Diagnosing pre-service science teachers' understanding of chemistry concepts by using computer-mediated predict–observe–explain tasks

Abstract

The purpose of this study was to investigate pre-service science teachers' understanding of surface tension, cohesion and adhesion forces by using computer-mediated predict–observe–explain tasks. 22 third-year pre-service science teachers participated in this study. Three computer-mediated predict–observe–explain tasks were developed and applied to collect data. In the first stage of each task, pre-service science teachers were required to watch video related to the aforementioned concepts. They were asked to write their predictions individually, and to justify or give a reason for their predictions. In the second stage, pre-service science teachers were required to watch the continued video carefully. They recorded their observations individually. In the last stage, the pre-service science teachers were required to reconcile any conflict between their own predictions and observations. Their written responses were analysed to investigate their understanding. Results indicated that pre-service science teachers had difficulties related to surface tension, cohesion and adhesion forces. The obtained results underlined that the computer-mediated predict–observe–explain task was an effective method to diagnose students' understanding.

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Introduction

Students come to science classes with prior ideas, formed through their interaction with the world around them. Some of their ideas may be scientifically incorrect conceptions called misconceptions, and these misconceptions may stand in the way of learning the correct concepts (Jonassen, 1991; Sanger and Greenbowe, 1997). As learning involves the construction of new meanings and understandings through the linking of new ideas with existing ones, misconceptions need to be addressed as they will subsequently influence students' ability to acquire scientific conceptions (Chin, 2001).

Determination of students' misconception is difficult. Researchers have used different techniques to identify students' understanding and misconceptions of scientific concepts. The most used these techniques are: open-ended questions (Glazar and Vrtacnik, 1992; Bowen and Bunce, 1997), multiple choice tests (Nakiboglu and Tekin, 2006), two-tier diagnostic tests (Treagust, 1988; Odom and Barrow, 1995; Ince et al., 2012), concept mapping (Ross and Munby, 1991; Hazel and Prosser, 1994), interviews about instances and events (Osborne and Gilbert, 1980; Osborne and Cosgrove, 1983), interviews about concepts (Abdullah and Scaife, 1997; Coll and Taylor, 2001), drawings (Smith and Metz, 1996), word association tests (Maskill and Cachapuz, 1989), and predict–observe–explain tasks (Liew and Treagust, 1995; Palmer, 1995; Liew, 2004).

Research underlined that multiple-choice tests often fail to explore the reasoning processes and sources of conceptual problems of the subjects (Hernandez and Caraballo, 1993; Odom and Barrow, 1995). Simonson et al. (2000) indicated that multiple-choice items can be used effectively in testing the items that demand low level of cognitive effort such as recalling previously memorized knowledge, yet items that require students to use higher order thinking skills such as analyzing and synthesizing are more difficult to produce. Clinical interviews, usually based on questions referring to particular instances or events, can probe students' mental processes more specifically, but they are time-consuming to administer and require expert skills if they are to be conducted successfully (Piaget, 1969; Osborne and Gilbert, 1980; Posner and Gertzog, 1982). Written tests with open-ended questions, on the other hand, may elicit students' in-depth thinking more effectively, but are difficult to quantify and sometimes too subjective (Simpson and Marek, 1988; Themane, 1990). These assessment techniques can be applied before or after the treatment. However, it is important to assess a student during the learning process. Predict–observe–explain (POE) tasks are a useful technique to assess students' understanding as well as to teach concepts (Mthembu, 2001; Liew, 2004).

There are three stages in POE. Firstly, the students are given a situation or an event and they are asked to predict what will happen when something is done to the situation and to justify their prediction (P: Predict). Secondly, they describe their observations (O: Observe). Finally, they describe what actually happened, and explain any discrepancy between their prediction and observation (E: Explain). POE requires students to apply their knowledge to reason out an answer. In this process, students' understanding is revealed. The POE technique helps to uncover deeply held beliefs about scientific principles and phenomena beyond the superficial understanding of facts and algorithms (Chin, 2001). White and Gunstone (1992) have promoted the POE procedure as an efficient strategy for eliciting students' ideas and also promoting student discussion about their ideas.

Although POE is well researched (Champagne et al., 1980; Gunstone, 1995; Liew and Treagust, 1995), few studies have investigated the use of POE in diagnosing students' understanding of chemistry concepts. Mthembu (2001) used POE to enhance students' understanding of redox reactions and underlined that students' prior knowledge and beliefs, and hence their expectation of the outcome, influences their observation. Köse et al. (2003) developed three POE tasks about electromagnetism, boiling and photosynthesis to determine students' misconceptions. They found that POE was an effective technique to identify students' understanding and teach the scientific concepts. Ipek et al. (2010) investigated students' understanding of solubility, dissolution and the effect of substance type on solubility by using the POE technique. They collected data from POE worksheets and interviews, and concluded that POE was useful in identifying and overcoming students' misconceptions. A more extensive study has been done by Liew (2004). He used POE tasks concerned with heat and expansion of water, solubility of salt, and power and resistance of light globes to investigate the effectiveness of POE on diagnosing students' understanding. Liew (2004) underlined that students' pre-instructional knowledge persisted despite formal instruction and POE could be effective in diagnosing students' pre-instructional knowledge as well as in identifying students' level of achievement after the instruction.

This study focuses on investigation of pre-service science teachers' understanding of surface tension, adhesion and cohesion by using computer-mediated predict–observe–explain (CMPOE) tasks. These concepts have an important role especially for understanding not only characteristic properties of water but also explaining everyday situations such as floating substances on the surface of the water, and transport of water and minerals in plants. They are also related to chemistry, biology and physics lessons. However, research investigating students' understanding of the aforementioned concepts is limited. Eilam (2004) investigated high school students' written explanations of their observation during individually performed experiments related to observing the number of drops of water and of soap solution that fall from droppers into waste dishes. Results indicated that students' use of scientific terms did not necessarily indicate meaningful understanding of the cohesion concept and they could not adequately explain the reason of soap solution dropped more than water.

Hapkiewicz (1992) indicated that some students thought that cohesion, which enables formation of huge clusters of water molecules as a result of water molecules pulling each other, and adhesion, which arises as a result of the pulling of water molecules by other molecules, are the same and they also think that liquids rise in capillary tubes as a result of the suction power.

Oztas and Bozkurt (2011) investigated whether biology teacher candidates had the ability to explain some water-related events they had observed in daily life with chemical, physical and biological mechanisms. They determined students' understanding of surface tension, adhesion, and cohesion with a questionnaire featuring open-ended questions that demanded short answers.

Purpose of the study

There have been several studies focusing the use of POE tasks in a virtual learning environment (Tao and Gunstone, 1999a,b; Tao, 2000; Kearney et al., 2001; Kearney, 2004). However, research on the use of POE in a virtual environment with the aim of diagnosing student understanding of scientific concepts has been limited in the literature. Although surface tension, cohesion and adhesion concepts are important to understanding of chemical, physical and biological aspects of everyday situations, there has not been adequate research on students' understanding of these concepts. For this reason, this present study aims to diagnose pre-service science teachers' understanding of surface tension, adhesion and cohesion concepts by computer-mediated prediction–observation–explanation tasks (CMPOE). The research questions are:

1. What is the level of students' knowledge about the situations that were asked about at the prediction stage of each CMPOE tasks?

2. What is the students' understanding of the experiments shown at the observation stage of each CMPOE tasks?

3. Are there any differences between students' responses at the prediction and explanation stages of each CMPOE tasks?

Methodology

Participants

The participants of this study consisted of 22 third-year pre-service science teachers in a faculty of education sited in Istanbul, Turkey. The pre-service science teachers were from different cities in Turkey. All participants were similar in socioeconomic status, with the majority coming from middle-class families. The pre-service science teachers enrolled in the faculty of education to be a primary science and technology teacher based on their scores in the Turkish University Entrance Exam.

Participants' prior knowledge

At the time of the study, students had already been taught the chemistry, physics and biology knowledge required to perform the CMPOE tasks. They had learned cohesion and adhesion concepts in high school biology and university general biology lessons under the subject of transporting matter and water in plants. Cohesion, adhesion and surface tension concepts had been also taught in high school chemistry and university general chemistry lessons under the heading of intermolecular forces. Pre-service science teachers had learned chemical properties of detergents as surfactants in high school chemistry and special topics in chemistry lessons in university.

Data collection and analysis

Pre-service science teachers' written responses for each CMPOE task were used to collect data. CMPOE tasks related to colour change of tulips, run-away black-pepper, and dance of the colours were accomplished in the class, and pre-service science teachers were required to independently write their own prediction, observation and explanation on the worksheets given for each task. The researcher and two chemistry instructors analysed and categorised the written responses to determine the participants' understanding.

Procedure

Development of CMPOE tasks

In this study, three CMPOE tasks were developed related to surface tension, adhesion and cohesion concepts. At the beginning of the study, five POE tasks were developed by the researcher. To ensure their validity, they were evaluated by three chemistry instructors. According to their comments, three POE tasks were selected and corrections were made. The experiments were conducted in a real environment and videotaped. Then, the videos were edited based on the stages of POE. After video presentations were examined by the same chemistry instructors, a pilot study of CMPOE tasks was conducted with participation of 12 pre-service science teachers. During this process, the researcher asked the pre-service science teachers to determine the video presentations to ensure that they understood the CMPOE tasks. The pre-service teachers were also allowed to ask questions about the tasks. According to their comments the CMPOE tasks were prepared for real implementation.

Implementation of CMPOE tasks in class

At the beginning of the study, pre-service science teachers were informed about the learning process and CMPOE tasks. Pre-service science teachers were required to follow the directions on CMPOE worksheets, and to independently write their responses. There were three parts in the worksheets. In the first step, the instructor made a video presentation about the related subject and then the pre-service science teachers independently wrote down their predictions and their prediction reason on the worksheet before making observations (P: Predict). In the second step, the video presentation of the hands-on activity was shown. The pre-service science teachers were required to watch the video carefully and then to write down their own observations independently on the worksheet (O: Observe). During the third step, the pre-service science teachers were required to independently write down their reasons and explanations for any inconsistency between what they predicted and what they observed (E: Explain). During this process no discussion or communication of any kind was allowed in order to determine participants' understanding. The CMPOE tasks are summarized in Table 1.

Table 1 CMPOE tasks used in this study

CMPOE tasks	Predict	Observe	Explain
1. Colour change of tulips	Watch a video that shows cutting stems of white tulips under water and then placing in cups containing coloured water with food colouring. Predict what will happen to the each white tulip. Independently write down your prediction. State and explain the reasons of your prediction.	Watch a video presentation that shows a hands-on activity related to colour changes of the tulips during a 24 hour period. Write down your observations independently.	Compare your prediction and observation. Are they in agreement or disagreement? Explain your reasons.
2. Run away black-pepper	Watch a video that presents sprinkling black-pepper over a dish filled with water. Predict what will happen when a cotton swab dipped in dishwashing detergent is touched to the centre of the dish. Independently write down your prediction. State and explain the reasons of your prediction.	Watch a video that presents black-pepper receding quickly when a cotton swab dipped in dishwashing detergent is touched to the centre of the dish. Write down your observations independently.	Compare your prediction and observation. Are they in agreement or disagreement? Explain your reasons.
3. Dance of the colours	Watch a video that presents dropping food colouring in different colours onto milk in a dish. Predict what will happen when a cotton swab dipped in dishwashing detergent is touched to the centre of the dish. Independently write down your prediction. State and explain the reasons of your prediction.	Watch a video that presents swirling colours when a cotton swab dipped in dishwashing detergent is touched to the centre of the dish. Write down your observations independently.	Compare your prediction and observation. Are they in agreement or disagreement? Explain your reasons.

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Results and discussion

Results of first CMPOE task

The first CMPOE task required pre-service science teachers' to explain the reason for the colour change of white tulips by using transpiration, cohesion and adhesion concepts. The expected explanations were the determination of transpiration as a result of evaporation of water from the surfaces of cells in the leaves, and as water molecules were removed by transpiration from the leaves the next molecules moved upwards to take their place, pulling the stream of molecules continuously along. It was also expected that participants explained that transpiration in leaves created tension (differential pressure) in the mesophyll cells, and because of this tension water was literally being pulled up from the roots into the leaves, helped by cohesion (the pull between individual water molecules, due hydrogen bonds) and adhesion (the stickiness between water molecules and the hydrophilic cell walls of plants). This mechanism of water flow works because of water potential (water flows from high to low potential) and the rules of simple diffusion (Campbell and Reece, 2001). Colouring the water with food colouring allowed the movement of water through the roots to the shoots to be seen.

The results of pre-service science teachers' written responses at the prediction and explanation stages reflected that they could not give the expected answers (Table 2). Thirteen of them predicted that colour of the tulips would be the same colour as the water including food colouring. They stated that any tulip placed in a cup containing coloured water with red food colouring would change to red. Only two pre-service science teachers explained the colour change by using adhesion and cohesion concepts. On the other hand, nine of them indicated that colour of tulips would not change. Five of them explained that tulips used only water not food colouring and the others indicated that flower did not interact with coloured water, so the colours of the tulips would not change (Table 2).

Table 2 Number of pre-service science teachers' explanations in the prediction and explanation stages for the first CMPOE task

Explanations	Prediction that the colour of the tulips will be the same as the water (n = 13)		Prediction that the colour of the tulips will not change (n = 9)
	Predict stage	Explain stage	Predict stage	Explain stage
Colour of the tulips changes. Because food colouring is pulled up by cohesion force.	3	3	0	2
Colour of the tulips changes. The reason behind the tulips' changing colour is the effects of adhesion and cohesion forces.	2	2	0	2
Colour of the tulips changes. Tulip absorbs/sucks the colouring and displays that colour.	8	8	0	5
Colour of the tulips does not change. Because the tulips use only water.	0	0	5	0
Colour of the tulips does not change. Because the flower does not interact with coloured water.	0	0	4	0

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At the observation stage, all the pre-service science teachers observed that the colour changes of the tulips depend on the colour of food colouring added to the water. At the explanation stage, pre-service science teachers who had predicted colour change did not change their explanations after the video presentation. The others, who could not predict the colour change, changed their explanations. They explained the reason for colour changes by using the concepts of cohesion force (n = 2), absorption (n = 5) and cohesion–adhesion forces (n = 2) as indicated in Table 2.

The results indicated that pre-service science teachers had difficulties in explaining colour change of tulips by giving adequate explanations. In total, five participants explained the reason of colour change by using the term of ‘cohesion attraction’. However, they presented various definitions in explaining cohesion attraction. They stated that ‘cohesion is the pressure upwards’ (n = 1), ‘cohesion force is a sucking force which occurs in the roots of the flowers’ (n = 2), ‘tulips suck up the water, known as a cohesion attractive force’ (n = 2). Four pre-service science teachers gave the reason behind the colour change as the effects of adhesion and cohesion forces. However, they could not scientifically define these concepts. They explained that ‘cohesion in the plants sucks up the water from the roots, adhesion transfers the colouring to the leaves, the most distant parts of the plant, (n = 2), ‘adhesion holds water together, cohesion moves water up, (n = 1), ‘adhesion and cohesion forces take up the water and transmit it to the upper parts of the plant’ (n = 1). Thirteen pre-service science teachers explained that tulip absorbed the colouring and it changed to that colour. They indicated that ‘there is an absorption reaction between tulip molecules and food colouring’ (n = 3), ‘tulips’ roots suck food colouring because of osmosis’ (n = 5), ‘tulips suck coloured water, and if it is washed it will be white again’ (n = 3), ‘absorption occurs between tulips’ leaves and food-colouring because of turgor pressure’ (n = 2).

Although all the pre-service science teachers learned the transpiration concept in primary science, high school biology and undergraduate general biology lessons, none of them indicated this concept. Cohesion and adhesion concepts were also learned in high school chemistry and university general chemistry lessons under the heading of intermolecular forces. However, pre-service science teachers could not give scientific definitions of these concepts. The results reflected that pre-service science teachers had misconceptions about the basic physical and biological aspects of water molecule transport to plant leaves as indicated by Salisbury and Ross (1985) and Oztas and Bozkurt (2011). It was also found that they confused adhesion and cohesion. This result is also in agreement with the study by Hapkiewicz (1992), who underlined that some students thought that cohesion, which enables formation of huge clusters of water molecules as a result of water molecules' pulling each other, and adhesion, which arises as a result of the pulling of water molecules by other molecules, were the same. They also thought that liquids rise in capillary tubes as a result of suction power. Seven pre-service science teachers who focused on absorption and suction indicated osmosis and turgor pressure, as underlined in previous studies by Hapkiewicz (1992) and Oztas and Bozkurt (2011).

Results of second CMPOE task

The second CMPOE task aimed for pre-service science teachers to explain the reason of black pepper spreading by associating the surface tension of water. Water molecules are attracted to one another by cohesive forces. The molecules in the middle of a container of water have molecular forces exerted on them by water molecules on all sides. Molecules on the surface of the container have molecular forces exerted on them by water molecules underneath and air molecules above them. The force of attraction produced by air molecules is much weaker than the force exerted by water molecules. The water molecules beneath the surface exert an inward pulling force on the surface of the water that tightens the surface of the water. This is called surface tension (Walker and Wood, 2008). Surface tension allows liquids as such as water to resist an external force. This is revealed, for example, in the floating of some objects, such as black pepper, on the surface of water, even though they are denser than water. If something comes along to break that surface tension, the floating items will either move to accommodate the break or sink. The addition of surfactants, such as soap or detergent, can reduce the surface tension, and this causes the black pepper to run away.

The results of the second CMPOE tasks underlined that pre-service science teachers had difficulties in explaining surface tension. As seen in Table 3, four of them predicted that there would be no change when detergent interacted with water. They thought that because the density of black pepper was lower than water, it would be layered over the top of the water (n = 2) and because both black pepper and detergent were basic, they could not react (n = 2). Seven pre-service science teachers predicted that black pepper would be congregate around the swab. Their explanations in the prediction stage were: ‘cotton absorbs water and adsorbs black pepper’ (n = 3), ‘cotton attracts positively charged pepper’ (n = 3) and ‘detergent ruptures the surface tension of water’ (n = 1). Only eleven pre-service science teachers predicted spreading of black pepper. However, there were only five participants who focused on surface tension of water. The other explanations were: ‘cotton attracts positively charged pepper’ (n = 3), ‘detergent is a base and pepper is an acid, so they react’ (n = 2), and ‘as the detergent dissolves in the water, the pepper spreads’ (n = 1).

Table 3 Number of pre-service science teachers' explanations in the prediction and explanation stages for the second CMPOE task

Explanations	Prediction that there will not be any change (n = 4)		Prediction that black pepper will congregate around the swap (n = 7)		Prediction that black pepper will spread (n = 11)
	Predict stage	Explain stage	Predict stage	Explain stage	Predict stage	Explain stage
Density of black pepper is lower than water. So it is layered over the top of the water.	2	0	0	0	0	0
Because both black pepper and detergent are basic, they do not react.	2	0	0	0	0	0
Cotton absorbs water and adsorbs pepper.	0	0	3	0	0	0
Cotton attracts positively charged pepper.	0	0	3	3	3	3
Because detergent is a base and black pepper is an acid, they react.	0	2	0	1	2	2
As the detergent dissolves into the water, black pepper spreads.	0	2	0	2	1	1
Detergent ruptures the surface tension of water.	0	0	1	1	5	5

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At the observation stage, pre-service science teachers observed that black-pepper floating on top of the water was carried to the outer edge of the plate when a cotton swab dipped in dishwashing detergent was touched to the centre of the dish. In Table 3, it is seen that while pre-service science teachers who predicted spreading of black pepper did not change their explanations after their observations, the others changed their explanations.

The results of the second CMPOE application reflected that pre-service science teachers had difficulties in explaining the reason for black pepper cotton attracts positively charged pepper. Six of them explained that cotton attracted positively charged pepper. They indicated that ‘(+) and (−) charged poles are created when the cotton swab is touched to the water’ (n = 1), ‘because of the polarization, as the negative poles push each other, black pepper scatters when the swab is touched’ (n = 3), and ‘polarization occurs between liquid detergent and black pepper and the pepper particles move to the edge of the dish’ (n = 2). The other five pre-service science teachers explained that detergent was a base and black-pepper was an acid, and therefore a neutralisation reaction occurred. The other five underlined that as detergent dissolved into water the black pepper spread. Only six pre-service science teachers focused on surface tension. Unfortunately, they could not explain the reason for the black pepper running away as required. Two of them indicated that detergent was a cleaner and it cleaned black pepper by reducing surface tension. Four of them explained that the positive pole of detergent attracted negatively charged oxygen atoms and the negative pole of detergent attracted positively charged hydrogen atoms to reduce surface tension. The results indicated that pre-service science teachers had difficulties related to surface tension, as described in other studies by Hapkiewicz (1992) and Oztas and Bozkurt (2011).

Results of third CMPOE task

The last CMPOE task aimed for pre-service science teachers to explain the reason for swirling colours. Milk contains a lot of different types of molecules, including vitamins, minerals, fat, and proteins. Fats and proteins are sensitive to changes in the surrounding milk. Detergent, because of its bipolar characteristic, weakens the chemical bonds that hold the proteins and fats; in solution, the hydrophilic end of the detergent dissolves in water and the hydrophobic end attaches to fat globules in the milk. Detergent also lowers the surface tension of the liquid so that the food colouring is free to flow throughout the milk. The detergent also reacts with the protein in the milk, altering the shape of those molecules and setting them in motion. The reaction between detergent and fat forms micelles. As the micelles form, the pigments in the food colouring are pushed around. Eventually equilibrium is reached, but the swirling of the colours continues for quite a while before stopping (Spangler, 2011).

The pre-service science teachers' explanations of their own predictions of the third CMPOE task are presented in Table 4. Three of them predicted that there would be no change if detergent interacted with milk. They thought that because food-colouring was water-based, it did not dissolve in the milk. Ten pre-service science teachers predicted dispersion of colours. They explained that ‘detergent is a cleaner and so it cleans colour’ (n = 3), ‘because milk is acid and detergent is base, they neutralise, (n = 3), and ‘detergent ruptures the surface tension of milk’ (n = 4). Nine pre-service science teachers predicted the vanishing of the colours on the milk. They also thought that ‘detergent is a cleaner and so it cleans the colour on the milk’ (n = 4), ‘because milk is acid and detergent is base, they neutralise’ (n = 3), and ‘detergent ruptures the surface tension of milk’ (n = 2).

Table 4 Number of pre-service science teachers' explanations in the prediction and explanation stages for the third CMPOE task

Explanations	Prediction that there will not any change (n = 3)		Prediction that colours will disperse (n = 10)		Prediction that colours will vanish (n = 9)
	Predict stage	Explain stage	Predict stage	Explain stage	Predict stage	Explain stage
Because food colouring is water-based, it will not dissolve in the milk.	3	0	0	0	0	0
Detergent cleans the colour on the milk.	0	3	3	3	4	4
Because milk is acid and detergent is base, they neutralise.	0	0	3	3	3	3
Detergent ruptures the surface tension of milk.	0	0	4	4	2	2

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At the observation stage, pre-service science teachers observed the bursting of colours when a cotton swab dipped in dishwashing detergent was touched to the centre of the dish. As presented in Table 4, pre-service teachers who predicted dispersion and vanishing of the colours did not change their explanations after their observations. The others' explanations were changed as in the first and second CMPOE tasks. The results showed that none of the pre-service science teachers explained the reason for bursting colours adequately. As shown in Table 4, in the explanation stage, ten of them indicated that detergent cleaned the colour on the milk. They said that because detergent was a surfactant, it reacted with milk. But, they could not explain this reaction. Six pre-service science teachers focused on a neutralisation reaction between acidic milk and basic detergent. They thought that detergent reacted with lactic acid in the milk, so the colours were burst. The other six pre-service science teachers indicated that detergent ruptured the surface tension of milk. However, they could not explain the effects of detergent on surface tension.

Recommendations and conclusion

The results of this study showed that pre-service science teachers had difficulties related to surface tension, cohesion and adhesion forces. Although, they had learned the mentioned concepts in primary science, high school and university chemistry and biology lessons, it is interesting that most of them could not give a scientific explanation about the phenomenon in CMPOE tasks.

The results underlined that pre-service science teachers especially confused adhesion and cohesion forces, could not explain the role of detergent as surfactant, and focused on acid–base reactions while explaining dispersion the colors on the milk. It is found that generally pre-service science teachers who observed their prediction did not change their thoughts even if they were wrong, and their existing ideas were often strongly held. This underlined that their prior knowledge and the expectation of the outcome influenced their observation, as discussed by Mthembu (2001). Mthembu (2001) argued that students may undergo instruction in a particular science topic and yet do not change their original ideas pertaining to the topic even if these ideas are in conflict with the scientific topic they are taught (Fetherstonhaugh and Treagust, 1992). This is attributed to students being satisfied with their own conceptions and therefore seeing little value in the new concepts (Duit and Treagust, 1995).

This research aimed to investigate pre-service science teachers' individual understanding of the aforementioned concepts. Therefore, during CMPOE instruction, independent responses were taken and no discussion or communication of any kind was allowed. The CMPOE tasks can be also used to teach the concepts by encouraging participants to work in cooperative groups. In this way, they can research, use different sources and discuss with their peers. Thus, their thoughts can change, as underlined in the other studies (Liew, 2004; Coştu et al., 2010). In this study, POE tasks were accomplished in a computer environment. Hands-on experiments were done in a real environment and videotaped. Pre-service science teachers were only required to watch videos and follow up the stages of POE. In this way, pre-service science teachers observed the hands-on experiments easily. It was also useful for observing long term hands-on experiments.

Consequently, the obtained results underlined that CMPOE tasks are an effective method in diagnosing learners' understanding of scientific concepts. It is suggested to develop CMPOE tasks for other chemistry topics and to use them as an alternative assessment technique as well as learning materials.

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