[Glorzifen]

There are a few questions in my textbook of this variety:

What reagent solution might you use to separate the cations in the following mixtures, that is, with one ion appearing in solution and the other in a precipitate?

(a) BaCl₂(s) and MgCl₂(s)
(b) MgCO₃(s) and Na₂CO₃(s)
(c)AgNO₃(s) and Cu(NO₃)₂(s)

Any insight as to how to go about doing these would be appreciated. I don't get why there are 2 compounds given...am I trying to find a reagent that will separate Cl- in both cases? I can figure some sort of answer out from the solubility chart but I was wondering if there's something I'm missing?

[Borek]

You are asked to separate cations. If you can add something that will selectively precipitate only one cation, leaving other in the solution - you are done.

[marquis]

A starting point.

In problem a, how would sulfate anion react with barium and magnesium?

[Glorzifen]

(a) BaCl₂(s) and MgCl₂(s)

It looks like the sulfate anion would precipitate barium, but would still form an aqueous solution with magnesium. Would KCO^2-₃ be suitable to precipitate both, since its carbonate anion would form a solid with the cation of both BaCl and MgCl, while its group 1 cation would form aqueous KCl?

(b) MgCO₃(s) and Na₂CO₃(s)

For this, I used potassium sulfide (K₂S), which would form MgS(s) and Na₂S(s)...and KCO3(aq) as the other product. Am I right in thinking that since KCO₃ contains a group 1 cation...its soluble? (just making sure I'm using the guidelines correctly).

(c)AgNO₃(s) and Cu(NO₃)₂(s)

Not sure about this one, since the anion on the products side needs to be aqueous, but they'll all have nitrate in them. Are there any exceptions that make a compound with nitrate insoluble? Or am I missing something?

Thanks for the help...making more sense with every question I do.

[UG]

I think you misunderstood Borek's comment, you only want to precipitate out one cation (a positive ion), so for the first one the sulfate ion would precipitate out barium but not magnesium because magnesium sulfate is soluble.
For the second, I'll just remind you that ALL sodium salts are soluble so adding something like sodium hydroxide will cause a precipitate of magnesium hydroxide.
For the third one, what is an insoluble silver salt?