[Chiram]

I've been trying to figure out how to calculate this, can anybody help
My problem is this:

A solution is 0.040M in Na2SO4 and 0.050M in NaIO3. To this is added a solution containing Ba2+. Assuming that no HSO4- is present in the original solution. What is the concentration of the anion that forms the less soluble barium salt when the more soluble precipitate begins to form?

ksp BaSO4 = 1,1E-10
ksp Ba(IO3)2 = 1,57E-9

[Borek]

What is the concentration of barium at the moment less soluble salts starts to precipitate? What does this concentration tell you about less soluble salt anion concentration?

[Chiram]

All right. Do you mean I solve for [Ba2+] in the first equation.

[Ba2+] = ksp/[SO42-] = x

Then add x to the second equation?

[IO3-] = ksp/[Ba2+] = y

The number would be rather small..

that is 0.050M - y NaIO3 whould be almost 0.050M by aproximation.

Or am I not going in the right direction?
What whould for examble the Mass balance equation be?

[Borek]

Sorry, mistake in my previous post 

It should read:

What is the concentration of barium at the moment more soluble salt starts to precipitate? What does this concentration tell you about less soluble salt anion concentration?

The way it works is that at first less soluble salt precipitates. The more of it precipiates, the less the anion concentration is, the higher the Ba²⁺ concentration. At some point [Ba²⁺] is high enough to start precipitate the other anion.

Write expressions for both Ksp, check which salt will start to precipiate first.

[Chiram]

Okay thanks alot I got the right answer now