Question

If a dilute AgNO3 solution is slowly added to the solution, what is the first compound to precipitate: Ag2CrO4 ( Ksp = 1.2×10?12), Ag2CO3 ( Ksp = 8.1×10?12), or AgCl ( Ksp = 1.8×10?10)?

Problem 17.75 A solution contains three anions with the following concentrations: 0.20 M Cro 0.10 M CO and 0.010 M Cl Part A If a dilute AgNO3 solution is slowly added to the solution, what is the first compound to precipitate: Aga Cro4 Ksp 1.2 x 10 12), Ag CO3 K. 8.1 x 10 12 or AgCl K 1.8 x 10 10 8p sp O Ag Cro4 O Ag,CO O AgCl Submit My Answers Give Up Continue Provide Feedback

Answer 1

You have to apply the definition of Ksp (constant equilibrium solubility):

for the first one CrO₄^-2

Ag₂CrO₄ === 2 Ag⁺ + CrO₄^-2

........................2x.....................x

we already know the concentration of [CrO4] = 0.2

ksp = 1.2 x 10^-12 = 4x² * 0.2

4x² = 1.2 x 10^-12 / 0.2

x = 6.12 x 10^-7 M

for the second ion

Ag₂CO₃ ==== 2 Ag + CO₃

.........................2x..............x

ksp = 8.1 x 10^-12

ksp = (2x)² * x

concentration of CO3 is 0.1M

8.1 x 10^-12 = 4x² * 0.1

x = 4.5 x 10^-6

fo the chloride

AgCl ==== Ag + Cl

...................x.........x

ksp = 1.8 x 10^-10 = x (0.01)

the concentration of cl is 0.01

x = 1.8 x 10^-8 M

according to the calculations we need a small amount of Cl (compared to the other anions) to produce a precipitate so the first compound to precipitate is AgCl

*hope it helps =)