Question #83607

2 Answers
Sep 4, 2015

There are several possibilities for X. I'll nominate copper(II) chloride.


Copper(II) chloride is #CuCl_(2(aq))#. It is readily soluble. No precipitate would occur if chloride, sulfate or nitrate ions were added because these ions are all soluble with copper(II).

Copper(II) carbonate is a green, insoluble substance so a green precipitate would result if carbonate ions were added:


Sep 4, 2015

Another candidate is magnesium nitrate.


The idea here is that you're looking for a cation that will not form a precipitate when mixed with those three anions, chloride, sulfate, and nitrate, but that it will form one when mixed with a solution that contains carbonate anions.

My cation of choice is the magnesium cation, #"Mg"^(2+)#. When mixed with carbonate anions it forms magnesium carbonate, a white insoluble solid that precipitates out of solution.

#"Mg"_text((aq])^(2+) + "CO"_text(3(aq])^(2-) -> "MgCO"_text(3(s]) darr#

Magnesium chloride, #"MgCl"""_2#, magnesium sulfate, #"MgSO"_4#, and magnesium nitrate, #"Mg"("NO"_3)_2#, are all soluble compounds, so they will not precipitate out of solution when solution #X# is mixed with the chloride, sulfate, and nitrate solutions.

If you assume that solution #X# can contain one of the anions with which it does not form a precipitate when mixed, then you can say that solution #X# can be magnesium nitrate, magnesium sulfate, or magnesium chloride.