Acid-base indicator properties of dyes from local plants I: dyes from Basella alba (Indian spinach) and Hibiscus sabdariffa (Zobo)

W-AL Izonfuo, GK Fekarurhobo, FG Obomanu, LT Daworiye
2006 Journal of Applied Sciences and Environmental Management  
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 (Indian spinach), two local plants, were investigated. A purple coloured dye obtained from the ripe fruits of Basella alba showed a λ max 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 λ max of 520nm and 540nm and
more » ... tivities 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 K a 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 . @JASEM
doi:10.4314/jasem.v10i1.17295 fatcat:hd743e4gobecvmcfjeskfwehee