Question

A solution of NaF is added dropwise to a solution that is 0.0144 M in Ba 2 . When the concentration of F - exceeds __________ M, BaF 2 will precipitate. Neglect volume changes. For BaF 2,

Answer 1

When [F⁻] exceeds 0.0109M concentration, BaF₂ will precipitate

Step-by-step explanation:

Ksp of BaF₂ is:

BaF₂(s) ⇄ Ba²⁺(aq) + 2F⁻(aq)

Ksp = 1.7x10⁻⁶ = [Ba²⁺] [F⁻]²

The solution will produce BaF₂(s) -precipitate- just when [Ba²⁺] [F⁻]² > 1.7x10⁻⁶.

As the concentration of [Ba²⁺] is 0.0144M, the product [Ba²⁺] [F⁻]² will be equal to ksp just when:

1.7x10⁻⁶ = [Ba²⁺] [F⁻]²

1.7x10⁻⁶ = [0.0144M] [F⁻]²

1.18x10⁻⁴ = [F⁻]²

0.0109M = [F⁻]

That means, when [F⁻] exceeds 0.0109M concentration, BaF₂ will precipitate