The acid HIn has an acid dissociation constant of 5.20 x 10. The following data

Question

The acid HIn has an acid dissociation constant of 5.20 x 10. The following data are for a HIn solution of 7.50 x 10 M. Calculate the absorbance at 450 nm of a solution in which the total concentration of HIn is 7.5 x 10 M. The pH of the solution is 4.67. 1. Wavelength Absorbance at pH 1.0 Absorbance at pH-13.0 445 450 455 470 510 550 570 585 595 610 0.657 0.658 0.656 0.614 0.353 0.119 0.068 0.044 0.032 0.019 0.068 0.076 0.085 0.116 0.223 0.324 0.352 0.360 0.361 0.355 The following data have been determined previously. Calculate the concentrations of P and R in the mixture. 2· Concentration Absorbance 365nm 0.150 0.684 0.71 Absorbance 470nm 0.642 0.088 0.604 Compound 1 x 10 M 2 x 104M Unknown

Explanation / Answer

The absorbance of the solution at the particular wavelength is equal to the sum of the individual absorbance of acid and base form of the indicator at that wavelength.

According to the above data,

Absorbance of solution at 450 nm = 0.658 + 0.076 = 0.734

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