Which would make a better buffer solution--A solution with a pH of 9, or 7

A solution with a pH of 7, or a solution with a pH of 9?

That's all it says, I was under the impression that the pH doesn't matter in this case, like both solutions could be a good buffer, am I wrong? If I am could you provide a small explanation? Thanks!

Your right in a way that pH doesn't matter. But think about the characteristics of a buffer. How good a buffer is depends on:

(i) The concentration of the initial buffering components. The greater the concentration, the more you can add without experiencing a significant change in pH.

(ii) The proportion of the components. A ratio of 1:1 of a weak acid and its conjugate base (or vice versa) has the greatest buffering capacity.

Now think about that last point. A buffer should have a weak acid + conjugate base "or" weak base + conjugate acid to be sufficient. If you were to maximise the buffering capacity, you'd put each of these components in the ratio of 1:1. With a 1:1 ratio, it's impossible to reach a neutral pH of 7 (one component is stronger than the other) --> you'd have to increase the conc. of one component.

So even though the question isn't clear, technically, it's possible to make a better buffer at pH 9 .

A compound can buffer the pH of a solution only when its concentration is sufficient and when the pH of the solution is close (within about one pH unit) to its pKa.

(http://www.science.smith.edu/departments…

So it really depends on what you are trying to buffer.