A Comparative Study of French and Turkish ... - ACS Publications

Research: Science and Education edited by

Diane M. Bunce The Catholic University of America Washington, DC 20064

A Comparative Study of French and Turkish Students' Ideas on Acid-Base Reactions

Melanie M. Cooper Clemson University Clemson, SC 29634

Aytekin Cokelez* Faculty of Education, Science Education Program, Ondokuz Mayis University, Samsun, Turkey *[email protected]

It is well-known that students' acquisition of knowledge bears a complex relationship with what they are taught (1). To give sense to the abstract conceptions, students develop alternative conceptions that do not match what they are taught but nevertheless are necessary so that they can assimilate the new knowledge. This conceptual structuring takes time during learning (2) and, according to the general constructivist theory of knowledge (3), is not always easy. Students elaborate an alternative conceptual framework while trying to adapt their conceptions to the teaching (4). These conceptions have been labeled “intermediate conceptions” (5), “synthetic mental models” (6), and “alternative frameworks” (7). These are diverse, complex, and interconnected. Some studies (8, 9) list sources of students' misconceptions as the teacher's instruction, textbooks, language and words, the experience of daily life, and the causal effect that goes along with their social environment and intuition. This goal of this article is to examine this step of the didactic transposition resulting from student efforts (10) with acid-base reactions. To accomplish this goal, the answers to identical questionnaires administered to French and Turkish students at the same educational levels but who had not received identical teaching were compared. Comparative Analysis of Instruction To better understand the alternative student conceptions of acid-base reactions, Turkish and French national curricula were examined to determine how these curricula presented the concept of acid-base reactions. The definitions of acids and bases, which are taught in grade 9 in France and Turkey, are similar: The acidic or basic character of a solution is characterized by the pH value: acid if pH < 7, basic if pH > 7, and neutral if pH = 7. An acidic solution has more Hþ ions than OH- ions, the reverse holds for a basic solution, and a neutral solution contains as many Hþ ions as OH- ions. In the curricula of France and Turkey at this level, the characterization of an acid (usually hydrochloric acid) is demonstrated by means of its action on marble (release of CO2) and on certain metals (formation of hydrogen gas and ions in solutions). The action of an acid on a base is not presented in France, whereas in Turkey, it is taught that acids and bases are neutralized to give a salt. The curricula for grade 11 differ in the two countries: in France, the reaction between an acid and a base is introduced by using Brønsted's model, whereas in Turkey, three models (Arrhenius, Brønsted-Lowry, Lewis) are introduced. To explain acid-base titration, French students are taught “to define equivalence during titration and to infer the quantity of matter of the titrated reactant” (11). Equivalence is defined as the “the state of the system in which the titrated reactant becomes the

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limiting reactant”. The definition results because the acid-base reaction is a proton transfer reaction in the Brønsted model, so that acids and bases never disappear: acid1 þ base2 f acid2 þ base1 For example CH3 CO2 H þ OH - f CH3 CO2 - þ H2 O An acid reacts with a base to produce a new acid and a new base. The amphoteric character of water is emphasized in France; whereas, the self-ionization of water is not taught in France. Student experimental activities involving titration in France use “conductimetry for the titration of a scaling substance by a sodium hydroxide solution, or measuring a drain cleaner by a solution of hydrogen chloride ( hydrochloric acid)” (11). That is, the experiments relate to the titration of monoacids or monobases: H3 Oþ þ OH - ¼ 2H2 O The use of an advancement chart allows for the deduction that n(H3Oþ)initial = n(OH-) poured at equivalence so that CAVA = CBVBeq, where n is the amount of substance, C is the concentration, and V is the volume. In Turkey, grade 11 students must be able to explain the neutralization concept and to master the concept of titration reaction and solve problems. Initial presentations to students stress reactions between a monoacid (strong or weak) and a monobase (strong). Acid-base reactions are defined as reactions of neutralization, which can be seen in the following two examples from Turkish grade 11 textbooks: “Acids and bases neutralize each other and produce a salt and water; this phenomenon is called `neutralization'” (12, 13) and “Neutralization is the disappearance of acidic and basic characters during the reaction between acid and base. That is, an Hþ ion from the acid and an OH- ion from the base unite to produce water. The neutralization reaction is (13) Hþ ðaqÞ þ OH - ðaqÞ f H2 OðaqÞ The Turkish instruction is a generalization of the Arrhenius model, which can be expressed as ðHþ þ Cl - Þ þ ðNaþ þ OH - Þ f ðNaþ þ Cl - Þ þ HOH acid þ base f salt þ water That is Hþ þ OH - f HOH Practical work on the titration reaction can be done either by use of an indicator whose color changes at equivalence (i.e., when acid and

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Research: Science and Education

base are found in stoichiometric quantities, when nacid = nbase) or by using the pH metric technique. At equivalence, equality of the quantities of acid and base is expressed as CAVA = CBVBeq. Analysis of Previous Research Several studies (14-20) have shown that students do not understand the symbolization of acid-base reactions in solution and therefore are unable to identify the reactants and products in the solution. They prefer to use a molecular equation (double decomposition reaction) or dissociation reaction, rather than the reaction between the specific reacting species (ions or molecules) (19-22). Acids and bases react by addition, not by breaking apart and forming ions and water (16, 17). Some studies (23, 24) have reported that the difficulty students encounter in writing an ionic equation might result from the great number of tasks implied in this activity: writing ionic formulas, writing full ionic equations, and deciding what information is redundant and discarding the spectator ions. Students have the most difficulty with the last step (24-27). In the Arrhenius model, a solution is neutral if its pH = 7 (at 25 °C); in the analytic context an acid can be neutralized by an equivalent quantity of base, but neutralization does not necessarily result in a neutral solution (22, 28). In the Brønsted model the terms neutral and neutrality lack meaning (29). However, many students believe that neutralizing an acid and a base always produces a neutral solution (9, 29-33) with a pH of 7. Schmidt (29) attributed this misconception to students relating “neutralization” to its literal meaning: the solution obtained is neutral. Students think that a solution resulting from neutralization of acids by bases contains neither Hþ ions nor OH- ions because equal amounts of acids and bases completely consume each other in neutralization reactions and the salt produced does not contain these ions (29, 32-34). The failure to take into account the self-ionization of water was also noted by Banerjee (35) and Goffard (14). To students, a basic solution (or pure water) cannot contain H3Oþ ions, and an acid solution cannot contain OH- ions. Further, since neutralization reactions are usually presented with examples in which strong acids react with strong bases to produce a neutral solution, the word “neutralization” is associated in many students' minds with the action of a strong acid on a strong base: Hþ and OHions mutually neutralize (29, 31). Thus, with the titration of weak acids and bases, the students have problems envisaging the pH (pH 6¼ 7) of the solution to equivalence (34). Mental Models Lin and Chui (9) examined Taiwanese students' conceptions of neutralization reactions and suggested three mental models to explain the student understanding: character-symbol model, inference model, and phenomenon model. In the character-symbol model, students grasped superficial meanings of scientific terminology (e.g., names, functional groups H or OH in chemical formulas) and that mixing any kind of acid and base resulted in neutral solutions because the acidic and basic ions are consumed or positively charged ions counterbalance negatively charged ones. The characteristic of the inference model was an incorrect link among some fragmentary scientific concepts. The inference model has two submodels: generative-inference and pithy-formula. In the generating-inference model a neutralization reaction produced salt, and salt hydrolysis affected the

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acidic or basic nature of solutions. In the phenomenon model, students define acidic and basic substances by their macroscopic characteristics such as toxic, corrosive or stronger flavor. In the pithy-formula model the determinant was the strength of the acids or bases (9); students simply memorized some sentence such as adding a strong acid to a weak base will result in an acidic solution. Purpose and Research Questions Studies that explore learning difficulties (and successes) in relation to the details of specific curricula and linguistic contexts can assist in developing more effective pedagogy in teaching the challenging aspects of science. This article presents a crosssectional study of the way French and Turkish students at the upper secondary-school level (grades 11 and 12) understand acid-base reactions. The specific purpose is to examine how French and Turkish upper secondary-school students assimilate knowledge and to compare this knowledge across the two countries, as well as with the knowledge to be taught according to the national curricula. The following research questions were addressed:

• What differences exist between French and Turkish students' alternative frameworks on the concept of acid-base reactions and between the knowledge to be taught and the assimilated knowledge by students for both countries? • What alternative conceptions and what mental models do the students use to interpret acid-base reactions? • Do the students' understanding of acid-base reactions evolve over these two teaching years; if so, how?

Methodology Data were collected from three teachers in Pau, France, and two teachers in Karabuk, Turkey. Before the relevant teaching was conducted during the school year, 286 French students (128 grade 11 and 158 grade 12 students) and 242 Turkish students (119 grade 11 and 123 grade 12 students) completed a written questionnaire that included one open-ended question, three multiple-choice questions with short answers, and two multiple-choice questions. By testing 11th and 12th grade students, the evolution of the knowledge could be examined as the grade 11 students had not been taught about the acid-base reactions and the grade 12 students had been taught these concepts in 11th grade. Although each nationality's students came from a single town, they attended different secondary schools. All the students were on a scientific path, and the teachers followed their country's national curriculum. Thus, each school and its teachers were considered similar to the other schools in each town. For these reasons, the groups were considered similar enough to be compared. The questions were written in French and in Turkish, the languages of instruction in the two countries. However, for this article the questions and answers were translated into English. The students gave a large number of answers to the openended question. Different elements of explanations were identified, several of which could appear in a single answer so number of elements was larger than the number of students. The elements of explanations were combined into several categories. Answers to the other questions were analyzed by calculating students' rates for each response, and the short ans-

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Research: Science and Education Table 1. Students' Alternative Conceptions and Associated Mental Models Mental Modela

Topic

Alternative Conception

Acidity or basicity of solution

Students consider the presence of functional groups H or OH in the formula to determine the acid or basic character of a solution (grades 11 and 12, France)

Acid-base reaction

The mixing of any kind of acid with any kind of base leads to a compensation of their acid-base properties or to the preponderance of acid-base character of the added species (grades 11 and 12, France)

“Neutralization”

The neutralization is the reaction between any kind of acid with any kind of base to obtain water and salt (grades 11 and 12, Turkey)

Character-symbol model: “superficial meaning of words, formula, functional group, ... and incorrect generalization”

Acid-base neutralization (reaction) always gives a neutral product and the pH of the solution is equal to 7 (grades 11 and 12, Turkey and France) Neutrality

In a neutral solution there are neither H3Oþ ions nor OH- ions (grade 12, France)

Acid-base reaction

Adding strong acids (bases) into the weak bases (acids) will produce acid (basic) solutions (grade 12, Turkey)

“Neutralization”

At equivalence there is as much acid as base, all reacts, the solution becomes neutral (grade 12, France)

Pithy-formula model: “incorrect links between some fragmentary scientific concepts”; “the reasoning is determined by keywords as “strength of acid and base” or “equivalence”

Adding strong acids into strong bases will produce neutral solution (grade 12, Turkey) Neutrality

Whatever the quantities added, the solution resulting from the mixing of hydrochloric acid (strong acid) and sodium hydroxide (strong base) contains as many H3Oþ ions as OHions (grades 11 and 12, Turkey and France)

Acid-base reaction

Any kind of acid reacts with any kind of base to obtain water and salt (grades 11 and 12, Turkey)

Generative-inference model”:Incomplete links between scientific concepts”

The proton released by the acid is gained by the base or two conjugated acid-base pairs are implicated in the reaction (grade12, France) a

Mental models from ref 9.

wers to the multiple-choice questions were categorized according to the main ideas used by students in both countries and grades. Discussion The questions, student answers, and analysis from this study are provided in the supporting material. The alternative conceptions identified for the various student populations are presented in Table 1 and are categorized into the mental models suggested by Lin and Chiu (9). Acid-Base Interaction To explain what takes place when an acid and a base are mixed, the majority of students were aware that a chemical reaction occurred. But the students' explanations contained only some elements of the definition they were taught. For the Turkish grade 12 students the acid-base reaction produces salt and water, whereas the French grade 12 students believed the reaction resulted from a proton transfer or involved two conjugated acid-base pairs. These partially correct but incomplete 104


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explanations were grouped as representing a generative-inference mental model. At the beginning of grades 11 and 12, a majority of the Turkish students preferably use the mental model that any kind of acid reacts with any kind of base to produce water and a salt, and one-quarter of Turkish grade 12 students associated this explanation with the term neutralization. The meaning of neutralization for these students seems limited to the Arrhenius context (it produces water and salt) and contains no analytic context (an acid can be neutralized by an equivalent quantity of base). We have classified this conception as a character-symbol mental model and hypothesize that it is generated by the definition given in grade 11 (neutralization is defined by the disappearance of acid-base character during the reaction between acid and base). The understanding of the French students evolved after teaching from a character-symbol mental model at the beginning of grade 11 (The solution becomes neutral; The pH draws near/is stabilized/becomes 7) to a generative-inference model (the proton released by the acid is gained by the base) by grade 12.


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Acid-Base Character of the Solution at Equivalence The answers to the question about the end of the titration show that a large number of students associated equivalence, or neutralization in an analytical context, with a neutral solution. They explained this by using a character-symbol mental model: Acid-base neutralization ( reaction) always produces a neutral product, and the pH of the solution is equal to 7. However, a majority of Turkish grade 12 students said that the question was impossible to answer because the strengths of the acid and the base were not given. For these students, the absence of the key phrase about the strength of the acid and base did not permit an answer. However, for some French grade 12 students the keyword equivalence was associated with total consumption of the acid and the base; therefore, the solution would be neutral. pH at Equivalence The analysis of the answers from the two questions about equivalence shows that the reasoning does not take into account either the titration reaction or the major chemical species in the solution at equivalence, that is, the conjugated acid or base for French grade 12 students or the hydrolysis of salt for Turkish grade 12 students. Further, for Turkish grade 12 students, the pithy-formula model, which refers to the strength of the acid and the base, and the character-symbol model, which considers that all acid-base reactions lead to a neutral product, were balanced in students' minds. For French grade 12 students, it seems that the term equivalence, the central object of teaching in grade 11, generated a pithy-formula mental model, present in the majority of the minds of this student population. This led the students to consider that “all interact” and consequently that at the end of a titration reaction the solution is neutral. Only the use of the character-symbol model, making reference to the preponderance of the acid-base character of the added species, allowed some of the French students to give the expected answer.

a conjugated acid-base pair for French students and that of hydrolysis of salts for Turkish students are inoperative to predict the acid-base character of the final solution. Since the curricula are different in the two countries and French and Turkish students are presented acid-base information in different ways, it is not surprising that the assimilated knowledge by two countries' students is not the same. Turkish students are taught according to chemistry curricula (Kimya Programi) (38) issued in 1997 and composed only of a textbookbased syllabus, with no accompanied teacher guides, laboratory manuals, or computer programs for simulation and so forth (33). However, French curricula (Physique-Chimie, classe de premiere, serie scientifique) (39), issued in 2000 and developed within a constructivist framework, comprise activities for meaningful learning and real-life examples appropriated for student levels. Because the terms neutralization and strength of acids and bases in the Arrhenius context and neutralization in the Brønsted context generate character-symbol or pithy-formula mental models, a hypothesis could be presented that this occurs because the students' alternative conceptions about acid-base reactions were not taken into account during teaching. It should not be surprising that, following their first encounter with abstract knowledge, students have difficulty integrating it into their conceptual schemes (4). Therefore, to help the students adopt abstract concepts it is necessary to provide activities that allow them to rationalize the organization of conceptual knowledge and thus consolidate new learning. Classroom discussion based on questioning or problem resolution could make students aware of alternative conceptions, thereby supporting the integration of new knowledge. Several studies (40-42) have emphasized how the acid-base concept is addressed in textbooks. I also suggest avoiding the term neutralization in teaching acid-base reactions in Turkey. Indeed, when students use this word in everyday life, they do not think directly of its scientific meaning; as a result, many students assume that the neutralization process always results in a neutral solution.

Neutrality Concept

Acknowledgment

The neutrality concept considers that as many H3Oþ ions as OH- ions exist in a solution. A large number of students in all groups seemed to have associated this, by the means of the pithy-formula mental model, with the reaction between a strong acid and a strong base, independent of the amounts of acid and base. Moreover, when the acidic or basic chemical species was absent, the students are not able to answer the question. As they did not take into consideration the selfionization of water, a significantly number of French grade 12 students developed a character-symbol mental model that led them to believe that neither H3Oþ nor OH- ions are present in a neutral solution.

I thank Alain DUMON for his help in the production of this manuscript. I also wish to thank the reviewers for their helpful and valuable comments. Literature Cited

Conclusions and Implications The observations from the study show that the meanings of the central concepts introduced in grade 11, neutralization in an analytical context for Turkish students and equivalence for French students, were not well assimilated. For many students, these concepts generated the idea that an acid-base reaction produces a neutral solution, irrespective of the nature and quantities of the acids and the bases. Moreover, the concept of


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Supporting Information Available Questions, student answers, and analysis of this study. This material is available via the Internet at http://pubs.acs.org.


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