0
$\begingroup$

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!

New contributor
user080522 is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
$\endgroup$
1
  • 1
    $\begingroup$ You have not clarrified what percentages you are talking about. Is it by weight or volume? $\endgroup$ 2 days ago

1 Answer 1

1
$\begingroup$

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.

$\endgroup$
3
  • $\begingroup$ 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
    2 days ago
  • $\begingroup$ Would you give the references for these values? $\endgroup$ 2 days ago
  • $\begingroup$ 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
    yesterday

Your Answer

user080522 is a new contributor. Be nice, and check out our Code of Conduct.

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.