Skip to 0 minutes and 10 seconds An alternative way of doing the same practical is to use a Petri dish where we’ve fitted some carbon rods. These are available from a lot of hobby shops for making kites, and they’re virtually pure carbon, although sometimes they’re covered in a layer of varnish, which can be removed with some abrasive paper. And then they can be cut to length with a pair of pliers and inserted into the Petri dish and held in place with small amounts of glue. This allows us to do electrolysis on a much smaller scale, and we’re going to use some copper sulphate solution to do this electrolysis.
Skip to 0 minutes and 41 seconds If we were going to do brine, where one of the products is chlorine, then we could put the lid on top of the Petri dish, which would contain the chlorine and prevent students from breathing it in. But in this case, as we using copper sulphate and our two products are oxygen and copper, we can leave it open. We’re going to connect up our electrodes.
Skip to 1 minute and 6 seconds And then we’re going to add a few drops of slightly more concentrated solution. This time, we’re going to use 0.5 molar copper sulphate, but we’re going to use very small quantities. And we’re going to place enough between the two electrodes that they touch. You can fill the dish if needed, but that means you will use more solution. We’re then going to connect our system back up and allow electrolysis to take place. So at the negative electrode, we should start to be able to see some copper being produced. At the positive electrode, we should start seeing oxygen being produced.
Alternative electrolysis: Petri dish small scale
This is a variation of using pencil leads in a petri dish. Here, carbon electrodes are made from kite rods (often available from hobby and craft shops) inserted through holes in the petri dish and sealed with hot glue.
As the petri dish lid fits over the top, it helps contain any gases produced, so reducing the risk to the user even further. However, any gases produced will be concentrated, so it is important that the lid is not removed during electrolysis. Afterwards, students should be warned to remove the lid without being too close (especially if chlorine is produced, for example) and allow the gas to dissipate into the air.
- Carbon rods
- Petri dishes (with lids if Cl2 is being produced)
- Hot glue gun (to seal holes)
- Small drill bit or cork borer to make holes
- Leads and crocodile clips
- D Cells or battery pack to give 3 to 6V DC supply
Make a few notes about this practical. Share what you think the advantages and disadvantages are if you were to do this practical in your classroom. You’ll look at one of the three electrolysis practicals in more depth in step 1.13.
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