Problem: Given the following information:H3PO4              Ka1 = 7.5 x 10-3                      H2SO4                  Ka1 is large                          Ka2 = 6.2 x 10-8                                                 Ka2 = 1.2 x 10-2                          Ka3 = 4.8 x 10-13Which one of the following combinations would be the best choice for preparing a buffer of pH 7.0?A. H3PO4 and NaH2PO4B. Na2HPO4 and Na3PO4C. NaH2PO4 and Na2HPO4D. NaHSO4 and Na2SO4E. H2SO4 and NaHSO4

FREE Expert Solution

We’re being asked to determine which of the given solutions is a good buffer system.


Recall that a buffer can be composed of the following:

weak base and its conjugate acid
weak acid and its conjugate base
weak acid and a strong base 

▪ concentration of weak acid > concentration of strong base

weak base and a strong acid 

concentration of weak base > concentration of strong acid


The maximum buffering capacity of a solution is when the pH of the solution is equal to pKa and the buffer range of a solution is pH = pKa ± 1

 maximum buffering capacity:              pH = pKa

 buffering range:              pH = pKa ± 1

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Problem Details

Given the following information:

H3PO4              Ka1 = 7.5 x 10-3                      H2SO4                  Ka1 is large

                          Ka2 = 6.2 x 10-8                                                 Ka2 = 1.2 x 10-2

                          Ka3 = 4.8 x 10-13

Which one of the following combinations would be the best choice for preparing a buffer of pH 7.0?

A. H3PO4 and NaH2PO4

B. Na2HPO4 and Na3PO4

C. NaH2PO4 and Na2HPO4

D. NaHSO4 and Na2SO4

E. H2SO4 and NaHSO4

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