GC question- Ksp

[JustwantDDS]

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The solubility of CaF2 ksp = 4.0 x 10^-11 in 0.1M Ca (NO3)2 is???


ksp= [ca2+][F-]^2
wouldn't x=0.1 M because of the Ca(NO3)2 at 0.1 M

I tried that and its not correct...

 

[CANgnome]

The solubility of CaF2 ksp = 4.0 x 10^-11 in 0.1M Ca (NO3)2 is???


ksp= [ca2+][F-]^2
wouldn't x=0.1 M because of the Ca(NO3)2 at 0.1 M

I tried that and its not correct...

CaF2 ----> Ca 2+ + 2 F-

Ksp = [Ca 2+][2F-]^2

(i skipped the ICE table, but i suggest you write it out)

Ksp = 4.0 x 10^-11 = [0.1 + x][4x^2]

(x in 0.1 + x can be negated because it is so small)

4.0 x 10^-10 = 4x^2

solve for x?

 

[JustwantDDS]

why would it be [2F-]
doesnt the ^2 represent the 2F- ?

 

[JustwantDDS]

your answer is right
1*10^-5

 

[JustwantDDS]

ps: we're both taking the dat same day!

 

[CANgnome]

XD

good luck.


if you write out the ICE table you get:

CaF2 ----> Ca 2+ + 2 F-
I not matter 0 0
C -x +x +2x
E not matter x 2x

so when it dissolves, the concentration of F- is twice as much as the concentration of Ca2+.

innately, Ksp for CaF2 is [Ca][F]^2. plug in F-, which is 2x, you get [2x]^2

 

[doglovernonesto]

Question: how did 4 x 10^11 turn into 4 x 10^10?

P.S. Good luck on the exam!