6A.3 part c

[Kaethe Zappacosta 2L]

Write the chemical equations for the proton transfer equilibria of the following acids in aqueous solution and identify the conjugate acid–base pairs in each case: H2PO4-

The answer is that H2PO4- is an acid and it becomes HPO4^2-, but why isn't it a base to become H3PO4?

[505766240]

Since H2PO4- is the acid, it will be the one to donate an H+ to H2O, making it H3O+. If H2PO4- is an acid, it's not going to accept another H+ as it's a proton donor.

[Andrew Nguyen 1E]

Hi,
H2PO4 - is an amphoteric compound since it can either accept a proton to become H3PO4 (and thus act as a base) or it can lose a proton to become HPO4 2- (and thus act as an acid). The textbook just only shows the reaction in which H2PO4 - acts as an acid.