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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: dddawsonnn on December 08, 2012, 09:59:52 AM

Title: Acetic acid uptake in the presence of a 1-octanol film?
Post by: dddawsonnn on December 08, 2012, 09:59:52 AM

In an experiment where the uptake of acetic acid vapour is measured, why is the uptake into water increased when a 1-octanol film is present at the liquid-gas interface? Why does a small chain surfactant like that make the surface more permeable? Any help would be great?

Title: Re: Acetic acid uptake in the presence of a 1-octanol film?
Post by: discodermolide on December 08, 2012, 10:05:04 AM

Well I'm not 100% sure but I think it is to do with the partition coefficient.
The log_p of drugs is measured by partitioning between octanol and water.
It gives a measure of membrane permeability.
So, I hope this may help you.

Title: Re: Acetic acid uptake in the presence of a 1-octanol film?
Post by: curiouscat on December 08, 2012, 10:23:43 AM

This should happen if the product of the octanol-gas and water-octanol coefficients is greater than the water-gas coefficient. Not sure if it is.

Rather, you probably should use Henry's law at the G-L interface and Partition Coefficents at the L-L interface. Hence

[tex]
K_{Henry}^{Air-Octanol} \cdot  10^{P_{Oct/H2O}}    < K_{Henry}^{Air-H2O} \\
[/tex]
If I did my math right.  ;D

To use some numbers
[tex]
K_{Henry}^{Air-H2O} = 9.3E-2 (Pa \cdot m^3 mol^{-1})   \\
log P_{Oct/H2O}=-0.17
[/tex]

Too bad I can't find a Henry const. for acetic acid in octanol