Will a reaction occur in the following case? If so, write a net ionic equation for it:
$\ce{(NH4)2SO4 (aq) + ZnCl2 (aq) -> ?}$
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?