Write equation that showss `H_(2)PO_(4)^(-)` acting both as an acid and as a base.

Explanation

As an acid `H_(2)PO_(4)^(-) to H^(+) HPO_(4)^(-2)`
Proton donar
As a base
`H_(2)Po_(4)^(-)+H^(+) to H_(3)PO_(4)`
Proton acceptor