Which of the following conjugate acid–base pairs should you choose to prepare a buffer solution that has pH = 4.50? Explain. (a) HSO4- and SO42- (b) HOCl and OCl- (c) C6H5CO2H and C6H5CO2-.

Buffer solutions are mixtures that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. The effectiveness of a buffer is determined by the pKa of the weak acid relative to the desired pH, as well as the concentrations of the acid and base components.

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the weak acid and the ratio of the concentrations of the conjugate base to the weak acid. It is expressed as pH = pKa + log([A-]/[HA]). This equation is crucial for determining the appropriate conjugate acid-base pair to achieve a specific pH in a buffer solution.

Conjugate acid-base pairs consist of an acid and its corresponding base, which differ by a proton (H+). For example, in the pair HSO4- (acid) and SO42- (base), HSO4- can donate a proton to form SO42-. The choice of conjugate pairs is essential for buffer preparation, as the pKa of the acid should be close to the desired pH for optimal buffering capacity.