Problem: A solution contains one or more of the following ions: Hg2 2 + , Ba2 + , and Fe2 + . When potassium chloride is added to the solution, a precipitate forms. The precipitate is filtered off and potassium sulfate is added to the remaining solution, producing no precipitate. When potassium carbonate is added to the remaining solution, a precipitate forms.Which ions were present in the original solution?

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Addition of potassium chloride (KCl):

Halides (Cl, Br, and I) are soluble except when paired with Ag+, Pb2+, Cu+, Hg22+

2 KCl + Hg22+Hg2Cl2 + 2 K+

Hg2Cl2 → insoluble

Hg22+ → present in the solution 

2 KCl + Ba2 + BaCl2 + 2 K+

BaCl2 → soluble → for next step

2 KCl + Fe2+FeCl2 + 2 K+

FeCl2 → soluble → for next step


Addition of potassium sulfate (K2SO4):

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Problem Details

A solution contains one or more of the following ions: Hg2 2 + , Ba2 + , and Fe2 + . When potassium chloride is added to the solution, a precipitate forms. The precipitate is filtered off and potassium sulfate is added to the remaining solution, producing no precipitate. When potassium carbonate is added to the remaining solution, a precipitate forms.

Which ions were present in the original solution?

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