How many acidic hydrogens does phosphoric acid contain?

How many acidic hydrogens does phosphoric acid contain?

• A. 1
• B. 2
• C. 4
• D. 3

Answer: (D)

Phosphoric acid is triprotic, meaning it can donate three protons. Its structure has three hydroxyl groups, each with one O–H bond that can release a proton. As a result, there are three acidic hydrogens in H3PO4. The acid dissociates stepwise: H3PO4 → H2PO4− → HPO4^2− → PO4^3−, reflecting these three removable protons. There aren’t four acidic hydrogens because there are only three hydrogens bonded to oxygen in this molecule, and none are bound directly to phosphorus. Hence, the count is three.

Phosphoric acid is triprotic, meaning it can donate three protons. Its structure has three hydroxyl groups, each with one O–H bond that can release a proton. As a result, there are three acidic hydrogens in H3PO4. The acid dissociates stepwise: H3PO4 → H2PO4− → HPO4^2− → PO4^3−, reflecting these three removable protons. There aren’t four acidic hydrogens because there are only three hydrogens bonded to oxygen in this molecule, and none are bound directly to phosphorus. Hence, the count is three.