Natural Indicator for Acid-Base Titration from Thai Yellow Flower Extracts

Abstract

This study was aimed at investigating the efficiency of extract indicators from three yellow flowers in Thailand (Acacia auriculiformis A. Cunn., Crotalaria juncea L. and Sesbania javanica Miq.). The flowers were extracted with deionized water and evaporated in order to get dried extracts. The flower extracts (5% w/w) were prepared as indicator. In the primary experiment, the flower extracts were tested in order to determine their indicator property using three types of solutions, different pH, buffer solutions, HCl/NaOH solutions and CH3COOH/NaOH solutions. The results show that the colors will be changed in basic solution. Then, the indicator activities of flower extracts were used in acid-base titration in which a strong base was used as a titrant and the results were compared using a standard indicator, phenolphthalein. The results suggest that the flower extracts can be used as an alternative indicator for strong acid (HCl) – strong base (NaOH) titration and weak acid (CH3COOH) – strong base (NaOH) titrations. The color of solution will be changed from light brown to dark brown for A. auriculiformis A. Cunn., and transformed from light brown into yellow for C. juncea L. and S. javanica Miq. when the solutions have more basicity. The color changes were clear and sharp when the strength of NaOH solution was increased. Therefore, the use of these flowers’ extracts as indicators is their new application which can be applied in the chemistry class because these natural indicators are safe, cheap and easy to prepare.