I am tasked with writing a molecular equation, an overall ionic equation, and a net ionic equation for the reaction between an aqueous solution of phosphoric acid, $\ce{H3PO4{(aq)}}$ and an aqueous solution of sodium hydroxide. The products are sodium phosphate and water.
I have already figured out the balanced molecular equation of the following:
$$\ce{H3PO4 {(aq)} + 3 NaOH {(aq)} -> Na3PO4 {(aq)} + 3 H2O {(l)}}$$
However, I am uncertain how to write the proper ionic equations. I know that the ions are separated, but how do you format this properly when writing with multiple molecules. If this is based on the disassociation of the chemicals, how do you determine which ions disassociate?
I have arrived at:
$$\ce{3H+ {(aq)} + PO4^3- {(aq)} + 3 Na+ {(aq)} + 3 OH- -> 3 Na+ {(aq)} + 3 H2O {(l)} + PO4^3- {(aq)}}$$
However, I still do not know why this is the best answer. Why does the $\ce{NaOH}$ show separated in the equation while the $\ce{PO4}$ does not? How would you know which ones separate by simply looking at the problem?