There is no life without energy, and the energy used by all living organisms is obtained by cycles of electron transfer between donors and acceptors. Reactions of electron transfer or redox reactions are therefore intrinsically connected to life.

Redox reactions are a group of fundamental reactions in chemistry, studied in different areas, such as general chemistry, physical chemistry, organic and inorganic chemistry. They are also important in various industrial processes, and are present in our day-to-day life, in the batteries. However, these reactions are considered difficult to teach and to learn. In several countries, research in chemistry education focuses on understanding the obstacles faced by teachers and students in electrochemistry learning.

At the Instituto de Química at Universidade de São Paulo (USP), the group of Professor Carmen Fernandez, Education and Knowledge Diffusion Coordinator of the Center for Research of Redox Processes in Biomedicine (RIDC Redoxoma), investigates chemistry teachers' knowledge and has been conducting research on the teaching of redox reactions.

According to the researcher, difficulties encountered by students may be associated with problems such as the complexity involving the concept of oxidation number and the difficulty in identifying the oxidizing and reducing agents, the terminology used by teachers, and even the imprecise and sometimes inappropriate language used in textbooks. Verbal obstacles and misinformation tend to reinforce alternative conceptions of teachers and students.

However, the major problem in the chemical study, and not just in electrochemistry, is that it requires the students to deal with three representational levels: the macroscopic, of the visible phenomena; the submicroscopic, of abstract concepts; and the symbolic, of chemical language.

Fernandez acknowledges that Chemistry is not very popular with students because it is considered difficult and abstract. And worse, a good deal of the chemical concepts at school does not make sense to a significant number of students. To make chemistry more attractive, one possibility would be to integrate chemistry and biology education. “Chemistry for chemistry is very arduous and easily related to negative things like pollution and pesticides, which discourages students. So the biochemistry's call to understand life through chemistry is very interesting, especially for teenagers.”

The teaching of redox chemistry

The conceptions, representations, strategies, and difficulties of chemistry teachers regarding the content of redox reactions have been evaluated by Fernandez group on several fronts. In the first half of 2018, 40 high school teachers from public schools participated in a continuing education course developed by doctoral student Luciane Fernandes de Goes. The course, taught by Goes and the doctoral student Pablo Micael Araujo Castro, addressed the difficulties regarding the content of redox reactions and the strategies to overcome them.

To elaborate the course, the researcher surveyed the main conceptions and difficulties reported in the literature over 10 years and verified the strategies of success used. She analyzed the redox reactions representations in textbooks, to see how the images relate to the text. And she also spent a year in Germany, where she accompanied teachers and found that they have similar difficulties to Brazilian teachers in relation to the teaching of redox reactions.

In the course, the researchers applied a questionnaire developed by Castro in his doctorate to evaluate how teachers teach electrochemistry. The questionnaire addresses five aspects related to teaching: how the teacher organizes the concepts of a curriculum, what difficulties he perceives in teaching, what difficulties students have, how he chooses the representations and what conceptual strategies he uses.

Both in the evaluation of the course and in the results obtained with the questionnaire, which has already been answered by more than 100 teachers, the researchers point out that the main difficulties of chemistry teachers are the elaboration of teaching strategies and the choice of representations. “The course influenced the development of teachers. We observed that they started to justify strategies and to better understand some concepts”, says Goes.

The textbook is the teacher's support tool and, in many schools, determines the curriculum. Although the material is approved in the National Textbook Plan (PNLD - Plano Nacional do Livro Didático), it is not without problems, and some difficulties of working the redox content can come from the representations in the books themselves, as explained by the master student Anike Araujo Arnaud. She analyzes chemistry books used in elementary school 1 and 2 and high school, especially those that were approved by the PNLD. In three collections most used in elementary school, she is verifying the presence of topics pertinent to redox reactions. In the books approved for high school in 2018, she is evaluating the models used to teach redox reactions.

According to Arnaud, textbooks used in high school follow a pattern: they define the terms of redox reactions, they teach how to calculate the number of oxidation, and how to do balancing. Then they go to electrolytic cells, batteries, and electrolysis. These contents are often given in different years. Although photosynthesis is presented to children in elementary school, books do not work the terms related to redox reactions.

“When submitted to TALP, a free word association technique, almost all chemistry professors who participated in the courses and workshops associate redox reactions to batteries. Photosynthesis or breathing, for instance, almost never are mentioned,” notes Castro.

In the last three years, 277 chemistry teachers of high school participated in workshops and courses developed and taught by the Fernandez group.

And all of these studies form a background to the research of the Pedagogical Content Knowledge (PCK) of chemistry professors on redox processes. The PCK represents the knowledge that teachers use in the teaching process, distinguishing the teacher of a given discipline from an expert of that discipline. According to Fernandez, the PCK study is important to understand professional development and especially to contribute to teacher training. “To teach is not enough to know the content, it is necessary to fill this content with a series of circumstances, activities, and strategies to reach the student and get around the alternative conceptions he will have of that content.”

Alternative Concepts

Alternative conceptions are not simple errors. They are internally consistent, universal, persistent, and generalized, being found in both teachers and students at all levels. And, of course, they represent an obstacle to learning.

Often, language can be responsible for creating an alternative conception, since many words used in science have different meanings from everyday language. For example, when talking about the equilibrium of a chemical reaction. The word balance refers to a two-plate balance in the static state. In chemistry, when a reaction reaches equilibrium, it does not stop. Equilibrium means that both the direct and the inverse reactions occur at the same rate and the ratio of the reactants to the products does not change.

Also counterintuitive, reducing is gaining electrons, and, in a redox reaction, the oxidizing agent is reduced and the reducing agent is oxidized. Here, questions of terminology interfere with the understanding of concepts.

Another example of a verbal obstacle is the fact that the word oxidation refers to oxygen, and in some books, the first example of a redox reaction is a reaction involving oxygen. An alternative conception in the redox area is to consider that redox reactions always involve oxygen.

Students also often have difficulty realizing that oxidation and reduction processes are simultaneous. In this case, when the teachers work the redox reactions, they use semi-reactions to facilitate the visualization of the process. But they end up complicating since students tend to think that oxidation and reduction occur independently.

In the researches, Fernandez and his group seek to identify the main alternative conceptions about redox reactions and to understand how they are formed and reinforced.