Would Solvent Move Through a Membrane to Air in Osmosis?

[u0362565]

Hi all,

In osmosis a solvent moves across a semi-permeable membrane when the solvent is on both sides of the membrane but the concentration of the solute differs. Normally solvent moves from the side with high osmotic pressure (solvent containing less solute) to side containing more solute. However if one side of the membrane contained a solution and the other side was just air would the solvent move through the membrane to the air side by diffusion? If it did then immediately the solvent that passed through which would not not contain solute would move back to the side with higher solute concentration due to osmosis? If no water would move across why not?

 

[Greg Bernhardt]

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[epenguin]

Hi all,

In osmosis a solvent moves across a semi-permeable membrane when the solvent is on both sides of the membrane but the concentration of the solute differs. Normally solvent moves from the side with high osmotic pressure (solvent containing less solute) to side containing more solute. However if one side of the membrane contained a solution and the other side was just air would the solvent move through the membrane to the air side by diffusion? If it did then immediately the solvent that passed through which would not not contain solute would move back to the side with higher solute concentration due to osmosis? If no water would move across why not?

By 'air' you have an essentially infinite reservoir for a volatile solvent to move into so eventually it all dries out if the air is dry. For your 'moving back' question, things like this are always happening both ways at the same time, but happening more one way than the other until equilibrium is reached (which it never would be with and infinite reservoir of air). But as the solute gets more concentrated it would hold on more to the solvent and the process would slow down. Probably something else would happen, the solvent would crystallize.

You do not need a membrane for this to happen. Your setup reminds me of 'microdialysis' as well as of vapor diffusion used for crystallizing proteins by slowly increasing their concentration and that of the salts with them. http://en.m.wikipedia.org/wiki/Protein_crystallization#Vapor_diffusion