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I would like to ask a chemistry question: The freezing point of methanol aqueous solution between 0% and 90% is lower than that of ethanol aqueous solution; but why is the freezing point of ethanol aqueous solution between 90% and 100% lower than that of methanol aqueous solution?

Thanks in advance!

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    $\begingroup$ You have not clarrified what percentages you are talking about. Is it by weight or volume? $\endgroup$ Commented Aug 6, 2022 at 22:35

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The OP's claim that "The freezing point of methanol aqueous solution between 0% and 90% is lower than that of ethanol aqueous solution" is correct as data given in Engineering Tool Box (methanol/water) and Engineering Tool Box (ethanol/water): $$ \begin{array}{c|c|c|c} \text{% MeOH (v/v) or (w/w)} & \text{The freezing point } (\pu{^\circ C}) & \text{% EtOH (v/v)} & \text{The freezing point } (\pu{^\circ C}) \\ \hline 0 & 0 & 0 & 0 \\ 13 \text{ or }10 & -7 & 10 &-4 \\ 24 \text{ or }20 & -18 & 20 & -9\\ 35 \text{ or }30 & -26 & 30 & -15\\ 46\text{ or }40 & -40 & 40 & -23\\ 56\text{ or }50 & -54 & 50 & -32\\ 66\text{ or }60 & -71 & 60 & -37\\ 75\text{ or }70 & -82 & 70 & -48\\ 83\text{ or }80 & -87 & 80 & -59\\ 92\text{ or }90 & -90 & 90 & -73\\ 100 & -98 & 100 & -115\\ \hline \end{array} $$

However the two last data points are simply the comparison of the freeing point of $100\%$ methanol and that of $100\%$ ethanol. Evidently, the freeing point of $100\%$ methanol is greater than the freeing point of $100\%$ ethanol (See Table of Melting points of alcohols). Thus, there is not an unusual reason for this change in trend.

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  • $\begingroup$ Methanol water has a eutectic 157 K ~0.88methanol; Ethanol water 150 K ~0.80ethanol. Just to show fp depression works both ways. $\endgroup$
    – jimchmst
    Commented Aug 7, 2022 at 3:45
  • $\begingroup$ Would you give the references for these values? $\endgroup$ Commented Aug 7, 2022 at 7:47
  • $\begingroup$ I googled it; look it up. You should have been suspicious that the freezing point tables you listed showed no eutectic and researched a bit further. When a source seems to violate what one thinks he knows about chemistry it is time to look further; one or the other or perhaps both needs some refining. $\endgroup$
    – jimchmst
    Commented Aug 7, 2022 at 22:21

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