---
title: "A student separately titrates a \\(25.0\\text{ mL}\\) sample of \\(0.100\\text{ M HCl(aq)}\\) and a \\(25.0\\text{ mL}\\) sample of \\(0.100\\text{ M}\\) monoprotic weak acid \\(\\text{HA(aq)}\\) with \\(0.100\\text{ M NaOH(aq)}\\) at \\(25^\\circ\\text{C}\\). The resulting titration curves are shown in the figure.  Which choice correctly identifies the curve for \\(\\text{HA(aq)}\\) and explains the broad region of gradual pH change before the equivalence point?"
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url: "https://nerd-notes.com/ubq/119500/"
date_modified: "2026-08-19T12:40:50+00:00"
---

# A student separately titrates a \(25.0\text{ mL}\) sample of \(0.100\text{ M HCl(aq)}\) and a \(25.0\text{ mL}\) sample of \(0.100\text{ M}\) monoprotic weak acid \(\text{HA(aq)}\) with \(0.100\text{ M NaOH(aq)}\) at \(25^\circ\text{C}\). The resulting titration curves are shown in the figure.

Which choice correctly identifies the curve for \(\text{HA(aq)}\) and explains the broad region of gradual pH change before the equivalence point?

A student separately titrates a \(25.0\text{ mL}\) sample of \(0.100\text{ M HCl(aq)}\) and a \(25.0\text{ mL}\) sample of \(0.100\text{ M}\) monoprotic weak acid \(\text{HA(aq)}\) with \(0.100\text{ M NaOH(aq)}\) at \(25^\circ\text{C}\). The resulting titration curves are shown in the figure.

Which choice correctly identifies the curve for \(\text{HA(aq)}\) and explains the broad region of gradual pH change before the equivalence point?

![Draw a grayscale Cartesian graph with bare axes and no gridlines. The horizontal axis is labeled “Volume of NaOH added (mL)” from 0 to 50, with ticks at 0, 12.5, 25, and 50. The vertical axis is labeled “pH” from 0 to 14, with ticks at 0, 7, and 14. Plot two smooth curves. A compact legend in the upper left maps X to a solid line and Y to a dashed line. The solid line passes through approximately (0, 1.0), (20, 2.0), (24, 2.7), (25, 7.0), (26, 11.3), and (50, 12.5). The dashed line passes through approximately (0, 2.9), (2.5, 3.7), (12.5, 4.7), (22.5, 5.7), (24, 6.1), (25, 8.7), (26, 11.3), and (50, 12.5). Connect each set continuously, showing a steep rise near 25 mL. No other labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787143250-vTipSj.jpg)

- **A.** Curve Y; excess \(\text{OH}^-\text{(aq)}\) and \(\text{A}^-\text{(aq)}\) present before equivalence consume added acid or base.
- **B.** Curve Y; partial neutralization produces a mixture of \(\text{HA(aq)}\) and \(\text{A}^-\text{(aq)}\) that consumes added acid or base.
- **C.** Curve X; partial neutralization produces a mixture of \(\text{HA(aq)}\) and \(\text{A}^-\text{(aq)}\) that consumes added acid or base.
- **D.** Curve X; \(\text{HCl(aq)}\) and \(\text{Cl}^-\text{(aq)}\) form a buffer that consumes added acid or base.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119500/*