What is the conjugate acid of HPO42− ?
The correct answer and explanation is :
The conjugate acid of HPO₄²⁻ is H₂PO₄⁻ (dihydrogen phosphate ion).
Explanation:
- Understanding Conjugate Acids and Bases
In acid-base chemistry, a conjugate acid is formed when a base gains a proton (H⁺). Conversely, a conjugate base is formed when an acid loses a proton. - Determining the Conjugate Acid of HPO₄²⁻
- The hydrogen phosphate ion (HPO₄²⁻) can act as a base and accept a proton (H⁺).
- When HPO₄²⁻ gains one proton, it forms H₂PO₄⁻ (dihydrogen phosphate ion).
- This reaction is:
[
HPO₄^{2-} + H^+ \rightarrow H_2PO_4^-
]
- Why is H₂PO₄⁻ the Correct Answer?
- Phosphate-containing species exist in equilibrium in aqueous solutions:
- H₃PO₄ (phosphoric acid) → H₂PO₄⁻ (dihydrogen phosphate) → HPO₄²⁻ (hydrogen phosphate) → PO₄³⁻ (phosphate ion)
- Since HPO₄²⁻ is a base in this case, adding H⁺ results in H₂PO₄⁻, which is its conjugate acid.
- Relevance in Buffer Systems
- The phosphate system (H₂PO₄⁻/HPO₄²⁻) is a crucial buffer in biological systems.
- It helps maintain pH stability in cells and blood.
Here is an image illustrating the conjugate acid-base relationship of phosphate species in solution, showing the stepwise loss or gain of protons (H⁺).