How do I know if something is an acid so I can avoid eating it?

I'm going to have a lab coming up. Normally I use litmus paper to see if something is an acid or base. To keep it short, how can I tell if something is basic or acidic?

I'm dealing with NaCl, BaCl2, CuCl2, AgNO3, Cu(NO3)2, Fe(NO3)2, NaI, Na2SO4, Na2CO3

just an explaniation on how to do it is fine, thank you :D

write a mechanism for creating something other than benzoic acid using the grignard reagent (hint: look at your Solomons textbook; don't use "R" groups, write out the actual chains) USE ARROWS