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

How to distinguish Isopropanol?

  1. Nov 28, 2009 #1
    Hello:

    I have a liquid in a bottle. I want to know whether it is Isopropanol or not. I want to distinguish it among Methanol, Acetone and Ethelin.

    Can you help?

    Thanks.
     
  2. jcsd
  3. Nov 28, 2009 #2
    There are a ton of methods for this, but some are easier and more practical. What kind of lab equipment do you have available, if any?
     
  4. Nov 28, 2009 #3
    Thanks.
    I have those materials, and about stuffs, we've got Ni gas, ultrasonic bath and other ordinary equipments that can be found in any lab.
     
  5. Nov 29, 2009 #4
    I'm sure the best way would be to use spectroscopy (NMR, IR, etc.), but I don't know what type of lab you're in. Those machines can be found at most universities, which, if I had to guess, is the type of lab you mean.

    I'm not sure what to do with Ni gas or an ultrasonic bath, as I've only had one semester of chem lab so far, not counting high school. I can't really give any specific methods (besides spectroscopy) for identifying your solvents, but I know someone else here can probably suggest something.
     
  6. Nov 29, 2009 #5

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Methanol isn't soluble in hexanes. Acetone will test positive for a methyl ketone(google "iodoform test"). BP of ethanol and acetone are pretty different from each other and from IPA. Any help?
     
  7. Nov 29, 2009 #6
    Thanks a lot!

    Just to clear something: I know nothing about chemistry! I just wanted to know is there any "simple" way to distinguish Isopropanol from Acetone and Methane and Ethelin?
    I used it for cleaning something.

    Thanks again.
     
  8. Nov 29, 2009 #7
    Just to confirm, is it methane, or methanol that is one of the unknowns you want to eliminate? And what is "Ethelin"? ethylene (ethene) ?
     
  9. Nov 29, 2009 #8
    Thanks again.

    OK, we have four materials:
    Isopropanol, Acetone, Methanol, Ethylene.
    All of them are colorless, so I can't distinguish them by color.
    I can somehow distinguish by smelling them.
    But I want to know whether is there any other way to distinguish the Isopropanol among these materials?
    So, I am interested in distinguishing Isopropanol.

    Thanks alot.
     
  10. Nov 29, 2009 #9
    Well, at room temperature and pressure, ethylene is a gas, so that's easily identified. Acetone will have a characteristic IR stretch for the carbonyl, and methanol and IPA have a difference of around 20 degrees C for boiling point, so that's enough of a difference to separate them if you're careful.
     
  11. Nov 29, 2009 #10
    Thank you very much.

    I think I gave you a wrong name. Since it is a liquid, so I think it is Ethanol.

    What is this IR stretch? (as I said, I am not familiar with chemistry and I am using this IPA for cleaning only)

    Great! So far, I can distinguish methanol and IPA? BTW, can I simply pour some of these two liquids in separate beakers and then warm them up to boil? and I will notice which one boils first. Is this correct?

    Thanks a lot again.
     
  12. Nov 29, 2009 #11
    Considering you know very little about chemistry, boiling point might be the easiest way to distinguish between them. Like chemisttree said, the boiling points are pretty far apart, so you just need a thermometer and a hot plate (and eyes of course) to get a general idea of which is which.
     
  13. Nov 29, 2009 #12
    NMR all these other techniques are outdated. You don't even need to know anything about NMR, just take one and match it to a reference. NMR will tell you EXACTLY what you have.
     
  14. Nov 29, 2009 #13
    Very true, NMR is probably the best way to identify any organic compound. For the OP's purpose though, I think boiling point will suffice.
     
  15. Nov 30, 2009 #14

    Borek

    User Avatar

    Staff: Mentor

    Overkill. NMR is expensive when compared with other techniques proposed and is not easily available in every place.

    When my car has small scratch I am not thinking about building a robotic paint shop, I am rather looking for a small brush and a can of paint.

    --
     
  16. Nov 30, 2009 #15

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    OH! In that case do the following:

    1. Try to clean with your unknown.
    2. Examine the result. If it cleans it, get on with your life.
    3. If not clean, choose another solvent and GOTO 1....
     
  17. Dec 3, 2009 #16
    Good hints!
    Thanks all.
     
  18. Dec 4, 2009 #17

    -DB

    User Avatar

    But, IR would work just as well and it's not overkill.
     
  19. Dec 4, 2009 #18

    Borek

    User Avatar

    Staff: Mentor

    Any instrumental approach when simple chemical test will do is an overkill. Test tube and few mL of reagents are in the $ range, instruments are in the k$ range.

    Sure, if you have many such tests to do IR (or any other instrument) can be economically viable, but in the case of single analysis it is not.

    --
     
  20. Dec 5, 2009 #19
    To tell if it is IPA vs Acetone add a strong base or a strong acid.. this will cause the acetone to dimerize while not affecting the IPA

    Add the substance to a satured salt solution, if it stays on top it is either acetone, or IPA.. If it is methanol or ethanol... it should mix with the water completely.

    How to tell ethanol from methanol? I'd say try oxidizing it - ethanol when oxidized to acetaldehyde or acetic acid will smell of green apples or vinegar..
    methanol will produce formaldehyde and formic acid - this smells much different...

    I'm sure there are other ways, but I do not know what they are...

    perhaps oxidize the unknown alcohol with KMnO4- this will either produce a formate or an acetate... decarboxylation of an acetate salt will produce methane while the decarobxylation of formate salt will produce nothing..
     
  21. Dec 5, 2009 #20
    Dear all:

    Thank you very much again. That was a great help.

    Best.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook