---
title: "A student uses a volumetric pipet to transfer a \\(25.00\\text{ mL}\\) sample of an unknown monoprotic acid, \\(\\text{HA(aq)}\\), into a flask. The student titrates the sample with standardized \\(0.1000\\text{ M}\\) \\(\\text{NaOH(aq)}\\), using phenolphthalein as the indicator. The neutralization reaction has a \\(1:1\\) mole ratio.  Near the endpoint, the student adds too much titrant, producing a persistent deep-pink solution rather than the first persistent pale-pink color. The student records \\(28.64\\text{ mL}\\) as the volume of titrant delivered and uses this volume to calculate the initial concentration of the acid. All other measurements are made correctly.  Which statement correctly describes how the error affects the calculated concentration of \\(\\text{HA(aq)}\\)?"
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url: "https://nerd-notes.com/ubq/119503/"
date_modified: "2026-08-19T12:40:51+00:00"
---

# A student uses a volumetric pipet to transfer a \(25.00\text{ mL}\) sample of an unknown monoprotic acid, \(\text{HA(aq)}\), into a flask. The student titrates the sample with standardized \(0.1000\text{ M}\) \(\text{NaOH(aq)}\), using phenolphthalein as the indicator. The neutralization reaction has a \(1:1\) mole ratio.

Near the endpoint, the student adds too much titrant, producing a persistent deep-pink solution rather than the first persistent pale-pink color. The student records \(28.64\text{ mL}\) as the volume of titrant delivered and uses this volume to calculate the initial concentration of the acid. All other measurements are made correctly.

Which statement correctly describes how the error affects the calculated concentration of \(\text{HA(aq)}\)?

A student uses a volumetric pipet to transfer a \(25.00\text{ mL}\) sample of an unknown monoprotic acid, \(\text{HA(aq)}\), into a flask. The student titrates the sample with standardized \(0.1000\text{ M}\) \(\text{NaOH(aq)}\), using phenolphthalein as the indicator. The neutralization reaction has a \(1:1\) mole ratio.

Near the endpoint, the student adds too much titrant, producing a persistent deep-pink solution rather than the first persistent pale-pink color. The student records \(28.64\text{ mL}\) as the volume of titrant delivered and uses this volume to calculate the initial concentration of the acid. All other measurements are made correctly.

Which statement correctly describes how the error affects the calculated concentration of \(\text{HA(aq)}\)?

- **A.** The calculated concentration is lower than the actual concentration because, at fixed \(\text{NaOH(aq)}\) concentration, a larger delivered volume corresponds to fewer moles of \(\text{OH}^-\text{(aq)}\).
- **B.** The calculated concentration is equal to the actual concentration because any \(\text{OH}^-\text{(aq)}\) added after equivalence remains unreacted and therefore cannot affect the titration calculation.
- **C.** The calculated concentration is higher than the actual concentration because the deep-pink color indicates that \(\text{HA(aq)}\) remains in excess at the endpoint.
- **D.** The calculated concentration is higher than the actual concentration because the recorded \(\text{NaOH(aq)}\) volume is too large, causing too many moles of \(\text{HA(aq)}\) to be inferred from the \(1:1\) mole ratio.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119503/*