My IB seniors are just wrapping up our unit on electrochemistry and redox. This has always been a challenging topic within the IB curriculum. Admittedly, electrochemistry has not ever been my strong suit either, so this year I aimed to strengthen the unit with two additional demonstrations.
Over the summer I ordered a Hofmann apparatus to demonstrate the electrolysis of aqueous solutions. When I tried this demo last fall, I discovered that my glassware was broken. But I'll write about that in a future blog post. Instead, I'll focus on one of the easiest demos I have ever set up. Here is the complete list of equipment and materials:
400 mL beaker
200 mL 1 M CuSO4
A set of alligator clip wires
The 9V battery provides the needed energy to drive the non-spontaneous process in this electrolytic cell. For my demonstration, I connected the battery and let the cell run for about 30 seconds. There isn't much happening visually. But there is a lot going on! The copper ions in solution are reduced, plating the paperclip in a nice coating of relatively pure copper. And the copper electrode is being oxidized, thus replacing the copper ions that plate the paperclip. This keeps the concentration of copper ions in solution at a constant level.
The oxidation half-reaction at the copper anode:
Cu(s) --> Cu 2+ (aq) + 2 e-
The reduction half-reaction at the paperclip cathode:
Cu 2+ (aq) + 2 e- --> Cu (s)
Below is a picture of the paperclip with a copper coating and the clean shine of the portion of the copper electrode that was submerged in the solution. I only ran the electrolysis for about 30 seconds, but I'd like to try it for a longer time and see how much copper will plate the paperclip. I've got some milligram balances in my room to put to the test to see if the rate of plating can be calculated also. In a scenario where I had a bit more time (and less need to plow through the HL Chemistry curriculum so quickly), I'd like to extend this a bit to have students explore factors that affect the rate of electroplating such as concentration, voltage and temperature of the solution.
Do you have any extensions for this demonstration? Or suggestions for additional ways to show students electrolysis? I would love to hear about your use of this or other demos related to electrochemistry.