Reduction in gas concentration of water with solutes

[rwooduk]

When salt (polar) is added to water (polar) it makes the water more polar and causes the oxygen (non-polar) to be "driven" from solution. So I'm assuming this is an electrostatic repulsion(?).

Aside from salt what other solutes would cause this to happen? Would a solute have to have very polar molecules? In particular would phenol, which can dissolve in water due to hydrogen bonding, but is mostly non-polar cause this 'degassing' effect?

Any feedback on the above would be very much appreciated.

 

[Christopher Grayce]

The origin of salting out phenomena is still a subject of active debate and study, so I don't think there is any definitive answer to your question, although theories, both serious and pop science, abound. The bottom line appears, so far, to be that certain ionic solutes cause an enhanced "structuring" of the water and the solubility of hydrophobic solutes (like O2) may be decreased for no more complicated reason than that the effective volume of water in which they can dissolve is reduced. What's important to your question, therefore, is whether phenol is a more "structure-making" solute than, say, NaCl. It probably isn't: generally larger solutes appear to be less likely to be "structure making."

 

[rwooduk]

The origin of salting out phenomena is still a subject of active debate and study, so I don't think there is any definitive answer to your question, although theories, both serious and pop science, abound. The bottom line appears, so far, to be that certain ionic solutes cause an enhanced "structuring" of the water and the solubility of hydrophobic solutes (like O2) may be decreased for no more complicated reason than that the effective volume of water in which they can dissolve is reduced. What's important to your question, therefore, is whether phenol is a more "structure-making" solute than, say, NaCl. It probably isn't: generally larger solutes appear to be less likely to be "structure making."

Many thanks for the reply that's extremely helpful. I'll see if I can find some papers on salting out, however the ones I've seen don't really talk about a reduction in gas concentration. Could you perhaps explain the "structuring" aspect a little more?

 

[Borek]

Could you perhaps explain the "structuring" aspect a little more?

Google solvation, solvation shell - molecules involved in solvation are no longer part of the bulk solvent..

 

[rwooduk]

Google solvation, solvation shell - molecules involved in solvation are no longer part of the bulk solvent..

Excellent, will do. Thanks again.