In which solution is AgCl most soluble? A. in a solution that is 0.20 M in CaCl2B. in a solution that is 0.20 M in AgNO3C. in a solution that is 0.20 M in KNO3

Answer: option C. in a solution that is 0.20 M in KNO₃.

Explanation:

This question deals with the common ion effect.

Any presence in a solution of a common ion with the solute will decrease its solubility and here you can find why.

AgCl (silver chloride) is highly insoluble in water.

Its solubility equation is given by this equilibrium equation:

AgCl (s) ⇄ Ag⁺ (aq) + Cl⁻ (aq)

The constant for this equilibrim is called constant of solubility product and is indicated as Ksp:

Ksp = [Ag⁺][Cl⁻]

Then, any increase of the product ions (on the right side of the equilibrium equation), will result, according to Le Chatelier's principle in a shift of the equilibrium toward the left side, this is in an increase of the AgCl (s), meaning that less AgCl will be soluble.

Let's see in which of the given solutions is AgCl most soluble

A. Solution 0.20 M in CaCl₂

CaCl₂ is a ionic compound which also ionizes in solution, given Ca²⁺ and Cl⁻ ions. So, you can see that it will increase the concentration of Cl⁻, which means that the equlibrium AgCl (s) ⇄ Ag⁺ (aq) + Cl⁻ (aq), will be shifting to the left, decreasing the solubility of silver chloride.

B. Solution 0.20 M in AgNO₃

AgNO₃ is also a ionic salt which dissociates in water giving Ag⁺ and NO₃ ions. So, it will increase Ag⁺ ions, also shifting the equilibrium AgCl (s) ⇄ Ag⁺ (aq) + Cl⁻ (aq) to the left, decreasing the solubility of silver chloride.

C. Solution 0.20 M in KNO₃

Since KNO₃ has no common ions with AgCl, it will not affect the equilibrium equation in the same manner and you can expect that AgCl is most soluble in KNO₃.