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Science Forum

  1. 05 Dec '11 17:04 / 1 edit
    Last week I was returning from Florida to California and asked for a 7-up. As I poured it I noticed that the bubble formation was very rapid but also the breakdown of the bubbles was very rapid. I have observed this many times before, but never thought about it.

    According to Wikipedia, aircraft cabin pressurization is expressed as cabin altitude and typically is held at 5000-7000 feet (1500-2100m) when at maximum altitude of 40000 feet (12000m). This means that the barometric pressure is at most, like that of Denver.

    If the rapid bubble formation/collapse observed when pouring a carbonated beverage is real, what do you think might explain it? Would bubble walls be thinner?

    I am wondering too, about the possibility that the air is dryer, but it seems unlikely that bubble wall-thinning evaporation rate would differ that much.
  2. 05 Dec '11 17:16
    Originally posted by JS357
    If the rapid bubble formation/collapse observed when pouring a carbonated beverage is real, what do you think might explain it? Would bubble walls be thinner?
    I think you need look no further than it being easier for them to both get created and grow to bursting point against a lower surrounding pressure. Wall thickness might have something to do with it, but I would suspect only as a consequence of this more rapid creation.

    Richard
  3. Subscriber WoodPush
    Pusher of wood
    05 Dec '11 20:11
    I agree with ShallowBlue.

    It sounds like you've discounted the air pressure as being a factor, but I wouldn't be that quick to do so.

    At sea level, air pressure is about about 14.7 psi. At 7000 ft, its about 10.2 psi. In other words, about 30% less. That significantly increases the nucleation rate of carbon dioxide bubbles.

    Temperature should work similarly. Another fun experiment would be to warm your 7-up... and the bubbles will form and pop even faster. Try putting that 7-up can in a pot of boiling water, pull it out, and pop the lid, and imagine you should get a pretty messy result. (And get you a nasty burn if you're not careful).
  4. Standard member sonhouse
    Fast and Curious
    05 Dec '11 20:33
    Originally posted by WoodPush
    I agree with ShallowBlue.

    It sounds like you've discounted the air pressure as being a factor, but I wouldn't be that quick to do so.

    At sea level, air pressure is about about 14.7 psi. At 7000 ft, its about 10.2 psi. In other words, about 30% less. That significantly increases the nucleation rate of carbon dioxide bubbles.

    Temperature shoul ...[text shortened]... gine you should get a pretty messy result. (And get you a nasty burn if you're not careful).
    And going the other way pressure wise, there is not much in the way of bubbles inside the can before it is opened because it is at a slightly higher pressure.

    If you were to put that carbonated drink in a vacuum system, you could modulate the rate of release of bubbles by running the air pressure down and then slow them down again by pumping air in again.
  5. 02 Jan '12 17:29
    The determining factor is the partial pressure of carbon dioxide in the gas above your 7-up. This partial pressure is equal to the relative gas fraction times the total pressure (the sum of all partial pressures).

    The effect of applying pressure to your drink is thus dependent on the type of gas you use: pure air of carbon dioxide.
  6. Standard member sonhouse
    Fast and Curious
    02 Jan '12 19:48
    Originally posted by tvochess
    The determining factor is the partial pressure of carbon dioxide in the gas above your 7-up. This partial pressure is equal to the relative gas fraction times the total pressure (the sum of all partial pressures).

    The effect of applying pressure to your drink is thus dependent on the type of gas you use: pure air of carbon dioxide.
    So the gist of that is, if the air in the cabin was pure CO2, there would be no fizzing?
  7. 02 Jan '12 23:27 / 1 edit
    Originally posted by sonhouse
    So the gist of that is, if the air in the cabin was pure CO2, there would be no fizzing?
    No, that's nonsense. (EDIT: to be clear it does sound like that is what he is saying,
    I am just saying that what he's saying is nonsense.)

    It's the total pressure acting on the liquid, the composition of the air above is irrelevant.

    Bubble formation happens well below the surface, how would the bubble below know
    what the composition of the air above was?

    The only relevant factors as far as the bubble formation is concerned is total pressure,
    nucleation sites, concentration of dissolved gas, and temperature.

    The composition of the external air mix is irrelevant.
  8. 03 Jan '12 00:27 / 1 edit
    Originally posted by googlefudge


    The composition of the external air mix is irrelevant.
    Yup that is true. Only the pressure of the external gas is relevant. It doesn't matter what the gas is, or what is causing the pressure of that gas, only the pressure is relevant. The type of gas dissolved might have some effect on it due to its volume at various temperatures and pressures, and also how soluble it is in the defined liquid.
  9. 03 Jan '12 01:41
    Originally posted by jimslyp69
    Yup that is true. Only the pressure of the external gas is relevant. It doesn't matter what the gas is, or what is causing the pressure of that gas, only the pressure is relevant. The type of gas dissolved might have some effect on it due to its volume at various temperatures and pressures, and also how soluble it is in the defined liquid.
    Ah, yes, in the general case then the relevant properties of the liquid and dissolved gas are
    relevant.

    However I was talking about the specific case of CO2 dissolved in 7up (or whatever it was)
    in which case the dissolved gas and liquid are constants.
  10. Standard member sonhouse
    Fast and Curious
    03 Jan '12 05:02 / 1 edit
    Originally posted by jimslyp69
    Yup that is true. Only the pressure of the external gas is relevant. It doesn't matter what the gas is, or what is causing the pressure of that gas, only the pressure is relevant. The type of gas dissolved might have some effect on it due to its volume at various temperatures and pressures, and also how soluble it is in the defined liquid.
    And the pressure doesn't even have to come from a gas, it could just as easily be a piston pushing down on a cup with carbonation in it and that would inhibit the generation of C02. I gather there is a rather fine line between outgassing in a closed can of soda and when you pull the tab.

    Anyone know how much pressure is on the inside of a soda can before it is opened? I would assume the lower the temp. the less carbonation escapes but is there some empirical rule saying what an average pressure is inside the can before it is opened?

    I know champagne bottles have to hold up something like 90 PSI inside but ordinary soda cans wouldn't have anything like that kind of pressure would they?

    I wonder how high a temperature you would need to heat up a typical filled soda can to make it explode? My bet would be it would blow way before it reached the boiling point of water, 100 degrees C.
  11. 03 Jan '12 15:18
    This comes from Wikipedia: http://en.wikipedia.org/wiki/Henry's_law

    "An everyday example of Henry's law is given by carbonated soft drinks. Before the bottle or can is opened, the gas above the drink is almost pure carbon dioxide at a pressure slightly higher than atmospheric pressure. The drink itself contains dissolved carbon dioxide. When the bottle or can is opened, some of this gas escapes, giving the characteristic hiss (or "pop" in the case of a champagne bottle). Because the pressure above the liquid is now lower, some of the dissolved carbon dioxide comes out of solution as bubbles. If a glass of the drink is left in the open, the concentration of carbon dioxide in solution will come into equilibrium with the carbon dioxide in the air, and the drink will go "flat". Note that the pressure acting above the drink in the sealed container must come from the partial pressure of carbon dioxide. If the gas is only air it would not produce the same effect even if the pressure value is the same."
  12. 04 Jan '12 02:45
    Originally posted by tvochess
    This comes from Wikipedia: http://en.wikipedia.org/wiki/Henry's_law

    "An everyday example of Henry's law is given by carbonated soft drinks. Before the bottle or can is opened, the gas above the drink is almost pure carbon dioxide at a pressure slightly higher than atmospheric pressure. The drink itself contains dissolved carbon dioxide. When the bottle o ...[text shortened]... ly air it would not produce the same effect even if the pressure value is the same.
    "[/b]
    You are talking about a different effect.

    If you were to open your can of fizzy drink in an atmosphere of pure CO2 and pour it
    it would fizz and bubble just like it would in regular air.

    The fizzing and bubbling is a different process to dissolving and evaporating that happens
    at the surface.

    The CO2 molecules in solution will be constantly evaporating off the surface but in also CO2
    molecules in the air will dissolve into it.
    The concentration of CO2 dissolved in the liquid will stabilise at the concentration that sustains
    an evaporation rate equal to the rate at which CO2 is being absorbed.
    Using a 100% CO2 mix in the can helps keep the drink fizzy until use.
  13. 04 Jan '12 10:15
    "The fizzing and bubbling is a different process to dissolving and evaporating that happens at the surface."

    I do not really agree with that statement.

    I'm no native English speaker, so I have to guess what you mean with fizzing. The bubbling is obviously the formation of bubbles, which is exactly a mode of evaporation.

    Since you brought up the phrase "at the surface", I'd like to note that the evaporation of CO2 dissolved in water is similar to the evaporation of pure water. There is either evaporation "at the surface" or there is boiling (= bubbles). Both occur when there is not yet thermodynamic equilibrium between the liquid and gas phase. Which of these two (but there may be more) modes occur depends on the severity of the non-equilibrium.

    Nevertheless, the equilibrium state is irrespective of the mode (surface evaporation or bubbling) with which it is reached and is dependent on the amount of CO2 in the gas used to pressurize. However, the way to get there may be different and it sounds very plausible that the concentration of CO2 on top of the liquid surface has no immediate effect on the internal bubble formation.

    Is that a point of view we can agree on? I may have been talking about a different observation then.
  14. 04 Jan '12 12:01
    If we shake a can of coke it fizzes more when opened than if it was not shaken, right?
    What if the can is filled with coke to its top, so there isn't room for any air, will it fizz when shaken too?
  15. 04 Jan '12 13:03
    Originally posted by FabianFnas
    If we shake a can of coke it fizzes more when opened than if it was not shaken, right?
    What if the can is filled with coke to its top, so there isn't room for any air, will it fizz when shaken too?
    Due to the shaking, the thin layer of gas (mostly CO2) mixes with the coke to form bubbles all over the inner surface of the can. The CO2 remains gas and is not dissolved! If the can opens, the pressure is relieved. This causes the bubbles to grow and more bubbles are formed. A lot of the bubbles detache from the sides and rise up, carrying a lot of coke with it that will be spoiled on the ground and your hands.

    So, if the can is filled up with coke, there should be no effect of the shaking.