Question

Why does a clear, saturated solution of PbI2 form a yellow precipitate when a small amount of KI is added to the solution?

A. KI is insoluble in PbI2.
B. PbI2 is always insoluble in water.
C. Adding KI is like adding I-, which drives the reaction toward the formation of I-.
D. Adding KI is like adding I-, which drives the reaction toward the formation of PbI2.

Answer 1

PbI2 ==> Pb^2+ + 2I^-
If you have a saturated solution of PbI2 then Qsp = Ksp = (Pb^2+)(I^-)^2

Adding KI ==> K^+ + I^-
So you are increasing the (I^-), that is adding the common ion I^- to the saturated solution so the reaction shifts to the left forming more PbI2.

OR, you can say that adding I^- increases Qsp so it is larger than Ksp so a ppt of PbI2 forms because Qsp>Ksp.

D is the answer but you need to understand why D is the answer.

Answer 2

We don’t need to understand bob. Give us the answer

Answer 3

Thank you for your explanation!

Answer 4

We need to understand, thank you for taking the time to explain Drbob.