You need to use KH₂PO₄ and K₂HPO₄ to prepare a buffer with a pH of 7.45. Which of the following ratios of [base]/[acid] is required? For phosphoric acid, (H₃PO₄), K_a2 = 6.2 *10¯⁸ A) [base]/[acid] = 1.75 B) [base]/[acid] = 1.27 C) [base]/[acid] = 1.24 D) [base]/[acid] = 0.79 E) [base]/[acid] = 0.57

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Quizplus · Accepted Answer

The Henderson-Hasselbalch equation is used to calculate the ratio: pH = pKa + log([base]/[acid]). For the second dissociation of phosphoric acid, pKa2 = -log(6.2 * 10^-8) ≈ 7.21. Solving 7.45 = 7.21 + log([base]/[acid]) gives [base]/[acid] ≈ 1.75.

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