K_a for HA is 4.9 × 10^-10.What is the pH of a 0.068 M aqueous solution of A^-?

Question

Quizplus · Accepted Answer

Given the acid dissociation constant (Ka) for HA is 4.9 × 10^-10, and we're asked to find the pH of its conjugate base (A^-) solution. For the conjugate base of a weak acid, we use the Kb value to find pOH first, then convert to pH. Kb can be found using the relation Kw = Ka × Kb, where Kw = 1.0 × 10^-14 at 25°C. Thus, Kb = Kw / Ka = (1.0 × 10^-14) / (4.9 × 10^-10) = 2.04 × 10^-5. Using the formula for Kb, [OH-] = sqrt(Kb × [A^-]), and then pOH = -log[OH-], we can find pOH and then pH = 14 - pOH. The calculations lead to a pH of approximately 11.07.

Ka for HA Is 4

K_a for HA Is 4