Use of extract of the Alternanthera brasiliana L. as an acid-base indicator in the teaching of chemistry

Abstract

The use of didactic proposals in the teaching of chemistry, which make use of experimentation can help in the understanding of abstract contents, such as contributing to motivate and awaken the interest of students during classes. Therefore, the present study aimed to investigate the ability of extract from the leaves of the species Alternanthera brasiliana as a natural indicator for use in an experimental chemistry class. Therefore, it was necessary to quantify the total monomeric anthocyanin content, in addition to determining the wavelength of maximum absorbance of the extract as well as the pK_ind value. In the staining test, solutions ranging from pH 2 to 12 were prepared, and 6 drops of the natural indicator were added in each solution, in order to observe the variation of the staining of the solutions in relation to the pH of the medium. The colors presented by the solutions were: pink (pH of 2 to 9) and yellow (pH 10 to 12). From the other analyses performed, it can be concluded that although the extract of the leaves does not present high levels of anthocyanins (7.54 mg/100 g), it demonstrated potential to indicate alkaline solutions above pH 9, and a visible color change from rose to yellow can be noted. Thus, the methodology used in this research can be incorporated as laboratory practice in chemistry classes.

Keywords: experimentation in chemistry, natural indicators, teaching and learning.