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Author: Subject: Salting out isopropyl alcohol
ampakine
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[*] posted on 19-7-2011 at 09:05
Salting out isopropyl alcohol


I read on its wiki page that isopropyl alcohol is far less soluble in saline water than pure water and will form its own layer when salt is added to a concentrated IPA solution. I tried this just there but could not see any layers. I considered that it may just be difficult to see because they are both clear and colorless liquids but I've seen bilayer mixtures of white spirit and water before and remember the interphase between the 2 layers being highly visible. Is it just harder to see the interphase between these 2 solvents because they are so similar in molecular weight?


[Edited on 19-7-2011 by ampakine]
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gsd
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[*] posted on 19-7-2011 at 09:36


Quote: Originally posted by ampakine  
Is it just harder to see the interphase between these 2 solvents because they are so similar in molecular weight?


[Edited on 19-7-2011 by ampakine]


???

Water - H2O - MW:18
IPA - CH3CHOHCH3 - C3H8O - MW:60

If you are unable to see layers then the simple explanation is they are not yet formed.

Just keep adding more salt till you see the separation.

gsd
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cyanureeves
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[*] posted on 19-7-2011 at 10:40


true i didnt see any layers form either so i assumed all the water was in the salt slurry. i added about a quarter ways up of salt in a bottle of 91% isopropyl and syphoned out the alcohol and stopped before i got to the salt.
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HexJam
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[*] posted on 21-7-2011 at 23:52


I've seen IPA split into 2 layers if you use MgSO4, however they're -very- difficult to spot. I remember trying this a while back and totally missed seeing it the fist few times and was baffled what was going on. Try leaving your beaker to sit and settle for a while then very gently swirl it to help you see the layers, your water might also just be a small clear blob on the bottom of your flask.
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UnintentionalChaos
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[*] posted on 22-7-2011 at 08:08


NaCl will only remove water up until ~91%. After that, you need to switch to NaOH. See http://www.sciencemadness.org/talk/viewthread.php?tid=13680

Difficulty in seeing the difference between phases comes from similar indexes of refraction.

[Edited on 7-22-11 by UnintentionalChaos]




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FrankRizzo
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[*] posted on 22-7-2011 at 20:22


I believe a laser pointer aimed through the solution could show you the boundary. There should be a slight bend in the line of light as it hits the boundary.
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