Which of the following represent conjugate acid-base pairs? For those pairs that are not conjugates, write the correct conjugate acid or base for each species in the pair. a. \(\mathrm{H}_{2} \mathrm{O}, \mathrm{OH}^{-}\) b. \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{4}^{2-}\) c. \(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) d. $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}, \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}$

To find the conjugate acid of a base, add \(\mathrm{H}^{+}\) to the species, and to find the conjugate base of an acid, remove \(\mathrm{H}^{+}\) from the species. a. \(\mathrm{H}_{2} \mathrm{O}, \mathrm{OH}^{-}\) Here, \(\mathrm{OH}^{-}\) is the conjugate base of water \(\mathrm{(H}_{2}\mathrm{O)}\), as it differs by the presence or absence of one hydrogen ion. b. \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{4}^{2-}\) Here, \(\mathrm{SO}_{4}^{2-}\) is not the conjugate base of \(\mathrm{H}_{2}\mathrm{SO}_{4}\). The correct conjugate base for \(\mathrm{H}_{2}\mathrm{SO}_{4}\) would be \(\mathrm{HSO}_{4}^{-}\) as it differs by the presence or absence of one hydrogen ion. c. \(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) In this pair, \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) is the conjugate base for \(\mathrm{H}_{3} \mathrm{PO}_{4}\), as they differ by the presence or absence of one hydrogen ion. d. $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}, \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}$ Similarly, \(\mathrm{C}_{2}\mathrm{H}_{3} \mathrm{O}_{2}^{-}\) is the conjugate base for \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\), as they differ by the presence or absence of one hydrogen ion. As a conclusion, the given pairs in a, c, and d are conjugate acid-base pairs, while the given pair in b is not a conjugate acid-base pair.