The concept of conjugate acid-base pairs is fundamental in acid-base chemistry. When an acid donates a proton (H⁺), it forms its conjugate base, and when a base accepts a proton (H⁺), it forms its conjugate acid. Let's analyze the given reaction step by step in the context of conjugate acid-base pairs:
[tex]\[
H_2PO_4^{-} + H_2O \rightarrow H_3O^+ + HPO_4^{2-}
\][/tex]
1. Identify the species involved in the reaction:
- [tex]\(H_2PO_4^{-}\)[/tex]
- [tex]\(H_2O\)[/tex]
- [tex]\(H_3O^+\)[/tex]
- [tex]\(HPO_4^{2-}\)[/tex]
2. Determine which substances act as acids and bases:
- [tex]\(H_2PO_4^{-}\)[/tex] donates a proton (acts as an acid) and becomes [tex]\(HPO_4^{2-}\)[/tex].
- [tex]\(H_2O\)[/tex] accepts a proton (acts as a base) and becomes [tex]\(H_3O^+\)[/tex].
3. Match the acids with their corresponding conjugate bases:
- [tex]\(H_2PO_4^{-}\)[/tex] (acid) loses a proton to become [tex]\(HPO_4^{2-}\)[/tex] (conjugate base).
- [tex]\(H_2O\)[/tex] (base) gains a proton to become [tex]\(H_3O^+\)[/tex] (conjugate acid).
Using above information, we can identify the base-conjugate acid pairs:
- [tex]\(H_2O\)[/tex] and [tex]\(H_3O^+\)[/tex] form a conjugate acid-base pair.
- [tex]\(H_2PO_4^{-}\)[/tex] and [tex]\(HPO_4^{2-}\)[/tex] form another conjugate acid-base pair.
Thus, the correct answer to the given question is:
[tex]\(H_2PO_4^{-}\)[/tex] and [tex]\(HPO_4^{2-}\)[/tex].
