The molar absorptivities at 430 and 570 nm of the weak acid HIn (Ka = 1.42 ? 10-5) and its conjugate base In- were determined by measurements of strongly acidic and strongly basic solutions of the indicator. Under this conditions, essentially all of the indicator was in the HIn and In- form, respectively. The molar ab-sorptivities of HIn and In- at 430 nm and 570 nm were 6.30 ? 102 and 7.12 ? 103, and 2.06 ? 104 and 9.61 ? 102, respectively. Calculate absorbance data for unbuffered solutions that have total indicator concentrations ranging from 2 ? 10-5 to 16 ? 10-5 M.