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title: "A student titrates a sample of a weak diprotic acid, \\(\\text{H}_2\\text{A(aq)}\\), with standard \\(0.10\\text{ M }\\text{NaOH(aq)}\\). The acid has ionization constants \\(K_{a1} = 1.0 \\times 10^{-4}\\) and \\(K_{a2} = 1.0 \\times 10^{-9}\\). Exactly one stoichiometric equivalent of \\(\\text{NaOH(aq)}\\) is added, reaching the first equivalence point of the titration according to the following equation:  \\[ \\text{H}_2\\text{A(aq)} + \\text{OH}^-\\text{(aq)} \\rightarrow \\text{HA}^-\\text{(aq)} + \\text{H}_2\\text{O(l)} \\]  Which of the following correctly identifies the predominant A-containing species in the resulting solution and its acid-base role?"
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url: "https://nerd-notes.com/ubq/123777/"
date_modified: "2026-09-28T12:30:16+00:00"
---

# A student titrates a sample of a weak diprotic acid, \(\text{H}_2\text{A(aq)}\), with standard \(0.10\text{ M }\text{NaOH(aq)}\). The acid has ionization constants \(K_{a1} = 1.0 \times 10^{-4}\) and \(K_{a2} = 1.0 \times 10^{-9}\). Exactly one stoichiometric equivalent of \(\text{NaOH(aq)}\) is added, reaching the first equivalence point of the titration according to the following equation:

\[ \text{H}_2\text{A(aq)} + \text{OH}^-\text{(aq)} \rightarrow \text{HA}^-\text{(aq)} + \text{H}_2\text{O(l)} \]

Which of the following correctly identifies the predominant A-containing species in the resulting solution and its acid-base role?

A student titrates a sample of a weak diprotic acid, \(\text{H}_2\text{A(aq)}\), with standard \(0.10\text{ M }\text{NaOH(aq)}\). The acid has ionization constants \(K_{a1} = 1.0 \times 10^{-4}\) and \(K_{a2} = 1.0 \times 10^{-9}\). Exactly one stoichiometric equivalent of \(\text{NaOH(aq)}\) is added, reaching the first equivalence point of the titration according to the following equation:

\[ \text{H}_2\text{A(aq)} + \text{OH}^-\text{(aq)} \rightarrow \text{HA}^-\text{(aq)} + \text{H}_2\text{O(l)} \]

Which of the following correctly identifies the predominant A-containing species in the resulting solution and its acid-base role?

- **A.** \(\text{H}_2\text{A}\), which acts as a diprotic acid in dynamic equilibrium with excess \(\text{OH}^-\text{(aq)}\)
- **B.** \(\text{HA}^-\), which acts as an amphiprotic species capable of both donating and accepting a proton
- **C.** \(\text{HA}^-\), which acts exclusively as a Brønsted-Lowry base because its acidic proton has already been neutralized
- **D.** \(\text{A}^{2-}\), which acts as a diprotic base produced by the complete deprotonation of \(\text{H}_2\text{A}\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123777/*