When a ionic compound like $\ce{NaCl}$ dissolves, it doesn't always full dissociate due to ionic pairing. This is measured by the van 't Hoff factor. Now, this is what I'm looking at for my chem experiment - how does ionic pairing affect freezing point depression. With changing radius the ionic pairing should change, and hence the van 't Hoff factor and freezing point depression should vary. Is this a valid hypothesis?

If so, my main issue lies with what solvents does ionic pairing occur in? Does it occur in all 3 of polar protic, polar aprotic and non polar solvents? I'm having trouble deciding which type of solvent to use. I was initially modelling water, but now I don't know how solvent type affects ionic association. Any help is appreciated. I'm not sure if ionic pairing occurs at all in all 3 types of solvents.

  • $\begingroup$ When you dissolve $\ce{NaCl}$ in water it almost completely dissociates into free mobile ions! $\endgroup$ Sep 24 '20 at 10:31
  • $\begingroup$ Have you seen pubs.acs.org/doi/10.1021/cr040087x? $\endgroup$ Sep 24 '20 at 12:56
  • $\begingroup$ All of them, maybe? $\endgroup$ Sep 24 '20 at 14:46
  • $\begingroup$ The solubility depends roughly inversely on dielectric constant of the solvent, approx values are water 78, acetonitrile 37, acetone 21 cyclohexane/benzene, hexane all about 2 to 3. So generally soluble in high dielectric solvents and less so as this value decreases. (The electric field of ion spreads out into surrounding solvent, when dielectric is low this filed goes along way so ions will remain in contact with one another as energy to separate is too large vs energy to become separated & solubility is low) $\endgroup$
    – porphyrin
    Sep 24 '20 at 15:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.