Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is a water bubble?

  1. Aug 11, 2010 #1
    This seems to be a very simple (stupid) question:

    If an inert gas is purged inside a distilled water container, bubbles are formed on the surface. The question is what are the constituents of those bubbles? and those constituents seems to be formed during a physical process, not a chemical one. What is the process?

    Thank you.
     
  2. jcsd
  3. Aug 24, 2010 #2
    Can anyone help? Thanks.
     
  4. Aug 24, 2010 #3

    russ_watters

    User Avatar

    Staff: Mentor

    What does "purged" mean in this context? Could you give a little more description about what the process is you are trying to describe?
     
  5. Aug 24, 2010 #4
    Thank you. ok.
    Consider an Ar cylinder as the source. A pipe is connected to the Ar source. The other end of the pipe is inside a container which is filled with distilled water. Ar gas enters (purges) inside the water. Because of that, bubbles are formed inside the water container. Bubbles go up to the surface of the water and upon reaching the surface, they burst. The question is about the constitutes of the bubbles? Do they contain water molecules or maybe H2 or O2 atoms or something like that?
    Thanks.
     
  6. Aug 25, 2010 #5

    Borek

    User Avatar

    Staff: Mentor

    Why do you think these are not just bubbles of Ar?

    --
    methods
     
  7. Aug 25, 2010 #6
    This technique is used to add water (in gas phase) along with the Ar gas to the process. As you can see in the figure, the Ar gas enters the container (they call it bubbler, but it is just a container of water) from the left side and then after mixing with water, the output goes to the right-side outlet.
    So, at the output (right-side) of the bubbler, besides the Ar gas, there should be also water. I wonder how that water mixes with the Ar gas? Is it just becasuse of the evaporation or bubbles do something or something else is happening there?

    [URL]http://uploadpic.org/storage/originals/thumb_nn8slrj89d3eff3e8nnsl32df8.jpg[/URL]
     
    Last edited by a moderator: Apr 25, 2017
  8. Aug 25, 2010 #7
    It looks like you're describing a bubble [tower] humidifier. Yes, you are correct in that as the gas bubbles rise through the tower the gas will become humidified. The amount of water absorbed by the gas ultimately depends on the temperature of the gas and the water since the vapor pressure of water is almost entirely dependent upon temperature. As for the mechanisms of how they mix, well its a little more complicated.
     
  9. Aug 25, 2010 #8
    Thanks. So the output is 'humidified Ar gas'? Is it some kind of physical or chemical process? I wonder what happens to H2O molecules? Are they carried by Ar as H2O or they split to H2 and O? If they remain H2O, can they be split to H2 and O later and under high temperature - like more than 700 C?
     
  10. Aug 25, 2010 #9

    Borek

    User Avatar

    Staff: Mentor

    Just evaporation. Bubbling probably makes the process faster by increasing water surface and keeping everything in motion (faster mixing).
     
  11. Aug 25, 2010 #10
    So I assume evaporation is just a change in the physical properties of the water and does not break the H2O molecules.
    In order to break the bonds of the molecule, a source of energy (eg. heat) is exerted to the water vapor and that breaks the H2O molecules to H2 and O2. This process is takes place in an inert medium, like Ar gas. I wonder is there any chance that H2 and O2 react again and form H2O molecules.
     
  12. Aug 25, 2010 #11

    Borek

    User Avatar

    Staff: Mentor

    It is not that easy to split water into hydrogen and oxygen by heating it. For decomposition you need temperatures in the kC range, then you need to cool the gases down and separate. At this stage they will tend to react back forming water as long as they are mixed and temperature is in the range of hundreds deg C.

    --
     
  13. Aug 25, 2010 #12
    Yes, there are no chemical reactions that take place. H2O remains H2O and does not split (for the most part). The separation of H2O due to the absorption of heat is dissociation or thermolysis and theoretically does occur at low temperatures where H2O splits into H2 and O2 and then back to H2O as you stated. However this happens with very low concentrations of O2 and H2, so low that I don't believe the concentrations can even be measured.
     
  14. Aug 25, 2010 #13
    Thank you.
    The following setup is related to the previous bubbler. Suppose that water vapour, from the left side, is purged inside a tube where the temperature is around 800 deg C. A reaction is happening in the middle of the tube. The water vaopur will arrive on top of the reaction boat and at high temperature. So it supplies water for the reaction or H2 and O2? Since you said H2/O2 reacts quickly and form water again, I assume there's water vapour on top of the reaction boat. If so, and if water want to participate in the chemical reaction, it should dissolve to H2/O2 or it depends on the reaction that is happening there?

    [URL]http://uploadpic.org/storage/originals/thumb_ff32k9jj98fd2288fl9n2sue3f.jpg[/URL]
     
    Last edited by a moderator: Apr 25, 2017
  15. Aug 25, 2010 #14

    Borek

    User Avatar

    Staff: Mentor

    At these temperatures (800 deg C) we are still talking about just water.

    --
    methods
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook