Ideally, and assuming it works, I would like to use a solution to test for nitrates. There are those fish tank and spa tester kits that test for nitrates, but I want the kids to really have to see the chemicals involved in the test.
Ideally, I'd like something that will form a precipitate when reacting with a nitrate solution, but any obvious reaction would be ok, too. Color change, for example. But in most of the reactions I'm trying, the nitrate is always not the compound forming the precipitate, instead being a spectator ion. I've got all sorts of nitrate compounds, and they could be used in a control situation, to show the precipitate formed from the nitrates. But! I cannot figure out how to get the nitrate to precipitate out.