The largest change in pH for an effective buffer occurs when the base is how many times as concentrated as the acid?
A) 8
B) 5
C) 10
D) 25
E) 40

Question

Quizplus · Accepted Answer

The Henderson-Hasselbalch equation states that pH = pKa + log([A-]/[HA]). For an effective buffer, the concentration of [A-] should be roughly equal to the concentration of [HA], meaning that [A-]/[HA] is approximately equal to 1. Therefore, pH = pKa + log(1) = pKa. To get the largest change in pH, we want to maximize the ratio of [A-]/[HA] while keeping pH near the pKa. This occurs when [A-] is ten times as concentrated as [HA]. Therefore, the base is 10 times as concentrated as the acid, and the answer is C.

The Largest Change in PH for an Effective Buffer Occurs