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Ok, so I understand that solubility is a measure of how well a compound is solvated by the solvent. And dissociation is a measure of how much of a compound splits into its ionized forms. Does HF have high solubility, but low dissociation (weak acid)? How can that be?

Is it because it forms strong hydrogen bonds in solution and thus forms stable solvation spheres (solubility), but its high electronegativity prevents H+ atoms from leaving its vicinity (dissociation)?

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    $\begingroup$ Solubility and dissociation are totally unrelated things, like bulimia and amnesia. Sugar (or better yet, ethanol) dissolves extremely well, but does not dissociate at all. $\ce{AgCl}$ is an example of the opposite kind. $\endgroup$ – Ivan Neretin Oct 5 '16 at 13:24
  • $\begingroup$ @IvanNeretin - For chemicals which are considered to be ionic compounds solubility and dissociation are somewhat linked. $\endgroup$ – MaxW Oct 5 '16 at 13:55
  • $\begingroup$ Yeah, maybe, somewhat. BTW, would you consider $\ce{HF}$ ionic? To me, it isn't (that is, unless dissolved in water, but even then, not quite). $\endgroup$ – Ivan Neretin Oct 5 '16 at 14:09
  • $\begingroup$ see chemistry.stackexchange.com/questions/34818/… $\endgroup$ – Mithoron Oct 5 '16 at 20:09
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I think your last sentence answers your own question very well:

It is because it forms strong hydrogen bonds in solution and thus forms stable solvation spheres (solubility), but its high electronegativity prevents $\ce{H+}$ atoms from leaving its vicinity (dissociation).

Dissociation is one mechanism of dissolution, but not the only one. Also, however, the $\ce{H-F}$ bond strength is not solely determined by electronegativity.

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  • $\begingroup$ Agreed. Dissociation, and (in most cases) the resulting formation of separated charge pairs, is an important mechanism of solubility for many ionic species in polar solvents. $\endgroup$ – hBy2Py Feb 26 '17 at 18:37
  • $\begingroup$ Electronegativity is one thing, but bond strengths are also important to consider: see for example chemistry.stackexchange.com/questions/13609/… $\endgroup$ – orthocresol Feb 26 '17 at 18:56
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    $\begingroup$ @orthocresol, very good point. I kind of lumped bond strength with the difference in electronegativities of H and F in my mind, which isn't right. I made a slight edit to at least address that. Maybe not enough so, but for this specific question I hope that's sufficient. $\endgroup$ – airhuff Feb 26 '17 at 19:12

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