---
title: "A student prepares a sample of a weak monoprotic acid, \\(\\text{HA(aq)}\\), with a concentration of \\(0.20\\text{ M}\\) and an acid-dissociation constant of \\(K_a = 1.8 \\times 10^{-5}\\) at \\(298\\text{ K}\\). The student then adds an equal volume of distilled water to the solution at constant temperature. Which of the following correctly describes the effect of this dilution on the percent ionization of \\(\\text{HA}\\) and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/123795/"
date_modified: "2026-09-28T12:30:19+00:00"
---

# A student prepares a sample of a weak monoprotic acid, \(\text{HA(aq)}\), with a concentration of \(0.20\text{ M}\) and an acid-dissociation constant of \(K_a = 1.8 \times 10^{-5}\) at \(298\text{ K}\). The student then adds an equal volume of distilled water to the solution at constant temperature. Which of the following correctly describes the effect of this dilution on the percent ionization of \(\text{HA}\) and provides the correct justification?

A student prepares a sample of a weak monoprotic acid, \(\text{HA(aq)}\), with a concentration of \(0.20\text{ M}\) and an acid-dissociation constant of \(K_a = 1.8 \times 10^{-5}\) at \(298\text{ K}\). The student then adds an equal volume of distilled water to the solution at constant temperature. Which of the following correctly describes the effect of this dilution on the percent ionization of \(\text{HA}\) and provides the correct justification?

- **A.** The percent ionization of \(\text{HA}\) decreases because the value of \(Q\) immediately after dilution is greater than \(K_a\), which causes the system to shift toward the reactants.
- **B.** The percent ionization of \(\text{HA}\) decreases because the concentration of \(\text{H}_3\text{O}^+\text{(aq)}\) in the solution at the new equilibrium is lower than it was in the original solution.
- **C.** The percent ionization of \(\text{HA}\) increases because the value of \(Q\) immediately after dilution is less than \(K_a\), which causes the system to shift toward the products.
- **D.** The percent ionization of \(\text{HA}\) increases because the addition of water increases the value of \(K_a\), which favors the formation of ions.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123795/*