Final answer:
The pH region for a buffer containing equal concentrations of benzoic acid and sodium benzoate can be determined using the Henderson-Hasselbalch equation. The pH equals the pKa of benzoic acid, which is slightly less than 7. Therefore, the answer is A) pH < 7.
Step-by-step explanation:
The question relates to the establishment of the pH region for a buffer solution containing benzoic acid and sodium benzoate at 25 °C. In this case, the buffer consists of equal concentrations of benzoic acid and sodium benzoate, each at 0.0080 mol in 1.00 L of solution, which means their molar concentrations are also equal. To determine the pH region, we need to use the Henderson-Hasselbalch equation: \[ pH = pKa + \log \left(\frac{\text{[Benzoate ion]}}{\text{[Benzoic acid]}}\right) \]
Given that the concentrations of the benzoate ion (from sodium benzoate) and benzoic acid are equal in the buffer solution, the ratio of [Benzoate ion]/[Benzoic acid] is 1. In this case, the log of 1 is 0, so the pH equals the pKa value of benzoic acid. The pKa value for benzoic acid is not provided directly in the question, but the Ka value for acetic acid is given as 6.3 x 10^-5. Since acetic acid's acid dissociation constant is not relevant for benzoic acid, and a commonly known pKa for benzoic acid is approximately 4.2, we can deduce the pH is slightly acidic.
Therefore, the pH of this benzoic acid/sodium benzoate buffer solution would be slightly less than 7, which corresponds to option A) pH < 7.