The correct formula for the hydrogen phosphate anion is HPO4^2-.
The Correct Answer and Explanation is:
Correct Answer: The correct formula for the hydrogen phosphate anion is HPO₄²⁻.
Explanation:
Hydrogen phosphate is a polyatomic ion that belongs to the phosphate family. This ion forms when one hydrogen ion (H⁺) combines with the phosphate ion (PO₄³⁻). Phosphate (PO₄³⁻) is a tetrahedral anion consisting of one phosphorus atom centrally bonded to four oxygen atoms. By introducing one hydrogen ion (H⁺) to the phosphate structure, the resulting species becomes hydrogen phosphate (HPO₄²⁻), carrying a net charge of negative two.
In this ion, the hydrogen attaches to one of the oxygen atoms, typically forming a P–O–H bond. The other oxygen atoms carry negative charges to balance the overall -2 charge. This ion is part of a series of conjugate bases formed by successive deprotonation of phosphoric acid (H₃PO₄). The progression occurs in three steps:
- H₃PO₄ (phosphoric acid) loses one hydrogen ion to form H₂PO₄⁻ (dihydrogen phosphate).
- H₂PO₄⁻ loses another hydrogen ion to form HPO₄²⁻ (hydrogen phosphate).
- HPO₄²⁻ can lose the last hydrogen ion to become PO₄³⁻ (phosphate).
This series illustrates how hydrogen phosphate occupies the intermediate stage between dihydrogen phosphate and phosphate. In aqueous solution, hydrogen phosphate acts as a weak base and can accept a proton to form dihydrogen phosphate again or lose a proton to become phosphate.
Hydrogen phosphate is important in biological systems, especially in buffering systems that maintain pH in blood and cells. Its formula, HPO₄²⁻, accurately reflects the presence of one hydrogen atom, one phosphorus atom, and four oxygen atoms, with an overall charge of -2 resulting from the loss of two protons from phosphoric acid. This specific formula must be used to distinguish it from related ions like dihydrogen phosphate (H₂PO₄⁻) and phosphate (PO₄³⁻).
