---
title: "A student titrates separate \\(25.0\\text{ mL}\\) samples of two different \\(0.100\\text{ M}\\) diprotic acids, Acid 1 (\\(\\text{H}_2\\text{A}\\)) and Acid 2 (\\(\\text{H}_2\\text{B}\\)), with a standardized \\(0.100\\text{ M }\\text{NaOH(aq)}\\) solution at \\(298\\text{ K}\\). The resulting titration curves are shown in the graph below.  Which of the following statements correctly explains the differences in the shapes of the two curves and the number of equivalence points observed?"
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url: "https://nerd-notes.com/ubq/123861/"
date_modified: "2026-09-28T12:30:36+00:00"
---

# A student titrates separate \(25.0\text{ mL}\) samples of two different \(0.100\text{ M}\) diprotic acids, Acid 1 (\(\text{H}_2\text{A}\)) and Acid 2 (\(\text{H}_2\text{B}\)), with a standardized \(0.100\text{ M }\text{NaOH(aq)}\) solution at \(298\text{ K}\). The resulting titration curves are shown in the graph below.

Which of the following statements correctly explains the differences in the shapes of the two curves and the number of equivalence points observed?

A student titrates separate \(25.0\text{ mL}\) samples of two different \(0.100\text{ M}\) diprotic acids, Acid 1 (\(\text{H}_2\text{A}\)) and Acid 2 (\(\text{H}_2\text{B}\)), with a standardized \(0.100\text{ M }\text{NaOH(aq)}\) solution at \(298\text{ K}\). The resulting titration curves are shown in the graph below.

Which of the following statements correctly explains the differences in the shapes of the two curves and the number of equivalence points observed?

![A titration graph plotting \(\text{pH}\) on the vertical y-axis (scale \(0\) to \(14\), gridlines every \(2\) units) versus Volume of \(0.100\text{ M }\text{NaOH}\) added (\(\text{mL}\)) on the horizontal x-axis (scale \(0\) to \(60\), gridlines every \(10\text{ mL}\)). A legend in the upper left indicates: solid line = Acid 1, dashed line = Acid 2. Curve 1 (solid line) starts at \(\text{pH} = 2.5\) at \(0\text{ mL}\), shows a buffer plateau at \(\text{pH} = 3.8\) at \(12.5\text{ mL}\), a first inflection at \(25.0\text{ mL}\) (\(\text{pH} = 6.0\)), a second buffer plateau at \(\text{pH} = 8.2\) at \(37.5\text{ mL}\), a second inflection at \(50.0\text{ mL}\) (\(\text{pH} = 10.0\)), and levels off at \(\text{pH} = 12.5\). Curve 2 (dashed line) starts at \(\text{pH} = 0.7\) at \(0\text{ mL}\), rises smoothly below \(\text{pH} = 2.0\) until \(45\text{ mL}\), undergoes a single steep inflection at \(50.0\text{ mL}\) through \(\text{pH} = 7.0\), and merges with Curve 1. No other curves, points, labels, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1790598636-c9bx3S.jpg)

- **A.** Acid 1 is a weak diprotic acid that undergoes stepwise neutralization, producing a buffer plateau centered at \(12.5\text{ mL}\) where \([\text{H}_2\text{A}] \approx [\text{HA}^-]\), whereas Acid 2 is a strong diprotic acid whose complete dissociation produces only a single equivalence point at \(50.0\text{ mL}\).
- **B.** Acid 1 has a greater initial molarity of acidic protons than Acid 2 because Acid 1 exhibits two equivalence points, whereas Acid 2 exhibits only one equivalence point.
- **C.** Acid 1 has its maximum buffering capacity at \(25.0\text{ mL}\) because \([\text{HA}^-] = [\text{A}^{2-}]\), whereas Acid 2 cannot buffer at any point because it lacks conjugate acid-base pairs.
- **D.** Acid 2 has a smaller acid-ionization constant than Acid 1 because its \(\text{pH}\) changes more slowly between \(0\text{ mL}\) and \(40.0\text{ mL}\), resulting in an extended intermediate buffer plateau.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123861/*