What is the approximate $pKa$ value of acetic acid (${\mathrm{CH}}_3\mathrm{COOH}$)?

• A. $4.8$
• B. $1.0$
• C. $7.0$
• D. $9.2$

Answer: (A)

Verified step by step guidance

1. Understand that the pKa value is a measure of the acidity of a compound, representing the negative logarithm of the acid dissociation constant (Ka): \(\mathrm{p}K_a = -\log K_a\).
2. Recall that acetic acid (CH\_3COOH) is a weak acid commonly studied in organic chemistry, and its acidity is influenced by the resonance stabilization of its conjugate base (acetate ion).
3. Recognize that typical carboxylic acids, like acetic acid, have pKa values in the range of about 4 to 5 due to the resonance stabilization of the carboxylate ion formed after deprotonation.
4. Compare the given options (4.8, 1.0, 7.0, 9.2) with known typical pKa values of common acids: strong acids have pKa near or below 1, neutral water is about 15.7, and alcohols are around 16-18, so 4.8 fits well for acetic acid.
5. Conclude that the approximate pKa value of acetic acid is around 4.8, reflecting its moderate acidity as a carboxylic acid.