---
title: "A student titrates a \\(25.0\\text{ mL}\\) sample of a weak monoprotic acid, \\(\\text{HA(aq)}\\), with \\(0.100\\text{ M }\\text{NaOH(aq)}\\) at \\(25\\text{ }^\\circ\\text{C}\\). The titration curve obtained from the experiment is shown below.  Based on the titration curve, which of the following gives the best estimate of the \\(\\text{p}K_a\\) of \\(\\text{HA}\\) and provides the correct explanation for why the \\(\\text{pH}\\) at the equivalence point is greater than \\(7.00\\)?"
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date_modified: "2026-08-23T05:04:57+00:00"
---

# A student titrates a \(25.0\text{ mL}\) sample of a weak monoprotic acid, \(\text{HA(aq)}\), with \(0.100\text{ M }\text{NaOH(aq)}\) at \(25\text{ }^\circ\text{C}\). The titration curve obtained from the experiment is shown below.

Based on the titration curve, which of the following gives the best estimate of the \(\text{p}K_a\) of \(\text{HA}\) and provides the correct explanation for why the \(\text{pH}\) at the equivalence point is greater than \(7.00\)?

A student titrates a \(25.0\text{ mL}\) sample of a weak monoprotic acid, \(\text{HA(aq)}\), with \(0.100\text{ M }\text{NaOH(aq)}\) at \(25\text{ }^\circ\text{C}\). The titration curve obtained from the experiment is shown below.

Based on the titration curve, which of the following gives the best estimate of the \(\text{p}K_a\) of \(\text{HA}\) and provides the correct explanation for why the \(\text{pH}\) at the equivalence point is greater than \(7.00\)?

![The graph is a standard grayscale plot of pH versus volume of added titrant. The horizontal axis is labeled 'Volume of 0.100 M NaOH Added (mL)' with major tick marks and light gray gridlines at 0, 5, 10, 15, 20, 25, and 30 mL. The vertical axis is labeled 'pH' with major tick marks and light gray gridlines at 0, 2, 4, 6, 8, 10, 12, and 14. A single solid black curve begins at (0, 2.9), increases gradually through a buffer region to (10.0, 4.8), rises steeply through an inflection point at (20.0, 8.7), and levels off toward pH 12.3 at 30 mL. A vertical dashed gray line extends from 10.0 mL on the horizontal axis up to (10.0, 4.8). A second vertical dashed gray line extends from 20.0 mL on the horizontal axis up to (20.0, 8.7). No other particles, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787461496-kNT8GY.jpg)

- **A.** The \(\text{p}K_a \approx 8.7\); at the equivalence point, unreacted \(\text{OH}^-\text{(aq)}\) ions from the titrant are in excess.
- **B.** The \(\text{p}K_a \approx 8.7\); at the equivalence point, the conjugate base \(\text{A}^-\text{(aq)}\) hydrolyzes water to produce \(\text{OH}^-\text{(aq)}\).
- **C.** The \(\text{p}K_a \approx 4.8\); at the equivalence point, unreacted \(\text{OH}^-\text{(aq)}\) ions from the titrant are in excess.
- **D.** The \(\text{p}K_a \approx 4.8\); at the equivalence point, the conjugate base \(\text{A}^-\text{(aq)}\) hydrolyzes water to produce \(\text{OH}^-\text{(aq)}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121510/*