- #1

vertciel

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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, BaF

_{2}, at 25

^{O}C to raise the fluoride concentration to 3.0 x 10

^{-2}mol/L? The solubility product constant for BaF

_{2}is K

_{sp}= 1.7 x 10

^{-6}at 25

^{O}C.

## The Attempt at a Solution

BaF

_{2}---> Ba

^{2+}+ 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!