Question

Calculate the mass of solid AgNo3 that can be added to 2.0 L of 0.10M K2CrO4 solution in order to just start precipitation?

Here is what I have done so far:

2AgNO3(aq) + K2CrO4(aq) ==> Ag2CrO4(s) + 2KNO3(aq)

Ag2CrO4(s) ===> 2Ag^+ CrO4^^2-

Ksp = [Ag^+]^2[CrO4^2-]

Ksp = (2x)^2(0.1)

Please help me in what do next and show me how to get to answer.

Answer 1

Ksp = (2x)^2(0.1)
You can look up the Ksp for Ag2CrO4. It's approximately 9E-12 but you should use the value in your book's table of Ksp values.
9E-12 = 4x^2(0.1)
9E-12/0.1 = 4x^2
9E-11 = 4x^2
9E-12/4 = 2.25E-11 = x^2
x = sqrt 2.25E-11 = 4.47E-6 M
In 2L that is 4.47E-6 x 2 = ?
Then grams AgNO3 = mols rom above x molar mass AgNO3.