Can anyone explain this buffer solution question?

The question is this:

'; A buffer solution of acetic acid-sodium acetate has a pH of 7.00. Upon addition of an acid, 0.5 mmol of H+ was produced in the solution. What is the concentration of the buffer if the change in pH is less than 0.5? The initial volume of the buffer is 75.0 cm^3. ';



Can anyone explain to me how to solve this? No need to solve. Just a clear explanation would be sufficient.Can anyone explain this buffer solution question?
It's not a very good question. First of all, an acetic acid - sodium acetate buffer won't be much of a buffer with a pH of 7. The maximum buffering capacity will be when the amount of weak acid and it conjugate base are the same. If that is the case then pH = pKa. Since the Ka of acetic acid is 1.8 x 10^-5, then pKa = 4.74.



A buffer is a mixture of a weak acid (HC2H3O2) and its conjugate base (C2H3O2^-). The action of a buffer can be explained with Le Chatelier's principle, and the pH of a buffer depends on the concentrations of the weak acid and the conjugate base, and the Ka of the weak acid. The pH of a buffer can be approximated using the Henderson-Hasselbalch equation.



Secondly, you don't have a ';concentration of the buffer';. You have a concentration of H+, and a concentration of C2H3O2-, and a concentration of undissociated HC2H3O2. But there is no concentration of the buffer.



Now I see why you are having a hard time with this question. I suspect that the writer of this question may not have firm grasp of buffer systems.