Blooming chemistry: Vinca as your pocket-friendly pH indicator

Abstract

This study investigates the extraction of anthocyanins from Vinca flower by cold extraction method. The pH sensitivity of the extracts was evaluated across a broad range (pH 1-14), with distinct color changes observed: red/pink in acidic conditions (pH 1-3), colorless at pH 5, green in the neutral to slightly alkaline range (pH 7-9), and yellow in strongly alkaline solutions (pH 11-14). Ultraviolet-visible spectroscopy confirms anthocyanins as a primary pigment with additional sugars. In acid-base titration experiments the Vinca flower provide a clear, concise and reliable pH endpoints, comparable to synthetic indicators involving sodium hydroxide versus hydrochloric acid (Methyl Red (10.339), Methyl Orange (10.350), Phenolphthalein (10.348); Vinca: Purple (10.351), Red (10.348), Violet (10.346), Pink (10.346), Light Pink (10.346), White (10.351), hydrochloric acid versus ammonium hydroxide (Methyl Red (10.380), Methyl Orange (10.368), Phenolphthalein (10.381); Vinca: Purple (10.383), Red (10.382), Violet (10.38), Pink (10.385), Light Pink (10.386), White (10.387), and sodium hydroxide versus acetic acid (Methyl Red (10.339), Methyl Orange (10.343), Phenolphthalein (10.36); Vinca: Purple (10.347), Red (10.346), Violet (10.363), Pink (10.366), Light Pink (10.363), White (10.368). The pH endpoints observed with the Vinca extracts closely matched those obtained with the synthetic indicators, demonstrating their accuracy and reliability. This study highlights the unique application of Vinca flowers as a natural, eco-friendly, and cost-effective substitute for synthetic pH indicators in both educational and practical settings.

Keywords

• Vinca
• Catharanthus roseus
• pH indicator
• natural indicator
• acid-base titrations

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