CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 41 reorganization, the researcher felt that there was no need to change other aspects of the test. Table 1 Pretest Posttest Questions and Related Concepts Pretest Posttest Questions Concepts Related to Stoichiometry Representative Particles Mole Ratio Limiting Reagent Theoretical Yield 1 2 3 4 5 6 7 8 9 10 Attitudes Towards the Use of Particle Diagrams Questionaire A 10-item Attitude Towards the Use of Particle Diagrams (ATPD) questionnaire was administered to the students at the end of the Stoichiometry unit to determine their attitudes to the use of particle diagrams, and whether or not it helped them understand Stochiometric concepts. The questionnaire was developed by the researcher, specifically for the study and was content validated by one high school Physical Science teacher, one Chemistry professor at APIU, and another professor at the same university who had had experience teaching a first-year Chemistry course. Their task was to ensure that the questionnaire items covered the four concepts of
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 42 stoichiometry addressed in the first research question and that the wording was straightforward and unambiguous. Each item was rated on a Likert scale using five response categories; Strongly Agree (SA), Agree (A), Not Sure (NS), Disagree (D), and Strongly Disagree (SD). A pilot study was carried out for the questionnaire in which ten grade twelve students were the respondents. Although the questionnaire was designed to obtain information from respondents who have undergone the specific treatment in the research, the pilot study was essential to ensure the clarity of the questions. The results of the pilot study suggested that no change in the questionnaire was necessary. Procedure The initial contact was made with the administrators of Adventist International Mission School, Muak Lek, in January 2019. A letter was sent to the AIMS Administrative Council explaining the purpose of the research and requesting permission to enlist all thirteen students of General Chemistry in grade ten as study participants, to implement the treatment in their Chemistry class, and to administer the pretest & posttest as well as the questionnaire. Once permission was granted, the researcher communicated the study to the students involved. The significance of the research was communicated to the thirteen student participants before the instruments were presented to them. They were informed verbally of the purpose of the study, the nature and implementation of the treatment, and their participation, which included answering pretest/posttest questions and completing a questionnaire. The participants understood that the treatment would not cause any disruption on their Chemistry lessons and that their written responses in the TPW booklet were going to be used only for academic purposes and the purposes of the study. They were also assured that any other information they contributed would
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 43 be anonymous and confidential. All participants expressed willingness and eagerness to participate in the study. Piloting of Instruments In January 2019, the researcher piloted the Stoichiometry pretest/posttest in the research with nine grade ten students who were not participants of the study. The pilot study resulted in a minor reorganization of the questions. In March 2019, a pilot study was also carried out for the questionnaire in which ten grade twelve students were the respondents. Their responses affirmed the comprehensibility of the questionnaire. Data Collection As alluded above, the researcher applied two methods of data collection techniques – pretest/posttest and questionnaire. These techniques were used to collect adequate and relevant data to address the research questions of the study. The pretest was administered to the participants on February 6, 2019, in one class period before their lessons on The Mole, Chemical Reactions, and Stoichiometry. All of these three topics contained concepts of Stoichiometry and were covered consecutively during an entire four-week treatment period. The treatment began in the first week of February 2019 and ended in the first week of March 2019. During the treatment period, Chemistry classes continued as scheduled, and the TPW companion booklet was used in all of the Chemistry lessons as a source of content knowledge and illustrations for explanation and reinforcement of concepts, as well as for assessments. After the approximately four-week duration, the participants took the posttest and completed the questionnaire. Data Analysis
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 44 Data collected from the Conceptual Stoichiometry Test (CST) pretest and posttest were used to address research question 1. Data collected from the Attitude Towards the Use of Particle Diagrams (ATPD) questionnaire were used to address research question 2. The following strategies were implemented for data analysis to answer each of the two research questions. First, the data computed for research question 1 were analyzed using the paired-sample (correlated) t-test. According to Pallant (2011), the paired sample t-test is a statistical procedure used “when there is only one group of people and data is collected from them on two different occasions or under two different conditions. Each person in the group is assessed on some continuous measure at Time 1 and then again at Time 2, after exposing them to some experimental intervention.” In this study, there was only one group of student participants. The continuous measure was a conceptual understanding of Stoichiometry. Time 1 and Time 2 were the two different occasions when the same student participants were assessed on their conceptual understanding of Stoichiometry using pretest and posttest; that is BEFORE the use of particle diagrams and AFTER the use of particle diagrams in the teaching and learning of lessons related to concepts of Stoichiometry. Specifically, the paired ttest was used to determine whether the was a statistically significant difference between the mean scores for Time 1 and Time 2 (Pallant, 2011). Next, the data computed for research question 2, were analyzed using descriptive statistics in the forms of means, standard deviations, and percentages. These statistics provide information about students’ attitudes towards the use of particle diagrams in their learning of concepts related to Stoichiometry. Summary
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 45 This chapter explained the methods used in the study of the effects of a visualbased pedagogical approach to AIMS students’ conceptual understanding of stoichiometry. The chapter was organized to include an introduction, a restatement of the research questions, a description of the research design, the instrumentation and procedure used to collect data. The chapter ended with an explanation of the data analysis strategies used for answering the research questions. The next chapter details the analysis process and describes the findings of the research.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 46 CHAPTER 4 RESULTS Introduction The purpose of this study is to investigate the effects of using particle diagrams on the conceptual understanding of stoichiometry among tenth-grade students at AIMS, Muak Lek, Thailand. Specifically, the study examines the extent to which the use of particle diagrams affects the students’ conceptual understanding of representative particles, mole ratio, limiting reagent, and theoretical yield. It further examines the attitudes of the students towards the use of particle diagrams in their learning of these concepts. This chapter presents all data collected for the study in the forms of descriptive and inferential statistics. The chapter begins with a description of the sample, followed by a preliminary analysis of major variables, and the interpretation of results. The analysis and interpretation are carried out in two parts. The first part addresses research question 1 and is based on the results of the CST pretest and posttest. The second part addresses research question 2 and is based on the results of the ATPD survey. The chapter concludes with a summary of the major findings. Description of the Sample The sample consisted of thirteen tenth-grade students who were enrolled in the General Chemistry class in the academic year of 2018 -19 at the Adventist International Mission School, Muak Lek, Thailand. Seven of these students had been classmates since they were in seventh grade, had been taught by the same Science
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 47 teacher in the three years preceding tenth grade, and therefore had been exposed to the same instruction and foundation of Chemistry in middle school. Middle school introduction to Chemistry includes topics such as Matter, Changes of States, The Periodic Table, and Chemical Change, which are preliminary to the study of Stoichiometry. Six of these seven students were Thai, and one was an American. Five of the remaining six students were from China and one from India. The five students from China had undergone an intensive ESL program at AIMS for a year before joining the mainstream in 2017. Before enrolling at AIMS, they studied at government and private schools in different provinces in China and confessed to having had rudimentary exposure to basic concepts of Chemistry. The student from India had studied at Spicer Memorial College Academy, enrolled at AIMS in 2017, and demonstrated sufficient knowledge of middle school Chemistry. Out of the thirteen participants, seven were males, and six were females. All of them participated in the CST pretest and posttest and completed the ATPD survey. Table 2 summarizes the participants’ demographic profile. Participants’ Overall Performance in Chemistry The instruments were administered to the participants in the third quarter of the academic year 2018-19. By then, they had learned enough General Chemistry topics in the first and second quarters for their proficiency in and aptitude for the subject, as reflected by their grades, to be assessed. Their grades ranged from D- (58.86%) to A-(92.92 %). This information tells that the thirteen-participant sample represented a wide range of competencies in Chemistry. Though not the focus of the study, this information may have implications on the effectiveness of the use of particle diagrams on students of varying degrees of inclination to Chemistry.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 48 Table 2. Demographic Profile of Sample Demographic Variable N % Gender Male 7 53.8 Female 6.0 Total 13 100.0 Age 15 – years 1 7.7 16 – years 8 61.6 17 – years 3 23.0 18 – years 1 7.7 Total 13 100.0 Nationality American 1 7.7 Chinese 5 38.4 Indian 1.0 Thai 6.0 Total 13.0 Figure 7 summarizes the participants’ percent grades for Chemistry at the end of the first and second quarters, respectively. Pseudonyms are used to represent individual participants. Figure 7 shows that each participant’s performance in Chemistry was generally consistently the same in the first and second quarters. This consistency may reflect their attitude towards the subject. Analysis and Interpretation of CST Results The thirteen participants were assessed on a Conceptual Stoichiometry Test (CST) before and after the intervention. The CST contained questions on all the four concepts of Stoichiometry: representative particle, mole ratio, limiting agent, and theoretical ratio.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 49 Figure 7. Participants’ Chemistry Percent Grades for The First and Second Quarters of 2018- 19. Analysis and Interpretation of CST Results The thirteen participants were assessed on a Conceptual Stoichiometry Test (CST) before and after the intervention. The CST contained questions on all the four concepts of Stoichiometry: representative particle, mole ratio, limiting agent, and theoretical ratio. Since the difference between pretest to posttest was the focus of interest in research question 1, the posttest versus pretest scores of each of the participants, as well as their overall scores on each concept was summarized and presented in Figure 8. Figure 8 shows the individual pretest and posttest scores (in %) of each of the thirteen participants. Pseudonyms are used to denote each participant. The graph shows that eleven of the thirteen participants scored higher in the CST posttest than 0 20 40 60 80 100 An Bo Ch Ci Ea Hy In Jo Mi Pl So Te We Chemistry Grade % Participant 1st Quarter 2nd Quarter
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 50 Figure 8. Pre and Post Scores on CST by Participants in the pretest. One participant scored higher in the CST pretest than in the posttest. One participant scored the same in the pretest and posttest. Figure 9 shows pretest and posttest scores (in %) of all participants on each concept. The graph shows that overall, the participants scored higher on all four concepts in the CST posttest than in the pretest. Results of paired-samples t-test Research Question 1. To what extent does the use of particle diagrams affect students’ conceptual understanding of representative particles, mole ratio, theoretical yield, and limiting reagent? To answer this question, paired sample t-tests were conducted to determine if there are statistically significant differences between pretests and posttests scores. Table 3 reports pretest and posttest means, standard deviations, and skewness statistics for each of the four stoichiometry concepts. As a 0.0 20.0 40.0 60.0 80.0 100.0 120.0 An Bo Ch Ci Ea Hy In Jo Mi Pl So Te We Score % Participants Pretest % Posttest %
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 51 Figure 9. Pre and Post Scores on CST by Concept Table 3. Pretest Posttest Mean, Standard Deviation and Skewness (N=13) Concept Group Max M SD SE Skewness Representative particle Pretest 7.46 2.73 0.76 0.705 Posttest 11.00 2.38 0.66 -0.394 Mole ratio Pretest 16.31 3.68 1.02 -1.294 Posttest 18.62 2.36 0.66 -0.439 Limiting reagent Pretest 5.77 1.42 0.39 0.888 Posttest 7.31 2.06 0.57 -0.421 Theoretical yield Pretest 5.77 1.42 0.39 0.888 Posttest 7.31 2.06 0.57 -0.421 rule of thumb, skewness beyond ± 2 is indicative of departure from normality (George & Mallery. 2003; Morgan, Griego & Gloeckner, 2001). Skewness statistics for all pretest and posttest scores are within ± 2, and thus, may be treated as meeting 50.5 50.2 44.9 44.9 73.6 56.3 55.1 55.1 0 10 20 30 40 50 60 70 80 Rep Part Mole Ratio Lim Reagent Theo Yield Score % Stochiometry Concept Pretest % Posttest %
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 52 the normality assumption for t-tests. The level of significance was set at .05. Cohen’s d was used as a measure of effect size with d ≤ .20 as small, d between .2 and .79 as medium and d ≥ .80 large (Warner, 2013). Results of the paired t-tests to compare pretest and posttest scores are summarized in Table 4. Mean differences between pretest and posttest scores are negative and are statistically significant (p<.05) for all four stoichiometry concepts. Table 4. Mean Difference, Paired T-Test Results and Effect Size (N=13) Concept M SD SE CI95 (U, L) t df p ES(d) Representative particle -3.54 2.30 0.64 -4.93, -2.15 -5.56 12 <.001 1.54 Mole ratio -2.31 2.39 0.66 -3.75, -0.86 -3.48 12 .005 0.96 Limiting agent -1.54 1.71 0.47 -2.57, -0.50 -3.24 12 .007 0.90 Theoretical yield -1.54 1.71 0.47 -2.57, -0.50 -3.24 12 .007 0.90 For Representative Particles, the pretest mean score was 7.46 (SD=2.38), and the posttest mean score was 11.00 (SD=2.38) for a mean increase of 3.54 (SD=2.30). This difference in score is statistically significant (t (12) = -5.56, p < .001, ES(d)=1.54). With an effect size of 1.54, the magnitude of the difference is very large. For Mole Ratio, there was a statistically significant increase in pretest scores prior to intervention (M = 16.31, SD = 3.68) to posttest scores after intervention (M = 18.62, SD = 2.36), t (12) = -3.476, p < .005 (two-tailed). The mean increase in posttest scores was 3.54 with a 95% confidence interval ranging from -3.75 to -0.86. The effect size was large at0.90. The increase between pretest and posttest scores for both Limiting Reagent and Theoretical Yield were precisely the same. Pretest mean scores prior to intervention were 5.77 (SD = 1.42), and posttest mean scores after intervention were
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 53 7.31 (SD = 2.06). Differences between pretest and posttest scores were statistically significant (t (12) = -3.237, p < .007, ES(d)=.90). The mean increase in posttest scores was 1.54, with a 95% confidence interval ranging from -2.57 to -0.50. With effect sizes of 0.90, these increases are deemed large. Analysis and Interpretation of ATPD Survey Results Research Question 2. What are the students’ attitudes towards the use of particle diagrams? A survey questionnaire consisting of 12 items was developed to determine the attitudes of the students towards the use of particle diagrams. In the questionnaire, the participants were requested to indicate their responses to the 12 statements regarding the use of particle diagrams in their learning of four concepts of Stoichiometry. Each item was rated on a Likert scale using five response categories; Strongly Disagree (SD), Disagree (D), Not Sure (NS), Agree (A), and Strongly Agree (SA Reliability analysis for the questionnaire is reported in Table 5. Total scale reliability (Cronbach’s alpha) is 0.80. That is, approximately 80% of the variance in attitudes are shared by these 12 items. Corrected item-total correlation of ≤ .3 is generally considered poor items (Warner, 2013). Using this criterion, it appears that 4 items may be considered ‘poor’ questions. Excluding these 4 items resulted in reliability estimates of .82, an increase of 2% shared variance. Including these 4 items do not appear to substantially affect internal consistency reliability. Reliability estimates of groups of items assessing attitudes towards specific stoichiometry concepts are reported in Table 6. Internal consistency reliability of .6 is acceptable, given that this is an exploratory survey
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 54 Table 5. Attitude questionnaire reliability analysis (n=13) Statement r a Alphab Q1 Particle diagrams help me visualize the particles that make up compound, mixture, and elements. .307 .795 Q2 Particle diagrams help me differentiate among atoms, molecules, ions, and combinations of these. .660 .763 Q3 Particle diagrams help me understand what happens to the particles of reactants during chemical reactions. .660 .767 Q4 Particle diagrams help me understand what the coefficients in balanced chemical equations represent. .530 .775 Q5 Particle diagrams help me determine how many of each kind of atom takes part in a chemical reaction in the lowest whole number ratio. .609 .770 Q6 Particle diagrams help me relate coefficients to mole ratio. .279 .801 Q7 Particle diagrams help me determine the amounts of substances needed or produced in a chemical reaction. .220 .800 Q8 Particle diagrams show that in some chemical reactions, reactants are not necessarily all used up. .293 .796 Q9 Particle diagrams help me identify the reactant that is all used up first (limiting reagent). .115 .810 Q10 Particle diagrams help me identify the reactant that is NOT all used up (excess reagent). .448 .783 Q11. Particle diagrams help me understand the difference between theoretical yield and actual yield. .655 .759 Q12. Particle diagrams help me identify which reactant determines the theoretical yield. .533 .775 Note. a corrected item-total correlation; bCronbach’s alpha if item is deleted. instrument (Warner, 2013). The overall mean attitude scale score was 4.14 (SD=0.44), with a skewness statistic of -0.50. This suggests that overall, the students agree that particle diagram helps them learn the 4 concepts of stoichiometry. The use of particle diagrams for representative particle (M=4.49), limiting agent (M=4.46), and mole ratio (M=4.15) appear to be much more positive than for theoretical yield
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 55 (M=3.12). The students appear to be quite neutral to the use of particle diagrams for theoretical yield. Specific item statistics are reported in Tables 7-10 Table 6. Concept Attitude Descriptive Statistics, Skewness, and Reliability Estimates (N=13) Attitude area M SD skewness # of item Cronbach’s alpha Overall 4.14 0.43 -.498 12 .80 Representative Particle 4.49 0.50 -.950 3 .65 Mole Ratio 4.15 0.55 -.725 4 .63 Limiting Agent 4.46 0.54 -.888 3 .68 Theoretical Yield 3.12 0.92 -.881 2 .78 The results of the questionnaire were further analyzed by concept, as shown in Tables 7 – 10. All statements in the questionnaire were positively worded. An answer to Strongly Disagree was attributed to a score of 1, Disagree = 2, Not Sure =3, Agree = 4, and Strongly Disagree =5 for each statement. Table 7 shows that more than eighty percent (84.6% - 100.0%) of the participants responded with Agree and Strongly Agree, and scored between 4 – 5 (4.38 – 4.62) on a 5-point Likert scale on the concept of Representative Particles. These results suggest that the majority of the participants agreed that the use of particle diagrams helped develop an understanding of this concept. point Likert scale on the concept of Mole Ratio. These results suggest that the majority of the participants agreed that the use of particle diagrams helped develop an understanding of this concept. Table 9 shows that more than eighty-five percent (85.6% - 92.3%) of the participants responded with Agree and Strongly Agree, and scored between 4 – 5 (4.31 – 4.62) on a 5-point Likert scale on the concept of Limiting Reagent. These
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 56 results suggest that the majority of the participants agreed that the use of particle diagrams helped develop an understanding of this concept. Table 7. Descriptive Statistics for The Concept of Representative Particles (N=13) Statement M SD %a 1. Particle diagrams help me visualize the particles that make up compound, mixture, and elements. 4.62 0.51 100.0 2. Particle diagrams help me differentiate among atoms, molecules, ions, and combinations of these. 4.46 0.78 84.6 3. Particle diagrams help me understand what happens to the particles of reactants during chemical reactions. 4.38 0.65 92.3 Note: Percent Agree/Strongly Agree Table 8. Descriptive Statistics for Mole Ratio (N=13) Statement M SD %a 4. Particle diagrams help me understand what the coefficients in balanced chemical equations represent. 4.23 1.01 76.9 5. Particle diagrams help me determine how many of each kind of atom takes part in a chemical reaction in the lowest whole number ratio. 4.15 0.69 84.6 6. Particle diagrams help me relate coefficients to mole ratio. 3.69 0.86 61.6 7. Particle diagrams help me determine the amounts of substances needed or produced in a chemical reaction. 4.54 0.52 100.00 Note. aPercent Agree/Strongly Agree
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 57 Table 9. Descriptive Statistics on Limiting Agent (N=13) Statement M SD %a 8. Particle diagrams show that in some chemical reactions, reactants are not necessarily all used up. 4.62 0.65 92.3 9. Particle diagrams help me identify the reactant that is all used up first (limiting reagent). 4.46 0.66 92.3 10. Particle diagrams help me identify the reactant that is NOT all used up (excess reagent). 4.31 0.75 85.6 Note. aPercent Agree/Strongly agree Table 10 shows that less than fifty percent (30.8% - 46.2%) of the participants responded with Agree and Strongly Agree, and scored between 3 – 4 (3.08 – 3.15) on a 5-point Likert scale on the concept of Theoretical Yield. These results suggest that less than half of the participants agreed that the use of particle diagrams helped develop an understanding of this concept. Summary of Major Findings Results from the analyses suggest the following: (1) There were statistically significant gains (p<.01) in scores between pretest and posttest in all four concepts of stoichiometry. (2) The gains are large (ES(d) ≥ .90 (3) Overall, attitude towards the use of particle diagrams are favorable (M=4.14), particularly in the areas of Representative particle (M=4.49), Mole ratio (M=4.15), limiting reagent (M=4.46). (4) Attitude was neutral about the use of particle diagrams for theoretical yield (M=3.12).
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 58 Table 10. Descriptive Statistics of Theoretical Yield (N=13) Statement M SD %a 11. Particle diagrams help me understand the difference between theoretical yield and actual yield. 3.15 0.99 46.2 12. Particle diagrams help me identify which reactant determines the theoretical yield. 3.08 1.04 30.8 Note. aPercent Agree/Strongly agree
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 59 CHAPTER 5 SUMMARY Introduction This chapter presents the findings and conclusions based on the data analyzed in the previous chapter, explains the implications and recommendations based on these findings, and identifies some limitations that might have influenced the results. This chapter also includes a summary of significant findings in the literature pertaining to this study. Purpose of the Study The purpose of this study was to investigate the effects of using particle diagrams on AIMS high school students’ conceptual understanding of Stoichiometry, specifically on the concepts of representative particles, mole ratio, limiting reagent, and theoretical yield. The research questions that guided this study were: Research Question 1. To what extent does the use of particle diagrams affect students’ conceptual understanding of representative particle, mole ratio, limiting reagent, and theoretical yield? Research Question 2. What are the students’ attitudes towards the use of particle diagrams? In this study, the impact of incorporating particle diagrams on stoichiometry instruction was researched by examining to what extent they affected the participants’
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 60 understanding of stoichiometry concepts, and in what ways the students had found them helpful in their study of stoichiometry. Review of the Literature Stoichiometry is a subject of Chemistry that deals with numerical relationships in chemical reactions, and in which the students’ main task is to calculate quantities of substances using balanced chemical equations (Wilbraham, 2012). Stoichiometry problem-solving requires students to track and tally the amounts of reactants and products using ratios of moles of representative particles derived from chemical equations. Although it sounds like a simple form of bookkeeping, studies have shown that most students find this subject challenging to grasp and therefore discouraging or unmotivating (Sangar, 2005; Parchman, 2006; Gulacor, 2013; Kimberlin & Yezierski: 2016). Studies also show that teachers lack understanding of how to teach stoichiometry and admit that stoichiometry is a complicated and difficult subject to teach (Parchman, 2006; Bridges, 2015; Hand et al., 2007; Pedretti, 2010; Gulacor et al., 2013). Stoichiometry derives its reputation as a problematic subject primarily from its dominant problem-solving nature. Problem-solving in stoichiometry calls for students to be proficient with mathematical skills and to have a solid understanding of stoichiometry concepts. Studies indicate that the learning and instruction of stoichiometry have been mainly through the use of flowcharts, undefined strategies and algorithms (Schmidt & Jignéus, 2003; Haider & Al Naqabi, 2008; Okanlawon, 2010; Hanson, 2014; Kusi, 2013; Goldberg, 2015), which do not foster conceptual understanding and may lead to confusion and wrong answers if not appropriately applied. While students have developed procedural fluency through the use of algorithms and, therefore, can solve simple numerical problems, it does not
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 61 necessarily mean that they understand the underlying concepts (Boujaoude & Barakat 2003; Antwi, 2013). In fact, for years, students have struggled with understanding the conceptual underpinnings of stoichiometry problems and have not been successful in solving conceptual-type problems and complex numerical problems that require conceptual justification (Dahsah & Coll, 2007; Salta & Tzougraki, 2011). Students who have a conceptual knowledge base are more successful in solving complex problems and making fewer algorithmic mistakes (Gulacar, 2007; Wolfer, 2012; Kimberlin & Yezierski, 2016). Many teaching strategies that support conceptual understanding of stoichiometry have been developed over the years (Opara, 2010; Mansoor & Montes, 2012; Cotes & Cotua, 2014; Sedumedi, 2014; Adekunle et al., 2015; Yezierski & Kimberlin, 2016), including the “three-levels-of-chemistry” approach. This approach aims at fostering a conceptual understanding by teaching students to interpret chemical reactions at the macroscopic, submicroscopic, and symbolic levels consecutively (Cheng & Gilbert, 2014). Studies have shown that macro–sub micro– symbolic teaching enhances students’ understanding of stoichiometry concepts such as chemical reactions which are the basis of all stoichiometry problems (Jaber & Boujaoude, 2012; Khan & Slate 2015; Sujak & Daniel, 2017), limiting reagent (Weng, 2014), balancing chemical equations (Gulacar et al., 2013), and the mole (Indiryanti & Barke, 2017). These studies confirm that the three-level approach to teaching stoichiometry supports and promotes conceptual understanding. The three-level approach teaches that all chemical reactions can be explained in terms of particles and processes at the sub-microscopic level. Therefore, the macroscopic and symbolic representations of chemical reactions are better understood
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 62 if stoichiometry instruction focuses first on the sub-microscopic explanations (Sanchez, 2018). Incorporating particle diagrams in stoichiometry instruction is a way to help students focus on submicroscopic phenomena before linking them to macro events and chemical equations. An understanding of the submicroscopic composition of chemical substances in chemical reactions is an essential prerequisite to interpreting and solving stoichiometric problems especially the conceptual ones (Davidowitzs et al., 2009; Jaber & Boujaoude, 2012; Sujak & Daniel, 2017). Methods The research approach used in this study was the pre-experimental one-group pre-test post-test design (or paired-sample design). The participants of this study were thirteen 10th grade students who enrolled in the General Chemistry class for the academic year 2018-19 at AIMS. These students happened to be the researcher’s students in her Chemistry class and therefore were conveniently available for the study and enabled the researcher to conduct the research in a real classroom setting. The researcher applied two data collection techniques in the study – pretest/posttest and questionnaire. A published instrument called Conceptual Stoichiometry Test (CST) was used for the pretest and posttest and was administered to the students approximately four weeks apart. During the four-week interval, students continued their Chemistry classes as scheduled, and particle diagrams compiled in a booklet entitled Thinking the Particulate Way (TPW) was used consistently and systematically in all their stoichiometry lessons. An Attitude Towards the Use of Particle Diagrams (ATPD) questionnaire devised for the study by the researcher was completed by the participants at the end of the four-week intervention.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 63 Data collected from the CST pretest and posttest was used to address research question 1. The test scores were keyed into SPSS and were analyzed using the pairedsample (correlated) t-test to determine whether there was a statistically significant difference between the mean scores for the pretest and the posttest. Data collected from the ATPD questionnaire was used to answer research question 2. The data were analyzed using descriptive statistics in the forms of means, standard deviations, and percentages. Results The results obtained from this study are summarized as follows. The results of the paired-sample t-test show that there was a statistically significant increase in pretest scores before intervention to posttest scores after intervention for each of the concepts of representative particles, mole ratio, limiting reagent, and theoretical yield. Cohen’s d values show that the treatment had a substantial effect on the difference between the pretest and posttest scores on the concepts of representative particles, mole ratio, limiting reagent, and theoretical yield. Students’ responses to the questionnaire show that more than half of them agreed and strongly agreed that the use of particle diagrams helped them develop an understanding of the concepts of representative particles, mole ratio, and limiting reagent. However, less than half of the students agreed that the use of particle diagrams helped them develop an understanding of the concept of theoretical yield. Discussion of the Findings
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 64 Finding 1. The posttest results show that the students’ improved significantly in their understanding of the concept of representative particles after using particle diagrams in their lessons, and the majority of them agreed that the use of particle diagrams helped develop an understanding of this concept. Explanation 1. By the end of the four-week intervention, students had interpreted and constructed more than fifty particle diagrams that illustrated the chemical compositions of various pure substances. Through repeated exposure, students would have observed that chemical elements and compounds are composed of submicroscopic particles as represented by individual spheres or groups of spheres in particle diagrams. They also learned that these submicroscopic particles, which could be atoms, molecules, or ions/formula units, are the smallest units into which a substance can be broken down without a change in composition (Wilbraham et al., 2012). Students were guided to attach meanings to different characteristics of the particle diagrams, and the following representations would have become embedded in their long-term memory. (1) Spheres of different colors and sizes represent different types of atoms, (2) individual spheres of the same color and size represent an element, (3) clusters of spheres of the same color and size represent an element, (3) spheres of different colors or sizes in tight clusters represent molecules of covalent compounds, and (4) spheres of different colors or sizes in an array represent ions or formula units of ionic compounds. There were four questions related to this concept in the CST test. Questions 2,3 and 4 required the students to select the particle diagrams that best illustrated the
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 65 representative particles of either a reactant or a product. Question 9 required students to draw a particle diagram that illustrated the representative particles of a product. The majority of the students answered these questions correctly. Anchoring concepts with the help of characteristics such as color and size help students visualize and understand abstract chemical concepts in terms of more familiar and concrete representations (Baluyut, 2015). The students learned what precisely was represented by the different features of the particle diagrams, and consequently were able to visualize the submicroscopic representative particles that constitute the reactants and form the products in chemical reactions. This learning experience explains the significant increase in the students’ understanding of the concept of representative particles, as indicated by the posttest score and their affirmative response in the questionnaire. Finding 2. The posttest results show that the students’ improved significantly in their understanding of the concept of mole ratio after using particle diagrams in their lessons, and the majority of them agreed that the use of particle diagrams helped develop an understanding of this concept. Explanation 2. During the intervention period, students had plenty of opportunities to improve and apply their translational skills among the macroscopic, symbolic, and microscopic representations of chemical reactions. In some practice exercises, the students had to translate particle diagrams into balanced chemical equations. In others, they had to illustrate balanced chemical equations by constructing particle diagrams that show the submicroscopic processes and the correct number of
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 66 submicroscopic particles (atoms, molecules, ions, or formula units) involved in those processes. In doing so, they observed that the coefficients in front of chemical formulas in a balanced chemical equation represent the quantities of reactant and product particles necessary to conserve mass during a chemical reaction. From these coefficients, students determined the lowest ratio between any two substances in a chemical reaction and extrapolated it to a mole ratio. There were five questions related to the concept of the mole ratio in the CST test. Questions 1 and 6 asked for the number of moles of a reactant and product, respectively, according to a given balanced chemical equation. In question 5, students had to extrapolate of moles of molecules to millions of molecules. In question 7, students had to write a chemical equation that included the correct mole ratio, and in question 8, students explained the necessity of coefficients in chemical equations. The majority of the students answered these questions correctly. The practice exercises helped students understand the idea of the mole as the conversion from the atomic/sub-microscopic to the macroscopic scale and that mole ratio represents the quantitative relationships among substances in chemical reactions in terms of the number of moles. This learning experience explains the significant increase in the students’ understanding of the concept of mole ratio as indicated by the posttest score and their affirmative response in the questionnaire. Finding 3. The posttest results show that the students’ improved significantly in their understanding of the concept of limiting reagents after using particle diagrams in their lessons, and the majority of them agreed that the use of particle diagrams helped develop an understanding of this concept.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 67 Explanation 3. The limiting reagent is the reactant that is first to run out in a chemical reaction. This reactant limits the amounts of products formed since the chemical reaction can no longer proceed without it. During the intervention, students simulated this concept crossing out reactant spheres and product spheres alternatively on the particle diagrams until all the product spheres were accounted for, which meant the reaction could no longer continue. This simple task helped students to “see” that the reactant spheres that were the first to run out and limited the amounts of products. This task also helped dispel two common misconceptions about limiting reagent. (1) that the reactant with the lowest number of moles is necessarily the limiting reagent and (2) both reactants are totally converted at the end of the transformation whatever the proportions (Gauchon, 2007) There were three questions related to the concept of limiting reagent in the CST test. Question 4 required the students to select the particle diagram that best represented the product (and leftover reactant if there was any) of a chemical reaction. Students could only answer this question correctly if they had identified the limiting reagent correctly in the chemical reaction by tallying reactant particles and product particles. Question 9 asked students to construct a particle diagram that illustrated the product particles of a chemical reaction, taking into consideration that one of the reactants was a limiting reagent. Question 10 asked the students to identify the limiting reagent in question 9. The majority of the students answered these questions correctly. With the help of particle diagrams, students were able to visualize the concept of limiting reagent and its role in chemical reactions. This learning experience explains the significant increase in the students’ understanding of the concept of
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 68 limiting reagent, as indicated by the posttest score and their affirmative response in the questionnaire. Finding 4. The posttest results show that the students’ improved significantly in their understanding of the concept of theoretical yield after using particle diagrams in their lessons, but the majority of them disagreed that the use of particle diagrams helped develop an understanding of this concept. Explanation 4. The theoretical yield is the maximum amount of product that could be formed from given amounts of reactants (Wilbraham et al., 2012). To understand this concept, students first identified or constructed particle diagrams that illustrated the given amounts of reactants in terms of the number of representative particles. Then students “formed” the product(s) by tallying or drawing as many product particles as could be generated from the number of reactant particles available until the particles of one of the reactants were all used up. The students were informed that the number of product particles obtained at the end of this exercise represented the theoretical yield. There were three questions related to the concept of theoretical yield in the CST test. Questions 4 and 9 required the students to select and construct a particle diagram that best represented the product of a chemical reaction, respectively. Correct answers would have indicated that the students had correctly determined the number of product particles from the numbers of reactant particles. Question 10 asked the students to identify the limiting reagent in question 9. A correct would have
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 69 indicated that the students had determined the theoretical yield correctly. The majority of the students answered these three questions correctly. The basis of solving theoretical yield problems is merely applying the concepts of mole ratio and limiting reagent, which the results showed that the students had understood very well. All the particle diagram exercises intended for reinforcing students’ understanding of these prerequisite concepts were also intended for clarifying the concept of the theoretical yield. This learning experience explains the significant increase in the students’ understanding of the concept of limiting reagent as indicated by the posttest score The students' unfavorable response in the questionnaire was contradictory to the posttest score. A short discussion with the students about responses to the questionnaire revealed the following: (1) Some students misinterpreted the term “theoretical yield,” and mistaking it for “actual yield” which was another concept they had learned in stoichiometry, (2) some students had a wrong conception of the term “theoretical yield,” and (3) a few did not know or remember what the term meant. They inadvertently equated their lack of familiarity or knowledge of the term “theoretical yield” to lack of understanding of the concept. Most of the findings discussed above are consistent with Davidowits and others (2010), who noted that instruction that required students to interpret and construct diagrams of chemical reactions at the sub micro level led to a deeper conceptual understanding of chemical reactions. Conclusions This study has gathered evidence supporting the view that the use of particle diagrams supports a conceptual understanding of the concepts of representative particles, mole ratio, limiting reagent, and theoretical yield among AIMS tenth grade
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 70 Chemistry students. Through the test of significance, it was shown that there was a significant correlation between the use of particle diagrams and the students’ conceptual understanding of each of these concepts. Results from the questionnaire reveal that AIMS high school chemistry students demonstrated a favorable attitude towards the use of particle diagrams for developing a conceptual understanding of the concepts mentioned above except the concept of theoretical yield. AIMS students’ responses to the use of particle diagrams matched with what was already described in the literature and confirmed the positive effects of using particulate models to enhance understanding of chemistry concepts. Limitations The present study has the following limitations. 1. The sample size was small. The small sample size did not allow for sufficient statistical power to extrapolate the statistical analysis results to an overall population. However, the researcher does not intend to use the results as a parameter on which to propose the intervention to any population. 2. The research design requires the same group to be given the same treatment and tested before and after the treatment. Factors other than the treatment alone could have contributed to the difference between the pretest and posttest results. Because of this and the absence of a comparison group, the results may not demonstrate a cause-and-effect relationship. 3. This study only focused on the effects of the use of particle diagrams on the conceptual understanding of students in one school. Therefore, the researcher does not claim that the results can be generalized to other students or in other schools. The same research done with other students or in other schools may yield different findings.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 71 4. Although the intervention period was four weeks, in actuality, the students spent only twenty 40-minute contact periods in chemistry class. Because the teacher was obliged to cover content and it was her first time to implement the treatment, the assimilation of particle diagrams in the regular lessons may not have been done effectively, and students may have been rushed into “thinking the particulate way” without fully internalizing it. These could have affected their answers to the posttest and responses to the questionnaire. 5. The Chemistry teacher of the students involved in this study was also the researcher of this study. Because the teacher was both a familiar and an authority figure in their everyday lives, students might have intentionally or unintentionally responded more favorably to the questionnaire. Implications The findings of this study add modestly to the body of literature on intervention strategies in the teaching of chemistry, specifically stoichiometry. Visual-based conceptual approaches to teaching chemistry have been the primary trend, and they are likely to keep being used. Simple interventions such as the incorporation of simple particle diagrams in chemistry lessons can be the basis or beginning for more assertive, sophisticated, or elaborate pedagogies that support or enforce progressive conceptual understanding. Using particle diagrams could be an effective way to help students build conceptual understanding in the way this study has not been unable to demonstrate. Recommendations for Future Research Suggestions with reference to the limitations and implications mentioned earlier are:
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 72 1. The findings of this research must not be generalized to other schools because the sample for this study was small and was limited in scope in that it considered students only in one school setting. Further research can be conducted with a larger sample size from schools situated in different areas throughout Thailand. 2. Other factors that may influence students’ ability to acquire conceptual understanding, such as their study habits, attitudes toward study, interests, intelligence, academic competency, academic motivation, self-efficacy, parental socio-economic background, etcetera, should also be considered for further research. 3. Research to compare the effects of using 2-D representations (such as particle diagrams) and 3-D models (such as sticks and spheres) in developing student’s understanding of chemistry concepts. 4. Future research works on intervention strategies that support different types of learning styles (kinesthetic, linguistic, mathematical, etcetera) to develop a conceptual understanding of chemistry.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 73 REFERENCES LIST Agung, S., & Schwartz, M. S. (2007). Students’ understanding of conservation of matter, stoichiometry and balancing equations in Indonesia. International Journal of Science Education, 29(13), 1679–1702. doi:10.1080/09500690601089927 Bridges, C. D. (2015). Experiences teaching stoichiometry to students in grades 10 and 11 (Doctoral dissertation, Walden University, United States). Retrieved from http://scholarworks.waldenu.edu/ cgi/viewcontent.cgi?article=1290&context=dissertations Chandrasegaran, A. L., Treagust, D. F., Waldrip, B. G., & Chandrasegaran, A. (2009). Students’ dilemmas in reaction stoichiometry problem solving: deducing the limiting reagent in chemical reactions. Chemistry Education Research and Practice., 10(1), 14–23. doi: 10.1039/b901456j Cheng, M., & Gilbert, J. (2014). Teaching stoichiometry with particulate diagrams – Linking macro phenomena and chemical equations. In B. Eilam, & J. Gilbert (Eds.), Science teachers’ use of visual representations (pp. 123–143). doi: 10.1007/978-3-319-06526-7_6 Chiu, Mei-Hung. (2001). Algorithmic Problem Solving and Conceptual Understanding of Chemistry by Students at a Local High School in Taiwan. Proceedings of the National Science Council, 11(1), 20-38.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 74 College Board. (2014). AP chemistry course and exam description (revised ed.). New York, NY: The College Board. Retrieved from https://securemedia.collegeboard.org/digitalServices/pdf/ap/ap-chemistry-course-and-examdescription.pdf Copolo, C. E., & Hounshell, P. B. (1995). Using three-dimensional models to teach molecular structures in high school chemistry. Journal of Science Education and Technology, 4(4), 295–305. doi: 10.1007/bf02211261 Cotes, S. & and Cotuá, J. (2014) Using Audience Response Systems during Interactive Lectures To Promote Active Learning and Conceptual Understanding of Stoichiometry. Journal of Chemical Education, 91(5), 673- 677. doi: 10.1021/ed400111m Dahsah, C., & Coll, R. (2007). Thai grade 10 and 11 students’ conceptual understanding and ability to solve stoichiometry problems. Research in Science & Technological Education, 25(2), 227–241. doi:10.1080/02635140701250808 Davidowitz, B., & Chittleborough, G. (2009). Linking the Macroscopic and Submicroscopic Levels: Diagrams. Models and Modeling in Science Education Multiple Representations in Chemical Education, 4, 169-191. doi: 10.1007/978-1-4020-8872-8_9 Fach, M., Boer, T., & Parchmann, I. (2007). Results of an interview study as basis for the development of stepped supporting tools for stoichiometric problems. Chemistry Education Research and Practice, 8(1), 13-31. doi:10.1039/b6rp90017h
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 75 Gabel, D. (1994). Handbook of research on science teaching and learning. New York: Macmillan. George, D. and Mallery, P. (2003). SPSS for windows step by step: A simple guide and reference 11.0 update (4th ed.). Boston, MA: Allyn and Bacon. Goldberg, D. (2015). Fundamentals of Chemistry (5th ed.). New York, NY: McGrawHill Education. Gulacar, O. (2007). An Investigation of Successful and Unsuccessful Students' Problem-solving in Stoichiometry. Retrieved from https://scholarworks.wmich.edu/dissertations/870 Gulacar, O., Overton, T. L., Bowman, C. R., & Fynewever, H. (2013). A novel code system for revealing sources of student’s difficulties with stoichiometry. Chemistry Education Research and Practice, 14(4), 507–515. doi: 10.1039/c3rp00029j Hand, B., Yang, O. E.-M., & Bruxvoort, C. (2006). Using Writing-to-Learn Science Strategies to Improve Year 11 Students’ Understandings of Stoichiometry. International Journal of Science and Mathematics Education, 5, 125-143. doi: 10.1007/s10763-006-9029-8 Hanson, R. (2016). Ghanaian Teacher Trainees’ Conceptual Understanding of Stoichiometry. Journal of Education and e-Learning Research, 3(1), 1–8. doi: 10.20448/journal.509/2016.3.1/509.1.1.8
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 76 Hanson, R. & E. K. Oppong, (2014). Conceptual understanding of stoichiometry and translations of problems among high school students. Journal of Science Education and Research, 1(1), 1-8. Hanson, R. (2014). Undergraduate chemistry teacher-trainees understanding of stoichiometry- a case study in the university of education, Winneba. Winneba: Faculty of Science Education, University of Education, Winneba. Harrison, A. G., & Treagust, D. F. (2002). The Particulate Nature of Matter: Challenges in Understanding the Submicroscopic World. Chemical Education: Towards Research-Based Practice Science & Technology Education Library, 17, 189–212. doi: 10.1007/0-306-47977-x_9 Kimberlin, S., & Yezierski, E. (2016). Effectiveness of Inquiry-Based Lessons Using Particulate Level Models to Develop High School Students’ Understanding of Conceptual Stoichiometry. Journal of Chemical Education, 93(6), 1002–1009. doi: 10.1021/acs.jchemed.5b01010 Jaber, L. Z., & Boujaoude, S. (2012). A Macro–Micro–Symbolic Teaching to Promote Relational Understanding of Chemical Reactions. International Journal of Science Education, 34(7), 973–998. doi: 10.1080/09500693.2011.569959 Jaoude, S. B., & Barakat, H. (2005). Students' Problem-Solving Strategies in Stoichiometry and their Relationships to Conceptual Understanding and Learning Approaches. The Electronic Journal for Research in Science & Mathematics Education, 7(3), 165–174. doi: 10.18848/1447- 9494/cgp/v17i06/47098
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 77 Johnstone, A. (2000). Teaching of chemistry – Logical or psychological? Chemistry Education Research and Practice 1(1), 9–15. doi: 10.1039/a9rp90001b Joyner, R. L., Rouse, W. A., & Glatthorn, A. A. (2013). Writing the winning thesis or dissertation: a step-by-step guide (3rd ed.). Thousand Oaks: Corwin. Lamidi, B. T., Oyelekan, O. S., & Olorundare, A. S. (2015). Effects of Mastery Learning Instructional Strategy on Senior School Students’ Achievement in the Mole Concept. Electronic Journal of Science Education, 19(5). doi: 10.20944/preprints201702. 0018.v1 Makhechane, M., & Qhobela, M. (2019). Understanding How Chemistry Teachers Transform Stoichiometry Concepts at Secondary Level in Lesotho. South African Journal of Chemistry, 72, 59–66. doi: 10.17159/0379- 4350/2019/v72a9 Morgan, G. A., Griego, O. V., and Gloekner, G. W. (2001). SPSS for windows: An introduction to use and interpretation in research. Mahwah, NJ: Lawrence Erlbaum. Niaz, M., & Montes, L.A. (2012). Understanding Stoichiometry: Towards a History and Philosophy of Chemistry. Chemistry Education, 23(2), 290-297. doi.org/10.1016/S0187-893X (17)30156-8 Opara, M.F. (2010). Mind mapping as a Self-regulated Learning Strategy for Students’ Achievement in Stoichiometry. The Nigerian Journal of Research and Production, 17(1).
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 78 Pallant, J. (2011). Spss survival manual: a step by step guide to data analysis using the Spss program (4th ed.). Sydney, NSW: Allen & Unwin. Prilliman, S. G. (2014). Integrating Particulate Representations into AP Chemistry and Introductory Chemistry Courses. Journal of Chemical Education, 91(9), 1291–1298. doi: 10.1021/ed5000197 Rahayu, S., & Kita, M. (2009). An analysis of Indonesian and Japanese students’ understandings of macroscopic and submicroscopic levels of representing matter and its changes. International Journal of Science and Mathematics Education, 8(4), 667–688. doi: 10.1007/s10763-009-9180-0 Riaz, M. (2004). Helping children to understand particulate nature of matter. Alberta Science Education Journal, 36(2), 56-59. Salta, K., & Tzougraki, C. (2010). Conceptual Versus Algorithmic Problem-solving: Focusing on Problems Dealing with Conservation of Matter in Chemistry. Research in Science Education, 41(4), 587–609. doi: 10.1007/s11165-010-9181-6 Sanchez, J. M. P. (2018). Translational Skills of Students in Chemistry. Science Education International, 29(4), 214–219. doi: 10.1063/1.4983904 Sanger, M. (2000). Using particulate drawings to determine and improve students' conceptions of pure substances and mixtures. Journal of Chemical Education, 77(6), 762. doi:10.1021/ed077p762
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 79 Sanger, M. J. (2005). Evaluating students' conceptual understanding of balanced equations and stoichiometric ratios using a particulate drawing. Journal of Chemical Education, 82(1), 131. doi:10.1021/ed082p131 Schmidt, H., & Jignéus, C. (2003). Students´ strategies in solving algorithmic stoichiometry problems. Chemistry Education Research and Practice, 4(3), 305–317. doi: 10.1039/b3rp90018e Sedumedi, T. D. (2014). The Use of Productive Inquiry in the Teaching of Problem Solving in Chemical Stoichiometry. Mediterranean Journal of Social Sciences, 5(20), 1346–1359. doi: 10.5901/mjss.2014.v5n20p1346 Seetso, I., & Taiwo, A. (2005). An evaluation of Bostswana senior secondary school chemistry syllabus. Journal of Baltic Science Education, 2(8), 5–14. Retrieved from http://oaji.net/articles/2016/987-1481284752.pdf Simon, M. K. (2011). Dissertation and scholarly research: Recipes for success (2nd Ed.). Seattle, WA, Dissertation Success, LLC. Shadreck, M., & Enunuwe, O. C. (2017). Problem Solving Instruction for Overcoming Students’ Difficulties in Stoichiometric Problems. Acta Didactica Napocensia, 10(4), 69–78. doi: 10.24193/adn.10.4.8 Sujak, K., & Daniel, E.G.S. (2017). Understanding of Macroscopic, Microscopic and Symbolic Representations Among Form Four Students in Solving Stoichiometric Problems. Malaysian Online Journal of Educational Sciences, 5(3), 83-96.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 80 Sunyono, Yuanita, L., & Ibrahim, M. (2015). Mental models of students on stoichiometry concept in learning by method based on multiple representations. The Online Journal of New Horizons in Education, 5(2), 30- 45. Retrieved from http://www.tojned.net/journals/tojned/articles/v05i02/v05i02-05.pdf Taha, H., Hashim, R., Ismail, Z., Jusoff, K., & Yin, K. (2014). The influence of students' concept of mole, problem representation ability and mathematical ability on stoichiometry problem solving. Proceedings of the 2014 WEI International Academic Conference Proceedings, USA, 21(1), 122-136. Retrieved from https://www.westeastinstitute.com/wpcontent/uploads/2014/06/Hafsah-Taha-1.pdf Tai, R. H., Ward, R. B., & Sadler, P. M. (2006). High school chemistry content background of introductory college chemistry students and its association with college chemistry grades. Journal of Chemical Education, 83(11), 1703. doi:10.1021/ed083p1703 Toth, Z., & Sebestyén, A. (2009). Relationship between Students’ Knowledge Structure and Problem-Solving Strategy in Stoichiometric Problems based on the Chemical Equation. Eurasian Journal of Physics & Chemistry Education, 1(1). doi: 10.1787/9789264208070-table86-en Warner, R. M. (2013). Applied statistics: From bivariate to multivariate techniques (2nd Edition). Los Angeles, CA: Sage Publications, Inc. Wilbraham, A. C., Staley, D. D., Matta, M. S., & Waterman, E. L. (2012). Pearson chemistry. Boston, MA: Pearson.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 81 Wood, C. & Breyfogle, B. (2006). Interactive demonstrations for mole ratios and limiting reagents. Journal of Chemical Education 83(5), 741-746. doi.org/10.1021/ed083p741 Zike, D., Hainen, N., Dingrando, L., & Buthelezi, T. (2017). Glencoe chemistry: matter and change. Columbus, OH: Glencoe/McGraw Hill
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 82 APPENDIX QUESTIONNAIRE Students’ Attitudes towards the Use of Particle Diagrams in Understanding Concepts of Stoichiometry 1- Strongly Disagree (SD), 2- Disagree (D), 3- Not Sure (NS), 4- Agree (A), 5- Strongly Agree SA) Direction: Please check (√) and rate yourself honestly based on how you feel the use of particle diagrams has helped you in understanding concepts of Stoichiometry. CONCEPT 1 – REPRESENTATIVE PARTICLES 1 2 3 4 5 1. Particle diagrams help me visualize the small particles that make up compound, mixture and elements. 2. Particle diagrams help me differentiate among atoms, molecules, ions, and combinations of these. 3. Particle diagrams help me understand what happens to the particles of reactants during chemical reactions. CONCEPT 2 – MOLE RATIO 1 2 3 4 5 4. Particle diagrams help me understand what the coefficients in balanced chemical equations represent. 5. Particle diagrams help me determine how many of each kind of atom take part in a chemical reaction in the lowest whole number ratio.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 83 6. Particle diagrams help me use coefficients to calculate amounts of substances needed or produced in a chemical reaction. CONCEPT 3 – LIMITING REAGENT 1 2 3 4 5 7. Particle diagrams show that in some chemical reactions, reactants are not necessarily all used up. 8. Particle diagrams help me identify the reactant that is all used up first (limiting reagent). 9. Particle diagrams help me identify the reactant that is NOT all used up (excess reagent). CONCEPT 4 – THEORETICAL YIELD 1 2 3 4 5 10. Particle diagrams help me understand the difference between theoretical yield and actual yield. 11. Particle diagrams help me identify which reactant determines the theoretical yield. Conceptual Understanding of Stoichiometry Pretest/Posttest Revised by Kimberly and Yezierski (2015) Student Name: MULTIPLE CHOICE ITEMS _____ 1. Consider the following generic chemical equation: 3A + 2B → 4C How many moles of B would you need to react completely with 5 moles of A? A) 1.2 B) 1.5 C) 2 D) 3.3 _____2. Hydrogen peroxide will decompose to form water and oxygen gas according to the following equation. 2H2O2 2H2O + O2 hydrogen water oxygen peroxide Use the following key for the diagrams
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 84 Which diagram is the best representation of the hydrogen peroxide before it decomposes? A) B) C) D) _____3. Hydrogen peroxide will decompose to form water and oxygen gas according to the following equation. 2H2O2 → 2H2O + O2 hydrogen water oxygen peroxide Use the following key for the diagrams Which diagram is the best representation of the products after hydrogen peroxide decomposes? A) B) C) D) _____4. The diagram represents a mixture of S and O2 molecules in a closed container. Which diagram shows the results after the mixture reacts as completely as possible according to the equation: 2S + 3O2 → 2SO3 A) B) C) D)
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 85 _____5. Your body reacts sugar with oxygen to form carbon dioxide and water according to the following chemical equation: C6H12O6 + 6O2 → 6CO2 + 6H2O sugar oxygen carbon water dioxide If you had two million sugar molecules how many millions of oxygen molecules would be needed to react completely with the sugar. A) 3 B) 6 C) 9 D) 12 _____6. Butane is combusted completely with excess oxygen to form water and carbon dioxide. 2C4H10 + 13O2 → 10H2O + 8CO2 butane oxygen water carbon dioxide The reaction produced one mole of water, how many moles of carbon dioxide were produced? A) 0.8 B) 1.25 C) 4 D) 8 FREE RESPONSE ITEMS Question 7 Score Methane (CH4) will react with oxygen gas (O2) to produce carbon dioxide (CO2) and water (H2O). Write a balance chemical equation in the box below to symbolize the reaction that is taking place. Question 8 Score When Iron is exposed to humid air for a period of time, it rusts. The chemical equation for this reaction is: 4Fe + 3O2 → 2Fe2O3 Explain the necessity of the underlined numbers.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 86 Question 9 Score Ethanol, an additive used in some gasoline, combines with oxygen to produce carbon dioxide and water. The chemical equation that symbolizes this reaction is the following: C2H6O + 3O2 → 2CO2 + 3H2O The following diagram represents a mixture of ethanol and oxygen in a closed container. In the box below, draw what the products of the reaction would look like after the mixture reacts as completely as possible according to the equation above. Question 10 Score Name the reactant that would be consumed completely in the reaction above.
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 87 Selected pages from the Thinking the Particulate Way Booklet
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 88
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 89
CONCEPTUAL UNDERSTANDING OF STOICHIOMETRY 90