The dihydrogenphosphate ion, H2PO4-, has both a conjugate acid and a conjugate base. These are,respectively
The Correct Answer and Explanation is:
The dihydrogenphosphate ion (H₂PO₄⁻) has both a conjugate acid and a conjugate base.
- The conjugate acid of H₂PO₄⁻ is H₃PO₄ (phosphoric acid).
- The conjugate base of H₂PO₄⁻ is HPO₄²⁻ (hydrogenphosphate ion).
Explanation:
To understand why, let’s first review what conjugate acids and bases are. In acid-base chemistry, a conjugate acid is formed when a base accepts a proton (H⁺), and a conjugate base is formed when an acid donates a proton (H⁺).
- Conjugate Acid (H₃PO₄):
- The dihydrogenphosphate ion (H₂PO₄⁻) can act as a base by accepting a proton (H⁺).
- When it accepts a proton, it becomes H₃PO₄, which is phosphoric acid. Therefore, H₃PO₄ is the conjugate acid of H₂PO₄⁻. The reaction can be written as: [
\text{H₂PO₄⁻} + \text{H⁺} \rightarrow \text{H₃PO₄}
]
- Conjugate Base (HPO₄²⁻):
- The dihydrogenphosphate ion (H₂PO₄⁻) can also act as an acid by donating a proton (H⁺).
- When it donates a proton, it becomes HPO₄²⁻, which is the hydrogenphosphate ion. Therefore, HPO₄²⁻ is the conjugate base of H₂PO₄⁻. The reaction can be written as: [
\text{H₂PO₄⁻} \rightarrow \text{HPO₄²⁻} + \text{H⁺}
]
Conclusion:
- The conjugate acid of H₂PO₄⁻ is H₃PO₄.
- The conjugate base of H₂PO₄⁻ is HPO₄²⁻.
This behavior is consistent with the principles of acid-base theory, where the proton transfer results in the formation of conjugate pairs.