Henderson-Hasselbalch Equation

AP Chemistry· difficulty 3/5

Plot of fraction protonated (% HA) vs pH for a weak acid HA.

pH % HA pKa 50%

At what pH is HA exactly 50% protonated?

  • A

    pH = pKa

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  • B

    pH = 14 - pKa

  • C

    pH = 7

  • D

    pH = pKa - 1

Explanation

From Henderson-Hasselbalch, when [HA] = [A-] (50% each), log(1) = 0, so pH = pKa.

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