Question

Construct a scenario where Barium fluoride is precipitating.

Barium fluoride (BaF2) Ksp=1.7x10^-6

Answer 1

Assuming we have a liter of solution, to which we add M moles of BaF₂:

[BaF₂] = moles / Volume = M / 1 = M

[BaF₂] = [Ba²⁺] = M

[F^-] = 2 * [BaF₂] = 2M

Now using the expression for K_sp= [Ba²⁺] * [F^-] ²

1.7 * 10^-6 = M * (2M)²

1.7 * 10^-6 = 4M³

Solving, M = 7.52 * 10^-3 moles

Mass of BaF₂ added = moles * molar mass = 7.52 * 10^-3 * 175.3 = 1.32 g

Therefore we add 1.32 g of this salt to a liter of water to make it just precipitate