Which may be used to prepare a buffer having a pH of 8.8? K_a = 7 × 10^-3 for H₃PO₄; 8 × 10^-8 for H₂PO₄^-; 5 × 10^-13 for HP O₄^2- A)NaH₂PO₄ only B)NaH₂PO₄ and Na₂HPO₄ C)Na₃PO₄ and Na₂HPO₄ D)NaHPO₄ and H₃PO₄ E)H₃PO₄ and Na₃PO₄

Question

Quizplus · Accepted Answer

To prepare a buffer with a pH of 8.8, we need to select a weak acid and its corresponding conjugate base that has a pKa close to 8.8. Looking at the options given, we see that NaHS and NaH2PO4 are weak acids with pKa values of 7.2 and 7.2/12.4 (depending on which hydrogen is considered acidic), respectively. Therefore, we cannot use them to prepare a buffer with a pH of 8.8.
On the other hand, NaHCO3 is a weak acid with a pKa of 6.4, which is too far away from 8.8 to be useful. The only option left is NaH2PO4 and Na2HPO4, which are a conjugate pair with pKa values of 7.2 and 12.4, respectively. By choosing an appropriate ratio of NaH2PO4 and Na2HPO4, we can prepare a buffer with a pH close to 8.8. Therefore, the best choice is B, which includes both NaH2PO4 and Na2HPO4.

Which May Be Used to Prepare a Buffer Having a PH