Here are the essential concepts you must grasp in order to answer the question correctly.
Solubility Product Constant (Ksp)
The solubility product constant (Ksp) is an equilibrium constant that applies to the solubility of sparingly soluble ionic compounds. It represents the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced equation. For example, for the dissolution of FeS, Ksp = [Fe2+][S2-]. A higher Ksp indicates greater solubility, which is crucial for determining whether a precipitate will form when H2S is bubbled through the solution.
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Solubility Product Constant
Precipitation Reaction
A precipitation reaction occurs when two soluble salts react to form an insoluble compound, or precipitate. In this scenario, H2S can react with Fe2+ and Sn2+ ions to form FeS and SnS, respectively. The formation of a precipitate depends on the concentration of the ions and the Ksp values of the resulting compounds. If the product of the ion concentrations exceeds the Ksp, a precipitate will form, allowing for the separation of the ions.
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Selective Precipitation
Selective precipitation is a technique used to separate ions in a solution based on their differing solubility products. By controlling the concentration of a precipitating agent, such as H2S, one can selectively precipitate one ion while leaving others in solution. In this case, the Ksp values for FeS and SnS indicate that FeS is more soluble than SnS, suggesting that under certain conditions, Fe2+ can remain in solution while Sn2+ precipitates, allowing for their separation.
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