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Solubility Problem - Involves Addition of Another Ion

  • Thread starter vertciel
  • Start date
  • #1
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Homework Statement



How many moles of solid sodium fluoride should be added to 1.0 L of a saturated solution of barium fluoride, BaF2, at 25OC to raise the fluoride concentration to 3.0 x 10-2 mol/L? The solubility product constant for BaF2 is Ksp = 1.7 x 10-6 at 25OC.

The Attempt at a Solution



BaF2 ---> Ba2+ + 2F-

Initial Concentrations: 0, 0
Change: + x, + 2x

Therefore:

1.7 x 10-6 = x(2x)2

x = 0.00752 M.

So: [F-] = 0.01504 mol/2 L.

I thought to have the desired fluoride concentration, only 1.5 x 10-2 mol would need to be added. However, the correct answer is
2.6 x 10-2 mol
.

Thank you for your help!
 

Answers and Replies

  • #2
Borek
Mentor
28,326
2,709
What happens when you add F- to the solution?
 

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