Acid-dissociation constants of two acids are listed in the table below. [VISUAL] A 20. mL sample of — Acids and Bases Chemistry Question

STEPS:

1. Identify the chemical species present at the equivalence point: At the equivalence point of a titration between a weak acid and a strong base ($\text{NaOH}$), the acid is stoichiometrically neutralized and completely converted into its conjugate base. Therefore, Solution 1 contains the acetate ion ($\text{CH}_3\text{CO}_2^-$), and Solution 2 contains the trifluoroacetate ion ($\text{CF}_3\text{CO}_2^-$).
2. Compare the strengths of the two starting acids: Look at the given acid-dissociation constants ($K_a$) in the table:
* Acetic acid ($\text{CH}_3\text{CO}_2\text{H}$): $K_a = 1.75 \times 10^{-5}$
* Trifluoroacetic acid ($\text{CF}_3\text{CO}_2\text{H}$): $K_a = 1.0 \times 10^0$
Comparing these values, trifluoroacetic acid is a much stronger acid (larger $K_a$) than acetic acid (smaller $K_a$).
3. Relate acid strength to conjugate base strength: The strength of an acid and its conjugate base are inversely related by the autoionization constant of water ($K_w = K_a \times K_b$). This fundamental concept means that the weaker the acid, the stronger its conjugate base. Since acetic acid ($\text{CH}_3\text{CO}_2\text{H}$) is the weaker acid of the two, its conjugate base ($\text{CH}_3\text{CO}_2^-$) is the stronger conjugate base.
4. Determine the effect of conjugate base strength on pH: Because the conjugate base in Solution 1 ($\text{CH}_3\text{CO}_2^-$) is a stronger base than the conjugate base in Solution 2 ($\text{CF}_3\text{CO}_2^-$), it will undergo base hydrolysis with water to a greater extent:
$$\text{CH}_3\text{CO}_2^-(aq) + \text{H}_2\text{O}(l) \rightleftharpoons \text{CH}_3\text{CO}_2\text{H}(aq) + \text{OH}^-(aq)$$
This higher extent of hydrolysis yields a greater concentration of hydroxide ions ($\text{OH}^-$) at the equivalence point, which leads to a lower $\text{pOH}$ and consequently a higher pH in Solution 1.
5. Select the correct option: This reasoning directly proves that Solution 1 has a higher pH at the equivalence point because $\text{CH}_3\text{CO}_2\text{H}$ has the stronger conjugate base, matching Option B.

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WHY_OTHERS_WRONG:

• Option A is incorrect: While it correctly identifies that Solution 1 will have a higher pH, it provides an incorrect explanation by claiming $\text{CH}_3\text{CO}_2\text{H}$ is the stronger acid. As shown by the $K_a$ values, $\text{CH}_3\text{CO}_2\text{H}$ is actually the weaker acid ($1.75 \times 10^{-5} < 1.0$).
• Option C is incorrect: This option incorrectly claims that Solution 1 has a *lower* pH at the equivalence point and that $\text{CH}_3\text{CO}_2\text{H}$ is the stronger acid. The stronger acid ($\text{CF}_3\text{CO}_2\text{H}$) produces a much weaker conjugate base that hydrolyzes minimally, which actually gives Solution 2 a lower pH (closer to neutral) than Solution 1.
• Option D is incorrect: Although this option correctly notes that $\text{CH}_3\text{CO}_2\text{H}$ has the stronger conjugate base, it incorrectly concludes that this results in a *lower* pH. A stronger conjugate base reacts more with water to generate more $\text{OH}^-$ ions, which raises the pH rather than lowering it.