I would like to understand when the water is boiled only pure vapor is produced and ions do not exist with vapor. Why?

Can't the ions stick to water vapor?


Are Na+ and Cl- have boiling points? Why do they not evaporate?

  • 2
    $\begingroup$ Vaporisation involves a molecule dehydrating. The hydration free energy of Na and Cl is something like $10\times$ that of a water molecule. $\endgroup$ – lemon Dec 14 '18 at 16:24
  • $\begingroup$ This answer here chemistry.stackexchange.com/questions/31932/… shows how the ions are "bound" by H2O $\endgroup$ – anna v Dec 14 '18 at 18:22
  • $\begingroup$ I believe you can see salt evaporating from the sea level, on a windy day. It seems to keep close to the surface though. $\endgroup$ – Ján Lalinský Dec 14 '18 at 21:08

The ionic bond between sodium and chlorine ions is way stronger than the dipole-dipole interaction between water molecules. As a result, sodium chloride has much higher melting and boiling point than the boiling point of water.

So, sodium chloride does not vaporize at 100 degree centigrade under normal pressure.

  • 3
    $\begingroup$ But NaCl is not solid at the water. It's Na+ and Cl- $\endgroup$ – MEng Dec 14 '18 at 16:18
  • $\begingroup$ You cannot vaporize an isolated Na$^+$. It must take one Cl$^-$ with it. Once it leaves the water phase and goes into the vapour, it will solidify. This indecent can indeed happen as some ions will have enough kinetic energy (due to Maxwell-Boltzmann distribution) to leave the water liquid phase. $\endgroup$ – Archisman Panigrahi Dec 14 '18 at 16:28
  • $\begingroup$ But NaCl is not solid at the water. It's Na+ and Cl- – The sodium cations and chloride anions in solution are hydrated: i.e. they are surrounded by a mantle of water. What's more, the hydrated ions still interact, that is attract each other. Your view of a solution is risibly simple. Read up about watery, ionic solutions, ionic strength and such like. $\endgroup$ – Gert Dec 14 '18 at 16:39
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    $\begingroup$ @ArchismanPanigrahi You can absolutely evaporate a charged ion. It happens all the time in my simulations. $\endgroup$ – lemon Dec 14 '18 at 16:59
  • 1
    $\begingroup$ @Gert NaCl has a solubility product of about 40, I can't see how Na-Cl interactions are relevant here... $\endgroup$ – lemon Dec 14 '18 at 17:00

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