Picric acid has been used in the leather industry and in etching copper. However, its laboratory use has been restricted because it dehydrates on standing and can become shock sensitive. It has an acid dissociation constant of 0.42. What is the [H₃O⁺] for a 0.20 M solution of picric acid?

Question

Quizplus · Accepted Answer

The acid dissociation constant (Ka) of picric acid, Hpic, is given as 0.42. The dissociation can be represented as, Hpic ⇌ H+ + pic- At equilibrium, let the concentration of H+ be x M, then that of pic- will also be x M. The concentration of undissociated Hpic will be (0.20 - x) M. The Ka expression for the dissociation is, Ka = [H+][pic-]/[Hpic] Substituting the values, we get, 0.42 = x^2/(0.20 - x) On solving this quadratic equation, we get x = 0.15 M. Thus, [H₃O⁺] for a 0.20 M solution of picric acid is equal to 0.15 M. Therefore, the best choice is C.

Picric Acid Has Been Used in the Leather Industry and in Etching