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Chapter 14: Problem 144

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. \(\mathrm{H}_{2} \mathrm{O}, \mathrm{OH}^{-}\) c. \(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) b. \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{4}^{2-}\) d. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}, \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\)

Short Answer

Expert verified
Pairs a (\(\mathrm{H}_2 \mathrm{O}, \mathrm{OH}^-\)), b (\(\mathrm{H}_3 \mathrm{PO}_4, \mathrm{H}_2 \mathrm{PO}_4^-\)), and d (\(\mathrm{HC}_2 \mathrm{H}_3 \mathrm{O}_2, \mathrm{C}_2\mathrm{H}_3 \mathrm{O}_2^-\)) are conjugate acid-base pairs. Pair c (\(\mathrm{H}_2 \mathrm{SO}_4, \mathrm{SO}_4^{2-}\)) is not a conjugate acid-base pair; the correct conjugate base for \(\mathrm{H}_2\mathrm{SO}_4\) is \(\mathrm{HSO}_4^-\).

Step by step solution

01

Check pair a. \(\mathrm{H}_{2} \mathrm{O}, \mathrm{OH}^{-}\)

In this case, we need to remove one proton (H\(^+\)) from the \(\mathrm{H}_{2} \mathrm{O}\). Doing this gives us: \( \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{OH}^{-} + \mathrm{H}^{+}\). Since removing the proton results in the second species of the pair, \(\mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{OH}^{-}\) are a conjugate acid-base pair.
02

Check pair b. \(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

In this case, we need to remove one proton (H\(^+\)) from the \(\mathrm{H}_{3} \mathrm{PO}_{4}\). Doing this gives us: \( \mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{H}_{2} \mathrm{PO}_{4}^{-} + \mathrm{H}^{+}\). Since removing the proton results in the second species of the pair, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) are a conjugate acid-base pair.
03

Check pair c. \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{4}^{2-}\)

In this case, to get the second species, we need to remove two protons (H\(^+\)) from the \(\mathrm{H}_{2} \mathrm{SO}_{4}\) rather than one. Let us remove one proton to verify the conjugate: \( \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{HSO}_{4}^{-} + \mathrm{H}^{+}\). Since removing one proton gives \(\mathrm{HSO}_{4}^{-}\) rather than \(\mathrm{SO}_{4}^{2-}\), \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and \(\mathrm{SO}_{4}^{2-}\) are NOT a conjugate acid-base pair. Instead, the correct conjugate base for \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is \(\mathrm{HSO}_{4}^{-}\).
04

Check pair d. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}, \mathrm{C}_{2}\mathrm{H}_{3} \mathrm{O}_{2}^{-}\)

In this case, we need to remove one proton (H\(^+\)) from the \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\). Doing this gives us: \( \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2} \rightarrow \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-} + \mathrm{H}^{+}\). Since removing the proton results in the second species of the pair, \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) and \(\mathrm{C}_{2}\mathrm{H}_{3} \mathrm{O}_{2}^{-}\) are a conjugate acid-base pair.
05

Summary

In conclusion, pairs a (\(\mathrm{H}_{2} \mathrm{O}, \mathrm{OH}^{-}\)), b (\(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)), and d (\(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}, \mathrm{C}_{2}\mathrm{H}_{3} \mathrm{O}_{2}^{-}\)) are conjugate acid-base pairs. Pair c (\(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{4}^{2-}\)) is not a conjugate acid-base pair; the correct conjugate base for \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is \(\mathrm{HSO}_{4}^{-}\).

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Most popular questions from this chapter

Use Table \(14.3\) to help order the following bases from strongest to weakest. $$ \mathrm{NO}_{3}^{-}, \quad \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{NH}_{3}, \quad \mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N} $$

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Write the reaction and the corresponding \(K_{\mathrm{b}}\) equilibrium expression for each of the following substances acting as bases in water. a. \(\mathrm{NH}_{3}\) b. \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}\)

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