In the Foil Etching experiment we had copper burn a whole in the aluminium foil.
As you can see, aluminum Al is much more reactive than copper Cu, but nothing happens when aluminum foil comes into contact with the copper sulfate CuSO4 solution! How come? Unfortunately, it’s all a bit more complicated than it first looks. Being quite an active metal, aluminum Al reacts with oxygen O2 in the air, forming a very strong film of aluminum oxide Al2O3 on its surface . This film protects the metal from reacting any further.
When you add some sodium chloride NaCl, a vigorous reaction starts as Cl– ions are able to compromise the otherwise-strong Al2O3 shield. Once Cu2+ is face-to-face with the aluminum Al itself and not its Al2O3 shield, the reaction can proceed, and quite spectacularly!
In the next experiment, we obtained a magnetic substance from two non-magnetic ones, magnesium Mg and iron sulfate FeSO4, via a simple chemical reaction! The Fe2+ from the FeSO4 solution turned into metallic iron Fe on the surface of the magnesium particles, so we ended up with magnesium shavings covered with a thin layer of iron! The picture below shows how the magnesium shavings actually hold a heavy neodymium magnet in the air!
And lastly, we did what MEL Chemistry calls a “Metal Contest”, because here too, three metals (zink, copper and tin) were competing in reactivity. “If you arrange metals from more active to less active, you’ll see that zinc Zn is a more adventurous fellow than tin Sn and copper Cu. That’s why, when you put a zinc rod into a solution containing, say, copper ions Cu2+, the latter are happy to settle inside the comfortable cloud of electrons, forming metallic copper Cu on the surface of the rod. Zn ions Zn2+, in turn, go swimming in the solution. The reaction with the tin chloride SnCl2 solution is essentially the same”, MEL Science website explains.