At half-equivalence, what is pH relative to pKa?

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Prepare for the Acids, Bases, and Salts Test. Study with flashcards and multiple-choice questions, each question has hints and explanations. Get ready for your exam!

Multiple Choice

At half-equivalence, what is pH relative to pKa?

Explanation:
In buffer systems, pH is described by the Henderson–Hasselbalch equation: pH = pKa + log([A-]/[HA]). At the halfway point of an acid-base titration (half-equivalence), the amounts of the weak acid and its conjugate base are equal, so [A-] = [HA]. The ratio is 1, and log(1) = 0, which makes pH = pKa. This means the pH at half-equivalence equals the acid’s pKa, regardless of the exact pH of the added base.

In buffer systems, pH is described by the Henderson–Hasselbalch equation: pH = pKa + log([A-]/[HA]). At the halfway point of an acid-base titration (half-equivalence), the amounts of the weak acid and its conjugate base are equal, so [A-] = [HA]. The ratio is 1, and log(1) = 0, which makes pH = pKa. This means the pH at half-equivalence equals the acid’s pKa, regardless of the exact pH of the added base.

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