What is the difference between salting in and salting out electrolytes?

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Discussion Overview

The discussion revolves around the concepts of salting in and salting out electrolytes, particularly in relation to their effects on surfactants and solution stability. Participants explore the mechanisms behind these phenomena and seek to clarify their differences and implications in various contexts.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions the classification of NaOH as a salting in electrolyte, contrasting it with Na2SO4, Na2CO3, and NaCl, and seeks to understand the differences between salting in and salting out electrolytes.
  • Another participant expresses uncertainty about the meaning of salting in and attempts to relate it to the concept of salting out in the context of surfactants.
  • A participant suggests that salting out leads to surfactants being forced out of solution, while salting in may enhance solution stability, but they find a lack of experimental justification for this mechanism.
  • One contribution discusses the principle of "like dissolves like," indicating that polar solutions can better solubilize polar substrates, and that adding salt to moderately polar solutions decreases solubility, while it may increase solubility in very polar solutions absent a common ion effect.
  • A participant references a paper suggesting that salting out is related to an imbalance in chemical potential due to the salt's solubility around surfactant headgroups, questioning why the salt would be less soluble in that context.
  • Another participant elaborates on the organization of water near surfactant headgroups, proposing that this organization may hinder interactions with ions from the salt, though they acknowledge this explanation may lack robustness.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms and implications of salting in and salting out, with no consensus reached on the definitions or effects of these processes.

Contextual Notes

Some discussions involve assumptions about the polarities of solutions and the interactions of ions, which may not be universally accepted or fully explored. The explanations provided may depend on specific definitions and contexts that are not uniformly agreed upon.

thearny
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Recently I read an article describing NaOH as a salting in electrolyte, and I have long held the belief that Na2SO4, Na2CO3 and NaCl etc.. are salting out electrolytes. I cannot see any reason why NaOH should be different. What is the difference between salting in and salting out electrolytes, and what affect do they have? - Any thoughts much appreciated.
 
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Do you know what salting in means?
 
Not really. I can't quite envisage it. Salting out (I am applying this to surfactants) means that the surfactant is dragged/forced out of solution. So salting in presumably strengthens the solutions stability, but I can see no justification (experimentally) or mechanism for that.
 
Like dissolves like. Very polar solutions are better at solubilizing a polar substrate than less polar ones. So, adding salt to an aqueous solution of something that is only moderately polar (like a surfactant) will make it less soluble. Adding salt to something that is very polar can actually increase its solubility provided there is no 'common ion' effect.
 
I read a paper yesterday suggesting that salting out is due to an imblance in the chemical potential caused by salt being less soluble by the headgroups. The chemical potential explanation I can accept, but why would the salt be less soluble around the headgroup? - It just about fits... Many thanks.
 
Discussion about headgroups implies a surfactant is discussed.

The structure of water near the headgroup is somewhat organized. This somewhat organized water can potentially have less interaction with another ion in solution... the hydrogen bonds that 'organize' this water are somewhat less available to interact with the soluble ion from the salt. It does sound a bit like handwaving though.
 

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