It is possible to make two completely different buffers using the dihydrogen phosphate ion, \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) (a) In one buffer, \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) serves as the weak acid. What is the conjugate weak base? (b) Write the equations that show how the buffer in part (a) works when either \(\mathrm{H}_{3} \mathrm{O}^{+}\) or \(\mathrm{OH}^{-}\) is added. (c) In the other buffer, \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) serves as the weak base. What is the conjugate weak acid? (d) Write the equations that show how the buffer in part (c) works when either \(\mathrm{H}_{3} \mathrm{O}^{+}\) or \(\mathrm{OH}^{-}\) is added.

(a) The conjugate weak base of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) is \(\mathrm{HPO}_{4}^{2-}\). (b) Equations for buffer with \(\mathrm{H}_{3} \mathrm{O}^{+}\) and \(\mathrm{OH}^{-}\) added: 1. \(\mathrm{HPO}_{4}^{2-} + \mathrm{H}_{3} \mathrm{O}^{+} \rightarrow \mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{H}_{2} \mathrm{O}\) 2. \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{OH}^{-} \rightarrow \mathrm{HPO}_{4}^{2-} + \mathrm{H}_{2} \mathrm{O}\) (c) The conjugate weak acid of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) is \(\mathrm{H}_{3} \mathrm{PO}_{4}\). (d) Equations for buffer with \(\mathrm{H}_{3} \mathrm{O}^{+}\) and \(\mathrm{OH}^{-}\) added: 1. \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{H}_{3} \mathrm{O}^{+} \rightarrow \mathrm{H}_{3} \mathrm{PO}_{4} + \mathrm{H}_{2} \mathrm{O}\) 2. \(\mathrm{H}_{3} \mathrm{PO}_{4} + \mathrm{OH}^{-} \rightarrow \mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{H}_{2} \mathrm{O}\)