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Theory behind gas tubes in lab experiments

  1. May 6, 2017 #1
    For chemical experiments that involve gases as reactant and products, gas tube are used for their transport.

    Q1. Why are there differences in length of gas tube when in a round flask. In most case, entering tubes are longer than exiting tubes? Why is that?

    Q2. Why is sometimes the entering tubes submerged in the liquid (that is present in the flask) whereas sometimes they aren't?

    Q3. Are there any scenarios for which exiting tubes are submerged in the water/solvent?
     
  2. jcsd
  3. May 8, 2017 #2

    DrClaude

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    Staff: Mentor

    If you want the gas entering to go through a liquid, it needs the be longer to plunge in the liquid. On exit, you want only gas, so that tube has to be shorter, otherwise you will get liquid out.

    There are different reasons why you would want a gas to first go through a liquid. For instance, a solution of sodium hydroxide can be used to remove CO2. I guess that in some cases the liquid is used to keep the gases from going back through the entry tube.
     
  4. May 8, 2017 #3
    Okay perfect thank you.

    Is it also possible to just suck out insoluble gases by plugining the delivery tube in water?
     
  5. May 9, 2017 #4

    Borek

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    If you drink coke through a straw, do you suck out dissolved CO2, or the coke?
     
  6. May 9, 2017 #5
    Both I think
     
  7. May 9, 2017 #6

    Borek

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    Can you suck just the gas?
     
  8. May 10, 2017 #7
    No I don't think so.

    Thank you very much.
     
  9. May 10, 2017 #8
    So basically these gas tubes are nothing but suction tubes that suck due to a pressure difference.
     
  10. May 11, 2017 #9

    Borek

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    Staff: Mentor

    Yes, the pressure difference is the driving force (note: it doesn't have to be suction, all that matters is that there is a pressure difference), there is nothing else happening.
     
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