chromatography Watch

Izzyduignann
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So i am currently doing my Btec Science (a level) assignment on chromatography. we have had to separate a range of amino acids and plant pigment using paper chromatography, and then do plant pigment with TLC. as part of the assignment i have got to refer to polarity and non polarity of the mobile phase and stationary phase and also molecules when explaining why paper chromatography is more suitable for separating amino acids. it has really confused me. could someone please help me )
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TheMythicalBeast
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(Original post by Izzyduignann)
So i am currently doing my Btec Science (a level) assignment on chromatography. we have had to separate a range of amino acids and plant pigment using paper chromatography, and then do plant pigment with TLC. as part of the assignment i have got to refer to polarity and non polarity of the mobile phase and stationary phase and also molecules when explaining why paper chromatography is more suitable for separating amino acids. it has really confused me. could someone please help me )
https://www.chemguide.co.uk/analysis...paper.html#top

These are notes for the A Level version of chromatography, so some things you may not need to know, but here you’re looking at paper chromatography and how it works, talks about mobile and stationary phases and explains the polarity links. You probably know that non-polar molecules have no “poles” so the electrons are pulled equally by each of the atoms in the bond, hence there’s no kind of charge. Polar molecules, eg H2O, have dipoles due to one of the atoms pulling the electrons in the bond more than the other atom, hence creating a slight +ve or a slight -ve charge. It’s the same concept really with any substance that you use. If you have any more questions feel free to ask
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Izzyduignann
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(Original post by TheMythicalBeast)
https://www.chemguide.co.uk/analysis...paper.html#top

These are notes for the A Level version of chromatography, so some things you may not need to know, but here you’re looking at paper chromatography and how it works, talks about mobile and stationary phases and explains the polarity links. You probably know that non-polar molecules have no “poles” so the electrons are pulled equally by each of the atoms in the bond, hence there’s no kind of charge. Polar molecules, eg H2O, have dipoles due to one of the atoms pulling the electrons in the bond more than the other atom, hence creating a slight +ve or a slight -ve charge. It’s the same concept really with any substance that you use. If you have any more questions feel free to ask
Thank you so much you help has been amazing. just one question which i can't quite get my head around. so if the solvents are all polar which i used in my paper chromatography with amino acids, will the movement of the amino acids not travel fast/far?
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TheMythicalBeast
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(Original post by Izzyduignann)
Thank you so much you help has been amazing. just one question which i can't quite get my head around. so if the solvents are all polar which i used in my paper chromatography with amino acids, will the movement of the amino acids not travel fast/far?
The reason that mixtures separate/move up is because different substances (so amino acids in your case) have a different, unique balance between its attraction in the stationary phase and the mobile phase. So the stationary phase would be paper or silica, whatever you’re putting the solvent onto, and the mobile phase would be your solvent. If your solvent/mobile phase is polar, then your stationary phase is non-polar. The amino acids will move up depending on the polarity, so the most polar amino acid will move up more than any of the others, and the least polar will be the closest to your starting point.

It’s a bit weird to get your head around it, but the simple explanation is that if the substance tested is polar, it will interact most with the polar phase (if mobile is polar, then it will move up a lot, if stationary is polar then it might still move up but it’ll be much less of a distance). The amino acids you used all probably have a different polarity so you can say which one is most or least polar, I’ll try to attach a picture with an example
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TheMythicalBeast
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Izzyduignann
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(Original post by TheMythicalBeast)
Name:  1BC770F2-F5E7-4F94-A6A6-8E39D0015EBE.jpg.jpeg
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if a solvent is
5.5 parts cyclohexane and 4.5 parts ethyl
acetate is this polar or non polar?????
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