[jl]

Cu(NO₃)₂(aq) + H₂S(aq) ----> CuS(s) + 2HNO₃(aq)

According to the solution I was given, the answer should be:
Cu²+(aq) + H₂S(aq) ----> CuS(s) + 2H⁺(aq)

I do not understand why the hydrogen atom remains in the net ionic equation.  Hydrogen sulfide and nitric acid are soluble, so they break down in the aqueous solution.  Can someone explain this to me?

[Borek]

You start with H₂S, you end with H⁺. Some H⁺ was already present in the solution and is ignored.

Try to balance net ionic equation without H⁺ - you can't as there is no hydrogen between products.

[jl]

I am still not clear.  I think what is stumping me is that I am expecting them to dissociate, and therefore cancel on each side when looking at the total ionic equation.

I am expecting the total ionic equation to look like this:

Cu²⁺(aq) + (NO₃)₂(aq) + H₂⁺(aq) + S^2-(aq)  ---->  CuS(s) + 2H⁺(aq) + 2NO₃^-(aq)

That would allow the 2NO₃^-(aq) and the 2H⁺(aq) to cancel out on both sides, thus leaving Cu²⁺(aq) + S^2-(aq) ----> Cus(s)

[Borek]

2H⁺ instead of H₂⁺, as well as 2NO₃^- instead of (NO₃)₂ but these are (hopefully) minor technical details.

You are close to be right, but - H₂S is a very weak acid, almost not dissociated, especially in the acidic solutions. However, CuS is so weakly soluble that it 'steals' S^2- from H₂S, leaving H⁺ in solution.