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Solubility Problem - Involves Addition of Another Ion

  1. Apr 26, 2009 #1
    1. The problem statement, all variables and given/known data

    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.

    3. 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!
     
  2. jcsd
  3. Apr 27, 2009 #2

    Borek

    User Avatar

    Staff: Mentor

    What happens when you add F- to the solution?
     
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