What type of reaction produces a precipitate?

SO SORRY FOR LONG EXPLANATION - but I'm trying to make stuff clear.

Precipitate can be formed when non-soluble substance forms a solid product in a chemical reaction.

How to predict Precipitate?
To determine if a precipitate will form you should know the ions involved and be able to apply the solubility rules.

These are the solubility rules:
1) Group 1 metals on periodic table - all soluble
2) Nitrates (#NO_3^-#) - all soluble
3) Chlorides (#Cl-#) - all soluble EXCEPT #AgCl# and #PbCl_2#.
4) Sulfates (#SO_4^-2#) - all soluble EXCEPT #BaSO_4#,#PbSO_4#, and #CaSO_4#.
5) Hydroxides (#OH^-#) - all NOT soluble EXCEPT #KOH#and #NaOH#.
6) Carbonates (#CO_3^-2#) - all NOT soluble EXCEPT #K_2CO_3#, #Na_2CO_3#, and #(NH_4)_2CO_3#.

Let's say sodium chloride (NaCl) and lead nitrate (#Pb(NO_3)_2#) are given to you to mix them together.

#2NaCl + Pb(NO_3)_2 => 2NaNO_3 + PbCl_2#

#NaNO_3# is soluble (rule 1 and 2)
#PbCl_2# is Not soluble (rule 3)

Since #PbCl_2# is insoluble, therefore it will form a precipitate.

This is what precipitate looks like