A preliminary study on the possibility of developing representational competence pre-service chemistry teacher has done. The aim of study descriptive was to provide description about representational competence's profile of pre-service chemistry teacher in chemical problem solving and to give consideration about the learning strategies have been conducted. The results showed that most students were unable to provide explanations relating to the representation of sub-microscopic level, which were present through the macroscopic and symbolic levels of representation. There were tendency that students solve problems using a transformation from the macroscopic to the symbolic level of representation and vice versa, although they should give explanation at sub-microscopic level of representation. They did not understand the role of sub-microscopic representation to explain the phenomena that occur at the macroscopic level or transformed into symbolic level. Presumably the lack of student representation competence, because the lectures were held tend to separate the three levels of representation and influence the learning process they experienced in high school. Those problems need a serious efforts to find solution.
Key Words : Representational competence, three levels of chemical representation, chemical problem solving,
Currently, there is growing agreement among science educator that learning science requires representational practices of this subject matter. Scientific literacy means as knowing how to interpret and construct this literacy of science. From this perspective, learning concepts and the scientific method requires understanding and conceptualization linking multiple representations of this domain (Norris & Phillips in Waldrip, 2006).
Problem-solving ability as one of the high-level thinking skills uses representational competences (Waldrip, 2006; Kozma, 2005). Russel & Bowen (In Davidowitz & Chittelborough, 2009) have identified representational competence (the ability of student to transform representation in one form to equivalent representations in another) as an important aspect of successful problem solving in chemistry. In problem solving context, Bodner and Domin (in Rosengrant, Van Heuleven, & Etkina, 2006) distinguish between internal representations and external representation. Internal representation is a way of solving a problem by storing the internal components of the problem in mind (mental models). External representation is something related to representation of symbols or objects and/or processes. In this case, the representation is used to recall the mind through the description, portrayal or imagination (Chittleborough & Treagust, 2006).
The characteristics of chemistry involve three levels of chemical representation, i.e. macroscopic representation, submicroscopic representation and symbolic representation.
Macroscopic representations are chemical representation obtained through actual observation (tangible) of a phenomenon that can be seen (visible) and perceived by the senses (sensory level) or can be a daily experience of learners. For examples: color and temperature change, pH, formation of gases and precipitates in chemical reactions that can observe when chemical reactions take place. The learner could represent the observations or lab activities in a variety of modes of representation, for example in the form of written reports, discussions, oral presentations, vee diagrams, graphs and so on.
Submicroscopic (or molecular) representations provide explanations at the particulate level. Submicroscopic representations closely related to the underlying theoretical model in order to dynamics explanation of the particle level (atoms, molecules, and ions). Modes of representation at this level can express start from the simple to use computer technology i.e. using words, two-dimensional, three-dimensional images both still and moving (animation) or simulation.
Symbolic (or iconic) representations are representation to identify of entities (e.g. those involved in a chemical reaction) using qualitative and quantitative symbolic language, such as a chemical formula, diagrams, pictures, equation, stoichiometry, and mathematical calculations.
(Chittleborough & Treagust, 2007; Chandrasegaran, et.al, 2007).
The three levels of chemical representation contain inter-connectedness information. While the macroscopic observable chemical phenomena are the basis of chemistry, explanations of these phenomena usually rely on the symbolic and submicroscopic level of representations. Consequently, the ability of learners to understand the role of each level of chemical representation and the ability to transfer from one level to another is an important aspect of generating understandable explanations. The simultaneous use of macroscopic, submicroscopic, and symbolic representations has been shown to reduce learners alternative conceptions in the teaching and learning of chemical concepts. Connecting of the three levels of representations in teaching will give contribution to construct students understanding about chemical phenomena that occur in laboratory scale and daily life experience. In such way, they can use their concept to solve chemical problem.
Generally, teaching and learning was restricted to level of macroscopic and symbolic representations. Many high school teachers tend only use macroscopic level and symbolic levels. They do not integrate the three representations in their teaching but move between representational levels without highlighting their inter-connectedness. Teachers often assume that students are able to connect symbolic to submicroscopic representations on their own. (Tasker, 2006). The use of chemical models are not always appreciated by linking them with two real targets ; submicroscopic and macroscopic levels. Often, the models were seen as a comprehend symbol in mathematical context. Students solved mathematical problems became criterion that students have understood chemical concepts. Presumably, those views could hinder students to achieve representational competence.
Reviews of various empirical studies supported those statements; Devetak, et.al. (2004) stated that first year students had difficulty to describe the scheme and transfer of symbolic to submicroscopic representation in acid-base equilibrium. Case study conducted by Murniati & Sopandi (2007), showed that high school students have difficulty to represent submicroscopic levels of ionic equilibrium in a weak acid, weak base, hydrolysis of salts, and buffer solution. Savec, et, al, (2006), Weerawardhana, et.al, (2006) and Akselaa & Lundell, (2008) argued separately these problems due to lack of ability of teachers using various modes of submicroscopic representation and connecting these to the other level of representation.
Representational competence students tied to learning process in classrooms, practical laboratory and textbooks. The teacher or prospective chemistry teacher must achieve to internal connection of three levels of representations, as well as re-representing of three levels of representations in their teaching (external representation). Therefore, they must develop two dimensions of representation, i.e., internal representation and external representation.
Based on consideration of effectiveness of teaching and learning in school depend on teachers' competence, so the institutions of higher education of teaching have a task to improve quality of their graduates teacher. One of the effort is to provide pre-service chemistry teachers with ability of three levels of representation so they can become professional teachers later.
The theoretical and empirical studies need to be conducted before developing learning model design in order to achieve optimal results. Therefore, researcher conducted empirical studies at a teacher education program that located at Bandung. The main focus in descriptive research method was to acquired representational competence profile's of pre-service chemistry teachers in chemical problem solving and implementation of relevant lecture have been conducted to developing representational competence of pre-service chemistry teachers.
This research was a part of research and development (R & D) that involve four phases, i.e. preliminary study, design of model, validation and implementation phase. In preliminary research carried out theoretical studies and empirical studies. Research methods used in the first phase was descriptive research method.
Theoretical studies include: 1) Analysis of characteristics of chemical concepts, mapping relationship between concepts and level of chemical representation. For this purpose, researcher chose chemical equilibrium in aqueous solution concept for study, because this concept included one of difficult concept to understand and to teach based on three levels of chemical representation at senior high school. Empirical studies conducted through field studies at teacher training program that focused on representational competence profile of pre-service chemistryteacher in chemical problem solving and implementation of relevant lecture have been conducted to developing representational competence of pre-service chemistryteacher.
Collection data was done through: 1) Observation of implementation of relevant courses, 2) Distribution of questionnaires to acquire pre-service chemistryteachers' feedback on the implementation of courses which has been going on, 3) Interviewing lecturers and , 4) Administering test to acquire representational competence profile of pre-service chemistry teacher in chemical problem solving. There are four category transform levels of representations i.e. ability to transform level of macroscopic to symbolic representation, level of macroscopic to submicroscopic representation, level of submicroscopic to microscopic representation and level of submicroscopic to symbolic representation. Two tests type used to obtain ability of transform between level of representation to solve chemical problem i.e. multiple choice with reason of choice and essay tests. The set of test was administered to 78 prospective students' teachers (sixth semester). Interview to nine pre-service chemistry teacher (randomized chosen) was done to acquired detailed data.
The Characteristics of Concept of Chemical Equilibrium in Aqueous Solution
The concept of chemical equilibriums in aqueous solution is application of key concept of chemical equilibrium. Contextually, this concept plays a crucial role in many biological and environmental processes. For example, the pH of human blood is carefully controlled at a value of 7.4 by equilibrium involving, primarily, the conjugate acid-base pairs (H2CO3 and HCO3- ). The pH of many lakes and stream must remain near 5.5 for plants and aquatic to flourish. The process of formation kidney stones, etc. These phenomena require understanding, which involves three levels of representation.
In addition to result of concept analysis, indicate that there are three of concept type in main concepts of Chemical Equilibriums in Aqueous Solution, i.e. 1) Abstract concepts with concrete examples, 2) concepts by process and 3) concepts by principle. The Levels of representations include macroscopic, submicroscopic, and symbolic representations. Those concepts are complex enough, because they need prerequisite concepts covered three levels of representations, i.e. 1) proton transfer reaction (Bronsted-Lowry acid-base concepts), 2) weak acid, weak base and water dissociation, 3) the strength of acid-base and pH, 4) solubility. Those prerequisite concepts must be understandable in order to achieve three main concept, i.e. 1) salt hydrolysis; 2) buffer solution; 3) solubility equilibrium.
Equilibrium Constanta (K) is a key concept to connect three of main sub concepts in chemical equilibrium in aqueous solution. The value of K indicates to measure of dynamic equilibrium occurrence. At equilibrium, reactions take place continuously with same rate reactions both directions between the formation and decomposition products. Chemical equilibrium represented symbolically with value of K (equilibrium constant) and the equilibrium process represented in term of mathematics and chemical notation with two-way arrows. In chemical equilibriums in aqueous solutions, the value of K can be value of Kh, Kw, Kb, Ka and Ksp. That's various values for K are refer to different process of dynamic equilibrium type occur in aqueous solution i.e. Salt hydrolysis, buffer solution and solubility equilibrium. (Table 1 is describe result of concept analysis for main concepts)
The concept of equilibrium dynamic covered to level of submicroscopic representation. That concepts use to explain equilibrium in solution phenomena. Such kind of concepts internally contains difficulties in learning and teaching. The process of dynamic equilibrium in the electrolyte solution between dissolve ions and insoluble molecules or particles will difficult to understand and imagine when only explained by using words or two-dimensional static images or only symbolically expressed by using the equation. On the other hand, exploration of this concept through a macroscopic representation (for example; the lab activity) could not show the actual dynamics that occur at submicroscopic level.
Result of Empirical Study
There are four categories of representation, which traced the transformation levels in this study i.e. the ability to transform level of macroscopic representation to the symbolic representation, level of macroscopic representation to submicroscopic representation, level of submicroscopic representation to the symbolic representation and level of submicroscopic representation to the macroscopic representation. Here are presented the main findings of a profile representation competence students in solving chemistry problems:
The ability to transform level of macroscopic representation to the symbolic
The ability to transform the macroscopic level to the symbolic expressed through a series of questions that show macroscopic representation, i.e. the characteristics or physical phenomena derived from the observation / measurement, such as ka / kb data, solution molarity, solution volume, solution properties (acidic or alkaline), size of the substance. Using these data the students were asked to solve problems related to the symbolic level that is; using the equation and solve chemical calculations.
Based on the results of data analysis, known as much as 70% of students (N = 78) able to solve problems regarding: 1) the relationship between the strength of the acid / base with a value of Ka / cl, 2) calculate the pH of the reaction of weak acid and strong base with a number of molar equivalent, 3) calculate the pH of a buffer solution based on the reaction of weak acid and strong base, 4) calculate the pH of salt solution which had hydrolysis, 5) express the equation of equilibrium solubility of the saturated salt solution which is difficult to dissolve, 6) calculate the solubility of saturated salt based on the value of Ksp data. It shows most of the students have the ability to transfer the macroscopic level of representation to the level of symbolic representation. Students who are unable to provide the right solution, including: 1) can not be linking the value of Ka/Kb data with the strength of the acid/base, 2) consider the results of acid-base neutralization reaction with a molar equivalent amount is always generate a neutral salt (do not consider the power couple acid or its conjugate base), 4) wrong calculation operations and convert its chemical formula to the equation Ksp.
The ability to transform level of macroscopic representation to submicroscopic
This ability is expressed by the students' ability to provide a sub-microscopic explanation of macroscopic phenomena: a) how the buffer solution to maintain the pH of the solution, b) the occurrence of hydrolysis reaction of salt, c) the phenomenon of saturated solution and d) common ion effect on the saturated solution.
As many as 60% of students give explanation the nature of buffer solution by using arguments based on the symbolic level of representation. They gave proof through the calculation of solution pH before and after the addition of slightly acidic or alkaline solution. The answer given is not linked explicitly with the effect of common ions (due to the addition of slightly acidic or alkaline solution) and proton transfer reactions that cause a shift in equilibrium (sub-microscopic level). Other students who can not solve the problem, some states to maintain a pH buffer solution, because it contains a mixture of weak acid and its salts.
Almost all students (90%) gave explanation about the nature of the acidity or alkalinity of a solution of salt based on the origin of salt-forming acid or base. They claim CH3COONa is alkaline, because the salt is derived from the neutralization reaction of strong base (NaOH) and weak acid (CH3COOH). About 40% of students completing these answers by writing CH3COONa hydrolysis reaction and showed the formation of OH- , which causes the solution became alkaline. Although they can write the equation of the hydrolysis reaction, they can not give an explanation of how the proton transfer process in the hydrolysis reaction to produce OH-ions. Thus, they have not been able to provide problem-solving with the transformation of the macroscopic level of representation to the sub-microscopic. The transformation of sub-microscopic level should be based on proton transfer reactions and determining the strength of the acid / base conjugate, by comparing the value of ka of acid or kb of base with the value of Kw. Alleged incompetence because: 1) can not distinguish which of strong/weak conjugate acid / or strong/weak conjugate base; 2) the role of water solvent to influence on the solute when the dissolution process occurs, 3) students usually distinguish salt of acidic, alkaline and neutral with reference to the Arrhenius acid-base model.
Most students (80%) can explain that the solubility of salts containing the conjugate base anions will increase when pH decreases. But the reasons given are not using a sub-microscopic arguments, but symbolically. They can recognize the common ions in salt solution, but they can not explain the decrease in pH can lead to transfer of protons from hydronium ion (H3O+) and strong base conjugate, thus shifting the equilibrium reaction from the left (the formation of solid insoluble) to the right (towards the formation of soluble ions).
The ability to transform level of submicroscopic representation to symbolic and macroscopic
To determine these capabilities, students are asked to choose the representation of sub microscopic and give reasons for the selection of answers based on the representation of symbolic and macroscopic. Submikroskopik representation presented in the form of image / model particles. Based on the representation of sub-microscopic, they are required to: a) compare the acid strength, b) select a representation that shows the state of buffer solution and hydrolyzed salt solution, c) determine the stages of reaction titration of weak acid and strong base.
62% of students are able to determine which acid is stronger than another based on the amount of H3O + ions are depicted. 44% of students can choose a representation which shows the state of a buffer solution with good reason. However, no student who can correctly select the sub microscopic representation showing the state of hydrolyzed salt solution. 47% of students can choose an appropriate representation that shows where the stages of the titration process occurs, but the reason is not quite right. Most students look to make over-generalization by stating that the anion A-represents the salt which is always neutral. They do not refer to whether the anion A-is a strong conjugate base or weak (as seen from the pair of cation salts), so they fail to recognize the A- is alkaline because of hydrolysis reactions that produce OH- ions, thus decreasing the concentration of H3O+ in solution.
The weakness of the ability of student representation is influenced also by the process of learning in high school. Generally on the third sub-concept (buffer solution, salt hydrolysis and equilibrium solubility), in learning, teachers put more emphasis on presenting the macroscopic to the symbolic. This fact was revealed by the results of interviews with a number of students who were asked about how teachers teach these concepts when they were still in high school. Learning chemistry in high school is further reinforced on the concepts relating to the calculation (the symbolic level), while the concepts of 'declarative' which is actually associated with more frequent sub microscopic level by method of assignment summary and answer questions. The fact is in accordance with the results of research Sopandi & Murniati (2007).
Observations carried out on one of the courses aim to deepen the essential chemical concepts related to learning in secondary schools. In the lecture there is the tendency: 1) Students are more amplified at the macroscopic and symbolic levels, 2) explanation at the level of submicroscpik often ignored, for reasons that are related to chemical bonding concepts learned in other classes; 3) Strengthening of sub-microscopic level using the modeling (in the form of images and the use of molecular models molymod) was not associated contextually with macroscopic phenomena that occur, 4) The use of modeling to be intended for interpretation in the context of symbolic representation to indicate the chemical bonds in a compound, 5) In the course lecturer less focus on concepts essential that often lead to misconceptions; 6) Lack of interaction between students and lecturers or students with students in constructing knowledge because of time constraint.
The study showed the majority of student difficulties provides explanation regarding the representation of sub-microscopic provided by macroscopic and symbolic representations. Students tend to solve problems using macroscopic transformation to a symbolic level, or vice versa. Students did not fully understand the role of model or drawing (sub-microscopic representations) to explain phenomena that occur at the macroscopic level and transforming them into symbolic representations. Presumably the lack of student representation competence, because the lectures are held tend to separate the three levels of representation and influence the learning process they experienced in high school .
Therefore, it is suggested, students are given the ability of chemical representation through: a) the use of visualization tools to explain the processes that occur in a molecular (sub-microscopic) without separating its association with the symbolic representation and the macroscopic level, b) development of model courses that support the representational competence, especially at the lecture that aim to prepared teaching skill in high school, for example; Capita Selecta of Chemistry at School.
