4E10.15  BALLOON ON A FLASK


  • Version 1
  • A balloon on a flask expands when the flask is heated.
  • Don't heat flask too long.
  • A fire extinguisher is available in the cart.







        (use 1/2 m clamping stand and 1 L flask)
        (position flask above flame to protect balloon)
        (check fire extinguisher)


  • When the flask is cooled in LN, the balloon is drawn inside. You will have to help it slide into the neck to keep it from tearing.
  • Raise and lower the flask on the stand.

  • Version 2
  • Boil a small amount of water in a flask.
  • When steam is streaming out of the opening, turn the bunsen burner off.
  • A fire extinguisher is available in the cart.







        (use 1/2 m clamping stand and 1 L flask)
        (prestretch balloon)
        (check fire extinguisher)

  • Put a balloon over the opening as soon as boiling stops.
  • The balloon will be drawn into the tube.  You will have to help it slide into the neck to keep it from tearing.
  • The inversion happens suddenly, but it takes several minutes for the balloon to fill the flask.  Immersing the flask in a bowl of water speeds the process.
  • As a variation, start with the balloon in the flask and ask students how it got that way.








        (use bowl of water on lab jack to cool flask)



  • Reheat flask to reinflate balloon, or carefully lift lip of balloon to break seal and pull it out.
  • Do not heat flask too long or balloon will burst.  Remove balloon when pressure is minimal.

Back