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My teacher said unexplainedly that when alkali metals dissolves in liquid ammonia, there is a large increase in the volume. I found a paper that confirms this fact [1]:

In the course of recent research it was necessary to obtain the volume change associated with the solution of lithium, sodium and potassium in liquid ammonia. That the solution of these metals in liquid ammonia is accompanied by a relatively large increase in volume has long been known. From the densities of sodium and potassium solutions it has been shown that these volume changes pass through a maximum at about $3N.$

I am still unaware of the reason for the increase of final volume $V_\mathrm{f}$ after reaction between metal $\ce{M}$ and liquid ammonia $\ce{NH3}$:

$$V_\mathrm{f} \gg V_0(\ce{M}) + V_0(\ce{NH3})$$

Reference

  1. Marshall, P.; Hunt, H. Volume Changes for Metal Solutions in Liquid Ammonia. J. Am. Chem. Soc. 1955, 77 (19), 5016–5016. DOI: 10.1021/ja01624a022.
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    $\begingroup$ related chemistry.stackexchange.com/questions/72264/… $\endgroup$
    – Mithoron
    Feb 11, 2022 at 19:12
  • $\begingroup$ Volume always changes when you dissolve something, what's the point of this question? $\endgroup$
    – Mithoron
    Feb 11, 2022 at 19:13
  • $\begingroup$ Rather just > than >>, as the latter implies formation of gaseous phase. $\endgroup$
    – Poutnik
    Feb 12, 2022 at 13:08
  • $\begingroup$ i just meant a large increase in volume i don't know if a gaseous phase is formed or not,maybe something is linked to gaseous phase for the increase. $\endgroup$
    – TeslaBolt
    Feb 12, 2022 at 13:50
  • $\begingroup$ Excellent question. One reason I can think of is that the packing of atoms in solid alkali metals is pretty dense. When dissolved in ammonia, this packing is undone, creating a solvated alkali metal cation and a solvated "electron". Each of these solvated ions, consisting of shells of ammonia molecules presumably takes up a bunch of space. $\endgroup$
    – Curt F.
    Feb 17, 2022 at 16:47

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