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Dumb Question: What Happens to Alcohol When it Evaporates?

  1. Sep 5, 2014 #1
    So, let's say you have either a bottle of rubbing alcohol (isopropyl) or a bottle of drinking alcohol (ethanol) and you leave it in the open air for a day or two (or however long it takes for it to evaporate). What happens when the alcohol evaporates into the air? Supposedly, the alcohol from the liquid goes away and you're left with water right? That's why you have to put lid tightly on alcohol.

    My question is where does the alcohol go? Does it chemically break down or something and just no longer exist? Or is it still existing in some gaseous/vaporous state in the air? Like is the alcohol still lingering in the air around you (like in the form of fumes or something)?

    Oh and lastly, why does the alcohol part evaporate out and the other liquid part not go away so fast? Why doesn't the water just evaporate too?

    Thanks for your help!
     
  2. jcsd
  3. Sep 5, 2014 #2

    Borek

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    Molecules of alcohol just exist somewhere in the air. Sooner or later they will react with oxygen.

    Basically alcohol evaporates first because its boiling point is lower.
     
  4. Sep 5, 2014 #3

    SteamKing

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    Who says the water doesn't evaporate?

    When wine or spirits are put into oaken barrels for aging, a certain amount of liquid stored within is lost over time due to evaporation, and some of this loss unfortunately includes the alcohol. This lost portion is known as the 'Angel's Share':

    http://en.wikipedia.org/wiki/Barrel
     
  5. Sep 6, 2014 #4
    As was mentioned already, the alcohol doesn't disappear. It will diffuse away as a gas.

    Also, you will not evaporate ONLY the alcohol but a mixture of the alcohol and water which is enriched in alcohol due to the lower BP of the alcohol. At a certain point you will come to a mixture known as an azeotrope (http://en.m.wikipedia.org/wiki/Azeotrope) where no further enrichment will take place. This is for the case of ethanol/water, by the way. Not all mixtures form azeotropes but EtOH/water is a well known one.
     
  6. Sep 7, 2014 #5

    Thanks everyone. So it does linger in the air then. Interesting. Thanks for explaining.

    Quick follow-up: What'd you mean when you said that sooner or later it will react with oxygen? As in a "bad" way (like explode, etc.)?

    Lastly, is it safe to use for cleaning around the house? My roommate uses it ALL the time in the apartment on his computer stuff and it has a strong smell to it (which can give me a headache at times).

    He'll even use it in the bathroom (cleaning the toilet , counter, and floors with it) from what I've seen. Is this safe to do?
     
  7. Sep 7, 2014 #6

    Borek

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    For the explosion you would need quite high concentration (google explosion limits). In general ethanol will get oxidized, first to aldehyde, then to acetic acid, finally to just carbon dioxide and water.

    I see no reason to worry. If it is giving you headaches, ventilate the room (or look for another roommate).
     
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