H3PO4 is commonly known as Phosphoric acid. As the name suggests, this compound is an acid. Generally an acid, is a proton donor, has a pH below 7, neutralizes base and turns blue litmus paper to red. This also means that in a solution (in water) H3PO4 produces Hydronium ions (H3O+ ions).
The chemical equation for the dissociation of Phosphoric acid (H3PO4) in the solution can be written as:
H3PO4(s) + H2O(l) --->H3O+(aq) + H2PO4−(aq)
H2PO4−(aq)+ H2O(l) <--->H3O+(aq) + HPO42−(aq)
HPO42−(aq)+ H2O(l) <---> H3O+(aq) + PO43−(aq)
**H3PO4 contains 3 H's that can be protonated.
The first ionization (protonation) of Phosphoric acid can only be considered as strong acid.