(Leonard Sibley was key driver to the first ChemEd conference at the University of Waterloo in 1973)
Make an agar-agar gel by heating 300 mL of water to a boil. Stop heating. Stir into the water 2 g of powdered agar-agar. While the gel is still hot, have some Petri dishes ready. Place a straight nail and a bent nail in a Petri dish.
Into a test tube, put some hot gel — about 20 mL — and add 10 mL of KSCN solution (0.1 M). Pour this over the iron nails.
Into a second Petri dish, place three iron nails: one with copper wire wound around it, a second with magnesium ribbon wound around it and a third clean iron nail. Make up another gel solution containing KSCN and pour this into the Petri dish.
Look at these on the overhead over a period of two or three days.