University of Central Florida (UCF) CHM2045C Chemistry Fundamentals I Practice Exam 1

The dihydrogen phosphate ion is represented by the formula H2PO4-. This ion contains two hydrogen atoms attached to a phosphate ion (PO4) along with a single negative charge. The presence of the two hydrogen atoms indicates that it is a dihydrogen species, which distinguishes it from related phosphate ions.

To understand why H2PO4- is the correct formulation, consider that the 'di-' prefix in dihydrogen signifies that there are two hydrogen atoms bonded to the phosphate group. This ion plays a significant role in biological systems, particularly in energy transfer and storage.

The other formulas, such as HPO4^2- and PO4^3-, represent different oxidation states of phosphate. HPO4^2-, known as hydrogen phosphate, indicates one hydrogen atom is present, while PO4^3- represents the fully deprotonated phosphate ion with no hydrogen atoms attached, thus bearing a charge of three. NH4+ represents the ammonium ion, which is unrelated to phosphate chemistry.

Recognizing the composition and charge of these various phosphate species allows for easier identification of dihydrogen phosphate as H2PO4-.