What happens to the conductivity when a solution of sodium in liquid ammonia at $\pu{-33^{\circ}C}$ (Boiling point of ammonia) is further cooled?

I expected the solution to behave as any other solution that conducts through ions due to the $\ce{[Na(NH3)_x]+}$ and the solvated electrons $\ce{[e(NH3)_y]-}$, such that conductivity increases on decreasing the temperature due to lesser collisions between ions resulting in higher mobility.

However it seems to be the opposite. I tried going through some papers via Google Scholar however I couldn't make out much from the preview alone

  • $\begingroup$ A solution of sodium in liquid ammonia contains $\ce{Na^+}$ cations but no anions. It just contains solvated electrons. This may be the reason why its conductivity decreases by cooling it further down. $\endgroup$
    – Maurice
    Jul 8, 2021 at 21:03
  • $\begingroup$ Could it be related to the lower solubility of Na at the lower temperature, or a phase transition? researchgate.net/figure/… $\endgroup$ Jul 8, 2021 at 21:17
  • $\begingroup$ @Maurice the solvated electrons don't behave as anions? $\endgroup$ Jul 9, 2021 at 4:40
  • $\begingroup$ Ion pairs Na+(solv)e-(solv) may be more preferred at lower temperature. As conditions for forming ion pairs are substance specific. $\endgroup$
    – Poutnik
    Jul 9, 2021 at 8:53
  • $\begingroup$ The ion mobility decreases with temperature, hence the conductivity goes down, period. Watery solutions usually conduct by protons changing their hydrogen bonds on one side into covalent, and vice versa, i.e. it's actually electrons who are moving. Totally differenct concenpt. $\endgroup$
    – Karl
    Jul 9, 2021 at 11:02


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