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A test for hexan-1-ol and methylpentane-1-ol

  1. Oct 13, 2011 #1
    Hello!

    We will be given three bottles of an unknown organic compound, two will be a pure substance and the third will be a mixture of the previous two. How can you identify which bottle is the mixture? When doing the experiments, should you assume that the bottle which gives mixed results are the mixture? Is there a better and more scientific approach to the problem?

    What is a simple test to identify hexan-1-ol and methylpentane-1-ol? I know that the compounds have slightly different boiling point and solubility in water; however that is difficult to measure.

    Thank you in advance!
     
  2. jcsd
  3. Oct 14, 2011 #2
    If the components are completely unknown, I'd probably opt for physical tests. Read about colligative properties. This should indicate which bottle is the mixture fairly easily, but will not give any structural information. The problem is that if you have absolutely no idea of what could be in the bottles, random scanning for functional groups with different chemical tests could take a long time (but would work of course).

    It probably doesn't matter, but which of the 3 isomers of methylpentan-1-ol are you referring to?

    I can't think of a chemical test off the top of my head for those two, so bp may be the way to go. Maybe you could calculate the densities?
     
  4. Oct 14, 2011 #3
    Boiling point determination is probably the simplest/easiest method. I just checked wikipedia and it really depends on the isomer of methylpentanol (some are a good 10-20 degrees C away from heptan-1-ol).

    It could be a moot point though, if you know the BP's of each pure liquid than the mixed liquid will form something like an azeotrope and the BP will be different (typically lower but can be higher depending on conditions/mixtures etc) than either single liquid. If all you need to identify is the bottle with the mixed liquids then BP determination of all three bottles will give you a quick and dirty yes/no answer.

    As stated above, you may not be able to identify which bottle is which if the BP's are close together, but you should be able to identify the bottle containing the mixture.

    Thin layer chromatography may be another method, but it may be a pain to find the appropriate mobile phase and you may even need to do reverse phase TLC. Not a quick and dirty type of method unless you find literature describing your system. Then you can just do what they did. Otherwise it can take days/weeks to get the right solvent or solvent mixture to be able to resolve the constituents.
     
  5. Oct 15, 2011 #4
    Re: A test for hexan-1-ol and methylpentan-1-ol

    Hello! Thank you for the answers!

    Determining the boiling point of the different compounds is a great idea! There is only one minor issue. I know that the unknown substances may be hexane, hex-1-ene, hexan-1-ol and methylpentan-1-ol. In the experiment we can set up a bunsen burner, water in a beaker and the test tube in the beaker. Is is easy to calculate the b.p. of hexane and hex-1-ene since they have a b.p. bellow 100. How can we calculate the b.p. of hexan-1-ol and methylpentan-1-ol? Thank you in advance.

    We do not know the isomer of methylpentane-1-ol.
     
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