Ethanol-water solution has a flash point lower than ethanol's boiling point in almost all cases. So how is the fractional distillation of the solution possible? Why doesn't the solution ignite? Is it because there is no oxygen for the flames to be sustained?

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    $\begingroup$ The flash point is the temperature where an external ignition source can set the vapour alight, not the temperature where the vapour spontaneously ignites. If you do a distillation using a naked flame and the vapour leaks, this is a problem. But you should never use naked flames to distill flammable liquids. And you won't have a problem is the vessel doesn't leak. $\endgroup$
    – matt_black
    Commented Aug 27, 2021 at 16:17

1 Answer 1


According to Wikipedia, ethanol flash point is $\pu{55 ^\circ F} = \pu{12 ^\circ C}$. Auto-ignition temperature is $\pu{793 ^\circ F} = \pu{423 ^\circ C}$.
It means that ethanol vapor cannot be put on fire with a match at a temperature under $\pu{12 ^\circ C}$. But its vapor will not spontaneously ignite at temperature lower than $\pu{423 ^\circ C}$.


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