The acid/base indicator HIn undergoes the following reaction in dilute aqueous s

Question

The acid/base indicator HIn undergoes the following reaction in dilute aqueous solution:
HIn (color 1) < === > H+ + In- (color 2)
The following absorbance data were obtained for a 5.00 x 10-4 M solution of HIn in 0.1 M NaOH and 0.1
HCl. Measurements were made at a wavelength of 485 nm and 625 nm with 1.00 cm cell.
0.1 M NaOH A(485 nm)=0.052, A(625 nm)=0.823
0.1 M HCl A(485 nm)=0.454, A(625 nm)=0.176
In the NaOH solution, essentially all of the indicator is present as In-; in the acidic solution, it is essentially
all in the form of HIn.

a) What is the pH of a solution containing a small amount of the indicator that exhibits an absorbance of
0.530 at 485 nm and 0.216 at 625 nm (1.00 cm cells).

Explanation / Answer

ph=7.6(approx)

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