The highest pH for an effective buffer occurs when the base is how many times as concentrated as the acid?
A)2
B)5
C)10
D)20
E)15

Question

Quizplus · Accepted Answer

The Henderson-Hasselbalch equation for a buffer is pH = pKa + log([A-]/[HA]), where pKa is the dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid. At the highest pH for an effective buffer, the pH equals the pKa plus one. Thus, pH = pKa + 1. Taking the antilog of both sides, 10^pH = 10^pKa *[A-]/[HA]. Because the ratio of [A-]/[HA] must be less than 1 for an effective buffer, the concentration of the base must be at least 10 times greater than the concentration of the acid. Therefore, the answer is C, which represents a base concentration that is 10 times greater than the acid concentration.

The Highest PH for an Effective Buffer Occurs When the Base