O extrato de açaí como indicador ácido-base: um manual didático para experimentos com água de chuva no ensino de química

Abstract

Natural extracts can be obtained from various sources such as purple cabbage, beet, grape and açaí. And they serve as acid-base indicators because they contain a substance called anthocyanin and can be used in chemistry classes. One way to use them is in the analysis of rainwater, to verify the presence of acidity and consequently the formation of rain acid, a phenomenon that can be intensified with the presence of industries and / or presence of large flow of automobiles. In order to work on these issues, a didactic manual addressing these issues was constructed. It consists of: a brief summary on the acid and base teaching; natural indicators; industrial urban activity; the use of the acid rain theme in chemistry classes; the industrial pole of Barcarena. It also has a didactic sequence with a script of theoretical and practical classes. For the practical classes is presented an experimental kit with a highlight for the color change of natural dyes, rich in anthocyanins, which can be used as pH indicators. Contextualizing the Amazon region, the alcoholic extract of açaí was used for the assembly of this kit that was applied in the determination of acidity of rainwater and household materials. The acidity determined in the samples of rainwater may be related to the intense industrial activity in the region of Barcarena. The manual was applied in a 1st grade class with forty students from Jesus Barros Pereira Elementary School and Middle School Acy, where they answered questions before and after the application of the theoretical and experimental classes and the result showed that there was an improvement of the understanding and absorption of the concepts presented there. This methodology was presented to five professors of Chemistry of the state education network, who were enrolled in Barcarena schools. Teachers unanimously evaluated the proposed methodology by stating that they will use it in their chemistry classes. The use of the didactic manual evidenced the importance of applying experimental methods to provide the student with a more effective teaching-learning.