On the basis of the information above, a buffer with a pH = 9 can best be made by using A pure NaH2PO4

B H3PO4 + H2PO4–

C H2PO4– + PO42–

D H2PO4– + HPO42–

E HPO42– + PO43

D H2PO4– + HPO42–

Explanation:

The acid dissociation constant for are respectively.

The reason while option D is the best answer is that, the value of pKa for both

lies on either side of the desired pH of the buffer. This implies that one is slightly over and the other is slightly under.

Using Henderson-Hasselbach equation:

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i think? ?