---
title: "A student prepares two buffer solutions at \\(25^\\circ\\text{C}\\) by dissolving \\(\\text{CH}_3\\text{COOH}\\) (\\(\\text{p}K_a = 4.74\\)) and \\(\\text{CH}_3\\text{COONa}\\) in distilled water, as summarized in the table below.  | Buffer | Volume | \\([\\text{CH}_3\\text{COOH}]\\) | \\([\\text{CH}_3\\text{COO}^-]\\) | Initial \\(\\text{pH}\\) | | :— | :— | :— | :— | :— | | \\(\\text{X}\\) | \\(100.0\\text{ mL}\\) | \\(0.50\\text{ M}\\) | \\(0.50\\text{ M}\\) | \\(4.74\\) | | \\(\\text{Y}\\) | \\(100.0\\text{ mL}\\) | \\(0.050\\text{ M}\\) | \\(0.050\\text{ M}\\) | \\(4.74\\) |  The student adds \\(1.0\\text{ mL}\\) of \\(1.0\\text{ M HCl(aq)}\\) to each buffer solution. Which of the following correctly identifies the buffer that will experience the smaller change in \\(\\text{pH}\\), and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/121401/"
date_modified: "2026-08-23T05:02:05+00:00"
---

# A student prepares two buffer solutions at \(25^\circ\text{C}\) by dissolving \(\text{CH}_3\text{COOH}\) (\(\text{p}K_a = 4.74\)) and \(\text{CH}_3\text{COONa}\) in distilled water, as summarized in the table below.

| Buffer | Volume | \([\text{CH}_3\text{COOH}]\) | \([\text{CH}_3\text{COO}^-]\) | Initial \(\text{pH}\) |
| :— | :— | :— | :— | :— |
| \(\text{X}\) | \(100.0\text{ mL}\) | \(0.50\text{ M}\) | \(0.50\text{ M}\) | \(4.74\) |
| \(\text{Y}\) | \(100.0\text{ mL}\) | \(0.050\text{ M}\) | \(0.050\text{ M}\) | \(4.74\) |

The student adds \(1.0\text{ mL}\) of \(1.0\text{ M HCl(aq)}\) to each buffer solution. Which of the following correctly identifies the buffer that will experience the smaller change in \(\text{pH}\), and provides the correct justification?

A student prepares two buffer solutions at \(25^\circ\text{C}\) by dissolving \(\text{CH}_3\text{COOH}\) (\(\text{p}K_a = 4.74\)) and \(\text{CH}_3\text{COONa}\) in distilled water, as summarized in the table below.

| Buffer | Volume | \([\text{CH}_3\text{COOH}]\) | \([\text{CH}_3\text{COO}^-]\) | Initial \(\text{pH}\) |
| :--- | :--- | :--- | :--- | :--- |
| \(\text{X}\) | \(100.0\text{ mL}\) | \(0.50\text{ M}\) | \(0.50\text{ M}\) | \(4.74\) |
| \(\text{Y}\) | \(100.0\text{ mL}\) | \(0.050\text{ M}\) | \(0.050\text{ M}\) | \(4.74\) |

The student adds \(1.0\text{ mL}\) of \(1.0\text{ M HCl(aq)}\) to each buffer solution. Which of the following correctly identifies the buffer that will experience the smaller change in \(\text{pH}\), and provides the correct justification?

- **A.** Buffer \(\text{X}\), because the greater molar amounts of \(\text{CH}_3\text{COOH}\) and \(\text{CH}_3\text{COO}^-\) undergo a smaller fractional change in the ratio \(\dfrac{[\text{CH}_3\text{COO}^-]}{[\text{CH}_3\text{COOH}]}\) upon reaction with added \(\text{H}^+\).
- **B.** Buffer \(\text{X}\), because the higher concentration of \(\text{CH}_3\text{COO}^-\) suppresses the ionization of \(\text{CH}_3\text{COOH}\) more completely, resulting in a larger \(\text{p}K_a\) value for the buffer.
- **C.** Buffer \(\text{Y}\), because the lower concentration of conjugate acid allows the forward ionization of \(\text{CH}_3\text{COOH}\) to consume the added \(\text{H}^+\) more rapidly.
- **D.** Both buffers experience the identical change in \(\text{pH}\), because both solutions possess the same initial \(\dfrac{[\text{CH}_3\text{COO}^-]}{[\text{CH}_3\text{COOH}]}\) ratio of \(1.0\) and the same initial \(\text{pH}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121401/*