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Re: O2 and CO2 solubilities

> Date: Wed, 21 Mar 2001 10:50:06 EST
> From: K12Trout at aol_com
> Subject: Re:O2 and CO2 solubility
> i don't know what exactly is said in limnology but, 
> unless i'm gravely mistaken, it makes no chemical sense
>  for co2 to be very soluble in water or for O2 not to be
>  soluble.  oxygen is a very polar molecule and forms 
> hydrogen bonds with water very easily.

	O2 isn't polar.  It's a symmetrical diatomic molecule.

>  carbon dioxide,
>  despite carying two polar oxygen groups, is actually a 
> linear molecule and ends up have very little dipole 
> moment.

	It has no dipole moment at all, _but_ it has _two_ dipoles
back to back, with the C slightly positive and the O's slightly negative.
These charges let CO2 form associations with the water molecules'
dipoles and probably some hydrogen bonding as well.

>  it is therefore hydrophobic.

	No it isn't.

>  as for
>  "diffusivity", the diffusion constant for oxygen in 
> water is, if i remember correctly, on the order of 
> 10^-15


>, ie very very very fast.  i have witnessed this 
> myself from fluorescence quenching experiments.  if, on 
> the other hand, we are talking about diffusion through 
> membranes, it is true that co2 will pass readily through
>  a membrane for exactly the reason it is not readily 
> soluble in water.

	This depends on the membrane.  Different membranes let different
things through.

>  all of this discussion is, however, 
> largely inaccesible and totally unnecessary in the face
>  of the common wisdom on the mailing list.

	The point is that CO2 _is_ a lot more soluble in water than O2.

Paul Sears        Ottawa, Canada