What is in the water layer above the precipitate...?

Question

Cd(NO3)2 (aq) + Na2S (aq) → CdS (s) + NaNO3 (aq)

Assuming that there are no leftover reactants, what is in the water layer above the precipitate? Remember that ionic compounds are electrolytes and dissociate when dissolved in water. Polyatomic ions remain intact.

Answer 1

All the ions that don't precipitate.

That would be sodium ions, Na+, and nitrate ions (NO3-).

But in the real world, even if the reactants where completely stoichiometric there would be traces of the two ions which reacted, cadmium ions, Cd2+, and sulfide ions, S2-.

That's because even the most insoluble of compounds dissociates to a slight extent.  That dissociation is measured by the value of Ksp.  The Ksp values of sulfides tend to be very small, so that indicates that very, very little of the CdS(s) (Ksp = 1×10^-27) would dissociate.

Answer 2

Na+1 and (NO3)-1 ions are in the water above the CdS

Answer 3

The water layer contains ions of the soluble product, NaNO3. There are Na+(aq) and NO3-(aq) ions in the water above the precipitate.