In the Sorensen phosphate buffer system, what is the monohydrogen phosphate to dihydrogen phosphate ratio that will give a pH of 8.2? How do I know which is (A-) and which is (HA)?

The Sorensen phosphate buffer system consists of two components, monohydrogen phosphate (HPO4??) and dihydrogen phosphate (H2PO4?), which can act as both an acid and a base. The pH of the buffer system is determined by the relative concentrations of these two components. To calculate the monohydrogen phosphate to dihydrogen phosphate ratio that will give a pH of 8.2, we can use the Henderson-Hasselbalch equation: pH = pKa + log([A^-]/[HA]) where pKa is the dissociation constant of the weak acid, and [A^-] and [HA] are the concentrations of the conjugate base and acid, respectively. For the Sorensen phosphate buffer system, the pKa is 7.20, which means that at a pH of 7.20, the concentrations of HPO4?? and H2PO4? are equal. To achieve a pH of 8.2, we can rearrange the Henderson-Hasselbalch equation to solve for the ratio [A^-]/[HA]: [A^-]/[HA] = 10^(pH - pKa) [A^-]/[HA] = 10^(8.2 - 7.20) [A^-]/[HA] = 6.31 This means that the concentration of HPO4?? should be about 6.31 times higher than the concentration of H2PO4? in the buffer solution to achieve a pH of 8.2. As for which component is the conjugate acid (HA) and which is the conjugate base (A^-), it depends on the direction of the reaction. In an acidic solution, H2PO4? will donate a proton and become HPO4??, so H2PO4? is the conjugate acid and HPO4?? is the conjugate base. In a basic solution, HPO4?? will accept a proton and become H2PO4?, so HPO4?? is the conjugate acid and H2PO4? is the conjugate base.