Natural pH indicators consist of extracts or dyes extracted from vegetables, using water or
ethanol. However, those responsible for enabling the color change in acidic solutions, such as
vinegar and basic solutions, such as bleach, are anthocyanins. Pigments found in vegetables,
which allow this change every time an acidic or basic product comes into contact with the
indicator solution. Therefore, using these natural indicators to contextualize the subjects of acid
and base allows the science teacher to work on the concepts in an interactive way with the
students, not restricting themselves to the use of laboratory materials or substances. In this
context, the present work aims to apply an experimental lesson in the classroom, using the
natural indicators of red onion (Allium ceppa L.), turmeric (Curcuma longa L.) and pitaya
(Hylocereus polyrhizus) to work on the subject of acid base with 9th year elementary school
students. Therefore, this research is a descriptive research, with a qualitative-quantitative
approach, where the experiment and questionnaires (pre-test and post-test) were applied to a
9th year elementary school class at a state public school. located in the city of Manaus–AM.
The results of the analysis of the pre-test questionnaire showed that the theoretical class alone
was not enough for students to learn acid and base, as students were only able to filter some
parts of the subject presented in the theoretical class. Therefore, it is necessary to use practical
classes with natural indicators to better understand the subject. Due to the facts mentioned, it is
concluded that it is important to use the practical class with natural indicators, to contribute to
students' learning about the acid and base content.
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