A GC Question from Chad

[UCF FINatic]

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What is the maximum concentration of fluoride ions that could be present in 0.032M Ba(NO3)2 (Ksp,BaF2 = 3.2x10-8)?
a.)5.0x10-4M
b.) 1.0x10-6M
c.) 2.0x10-3M
d.) 1.0x10-3M

I thought the answer was 5.0x10-4, but that actual answer according to Chad is 1.0x10-3. Here is his explaination:

BaF2(s) → Ba2+(aq) + 2F-(aq)
Ksp = [Ba2+][F-]2
3.2x10-8 = (0.032)[F-]2

(1.0x10-6)1/2=[F-]
[F-]=1.0x10-3M


*******I just don't understand why 3.2x10-8 = (0.032)[F-]2 is NOT 3.2x10-8 = (0.032)[2F-]2 ****

If anyone could please explain, it would be greatly appreciated 👍

 

[Jab1113]

What is the maximum concentration of fluoride ions that could be present in 0.032M Ba(NO3)2 (Ksp,BaF2 = 3.2x10-8)?
a.)5.0x10-4M
b.) 1.0x10-6M
c.) 2.0x10-3M
d.) 1.0x10-3M

I thought the answer was 5.0x10-4, but that actual answer according to Chad is 1.0x10-3. Here is his explaination:

BaF2(s) → Ba2+(aq) + 2F-(aq)
Ksp = [Ba2+][F-]2
3.2x10-8 = (0.032)[F-]2

(1.0x10-6)1/2=[F-]
[F-]=1.0x10-3M


*******I just don't understand why 3.2x10-8 = (0.032)[F-]2 is NOT 3.2x10-8 = (0.032)[2F-]2 ****

If anyone could please explain, it would be greatly appreciated 👍

Because we are not looking for molar solubility, we do not bring down the exponent to represent 2 mol F-.

Just plug and chug the way you did orginially but for F-, the concentration would be X and not 2X.

Hope that makes sense, how I understand it

 

[UCF FINatic]

Because we are not looking for molar solubility, we do not bring down the exponent to represent 2 mol F-.

Just plug and chug the way you did orginially but for F-, the concentration would be X and not 2X.

Hope that makes sense, how I understand it

It makes sense, even though I don't understand it lol. My exam is in like 3 days though so I'll just remember that if its asking for concentration and not molar solubility to not bring the other 2 down. Thanks a lot!