Eylem
Yalçınkaya
a and
Yezdan
Boz
*b
aTunceli University, Faculty of Engineering, Department of Chemical Engineering, Tunceli, Turkey
bMiddle East Technical University – Faculty of Education, METU Üniversiteler Mah. Dumlupınar Blv. No:1, Ankara çankaya 06800, Turkey. E-mail: yezdan@metu.edu.tr
First published on 6th November 2014
The main purpose of the present study was to investigate the effect of case-based instruction on remedying 10th grade students' alternative conceptions related to gas concepts. 128 tenth grade students from two high schools participated in this study. In each school, one of the classes was randomly assigned as the experimental group and the other class, instructed by the same chemistry teacher, was assigned as the control group. The students in the experimental groups were instructed by case-based instruction based on conceptual change conditions while the control group students received traditionally designed chemistry instruction. As pre-tests, the science process skills test, the attitude and motivation towards chemistry and the gas concept test were applied to both groups of students. As a post-test, the gas concept test was administered to both groups of students to determine their alternative conceptions and understanding of gas concepts. One-way ANOVA was used to assess the effect of case-based instruction on students' understanding of gas concepts. The results revealed that case-based instruction was an effective method for overcoming students' alternative conceptions about the gas concepts.
1. Is there a significant mean difference between the groups exposed to case-based instruction based on conceptual change conditions and traditionally designed chemistry instruction with respect to tenth grade students' understanding of gas concepts and alternative conceptions?
2. What are the tenth grade students' alternative conceptions about gases after being exposed to case-based and traditional instruction?
Students believed that air flows from one place to another like water but is unevenly distributed. According to some students, atmospheric pressure pushes the gas molecules down (Lin et al., 2000); air does not exert the same pressure in different directions (Brook et al., 2003); and gas particles are unevenly scattered in any enclosed space (Novick and Nussbaum, 1981; Lee et al., 1993; Cho et al., 2000). Moreover, students supposed that when the air is compressed, particles are compacted like a solid and do not move or they stick together (Lonning, 1993). Some of the students thought that when the air is compressed in a syringe, air moves toward the opening of the syringe (Lee et al., 1993). She (2002) examined the process of conceptual change related to air pressure and reported that most of the students believed that air cannot be compressed. They also thought that air pressure has a direction.
Moreover, some naive conceptions have been identified regarding cold and warm air. Most students thought that a balloon would blow up or get larger due to hot air or heat instead of thermal expansion. Hence, they believed that hot air would rise and cold air would go down in a bottle, so there was hot air or heat in the top and cold air in the bottom. In addition to these, some students believed that when a substance evaporates, it becomes invisible and it no longer exists (Lee et al., 1993). Moreover, the stereotypical views like ‘air is everywhere’ and ‘hot air rises’ were often stated by pupils (Séré, 1986). Related to the kinetic theory of gases, students had some major alternative conceptions; for example, they considered that atmospheric pressure pushes gas molecules down; gas molecules rise and stay away from heat; and molecules expand when they are heated (Lin et al., 2000). Students believed that when the temperature is lowered, gas particles sink to the bottom of a container and the majority of the high school students explained the decrease in volume of a gas on cooling not in terms of decreasing particle motion but in terms of increasing attractive forces (Novick and Nussbaum, 1981). Sometimes students' intuitive thinking can be one of the sources of misconceptions; for example as a cause of deflation of the balloon students said, “The energy gradually dies, so the gas motion stops and balloon deflates” (Haidar and Abraham, 1991). Accordingly, most of the students were not able to draw the appropriate representation of gas particles inside a flask (Lin et al., 2000). Nussbaum (1985) asked how the distribution of gases would be after evacuating some of the air from a flask. While some of the students (14 years old) thought that the upper part of the flask is filled with air, the others believed that the lower part of the flask is filled with air.
Students also had difficulties in understanding and applying the ideal gas law appropriately. Students memorized the ideal gas formula, PV = nRT without understanding it conceptually (Lin et al., 2000). Many of the students focused on the relationship between two variables in the ideal gas law regardless of the others. For instance, they assumed that “Pressure is always inversely proportional to the volume” and “Pressure is always directly proportional to the temperature” (Kautz et al., 2005a). From the microscopic viewpoint, some of the students believed that the density of a gas decreases as a result of expansion and so in order to keep the pressure constant, the speed of the particles must increase. Some of them thought that when a gas is enclosed in a smaller volume, gas particles are more likely to come together and collide with each other frequently. Consequently, the temperature and then average kinetic energy increases; that is, they “Mistakenly assume that molecular collisions generate kinetic energy” (Kautz et al., 2005b). Some students even thought that these collisions may result in a change of atomic size (Griffiths and Preston, 1992). Similarly, in the context of the diffusion concept, students thought that molecular motion of gases stops at an ending point in the diffusion. In addition, students believed that the diffusion rate of gases increases with increasing molecular weight (Cho et al., 2000).
Consequently, research findings about students' conceptions of gases indicated that gases are one of the abstract subjects in which students have difficulties in understanding. As stated before, the constructivist approach considering the students' prior knowledge and stressing the active engagement of students in the learning process is influential in providing meaningful learning (Mayer, 1999). Accordingly, case-based learning environments providing both real life examples and social experience promote constructivist learning (Jonassen, 1994). Case-based instruction aims to teach the topic through cases. Cases are composed of two main parts: one of them is the case situation for the study and the other is the questions related to the case. Cases are complex teaching instruments in the form of narratives. The narratives are generally based on real life situations. Teacher and students study the problems related to daily life cooperatively (Wassermann, 1994). Cases can vary from a paragraph or two to a dozen pages but it is suggested that long cases be distributed and read before the class to prevent students getting confused and becoming lost in details. Learners solve the presented problem using their background knowledge (DeYoung, 2003).
At the end of each case, some study questions related to the cases help students to evaluate outcomes, concepts, and subjects of the case. The purpose of the study questions is to facilitate student understanding, rather than simply asking for the names, dates, or labels. Case-based teaching provides opportunities for students to study in small groups and discuss their responses before the whole-class discussion session occurs. During examination of the case, the teacher manages the class discussion by promoting the critical analysis of the real life problems with the students and helping students to discover the meaning. The teacher avoids imposing his or her own thoughts. Rather s/he lets students interpret their own understanding during the period of discussion (Wassermann, 1994).
Though studies regarding case-based instruction in science education are limited, some research studies showed that case-based instruction was effective in improving students' critical thinking skills and increasing their interest in learning science (Gabel, 1999); making laboratory courses interesting and relevant to daily life (Frerichs, 2012); establishing a link between science and non-science classes (Richmond and Neureither, 1998); and increasing students' performance and academic knowledge regarding the nervous system (Çakır, 2002) and the human reproductive system (Saral, 2008). Moreover, case-based learning was found to be an effective method for remediating students' misconceptions in the context of solubility equilibrium (Çam, 2009); solids, liquids and gases (Ayyıldız and Tarhan, 2013); and gene biodiversity (Gallucci, 2007). Consequently, it can be said that case-based instruction is a teaching strategy for promoting students' engagement in learning science and making improvements toward conceptual change. In the present study, the aim was to provide four conditions for conceptual change that Posner et al. (1982) identified; dissatisfaction, intelligibility, plausibility, and fruitfulness.
Although the related literature suggests that case-based instruction would be more effective compared to the traditional instruction, the success of any teaching instruction depends on several issues. To illustrate, both students and teachers in Turkey are not accustomed to any active teaching methods, i.e. case-based instruction. Teachers in Turkey are used to teaching in a traditional way. However, in case-based instruction, the role of the teacher will change from the disseminator of information to the facilitator that guides students to construct their own knowledge. Similarly, the role for the students will change from listening passively to participating in discussions to reveal their ideas explicitly. As Airasian and Walsh (1997) suggest, it would take some time for students and teachers to get accustomed to these roles. Woods (1994) observed that teaching habits can make it difficult for teachers to accept change. Moreover, Gallucci (2007) claimed that instructors' enthusiasm using the case-method is an important factor contributing to the effectiveness of this method. In addition, more class time is needed for students to construct knowledge, and this presents a difficulty for teachers who need to complete a topic in an allocated period of time determined by the curriculum. This also affects the application of case-based instruction. If a teaching method was not applied genuinely in the classroom, even if it is effective theoretically, one cannot obtain positive results in practice. Similarly, success of a teaching approach may depend on the nature of the topic and the characteristics of students. Students with an external locus of control, where success or failure is attributed to external issues such as luck, fate etc., rather than their personal control, tend to do better when instructed in a teacher-centered way (Peterson, 1979). Moreover, it is not clear if suggested teaching methods based on constructivism would be successful for different subjects or contents (Airasian and Walsh, 1997). Cobern et al. (2010) also mentioned the nature of a topic does influence the choice of the most effective method of instruction. Therefore, we thought that it would be meaningful to compare case-based instruction with traditional instruction in order to reveal which one would be more effective for the students in our country in the context of the gases topic.
Each item of the GCT was examined in detail by four chemistry educators and six chemistry teachers in terms of content validity and format. Based on these recommendations, the corrections on the test were made. Afterwards, GCT was piloted with 332 high school students from different schools who had learned the gas concept previously. The Cronbach-alpha value of the multiple-choice test was 0.70 in the reliability analysis. There was not any major change to the items on the test after the pilot study. Some questions involved diagrams related to representations of submicroscopic particles in order to make the questions more comprehensible. The final form of the test was administered to both group of students (control & experimental) as a pretest and a posttest in order to evaluate their understanding of concepts related to gases (see some examples of test items in Appendix I). Please note that all questions in the GCT were written in Turkish and the present article reports translated versions. The first author, who was a PhD candidate in chemistry education at the time of the study, translated questions in the GCT into English independently. Then, the equivalence of the translated and original version was checked by the second author, who is an instructor in the chemistry education department. They discussed any disagreements together in order to reach a consensus for the final English version of the GCT.
Sample items in SPST |
---|
A police chief is concerned about reducing the speed of autos. He thinks several factors may affect the automobile speed. Which of the following is a hypothesis he could test about how fast people drive? |
(A) The younger the drivers, the faster they are likely to drive. |
(B) The larger the autos involved in an accident, the less likely people are to get hurt. |
(C) The more policemen on patrol, the fewer the number of auto accidents. |
(D) The older the autos the more accidents they are likely to be in. |
A science class is studying the effect of wheel width on ease of rolling. The class puts wide wheels onto a small cart and lets it roll down an inclined ramp and then across the floor. The investigation is repeated using the same cart but this time fitted with narrow wheels. |
How could the class measure ease of rolling? |
(A) Measure the total distance the cart travels. |
(B) Measure the angle of the inclined ramp. |
(C) Measure the width of each of the two sets of wheels. |
(D) Measure the weight of each of the carts. |
Sub-headings | Sample items |
---|---|
Intrinsic goal orientation | In a class like this, I prefer course material that arouses my curiosity, even if it is difficult to learn. |
Extrinsic goal orientation | If I can, I want to get better grades in this class than most of the other students. |
Task value | I think the course material in this class is useful for me to learn. |
Control of learning beliefs | If I try hard enough, then I will understand the course material. |
Self-efficacy for learning and performance | I'm confident I can learn the basic concepts taught in this course. |
Test anxiety | When I take tests I think of the consequences of failing. |
This instrument was piloted with 324 tenth, eleventh and twelfth grade science students. As seen from Table 3, the instrument was found reliable enough.
N (sample size) | IGO | EGO | TV | CLB | SELP | TA | |
---|---|---|---|---|---|---|---|
ENG | 356 | 0.74 | 0.62 | 0.90 | 0.68 | 0.93 | 0.80 |
TUR (Sungur's) | 488 | 0.73 | 0.54 | 0.87 | 0.62 | 0.89 | 0.62 |
TUR (current) | 324 | 0.69 | 0.75 | 0.64 | 0.69 | 0.70 | 0.77 |
Interviewees were selected using the technique that Thompson and Soyibo (2002) used in their study in order to categorize students' attitudes into categories using the mean of the posttest scores and standard deviations. Similarly, in the present study, students whose scores were above one standard deviation from the mean were regarded as high achievers. Students whose scores were within one standard deviation below the mean and one standard deviation above the mean were considered as being moderate or neutral achievers. Students with scores below one standard deviation from the mean were classified as low or poor achievers. From the pool of high, moderate and low achiever students, two high achievers, two low achievers and four moderate achievers for both experimental and control groups were randomly selected by using the option (select random sample of cases) in SPSS. Extra questions were not prepared; instead test items used in GCT were used during the interviews. The purpose of the interviews was to probe the questions asked in the concept test and detect the reasons for selecting the wrong alternative. Also, both control and experimental group students were compared after treatment in terms of their conceptions about the gas topic in the light of the interviews. The elapsed time between the gas concept test and the interviews was about one to two weeks. The first author of the present study who was not a teacher of the students interviewed the students. Each interview was conducted individually and lasted about 50 minutes. All interviews were audio-taped and transcribed later.
One hundred and twenty-eight tenth grade students from a public high school (N = 83) and an Anatolian high school (N = 45) were the participants in the present study. In each school, one of the classes was randomly selected as experimental and one class as the control group. The experimental group students were instructed by case-based instruction based on conceptual change conditions (CBCC) whereas the control group students were instructed by traditionally designed science instruction. All groups of students in the two schools followed the same National Curriculum and the same concepts for the same amount of time. For example, similar daily life examples and alternative conceptions were mentioned in both groups, and no laboratory work or demonstrations was conducted in both groups. However, in the control group, the teacher transmitted information while in the experimental group the students tried to construct this knowledge. In each school, the same teacher instructed both control and experimental group students. The teacher was male in one school while the other teacher was female.
A month before treatment, a teacher manual containing theoretical information about case-based instruction and the conceptual change model, cases that students will carry out in groups, and some directing questions for the teacher to guide students' discussion were given to the teachers. After a week, for three weeks, approximately one-hour meetings were conducted with the teachers. In these meetings, case-based instruction, the conceptual change model, the roles of the teacher and the students in case-based instruction were again explained to the teachers. Teachers were trained about the new method and how to implement case-based instruction based on conceptual change conditions for the gas unit in chemistry. For this purpose, the researcher explained a sample lesson using the atmospheric pressure case. Moreover, how the teachers would provide four conditions of conceptual change was discussed in teacher training sessions. To clarify, it was mentioned that discussion of study questions in the case was designed to create dissatisfaction among students. Therefore, the teacher should take students' opinions about these questions and discuss the reasons for different answers with the class. At that stage, the teacher may ask some more questions to promote students' dissatisfaction with the ideas. For the intelligibility and plausibility steps, the teacher was to ask some prompting and challenging questions and guide students to find the intelligible and plausible conclusion. For the fruitfulness step, the teacher was to encourage students to link the concept with daily life. Actually, classroom observations showed that teacher training sessions were successful because teachers took these suggestions into account and could apply the conceptual change conditions successfully in the classroom.
Experimental group students received case-based instruction based on conceptual change conditions. Prior to treatment, in each school experimental group students were divided into groups of four or five students by their chemistry teachers so as to be as heterogeneous as possible in terms of their chemistry achievement and general attitude toward chemistry. Then, the teachers gave information about the new teaching method; what the case-based instruction is and how it is applied in classroom settings emphasizing the roles of students in detail. The role of students in each group was to read and discuss the given problem and scenario under teacher guidance. The role of teachers was to provide an arrangement of groups and avoid giving the direct answers of the case-based learning questions during group discussions. The same content was covered in experimental group classes as in control group classes but experimental group students were instructed basically by means of the presented cases, problems or scenarios working in small groups. Students' alternative conceptions of gas concepts and remedies based on conceptual change conditions were taken into account while preparing the cases. In this study, a total of fifteen cases generally based on real-life events and experiments were used for gas concepts (see a case example in Appendix II). The cases were about atmospheric pressure, Avogadro's law, Boyle's law, Charles's law, Gay-Lussac's law, Dalton's law, a combination of Boyle–Avogadro–Charles's laws, diffusion rate (two cases), partial pressure, properties of hot and cold air, and properties of gases (four cases) (for more information on cases, please see Appendix III). For the preparation of cases, researchers investigated daily life applications and some experiments related to gas concepts from the chemistry books and internet resources. Then, case scenarios were developed from these sources. Three cases were taken from the studies of İpek (2007) and Bilgin et al. (2009). Similarly, study questions related to them were prepared based on students' alternative conceptions about gas concepts found in the literature. To illustrate, some examples of the study questions related to the case given in Appendix II were: “Compare the inside pressure of a deflated bicycle tire with the outside pressure”; “What can be said about the motion/state of gas particles in the deflated bicycle tire?”; “Can using up the energy of the gas particles in time and ceasing their motion be the reasons for deflation of the bicycle tire? Why?”; “Draw the distribution of the gas particles in the inflated and the deflated bicycle tire.” These study questions were formed in the light of the alternative conceptions: “the pressure inside a deflated bike tire or balloon is different from the pressure outside”: “the energy gradually dies, so the gas motion stops and balloon deflates”: and “gas particles are unevenly scattered in any enclosed space.”
After the preparation, for the content validity, these case materials were given to two teachers who were involved in the implementation of them and two chemistry educators. After the feedback, cases were reorganized if required. Before treatment, the cases were discussed with the chemistry teachers to decide where the cases will fit in the class schedule.
In experimental groups, students in small groups analyzed the given cases and answered the related questions. Afterward, group members shared their ideas with the whole class and class discussion began. Discussion continued until a reasonable or plausible answer(s) were found to the case questions. Meanwhile, experimental group teachers guided students by asking open-ended and challenging questions and prompting further thinking. Since the discussion of cases began and ended in class, students did not have opportunities to search or investigate the subjects from different resources such as books, internet, and library. Therefore, sometimes the needed information or clues was provided in the class materials required to solve the given problem. For example, during the implementation of the air bag case, the reaction equation (2NaN3(s) + heat → 2Na(s) + 3N2(g)) was given by the teacher after students' discussion about swelling of the air bag. And then one of the group members wrote the answers. This active learning environment allowed students to work in groups, identify learning issues, share related information with their classmates and develop critical thinking ability about events.
Since one of the purposes of the present study was to remedy students' alternative conceptions about gas concepts by case-based instruction based on conceptual change conditions, scenarios or problems were prepared by considering these alternative conceptions. The teaching strategy was planned by considering the conceptual change principles needed to assist students in removing their alternative conceptions, the conceptual change principles being dissatisfaction, intelligibility, plausibility, fruitfulness.
For example, experimental group students were presented with the atmospheric pressure case and asked why water boils faster above sea level. The dissatisfaction created in students' minds by this case and learning environment provided students opportunities to discuss the given scenario or event with both their group mates and classmates. While studying the case about atmospheric pressure, each group began to discuss the reasons for boiling water faster on the mountain. At first, some groups could not relate that event to the atmospheric pressure; they just said that the boiling point should be lower. At that point, the teacher tried to prompt students' further thinking, making them think about the relationship between the reason for boiling water faster on the mountain and atmospheric pressure using an open-ended, challenging question: Teacher: Think about the atmospheric pressure. How does it change with the altitude?
Most of the students: Water would boil faster due to the decrease in atmospheric pressure with altitude.
After group discussions, each group revealed its ideas and tried to convince the other groups with different viewpoints to accept its viewpoints. Most of the group had the correct reasoning
Most students: In the mountains, there is less atmospheric pressure, in order to boil faster, water should boil at a lower boiling point, less atmospheric pressure causes the water boil faster.
Some students: As you go towards the mountains, pressure increases. Since pressure increases, water molecules collide more and water boils at a lower temperature, that is why water boils faster at the mountain
A group told: You are confusing vapour pressure with atmospheric pressure. You say that pressure increases on the mountains, this is atmospheric pressure not vapor pressure. Atmospheric pressure is the pressure exerted by air
Teacher: What is boiling?
A student: Boiling occurs at the temperature where atmospheric pressure is equal to the vapor pressure
Teacher: What do you say; in order to boil faster, water should boil at a lower temperature or higher temperature than 100 °C, right?
Students: Lower temperature
Teacher: If you say that boiling occurs when atmospheric pressure is equal to vapor pressure. Should we decrease or increase atmospheric pressure in order to make water boil at a lower temperature
Students: Decrease
Teacher: So what do you think? What should atmospheric pressure be for the water to boil faster at the mountain?
Students: If the water boils faster, the pressure on it should be lower hence the atmospheric pressure should decrease when you go higher
The whole class discussion continued until the intelligible and plausible answer(s) were found by the students. As understood from the dialogues, the teacher had an important role in guiding the discussion and helping students to construct the knowledge correctly. Sometimes students gave extraneous or irrelevant responses. In this case teachers asked challenging questions to extend the thinking about the topic without changing the direction of the discussion. In order to make the information more meaningful and permanent, other questions related to the topic were asked. For example, the teacher asked another question “why do the climbers make a camp at certain altitudes while climbing the mountain or why do their nose bleed while climbing?”. Besides, he asked them whether they have had such an experience or not. None of the students had such an experience but one of them said that he saw it in a movie and explained the cause of this event as pressure change. After that, students were asked “Why people living in uplands or plateau are ruddy-cheeked?” The responses were interesting. While some groups of students thought that it was the consequences of the healthy diet, most of them specified it was due to the atmospheric pressure. The teacher also initiated several discussions about the oxygen amount in uplands as well as adaptations and transport of oxygen in human blood. Through this case, students not only learned how the atmospheric pressure changes with altitude, they gave an explanation to some real life events. In this way, the fruitfulness (or usefulness) stage of the conceptual change was provided. At the end of the instruction, GCT was administered to both groups of students as a posttest to measure the change in alternative conceptions about gases.
Students in the control group were instructed by traditional instruction in which a teacher-centered learning strategy was adopted. In traditionally designed classes, teachers defined and explained the concepts and solved related or similar questions for students. For example, during teaching the atmospheric pressure concept, a control group teacher mentioned that atmospheric pressure decreases with altitude. At that point, he asked whether water boils at the mountain at a lower or higher temperature or the same temperature. Different answers came from students. The teacher told the students that water boils at a lower temperature than 100 degrees Celsius on the mountains. Further questions used in experimental group classes were also asked but a discussion platform was not created in these classes. In some cases, students failed to respond to the questions. In this case, the teacher, himself, gave the answer to the question. For instance, he clearly defined that the people living in the uplands look pink since the number of red blood cells in their blood increases after a while. In control groups, students were only motivated by teacher-directed questions, and there were not any activities like group work included during the teaching of a gas topic. Students in traditional classes asked very few questions. They generally responded to the questions asked by the teacher. Teachers allowed a certain amount of time to solve the presented question. Meanwhile he or she sat on his or her table or walked around the class. Then students' opinions about questions were usually taken verbally and their questions were solved on the board by the teachers. When students asked any questions about the subject matter, the teacher answered them. However, students simply acted as passive listeners taking notes. Instruction in the control group was based on informing students about gas concepts. Similar daily life examples and alternative conceptions to those presented to the experimental groups were also mentioned in the control groups by the teachers.
After completing the case activities, the researcher and a PhD student in chemistry education observed the instruction in the experimental classes once a week and completed the treatment verification checklist which was prepared by the researcher in order to check whether the case-based instruction method was applied as required. The treatment verification checklist consisted of two parts: the first part included “yes” or “no” type items and the second part included items with a 5-point Likert-type scale (always, usually, sometimes, rarely, and never). The percentages of items marked as “usually” and “yes” were 75%. This checklist indicated that case-based instruction was implemented in accordance with the purpose of the study. Thus, treatment fidelity was provided with the help of a treatment verification checklist.
Group | Pre-ASTC | Pre-SPST | Pre-GCT | Post-GCT |
---|---|---|---|---|
Mean | Mean | Mean | Mean | |
CG | 54.50 | 17.18 | 10.21 | 11.74 |
EG | 52.88 | 17.60 | 10.33 | 16.84 |
Moreover, after meeting normality, homogeneity of covariance matrices and independence of observations assumptions, one-way MANOVA was conducted before treatment to check whether control and experimental students were different with respect to motivational variables. It was found that there was no statistically significant mean difference between experimental and control group students with respect to the students' motivational collective dependent variables of intrinsic goal orientation (IGO), extrinsic goal orientation (EGO), task value (TV), control of learning beliefs (CLB), self-efficacy for learning and performance (SELP), test anxiety (TA), Wilks λ = 0.92, F(6,121) = 1.68, p = 0.13. Table 5 describes mean values of students' pre-motivational scores across both groups of students.
Dependent variables | CG | EG |
---|---|---|
Mean | Mean | |
Intrinsic goal orientation | 19.31 | 20.68 |
Extrinsic goal orientation | 22.11 | 21.73 |
Task value | 30.38 | 30.82 |
Control of learning beliefs | 22.06 | 21.63 |
Self-efficacy for learning and performance | 40.20 | 40.01 |
Test anxiety | 20.95 | 19.63 |
Alternative conceptions | Experimental group | Control group |
---|---|---|
When the gas in the container is cooled, each of the gas particles shrinks or gets smaller | 25.8 | 27 |
When the gas is cooled, gas particles accumulated at the bottom of the container like liquids | 8.1 | 42.9 |
When the gas is heated in a constant-volume container, gas particles condense in the wall of the container | 3.2 | 25 |
With decreasing temperature, air molecules are getting closer to each other and accumulated in the middle of the container | 16.1 | 52.3 |
Air molecules are accumulated at the bottom of the container with decreasing temperature | 9.7 | 36.9 |
Heated air is accumulated on the walls of the balloon | 9.5 | 14.1 |
Air is located between the particles of a gas | 12.9 | 55.4 |
Hot air is lighter than cold air | 30.6 | 28.1 |
Hot air is heavier than cold air | 1.6 | 12.5 |
According to three control group students, condition III has the biggest mass due to the increase in pressure in the container: “In condition III, the container is the heaviest due to the fact that it contains gas. Paper is not a heavy substance, and when it is in gas state it accumulates, so it is likely to make an effect on the pressure. The pressure would affect the mass of the container, but we cannot measure the pressure within the container and I think the mass of the container increased.”
The answers given to GCT indicated that most of the experimental group students (51.6%) made correct interpretation about the shape of the balloon when the pressure inside the cylinder is increased compared to the control group students (34.9%). Similarly, interviews revealed that experimental group students' conceptions were more adequate. Experimental group students had better reasoning when they stated that a gas exerts pressure in each direction. On the other hand, about half of the control group students (four students) and a few of the experimental group students (two students) deduced that the balloon shrinks only from the bottom or only from above because they thought that pressure shrinks the balloon in the direction in which they exert the force to the cylinder or the exact opposite direction to the force applied: Since we push the piston downward, only the bottom of the balloon may shrink, there will be no change on the sides.
Item analysis of GCT showed that most of the control (62.3%) and some experimental group (42.6%) students gave the correct answer by stating the direction of movement as a result of decreasing pressure within the container with decreasing temperature. The interviews related to the effect of temperature on gas pressure in a constant volume container showed that though most of the experimental (six students) and control group students (six students) predicted the direction of movement of the mercury droplet correctly, some control group (three students) and some of the experimental group students (two students) had the wrong reasoning. The following excerpts indicate one of the control and experimental group students' ideas related to the direction of the mercury droplet as shown in the above figure regarding the cooling of the system:
When the temperature is lowered, the pressure inside the container decreases. Gas particles might be getting smaller or clustered. Since the pressure decreases, the mercury moves to left.
I think it moves to the left because when the temperature decreases, mercury droplet will move towards the particles due to shrinkage. Mercury comes close to gas.
Students believed that gas pressure decreases in the container due to the shrinking or getting smaller of the gas particles or clustering of them in the container. As well, one student from each group claimed that the volume changes due to a change in the pressure ignoring the constant volume container in the given system and misusing the ideal gas law. The results concerning the application of Gay Lussac law indicated that some students were unable to establish the relationship between temperature and the pressure of a gas when all the other variables that affect the pressure of a gas are kept constant.
To conclude, both GCT and interview results indicated that experimental group students had superior understanding of gas concepts compared to control group students. However, some of the alternative conceptions were still existent among students from both groups even after instruction.
In addition, a frequency analysis of students' responses for each item in GCT and interviews with students indicated that case-based instruction based on conceptual change conditions helped to overcome students' alternative conceptions and remedied most of them compared to the traditionally designed instruction. However, though most of the experimental group students had better understanding on the gas concepts, it was impossible to remedy all the alternative conceptions. This means that students are persistent in their use of alternative conceptions even after instruction designed to address these alternative conceptions (Champagne et al., 1985; Anderson and Smith, 1987; Wandersee et al., 1994). However, still, case-based instruction was found to promote students' conceptual understanding of gas concepts.
This study has implications for chemistry teachers, teacher education programs and textbook writers. Firstly, teachers should be aware of possible alternative conceptions students may have and consider students' existing knowledge when designing lessons since new knowledge is constructed upon the existing one. Since this study reported the effectiveness of case-based instruction on improving students' understanding, we can recommend that teachers use case-based instruction to support meaningful learning. So, teachers should be trained about how to write and implement the cases in their routine classes. They should also be encouraged to use new teaching techniques like case-based instruction in order to enrich their lessons. Secondly, teacher training programs in universities should include this method of learning and present examples of the implementation of cases so that graduate pre-service teachers can know how to implement case-based instruction in their future classes. Lastly, textbook writers should include effective cases in textbooks since instruction with cases was found to be effective in enhancing students' understanding.
We can also make some recommendations for future study. In the present study, cases were not supported by use of laboratory work or demonstrations. As a future study, effectiveness of the use of laboratory work or demonstration with cases could be evaluated with respect to written cases. Besides, as a future study, we can suggest that the effectiveness of case-based instruction on students' retention of knowledge should be assessed.
Q1. The distribution of hydrogen gas molecules in a closed container at 25 °C and 1 atm pressure was given in the next. (the circles (○) represent the distribution of hydrogen molecules), Which of the following diagrams illustrate the distribution of H2 molecules when the temperature of the container is lowered to −15 °C? (note: before responding to this problem students were told that at −15 °C hydrogen is still gas).
Q2. When a constant-volume closed container filled with a gas is heated, increase in pressure is observed. In which of following alternative explains the reason of this event most accurately?
(A) Increase the size of gas particles
(B) Increase in the numbers of particles when the gas is heated
(C) Becoming heavier of the gas when it is heated
(*D) Increase in the number of the collisions when the gas is heated
(E) When the gas is heated, gas particles condense in the wall of the container
Q3. A constant-volume container filled with air is connected to a balloon as shown in the figure. When the tap of the container is opened and the container is heated, it is observed that balloon is swelling. Which of the following illustrate the distribution of air the best after swelling the balloon? (dots (.) represent the molecules within air.)
Q4. What exists between the particles of a gas?
(A) Air
(B) Water vapor
(C) Other gases
(*D) Nothing
(E) Foreign substances (dust, dirt, etc.)
Q5. As shown in following figure, a piece of paper is put in a closed glass container in condition I. In condition II paper is burning and in condition III ash is formed. In all three cases, glass container is weighted. Accordingly, which one of the following is true?
(A) Condition I has the biggest mass
(B) Condition II has the biggest mass
(C) Condition III has the biggest mass
(D) I and II has the same weight and III is less
(*E) All of them has the same mass
Q6. The following closed container, as shown in picture, contains a mixture of oxygen () and helium (■) gases at 25 °C. Which one of the following situations would lead to the partial pressure of the oxygen gas if the pressure of only oxygen gas was measured?
What can be said about the motion/state of gas particles in the deflated bicycle tire?
Compare the inside pressure of deflated bicycle tire with the outside pressure.
Compare the inner pressures of the deflated tire exerted to the sides and to the bottom, please explain the reason.
Can using up the energy of the gas particles in time and ceasing their motion be the reasons of deflation of the bicycle tire? Why?
Draw the distribution of the gas particles in the inflated and the deflated bicycle tire.
What exists between the particles of gas in the bicycle tire?
Name of the cases | Concept |
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Boiling of water on the mountains
Ali likes to climb on the mountains in his free time. One day, during the camp, he realizes that water boils faster on the mountain compared to the sea level and he decides to investigate the reason for this. Why do you think that water boils faster on the mountains? |
Air pressure |
Heating of water in the bottle covered with a balloon
Children put some water in a glass bottle and closes the mouth of the bottle with a balloon. They begin to heat the bottle slowly from its bottom. After a few minutes, they measure the circumference of the balloon. After water in the bottle is heated, what happened to the balloon? What is the reason for this? |
Avagadro's law |
Air bag
Ayse experiences an accident while travelling, fortunately air bag in the car saves her life. Do you have any idea about the working principle of air bags? Which properties should the gas filling in the airbag have? Does the gas in the air bag exert the same pressure on all parts of the air bag? |
Properties of gases |
Cold and hot air
Mervan is curious about similarities and differences between cold and hot air and he decides to do an experiment in order to find out the similarities and differences between cold and hot air. He closes the glass container tightly, in which there is air. He weighs it before heating this container and he also weighs it after heating. What can be said about the mass of the container after being heated? |
Properties of gases |
Soda
When CO2 gas is dissolved in the liquid either by high pressure or low temperature, carbonated drinks occur. When we open the bottle of soda and wait for a while, CO2 gas dissolved in liquid mixes into air. In this case, is there a difference in the mass of soda? Why? |
Properties of gases |
Bicycle tire (please see Appendix II) | Gas behavior, gas pressure |
Lung model
Breathing deeply can be associated with gas laws. When we breathe in, the muscles push the diaphragm downwards and the chest broadens. What is the effect of this on the pressure inside and volume of the lungs? When we take too much air in, how does it affect the elastic texture and the volume of the lungs? At the moment air taken in fills the lungs, if body temperature increases, what will happen to the volume of lungs? |
Boyle's law, Avagadro's law and Charles's law |
Book
As seen from the figure, Ozge placed half of a pipette in the plastic food storage bag with a zipper. Mouth of the bag is sealed tight with a zipper. In order to prevent the air escaping from the plastic bag, fingers were placed at each side of the pipette. Afterwards, a book was placed on the bag and air is blowed into the storage bag by pipette. After a while, it is seen that the book rises. What causes the book rise? |
Partial pressure, gas pressure |
Bottle covered with balloon
Children closes the mouth of a glass bottle, in which there is air, with a balloon that does not leak air in and out. First, they put the bottle in a cup that has hot water. After a while, what will be the shape of the balloon and why? Afterwards, they put the bottle in a cup full of ice in it. What will be the shape of the balloon after a while? |
Charles's law |
Air bubbles
As it is known, divers use scuba tanks that have compressed air (nitrogen–oxygen) in them. When we examine the actions of a diver swimming in the deep sea, we can observe that bubbles come out the mouth of the diver and these bubbles rise upwards. While these bubbles are rising up, it is seen that the volume of these bubbles increase gradually and they become several times bigger than they were at the beginning, Matter inside bubbles as well as chemical structure of matter do not change during the raise of bubbles. What may cause the change in the volume of the bubbles? (Assume that temperature of sea water is constant at each point of the sea) |
Boyle's law |
Vacuum pump
Dilek wants to remove some of the air in the flask by using vacuum pump in the laboratory. Figure A shows the flask without the vacuum pump being attached. In figure B flask is connected to the vacuum pump and some of the air in the flask is trapped in the vacuum pump. In figure C, process of evacuation of some air finishes and the mouth of the flask is closed tightly. Dilek could not observe the evacuation process since she cannot see gas particles. She wants to show the distribution of gases in the flasks by using dots. Could you please show these distributions in the flasks? |
Properties of gases |
Hot air balloon
Balloon can fly in the atmosphere by using heated air or light gases such as helium, hydrogen. How does heated air cause the balloon fly? What is the working principles of hot air balloons? If air in the balloon is cooled, what is the direction of the balloon? Is heated air in the flying balloon accumulated at the upwards of the balloon? Why? |
Gas behavior, gas pressure |
Competition of gases
In the competition where gases of He, H2, CH4, SO2 and SO3 race at the same conditions (same temperature and pressure), He and H2 gases finish the competition earlier, then CH4, SO2 and SO3 gases follow them respectively. What may be the reason for this? What type of information do we need to know in order to decide the order of gases in the competition? |
Diffusion of gases |
Formation of white ring
Two friends, Tugba and Aysel like to measure the diffusion rates of two different gases, NH3 and HCl by the help of apparatus below. They put cotton that is soaked into concentrated NH3 solution at one end of the apparatus and the other cotton was put at the other end of the tube and this cotton was soaked in the concentrated HCl solution (note that solutions are at the same environment) after a while, NH3 and HCl gases meet somewhere in the tube (temperature is constant during the experiment). Near to which end of the tube do these gases meet? Why? (HCl = 36.5 g mol−1, NH3 = 17 g mol−1) |
Diffusion of gases |
Boiling teapot
Ozlem is watching her mother cook. Her mother wants Ozlem take care of the food for a while, but when food begins to boil, Ozlem realizes that lid of the saucepan bounces up and she closes the cooker in panic. In another day, during the boiling of water in the teapot, Ozlem sees that the lid of the teapot moves similarly. She gets curious about this and wants to investigate the reason for this. What may be the reason for this? |
Gay-Lussac's law |
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