Investigative didactic sequence for the teaching of electrochemistry addressing the disposal of batteries

4.1 Stage 1. Prior knowledge of the theme

The DS was initiated as the application of an individual preliminary questionnaire, in which the relationship between electrochemistry and batteries was discussed. Initially, the focus was to investigate the students’ prior knowledge of the theme. Soon after, the researchers promoted a discussion with the students on the collected data to introduce the chosen content.

To better illustrate the contribution of DS in assisting the student in decision-making on issues involving the relations between electrochemistry and batteries, besides their effects on the environment, the results of the questionnaire were analyzed. Thus, we initially asked the students the questions presented in the following paragraph in quotation marks.

An environmental education team from EMLURB (Company for Urban Maintenance and Cleaning) carried out, in the neighborhoods of the city of Recife, a campaign to raise awareness about urban waste, which consists of about 1 % of solid waste containing toxic elements. They showed that among these elements are heavy metals such as cadmium, lead and mercury, components of batteries, which are dangerous to human health and the environment. During the work carried out, they highlighted the current Brazilian legislation (CONAMA, National Council for the Environment, Resolution 401/2008) which regulates the destination of cells and batteries after their energy depletion and determines to manufacturers and/or importers the maximum permitted amount of these metals in each type of cell/battery, but the problem persists. In this contest, answer: What is the relationship between the leakage of substances present in batteries with the nature of heavy metals and damage to human health and the environment? Regarding the disposal site for batteries, which place is more conducive to soil contamination with heavy metals, in the dump or sanitary landfill? Describe (with texts and drawings or construction of mental maps) a possible measure that could contribute to definitively ending environmental pollution by heavy metals highlighted in the text.

The problem situation above has three preliminary questions assigned in Q1, Q2 and Q3.

According to Ferreira et al. (2010) in an investigative proposal, it is necessary to explain the prior knowledge available about the activity, without which it becomes impossible to carry it out. To analyze the responses of Q1, Q2 and Q3 in the problem situation, we used Table 1, based on Lacerda (2008) and Silva et al. (2016); and da Silva et al. (2017). The responses were classified into the following categories: Satisfactory Response (SR); Partially Satisfactory Response (PSR); Unsatisfactory Response (UR) and No Response (NR).

All answers were evaluated by all researchers together in all stages. The responses were read out loud and classified by the reference parameters, confirmed by a consensus of the evaluators.

4.2 Stage 2. Developed hypotheses

Based on the students’ previous ideas, their hypotheses will be raised and tested to resolve the issue presented associated with the disposal of batteries in the environment. For this, the students used texts, drawings, mental maps and answered the three preliminary questions.

4.3 Stage 3. A class on electrochemistry

During the class, the researcher talked with the students, encouraging their participation. In this stage, the teacher worked on the electrochemistry content, emphasizing the concepts of the anode, cathode, electrode, electrolyte, reduction, oxidation, reduction and oxidation potential, oxidizing agent, and reducing agent. Then, it has been approached the contextualization of the chemical matter by exploring natural phenomena such as corrosion, fruit browning, and photosensitive technology in glasses. At the end of the class, students solved exercises individually to consolidate the definitions and concepts of the subjects previously discussed. The objective was to carry out a theoretical approach of the content articulated to the proposed problem.

4.4 Stage 4. Developing investigative experimentation activity

At this stage, an investigative experiment was used: the decomposition of batteries in saline solutions, whose objective was to simulate the disposal of batteries in semi-solid media and how electrochemical reactions can impact the balance of the system in which they are inserted. Thus, a general question was presented to students: What is the best way to collect and recycle batteries and what damage can disposal cause to the environment?

4.4.3 Steps

1. Production of the saline solution: in 200 mL of water, add 2.5 g of agar–agar; 3.0 g of sodium chloride; 0.07 g of sodium ferricyanide, and 1.0 mL of 1 % phenolphthalein solution.

2. With a blade, cut the lower part of the PET bottle in a circular shape to produce a ‘pool’ for soaking the batteries. Next, place the battery in the container until it is completely submerged. Follow the experiment and take notes.

The setup of the experiment in a gelatinous/saline medium is shown in Figure 2.

Figure 2:

Investigative experiment on the decomposition of batteries in saline solutions (The authors, 2023).

However, to direct the study and enable reflections on broader questions about the implications disposal of batteries, more specific questions were asked:

1. When placing the battery in the saline solution, does a reaction occur? How did you come to that conclusion?

2. What would be the best way to end environmental pollution caused by improper disposal of batteries?

3. When we dispose of batteries in landfills, can they contaminate the environment? Justify your answer.

4. Do you think electrolysis occurs in this procedure? Justify your answer.

5. What were the products of these reactions at the positive and negative poles? How to explain this phenomenon?

6. Observing the experiment, does the oxidation occur in the negative or positive pole? Justify your answer.

7. Check the pH of the medium and discuss whether it is as expected. Why is this question important?

In this stage, the teacher–researcher requested that the students should describe how the experiment was done, what results from they obtained, and whether the experiment worked or not. In addition, the students were asked to answer some questions related to the theme proposed in the activity.

4.5 Stage 5. Systematization

In the systematization stage, the students were asked to read the text: A Battery in the Mouth, by Chang (2007). After reading the text, four questions of systematization were proposed, which allowed problematizing the experience analyzed for critical interpretation, were required. They were:

1. Hygiene habits prevent the formation of cavities and, consequently, reduce the use of fillings. By flossing and brushing our teeth, we are removing sugar residues, which can serve as food for cavity-causing bacteria. What is the effect of poor brushing on the bacterial population?

2. What is the DDP between aluminum and the component with the greatest potential for reducing dental amalgam?

3. Considering that there is a battery between the gold and each of the metallic alloys presented, which of these batteries would present the highest electromotive force? What would be its value?

4. Electromotive is the force that tends to establish electric current. Electric current is known to be an ordered flow of electrons migrating from one point to another. Search the internet, dictionaries, or the library of your school or city for the meaning of the word motive and relate it to the definition of electromotive. Justify the existence of electric current.

After performing the experiment and solving the questions, the students were asked to produce a list with the main electrochemical terms studied during the previous stages of the DS. This material will be covered in the later step for conceptual purposes.

4.6 Stage 6. Communication results

The closure of the DS took place at the results communication stage, where the crucial point was the collective debate between the groups, on all the contents worked on since the first stage. At this stage, the issue of collecting batteries at school and in the neighborhood where they live was also discussed between the groups.

The evaluation criterion at this stage was attitudinal. In this class, participant observation was used as a data collection instrument, which consisted of recording the speeches/participation of students and the production of a list with the main electrochemical terms.

5.1 Problem situation, prior knowledge, and hypothesis

The research question sought to find out the students’ prior knowledge and other conceptual difficulties in the introduction of the content disposal of batteries. The exposed prior knowledge identified by the current study could be described as inside classroom-related (Osman & Sukor, 2013) and these could have been developed during the process of teaching and learning.

Therefore, the results of the pedagogical intervention will be discussed qualitatively and presented in graphs containing the percentages of responses framed in the categories available in Section 1 of the methodology. Figure 3 illustrates the results obtained in the first stages of the study.

Figure 3:

Categorization of students’ prior knowledge in the context of disposal of batteries.

According to Figure 3, it is observed that for the first question (Q1 – What is the relationship between battery leakage and the nature of heavy metals?) a high percentage of PSR was obtained because only the G5 group presented a UR. The members mentioned the relationship between the leak and the toxicity of battery components, but none of the groups was able to associate the internal chemical processes with the redox reactions.

The answers to the second question (Q2 – What is the most favorable place for soil contamination with heavy metals?) showed that most groups (G3, G4, G5, and G6) consider the dump as the most favorable location for environmental contamination due to improper disposal of this type of material, thus obtaining a high percentage of SR. One–third of the groups (G1 and G2) indicated UR because they did not specify where the most vulnerable place would be for this event and neither indicated the correct location for the drop.

The third question (Q3 – Suggest actions that can end environmental pollution by heavy metals.) had a high percentage of PSR because only the G1 group stood out with an SR. The groups produced materials containing strategies to remedy the problem available, but only G1 mentioned the importance of environmental education for the population.

Still, in Figure 3, it is observed that the SR is in smaller proportions than the sum of the PSR and UR responses. This indicates that most students did not demonstrate satisfactory knowledge on the topic of the correct disposal of batteries. Demonstrating that they have little prior knowledge of the subject.

During this stage, the students raised some questions of great importance for the development of the research. The first one was: how are batteries able to generate electricity? All groups said that a possible measure to definitively put an end to environmental pollution by heavy metals highlighted in the text would be to dispose of batteries in a suitable container. One of the groups pointed out that this suitable place called “electronic waste” should be installed in urban spaces with greater circulation of people.

5.2 Investigative experimentation

Locatelli (2021) describes myths and concepts that underlie inquiry-based learning, as well as presents an investigative experiment proposal to be used in the classroom.

In this sense, an investigative experiment called “Decomposition of Batteries in Saline Solutions” was developed by the students. During the development of the experiment, the students in some groups did not propose that the formation of products at the poles of the battery came from electrolysis. On the other hand, the phenomenological character of the apparatus (generation of colored substances and gas release) caught the students’ attention and some of them did not know how to associate the electron transfer reactions with the species formed during the event. The system pH was measured before and after the battery submergence, to evidence the formation of ions hydroxyls in one of the poles of the electrolysis (which got pinkish eventually, due to the presence of phenolphthalein in an alkaline medium), but some students understood the role of indicator in the experiment but are not able to explain the reason behind it. Another difficulty described by the students was the explanation of the formation of the complex that gives the intense hue of the compound known as Prussian blue, leading some of them to alternative and conceptually mistaken ideas. These results corroborate what was described by Ávila and Matos (2017) who proposed to students to carry out qualitative tests for the identification of iron ions, always emphasizing the color of the product formed.

In sequence, at the end of the experiment, the students answered the seven questions, and the results are shown in Figure 4.

Figure 4:

Students’ responses during the investigative experiment.

In Figure 4, it can be seen that in question 1 (Q1 – When placing the battery in the saline solution, does a reaction occur? How did you come to that conclusion?) 33.33 % of the answers were classified as PSR because groups G2 and G4 had gaps in their answers sentences and did not mention the formation of hydrogen gas in the medium, in addition to not making it clear that the phenomenon stemmed from redox.

Regarding question 2, (Q2 – What would be the best way to end environmental pollution caused by improper disposal of batteries?) 33.33 % of the responses were classified as PSR because groups G3 and G4 only partially mention the measures necessary to remedy the problem. These groups do not cite the installation of electronic material collectors, for example, as the other groups mentioned.

When evaluating question 3 (Q3 – When we dispose of batteries in the landfills, can they contaminate the environment? Justify your answer.) 33.33 % of the groups presented PSR. The similarity between them was that both groups (G2 and G3) did not relate the internal constitution of cells and batteries with their respective leaks and toxicities.

The classification as a UR (16.67 %) of G2 in question 4 (Q4 – Do you think electrolysis occurs in this procedure? Justify your answer.) occurred due to the erroneous correlation of the spontaneity of the reaction, where the students associated the concept of electrolysis with a spontaneous reaction. Half of the groups (50.00 %) presented PSR because they did not mention the generation of electric current provided by the battery (electrolysis) at any time.

In question 5 (Q5 – What were the products of these reactions at the positive and negative poles? How to explain this phenomenon?) 16.67 % of the groups suggested a UR answer because the students wrote that at the negative pole, there would be the formation of H⁺ ions, being evaluated as a conceptual error, considering that hydrogen gas is formed at the cathode.

Regarding question 6 (Q6 – Observing the experiment, does oxidation occur at the negative or positive pole? Justify your answer.) G3 and G5 (33.33 %) answered wrong because they indicated the negative pole for oxidation.

Regarding question 7 (Q7 – Check the pH of the medium and discuss whether it is as expected. Why is this question important?) only three groups had access to the measurement of the pH of the medium (G1, G5, and G6), they used litmus paper to determine the pH value at the positive and negative poles of the pile deposited in the water, thus obtaining the results of question 7 only for these three groups. Only one of the analyzed groups presented a satisfactory response because it articulated the impacts generated by sudden changes in pH both in the environment and in the human body.

It is observed in Figure 4 that most of the questions were SR, whereas only two questions (Q4 and Q7) had a higher percentage of PSR and only three questions had UR representing a lower percentage. The plausible explanations for this occurrence in Q4 and Q7 were that students described more visual aspects and did not directly correlate them with chemical reactions; associated damage to the environment mainly by color change and some portrayed the direct variation of the pH of the medium and consequently its impacts. This analysis indicates the success of the use of the apparatus in understanding the analyzed questions and potentiality in the teaching of electrochemistry by DS. Table 2 shows the examples of students’ responses during the investigative experiment.

5.3 Systematization

The systematization of knowledge is an element that enhances investigative activities, because it allows the socialization of the student’s knowledge, through reflection and investigation. During this time, ideally, all students should be able to understand the concept and scientifically expose the concepts and ideas about the topic addressed. According to Carvalho (2013) and Azevedo (2004), the systematization of knowledge is important to prevent a student from leaving class without understanding what was studied. Figure 5 illustrates the results at this stage.

Figure 5:

Students’ responses in the knowledge systematization stage.

Figure 5 shows that in question 1 (Q1 – What is the effect of poor brushing on the bacterial population?) equivalence was obtained in the categories of answers collected. Taking into account what was requested, some students only described the physical consequences of not brushing their teeth, such as yellowing or bad breath, disconnecting from the real reason for the degradation of amalgams, which would be caused by the great proliferation of bacteria in the mouth.

Data from question 2 (Q2 – What is the DDP between aluminum and the component with the greatest potential for reducing dental amalgam?) indicate a higher percentage of SR, where participants correctly demonstrated all half-reactions and the overall equation, including being successful in calculating the DDP. In the class of PSR, some students correctly proceeded with all the required electrochemical reasoning, however, there were small errors in the mathematical operations. A UR was considered the sentence of a single group that did not formulate the reduction equations and only tried to state in full which species undergo oxidation and reduction.

In question 3 (Q3 – Considering that there is a battery between the gold and each of the metallic alloys presented, which of these batteries would present the highest electromotive force? What would be its value?): the highest percentage of the groups presented RS, where, particularly, the only PSR addressed batteries using silver ions alone, without considering the presence of gold (cathode) in the context described. Only one group did not answer the problem proposed in this question (NR).

In solving question 4 (Q4 – Search the internet, dictionaries, or the library of your school or city for the meaning of the word motive and relate it to the definition of electromotive. Justify the existence of electric current): all participants demonstrated some ease in completing the problem, considering that the glossary (electronic or physical) was of great help in this step. The process of epistemological association about the term “electromotive” was achieved without major impasses and all responses were SR.

Figure 5 shows that, except for Q1, the other questions had a higher percentage of SR, which indicates good student performance. This step was extremely important, as it allowed students to raise questions regarding electrochemical terms, manage to select relevant information from the text and relate the reading to the different moments of the experimental activity.

5.4 Communication of results

Communication of results is the time to report the results, difficulties, and limitations of the investigation to the scientific community or society. Figure 6 illustrates the results of the analysis of the list produced with the main electrochemical terms studied during the previous stages of the DS.

Figure 6:

Students’ responses in the results communication stage.

The inappropriate electrochemical terms encompass other content taught during DS but they are not electrochemical terms such as environmental impact; nature of the battery; ionic species and concepts related to electricity.

In Figure 6, it can be seen that G3 was the one that suggested the most terms (48), even having the highest percentage of inappropriate electrochemical terms. G1 stands out for reaching the highest number of appropriate electrochemical terms (23), even having approximately 44 % of invalid responses in the evaluation. It is noted that among all the groups, only G6 had less expressiveness (11 terms), but it was not considered as a great discrepancy from the others, considering that its percentage of appropriate electrochemical terms exceeded 80 %.

It is believed that the expressive values in inappropriate electrochemical terms were due to competition between groups to be able to suggest more expressions in this activity.

The most repeated appropriate electrochemical terms were: oxidation/reduction; anode/cathode; reducing/oxidizing agent and batteries. In the first highlighted terms above, the percentage of terms defined correctly was 100 %. Only G1 presented an SR for the battery expression. In this last instrument, it is noted that G1 was the only one that presented coherent definitions in all seven main terms highlighted for the activity proposed in the communication. These data indicate a good level of electrochemistry learning during DS.

At this stage, the issue of collecting batteries at school and in the neighborhood where they live was also discussed between the groups. The students proposed to identify and publicize the battery collection stations close to the school, such as shops, pharmacies, and supermarkets, to realize the extension of environmental awareness in the community. To finalize the research, they built a battery collection container that was installed in the school.

Just like Lacerda et al. (2012) who studied the importance of agriculture in the production of food for our survival, this search also showed the importance of approach to scientific content in a teaching perspective that includes problems that portray themes of society.

The DS had some limitations due to the number of groups worked on simultaneously, so it was necessary the help of interns to record and take notes on the interventions, in addition to the participation of other researchers.