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Old May 5th 2017, 11:22 PM   #1
hahapigha
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Chemical equilibrium

What is the minimum concentration of CN- that will prevent the precipitation of AgX(s) from a solution that is
0.149 M in X-(aq) and 0.0184 M in Ag+(aq)? (Ksp for AgX(s) = 5.2 10^-17; Kf for Ag(CN)2- = 5.6 10^18)

I have no idea how to calculate this question

My attempt:
AgX(s) --> Ag+ + X-
Ag+ + 2CN- --> Ag(CN)2-
in order to prevent precipitation of AgX, the concentration of Ag+ is 5.2 10^-17/0.149 =3.4910^-16. Then √ 1/(5.6 10^183.4910^-16)= 0.02262M

BUT the answer is 3.1 10-3 M. How to get it???
THanks!
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