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Supercooled ethanol/distilled water solution

  1. Jan 25, 2015 #1
    How does the minimum(coldest) temperature that a supercooled solution of ethanol and distilled water depend on the concentration?
     
  2. jcsd
  3. Jan 25, 2015 #2

    Quantum Defect

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    If the solution is really "supercooled" (i.e. T<Tf) it is difficult to tell. If you merely want to determine the freezing point of a water solution to which some ethanol has been added, you can estimate this using the value of Kf(H2O) to calculate the freezing point depression. If the solution is mostly ethanol, you could do the same thing, but you would need to know what Kf(ethanol) is.
     
  4. Jan 25, 2015 #3
    The thing is that im trying to verify it experimentally. Apparently there is a supercooling curve that i have achieved only once. Any experience with a similar experiment? The solution reaches a low temperature and if done rightly, in a couple of second the temperature should suddenly rise indicating that the solution has frozen.
     
  5. Jan 25, 2015 #4

    Quantum Defect

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    Lots of people have done this with water and shared on youtube:

    e.g.

    [Water should be free of things that can act as nucleation sites for crystals]
     
  6. Jan 27, 2015 #5

    Borek

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    As far as I know there is no such thing as the minimum temperature of a supercooled solution.
     
  7. Jan 27, 2015 #6

    TeethWhitener

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    Here's what's going on, as far as my Google-fu will take me. (Caveat: This isn't really my area of expertise, but these papers and the papers that cite/are cited by them seem to be the core papers in this area.)

    Supercooled pure water forms a pretty distinct ice-like structure, due to its hydrogen bonding configuration. Introducing "structure breakers" like ethanol disrupts the supercooled water structure, as can be seen, for instance, in SAXS measurements found in this paper. Whereas supercooled pure water will eventually undergo a homogeneous crystallization at around -45°C, the presence of structure breakers will prevent homogeneous crystallization and tend to force the system toward a glassy transition at a lower temperature. This paper has some details about measuring the phase transition using the singularity in the heat capacity measurement (although that paper doesn't look at ethanol specifically), and it also suggests that the singularity disappears with increasing structure breaker concentration--another sign that the phase transition is glassy rather than crystalline.

    So, to answer your question, I'd imagine that the minimum temperature of the supercooled solution will decrease with higher concentrations of ethanol in water. Though I also imagine that once you get into a regime where it's mostly ethanol with a little bit of water, the function might not remain monotonic. My two cents...

    [Edit]: It just occurred to me that this function could get really non-monotonic if it turns out there are other stable ordered phases at certain special molar ratios.
     
    Last edited: Jan 27, 2015
  8. Jan 28, 2015 #7

    epenguin

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    This Thread, although I had forgotten what it was really about stirred a vague memory of mine that freezing as a method of concentrating alcohol had been used if not first discovered by Paracelsus, who essentially first named if not discovered alcohol. You would need a University library of History of Science to check that out. Here a couple of traces I found googling.


    https://books.google.it/books?id=XLLNMibvy4sC&pg=PA25&dq=paracelsus+freezing+purification++alcohol&hl=it&sa=X&ei=37rIVOXhFYLmasHfgKgD&ved=0CB8Q6AEwAA#v=onepage&q=paracelsus freezing purification alcohol&f=false

    https://books.google.it/books?id=XLLNMibvy4sC&pg=PA25&dq=paracelsus+purification++alcohol&hl=it&sa=X&ei=2bzIVNG_CcPsUubBg5AL&ved=0CCgQ6AEwAjgK#v=onepage&q=paracelsus purification alcohol&f=false

    I also found that the method had been used, mostly illegally, to make a concentrated alcoholic beverage "applejack" from cider in the US.

    Again traces from Google
    https://books.google.it/books?id=H9ufuzQeTgAC&pg=PA121&dq=what+is+applejack&hl=it&sa=X&ei=5b7IVLauFczxaK3TgdAO&ved=0CEQQ6AEwBQ#v=onepage&q=what is applejack&f=false

    There must be better sources.

    Maybe not quite thread topic but I just thought you might like to know. :oldsmile:
     
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