Reaproveitamento de eletrodos de pH para determinação de cloreto : uma abordagem experimental para o ensino de química

Abstract

This work addresses the reuse of a pH electrode for chloride determination, highlighting its essential role in Chemistry education. In this context, the reuse of damaged electrodes, previously used for pH measurements, was evaluated for chloride ion determination, proposing an educational approach for Analytical Chemistry classes. The first step of the study involved removing the ion-selective glass membrane from the pH electrode. Next, the electrode's response, in millivolts (mV), was evaluated in solutions with different chloride concentrations. These tests showed a high linear correlation (R > 0.96) between the electrode response and chloride concentrations in the range of 1.55 × 10⁻¹ M to 2.00 × 10⁻² M. The application of the modified electrode in potentiometric titrations was also assessed, yielding well-defined titration curves that enable discussions on topics such as the solubility equilibrium of silver chloride. Replicated experiments demonstrated that the responses were precise, with variation coefficients below 1.18%. Accuracy was evaluated by comparing the results obtained from potentiometric and conductometric titrations performed simultaneously on the same sample. No statistical differences were observed between the titrant volumes at the equivalence point obtained by both techniques, indicating high accuracy of the method (t = 2.13 < t₉₅% = 2.78). The results demonstrate that the modified electrode is a viable and efficient alternative not only for chloride ion determination but also for educational applications in Analytical Chemistry, promoting sustainability and environmental awareness. Furthermore, its use in education enhances active learning by bringing students closer to scientific practice. Finally, an experimental guide was developed to stimulate critical and interdisciplinary thinking in the classroom, aligning with the Science, Technology, Society, and Environment (STSE) approach by encouraging reflections on the environmental and social impact of laboratory practices.