What is the solubility of BaSO4

in a solution of
0.250 M Na2
SO4
? The Ksp of BaSO4
is 8.7 x 10-11.

2 answers

BaSO4 has a certain solubility by itself; with Na2SO4 the solubility is decreased due to the common ion effect. The common ion is the sulfate ion. You have two equilibria.
........Na2SO4 ==> 2Na+ + [SO4]^2-
I.......0.250.......0......0
C......-0.250.....0.50...0.250
E........0........0.50...0.250

.......BaSO4==> Ba^2+ + [SO4]^2-
I......solid....0.........0
C......solid....x.........x
E......solid....x.........x

Ksp = (Ba^2+)[(SO4)]^2-
Ksp you know.
(Ba^2+) is x
[(SO4)]^2- is x from the BaSO4 and 0.250 from the Na2SO4 so total is x+0.250
Substitute and solve for x.
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