Question

Assume you have a chemical compound (HA) that is a weak acid which changes color upon reacting with water:

HA(aq) + H2O(l) ⇆ A-(aq) + H3O+(aq)

       Yellow Blue

It is observed that HA exhibits a max at 476 nm with = 2.33 x 104 cm-1 M-1 at this wavelength, while A- has a max of 628 nm with a of 1.24 x 105 cm-1 M-1 at 628 nm. An experimenter places this compound in a pH = 4.00 buffer solution, such that the pH remains fixed at 4.00 and records the absorption spectrum below.

1a) Assuming the system follows the Henderson-Hasselbalch equation, determine the pKa for the chemical compound (HA). To receive credit, you must show all work in a legible, highly organized manner. (Responses that are illegible and/or lack organized supporting work will be scored a “zero.”)

1b)Continuing with the above chemical compound, what is the percent dissociation for the compound at a pH 7.00? To receive credit, you must show all work in a legible, highly organized manner.

1c)Still continuing with the above chemical compound, and assuming all other species present in the solution are colorless, what is the color of an aqueous solution of the compound at pH 7.00? In complete sentences, clearly justify your reasoning.

Answer 1