Phosphoric acid is a triprotic acid (K a1 = 6.9 * 10 - 3, K a2 = 6.2 * 10 - 8, and K a3 = 4.8 * 10 - 13). To find the pH of a buffer composed of H 2 PO - 4 (aq) and HPO 2 - 4 (aq), which p K a value should be used in the Henderson-Hasselbalch equation?

Question

Chemistry

Marisol Key

2 January, 11:50

Phosphoric acid is a triprotic acid (K a1 = 6.9 * 10 - 3, K a2 = 6.2 * 10 - 8, and K a3 = 4.8 * 10 - 13). To find the pH of a buffer composed of H 2 PO - 4 (aq) and HPO 2 - 4 (aq), which p K a value should be used in the Henderson-Hasselbalch equation?

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Answers (1)

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Alison Holland · Answer 1

Ka2 values should be used in obtaining pKa2 in the Henderson-Hasselbalch equation

Explanation:

During first dissociation from H3PO4 to H2PO4-, ka1 will be used, and from H2PO4-to HPO4-, ka2 values will be used, hence a buffer solution containing H2PO4-and HPO4-will use ka2 in obtaining pKa2 in the Henderson-Hasselbalch equation.