This experimental activity proposes the use of lily (Lilium sp.), agapanthus (Agapanthus sp.) and hydrangea (Hydrangea sp.) extracts to investigate the colorimetric profile of each extract between pH 1-14. Water, ethanol and ethanol/HCl 1% (w/w) were used as extractive solvents. Among the flowers tested, the extracts of orange lily and burnt yellow lily were the ones that presented the greatest color variation with the solution pH change. In addition, the total content of anthocyanins in relation to cyanidin-3-glycosidic was determined and in ascending order we have: yellow lily (LAM: 0,07 ± 0,03) < agapanthus white (AGB: 0,21 ± 0,03) < agapanthus violet (AGV: 1,72 ± 0,13) < blue hydrangea (HAZ: 1,83 ± 0,47) < orange lily (LAL: 2,87 ± 0,52) < burnt yellow lily (LAQ: 9,55 ± 0,46). For this determination methanol/HCl 1% (w/w) was used as the solvent. Using UV-Vis spectroscopy, it is suggested that the behaviors are due to the presence of cyanidin in AGB, AGV, LAL and LAQ, delphinidin in HAZ and apigeninidine in LAM. This activity can be applied in courses that have Chemistry in their curricular matrix and in General Chemistry subjects when the acid-base theme is approached.
Keywords:
natural pH indicator; anthocyanins; experiment proposal; acid-base
