Can something that dissolves in water be hydrophobic?

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Discussion Overview

The discussion revolves around the question of whether a substance that dissolves in water, specifically carbon dioxide forming carbonic acid (H2CO3), can exhibit hydrophobic characteristics. Participants explore the implications of this question in the context of driving molecules to the surface of a liquid, with references to methods such as salting out and the properties of molecules.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions if H2CO3 molecules could be hydrophobic, given their formation from dissolved CO2 in water.
  • Another participant suggests that dissolved substances are generally uniformly distributed in a solution, with concentration gradients occurring only under specific conditions, such as the addition or removal of substances.
  • A later post references a paper discussing the use of salt to increase ionic strength and drive hydrophobic organic pollutants to the surface, seeking clarification on how this differs from the CO2 scenario.
  • Participants discuss the concept of "salting out" and inquire about methods to make a molecule hydrophobic without altering its fundamental structure.
  • It is noted that changing the properties of small molecules typically requires changing the molecule itself, while larger molecules like proteins present more complexity in this regard.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the hydrophobic nature of H2CO3 and the feasibility of driving it to the surface. There is no consensus on whether or how a molecule's properties can be altered to achieve hydrophobicity without changing the molecule itself.

Contextual Notes

Participants acknowledge limitations in their understanding of the mechanisms involved in molecular behavior in solutions, particularly regarding the conditions under which concentration gradients form and the complexities involved with larger molecules.

rwooduk
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This may be a really stupid question, but I'm going to go ahead anyway.

Say I have CO2 and dissolve it in water to give H2CO3, are / could the H2CO3 molecules be hydrophobic?

To put this in context I want to somehow drive the H2CO3 molecules to the surface of the liquid. Does this make sense? Would this be possible?
 
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rwooduk said:
Does this make sense?

Not much. Whatever is dissolved is more or less uniformly distributed. Sure, there can be a concentration gradient, but that happens when there is no mixing and you either add or remove the substance on the solution surface. Otherwise it is unlikely.
 
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Borek said:
Not much. Whatever is dissolved is more or less uniformly distributed. Sure, there can be a concentration gradient, but that happens when there is no mixing and you either add or remove the substance on the solution surface. Otherwise it is unlikely.

That's very helpful, thanks!

To be more specific, I am reading a paper that uses salt to increase the ionic strength of a liquid, so that hydrophobic organic pollutants in the liquid are driven to the surface. Please could you lend some insight into how this differs from the CO2 case above?

Again, apologies if this makes little sense.
 
Borek said:

Interesting. I see it has a similar method.

Do you know of any methods to make a particular molecule hydrophobic, so that it could be "salted out"?
 
I general you can't change properties of a molecule* without changing the molecule itself.

*At least for small, simple ones. when it comes to large ones like proteins things get more complicated, as a lot depends on what you mean by "changing" the molecule.
 
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Borek said:
I general you can't change properties of a molecule* without changing the molecule itself.

*At least for small, simple ones. when it comes to large ones like proteins things get more complicated, as a lot depends on what you mean by "changing" the molecule.

Hm, that's unfortunate, but okay you have been very helpful, thanks again!
 

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