---
title: "A student prepares a buffer solution by dissolving \\(0.10\\text{ mol}\\) of \\(\\text{CH}_3\\text{COOH}\\) and \\(0.10\\text{ mol}\\) of \\(\\text{NaCH}_3\\text{COO}\\) in distilled water to yield \\(1.0\\text{ L}\\) of solution (for \\(\\text{CH}_3\\text{COOH}\\), \\(\\text{p}K_a = 4.75\\)). The initial \\(\\text{pH}\\) of the solution is \\(4.75\\). If \\(0.010\\text{ mol}\\) of \\(\\text{HCl}(g)\\) is added to the solution with negligible volume change, which of the following best predicts and explains the resulting \\(\\text{pH}\\) of the solution?"
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url: "https://nerd-notes.com/ubq/121386/"
date_modified: "2026-08-23T05:02:01+00:00"
---

# A student prepares a buffer solution by dissolving \(0.10\text{ mol}\) of \(\text{CH}_3\text{COOH}\) and \(0.10\text{ mol}\) of \(\text{NaCH}_3\text{COO}\) in distilled water to yield \(1.0\text{ L}\) of solution (for \(\text{CH}_3\text{COOH}\), \(\text{p}K_a = 4.75\)). The initial \(\text{pH}\) of the solution is \(4.75\). If \(0.010\text{ mol}\) of \(\text{HCl}(g)\) is added to the solution with negligible volume change, which of the following best predicts and explains the resulting \(\text{pH}\) of the solution?

A student prepares a buffer solution by dissolving \(0.10\text{ mol}\) of \(\text{CH}_3\text{COOH}\) and \(0.10\text{ mol}\) of \(\text{NaCH}_3\text{COO}\) in distilled water to yield \(1.0\text{ L}\) of solution (for \(\text{CH}_3\text{COOH}\), \(\text{p}K_a = 4.75\)). The initial \(\text{pH}\) of the solution is \(4.75\). If \(0.010\text{ mol}\) of \(\text{HCl}(g)\) is added to the solution with negligible volume change, which of the following best predicts and explains the resulting \(\text{pH}\) of the solution?

- **A.** The \(\text{pH}\) will increase slightly because the added \(\text{H}^+\text{(aq)}\) ions react with \(\text{CH}_3\text{COOH}\text{(aq)}\) to form additional \(\text{CH}_3\text{COO}^-\text{(aq)}\).
- **B.** The \(\text{pH}\) will decrease dramatically to approximately \(2.00\) because \(\text{HCl}\) is a strong acid that completely ionizes in aqueous solution.
- **C.** The \(\text{pH}\) will remain exactly \(4.75\) because the conjugate pair neutralizes the added acid with no net change in the hydronium ion concentration.
- **D.** The \(\text{pH}\) will decrease slightly because the added \(\text{H}^+\text{(aq)}\) ions react with \(\text{CH}_3\text{COO}^-\text{(aq)}\), decreasing the ratio \(\dfrac{[\text{CH}_3\text{COO}^-]}{[\text{CH}_3\text{COOH}]}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121386/*