---
title: "An acid-base indicator, \\(\\text{HIn}\\), dissociates in aqueous solution according to the following equilibrium equation:  \\[ \\text{HIn(aq)} + \\text{H}_2\\text{O(l)} \\rightleftharpoons \\text{H}_3\\text{O}^+\\text{(aq)} + \\text{In}^-\\text{(aq)} \\]  The indicator has a \\(\\text{p}K_a\\) of \\(4.2\\). A student adds several drops of this indicator to a buffer solution maintained at a \\(\\text{pH}\\) of \\(6.5\\). Which of the following correctly predicts the predominant form of the indicator in this solution and gives the correct justification?"
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url: "https://nerd-notes.com/ubq/119994/"
date_modified: "2026-08-21T08:31:41+00:00"
---

# An acid-base indicator, \(\text{HIn}\), dissociates in aqueous solution according to the following equilibrium equation:

\[ \text{HIn(aq)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{H}_3\text{O}^+\text{(aq)} + \text{In}^-\text{(aq)} \]

The indicator has a \(\text{p}K_a\) of \(4.2\). A student adds several drops of this indicator to a buffer solution maintained at a \(\text{pH}\) of \(6.5\). Which of the following correctly predicts the predominant form of the indicator in this solution and gives the correct justification?

An acid-base indicator, \(\text{HIn}\), dissociates in aqueous solution according to the following equilibrium equation:

\[ \text{HIn(aq)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{H}_3\text{O}^+\text{(aq)} + \text{In}^-\text{(aq)} \]

The indicator has a \(\text{p}K_a\) of \(4.2\). A student adds several drops of this indicator to a buffer solution maintained at a \(\text{pH}\) of \(6.5\). Which of the following correctly predicts the predominant form of the indicator in this solution and gives the correct justification?

- **A.** \(\text{HIn}\), because the \(\text{pH}\) of the solution is greater than the \(\text{p}K_a\) of the indicator.
- **B.** \(\text{HIn}\), because the concentration of \(\text{H}_3\text{O}^+\) in the solution is greater than \(1.0 \times 10^{-7}\text{ M}\).
- **C.** \(\text{In}^-\), because the \(\text{pH}\) of the solution is greater than the \(\text{p}K_a\) of the indicator.
- **D.** \(\text{In}^-\), because the concentration of \(\text{OH}^-\) in the solution is less than the concentration of \(\text{H}_3\text{O}^+\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119994/*