---
title: "A student titrates a \\(25.0 \\text{ mL}\\) sample of \\(0.100 \\text{ M } \\text{HCl(aq)}\\) with \\(0.100 \\text{ M } \\text{NaOH(aq)}\\). The initial \\(25.0 \\text{ mL}\\) sample of \\(\\text{HCl(aq)}\\) is represented at the particulate level by a sample containing \\(6\\) \\(\\text{H}^+\\text{(aq)}\\) ions and \\(6\\) \\(\\text{Cl}^-\\text{(aq)}\\) ions. The diagram below represents a representative microscopic volume of the solution after the addition of a certain volume of the \\(\\text{NaOH(aq)}\\) titrant. (Water molecules are omitted for clarity.)  Based on the particulate model, which of the following correctly identifies the volume of \\(0.100 \\text{ M } \\text{NaOH(aq)}\\) added to the flask and explains why the count of \\(\\text{Cl}^-\\text{(aq)}\\) ions is unchanged?"
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date_modified: "2026-09-28T12:02:15+00:00"
---

# A student titrates a \(25.0 \text{ mL}\) sample of \(0.100 \text{ M } \text{HCl(aq)}\) with \(0.100 \text{ M } \text{NaOH(aq)}\). The initial \(25.0 \text{ mL}\) sample of \(\text{HCl(aq)}\) is represented at the particulate level by a sample containing \(6\) \(\text{H}^+\text{(aq)}\) ions and \(6\) \(\text{Cl}^-\text{(aq)}\) ions. The diagram below represents a representative microscopic volume of the solution after the addition of a certain volume of the \(\text{NaOH(aq)}\) titrant. (Water molecules are omitted for clarity.)

Based on the particulate model, which of the following correctly identifies the volume of \(0.100 \text{ M } \text{NaOH(aq)}\) added to the flask and explains why the count of \(\text{Cl}^-\text{(aq)}\) ions is unchanged?

A student titrates a \(25.0 \text{ mL}\) sample of \(0.100 \text{ M } \text{HCl(aq)}\) with \(0.100 \text{ M } \text{NaOH(aq)}\). The initial \(25.0 \text{ mL}\) sample of \(\text{HCl(aq)}\) is represented at the particulate level by a sample containing \(6\) \(\text{H}^+\text{(aq)}\) ions and \(6\) \(\text{Cl}^-\text{(aq)}\) ions. The diagram below represents a representative microscopic volume of the solution after the addition of a certain volume of the \(\text{NaOH(aq)}\) titrant. (Water molecules are omitted for clarity.)

Based on the particulate model, which of the following correctly identifies the volume of \(0.100 \text{ M } \text{NaOH(aq)}\) added to the flask and explains why the count of \(\text{Cl}^-\text{(aq)}\) ions is unchanged?

![A single square box represents a microscopic cross-section of the titration solution with a legend placed directly above it. The legend defines three symbols: an open white circle with a black border represents \(\text{H}^+\text{(aq)}\); a solid gray circle represents \(\text{Na}^+\text{(aq)}\); and a solid black circle represents \(\text{Cl}^-\text{(aq)}\). Inside the square container, there are exactly 12 total particles distributed uniformly: exactly 6 solid black circles (\(\text{Cl}^-\)), exactly 3 solid gray circles (\(\text{Na}^+\)), and exactly 3 open white circles (\(\text{H}^+\)). The particles are dispersed without overlapping or forming clusters. No solvent water molecules, hydroxide ions, bonds, charges inside the circles, or additional text annotations appear inside or outside the box.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790596934-Z63PwT.jpg)

- **A.** \(6.25 \text{ mL}\), because \(\text{Cl}^-\text{(aq)}\) is a spectator ion whose molar concentration remains constant throughout the titration.
- **B.** \(12.5 \text{ mL}\), because \(\text{Cl}^-\text{(aq)}\) reacts with \(\text{Na}^+\text{(aq)}\) to form an insoluble precipitate of \(\text{NaCl(s)}\).
- **C.** \(12.5 \text{ mL}\), because \(\text{Cl}^-\text{(aq)}\) is a spectator ion that does not react, conserving its mole amount while half of the initial \(\text{H}^+\text{(aq)}\) has been neutralized.
- **D.** \(25.0 \text{ mL}\), because the equal number of \(\text{H}^+\text{(aq)}\) and \(\text{Na}^+\text{(aq)}\) ions indicates that the stoichiometric equivalence point has been reached.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123733/*