Acid-Base Indicator Properties of Dye from Local Plant: The Rosella Calyces (Hibiscus Sabdariffa)

Abstract

The dye from the Calyces Hibiscus Sabdariffa (Zobo) was extracted and used as acid-base indicator for the standardization of acid and determination of the molar masses of some selected acids. The Calyces Hibiscus sabdariffa was peeled, washed and heated in an oven at 60°C. It was ground into powder and soaked in hot and cold ethanol for the extraction. Part of the extract was filtered and concentrated by subjecting the extract to slow heating which yielded 1.5 kg of the Hibiscus sabdariffa indicator. Hot and cold extracts of the Hibiscus sabdariffa were used for the standardization of acid with 0.03 M concentration of the bases. On the preliminary test carried out on basic medium, the calyces Hibiscus sabdariffa indicator turned red in acidic condition and green in basic medium, both hot and cold indicators yielded sharp and intense colours at the end points during titration processes. However, there were no colour changes for weak acid versus weak bases (H2C2O4/Na2CO3 and H2C2O4/B4Na2O7). The mean volumes of the acids used were determined and used for the determination of the molar concentration and mass concentration of all the acids used in the research work.