Is HPO4^2- an Acid or a Base? Identify Its Conjugate Acid or Base.

HPO4^2- is considered a base. This is because it can accept a proton (H⁺) to form H2PO4^–, which is its conjugate acid.

In the context of the Brønsted-Lowry acid-base theory, an acid is defined as a proton donor and a base as a proton acceptor. Since HPO4^2- can accept a proton, it fits the definition of a base. When it reacts with an acid (such as HCl), it can take up a proton to yield H2PO4^–:

HPO4^2- + H⁺ → H2PO4^–

Thus, HPO4^2- is classified as a base, and its conjugate acid is H2PO4^–.