Hippeastrum hybridum anthocyanins as indicators of endpoint in acid – base titrations

Abstract

Anthocyanins from Hippeastrum hybridum (Amaryllis) were investigated as indicators of endpoint in acid- base titrations. Extraction of the anthocyanins was done using distilled water, methanol and methanol containing 0.5% acetic acid. The extracts were used in determination of endpoint in titrations between strong acid/strong base, strong acid / weak base, weak acid / strong base and weak acid / weak base at concentration levels of 0.1 M, 0.5 M and 1.0 M. The titres were compared to those obtained using phenolphthalein, methyl orange and mixed indicator. The shelf life of anthocyanin extracts kept in amber bottles at room temperature (16.8 ⁰C – 29.1 ⁰C) was also investigated. The plant extracts gave accurate and precise results in titration of strong acids with strong bases and weak acids against strong bases at all concentrations investigated (0.1, 0.5 and 1.0 M) that were very comparable to the values obtained using phenolphthalein, methyl orange and mixed indicator. In titration of weak acids against weak bases, the plant extracts gave accurate results when concentration was 0.1 M but failed for 0.5 M and 1.0 M. On average the anthocyanins from Hippeastrum hybridum could be used in the titration of strong acid versus strong base, weak acid versus strong base and weak acid versus weak base. The anthocyanins from Hippeastrum hybridum had a good shelf life of 90 days when kept at room temperature. The extracts can thus be used in any place including those that have no access to refrigeration facilities since they can be kept at room temperature for some time before they undergo degradation.

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Keywords: Hippeastrum hybridum, anthocyanins, pH indicators, acid-base titrations, shelf life