Question

How do know what happens when `A.` `"calcium nitrate"` is added to `"sodium carbonate"`, and `B.` `"sodium chloride"` is added to `"copper nitrate"`?

Answer 1

How else do you predict but by reference to PRIOR experiment?

Explanation:

When a salt, say common salt, dissolves in water, a chemical reaction occurs:

`NaCl(s) rarr Na^(+) + Cl^(-)`

The ionic species are the aquated ions; which we could represent as `[Na(OH_2)_6]^(+)` or `[Cl(H_2O)_(4-6)]^(-)`. Now we conceive these species to float around as discrete particles in aqueous solution. Add some silver salt to solution, say as `AgNO_3`, likewise we get `Ag^(+)` or `NO_3^(-)` (again as the aquated ions), the silver ions react irreversibly with the chloride ions to form `AgCl(s)` as a curdy white precipitate.

`Ag^(+) + Cl^(-) rarr AgCl(s)darr`

So for your reactions (`A.`):

`Ca(NO_3)_2(aq) + Na_2CO_3(aq) rarr CaCO_3(s)darr + 2NaNO_3(aq)`

Or, as the net ionic equation:

`Ca^(2+) + CO_3^(2-) rarr CaCO_3(s)darr`

Calcium carbonate is (reasonably) insoluble in water, and precipitates from solution. And all of this is the province of experiment.

For `B.`, metathesis (which is only `"conceived"` to occur) gives `"potential"` salts that are both soluble. I write `"potential"` in that we don't know a priori that the salts are soluble; this is the province of experiment.

`NaCl(aq) + Cu(NO_3)_2(aq) rarr Na^(+) + Cl^(-) +Cu^(2+) + 2NO_3^(-)`

Ionization certainly occurs; i.e. there are discrete sodium, chloride, cupric ions etc. in solution, but because an insoluble salt is NOT formed, there is no precipitation of any salt. The partner exchange is conceptual and not actual.

Does this help? If you want to clarify a point, I (and others) will certainly be available for comments/corrections/clarification.