Question

Solid iron(II) fluoride (FeF2, Ksp= 2.36 x 10-6) is dissolved in water. If 8.1 x 10-3 mol L-1 of iron(II) ion is found to be in solution, how can we describe the solution?

Select one:
a. desaturated
b. unsaturated
c. saturated
d. supersaturated

Answer 1

The solution is b. unsaturated.

Explanation:

At equilibrium we have

`color(white)(mmmmmm)"FeF"_2 ⇌ "Fe"^"2+" + "2F"^"-"`
`"E/mol·L"^"-1": color(white)(mmmmmll)xcolor(white)(mml)2x`

`K_text(sp) = ["Fe"^"2+"]["F"^"-"]^2 = x(2x)^2 = 4x^3 = 2.3 × 10^"-6"`

`x^3 = (2.3 × 10^"-6")/4 = 5.75 ×10^"-7"`

`x = 8.32 × 10^"-3"`

A saturated solution contains `8.32 × 10^"-3" color(white)(l)"mol/L Fe"^"2+"`.

Your solution contains only `8.1 × 10^"-3" color(white)(l)"mol/L Fe"^"2+"`.

The solution is unsaturated.