Question

The mineral CaF2 has a solubility of 2.1 x 10^-4 M. What is the Ksp of CaF2?


pls Bob if you're here!

Answer 1

CaF2 ==> Ca^+2 + 2F^-
Ksp = (Ca^+2)(F^-)^2
You know solubility CaF2 = 2.1 x 10^-4; therefore, (Ca^+2) = 2.1 x 10^-4. Since (F^-) is twice that, (F^-) = 4.2 x 10^-4. Plug those values into the Ksp expression I wrote above and solve for Ksp.

Answer 2

................CaF2 ==> Ca^2+ + 2F^-
I.................solid...........0............0
C............... solid...........x.............2x
E.................solid...........x............2x
Ksp = (Ca^2+)(F^-)^2 = (x)(2x)^2 = 4x^3
The problems tells you the value of x. Plug and chug.
Note: You can plug in differently depending upon how you want to do it.
Ksp = (Ca^2+)(F^-)^2 = (2.1E-4)(4.2E-4)^2 = ?
You should get the same number either way. Try it.

Answer 3

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