How many grams of MgF2 will dissolve in 150 ml of 0.100 M NaF SOLUTION ? Ksp for MgF2 IS 6.4 X 10-9

Question

Anonymous · Accepted Answer

i need help PLEASE

DrBob222 · Answer

MgF2 is slightly soluble and has a Ksp so---
......................MgF2 ==> Mg^2+ + 2F^-
I......................solid.............0...........0
C.....................solid..............x..........x
E......................solid..............x...........x

NaF is very soluble and dissociates completely so---
.........................NaF==> Na^+ + F^-
I.........................0.1M.......0..........0
C......................-0.1M........0.1M....0.1M
E.........................0............0.1M.....0.1M

Therefore, in solution you have xM of Mg^2+ and 2x M of F^- from the MgF2. In addition you have 0.1 M F^- from the NaF. Ksp looks like this.
Ksp = (Mg^2+)(F^-)^2
6.4E-9 = (x)(2x+0.1)
Solve for x = molar solubility (moles/L) of MgF2
Convert to grams/L. mols x molar mass = grams MgF2.
Then convert g/L to g/150 mL.
Post your work if you run into trouble.