how do the tests on known solutions containing cations and anions make it possible for you to identify the cations or anions in an unknown solution?

Question

 This is my chemistry homework question that I am stuck on, please help!

Answer 1

The known solutions provide a guide to figuring out the unknowns.  If the known solution forms a precipitate, for example, when you add another known solution, that tells you a lot, and when you perform the same test on the unknown, and you get, or don't get a precipitate, that helps you narrow down what the unknown is.  An example might be as follows: known cation solution is Ag+ (silver). Known anion solution is chloride (Cl-).  Add the Cl- solution to the Ag+ solution and you will get a white precipitate.  Add the Cl- to your unknown cation solution and if you do NOT get a precipitate, then the unknown cation solution cannot contain silver and must be another one of the cations.  A simpler answer is you just match up the observations you make when mixing the different known solutions (precipitate, color change, gas formation, etc), to those you see when adding known solutions to unknown solutions.