---
title: "At \\(25^\\circ\\text{C}\\), a student analyzes a metal-treatment rinse containing a weak monoprotic acid, \\(\\text{HA}\\). The student prepares a \\(0.102\\text{ M}\\) solution of the acid and measures its pH to be \\(2.70\\). The acid ionizes according to the equation \\(\\text{HA(aq)}+\\text{H}_2\\text{O(l)}\\rightleftharpoons\\text{H}_3\\text{O}^+\\text{(aq)}+\\text{A}^-\\text{(aq)}\\). Assume that the contribution of water autoionization to \\([\\text{H}_3\\text{O}^+]\\) is negligible. Which of the following is closest to the value of \\(K_a\\) for the acid?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/119466/"
date_modified: "2026-08-19T12:40:34+00:00"
---

# At \(25^\circ\text{C}\), a student analyzes a metal-treatment rinse containing a weak monoprotic acid, \(\text{HA}\). The student prepares a \(0.102\text{ M}\) solution of the acid and measures its pH to be \(2.70\). The acid ionizes according to the equation \(\text{HA(aq)}+\text{H}_2\text{O(l)}\rightleftharpoons\text{H}_3\text{O}^+\text{(aq)}+\text{A}^-\text{(aq)}\). Assume that the contribution of water autoionization to \([\text{H}_3\text{O}^+]\) is negligible. Which of the following is closest to the value of \(K_a\) for the acid?

At \(25^\circ\text{C}\), a student analyzes a metal-treatment rinse containing a weak monoprotic acid, \(\text{HA}\). The student prepares a \(0.102\text{ M}\) solution of the acid and measures its pH to be \(2.70\). The acid ionizes according to the equation \(\text{HA(aq)}+\text{H}_2\text{O(l)}\rightleftharpoons\text{H}_3\text{O}^+\text{(aq)}+\text{A}^-\text{(aq)}\). Assume that the contribution of water autoionization to \([\text{H}_3\text{O}^+]\) is negligible. Which of the following is closest to the value of \(K_a\) for the acid?

- **A.** \(4.0\times10^{-6}\)
- **B.** \(4.0\times10^{-5}\)
- **C.** \(2.0\times10^{-3}\)
- **D.** \(2.0\times10^{-2}\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119466/*