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Homework Help: Dry CO2

  1. Aug 8, 2009 #1
    1. The problem statement, all variables and given/known data

    Hi there, could anyone help me pls. I want to show my sons kinder class what happens when you put Dry Ice (solid CO2) into water but would like to know for them and for me what the actual process is when it sublimates. I dont understand why there are so many bubbles or even why there is a vapour. I need to make it extremely simple for them but think an acurate explanation is important and I love these things myself so would like to know as well. Also, is there anything I should be careful of, I am going to buy a kilo as that is the smallest amount I can purchase and pop it in a glass jar. Thanks so much for any help you are able offer.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Aug 8, 2009 #2
    The CO2 sublimates because the temp and the pressure of the surroundings. CO2 can be liquid, but requires conditions of temp. and pressure that we do not normally encounter. When you put dry ice in water, it sublimates more rapidly at first because the room temp water is heating the CO2 more rapidly than if it was just in room temp. air. The bubbles are gaseous CO2. The CO2 is not all going to dissolve in the water, especially considering that water is much more polar. The vapor you see is actually just like fog. Its water in the air condensing out into tiny droplets because the dry ice has cooled it so much the water condenses into these little droplets. So The vapor you see is not gaseous CO2 its water. This is my understanding anyways. and it makes sense to me.
  4. Aug 8, 2009 #3
    Thank you so much for your help! I really do appreciate it. I think the kids should really enjoy it (I do)
  5. Aug 8, 2009 #4


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    Do it with kool-aid or grape juice, and lots of sugar, and you'll have soda pop!

    Make sure to avoid prolonged skin contact with the dry ice, though, it can give you frostbite.
  6. Aug 13, 2009 #5
    thanks very much for your advice, if I can get some dry ice today I will be taking it in and will try your suggestion, thanks!
  7. Aug 13, 2009 #6
    As far as why there are so many bubbles, gaseous CO2 has a much lesser density than solid CO2
    1.562 g/mL (solid at 1 atm and −78.5 °C)
    1.977 g/L (gas at 1 atm and 0 °C)

    Notice, that's more than 100 times the density. In other words, for every mL of dry ice you place in the water, you will get more than one liter of CO2 gas.
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