A 25.00 mL aliquot of a solution of purified weak organic acid HX required exact

Question

A 25.00 mL aliquot of a solution of purified weak organic acid HX required exactly 24.20 mL of a
standard solution of a strong base to reach a phenolphthalein end point. When exactly 12.10 mL of the
base were added to a second 25.00 mL aliquot of the acid, which contained a small amount of the
indicator under consideration, the absorbance was found to be 0.306 at 485 nm and 0.555 at 625 nm
(1.00 cm cells). Calculate the pH of the solution and Ka for the weak acid. What would be the absorbance of a solution at 485 and 625 nm (1.25 cm cells) that was 2.00 x 10-4 M in the indicator and was buffered to a pH of 6.000?

Explanation / Answer

ph=7.5(approx)

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