topscore GC #45 test #3

[barnes1991]

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Can someone explain to me what the answer to this problem would be: What is the F- concentration in a saturated solution of BaF2, Ksp= 1.7x10^-6?
I thought that when you are doing concentration you do not put like a 2 or 3 in front of x....so i thought that this would be x^3 and the answer would be 2( (1.7x10^-6)^1/3).

but topscore says that you have to first divide the Ksp by 4.

 

[Kingsta2426]

Yes because its (x)(x)^2 which = 4x^3 so u take the ksp divde by 4 then cube root it

 

[ScarletKnight24]

Can someone explain to me what the answer to this problem would be: What is the F- concentration in a saturated solution of BaF2, Ksp= 1.7x10^-6?
I thought that when you are doing concentration you do not put like a 2 or 3 in front of x....so i thought that this would be x^3 and the answer would be 2( (1.7x10^-6)^1/3).

but topscore says that you have to first divide the Ksp by 4.

BaF2 <---> Ba+2 + 2F-

ksp= [Ba+2] [F-]^2

ksp= (x) (2x)^2

so

4x^3 = ksp

you have the value of ksp so just solve for x to get the molar solubility and multiply that by 2 since you get 2 mole of F- ions for every 1 mole of BaF2