Question

Which of the following is TRUE?

A. An effective buffer has a [base]/[acid] ratio in the range of 10 - 100.
B. A buffer is most resistant to pH change when [acid] = [conjugate base].
C. An effective buffer has very small absolute concentrations of acid and conjugate base.

Answer 1

Answer:

B. A buffer is most resistant to pH change when [acid] = [conjugate base].

Explanation:

Considering the Henderson–Hasselbalch equation as:

$pH\ of\ the\ buffer=pK_a+log\frac {[conjugate base]}{[Acid]}$

If the concentration of the acid and the conjugate base becomes equal, then the pH becomes equals to pKa which is a constant.

At this concentration , further addition of anything (acid or base) in any amount will not change the pH of the buffer as it has become constant.

So, a buffer is most resistant to pH change when [acid] = [conjugate base].