Colligative properties and binary phase diagrams

I'm having troubles with colligative properties and how to relate them to binary liquid-vapour and solid-liquid phase diagrams.


First of all, in my book it is indicated that colligative properties are defined in the presence of a non-volatile solute, so much so that it simultaneously determines a lowering of the vapor pressure, an ebullioscopic raising and a cryoscopic lowering of the solution with respect to what happens in the ambit of the pure solvent. But this does not seem entirely correct.
In fact, even a water-ethanol mixture can undergo cryoscopic lowering, i.e. a eutectic is reached, although both constituents are volatile (therefore the solute is volatile, whether it is water or alcohol).
The same argument can be made, for the same volatile mixture, in the context of boiling point:
[![](https://i.stack.imgur.com/iw0qJ.jpg)](https://i.stack.imgur.com/iw0qJ.jpg)


to the right of the azeotrope, an ebullioscopic rise is observed even though both compounds are volatile.


So, actually, when do these two colligative properties manifest themselves? Is it really necessary for the solute to be volatile?


The other doubt, as already mentioned, concerns about the correlation between state diagrams and the same colligative properties.


[![](https://i.stack.imgur.com/BqGG8.jpg)](https://i.stack.imgur.com/BqGG8.jpg)


This state diagram refers to two substances that are miscible in the liquid state, but immiscible in the solid state, and which reach a eutectic, so the graph is based on the cryoscopic lowering. If freezing point lowering is defined only in the presence of non-volatile solutes, how does this graph hold true even in the presence of a volatile solute? (as in the case before, I mention the water+ethanol mixture, which reaches a eutectic)


[![](https://i.stack.imgur.com/iyEZK.jpg)](https://i.stack.imgur.com/iyEZK.jpg)


This other graph, on the other hand, is a state diagram which refers to two miscible substances both in the liquid state and in the solid state. In this case a eutectic is not achieved and the graph, at least at first glance, is not based on the freezing point lowering, given that starting from A and progressively adding B, the melting/freezing temperature of the mixture increases.


Why is there this difference?


Thanks for every help, because i'm stuck.


