Question

how can you tell if a combination in a mixture forms a precipatate or not?How can you tell from the sollubility table?

Answer 1

Here is a simplified set of solubility rules.
http://www.files.chem.vt.edu/RVGS/ACT/notes/solubility_rules.html
An example follows:
Suppose you have this equation and you don't know if it will react or not.
BaCl2 + Na2SO4 ==>...
You look at the solubility chart. Rule 4 says that all sulfates are soluble EXCEPT for Ba, Sr, Ca, Pb, Ag, and Hg(I) salts. So we know BaSO4 will form and we write
BaCl2 + N2SO4 ==> BaSO4 + 2NaCl.

But if we have
NaCl + K2SO4 ==> we write no reaction because any combination of these two compounds will not produce an insoluble material; i.e., Na2SO4 is soluble, KCl is soluble.