Greening the Chemistry Laboratory: Use of Flower Extracts as Substitutes for Synthetic Acid-Base Indicators

Due to environmental friendliness, availability and cost, the search for natural compounds as acidbase
indicators has continued. Certain highly coloured pigments obtained from plants produce
changes in colour with varying pH. This study has been conducted to investigate the indicator
property of ethanolic and acidified ethanol extracts of Acanthus sennii chiovenda flower and compare
the results with that of already existing synthetic indicators (phenolphthalein, bromothymol blue and
methyl red). Flower extracts of the plant were characterized with ultraviolet-visible spectrophotometer
and phytochemical screening test. The colour change with respect to varying pH was also examined
by adding four drops of flower extracts of this plant to definite volume of solutions at various pH. The
flower extracts of the plant were applied in titrimetric analysis for four types of acid-base titrations.
Phytochemical analysis and spectral studies confirmed presence of anthocyanins and flavonoids in
ethanol and acidified ethanol Acanthus sennii chiovenda flower extracts responsible for accurate and
sharp colour change at the end point. The results indicated that flower extracts of this plant can be
used as acid-base indicators. Statistical tests and comparisons are made with performances of the
synthetic indicators.