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Journal of Applied Sciences and Environmental Management
World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt
ISSN: 1119-8362
Vol. 10, No. 1, 2006, pp. 5-8
Bioline Code: ja06001
Full paper language: English
Document type: Research Article
Document available free of charge

Journal of Applied Sciences and Environmental Management, Vol. 10, No. 1, 2006, pp. 5-8

 en Acid-base indicator properties of dyes from local plants I: Dyes from Basella alba check for this species in other resources (Indian spinach) and Hibiscus sabdariffa check for this species in other resources (Zobo)
IZONFUO, W-A L; FEKARURHOBO, G K; OBOMANU, F G; DAWORIYE, L T

Abstract

The acid-base indicator properties of aqueous and ethanol extracts from calyces of H. sabdariffa (Zobo) and a dye obtained from the ripe fruits of Basella alba check for this species in other resources (Indian spinach), two local plants, were investigated. A purple coloured dye obtained from the ripe fruits of Basella alba showed a λmax at 580nm, absorptivity of 0.2269 and was found to be photochemically unstable. A deep red coloured dye obtained from aqueous and ethanol extracts of H. sabdariffa had λmax of 520nm and 540nm and absorptivities of 0.1909 and 0.1187 respectively. The peaks are associated with n→Л* transitions. In strong acid/strong base titrations using the dyes as indicators, the end-points obtained agreed well with those obtained using conventional indicators. The dyes were found not suitable for weak acid/weak base titrations. The Ka of the purple dye from Basella alba was of the order of 10-5 while that of the red dye from H. sabdariffa was of the order of 10-6.

 
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