To provide some context, I am trying to understand in better detail how oxygen from the lungs passes through a membrane and enters the vasculature in order to be transported via blood. I have generalized the question so that it is purely a physics conceptual question and does not require any sort of biological background...please ignore hemoglobin and red blood cells.

I am trying to picture at the molecular level what it means for a gas to be soluble in a liquid (on a scale from 0% solubility to 100% solubility). I will be relying on pictures to offer clarity.

Imagine we have a large planar membrane that is permeable to gaseous oxygen but impermeable to “liquid”. On the one side of the membrane is a purely gaseous-oxygen rich environment. On the other side of the membrane is a flowing-in-one-direction “liquid”. (I’m not really looking for a fluid dynamics analysis...so you can largely dismiss the “flowing” behavior of the liquid; I only included the flowing part to try and somewhat recreate the blood vessel description) General Description of Problem

What I am trying to understand is the following: how does dissolved oxygen arrange itself within a “liquid” depending on the oxygen’s solubility in the “liquid”. For example, what would the molecular arrangement of O2 within a liquid that exhibits 25% solubility for O2 (called Liquid A) look like as compared to a liquid that exhibits 50% solubility for O2 (called Liquid B)? Is it as straight forward as depicted in the following two pictures? i.e. for a given cross section, the number of O2 is simply more densely distributed throughout?

Oxygen's Molecular Arrangement In Different Liquids

In the event that this is true, I then wonder what exactly is happening that allows more oxygen to enter. Is solubility of a gas in a liquid largely determined by surface effects (i.e. solubility can be viewed as the probability of a gaseous molecule passing through the surface of the liquid)? Or is solubility of a gas in a liquid largely determined by “inside” effects (i.e. solubility can be viewed as the probability of a gaseous molecule remaining inside a liquid after it has passed through the surface)?

  • $\begingroup$ I think (some of them) dissociate. I could be wrong, but Na-Cl has a dissociation energy of 769 kJ, while O2 is 498, so it could dissolve the same way as NaCl $\endgroup$ – Mohammad Athar May 15 '19 at 16:17
  • $\begingroup$ I’m unfamiliar with the physical meaning of ‘disassociate’. Are you saying that O2 becomes 2 oxygen ions and then these ions subsequently equally distribute amongst the solvent? $\endgroup$ – S.Cramer May 15 '19 at 16:22

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