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I have a doubt about the correlation between eutectic plots and freezing point lowering. The freezing point lowering, as well as all colligative properties, is defined in the presence of a volatile solvent and a non volatile solute. In fact, by adding NaCl to water, a freezing point lowering of the resulting solution is obtained, which follows this trend:

enter image description here

However, a similar trend is also obtained by adding ethanol (solute) to water:

enter image description here

But ethanol is volatile, so it shouldn't be referring to freezing point lowering.

So, is it correct to talk about freezing point lowering in the context of these diagrams? Or do we speak about freezing point lowering only in reference to the phase diagram of a single substance, like this?

enter image description here

Luckenberg
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    Water is volatile as well as ethanol, so I don’t understand your issue here. – Jon Custer Feb 16 '23 at 19:47
  • @JonCuster essentially I made a distinction between the two cases:
    1. Volatile solvent (water) + non-volatile solute (salt)
    2. Volatile solvent (water) + volatile solute (ethanol)

    Therefore, in the first plot, that trend is given by the colligative property (freezing point lowering) because we have a non-volatile solute. Does the second graph always refer to freezing point lowering even if the solute is volatile?

     – Luckenberg Feb 17 '23 at 10:44
  • or more generally, is there never a correlation between freezing point lowering and eutectic plots? So the cryoscopic lowering can be identified only in the third plot, i.e. in that of a single substance? – Luckenberg Feb 17 '23 at 10:47
  • https://chemistry.stackexchange.com/questions/138726/do-we-have-some-rule-of-thumb-to-estimate-the-miscibility-of-metals/138742#138742 Might be of interest. – Jon Custer Feb 17 '23 at 12:53
  • @JonCuster Thanks for the reply. I tried to take a look but it doesn't seem to answer my doubt. – Luckenberg Feb 17 '23 at 15:06
  • btw to be more exact, its not adding salt to water but adding salt to ice at its freezing point that causes freezing point lowering. – porphyrin Feb 20 '23 at 13:51

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