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Does mixing glycerol into water effect electrolysis of water?

  1. Oct 29, 2013 #1
    Does mixing glycerol into water effect electrolysis of water?
    I tried measuring ohm and the resistance of water is lower after mixing glycerol.
    Then I experiment electrolysis of water, first I measure the resistance of DI water and it turns out that the resistant is about 0.63 mega ohm.
    Then mix DI water and glycerol and the resistant went down to 0.6 mega ohm.
    I mix sodium sulfate and glycerol into water to decrease the resistant then suddenly the gas is produce.
    The gas that is produce seems to be 2:1 ratio (hydrogen:eek:xygen) but I can't analyse the gas so I'm not sure if the gas that is produce is hydrogen and oxygen or not.
    Does glycerol change into new compound due to electrolysis? Thanks.:biggrin:
     
  2. jcsd
  3. Oct 29, 2013 #2
    Organic compounds in solution can be oxidized at the anode in electrolysis. Oxidation products of glycerol could be things like dihydroxyacetone or tartronic acid, or the oxidation could proceed all the way to water and carbon dioxide.
     
  4. Oct 29, 2013 #3

    Borek

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    Staff: Mentor

    What water/glycerol ratio?

    What is responsible for the conductivity of water solutions?
     
  5. Oct 29, 2013 #4
  6. Oct 29, 2013 #5
    The water is 80 ml and glycerol is 5 ml. The electrode that used to measure the resistant of water is place roughly (but keeping the same distance)just to know that the resistivity change or not.
    The conductivity of DI water could be the contaminant of the beaker, the conductivity of water is ion, an ion carry electrical charge + and -, the cation is discharge at the anode and anion is discharge at the cathode.
     
  7. Oct 29, 2013 #6
    Thanks for the information hilbert2.
    I have research a little bit and it seems that glycerol doesn't change into other chemical since it is not ionic compound (it is polyol) so it doesn't carry electric charge. Am I correct? Correct me if I am wrong.Thanks.
     
    Last edited: Oct 29, 2013
  8. Oct 29, 2013 #7
    So any compound that conduct electricity does form new compound due to electrolysis?
     
  9. Oct 29, 2013 #8
    Even non-ionic compounds can often be oxidized electrolytically. One just has to add in the solution some other compound that makes it conductive. For example, if you electrolyze a solution of sodium chloride in water-ethanol mixture (using platinum electrodes), you will soon find that the resulting solution contains several oxidation and chlorination products of ethanol, such as acetic acid, chloral hydrate and trichloroacetic acid.
     
  10. Oct 29, 2013 #9
    Thanks for the answer, but why does it do that? Can't the electrolyte just ignore other compound and conduct electricity normally without oxidizing-reducing other compound? I though the conductivity of electrolyte is the movement of ion. How does movement of ion effect other compound?
     
  11. Oct 29, 2013 #10

    Borek

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    There is a slight problem with the table - it assumes conductivity of pure water to be around 107 MΩ (that is assuming I read the exponent correctly), while it should be around 1.8×107 MΩ.

    That's not to say it is completely wrong, but it is obviously a bit off.
     
  12. Oct 29, 2013 #11

    Borek

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    Staff: Mentor

    Good.

    Do you introduce any ions into the solution by adding glycerol?
     
  13. Oct 29, 2013 #12

    Borek

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    It is not about what is happening in the bulk of the solution, where the ions are mostly migrating as inert charge carriers. But the charge has to somehow pass the phase boundary (solution/electrode), and that's where the reactions take place.
     
  14. Oct 29, 2013 #13
    I have research a little and I found out that glycerol is miscible in water, so it does not introduce any ion, am I right?
     
  15. Oct 30, 2013 #14

    Borek

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    Miscibility doesn't matter, dissociation does. Does the glycerol dissociate?
     
  16. Oct 30, 2013 #15
    Alcohols should dissociate, slightly.
    For example, ethanol is almost as strong acid as water - in aqueous solution.
    The reactions
    HOH=H++OH-
    and
    C2H5OH=H++C2H5O-
    have very similar equilibrium constants - pKa is 15,7 for water and 16 for ethanol. If you dissolve alkali in ethanol, the reaction
    NaOH+C2H5OH=C2H5ONa+H2O
    is only slightly directed towards ethanol.
    Glycerol is very slightly stronger acid than water, because while aliphatic chain of ethanol is electron donor, the other hydroxyl groups are electron withdrawing.
    On the other hand, glycerol does have lower dielectric permittivity that water. At 25 degrees, I think 100 % water was 80 and glycerol was 41.
    Lowering permittivity should weaken the dissociation of both water and glycerol.
     
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