Answer
$H_3PO_4(aq) + H_2O(l) \lt -- \gt H_2{PO_4}^-(aq) + H_3O^+(aq)$
$H_2{PO_4}^-(aq) + H_2O(l) \lt -- \gt H{PO_4}^{2-}(aq) + H_3O^+(aq)$
$HP{O_4}^{2-}(aq) + H_2O(l) \lt -- \gt {PO_4}^{3-}(aq) + H_3O^+(aq)$
Work Step by Step
1. Write the ionization equation for the original acid.
- Write an equation where $H_3PO_4$ donates a proton to a water molecule.
2. Now, for polyprotic acids, the conjugate base is capable of donating one proton too, so write an equation where it does that.
- $H_2P{O_4}^-$ can act as an acid too, so write an equation where it donates a proton to a water molecule.
- Repeat "Step 2" for the next reaction, until the conjugate base is incapable of donating one proton.
