Which acid-base pairs would be best for preparing a buffer solution with a PH of 8.15?

HCN - CN⁻ (pair #4)

Explanation:

Hello,

In this case, for the selection of best pair for the preparation of the buffer solution with a pH of 8.15 we need to look for the one having the pKa closest to the required pH, considering the Henderson-Hasselbach equation:

In such a way, among the options, the pair HCN - CN⁻ (#4) has a pKa of 9.39 which is the closest in comparison to the others, taking into account the we will look for a [base]/[acid] ratio approaching 1.

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