Question

Suppose you have created a buffer solution that is 0.250 M in both benzoic acid (HC7H5O2) and potassium benzoate (KC7H5O2) and that the pH of this solution is 4.65. Assuming that the buffer capacity has not been exceeded, which of the pH values listed below would you expect after adding a small amount of a dilute strong acid solution?

8.85
4.49
4.81
2.88
There is not enough information to determine.

Answer 1

4.49

Step-by-step explanation:

We have a buffer form by a weak acid (HC₇H₅O₂) and its conjugate base (C₇H₅O₂⁻). The function of a buffer is to resist abrupt changes of pH when acids or bases are added. If a small amount of a dilute strong acid solution is added, pH will slightly decrease because the acid will be partially neutralized by the basic component of the buffer.

C₇H₅O₂⁻(aq) + H⁺(aq) ⇄ HC₇H₅O₂(aq)

If the pH of the buffer was originally 4.65, a slightly inferior value like 4.49 is plausible.