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If a solute that dissolves in a liquid solvent has reached high enough levels to cause saturation within the solution, is it possible for the remaining solute particles to form an evenly distributed phase from top to bottom similar to that of a colloid (where settling would not occur or take very long to occur)? I realize behavior varies depending on the solute and solvent in question, I am just curious if this is possible. Thanks so much!

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  • $\begingroup$ In inorganic qualitative analysis this happens frequently. The precipitates are highly insoluble so they form many small particles instead of a few large ones. A centrifuge is then used to force the particles to settle since they wouldn't own their own. $\endgroup$ – MaxW Feb 21 '17 at 21:10
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The density of the solute relative to that of the solvent will primarily determine whether the excess solute will float, sink or tend to disperse throughout the solution. Additionally, the particle size and porosity will play a role in the rate of settling or floating, as will the viscosity of the solvent, but it is the density that determines whether the particles will float or sink.

But, the answer to your question is no. Even if the density of the undissolved solute is essentially the same as that of the solvent, and the undissolved solute is very fine, then you could have a uniform looking solution, but it would still be a two-phase solution, with a solid phase suspended in a liquid phase.

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  • $\begingroup$ Okay I see, sorry I was communicating a bit vaguely, I meant to say could the solid particles of the remaining solute form their own roughly evenly distributed phase from top to bottom, suspended by the separate liquid solvent phase that's also spread from top to bottom. It seems that if the density and other factors are aligned, it is possible for the remaining solute to distribute roughly evenly from top to bottom within their own phase and that it is possible that this solute phase wouldn't settle easily? $\endgroup$ – Jon Yang Feb 21 '17 at 21:18
  • $\begingroup$ Speaking of the densities, is there a general minimum in difference of density of solute and solvent for settling to occur, assuming in this situation that density is the primary determinant of that? Thanks so much again for your insight, it has been a huge help! $\endgroup$ – Jon Yang Feb 21 '17 at 21:23
  • $\begingroup$ Regarding your first comment, yes you are correct, and I kind of thought that was what you really meant. Technically there are still two phases, but it can appear as a homogeneous suspension. Regarding your second comment, there is no general difference in densities, they just have to be "close" and it helps if the undissolved particles are small and the solvent is viscous. I hope that helps! $\endgroup$ – airhuff Feb 21 '17 at 21:54
  • $\begingroup$ Thank you so much again for continuing to check back and sharing your insight, it really means a lot and it's helping a ton! Would you say something like 338 daltons (solute) vs 46 daltons (solvent) be close enough? If the solute molecules are very small in terms of volume, perhaps that would change things given their seemingly disparate densities? Unfortunately, the solvent isn't viscous :( $\endgroup$ – Jon Yang Feb 21 '17 at 22:19

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