QuestionApril 29, 2025

Acetic acid has a pKa of 4.8. Select the representation that shows the majority species at pH7. CH_(3)COOH_(2)^+ CH_(3)COOH CH_(3)COO^- CH_(2)COO^2-

Acetic acid has a pKa of 4.8. Select the representation that shows the majority species at pH7. CH_(3)COOH_(2)^+ CH_(3)COOH CH_(3)COO^- CH_(2)COO^2-
Acetic acid has a pKa of 4.8. Select the representation that shows the majority species at pH7.
CH_(3)COOH_(2)^+
CH_(3)COOH
CH_(3)COO^-
CH_(2)COO^2-

Solution
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Answer

CH_{3}COO^{-} Explanation 1. Determine the relationship between pH and pKa Use the Henderson-Hasselbalch equation: **pH = pKa + \log\left(\frac A^- HA \right)**. At pH = 7, which is greater than pKa = 4.8, the solution is basic relative to the acid's pKa. 2. Analyze the species at given pH Since pH > pKa, the deprotonated form (CH_{3}COO^{-}) will predominate over the protonated form (CH_{3}COOH).

Explanation

1. Determine the relationship between pH and pKa<br /> Use the Henderson-Hasselbalch equation: **$pH = pKa + \log\left(\frac{[A^-]}{[HA]}\right)$**. At $pH = 7$, which is greater than $pKa = 4.8$, the solution is basic relative to the acid's pKa.<br /><br />2. Analyze the species at given pH<br /> Since $pH > pKa$, the deprotonated form ($CH_{3}COO^{-}$) will predominate over the protonated form ($CH_{3}COOH$).
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