Based on Henderson-Hasselbalch equation, at what pH value a weak acid would be 99.9% ionized?

Question

Quizplus · Accepted Answer

The Henderson-Hasselbalch equation relates the pH of a solution to the pKa (acid dissociation constant) and the ratio of the concentrations of the deprotonated form (A-) to the protonated form (HA) of the acid. For a weak acid to be 99.9% ionized, the ratio of A- to HA must be 1000:1. According to the equation, pH = pKa + log([A-]/[HA]), when [A-]/[HA] = 1000, log(1000) = 3, so pH = pKa + 3.

Based on Henderson-Hasselbalch Equation, at What PH Value a Weak