Buffer Video Lessons

Concept:

# 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