how do you know if a precipitate forms in a reaction?

Question

i have to fill out this table and I can't figure it out. is it if there are two soluble compounds?

i know how to tell whether theyre soluble or not i just dont know what makes a precipitate and the online chart i have to fill in keeps saying its wrong for two solubles

CaCl2 Na2S Pb(NO3)2 (NH4)3PO4
Na2CO3
AgNO3
K2SO4
MgCl2

which one of these (read as a chart) can form precipitates and how do you know?

Answer 1

I'm in the same boat for chemistry class (same question, chem 102?)

The previous answer is right but I'll go into a little more detail.

Take the first element of the compound in the left column and the second element (or compound, whatever) of the compound in the top row. Check the solubility rules. If it's insoluble, then it is the precipitate. balance the charges and fill it in the blanks.

If it's not take the first element of the compound in the top row and the second part of the compound in the left row and check it's solubility. insoluble=precipitate. balance charges and fill in the blanks.

I haven't completely answered the question yet so I don't have answers

Actually I'm having trouble getting the answer right. I get the idea and I know how to do it but I must be making some mistakes so if you get it e-mail me

If you've got more questions I can give them a shot (but I'm not great at chem) UID: acarlbe2

Answer 2

Take the first ion from each compound along the top row, and the second ion from the column, and make them into a compound. Then look up its solubility in your table.

Then reverse the procedure - take the first ion from the column and the second ion from the row.

For example, CaCO3 is insoluble for your first entry.