[swatchmaster]

The lab question:
3. Compare your results to the predictions based on the solubility rules. Were
there cases where a precipitate formed when it should not have, or a
precipitate did not form where predicted? In each case, what might
have caused the discrepancy?

In the lab i did, a precipitate was formed when I reacted FeCl3 with KI, Ba(NO3)2 with AgNO3 and FeCl3 with Na2SO4. Solubility rules predicted that this would not happen. I'm confused at the last part of the question-- what might have caused this? I'm really confused!

[Arkcon]

Well, to start with, you can try to make a series of balanced chemical equations, looking for soluble or insoluble products.  Then you can try to see what is actually a discrepancy, or not.

[Big-Daddy]

Did you react these all together or in separate solutions? If it was all together, you may have a double salt somewhere and that might explain why you see a precipitate.

I cannot begin to guess what would cause precipitation in a solution of just Ba(NO3)2 with AgNO3. The thing to check though would be that you aren't crossing the Ksp of either salt when you add the ions together. I wouldn't guess you would, since nitrates are very soluble.

FeCl3 with KI - the precipitate is not surprising here. What are the products?

F- and Cl- cannot be oxidized by SO42- so forget about that. Again, it might help to think clearly about the products. It would help here to guess accurately how FeCl3 reacts.