A certain carboxylic acid has a K_a of 5.1 × 10^-7. What is the ratio of the ratio of the deprotonated to the protonated form, respectively, at physiological pH of about 7.4? Assume the following general reaction. HA(aq) + H₂O(l) → H₃O⁺(aq) + A^-(aq)

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Quizplus · Accepted Answer

The ratio of deprotonated to protonated form is given by the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). Here, pKa = -log(5.1 × 10^-7) ≈ 6.3. At pH 7.4, 7.4 = 6.3 + log([A-]/[HA]), so log([A-]/[HA]) = 1.1, which means [A-]/[HA] ≈ 13:1.

A Certain Carboxylic Acid Has a Ka of 5

A Certain Carboxylic Acid Has a K_a of 5