Abstract

This study reveals the potential of Vinca flowers (in hues of red, purple, violet, pink, light pink, and white) as vibrant and effective natural acid-base indicators for titration experiments. By employing a cold extraction method with 70% ethanol, we successfully isolated anthocyanin pigments from these flowers and explored their pH sensitivity across a broad range (pH 1-14). The extracts displayed striking color changes: red/pink in acidic conditions (pH 1-3), colorless at pH 5, green hues in the mid-range (pH 7-9), and yellow in basic solutions (pH 11-14). Notably, the purple, red and violet extracts showed the most distinct color shifts. UV-vis spectroscopy confirmed that anthocyanins are the principal pigments, with additional sugar content also identified. In practical titration experiments, including NaOH vs. HCl, HCl vs. NH4OH, and NaOH vs. CH3COOH, the Vinca flower extracts provided clear and reliable color transitions, comparable to synthetic indicators like methyl red, methyl orange, and phenolphthalein. The pH endpoints observed with these natural indicators matched those obtained with synthetic counterparts, underscoring the accuracy and reliability of Vinca flowers as pH indicators. This innovative approach not only offers a sustainable alternative to synthetic indicators but also highlights the valuable application of plant-based pigments in both educational and practical settings for acid-base titrations.