “At the particulate level, …there will probably be hydration shells, but I guess these hydration shells would not be fully complete, because there are too many sugar molecules in the medium, but the number of water molecules are not enough (S-SuC). I think, water molecules would not completely surround solute particles (S-DSu).”
R: “[see Fig. 1]. Here are sugar solutions prepared by using equal amount of water, and they exist at the same temperature. Only sugar molecules are shown in the picture. How would you classify each one?”
P 21L: “…the first one's concentration is certainly higher than the third one… In Picture II, there are dissolved sugar molecules, but there are also undissolved sugar molecules left at the bottom. Its density is less than the first one, but more than the third one. …I would call the most dense one [Picture I] as supersaturated (S-SuC; S-IDSu).”
R: “[see Fig. 1]. If you are asked to turn the first solution into the second one, what would you do?”
P 21L: “I would cool it down to room temperature.”
R: “They are already at the same temperature, what would happen when you cool it down?”
P 21L: “Hmm…, I started thinking if I could obtain a supersaturated solution at room temperature… In order to increase the solubility of solids, the only thing that I could do is to increase the temperature, and when the temperature drops, molecules energy also decrease, so some solid will precipitate. …well, …I do not think that I could obtain a supersaturated solution at room temperature (A-UeRT). Therefore, if all three are at the same temperature, I guess I missed that point, the first one is a saturated solution rather than supersaturated (A-IDSu).”
R: “Why did you change your mind?”
P 21L: “In fact, the density of the two solutions looks different [see Fig. 1, Pictures I & II], at first that is why I called the first one supersaturated. Yet, my mind is not clear if I could have a saturated and a supersaturated solution at the same temperature.”
Before the instruction, although participant 21L said that the concentration of supersaturated solutions have a higher concentration than the saturated ones (S-SuC), this idea was inconsistent with her visual identification of a supersaturated solution (A-DSu, A-IDSa); therefore, her level of conceptual understanding was identified to be alternative conceptions. Following the instruction, she showed a few elements of scientific criteria in her explanation (S-SuC; S-DSu) as well as holding some non-scientific conceptions. For example, she believed that a supersaturated solution can only exist above room temperature, and the excess solute immediately precipitates, even if the solution is slowly cooled down to room temperature (A-UeRT), and this non-scientific idea directly affected her identification of supersaturated solution among the given pictorial representations (Fig. 1). Although she first identified the supersaturated one, she then changed her mind and misclassified that solution [Picture I], calling it a saturated solution (A-IDSu). Thus, the features of her post-instruction level of understanding fit into the category of partial understanding with alternative conceptions.
Discussion and conclusions
This study examined how the extent of pre-service chemistry teachers' PNM understanding influenced the nature of their understanding of solution chemistry in the context of MR instruction. The statistical and descriptive findings of the study offered complementary and consistent evidence from multiple perspectives. The findings indicated a statistically significant difference between the high understanding of the PNM and low understanding of the PNM participants' understanding of solution chemistry before the MR instruction (see Table 5). Compared to the low understanding of the PNM group, the high understanding of the PNM participants were probably capable of utilizing the fundamental PNM ideas to explain more sophisticated natural phenomena (e.g., dissolution) before the instruction (see Liu and Lesniak, 2005; Othman et al., 2008).Moreover, the findings (from a Wilcoxon signed-rank test) revealed a statistically significant change in both the high understanding of the PNM and low understanding of the PNM participants' conceptual understanding of solution chemistry from pre- to post-instruction. Although this was not the main focus of the study, this result suggested that in a general sense, the use of MR instruction for learning were similarly effective for promoting both groups of participants' conceptual understanding of solution chemistry (see further discussion below for each specific aspect of solution chemistry).
Although both groups of participants exhibited substantial progress towards the scientific understanding of solution chemistry from pre- to post-instruction (see Wilcoxon signed-rank test result), the participants with a high understanding of the PNM still outperformed the participants with a low understanding of the PNM in terms of developing a more scientific conceptual understanding of the topic immediately after the MR instruction (see Table 6). Given the quasi-experimental nature of the study, the two groups of participants' different rates of progress towards a scientific understanding of solution chemistry might be associated with the interplay between the extent and nature of their prior knowledge, their representational competence, and the use of MR instruction for learning. Consistent with the core idea of learning, which states that new learning builds on existing conceptual frameworks (Taber, 2008; Stevens et al., 2010; Stieff, 2011), the well-established understanding of the PNM probably supported the high understanding of the PNM participants' further learning during the MR instruction, whereas a lack of understanding of the PNM may have acted as a barrier for the participants with a low understanding of the PNM, hindering their understanding of subsequent concepts (see Johnson, 1998; Liu and Lesniak, 2005; Othman et al., 2008; Adadan et al., 2010). Moreover, research exhibited a close mutual relationship between learners' representational competence and their conceptual understanding of the domain (Kozma and Russell, 1997; Stieff, 2011). In the current study, compared to the participants with a low understanding of the PNM, the participants with a high understanding of the PNM probably had a better representational competence, which may have facilitated their coordination of the transitions across different types and levels of representation during the MR instruction, and consequently, they were likely to build proper links between the new concepts and their existing conceptual framework, developing a scientific conceptual understanding of solution chemistry (Taber, 2008; Mayer, 2009).
Concerning the nature of dissolution, more than half (63%) of the participants with a high understanding of the PNM held either scientific or partial understanding before the MR instruction, whereas only one third (33%) of the participants with a low understanding of the PNM showed a partial understanding before the instruction (see Table 7). That is, the two groups started the instruction with different levels of understanding of the nature of dissolution. Before the MR instruction, the majority of participants in both groups lacked knowledge on the formation of hydration shells during dissolution. For example, participant 10H spontaneously stated in the post-interview:
”Before the instruction, I did not know how the hydration shells form around ions… I just knew that solute particles disperse among water molecules. Well, sodium and chloride ions stay separate among water molecules, but I knew nothing about how they are kept separate in a solution.”
Following the MR instruction, however, a similar percentage of participants (high PNM: 63%; low PNM: 67%) in each group demonstrated a full scientific understanding of the nature of dissolution. Even if about 20% of low understanding of the PNM participants' explanations included some alternative conceptions, the similarity across the two groups in terms of holding a scientific understanding of this concept can be attributed to the features of MR instruction implemented for teaching the nature of dissolution (see Table 1). Not only did all of the participants observe the macroscopic phenomenon, but they also verbally and pictorially represented it at the submicroscopic level based on their prior knowledge. However, until they viewed the dynamic particulate animation of dissolution, almost none of the participants could construct a complete verbal or visual representation of the phenomenon at the submicroscopic level due to their lack of knowledge about the formation of hydration shells. As the participants viewed the dynamic particulate animation of dissolution, they compared that with their own particulate representations. The participants described the differences between their own representations and the one represented to them, and then revised their initial verbal and visual particulate representations of dissolution on their activity sheets. That is, during the instruction, all of the participants experienced the nature of dissolution at multiple levels and through multiple modes (visual, verbal) of representation as well as selecting, processing, and integrating that knowledge through multiple channels (Mayer, 2009). Thus, engaging in viewing and drawing the submicroscopic representations of dissolution along with oral and written communication (Kozma and Russell, 1997; Rivard and Straw, 2000) possibly promoted the progress toward a scientific understanding in both groups' understanding of this phenomenon (Posner et al., 1982; Stieff, 2011). Thus, regardless of the extent of their understanding of the PNM, the majority of participants in both groups were able to connect the related pieces of the verbal and visual particulate representations with the macroscopically observed phenomenon and integrate them with their existing conceptual frameworks, building a scientific understanding of the nature of dissolution (Ainsworth, 2006; Mayer, 2009).
Both groups of participants started the MR instruction with similar but lower levels of understanding of the nature of saturated solutions. Very few participants in either group indicated a scientific understanding of this particular concept before the instruction (see Table 8). Consistent with the findings from Devetak et al.'s (2009) study carried out with grade 9 students, before the instruction, the majority of pre-service chemistry teachers in both groups were able to make distinctions between the concentration of saturated and unsaturated solutions in a sense that they considered a saturated solution more concentrated compared to an unsaturated solution. At the same time, however, these participants showed an understanding that there remains no undissolved solid at the bottom of a saturated solution. A saturated solution with some solid was identified as a supersaturated solution (A-IDSa, see Table 4). In fact, the existence of some solid solute is a distinct trait of saturated solutions. With respect to this issue, only a few participants in either group were aware of the dynamic equilibrium established between the particles of solid solute and the particles of saturated aqueous solution before the MR instruction (see the pre-interview excerpts of P 8H and P 7L for the nature of saturated solutions). In addition, given interview Task 3, in which about half of the saturated solution is evaporated off by boiling it, and then the resulting solution is cooled down to room temperature by stirring (see Table 2), some participants believed that the concentration increased, perceiving the solid solute precipitate as being part of the resulting solution (see pre-interview excerpt of P 7L). This finding also aligned with the findings from previous studies (Mulford and Robinson, 2002; Pinarbasi and Canpolat, 2003; Dahsah and Coll, 2008; Adadan and Savasci, 2012). In relation to Task 3, it is important to notice that no participants considered the case that as the resulting solution is cooled down, some solid stays dissolved while some solid precipitates in the solution, which makes it a supersaturated solution.
Following the MR instruction, the two groups of participants indicated different extents of progress toward a scientific understanding of the nature of saturated solutions (see Table 8). Although a substantial number (84%) of participants with a high understanding of the PNM held a scientific understanding, only about half of the participants with a low understanding of the PNM developed a scientific understanding of this concept. The other low understanding of the PNM participants' slight progress or lack of progress towards a scientific understanding might be explained by the use of MR instruction for learning the nature of saturated solutions. The participants experienced the actual phenomenon such that they prepared a saturated solution not containing any solid, and then evaporated about half of the solution by boiling it, cooling the resulting solution down to room temperature by stirring (see Table 1). They were then encouraged to visualize a particulate representation of a saturated solution with its precipitate in light of their prior knowledge (e.g., the behavior of particles in a liquid state, the nature of dissolution, and the submicroscopic representation of a solution) and their macroscopic observations. Thus, the participants constructed verbal and visual representations on their activity sheets depicting the nature of a saturated solution with its precipitate at the submicroscopic level by negotiating their ideas with their peers in the class. In their representations, only a few of the participants noticed the existence of dynamic equilibrium between dissolved and undissolved (precipitate) particles of a salt until they viewed the dynamic particulate animation of a saturated solution (see Table 1). However, this visual particulate representation was limited to exhibiting the existence of dynamic equilibrium between dissolved and undissolved particles of a saturated salt solution, and did not show how water molecules aligned with the ions of a salt in the solution. The participants had to complete the full visual particulate representation of a saturated solution on their own. In this respect, the participants with a high understanding of the PNM were more likely to link together the relevant pieces of representations from their prior knowledge and macroscopic observations, transform them into a new form, and generate their own verbal and visual particulate representations of a saturated solution, as well as to transfer a critical element from the dynamic particulate representation into their own representations (Kozma and Russell, 1997, Stieff, 2011). The participants with a low understanding of the PNM, on the other hand, probably would not be able to adequately manage this representation transformation, connection, and generation process due to their weak PNM conceptual framework. Thus, they fell behind in their high understanding of the PNM counterparts in terms of exhibiting progress toward a scientific understanding of the nature of saturated solutions (see Kozma and Russell, 1997; Cook et al., 2008; Othman et al., 2008; Adadan et al., 2010; Stieff, 2011).
Regarding the nature of supersaturated solutions, the two groups of participants initially demonstrated similar levels of understanding of this concept, but such understandings were conceptually quite poor and dominated by alternative conceptions (see Table 9). Before the MR instruction, the participants held two pervasive alternative conceptions; in fact, the existence of one probably gave rise to the second one. As was persistently reported in other studies conducted with different age groups (Pinarbasi and Canpolat, 2003; Adadan and Savasci, 2012; Tosun and Taskesenligil, 2013), a large number of participants identified a saturated solution containing some solid as a supersaturated solution. The participants who exhibited this alternative conception also believed that the concentration of a supersaturated solution was equal to the concentration of a saturated solution, ignoring the existing physical conditions (see pre-interview excerpt of P 8H).
Following the instruction, the two groups of participants showed dramatically different extents of progress toward a scientific understanding of the nature of supersaturated solutions (see Table 9). About 80% of the participants with a high understanding of the PNM developed a scientific understanding of the nature of supersaturated solutions, whereas only 20% of the participants with a low understanding of the PNM held a scientific understanding of this concept. During the instruction, the participants prepared a supersaturated solution as described in Table 1. Based on their macroscopic observations of a supersaturated solution and their prior knowledge (e.g., the behavior of particles in a liquid state, the dissolution of a salt, a visual particulate representation of a solution, and the effect of temperature on the solubility of solids), they predicted what would happen at the submicroscopic level as they prepared a supersaturated solution. Then, the participants verbally described the probable visual particulate representation of a supersaturated solution that they visualized (see Table 1). During the whole-class discussion, the participants came to a consensus on a detailed verbal particulate representation of supersaturated solutions, involving amount, behavior, and alignment of particles in a solution. Note that no dynamic or static visual particulate representations of supersaturated solutions were provided to the participants at all. Thus, the participants by themselves needed to connect macroscopic representations to the submicroscopic representations by utilizing their prior knowledge, developing a visual particulate representation of a supersaturated solution in their mind, as well as verbally expressing such a representation along with the behavior of particles (ions, molecules) in a solution to their peers and the instructor. It appeared that the majority of the participants with a high understanding of the PNM successfully coordinated this demanding representation process that required the ability to transform a macroscopic representation into a submicroscopic one, generate a visual (mental) representation for the phenomenon at hand, and verbally explain such a representation regarding the phenomenon in detail by considering its multiple aspects (Kozma and Russell, 1997; Stieff, 2011). In other words, compared to the participants with a low understanding of the PNM, due probably to their strong PNM conceptual framework, the participants with a high understanding of the PNM were likely to build visual particulate (mental) representations of the phenomenon without viewing the available visual representation of the phenomenon, turn it into a verbal particulate representation in their minds, and meaningfully integrate the newly created representation into their existing conceptual frameworks (Liu and Lesniak, 2005; Cook et al., 2008; Othman et al., 2008; Mayer, 2009).
From a conceptual change perspective (Posner et al., 1982; Hewson and Thorley, 1989), it seems that the majority of participants with a high understanding of the PNM were able to change their non-scientific conceptions of the nature of supersaturated solutions. They did so by lowering the status of such conceptions and restructuring their initial conceptual frameworks in light of the representations that they just built based on the available macroscopic evidence (see Table 9 and the interview excerpts of P 10H). In contrast, the participants with a low understanding of the PNM probably expanded their initial conceptual framework during the MR instruction by adding new scientific conceptions about the nature of supersaturated solutions or changing some of their non-scientific conceptions into scientific ones (see Table 9). For example, several of the participants with a low understanding of the PNM who, before the instruction, considered a saturated solution with its precipitate as being a supersaturated solution, started making distinctions between the concentrations of saturated and supersaturated solutions after the instruction. However, for these participants with a low understanding of the PNM, the existence of supersaturated solutions was only possible when the solution existed above room temperature, because dissolving an excessive amount of salt in a certain amount of water at room temperature appeared to be counterintuitive with respect to their understanding of the solubility concept (see post-interview excerpt of P 21L regarding supersaturated solutions).
Implications
The findings of the study imply that, as in the case of the nature of dissolution, when the learners were provided with opportunities to connect the macroscopic representations (experiences) with the dynamic and static visual particulate representations (visualizations) in an environment providing opportunities for explanation, and negotiation (models, see Kozma and Russell, 1997; Cheng and Gilbert, 2009; Talanquer, 2011; Taber, 2013), the learners could develop a scientific understanding of the particular scientific concepts regardless of the extent of their understanding of the PNM. Accordingly, teachers may consider offering similar learning environments when teaching solution chemistry, or other chemistry concepts, if possible. When they are not able to provide a well-designed visual particulate representation of the phenomenon to the learners, teachers should offer further guidance to learners with a low understanding of the PNM trying to generate their own visual (and verbal), mental and external representations of the macroscopically observed phenomenon.The findings of the study also reveal that the nature and extent of learners' understanding of the PNM evidently influences their levels of understanding of solution chemistry if there is no available visual particulate representation of the phenomenon. In other words, the evidence showed that learners with an advanced understanding of the PNM are more likely to develop a scientific understanding of solution chemistry even without viewing the available visual particulate representations (e.g., in the case of the nature of supersaturated solutions, see Table 9). This finding points to the importance of developing a well-established understanding of the PNM before introducing more sophisticated chemistry concepts. For example, the findings from Novak's (2005) longitudinal study showed that students who were instructed about the fundamental PNM ideas, starting as early as grade 2, exhibited fewer alternative conceptions and developed well-structured conceptual frameworks about the particle theory of matter when they were in high school. Thus, teachers or curriculum designers may prefer to introduce the basic particle ideas significantly earlier, along with allowing the exploration of the macro-properties of matter to promote the development of the understanding of the PNM, which may consequently serve to improve students' representational competence and learning of advanced chemistry concepts.
The findings of the study indicated that the participants' initial levels of understanding of solution chemistry concepts were usually poor and included some non-scientific conceptions. In this respect, instructors should pay particular attention to the possible alternative conceptions learners may hold about the aspects of solution chemistry, each of which might act as an obstacle to their learning. Instead of emphasizing the algorithmic aspects of solution chemistry (Devetak et al., 2009), instructors should directly address learners' common alternative conceptions of the topic by adopting the conceptual and contextual approaches (Talanquer, 2011), being explicit about how the new conceptions are related to the previous ones in their teaching (Taber, 2013), as well as fostering the development of metacognitive skills among learners (Vosniadou et al., 2001).
Appendix. A sample question from the PNM-DQ instrument
Question 9
Consider a dinner plate with a few water droplets on its surface. The plate is left on the kitchen counter over night. Then, it is observed that it is dry.Part A
Draw two pictures using drawing A and B to represent the change that occurs.
Part B
Describe the way in which the water droplets evaporate on the surface of the plate considering the particle theory of matter.Acknowledgements
The author would like to acknowledge the financial support provided by the Bogazici University Scientific Research Projects Fund with the Project Code 6335.References
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