Question

If I added sodium carbonate to magnesium nitrate, would it be insoluble & a precipitate forms?
If I added sodium carbonate to calcium nitrate, would it be insoluble & precipitate forms?
Adding sodium carbonate to strontium nitrate: insoluble, precipitate forms?
adding sodium carbonate to barium nitrate--> insoluble, precipitate forms?

Answer 1

All of these look ok to me.
Just as a side note, the formation of ppts and their color and what they will dissolve in, is the basis for qualitative analysis. For example, if I added dilute HCl to an aqueous solution of an unknown and I obtained a white ppt, I would immediately thing of Hg2Cl2, AgCl, AgBr, AgI, and PbCl2.
If it dissolves in hot water it's Pb. If it dissolves in NH3 it's one of the chlorides of Ag. And if it turns black when NH3 is added to test for the Ag halides, it is Hg(+1--not +2).

Answer 2

Ok, thanks!