Bi-Carb of soda + Citric Acid.

Discussion in 'General Electronics Chat' started by cjdelphi, Sep 13, 2010.

  1. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    Bi-Carb of soda + Citric Acid.

    Other than discovering 2 things, 1 it releases a lot of Carbon Dioxide and 2, it also creates an endothermic reaction... but a 3rd thing happened which has left me kinda puzzled.

    I took a beer bottle placed the citric acid and bicarb into the bottle, I placed a balloon on top of it... no prize for guessing what happened, the balloon started filling with CO2 and inflated, duh.... but, here's the confusing part, I decided to leave the bottle on the table, ok i was too lazy to remove the bottle.... and 3 - 4 days later I went back to the bottle...

    This time the balloon has all of the gas sucked out and was being sucked into the bottle, the balloon had been sucked somehwat inside the bottle not only did it de-flate but it's like a vacuum seal had been put in place, so not just empty but sucked out...

    Even if the water had re-adsorbed all the carbon dioxide, what would explain for the vacuum effect?
  2. Wendy


    Mar 24, 2008
    Balloons are not really air tight. They leak right through the rubber in the sides.
  3. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    yes that's true but why would there be any tension on the balloon? it would have simply deflated, but no, it's as though a vacuum has been applied to suck air out.... like breathing in on the balloon after it has been deflated or a space saver bag for your suitcase.
  4. DumboFixer

    Active Member

    Feb 10, 2009
    As the chemical reaction progressed pressure would have built up in the bottle thus causing the balloon to inflate. some of this pressure would have escaped from the balloon (osmosis ?). As the chemical reaction slowed and stopped the pressure would have reduced and tried to get back to a normal volume. however some of the volume has escaped through the balloon so the only way the pressure can be equalised is for the balloon to be sucked back into the bottle.

    Just a thought (my chemistry is a bit rusty)
  5. jpanhalt


    Jan 18, 2008
    Dumbofixer is on the right track. I would add that a great deal of the air in the bottle/balloon apparatus was displaced by CO2 before the balloon got affixed. CO2 is heavier than air and the displacement would be quite rapid.

    Latex balloons (and probably may other rubbers) are more permeable to CO2 than to nitrogen and/or air. Thus, the CO2 leaves by diffusion faster than it is replaced by other gases. Note, diffusion is of course reversible, but since the concentration in the balloon is very high compared to the surrounding atmosphere, it is essentially one way in this case.

    Here is a reference describing essentially the same phenomenon:

    I suspect there are much better references, but I just want to get to breakfast.