Abstract
Indicators used in acid-base titration show well marked changes of colour in certain intervals of pH. Most of these indicators are organic dyes and are of synthetic origin. Today synthetic indicators are the choice of neutralization titrations. But due to environmental pollution, availability and cost, the search for natural compounds as an acid-base indicator was started. The present work highlights the use of the ethanolic extract of the corolla of Roselle (Hibiscus sabdariffa) as a pH indicator in strong acid-strong base, strong acid weak base, weak acid strong base and weak acid-weak base titrations. This natural indicator is easy to extract as well as easily available. The results showed that the Roselle’s corolla indicator gave red color in acidic solution, while green in basic solution. The comparison indicators used in this research were phenolphthalein, methyl red and phenol red. Hopeful results were obtained when it was compared against standard synthetic indicators. The equivalence points obtained match with the equivalence points obtained by standard indicators. Therefore this natural indicator is found to be useful, economical, simple, precise and eco-friendly for acid base titration.
Highlights
Roselle (Hibiscus sabdariffa) is a species of Hibiscus belongs to Malvaceae family [1], probably native to West Africa
The equivalence points obtained by using flower extract matched with the equivalence points obtained by standard indicators
The alcoholic solution of proposed indicator Roselle’s corolla extract was screened for its use as an acid-base indicator and the results were compared with that obtained using phenolphthalein, methyl red and phenol red for strong acid-strong base (HCl and NaOH), weak acid-strong base (CH3COOH and NaOH), strong acid -weak base (HCl and NaHCO3) and weak acid-weak base (CH3COOH and NaHCO3) titrations
Summary
Roselle (Hibiscus sabdariffa) is a species of Hibiscus belongs to Malvaceae family [1], probably native to West Africa. It is an annual or perennial herb or woody-based sub-shrub, growing to 2– 2.5 m (6 – 8 ft) tall. It is cultivated either in tropical or subtropical area and start flowering at the age of 3‐4 months. It has been hypothesized that the flower extract could be utilized as an indicator for all four types of acid base titrations [4]. The equivalence points obtained by using flower extract matched with the equivalence points obtained by standard indicators
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