# ksp and solubility question

Discussion in 'DAT Discussions' started by duke2121, May 13, 2012.

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1. ### duke2121 5+ Year Member

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0
Feb 16, 2011
Bit of a mixup here.
So, find the maximum F- ions present in a 0.032 M Ba(NO3)2 where the ksp of BaF2 = 3.2x10^-8.

So I first write the Ksp expression which is Ksp= [Ba2+] * [F-]^2. So I solve for F- concentration by letting [Ba2+] equal 0.032M. In a quiz from chad's videos the concentration was not multiplied by 2, since BaF2 dissociates into Ba and 2F-? Why is it not multiplied by 2 because in DAT destroyer 2012 #122 the final calcium concentration is multiplied by 3.

On a side note, I understand if I am solving more molar solubility the expression I use is ksp=4x^3

3. ### BRZ24Banned

304
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May 13, 2012

I believe you are NOT supposed to multiply it by two because you were given the concentration of Ba+2. If you were not given any of the concentration, then you would have to find the molar solubility (solving the 4x^3=ksp) and then multiply the result by 2 to get the concentration of the fluoride ion.

Not sure if I am right though.

4. ### duke2121 5+ Year Member

413
0
Feb 16, 2011
That might be right. Because in the DAT destroyer problem the question was "Consider calcium phosphate. What is the calcium concentration if the ksp is such and such". In this problem molar solubility was solved for, and then mult by 3 since [Ca2+] =3x