Question

Which of the following conjugate acid-base pairs should you choose to prepare a buffer solution that has pH = 4.5? Explain.
a) HSO4- and SO4 2-
b) HOCl and OCl-
c) C6H5CO2H AND C6H5CO2-

Answer 1

Generally the pH of a buffer is equals to pKa±1, hence if we want to prepare the buffer solution with the given pH, definitely we should choose the pKa that is nearer to the pH.

For the given acids the pKa values are

For HSO3^- , the pKa value is 1.99, hence it is not suitable for preparing of the desired pH solution.

For HOCl the pKa would be 7.53, it is not suitable for the preparing the solution with given pH

For C6H5COOH, the pKa = 4.19, hence it is suitable to prepare a buffer with the pH = 4.5