# Melting Point of an Ethanol/Water Mixture

**URL:** <https://boards.straightdope.com/t/melting-point-of-an-ethanol-water-mixture/538069>\
**Category:** Factual Questions\
**Created:** [May 2, 2010, 10:08pm UTC](https://boards.straightdope.com/t/melting-point-of-an-ethanol-water-mixture/538069 "2010-05-02T22:08:16Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Taenia\_spp](https://avatars.discourse-cdn.com/v4/letter/t/b5e925/32.png) [@Taenia\_spp](https://boards.straightdope.com/u/Taenia_spp)\
**Post date:** [May 2, 2010, 10:08pm UTC](https://boards.straightdope.com/t/melting-point-of-an-ethanol-water-mixture/538069/1 "2010-05-02T22:08:16Z")

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I’ve been storing spirits (40% ABV) in the freezer and they’ve always remained liquid at that temperature. Recently, in my naive understanding, I placed a bottle of vermouth (18% ABV) in there and was surprised to find the next day all I had was a bottle of hard slush. This got me thinking: at what proportion of alcohol will that solution not freeze at typical freezer temperatures?

In my dim memory of chemistry, I remember that a mixture of two miscible compounds will have a melting point (freezing point) lower than the melting point of each compound individually, with a sharp depression at the eutectic point. Is there anywhere to find an ethanol-water melting point curve?

I suppose for the purposes of this question, we might first consider a solution of pure ethanol and water without impurities, but we could also consider the effects of the various other compounds typically found in alcoholic beverages.

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**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\
**Post date:** [May 3, 2010, 4:35pm UTC](https://boards.straightdope.com/t/melting-point-of-an-ethanol-water-mixture/538069/2 "2010-05-03T16:35:36Z")

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Ideal freezer temperature is variously quoted at 0˚F or -20˚C. This corresponds to roughly 32% - 33% alcohol. Here’s a rough table: [Ethanol Freeze Protected Water Solutions](http://www.engineeringtoolbox.com/ethanol-water-d_989.html)

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**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\
**Post date:** [May 3, 2010, 4:43pm UTC](https://boards.straightdope.com/t/melting-point-of-an-ethanol-water-mixture/538069/3 "2010-05-03T16:43:32Z")

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A quick search turns up this:

> **[File:Phase diagram ethanol water s l en.svg](https://commons.wikimedia.org/wiki/File:Phase_diagram_ethanol_water_s_l_en.svg)**

18% ABV freezes well before 40% ABV, so it’s not surprising. You really need quite a bit of ethanol – about 93-94%, judging from that picture – to get the eutectic point. -20C corresponds to about 30% alcohol, as **Nametag** said

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**Author:** ![Taenia\_spp](https://avatars.discourse-cdn.com/v4/letter/t/b5e925/32.png) [@Taenia\_spp](https://boards.straightdope.com/u/Taenia_spp)\
**Post date:** [May 4, 2010, 3:32pm UTC](https://boards.straightdope.com/t/melting-point-of-an-ethanol-water-mixture/538069/4 "2010-05-04T15:32:32Z")

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Aha! “Phase diagram”–the term I couldn’t think of. Thanks, Cal!