ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: /0 on January 04, 2009, 08:11:56 am
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I just read through the Heinemann chapter on chromatography but there are a few things I don't understand.
In paper chromatography the solvent supposedly moves up the paper by capillary action... how exactly does capillary action work? Also, does this mean that if I leave a piece of paper in glass of shallow water, will the entire piece of paper eventually become soggy?
In column chromatography, if you have an adsorbant solid as the stationary phase, how does the mobile phase and the sample get through it? The only way I could see it happening if adsorbant solids are also porous, so wouldn't that mean adsorbant solids and porous solids are the same thing? Finally, it says if the particles in the solid are small, then resistance to flow is increased... but shouldn't resistance decrease??
Thanks
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The whole thing in chromatography is the interplay between adsorption and desorption
Adsorption really is a cover-all term for the H-bonding, dipole-dipole interactions and dispersion forces that attract the contents of the mobile phase to the stationary phase. Capillary action (from what I remember) is due to cohesion and adhesion of water molecules, which also relies on H-bonding.
The adsorbant solids are called adsorbant solids because they facilitate the adsorption of compounds in the mobile phase. The mobile phase and sample gets through it because as far as I know the solid is porous to th emobile phase.
The particles in the solid are small, which creates a greater surface area for adsorption to occur. The more adsorption occurs, the more 'resistance to flow' and hence the slower the mobile phase moves.
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In chromatography they use a SPECIAL kind of paper.....ordinary paper does not work.....believe...ive tried it!
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Oh ok, thanks for the explanation, capillary action seems like a tricky thing :)