Calculate the molar solubility of magnesium fluoride (K_sp = 6.9 *10^-⁹)in a solution that also 0.010 M NaF.

Question

Quizplus · Accepted Answer

First, write the balanced chemical equation for the dissolution of magnesium fluoride:

MgF2 (s) ⇌ Mg2+ (aq) + 2F- (aq)

The equilibrium constant expression for this reaction is:

Ksp = [Mg2+][F-]2

The molar solubility of MgF2 is given by the expression:

s = [Mg2+]

Since NaF is a soluble salt, it will dissociate completely in water to give Na+ and F- ions:

NaF (aq) ⇌ Na+ (aq) + F- (aq)

The presence of F- ions in solution will cause some of the magnesium fluoride to dissolve according to Le Chatelier's principle. However, we must first calculate the concentration of F- ions in solution:

[MgF2] = s

[NaF] = 0.010 M

[F-] = [NaF] = 0.010 M

Now, we can write out the equilibrium constant expression with the concentrations plugged in:

Ksp = [Mg2+][F-]2 = s(0.010)2

We know from the problem statement that the value of Ksp is 6.9 x 10-10. Solving for s:

s = Ksp/[F-]2 = (6.9 x 10-10)/(0.010)2 = 6.9 x 10-6 M

Therefore, the molar solubility of magnesium fluoride in 0.010 M NaF is 6.9 x 10-6 M, which is equivalent to 6.9 x 10-3 mM or 6.9 μM. The best choice is A.

Calculate the Molar Solubility of Magnesium Fluoride (Ksp = 6

Calculate the Molar Solubility of Magnesium Fluoride (K_sp = 6