Using solubility guidelines to predict a reaction of two ionic, water-soluble salts Will a reaction occur in the following case? If so, write a net ionic equation for it:
$\ce{(NH4)2SO4 (aq) + ZnCl2 (aq) -&gt; ?}$

The book says that all possible combinations of positive and negative ions lead to water soluble compounds, all of the ions remain in solution. No reactions occur.
Now I am a little confused. Why didn't $\ce{(NH4)2}$ join with $\ce{Cl2}$ and why didn't $\ce{SO4}$ join with $\ce{Zn}$? Or did they?
Of course $\ce{NH4+}$ can join $\ce{Cl-}$ and $\ce{Zn^2+}$ can join $\ce{SO4^2-}$, but the formed salts are completely soluble in water, and they completely dissociate in water to gives the corresponding ions. 

On the other hand, the starting salts:  $\ce{(NH4)2SO4}$ and  $\ce{ZnCl2}$ are completely soluble in water, and they completely dissociate in water to gives the corresponding ions. 

So, all of the ions remain in solution, as if no reaction occurs.