Sequência didática sobre os conceitos de mistura e métodos de separação utilizando um modelo experimental de estação de tratamento de água

Abstract

This study falls within the scope of basic education chemistry teaching, specifically exploring the concepts of pure substances, mixtures and separation methods through experimental in-vestigative activities using a microscale model of a water treatment plant. The research partic-ipants were 9th grade students of elementary school and the educational proposal was applied at a public state school in the city of São Borja, Rio Grande do Sul, in the curricular compo-nent of science. Ausubel's theory of meaningful learning was used as a theoretical reference in conjunction with the project of activities that allowed the active participation of students dur-ing the construction of knowledge. This work presents three technical productions that were developed: (i) a knowledge test containing multiple choice questions validated using difficul-ty and discrimination indexes, (ii) a small scale prototype of a water treatment plant using low cost materials and sought to replicate some processes of separation of mixtures used in water treatment in large scale and (iii) a didactic sequence with five activities with the objective of contributing to the learning of the concepts of pure substances, mixtures and mixture separa-tion processes with the focus on the use of experimental activities with the prototype of the water treatment plant and a technical visit to the water treatment plant of the city of São Bor-ja. The research methodology included quantitative and qualitative methods for evaluating the effectiveness of the didactic sequence regarding students' comprehension and performance on the proposed topics. The data collection instruments were guides of practical activities an-swered by the participants of the research, a test of knowledge and a test of motivation to learn, both applied before and after the application of the didactic sequence, a questionnaire of opinion of the participants and the observations of the researcher. Wilcoxon's unilateral non-parametric hypothesis test indicated a statistically significant improvement in the performance of participants in the knowledge test after the application of the didactic sequence. The aver-age standardized learning gain for the knowledge test was 61.8%, indicating that for the class as a whole there was a significant learning gain after the application of the proposed didactic sequence. The results of the motivation for learning tests indicated that the students in the class had a motivation to learn near the center of the scale used. The analyzes of the partici-pants' responses to the activity guides and opinion questionnaire indicated that the students participated effectively in the activities and exercised their observation skills. In the responses to the activity guides it was observed a tendency of the students to limit their conceptions of pure substance and mixture to the macroscopic aspects, being recommended, therefore, that the teacher intensifies his discussions regarding the concepts of mixture and pure substance in the atomic scale. We conclude that teaching of the concepts of pure substances, mixtures and separation methods with the use of a prototype of a water treatment plant and participatory activities has the potential to contribute to improve the learning of these concepts and promote the approximation of local reality and chemical concepts.