If you are going to do a lot of experiments that require electricity (such as electrolysis of water, and electroplating), and you have old power sources, make this apparatus (or several) and you won’t have to keep buying 9V batteries. I got this idea from http://www.treasurenet.com/forums/cleaning-preser...
Besides the old power sources, you will need wire cutters, and alligator clips. You will also need EITHER a glue gun, epoxy, OR wire shrink wrap and a heat gun. To test your power source, you will need a glass jar, salt, regular tap water, and two nails.
Find old power sources from answering machines, phone units, flip phone chargers, and the like. I have seen recycled ones for sale for $5 each at my local science supply outlet, and I’ve seen them at Goodwill for $1 each. Look at the label to find the power output. Any that give a DC output of about 9 to 24 volts are good for this sort of application. Voltages as low as 3V will work for electrolysis of water, but I haven’t tried 3V for electroplating yet, so I’m not sure if it’ll work.
I bought some alligator clips at my local science supply outlet. When I ran out of those, I thought I could get cheaper clips from the craft store, in the jewelry section. All kinds of metals conduct electricity, right? Wrong. The craft store hair clips don’t conduct electricity, so don’t try that route.
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Step 1: Connect the Alligator Clips
Cut the connector off the end of the wire, and split the wires for about 3 or 4 inches of the wire’s length. Strip about 2 cm of insulation off the ends of each wire, and attach alligator clips. The clips I bought have a screw to hold the wire; if you don't see a screw, you are supposed to insert the exposed wire in a little channel and crimp (squeeze with the pliers) the wire.
Step 2: Insulate the Connection
Where you attached the alligator clips, seal any exposed metal with wire shrink wrap, hot glue or epoxy.
Step 3: Test the Device and Label the Terminals
(In the photo, I have short sections of drinking straws covering my connections. Another attempt at creative recycling, but this one failed. Drinking straws don't work as shrink insulation, and they don't label your wires very well.)
Your students will need to tell the positive and negative wires apart. The positive wire is usually marked by some kind of writing or markings, usually in white ink on black plastic insulation on one of the wires, but this can be a bit too subtle for students who are just beginning to work with electricity.
If you’re not sure which wire is delivering the positive charge, you need to test your device anyway, so here’s how to do that:
Get out a glass jar, and some steel nails. Make up a solution of salt water in the glass jar. Secure the nails in the clips, and drop them in the salt water solution, making sure the nails don’t touch. Plug in your device. You should see bubbles emerging energetically from one of the electrodes (well, with a 3V charger, they emerge kind of lazily, but you should see gas clearly evolving from one electrode more than the other).
Unplug your device and put red electrical tape on the wire that made the most bubbles; that is your positive wire. I put black electrical tape on the other alligator clip connection; this clearly distinguishes the positive and negative wires.
Step 4: Finished!
You now have a device that can be connected to replaceable electrodes, and you have a source of known voltage (those old 9V batteries in your drawer probably don't deliver 9V anymore). Just keep the alligator clips clean and dry, and you can use your device again and again. Use it to power electrolysis of water, electroplating, or making a pickle glow! Even if you paid $5 each for your power source, they pay for themselves after being used 3 times, since the cheapest 9V batteries I’ve found are $2 apiece.
Step 5: To Use for Electrolysis of Water
For electrolysis of water, I like the inexpensive and elegant setup devised at the University of the Philippines National Institute for Science and Mathematics Education Development (https://www.slideshare.net/upnismedmultimedia/construction-of-an-improvised-electrolysis-apparatus-2-13454227). It takes time to make these setups, but I like the fact that my alligator clips never touch the salt water solution, so they won’t corrode. Also, the apparatus holds the electrodes securely at the bottom of the reaction chamber, so I can place bells over them to collect O2 and H2 gases.
I haven’t built my version of these devices yet, since my electrolysis of water lab is not until November. I plan to use larger vessels (approx. 4.5” diam. by 8.5” tall HDPE tubs, recycled protein powder containers) so my gas collection bells can be bigger (I’ll use pesto and jelly jars that are approx. 2” diameter and 5.5” tall). I will use whatever screws or nails I have on hand, but if you wanted to make these devices and use them year after year (say, if you have a classroom and have the storage space), you can buy cheap graphite electrodes on eBay or at your local hobby shop – look for graphite struts for remote-controlled model planes. Graphite won’t corrode with repeated use, like metal electrodes will.