Application of red mangrove plant (Rhizophora racemosa) extracts as pH indicator

Despite the importance of dyes within the industrial and research settings, the literature lacks information on the utilization of red mangrove forest resources and its applications. In this research study, red mangrove plant (Rhizophora racemosa) extracts were characterized and evaluated for its potential as an indicator. The extraction was done using the traditional method of extraction with water and ethanol as solvents. The extracts were characterized using ultraviolet-visible (UV-vis) spectroscopy and Fourier transform infra-red (FT-IR) spectroscopy. Extracts from the plant were applied in different types of acid-base titrations. Following extraction, the UV-vis analyses of the water extract of Rhizophora racemosa showed a λmax at 450 nm while that of the ethanol extract revealed a λmax at 400 nm. However, after a 72 hour timepoint, the water extract of the Rhizophora racemosa showed a λmax at 559 nm while that of the ethanol extract demonstrated a λmax at 572 nm. The results of the FT-IR analysis revealed the presence of the O‒H for alcohol and phenol, C=O for carboxylic acid, C‒H for methyl group, and N‒O for the nitro group. Moreover, the endpoints for all titration conducted using red mangrove plant (Rhizophora racemosa) extracts were similar to the endpoints obtained using standard synthetic acid-base indicators. This was confirmed by a change in colour of the extracts from yellow in an acidic solution to red wine in the alkaline solution. The results provided established the suitability of Rhizophora racemosa as a pH indicator.