Question

phosphoric acid ($ce{h_3po_4}$) is a polyprotic acid. write balanced chemical equations for the sequence of reactions that phosphoric acid can undergo when its dissolved in water.

Explanation:

Step1: First Ionization

Phosphoric acid ($\ce{H3PO4}$) donates one $\ce{H+}$ to water. The reaction is $\ce{H3PO4(aq) + H2O(l) <=> H2PO4^{-}(aq) + H3O^{+}(aq)}$.

Step2: Second Ionization

The $\ce{H2PO4^{-}}$ formed donates another $\ce{H+}$. The reaction is $\ce{H2PO4^{-}(aq) + H2O(l) <=> HPO4^{2-}(aq) + H3O^{+}(aq)}$.

Step3: Third Ionization

The $\ce{HPO4^{2-}}$ donates the last $\ce{H+}$. The reaction is $\ce{HPO4^{2-}(aq) + H2O(l) <=> PO4^{3-}(aq) + H3O^{+}(aq)}$.

Answer:

1. $\ce{H3PO4(aq) + H2O(l) <=> H2PO4^{-}(aq) + H3O^{+}(aq)}$
2. $\ce{H2PO4^{-}(aq) + H2O(l) <=> HPO4^{2-}(aq) + H3O^{+}(aq)}$
3. $\ce{HPO4^{2-}(aq) + H2O(l) <=> PO4^{3-}(aq) + H3O^{+}(aq)}$