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Is this mixture hydrophilic or hydrophobic?

chromatography isopropyl solubility mobile phase

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#1 liika

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Posted 02 April 2014 - 04:58 AM

Hi,

 

i'm doing a report for a biochemistry lab where we performed TLC. for the mobile phase we used a mixture of isopropyl, water and amonia (in a ratio of 8:1:1, 8 being the isopropyl). I thought that this mixture is hydrophilic, since all of it's components are, but my tutor/instructor says that isopropyl is extremely hydrophobic, and so the mixture is also hydrophobic. i googled it and from what i saw IT IS considered hydrophilic.

so, if you can tell me what's right, and why, i'll be grateful:)

 

thanks


Edited by liika, 02 April 2014 - 08:40 AM.


#2 hobglobin

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Posted 02 April 2014 - 08:58 AM

I wonder how a mix containing water can be hydrophobic except you added a surfactant.
Anyway you can explain it to your supervisor using the functional groups and physical properties:
A water molecule is not linear and the oxygen atom has a higher electronegativity than hydrogen atoms, the oxygen atom carries a slight negative charge, whereas the hydrogen atoms are slightly positive. As a result, water is a polar molecule (copied from wikipedia).

I presume that you meant with isopropyl "isopropyl alcohol". The functional group of the unpolar carbon chain (C3) is here the polar OH- group (similar reason as in the water molecule) in the middle which makes it a mostly polar molecule, since the carbon-chain is short enough to play a minor role. Longer alcohols become more and more insoluble in polar liquids such as water as the long unpolar carbon chains "dominates" more and more due to it's length (a chemist would kick me now and explain it better wink.png ; better look it up the effects of long carbon chains in molecules with polar functional groups).


One must presume that long and short arguments contribute to the same end. - Epicurus
...except casandra's that belong to the funniest, most interesting and imaginative (or over-imaginative?) ones, I suppose.





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