Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Separate by boiling

  1. May 22, 2006 #1
    Hi folks,

    This is rather physics... Is it possible, to separate ethanol and water by boiling the ethanol. Will the ethanol go away? Or will there be always a little amount of it in the mixture? :bugeye:

    Thanks in advance!
  2. jcsd
  3. May 22, 2006 #2
    The ethanol would boil away at around 78 celsius, before the water would boil away (at 100). You could use a distiller or other apparatus to capture the ethanol that evaporates. As for obtainin pure ethanol, I imagine there would always be a littel water no matter what that boils away with the ethanol no mater how times you boiled it.
  4. May 22, 2006 #3
    Thank you, Daveb! My goal is get rid of the ethanol. So it seems that It is possible by simply boiling the mixture at 80C. And I guess that I can calculate the boiling time if I know the boiling heat, the mass of the ethanol, and the power of my heater. I hope so.. :)
  5. May 22, 2006 #4
    I mean:
    I have 5ml water, and 1ml ethanol. Question is that how much time do I need to get rid of the ethanol in the system?
    Boiling heat of ethanol: Qb=906.07kJ/kg
    mass of ethanol: meth=0.789g (If I take a density value 0.789g/cm3 --- ut this is valid at 18oC).
    Power of my heater: 400W

    So: To boil 1kg ethanol I need 906.7kJ. To boil 0.789g I need only 714J.
    So with 400W it takes only a few seconds... :rolleyes:
  6. May 22, 2006 #5
    With 400W it might well catch fire as vapour. Which is another way to get rid of it, I guess...
  7. May 22, 2006 #6
    Yesyes, but this 400W is not not only for hewating up the ethanol-water mixture. there is water bath around. 10l. So my previous calculation was just a first approximation.. :)
  8. May 22, 2006 #7


    User Avatar
    Science Advisor
    Homework Helper

    Telmerk, are you familiar with azeotropes?
  9. May 22, 2006 #8


    User Avatar
    Gold Member

    If you want to boil away some of the ethanol why don't you just dilute your mixture with more water?

    Edit: Or do you want to boil away all of it? So this is more about the experiment than the results I guess.
  10. May 22, 2006 #9
    Mr. GCT! No, I wasn't until this this moment. :bugeye: Thank you very much for your notification! So I can't separate my water-ethanol mixture theoretically and practically. Azeotrophy means - I hope I looked after well - that the composition is the same in the liquid and in the vapour phase. Bad news. Then what to do? :frown:
  11. May 22, 2006 #10
    Well, if I remember correctly the ethanol-water azeotrope is something around 95% ethanol and 5% water. So if you want to leave pure water behind, it's simple...all you gotta do is boil the ethanol-water azeotrope away. You'll be losing some of your water to the azeotrope though. Getting pure ethanol, however, is more difficult and cannot be achieved through simple distillation becuase you will always be stuck at 95%.
  12. May 22, 2006 #11


    User Avatar
    Science Advisor
    Homework Helper

    Telmerk, I'm not quite sure why you would want to separate the mixture completely, that is, there are plenty of ways to obtain pure ethanol or pure water from the mixture itself...but you don't need to split the mixture components entirely.
  13. May 22, 2006 #12


    User Avatar
    Science Advisor
    Homework Helper

    You might want to research on how distilled water is made (I'm not sure about deionized water); also, reverse osmosis is definitely another.
  14. May 23, 2006 #13
    I have a mixture with relatively low cc. of ethanol. (5 to 10 m%). So it not an azeotrope mixture. What I want is to obtain the pure water. I don't care what happens with the ethanol.

    My research is: I would like to make a suspension of SiO2 nanoparticles in water, and I have to use hydrophobic ones. That's the difficulty. One should use trick in order to force the particles into the liquid. I used ethanol, because this lowers the contact angle between the mixture and the particles, and then they go into the bulk liquid. And now I am inquirying what happens if the ethanol is removed? can I remove it simply by boiling? :confused: Will the particles stay into the water, or come out of it? I think they should come out.
    Yesterday I tried to boil the mixture, but I couldn't because it was overheated and didn't start to boil. But the particles remained in the liquid and so the ethanol.

    Boiling is no problem, today I carry out another measurement. I just don't know what I have to expect. Will the ethanol go away from the liquid, and if yes, how will I recognize? Through the particles behaviour? I hope this is also interesting for you!
    I am looking forward to making another boiling. :wink:
  15. May 23, 2006 #14


    User Avatar
    Science Advisor
    Homework Helper

    A sensitive, and somewhat less rigorous/practical method of determining the purity would be through index of refraction measurements, with pure distilled water as a control. The following page contains some methods for obtaining anhydrous ethanol, however, most of them may not be practical.

    Browse the page till you find "Purity"

  16. May 24, 2006 #15
    Right, then I think I will boil the mixture for several minutes and let's say, in every 3rd minute I will check and compare the refractive index. I will boil until I reach the refractive index of distilled water. Then it means that my mixture is free of ethanol.
    :surprised Ups, I should take into account the particles effect on refractive index! So I have to compare the mixture not with pure water but with water-particle suspension.
    Thanks so much. I hope I can get along.
  17. May 24, 2006 #16


    User Avatar
    Science Advisor
    Homework Helper

    Be sure to keep things at a relatively same temperature when comparing the index.

    Also, repeated measurements and incorporating quantitative analysis should also help in solidifying your data.

    hope you have lots of fun;)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Separate by boiling
  1. Boiling solvents (Replies: 11)

  2. Boiling points? (Replies: 5)

  3. Boiling Points (Replies: 3)

  4. Boiling point (Replies: 1)

  5. Boiling Point (Replies: 7)