Four glass bottles containing clear colorless solutions need to be tested for ions. Bottles 1 and 3 contain cations and the other two contain anions.
Nearby the labels Pb2+, Cl, Ag and (SO4)2 are laying. there are three beakers to mix the solutions. Bottle 1 + bottle 2, bottle 1 + bottle 4, and bottle 2 + bottle 3 are to be mixed to give white precipitates. Which labels go on which bottles?
Bottles 1 and 3 contain cations and bottles 2 and 4 contain anions. Our choices are Pb2+, Cl-, Ag+, and (SO4)2-. We are mixing bottles 1 and 2, 1 and 4, and 2 and 3. The result for all three are white insoluble precipitates. We know that we are mixing cations with anions to get new inorganic salts so lets look at it logically. We know that lead (Pb2+) forms many inorganic salts that are not water soluble. Mixing Pb2+ with Cl- will make PbCl2 and mixing Pb2+ with (SO4)2- will make Pb(SO4). Both of these are white solids that are not water soluble. So we could make bottle 1 be Pb2+, bottle 2 be Cl, and bottle 4 be (SO4)2-. By process of elimination, this would make bottle 3 be Ag+. We must also mix bottles 2 and 3 which would be mixing Cl- and Ag+ to give AgCl, which is also a white solid that is also insoluble in water. So the final labelling of the bottles would be:
Bottle 1: Pb2+ (cation)
Bottle 2: Cl- (anion)
Bottle 3: Ag+ (cation)
Bottle 4: (SO)2- (anion)