A solution is prepared by dissolving 0.23 mol of benzoic acid and 0.27 mol of sodium benzoate in water sufficient to yield 1.00 L of solution.The addition of 0.05 mol of HCl to this buffer solution causes the pH to drop slightly.The pH does not decrease drastically because the HCl reacts with the ________ present in the buffer solution.The K_a of benzoic acid is 1.36 × 10^-3. A)H₂O B)H₃O⁺ C)benzoate ion D)benzoic acid E)This is a buffer solution: the pH does not change upon addition of acid or base.

Question

Quizplus · Accepted Answer

In a buffer solution, the pH is maintained due to the presence of both a weak acid and its conjugate base (or a weak base and its conjugate acid). In this case, benzoic acid and sodium benzoate act as the weak acid and its conjugate base, respectively. When a small amount of HCl is added, it reacts with the sodium benzoate to form benzoic acid, which increases the concentration of the weak acid and shifts the equilibrium to maintain the pH. Thus, the solution is buffered by the benzoate ion, and the correct choice is (C).

A Solution Is Prepared by Dissolving 0