A solution is prepared by dissolving 0.23 mol of butanoic acid and 0.27 mol of sodium butanoate 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 butanoic acid is 1.36 × 10^-3. A) H₂O B) H₃O⁺ C) butanoate ion D) butanoic acid E) This is a buffer solution: the pH does not change upon addition of acid or base.

Question

Quizplus · Accepted Answer

A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). In this case, butanoic acid and sodium butanoate form a buffer system. When HCl is added to the solution, it reacts with the butanoate ion (conjugate base) to form more butanoic acid (weak acid). Therefore, the pH does not decrease drastically because the buffer system is able to resist changes in pH by absorbing the added HCl. Therefore, choice C (butanoate ion) is the correct answer.

A Solution Is Prepared by Dissolving 0