Question

What are all of the ions that may be formed when `H_3PO_4` ionizes in water?

Answer 1

`"H"^(+)` or `"H"_3"O"^(+)`

`"H"_2"PO"_4^(-)`

`"HPO"_4^(2-)`

`"PO"_4^(3-)`

Explanation:

In first reaction one way arrow is used.
Because phosphoric acid is strong acid, it dissolves totally. Thus all amount of reactants consumed to produce all amount of products. So that, reaction always goes products side. No back way reaction. Therefore, only one way arrow, which goes to products side, is used.

Because `"H"_2"PO"_4^(-)` and `"HPO"_4^(2-)` are not strong acids, in second and third reactions, some amount of products back to form some amount of reactants, Because of that, double arrow used. One of them goes products while one of them is going to reactants.