Why only Λs^3+ gets precipitated as Λs2 S3 not Zn^2- as ZnS when II2 S is passed through an ac

step 1 Dear students, in problem 149 of chapter 7, ionic equilibrium we have asked that why only AS3 as

Why only Λs^3+ gets precipitated as Λs2 S3 not Zn^2- as ZnS...

Why only $\Lambda \mathrm{s}^{3+}$ gets precipitated as $\Lambda \mathrm{s}_{2} \mathrm{~S}_{3}$ not $\mathrm{Zn}^{2-}$ as $\mathrm{ZnS}$ when $\mathrm{II}_{2} \mathrm{~S}$ is passed through an acidic solution containing $\Lambda s^{3-}$ and $Z n^{2-}$ ? (1) Solubility product of $\mathrm{As}_{2} \mathrm{~S}_{3}$ is less than that of $\mathrm{ZnS}$ (2) Enough As s' are present in the acidic medium (3) Zinc salt does not ionize in the acidic medium (4) Solubility product changes in the presence of an acid

Why only $\Lambda \mathrm{s}^{3+}$ gets precipitated as $\Lambda \mathrm{s}_{2} \mathrm{~S}_{3}$ not $\mathrm{Zn}^{2-}$ as $\mathrm{ZnS}$ when $\mathrm{II}_{2} \mathrm{~S}$ is passed through an acidic solution containing $\Lambda s^{3-}$ and $Z n^{2-}$ ?
(1) Solubility product of $\mathrm{As}_{2} \mathrm{~S}_{3}$ is less than that of $\mathrm{ZnS}$
(2) Enough As s' are present in the acidic medium
(3) Zinc salt does not ionize in the acidic medium
(4) Solubility product changes in the presence of an acid

Key Concepts

Effect of pH on Solubility Equilibria

The solubility of many salts is strongly affected by the pH of the solution. In an acidic or basic medium, the equilibrium of a sparingly soluble salt can shift due to protonation or deprotonation reactions involving the anions or cations. This alteration in equilibrium can either increase or decrease the solubility of the salt, thereby influencing whether precipitation occurs.

Solubility Product (Ksp)

The solubility product, or Ksp, is a constant that represents the equilibrium between a sparingly soluble salt and its dissolved ions in solution. A lower Ksp indicates that even a small concentration of the ions will exceed the solubility limit, leading to precipitation. This concept is fundamental in predicting when a salt will precipitate under given conditions.

Selective Precipitation

Selective precipitation is a technique used to separate ions in a solution based on differences in their solubility products. By controlling the concentration of a precipitating agent or the solution conditions like pH, one ion can be made to exceed its solubility limit and precipitate while others remain in solution, allowing for targeted separation.

Ionization and Dissociation in Acidic Medium

The degree of ionization or dissociation of salts in solution can change depending on the medium’s acidity. In an acidic environment, some salts may not fully ionize, which affects the concentration of free ions available for precipitation. Understanding how ionization is suppressed or enhanced in different pH conditions is crucial to predicting and controlling precipitation reactions.

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