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Chromatography as a separation techinique

  1. Nov 8, 2009 #1
    1. The problem statement, all variables and given/known data
    In detail, explain the theory behind the use of chromatography as a
    a.)separation technique.
    b.) identification technique.

    2. Relevant equations



    3. The attempt at a solution

    I know that chromatography can be used as a separation technique and also indetification technique. I'm just unsure when the question said in detail, explain the theory. But this was my answer.
    a. The theory behind chromatographys as a separation tehnique is to separate different types of organice compounds. It includes two phasses to separate the the compounds. The phases is the stationary phase which is the solid like alumina. The other phase is the moving phase which includes the solvents. When the mixture is passed through the stationary phase, different compounds will travel at different rate down the alumina. Sometimes more solvent is needed for different polarity of the compounds. Therefore, this technique can be used as a separating thenique.

    b. The theory behind the chromatogaphy can be used as a identification tehnique is that it can show what kind of compound is in the mixture by using a paper chromatography. The mixture is dotted on a special type of paper and then dipped into a solvent. The solvent will move up the paper and lines of colors will appear. The different types of colors are evidence as the different type of compounds included in the mixture. When compared the pigment of the lines can be identified. Therefore, this technique can be used to also identification tehnique.
     
  2. jcsd
  3. Nov 8, 2009 #2

    chemisttree

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    I'm going to play a bit of the Devil's advocate so don't get mad!

    You are pretty spot on concerning your description of chromatography as a separation technique.

    However....

    As an identification technique, how would you distinguish between two different compounds that had identical Rf values? Will the appearance of a spot help you identify an unknown spot? If you performed a certain reaction and you expected two possible products yet your chromatogram yields three spots, would you be able to identify all three compounds? How?
     
  4. Nov 8, 2009 #3
    ehhe I'm not goin to get mad. I appreciate your help!

    I truly don't know how to distinguish between two different compounds that had identical Rf values. I would do the experiemtn again? Can they be the same compounds or are closely related? Yes, the appearance of the spot would help me identify the unknown spot because same spot but diffent colors can also distinguish between the two. as for 3 spots, I can use a different solvents to determine the three compounds.
    Thank you for responding, your questions just make me clearer about the identification process.
     
  5. Nov 8, 2009 #4

    chemisttree

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    You were obviously using chromatography to separate the colors in a mixture. It can also be used to separate colorless compounds. How might you tell them apart?

    You are on to something here. Changing the parameters like solvent polarity or column chemistry can sometimes be used to separate two closely spaced spots. Google "two dimensional chromatography" for some background. Still, are they identified?
     
  6. Nov 8, 2009 #5
    use different temperature. The distance they travel is then used to calculate an Rf value which can be compared to known values to identify a substance. the 3 spots may or may not be identified. Can it be contaminated with an outside source, that's why there's 3 rather than 2?
     
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