certain reagents like AgNO3, when added to a sample that has a halide ion in it like cl-, Br- or I-, it will always give a ppt (solid)
acids like HCl or H2SO4 can tell you if carbonate or sulfites are present because they will give off a gas (fizzing) - what is the reaction?
KOH can also give ppt, depending on what is in solution. there should be a solubility chart of ionic compounds somewhere in your text book. the things that make ppt or gases will have similar ions
ex hydroxides are mostly insoluble so a rxn of Fe3+ and KOH will give a red ppt (of what?)