Question

Solubility of AgCl will be minimum in ---------.
A. 0.01 M $N{{a}_{2}}S{{O}_{4}}$
B. 0.01 M $CaC{{l}_{2}}$
C. Pure water
D. 0.001 M $AgN{{O}_{3}}$

Answer 1

The common-ion effect is the reason to decrease the solubility of an ionic precipitate due to the addition of a soluble compound with a common ion with the precipitate. Le Chatelier’s principle explains the chemical equilibrium in common-ion effect.

Complete step by step answer:
- The common-ion effect explains the concept in which addition of a common ion to two different solutes in a solution causes precipitation or decreases the ionization of the solute.
- Le Chatelier's principle states that a reaction will be in equilibrium till an external force is applied on it.
- If an external force like temperature or pressure or any chemical acted on a reaction in equilibrium then the reaction is going to shift to accommodate the force and re-introduces the equilibrium.
- In common ion effect, a chemical reaction can be shifted to backward direction by adding an ion that is common to both the solutes, therefore changing the concentration of the ion in solution shifts the equilibrium of the reaction.
- We have to find the solubility of the AgCl should be minimum in which of the given options.
- Coming to given options, Option A, 0.001 M $N{{a}_{2}}S{{O}_{4}}$ . Sodium sulphate does not have any common ion to AgCl. $N{{a}_{2}}S{{O}_{4}}$ contains two sodium cations and one sulphate anion. There is no common ion between sodium sulphate and silver chloride. Therefore, 0.001 M $N{{a}_{2}}S{{O}_{4}}$ does not affect the solubility of AgCl. So, option A is wrong.
- Coming to option B, 0.01 M $CaC{{l}_{2}}$ . Calcium chloride has one calcium cation and two chloride anions. Calcium chloride has a common ion to silver chloride. The common ion is chlorine. There are two chloride ions in calcium chloride. It will reduce the solubility of AgCl due to the presence of more number of chloride anions in calcium chloride. So, option B is correct.
- Coming to option C, Pure water. There is no common ion in between pure water and AgCl. So, pure water cannot reduce the solubility of AgCl.
- Coming to option D, 0.001 M $AgN{{O}_{3}}$ . Silver nitrate has a common ion to AgCl. Here the common ion is silver cation. It also decreases the solubility of the silver chloride.
- But the solubility of the silver chloride is very less in the presence of 0.01 M $CaC{{l}_{2}}$ when compared to 0.001 M $AgN{{O}_{3}}$ . Because in $CaC{{l}_{2}}$ contains two chloride ions common to AgCl, but $AgN{{O}_{3}}$ contains only one silver ion common to AgCl.

- So, the correct option is B.

Note: The common-ion effect plays an important role in the solubility of the few compounds. The two solutions 0.1 M HCl and 0.01 M HCl will reduce the solubility of AgCl. But 0.1 M HCl will decrease the solubility of AgCl more because of high concentration of chloride ions in 0.1 M HCl when compared to 0.01 M HCl.