Write the formula of the conjugate base for acid H3PO4 and what is the name of the base

Write the formula of the conjugate base for acid H3O+ and what is the name of the base
..........and how can i tell how to get it? i am lost

2 answers

Write the ionization of H3PO4.

H3PO4 + H2O ==> H3O^+ + H2PO4^-

So H3PO4, phosphoric acid, lost a proton to form H2PO4^- so H2PO4^- is the conjugate base of H3PO4, the acid. H3PO4/H2PO4^- is the acid/conjugate base pair. H2O gained a proton to form H3O^+; therefore, H2O is the base and H3O^+ is its conjugate acid. The H2PO4^- ion is named dihydrogen phosphate ion.
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