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 pH of a buffer solution: pH = pKa + log([base]/[acid]). Given that the pKa for the second dissociation of phosphoric acid (H3PO4) is 7.2 (from the provided K₂ = 6.2 × 10^-8, which corresponds to the second dissociation constant), and the desired pH is 7.45, we can rearrange the equation to solve for the ratio [base]/[acid]: 7.45 = 7.2 + log([base]/[acid]), which gives [base]/[acid] = 10^(7.45-7.2) = 10^0.25 ≈ 1.78. The closest given option to this calculated value is 1.75.

You Need to Use KH2PO4 and K2HPO4 to Prepare a Buffer

You Need to Use KH₂PO₄ and K₂HPO₄ to Prepare a Buffer