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DOI: 10.1039/C3RP20152J (Paper) Chem. Educ. Res. Pract., 2013, 14, 408-420

Case study applications in chemistry lesson: gases, liquids, and solids

Yıldızay Ayyıldıza and Leman Tarhan*b
aDokuz Eylul University, Institute of Educational Sciences, Department of Chemistry Education, Izmir, Turkey. E-mail: yildizayayyildiz@gmail.com; Fax: +90 232 4534188; Tel: +90 232 3018694
bDokuz Eylul University, Faculty of Science, Department of Chemistry, Izmir, Turkey. E-mail: leman.tarhan@deu.edu.tr; Fax: +90 232 4534188; Tel: +90 232 3018694

Received 13th November 2012 , Accepted 1st April 2013

First published on 7th May 2013

Abstract

This study aims at investigating the effects of case studies developed by the researchers on Science Teaching students' understanding of gases, liquids and solids, and their attitudes towards chemistry lessons. The study was conducted on 52 freshmen from the Department of Science Teaching at a university in Turkey. Pre-test and post-test experimental design with control group was used, and students were randomly assigned to experimental and control groups. A Prerequisite Knowledge Test was applied to both groups, and independent sample t-test results showed no significant difference between the groups. A preparatory course was applied on both groups to remedy students' lack of pre-knowledge identified by the test results. After the preparatory course, the same educator taught gases, liquids and solids with case study method to the experimental group and with a traditional teacher-centered approach to a control group. The Achievement Tests results showed that the experimental group significantly had higher scores and fewer misconceptions than the control group, and some misconceptions in the control group were identified for the first time in this study. With regard to Attitude towards Chemistry Lesson Scale results, chemistry education based on case studies significantly enhanced students' positive attitudes towards chemistry lessons.

Introduction

Students generally have numerous learning difficulties and misconceptions about chemistry subjects: atoms and molecules (Griffiths and Preston, 1992; Nakhleh and Samarapungavan, 1999; Skamp, 1999; Nakiboğlu, 2001); chemical reactions (Andersson, 1986; Ben-Zvi et al., 1987; Hesse and Anderson, 1992; Boo and Watson, 2001); chemical equilibrium (Hackling and Garnett, 1985; Bergquist and Heikkinen, 1990; Pedrosa and Dias, 2000; Voska and Heikkinen, 2000; Van Driel, 2002); dissolution and melting (Blanco and Prieto, 1997; Çalık et al., 2007); acids and bases (Hand and Treagust, 1991; Nakhleh, 1992; Nakhleh and Krajcik, 1994; Bradley and Mosimege, 1998; Sisovic and Bojovic, 2000; Acar and Tarhan, 2008); electrochemistry (Garnett and Treagust, 1992; Sanger and Greenbowe, 1997; Niaz and Chacon, 2003; Acar and Tarhan, 2007); and chemical bonding (Boo, 1998; Birk and Kurtz, 1999; Harrison and Treagust, 2000; Coll and Taylor, 2001; Coll and Treagust, 2001; Ayar Kayalı and Tarhan, 2004; Öztürk Ürek and Tarhan, 2005; Taber et al., 2012).

Gases, liquids, and solids are some of the chemistry subjects that students commonly fail to understand. Having important and fundamental roles to help perceive some facts in daily life and environmental problems, gases, liquids, and solids are related to many other chemistry subjects, and concepts such as matter; states of matter; the particulate nature of matter; atoms; ions; molecules; elements; the characteristic properties of matter such as mass, volume, density, flexibility, expansion; temperature, energy, the periodic table; atomic diameter; electronegativity; physical and chemical changes; and chemical bonds. Therefore, students' misconceptions should be identified, and learning environments should be reorganized to prevent those misconceptions (Vosniadou et al., 2001; Niaz, 2008).

In order to understand how students develop gas concepts, Stavy (1988, 1991) examined students' definition of the term gas, and the conception of changes in the state of matter. He determined that some students thought that ‘the gaseous state of matter is lighter than its liquid and solid forms’, and some students even believed that ‘gases had no weight’.

Benson et al. (1993) investigated common misconceptions related to the nature of gases in a student group varying between elementary school and university. They found that students believed that ‘air is a continuous (non particulate) substance’, ‘gas behaviour is similar to liquid behaviour (unlike the idea that gases expand to fill their containers)’, ‘there is relatively little space between gas particles’.

Hwang (1995) investigated students' understanding about the concept of gas volume of in junior high, senior high and university students. She found that students commonly had misconceptions such as ‘volume of a gas is the size of the particles’, ‘the gas can diffuse freely, gases do not have volume’, ‘the volumes of different gases are proportional to their particle numbers in a container’.

In another research, Lin et al. (2000) studied with both students and teachers about kinetic theory of gases. The study revealed many misconceptions such as ‘atmospheric pressure pushes gas molecules down’, ‘gas molecules rise and stay away from heat’, ‘molecules expand when they are heated’.

Griffiths and Preston (1992) stated that students thought ‘gases have larger and softer particles than liquids’, and ‘water molecules in steam are larger than those in ice’.

Osborne and Cosgrove (1983) addressed some questions to students in their research, and found that most of the students believed that the bubbles in the boiling water are made of either heat, air, oxygen or hydrogen. In another research, Kruger and Summers (1989) investigated the reason of this misconception. Questions similar to Osborne and Cosgrove's research were asked of students in the research. At the end of their research, they found that this misconception originated as the evaporation process was not taught in association with the particulate nature of matter.

Stavy (1990) and Barker (1995) investigated the relationship between evaporation and conservation of matter on students taught the particulate nature of matter, and determined that the students commonly thought that the amount of matter is not conserved in the evaporation process. Students said ‘gas weighs less than liquid’, so there was less gas present, thus explaining evaporation in terms of weight change rather than density change.

Stavy and Stachel (1985) examined the conceptions students have of solid and liquid. Students thought that substances which are not hard and rigid cannot be solids. According to them, ‘the easier it is to change the shape of the solid, the less likely it is to be a solid’, ‘water is a typical liquid’. Stavy and Stachel found that in general students classify new liquids more easily than solids, perhaps because liquids are less varied in their physical characteristics.

There are many more studies revealing that students develop incorrect conceptions about gases, liquids, and solids (Novick and Nussbaum, 1978, 1981; Séré 1986; Gabel et al., 1987; Mas et al., 1987; Andersson, 1990; Bodner, 1991; Nelson et al., 1992; Lee et al., 1993; Rollnick and Rutherford, 1993; Tveita, 1993; Stepans, 1994; Garnett et al., 1995; Tsai, 1999; Azizoğlu and Alkan, 2002).

In the light of all these studies, it is seen that although there is a large number of misconceptions of students at all levels related to gases, liquids, and solids, there are limited studies which aims at overcoming these misconceptions. Therefore, it is necessary to design student-centered active learning methods and strategies, which would help students to learn the correct concepts and integrate them with each other in order to prevent misconceptions and thus promote meaningful learning. It is a well-known fact that the teacher-centered educational approach is used in most chemistry classrooms around the world; however, this teaching approach does not provide an active learning environment for students. In an active-learning environment, in contrast to teacher-centered instruction, a teacher acts as a facilitator, and engages active participation of students in the learning process (Marx et al., 2004; National Research Council, 2005). When students are actively involved in the learning task, they learn more than when they are passive recipients of instruction. Active-learning includes various activities that engage active participation of students in the learning process. In this research, the case study which is one of such active learning methods was used.

Case study method gives students an insight into the real world of organizations, and case studies are real life stories used to promote student engagement in classroom lessons. The most important feature of case study method is that students face with responsibility to make a decision about a real example in daily life. Because of being based on a story, case study and problem based learning methods are similar to each other. The difference between case and problem based learning methods can be difficult to ascertain. The main difference is in the presentation of the problem. While a case study is about a simple subject or concept, problem based learning activity is about an extensive subject. With case based learning, the problem is accompanied by resource materials and questions; with problem based learning, only the problem is provided (MacDonald and Isaacs, 2001). In addition, while case studies are applied in short periods, a problem based learning activity can continue for a semester or even an academic year.

Herreid (1994), and Cliff and Curtin (2000) determined that the case study method developed ways to approach real life problems by increasing students' level of understanding facts and concepts, and helped teachers to reveal students' misconceptions. Similarly, Camp (1996) asserted that students keep knowledge in their memory longer and can transfer knowledge better with case study method. Furthermore, many researchers reported case study method improved students' collaborative and critical thinking skills (Krynock and Robb, 1996; Dori and Herscovitz, 1999; Gabel, 1999; Harland, 2002; Dori et al., 2003). Moreover, researchers underlined that using the case studies in science lessons provides an increase in students' positive attitude towards science (Krynock and Robb, 1996; Cliff and Curtin, 2000; Çakır et al., 2001; Ayyıldız and Tarhan, 2012). On the other hand, studies have shown that students' positive attitudes towards science are important in enhancing their achievement in science (Hofstein et al., 1977; Levin et al., 1991; Weinburgh, 1995; Freedman, 1997; House and Prison, 1998; Bennett et al., 2001; Salta and Tzougraki, 2004; Barnes et al., 2005).

Although it offers many advantages, there are also some limitations of case study method. First of all, the application of case study which is one of active learning methods seems to be difficult in crowded classrooms. As researchers have stated, an instruction based on case study like all active learning applications takes more time (Albanase and Mitchell, 1993; Berkson, 1993; Vernon and Blake, 1993), schools lack extrinsic rewards for active learning (Bridges, 1992). Teachers and students are unfamiliar with active learning, so adaptation by students to active learning cannot be easy (Bernstein et al., 1995) compared to traditional teacher-centered teaching. Active learning methods such as case study are not common in the science classroom. On the other hand, writing cases is difficult, and takes elaborate preparation and extensive research for the educator. Moreover, some researchers have stated that instruction based on case studies can not cover the same amount of information compared to traditional teacher-centered teaching (Herreid, 1994). If the students don't have sufficient knowledge, skills, and prior knowledge, it is not possible to carry out the learning objectives of the case study method.

Purpose of the research

The purpose of this study is to investigate the effectiveness of case studies related to gases, liquids, and solids on undergraduates' understanding, preventing misconceptions, and attitudes towards chemistry lesson. In order to achieve this purpose the following sub-questions were investigated;

Are case studies, which are developed and applied, effective in increasing undergraduate students' learning achievement about gases, liquids, and solids?

When compared to teacher-centered traditional approach, how effective is case study method in preventing undergraduate students' misconceptions about gases, liquids, and solids?

Does case study method contribute to undergraduate students' attitudes towards chemistry lesson?

Method

Participants

The participants of this study consisted of 52 first-year undergraduate students (18 and 19 years of age) enrolled in a General Chemistry Course at Department of Science Teaching in education faculty of a university cited in Izmir, Turkey. The number of women was 27, the number of men was 25. Although the undergraduates were from different cities in Turkey, they took same courses in their previous education. They enrolled in education faculty to be a science teacher based on the similar scores taken in university entrance examination. Most of the students thought the concepts in this course which was normally carried out with teacher-centered traditional approach as abstract and difficult in previous years. Since the subjects of gases, liquids, and solids are related to daily life, it is suitable to teach them with case study method.

Students were stratified randomly in experimental (N = 25) and control group (N = 27). While the students in the experimental group were instructed via case study applications, those in the control group were taught by traditional chemistry curriculum. All students in both groups were similar in socioeconomic status with the majority of them coming from middle-class families.

Instruments

Prerequisite knowledge test. The subjects of gases, liquids, and solids are related to many other chemistry concepts such as matter; states of matter; the particulate nature of matter; atoms; ions; molecules; elements; the characteristic properties of matter such as mass, volume, density, flexibility, expansion; temperature, energy, the periodic table; atomic diameter; electronegativity; physical and chemical changes; and chemical bonds. For this reason, a Prerequisite Knowledge Test (PKT) consisting of 30 multiple-choice items was developed to identify student prerequisite knowledge about their proficiency for learning the subjects of gases, liquids, and solids. The content of the test was validated by seven chemistry educators. The test was piloted with the sample of 130 undergraduate students for the reliability. After the item analysis, five items were eliminated and the reliability coefficient (KR-20) of the prerequisite knowledge test consisting of 25 items was found 0.84. For the analyses of the test, students' answers were classified as correct, incorrect, and no answers. The maximum score a student can achieve in the test was 100.
Achievement tests. The items in the achievement tests developed to identify students' understanding of gases, liquids, and solids were multiple choice items with open-ended parts where students are required to explain the reasons for their answers. The Gases Achievement Test (GAT), The Liquids Achievement Test (LAT), and The Solids Achievement Test (SAT) have 18, 17, 15 items, respectively. Prior to the development of the tests items, the content boundaries were defined and instructional objectives were identified. The test items were constructed by considering students' learning difficulties and misconceptions determined in the literature (Novick and Nussbaum, 1981; Gilbert et al., 1982; Osborne and Cosgrove, 1983; Gabel et al., 1987; Mas et al., 1987; Stavy, 1988, 1991; Griffiths and Preston, 1989; Bodner, 1991; Nelson et al., 1992; Benson et al., 1993; Lee et al., 1993; Rollnick and Rutherford, 1993; Stepans, 1994; Garnett et al., 1995; Tsai, 1999). For content and face validities of items in the tests seven chemistry educators' (experts') opinions were asked. They reviewed the tests in terms of the sampling adequacy of test content and responses, the appropriateness of the items to the cognitive domain taxonomy and the instructional objectives, the technical quality of test items. By taking experts' feedback into consideration, some minor revisions and modifications were made in the tests. The tests were piloted for reliability with the samples of 130 students who had learned the subjects. After the item analysis, the reliability coefficients (KR-20) were found as 0.78 for GAT, 0.75 for LAT, and 0.76 for SAT consisting of 15, 15, 12 items respectively. For the statistical analysis of the tests, multiple choice items were scored as correct, incorrect and blank. In addition to this, open-ended items were categorized as correct, partially correct, incorrect and no-response. Correct answers category involved completely correct explanations and the response reflected learning objectives in a detailed and clear way. Incorrect answers category included incorrect ideas and misconceptions on related subjects. On the other hand, correct answers with inadequate explanations were placed into the partially correct answers category. The maximum score which can be obtained from each test was 100.
Attitude towards chemistry lesson scale. To determine undergraduates' attitudes towards the chemistry lesson before and after the instruction based on case studies, the 5 point Likert-type Attitude Towards Chemistry Lesson Scale (ATCLS) developed by Acar and Tarhan (2008) was used. ATCLS consists of 25 items about Interest in chemistry lessons, Understanding and learning chemistry, Believing importance of chemistry in real-life, and Occupational choice related to chemistry. Its cronbach's alpha reliability coefficient was 0.81. The students' answers to ATCLS were labelled as strongly agree (SA), agree (A), partly agree (PA), disagree (D) and strongly disagree (SD) from the positive attitude to the negative attitude. For statistical analysis, the frequencies of these labels were calculated.

Procedure

The quasi experimental design chosen for the study was the pre and post testing control group design. This study was related to gases, liquids, and solids, and it was conducted at university level with the programme of chemistry lesson in Department of Science Teaching. Before the implementations all the students were informed about the aims of this study, privacy of the personal information and then student consent was taken for participation in the study. Before the instruction, to determine students' prerequisite knowledge about their proficiency for learning gases, liquids, and solids, The Prerequisite Knowledge Test was applied for both groups. In addition, The Attitude Towards Chemistry Lesson Scale was used to identify students' pre-attitudes. The independent samples t-test results revealed that there was no significant difference in the mean scores between the groups. A preparatory lesson was conducted with the participation of all students to remedy students' lack of knowledge and misconceptions determined according to PKT about previous subjects, and concepts in both groups.
Instruction in the experimental group. The instruction in the experimental group was accomplished via case studies developed by the researchers, under the guidance of the educator experienced on active learning methods. Throughout the lessons; the students were ensured that they learned why the subject was important by associating subjects, concepts, and sub-concepts to simple cases and real problems in daily life; they benefited from brainstorming, presentation technique, animation shows, videos; and question and answer technique was used to activate students to participate in the lessons. During the process, it was found that the students' interests towards the lesson increased gradually as they participated in the discussions, and it was seen that they started to ask more meaningful questions.

According to the literature review and experts' opinions, eight case studies related to the subjects of gases, liquids, and solids were developed by the researchers covering the general properties of gases, gas pressure, laws of gases, equation of ideal gas, differences between real gases and ideal gases, van der Waals equation, general properties of liquids and solids, attractive forces between molecules of matters in liquid and solid states, vaporization process, state changes related to energy changes and solid structures. Then these case studies were reviewed by seven university chemistry educators for content validity.


First case study: general properties of gases and gas pressure. In this activity, the intention was that the students would be able to debate on, associate with and comment on parameters defining gases in groups by considering the particulate nature of matter by giving everyday life examples like that;

Enlargement of a transparent balloon by blowing into it,

Taking different shapes of balloon when compressed between two hands, its explosion when compressed too much, and blowing out when it is left open,

Volume increase of a filled balloon when it is put into a hotter environment, and floating when put on water,

Balloons filled with He can fly and loose its volume more, although ones that filled with CO2 can't fly at the same temperature and pressure.

After completing this activity, it was intended that the students would be able to;

• Explain basic properties which define gases like pressure, volume, temperature, mol amount and density,

• Explain properties of gases like hanging volume, taking the shape of their container, compressibility considering the particulate nature of matter,

• Explain formation of pressure by molecular movements at constant volume and temperature,

• Define pressure (air pressure, atmospheric pressure) and explain how it is measured,

• Explain the effect of mol amount of a gas to its volume at constant temperature and pressure,

• Comment on the association between mol amount of a gas and its pressure at constant volume and temperature,

• Explain volume–temperature relation considering the particulate nature of matter at constant pressure and mol amount,

• Explain relation between collision frequency of particles and pressure in a container with constant volume

• Explain that density of gases are lower than that of solids and liquids,

• Distinguish the differences between diffusion and effusion concepts by explaining dispersion property of gases.


Second case study: laws of gases and equation of ideal gas. In this activity, it was intended that the students would be able to debate and form hypothesis on the relation of basic properties of gases. The ideal gas equation would be derived with the help of instructor and its unit would be found after R gas constant is calculated by looking for answers to cases like;

In which one of the two cube shaped metal containers different in volume, pressure would be higher when they are filled with the same gas at the same amount at the same temperature considering the particulate nature of matter and collision frequency in unit time; How the state would change when temperature of one of the containers changed;

The same questions are asked for two metal containers having the same volume filled with the same gas at different amounts.

After completing this activity, it was intended that the students would be able to;

• Explain the effect of volume of gas at constant mol amount and temperature on its pressure (Boyle's Law),

• Explain the effect of temperature of gas at constant mol amount and volume on its pressure (Gay Lussac's Law),

• Explain the effect of temperature of gas at constant mol amount and pressure on its volume (Charles's Law),

• Explain the effect of mol amount of gas at constant volume and temperature on its pressure (Dalton's Law of Partial Pressures),

• Explain the effect of mol amount of gas at constant pressure and temperature on its volume (Avogadro's Law),

• Form Ideal Gas Equation, by using the relations between the parameters which define gases,

• Calculate R gas constant considering that volume of 1 mol gas at standard conditions (273 K and 1 atm) is 22.4 liters.


Third case study: differences between real gases and ideal gases, and van der Waals equation. It is known that carbon dioxide, which is at gaseous state at normal conditions (1 atm, 0 °C), is in liquid and gaseous state at −50 °C and high pressure values like 7 and 4 atm respectively; and is in solid and gaseous state at 1 atm and, low temperature values like −79 °C and −60 °C respectively. Hence, the aim is;

To explicate why P and V values differ from the values at normal conditions,

To explicate the factors resulting in deviation from ideal gas equation,

To derive real gas equation (van der Waals) would be derived from ideal gas equation by the help of instructor.

After completing this activity, it was intended that the students would be able to;

• Explicate the reasons why gases deviate from ideal state at low temperature and/or high pressure,

• Make corrections for real gases at ideal pressure considering attractive forces between molecules,

• Explicate the necessity to omit total volume of gas molecules for real gases compared to the volume of the container that gas is in,

• Form Real Gas State Equation by declaring the necessity of a and b correction constants for gas pressure and volume values respectively, in Ideal Gas State Equation; and explaining the meanings of these constants with the help of instructor.


Fourth case study: general properties of liquids and solids. In this activity, the intention was that students would be able to explain;

How the molecules forming solid and liquid states behave in the example of an ice in one glass of water, using the information about general properties of gases,

Why humans cannot walk on water without sinking where a fly can,

Whether there are differences between attractive forces formed by water molecules on the surface and inside, forming liquid state, with the molecules at the wall,

General properties of liquids and solids with surface tension and viscosity properties of liquids by explicating the reasons of the shape water drops take; complete dispersion of rain drops on clean glass plate whereas they stay as drops on a varnished car,

The reasons why the flow speed of equal amounts of honey and motor oil inside same glass pipe are much more slower than water; why honey and motor oil form convex angles at the tip of the pipe during their flow, and why flow speed changes by temperature.

After completing this activity, it was intended that students would be able to;

• Explain that liquids and solids have higher attractive forces between molecules rather than gases, and their molecules move slower than gas molecules,

• Define the properties of liquids such as having definite volume, taking the shape of container, and their viscosity considering the particulate nature of matter,

• Explain that the change in pressure does not affect the volume of liquids as much as it does on gases,

• Comment on that volumes of liquids generally increase with increasing temperature and thus their density decreases, average kinetic energy of molecules increases and accordingly molecular movements increase, and attractive forces between molecules decrease,

• Explain the dispersion of liquids inside each other is a much slower process than dispersion of gases inside each other by associating this with collision amount per unit time,

• Explain the properties of viscosity and surface tension of liquids, and associate attractive forces between molecules with temperature.


Fifth case study: attractive forces between molecules of matters in liquid and solid states. In this activity, the aim is that the students would be able to explicate why melting and boiling temperatures are different considering structural properties like electronegativity differences between NaCl, H2O, NO, HCl, and N2 atoms, for which melting and boiling temperatures are given, their bond types, whether they are in solid, liquid or gaseous state at normal conditions; and the students would be able to explain London dispersion forces, dipole–dipole forces and hydrogen bonds between molecules according to ionic, polar covalent, apolar covalent properties of matters.

After completing this activity, it was intended that the students would be able to;

• Understand the formation of partial negative and positive poles at temporary dipole structures of apolar molecules,

• Comment on the relation between the difference in electronegativity between atoms forming molecules and dipole characteristics of molecule,

• Compare melting and boiling points of polar and apolar structured molecules,

• Explain the reasons for the difference in physical properties of matter as dipole–dipole forces related to polarity of molecules change,

• Explain the interactions of London dispersion forces, dipole–dipole forces and hydrogen bonds between molecules according to their ionic, polar covalent, apolar covalent properties,

• Define the factors affecting melting and boiling points,

• Understand the definition of London dispersion forces and which molecules they are formed between,

• Define the polar structured molecules and understand the factors affecting dipole–dipole forces,

• Understand which elements formed hydrogen bonds, and compare their magnitude with other type of bonds,

• Comment on the relation between the bond type between molecules and their melting and boiling points,

• Explain the relation between the boiling point and vaporization enthalpy of a compound and the molecular attractive forces.


Sixth case study: vaporization process. In this activity, the intention is that the students would be able to explain concepts like vaporization process, factors affecting vaporization, vapor pressure, and vaporization heat by the facilitating questions of the instructor. It is debated in groups what results may be observed;

When, ethyl alcohol and water is put into two identical containers in equal amounts and ethyl alcohol is put into two containers having different diameter in equal amounts and when all are left in the same environment for the same duration,

Three identical containers having equal amounts of water which are left in ice environment, room temperature and boiling water environment for the same duration,

Equal amounts water is put into two identical containers and left in the same environment for the same duration when one of them is closed and the other open.

After completing this activity, the aim is that the students would be able to;

• Explain vaporization process of liquids considering attractive forces between molecules,

• Comment on that liquids can vaporize at all temperatures,

• Explain whether vapor pressure of a liquid is related to the volume of the liquid and the volume of the container that it is in,

• Comment on the effect of volume change of vapor that is in equilibrium with its liquid on vapor amount in unit volume,

• Explain whether the equilibrium vapor pressure of liquids at the same temperature is related to their type,

• Explain whether vapor pressure of a liquid is related to its temperature or its pressure,

• Define the dynamic equilibrium and explain the relation between vapor pressure of a matter and vaporization speed,

• Tell what parameters are affecting vaporization speed of liquids; and explain the relation between them,

• Understand that boiling process happens when vapor pressure of the liquid equals to outer pressure.


Seventh case study: state changes related to energy changes. In this activity, the aim is that the students would be able to;

Explain state changes of a matter related to energy changes by giving the example that water molecules in solid state change into liquid first and then gaseous state by the changes in energy of the system; and be able to comment about state diagram of a matter;

Compare probable state and state equilibriums at different points on vertical and horizontal lines that are drawn on X and Y axes over randomly chosen pressure and temperature values; on the example of simultaneous existence of liquid and gaseous state equilibrium with its solid state at appropriate temperature and pressure values.

After completing this activity, it was intended that the students would be able to;

• Explain state changes for three states of water according to energy changes,

• Explain the process of sublimation,

• Find stable state/states of a matter at a definite temperature and pressure using state diagram of that matter,

• Predict relative densities of solid and liquid states of a matter using state diagram,

• Comment on cooling curve of a matter,

• Define dynamic equilibrium and explain the relation between vapor pressure of a matter and vaporization speed,

• Explain important properties of a state diagram (triple point, critical point).


Eighth case study: solid structures. In this activity, it is explained that solids like sugar, quartz, diamond, NaCl, copper and iron show crystalline properties, however the ones like glass, butter, lipstick, tire does not show that property. It is intended that students would be able to explain structure and properties of metals, ionic solids, web structured solids, covalent solids and molecular solids by comparing the particulate natures of and the attractive forces between those structures with the help of the instructor, using the example drawings of crystalline solids.

After completing this activity, the intention is that the students would be able to;

• Classify solids as crystalline and amorph, and explain their differences,

• Define the smallest particle of a crystal showing all of its properties,

• Classify the crystalline structures according to types of forces that holds the particles together,

• Tell about the structures and properties of metals, ionic solids, web structured solids, covalent solids, and molecular solids,

• Explain the structures of graphite and diamond, which are carbon allotropes; explain the relation between their properties and structures.

To ensure construction of knowledge by encouraging them to research, discuss, and share their knowledge in their small groups, some leading questions were asked to the experimental group students during the process. With the case study applications, the following subjects and concepts were reinforced: matter; states of matter; the particulate nature of matter; atom; atomic number; ion; mole; mole number; molecule; molecular weight; the characteristic properties of matter such as mass, volume, density, flexibility, expansion; pressure, volume, temperature, heat, energy, force, speed; general properties of gas, and liquid particles; atmospheric pressure, pressure units, international system of units; R gas constant; the characteristics of ideal gases; the ideal gas equation; periodic table; polarity; atomic diameter; electronegativity; melting/boiling point; intermolecular forces; melting, freezing, evaporation, condensation, boiling; hybridization; ionic, covalent, and metallic bonds; anion/cation; electrostatic attraction; and phase changes.

Instruction in the control group. The instruction in the control group was accomplished via already existing teacher-centered approach. Throughout the lessons, the same chemistry educator presented the same content as the experimental group to achieve the same learning objectives which is covered by detailed instruction in the experimental group section. This instruction included lectures, discussions and problem solving. During this process, the educator used the blackboard and asked some questions related to the subject. Students also used a regular textbook. While the educator explained the subject, students listened to her and took notes. The instruction was accomplished in the equal amount of time with experimental group.

After the instruction, experimental and control group students' understanding of gases, liquids, and solids was identified via GAT, LAT, SAT, and individual interviews; ATCLS was applied to identify students' post-attitudes.

Results and discussion

In this study, the effect of case studies on undergraduates' understanding of gases, liquids, and solids, preventing misconceptions, and attitudes towards chemistry lesson were investigated.

As mentioned in the literature review, researchers have shown that the reasons of students' misconceptions in gases, liquids, and solids are related their prior knowledge and learning difficulties about some chemistry subjects such as the particulate nature of matter especially and the characteristic properties of matter (Osborne and Cosgrove, 1983; Stavy and Stachel, 1985; Stavy, 1988, 1991; Kruger and Summers, 1989; Barker, 1995). Therefore, in order to identify the students' prior knowledge and learning difficulties of gases, liquids, and solids, PKT was administered in both control and experimental groups. An independent sample t-test was conducted to compare the mean scores of experimental and control groups. As seen in Table 1, the analysis results expressed that there was no statistically significant difference between the control and experimental groups in terms of PKT mean scores (p > 0.05).

Table 1 Independent sample t-test results of PKT
Group N Mean SD SE t p
Experimental 25 50.72 14.17 2.83 0.31 0.76
Control 27 49.33 17.61 3.39    

Instructions of gases, liquids, and solids were conducted with case studies developed by the researchers in the experimental group and with teacher-centered approach in the control group. In order to identify students' understanding of gases, liquids, and solids, GAT, LAT, SAT were applied after the instructions. The mean scores of both control and experimental groups for each test were compared by conducting an independent sample t-test, and the results showed there were statistically significant differences between groups (p < 0.05, Table 2).

Table 2 Independent sample t-test results of GAT, LAT, and SAT
Test Group N Mean SD SE t p
GAT Experimental 25 86.18 6.92 1.38 9.05 0.00
Control 27 59.04 13.43 2.58    
LAT Experimental 25 82.97 5.47 1.09 11.97 0.00
Control 27 55.34 10.27 1.98    
SAT Experimental 25 80.66 4.64 0.93 17.05 0.00
Control 27 49.07 8.12 1.56    

Based on the achievement tests' results, it was found that in the experimental group students had fewer misconceptions and understood the concepts more meaningfully than students in the control group. The students' misconceptions and the percentages of them determined at GAT, LAT, and SAT in experimental and control groups observed in the research were presented in Tables 3–5, respectively. According to the results, the number and percentage of misconceptions of the experimental group was significantly fewer than the control group of students. While four of the misconceptions in these tables were first identified in the context of this study, the rest of them had been previously documented in the literature. It was found that the students in the control group commonly failed to explain the particulate nature of matters, the general properties of gas, liquid, and solid particles; vapor, vapor pressure; kinetic theory of gases; evaporation, boiling and melting processes.

Table 3 The percentages of students' misconceptions about gases
Misconceptions Exp. Group (%) Cont. Group (%)
a First determined misconception in this study.
Gases have no mass or weight; they have only certain shapes or volumes. 0 41
Gases don't disperse homogeneously. 4 52
When gas molecules in a closed container are heated, most of the particles are collected at the topside of container. 4 44
There are very small spaces between gas particles. 0 15
When gas molecules are heated, the energy of gas molecules increases. Therefore they become heavier, and lower.a 0 15
The concepts of steam and gas are the same. 0 41
Collapsed balloon has less pressure than outside. 0 22
There are gases in a closed container but there are no gases in an open container. 0 15
The average rates of all gases at the same temperature are the same. 4 33
Pressure affects shapes of molecules. 0 22
Air pressure in a closed container increases from bottom side to upper side of the container. 0 15
Average kinetic energy of a gas only depends on molecular mass of the gas.a 4 30
Although some of the covalent bonds in the structure of water molecules are broken in liquid phase, all of the covalent bonds in the structure of them are broken in gas phase. 0 7

Table 4 The percentages of students' misconceptions about liquids
Misconceptions Exp. Group (%) Cont. Group (%)
a First determined misconception in this study.
Vaporization is an event that occurs all over matters. 0 22
Vaporization occurs in solid phase of the matter. 4 30
The conversion of matter from solid into vapor is called vaporization. 0 22
The heat energy required for evaporating of a gram of a matter is defined as the evaporation temperature. 0 33
Vaporization does not occur without boiling. 0 15
There are lots of spaces between liquid molecules. 0 44
Water molecules can have different dimensions in the same phase. 0 15
Water in pressure cooker boils at lower temperature than 100 °C.a 0 33
While vaporization and boiling are occurring, liquid particles are divided into their atoms. 0 7
Because boiling point is a characteristic property for each matter, it is fixed and does not change. 4 41
Final temperatures of two matters heated with identical heaters are the same. 0 7
There is air in the bubbles formed during boiling. 0 37
The lowest temperature for a liquid is its freezing point.a 0 22

Table 5 The percentages of students' misconceptions about solids
Misconceptions Exp. Group (%) Cont. Group (%)
The particles of solids do not move. 0 30
The particles of a solid have same properties with a material made of it (e.g. the particles of solids are rigid). 0 33
Water in solid phase has the heaviest and the largest molecules. 0 41
When solids melt, water is formed. 0 7
Molecules of solids are more rigid in comparison with liquids and gases. 4 33
Water molecules are found in the solid phase at 0 °C. 4 22
One mole of water occupies a volume of 22.4 liters in also three physical phases. 0 30
Decrease in mass during the conversion of solid in a closed container into a gas is more than decrease in mass during the conversion of it into a liquid. 4 22

The results obtained from GAT have shown that a large proportion of students thought that 'when gas molecules in a closed container are heated, most of the particles are collected topside of container'. This misconception is similar with the others such as ‘gases don't disperse homogeneously’, and ‘air pressure in a closed container increases from bottom side to upper side of the container’. They were revealed also in the studies of Lee et al. (1993), Novick and Nussbaum (1978, 1981), and also Mas et al. (1987), which indicated that students thought that gas molecules rise to higher places because of their low weight. These misconceptions indicated that students could not learn the particulate nature of matter meaningfully (Kruger and Summers, 1989; Lin et al., 2000). New misconceptions related to gases were also identified in this study: ‘When gas molecules are heated, the energy of gas molecules increases, therefore they become heavier, and lower’; ‘Average kinetic energy of a gas only depends on molecular mass of the gas’.

As stated by Garnett et al. (1995), students commonly believed that ‘there are lots of spaces between liquid molecules’. Similarly, the results obtained from LAT indicated that nearly half of the control group students had same misconception. As mentioned before, Osborne and Cosgrove (1983), Kruger and Summers (1989), and Bodner (1991) also indicated that students thought bubbles in boiling water occur from heat, air or hydrogen and oxygen. Similarly, 37% of the control group students in this present study said that ‘there is air in the bubbles formed during boiling’. Furthermore, new misconceptions related to liquids were first identified in the context of this study: ‘Water in pressure cooker boils at a lower temperature than 100 °C’; ‘The lowest temperature for a liquid is its freezing point’.

According to the results obtained from SAT, all misconceptions determined about solids have some similarities with those in the literature. For example, it was found that, as mentioned by Garnett et al. (1995), 41% of control group students commonly perceived that ‘water in solid phase has the heaviest and the largest molecules’ in this study. 33% of the control group students also thought that ‘the particles of a solid have same properties with a material made of it; for example, the particles of solids are rigid’, and ‘molecules of solids are more rigid in comparison with liquids and gases’. The same misconceptions were revealed also in the researches of Lee et al. (1993), and Tsai (1999).

For the assessment of the undergraduates’ pre- and post-attitudes towards chemistry, ATCLS was used. The frequencies for each label in ATCLS were calculated to compare the answers of the experimental and control groups. The results showed that while experimental and control groups had similar frequencies with respect to pre-attitude towards chemistry lessons (Table 6), significant differences were found between groups after the instruction (Table 7).

Table 6 The students' answers about ATCLS before the instruction
Group N SA (%) A (%) PA (%) D (%) SD (%)
Experimental 25 12 24 28 20 16
Control 27 11 19 22 26 22

Table 7 The students' answers about ATCLS after the instruction
Group N SA (%) A (%) PA (%) D (%) SD (%)
Experimental 25 40 36 12 8 4
Control 27 11 22 22 26 19

It has been important to develop students' positive attitudes towards science lessons since researchers confirmed that these attitudes were linked with academic achievement (Salta and Tzougraki, 2004; Barnes et al., 2005). On the other hand, the studies by Hewson and Hewson (1983), Stavy (1991), Sanger (2000) indicated that the difficulties of chemistry subjects cause negative attitudes towards this lesson.

According to the results obtained from ATCLS, it was found that instruction based on case studies positively affected students' attitudes as mentioned in previous research (Krynock and Robb, 1996; Cliff and Curtin, 2000; Cam and Geban, 2011; Kılınç Alpat et al., 2011; Ayyıldız and Tarhan, 2012; Yalçınkaya et al., 2012). In this study, the increases in the positive answers of experimental group can be interpreted in such a way that the case studies positively affected students' interest in chemistry lessons, understanding and learning chemistry, and their beliefs in importance of chemistry in real-life, and occupational choice related to chemistry.

If experimental group students' answers towards Interest in chemistry lessons are analysed, it is seen that the students' attitudes towards finding chemistry lessons more interesting and necessary increased. For example, while 60% of the students found chemistry lessons interesting before the instruction, 88% of those students thought in this way after the instruction.

Experimental group students' answers related to Understanding and learning chemistry indicated that they began to appreciate the value of learning the basic concepts for understanding chemistry. The percentage of students who thought that some knowledge in chemistry helped them understand the other science lessons more easily, increased significantly from 48 to 80. While 32% of the students found chemical symbols unintelligible as a foreign language that they do not know before the instruction, the percentage of those students decreased to 12 after the instruction. It was also found that students began to solve chemistry problems easily.

Experimental group students' answers towards Believing importance of chemistry in real-life showed that the highest increase was found for this way. For example, all of the students began to believe that chemical knowledge helped to interpret events in daily life, after the instruction based on case studies. It was also found that 96% of experimental group students thought that chemistry has a great role in the modern life and solving environmental problems.

According to the students' answers towards Occupational choice related to chemistry, the lowest increase was found for this way. The experimental group students' thoughts about choices of jobs related to chemistry were not changed significantly. This situation can be interpreted in such a way that the students receive education in Department of Science Teaching, and chemistry is already a part of their jobs. On the other hand, the percentage of the students who believed chemistry knowledge will need for their career after graduation increased from 80 to 88.

All results of ATCLS indicated that if students learned the subject of gases, liquids, and solids with simple cases and real problems in daily life, their negative attitudes would decrease.

Conclusions

This research was conducted to investigate the effectiveness of instruction with case studies, which have been newly developed by the researchers over teacher-centered approach on undergraduates' understanding of gases, liquids, and solids, preventing misconceptions, and their attitudes towards chemistry lessons.

According to the results, while the students who conducted case studies had few misconceptions about gases, liquids, and solids, the students in the traditional class had more misconceptions. Either texts of the case studies related to daily life on the subjects of gases, liquids, and solids or comments of the leading questions in these case studies were formed considering the particulate nature of matter, thus reinforcing the information learned recently. Similarly, other researches emphasised the importance of the particulate nature of matter in teaching of a new chemical concept or subject (Osborne and Cosgrove, 1983; Kruger and Summers, 1989; Stavy, 1990; Griffiths and Preston, 1992; Benson et al., 1993; Barker, 1995; Hwang, 1995; Lin et al., 2000). This situation has played an active role in preventing the misconceptions in the experimental group, which were encountered both in the literature and in the control group of this study in high percentages. Additionally, making comments in association with the concepts and information about intermolecular forces on the questions in the case studies related to the subjects of gases, liquids, and solids has prevented the lack of knowledge and misconceptions about states of matter, and physical and chemical properties of matter in the experimental group students. This result is also consistent with related literature (Novick and Nussbaum, 1978, 1981; Osborne and Cosgrove, 1983; Mas et al., 1987; Kruger and Summers, 1989; Bodner, 1991; Lee et al., 1993; Garnett et al., 1995; Tsai, 1999).

According to the results of the scale for the attitude towards chemistry lesson the case studies associated with daily life have increased the students' interests and motivations towards chemistry. The results were also in line with other researches (Dori and Herscovitz, 1999; Cliff and Curtin, 2000; Mayo, 2002, 2004; Kılınç Alpat et al., 2011; Yalçınkaya et al., 2012). It was also seen that the experimental group students learned chemical concepts and symbols more easily, and they thought that chemistry helped them understand the other science lessons. Other research on case study indicates the same results (Yadav et al., 2007; Cam, 2009; Cam and Geban, 2011; Ayyıldız and Tarhan, 2012). Consequently, it can be said that instruction based on case studies improves students' attitudes towards chemistry lessons, increases understanding and learning, forms belief in the importance of chemistry in real-life, and offers occupational options related to chemistry.

Throughout the lessons in the experimental group; the students participated in the discussions under the guidance of the educator. These discussions encouraged students to share their ideas, knowledge and concepts, connect prior concepts with new ones, and construct their knowledge effectively (Courtney et al., 1992; Herreid, 1994; Flynn and Klein, 2001; Bennett, 2010). Thus, students had learned the scientific view of the subjects more easily. For this reason, it can be said that the instruction based on case study method caused a significantly better acquisition of scientific conceptions than the traditional instruction. This result is consistent with respect to the literature on case study method in various subjects (Camp, 1996; Cliff and Curtin, 2000; Mayo, 2002; Cliff, 2006; Cam, 2009; Yadav and Beckerman, 2009). In contrast to the experimental group, the instruction in the control group was dependent on a teacher-centered traditional approach and students were required to use current textbooks. For this reason, textbooks should be improved in a way to include enough active learning activities. In other words, it can be said that it is very important to keep continually developing course materials based on contemporary instructional methods. Like in this research, development of various active learning activities such as case studies and validating them has a substantial contribution to the improvement process of course materials (Steffe and Gale, 1995; Hmelo, 1998; Healey and Roberts, 2004; Fletcher, 2005; Acar and Tarhan, 2008; Ayyıldız, 2012). Consequently, when various student-centered learning strategies are used, we believe that it is more likely that the formation of students' misconceptions will be prevented. Thus, meaningful and effective learning can be provided for students. For this reason, educators/teachers should be encouraged to apply student-centered learning strategies in their classes.

In the light of the results, it is believed that this research will contribute to the chemistry education literature. As a conclusion, this research reports evidence that case study method is very effective on undergraduate students' understandings about the subject, gases, liquids, and solids in General Chemistry Course at Department of Science Teaching preventing misconceptions. Case study as an active learning method does not only provide improvement in learning achievement but also in enhancing their positive attitudes towards chemistry lesson. Therefore, it is suggested that case studies should be constructed and used more widely in other chemistry subjects.

Limitations and assumptions

The external validity of this study is limited since the study was conducted with only 52 first-year students in one university. The application of a case study is limited with the subjects of gases, liquids and solids and with only a General Chemistry Course. The treatments in the experimental and control groups are also limited within the framework of a semester-long program. It is assumed that scientific backgrounds of undergraduates in the experimental and control groups were similar. During the construction process of the groups, it is assumed that educator was aware of undergraduates' characteristic and background. It is assumed that undergraduates followed directions in the case studies. Additionally, it was also assumed that the experimental and control groups did not interact during any application.

There can be some experimental group students who think that the existing teacher-centered lessons are boring in this study. In such cases, student-centered lessons which is a new learning approach can be more attracted students' interests, they can make more efforts to achieve. Additionally, according to the results of most studies in the relevant literature, it is known more or less that active learning methods are more effective than traditional methods in students' academic achievement. The existence of such uncontrolled parameters threatens the validity of experimental research. For this reason, in the high achievement of experimental group, albeit at a low rate, the novelty effects resulting from the application of a new learning approach for students, and the expectancy effects resulting from the known positive aspects of the learning approach should not be overlooked (Taber, 2008). On the other hand, common positive effects of active learning approaches constitute an ethical issue for the control group. Although the control group of this study is normally instructed via traditional approach, this ethical issue still threatens the validity of this study, and it is generally a weakness of experimental design with control group.

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