Question

A solution has a Pb2+ concentration of 1.9 x 10-3 M, and an F-1 concentration of 3.8 x 10-3 M. The value of Ksp for PbF2 at room temperature is 4 x 10-8. Will this solution form a precipitate? The solubility equilibrium equation is as follows.

Yes or No

Answer 1

Answer is: no, this solution will not form a precipitate.

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Answer 2

Answer is: no, this solution will not form a precipitate.
Chemical reaction: PbF₂(aq) → Pb²⁺(aq) + 2F⁻(aq).
Ksp = 4.00·10⁻⁸.
[Pb²⁺] = 1.9·10⁻³ M.
[F⁻] = 3.8·10⁻³ M.
Q = [Pb²⁺] · [F⁻]².
Q = 1.9·10⁻³ M · (3.8·10⁻³ M)².
Q = 2.7·10⁻⁸.
Q is less than Ksp.
Q is the solubility product when the system is not at equilibrium.