This is a problem to illustrate the common ion effect. The common ion, in this case, is F^- from KF and the presence of KF will decrease the solubility of LfF3 in water.
........LaF3 ==> La^3+ + 3F^-
I.......solid.....0.......0
C.......solid.....x.......3x
E.......solid.....x.......3x
and
........KF ==> K^+ + F^-
I.....0.013M....0.....0
C....-0.013...0.013...0.013
E......0......0.013...0.013
Ksp = (La^3+)(F^3-)^3
You know Ksp.
(La^3+) = x
(F^3-) = 3x from LaF3 and 0.013 from KF or 3x+0.013
Solve for x in mols/L
Calculate the solubility of LaF3 in grams per liter in the following solutions. The Ksp of LaF3 is 2.01 e-19.
0.013 M KF Solution
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