I am a teacher and I did this experiment with my class with limited success. It is easy to get a little bit of gas but I want enough to test with a splint.
I used a 12 v supply with copper electrodes and sodium carbonate and salt as an electrolyte.
I got a green compound on the electrodes. What was that?
What combination of these three conditions will get me better results? The Internet is no help. I need expert advice. Thanks.
Sounds like either patina or rust.
What were you trying to prove with the experiment? What were you hoping would happen when you hooked up the leads to the battery?
the copper is reacting with oxygen.
use platinum or stainless steel for electrodes.
don’t use salt (NaCl). sodium sulfate is good.
I want enough oxygen and hydrogen to test with a splint so that they can see that water is a compound. Ideally I want individual sit-ups for the students.
I would suggest using a higher voltage and/or running it for longer - maybe let it run overnight or until the next class.
The green stuff is probably cupric carbonate or chloride (or a mixture of the two). It is hardly surprising that you get it if you have carbonate and chloride in your electrolyte, and it may be coating your electrode and stopping the electrolysis. Also you may be getting some chlorine and CO2 as well as oxygen. I know really pure water (e.g., distilled) is not supposed to electrolyze easily, but I think you should only need a tiny bit of salt in there in order to get it going.
12 volts is fine; I used a 6 volt lantern battery as a kid.
I used two carbon rods (removed from dead D cells, the zinc-carbon type, alkaline batteries don’t have them–alkaline D cells weren’t available when I was a kid). Wrapped the copper wire around the bottom of the carbon rod and attached the other to the battery. I used tap water, no added electrolyte other than was naturally dissolved in the water. I inverted test tubes over the carbon rods and let it run, several hours IIRC.
NaCl is not a good choice for an electrolyte as it will liberate Chlorine gas. The electrolyte just speeds things up. When my Chemistry Teacher did this same experiment in HS, she added a couple of ml of H2SO4 (sulfuric acid) and had a proper 12V power supply, and she was able to collect enough in 10 minutes to 1) demonstrate that one side created twice as much gas as the other, 2) the low volume gas was oxygen since the smoldering punk would burst into flame when inserted in it, and 3) the other gas was hydrogen as evidenced by it going “POP” when exposed to the smoldering punk. In addition, water droplets were observed at the mouth of the test tube that went “POP”, indicating that the product of combustion was water.
There are hazards with this experiment, you should have proper safety equipment, techniques, etc… The “POP” was very loud and probably would not be tolerated in todays public schools, so you may want to avoid that part.
excavating (for a mind)
Thanks for all that. I have done the hydrogen test many times and it is often the highlight of the year for my students.
Rust. :smack:
May I politely ask you to show us where the iron was in the reactants?
Rust can refer to various forms of metallic corrosion, besides iron.
You can use carbon electrodes, but I don’t know if they work any faster. The conductivity of the electrodes combined with their surface area probably would probably reveal the ideal voltage and current requirements. Some people add things to the water to increase it’s conductivity. I hesitate to say just add some salt with metal conductors, it might rapidly increase corrosion of the metal reducing the effect.
When I was a kid, I just used the bare leads of simple copper wire with no salt and four D batteries in series.
I guess our well water had plenty of electrolytes in it.
I recommend thicker wires and greater electrode surface area.
I learned two new uses for words today, “splint” and “punk”.
Don’t forget that it is also possible that touching the electrodes together may cause a spark and an unwanted “event” resulting from that spark. The “event” being blowing one of the tubes up into the air and scaring the Chem teacher.
My chemistry teacher introduced us to hydrogen and alkalai metals by casually tossing some metallic sodium into a bucket of water while starting his lecture.
Clearly it made an impression…
Do you hold some kind of competition among your students for the honor of being the smoldering punk?
You can use graphite from pencils for electrodes if you don’t want to open up a battery. Do you need a “salt bridge” or some other selectively permeable membrane? Actually, you can just buy a water fuel cell demonstration kit.
I have tried some of your suggestions no increase in gas production.
We have an electrolysis kit in the lab. I believe it has platinum electrodes and its recommends sulfuric acid as an electrolyte.
I am still hoping to get suggestions.
Copper is out as an electrode. Graphite is way to fragile. I have access to many other common metals. Any suggestions?
The Nazis did it, why can’t I?
When I did it as a kid, we used plain old nails for electrodes. I don’t remember if we used an electrolyte, or just plain tap water. Worked just fine.
Yeah, I remember a teacher using hydrochloric acid to burn through a metal can, using sodium hydroxide to chemical burn holes in a shirt, then mixing the two and drinking them. Makes an impression!
You might try moving the electrodes closer together. This will decrease the resistance between them and allow more current to flow which should increase your gas production. If you get them too close though it gets difficult to separate the gases into separate tubes.
Increasing the surface area of the electrodes also helps.