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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.
andselisk
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TeslaBolt
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    related https://chemistry.stackexchange.com/questions/72264/what-is-happening-in-this-video-of-solvated-electrons-donated-from-sodium-in-amm – Mithoron Feb 11 '22 at 19:12
  • Volume always changes when you dissolve something, what's the point of this question? – Mithoron Feb 11 '22 at 19:13
  • Rather just > than >>, as the latter implies formation of gaseous phase. – Poutnik Feb 12 '22 at 13:08
  • 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. – TeslaBolt Feb 12 '22 at 13:50
  • 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. – Curt F. Feb 17 '22 at 16:47
  • @CurtF. If i consider only ammonia for an instance, then i am just adding a metal cation and a electron in between which also creates dipole-dipole attractions and is kind of filling voids present in solution so i think there should be a slight decrease or atleast not a large increase. – TeslaBolt Feb 17 '22 at 17:10

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