Question

A solution contains 0.01 M each of NaCl and Na₂CrO₄ . Solid AgNO₃ is gradually added to it. Which of the following facts is true ?

Given : K_sp (AgCl) = 1.7 x 10^-10 M² and Ksp (Ag₂CrO₄ ) = 1.9 x 10^-12 M³ 

(A) Cl^- ions are precipitated together

(B) CrO₄^2-  ions are precipitated first

(C) Both Cl^- and CrO₄^2- ions are precipitated together

(D) The second ions starts precipitating when half of the first ion is precipitated.

Answer 1

Correct option (A) Cl^- ions are precipitated together

Explanation : 

The solution contains 0.1 M each of Cl^- and CrO₄^2- 

The concentration of Ag^- required to ppt.

& the concentration of Ag⁺ required to ppt.

As the concentration of Ag^- required to precipitate Cl^- is less than that required to precipitate CrO₄^2-  , so Cl^- ions starts precipitating first.

When the second ion starts precipitating the amount of Cl^- left is

Thus % of [Cl] precipitated when CrO₄^2- starts precipitating = 100 - 0.039 = 99.961%