Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: John Chapman on 15/03/2009 19:13:33
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Every schoolboy knows that dry ice is solid (ie frozen) carbon dioxide. He may also knows that carbon dioxide turns from solid to gas without bothering to inconvenience itself with a liquid phase. A process which I believe is known as sublimation. But my question is this:
Since gaseous CO2 is colourless, and to all intents and purposes invisible, why does melting dry ice in water produce a thick fog? Dry ice and water provide the mechanism by which theatrical fog machines work.
I'm sorry guys. I don't know if this is a physics or chemistry question.
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Every schoolboy knows that dry ice is solid (ie frozen) carbon dioxide. He may also knows that carbon dioxide turns from solid to gas without bothering to inconvenience itself with a liquid phase. A process which I believe is known as sublimation. But my question is this:
Since gaseous CO2 is colourless, and to all intents and purposes invisible, why does melting dry ice in water produce a thick fog? Dry ice and water provide the mechanism by which theatrical fog machines work.
I'm sorry guys. I don't know if this is a physics or chemistry question.
It's an interesting question (and you are right about having difficulty defining it as a chemistry or physics question, infact it's "physical chemistry" [:)]) because the answer seems obvious but it's not, at least for me. I'm almost sure that water has the main purpose to heat solid CO2 quickly: water is at room temperature and being a liquid, it enters in contact with the solid piece through a great area.
What is the fog/smoke, is less obvious; it is presumably made of solid CO2 particles quickly detached from the vaporization process, but there could be others mechanisms, or be made also of solid water vapor freezed by the cold CO2. I'm almost sure it can't be carbonic acid because it shouldn't exist pure or in high concentrations.
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I suspect the CO2 fog is actually the water in air (~2% @ 20 oC) condensing into visible droplets in the very cold CO2 gas.
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I agree with RD.
When you place dry ice into some warm or hot water, clouds of white fog are created. This white fog is not the CO2 gas, but rather it is condensed water vapor, mixed in with the invisible CO2.
http://www.west.net/~science/co2.htm
As dry ice sublimes, the very-cold-but-now-gaseous CO2 vapor is invisible, but is plenty cold enough to condense water in the air. It is the condensed water vapor which is visible above a block of dry ice as "fog."
http://ocw.mit.edu/NR/rdonlyres/Music-and-Theater-Arts/21M-735Spring2004/10F93278-4C1B-44AA-BCE2-71AD21D7C13F/0/mpd_tn8.pdf
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good question dude, i think RD is right
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I agree with RD.
When you place dry ice into some warm or hot water, clouds of white fog are created. This white fog is not the CO2 gas, but rather it is condensed water vapor, mixed in with the invisible CO2.
http://www.west.net/~science/co2.htm
As dry ice sublimes, the very-cold-but-now-gaseous CO2 vapor is invisible, but is plenty cold enough to condense water in the air. It is the condensed water vapor which is visible above a block of dry ice as "fog."
http://ocw.mit.edu/NR/rdonlyres/Music-and-Theater-Arts/21M-735Spring2004/10F93278-4C1B-44AA-BCE2-71AD21D7C13F/0/mpd_tn8.pdf
Very interesting. Thank you.
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When reading this thread title, who else in their head went "ne ne ne, ne ne ne-ne, ne ne ne, ne ne"
(They all came down to Montreux...)
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I certainly thought of
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Nice one Dentstudent
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And a great recording too BC :)