I can't remember any of the weights of the individual elements but here is how you solve it:
Molecular weight of copper + nitrogen + 3 oxygens = molecular weight of the compound.
M = moles / liter
.350 moles / 1 liter
Do .350 moles / liter x the molecular weight (g / mole) of the compound = the answer in g / L
When a non metal gains or share by two electrons then the valency will be 2^- or 2^+
