Electrolysis to collect hydrogen and oxygen

Discussion in 'Supporting Chemistry' started by Alex Craig, Oct 11, 2019 at 12:27 PM.

  1. What would you use as the solution to collect hydrogen and oxygen at the electrodes? The teacher has suggested "sodium nitrate (or similar!)" on their order. I've never done it with sodium nitrate (does it work? Is there anything better?!) and before I spend lots of time trialling it I thought I'd ask the hive mind on here!

    I have used water before with a bit of sodium hydrogen carbonate to act as the electrolyte. When I did the hydrogen collected at the cathode popped ok when tested but the oxygen from the anode didn't do much and wouldn't relight a spill.

    Any help/advice gratefully received!
     
  2. karen b

    karen b COMMITTEE

    In a Hoffmann voltameter we fill it mostly with distilled water with a slug of sulphuric acid. I just looked on CLEAPSS and they say to use 0.5M sulphuric acid.
    It also notes it is important to use platinum electrodes, not carbon rods, as otherwise you get carbon dioxide, not oxygen. Which makes sense when you think about it, but it might not have occurred to me
     
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  3. Thanks Karen :) using carbon rods would obviously make carbon dioxide if I could engage my brain on a Friday afternoon! I have the glass bit of a Hoffman voltameter but no electrodes :( any ideas of anything I could substitute? This is the first time since I started at this school I've been asked for this practical and it was a very very long time ago I last did it myself!
     
  4. We use platinum electrodes like this with our Hoffman (screw top ones are my preference). They can be pricey though if you need to buy a pair... i'm not sure if you can substitute for anything else. We also use sulfuric acid in our Hoffman too- I think its 0.3M and it usually works well :)

    [​IMG]
     
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  5. Thanks Chemtech10. I have found 4 brand new ones of these with carbon rods but no platinum wire :confused:
     
  6. I've done it with carbon electrodes and it works - no carbon dioxide as the carbon is an immobile solid. just the normal Hydrogen at the cathode and oxygen at the anode.
     
  7. karen b

    karen b COMMITTEE

    I haven’t tried it, just quoting CLEAPSS on the matter
     
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  8. I'm very suprised that you got the required effect with Carbon Electrodes it's always done with Pt, though I haven't tried it with Carbon.:);)

    [​IMG]
     
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  9. I only tried because the platinum ones had fallen apart - have to say that carbon ones don't last and do start to dissolve - but they served a purpose
     
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  10. I got the idea from the mini electrolysis cells we use in chemistry - they have only carbon electrodes and are used for electrolysis of various solutions including acidified water. If there is any degradation of the carbon (producing CO2) it is negligible and doesn't effect the result.
     
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  11. Thank you Peter. I've tried it with carbon electrodes in a similar set up before and definitely had degradation of the carbon rod. We collected the gas and got hydrogen that popped but no positive test for oxygen so I think it was probably carbon dioxide made
     
  12. Try nichrome wire and dilute sulphuric acid. Use a solid bung and pass the wire up the side of the bung. Scrunch up some wire so that you have a useful surface area in the solution. You will end up with a solution of nickel/chromium sulphate but it should be so dilute as to cause no issue with disposal.
     
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  13. ooooh! Thank you. I will try this :)
     
  14. Carbon rods do work but do not give the gas ratio. For years it looks like our electrodes corroded and new ones purchased (at a ridiculously high cost) again and again. Luckily the previous tech(s) has the foresight to keep the Pt which of course did not corrode. When I learned how much they cost I came up with this. A copper rod smeared in silicon sealant with reused Pt. Total cost of replacement is a fraction of the cost of new!
    DSCF0017 (Small).JPG
     
  15. What's the set up for this? Looks funky and effective but more importantly cheap to make!
     
  16. karen b

    karen b COMMITTEE

    It's on the cleapss website, possibly as a voltameter
     
  17. It is as Karen @karen b has said but this is an actual one I set up and operated at York University. I recommend Ear Plugs when you Test for the gases. The Universal Indicator added all serves a useful purpose.:);)
     
    Last edited: Oct 15, 2019 at 9:33 AM
  18. Cool thanks I will have to look that up