A solution contains one or more of the following ions: Hg₂²⁺ , Ba²⁺ , and Fe²⁺ . When you add potassium chloride to the solution, a precipitate forms. The precipitate is filtered off, and you add potassium sulfate to the remaining solution, producing no precipitate. When you add potassium carbonate to the remaining solution, a precipitate forms. Which ions were present in the original solution?

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Identify the ions that form precipitates with the added reagents: Hg_2^{2+}, Ba^{2+}, and Fe^{2+}.

Consider the reaction with potassium chloride (KCl). Hg_2^{2+} forms a precipitate with Cl^- as Hg_2Cl_2, while Ba^{2+} and Fe^{2+} do not form precipitates with Cl^-.

After filtering off the precipitate formed with KCl, add potassium sulfate (K_2SO_4). Ba^{2+} would form a precipitate with SO_4^{2-} as BaSO_4, but no precipitate forms, indicating Ba^{2+} is not present.

Finally, add potassium carbonate (K_2CO_3). Fe^{2+} forms a precipitate with CO_3^{2-} as FeCO_3, indicating Fe^{2+} is present.

Conclude that the original solution contained Hg_2^{2+} and Fe^{2+} ions, as these are the ions that reacted to form precipitates with the added reagents.

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주요 개념

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Solubility Rules

Solubility rules are guidelines that help predict whether a compound will dissolve in water. For example, most chlorides are soluble, except for those of silver, lead, and mercury. In this question, the formation of a precipitate upon adding potassium chloride indicates the presence of an insoluble ion, which helps narrow down the possible ions in the original solution.

Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble salt, which precipitates out of the solution. The formation of a precipitate upon adding potassium chloride and potassium carbonate suggests that one or more ions in the original solution formed insoluble compounds with these anions, indicating their presence.

Ion Identification through Sequential Reactions

Sequential reactions can be used to identify ions in a solution by observing the formation or absence of precipitates. In this scenario, the lack of a precipitate with potassium sulfate suggests that the remaining ions are soluble with sulfate, while the formation of a precipitate with potassium carbonate indicates the presence of ions that form insoluble carbonates, aiding in the identification of the original ions.