Kids, everyone knows that a day or two after you blow up a balloon it gets smaller.  This is because some of the air leaks out through microscopically small holes in the balloon’s wall.  In this activity, you will test how the molecules that we can smell from a flavoring extract can move through the rubber wall of a balloon and into our noses.

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

You will need 3 rubber balloons, a permanent marking pen, 3 disposable 3 oz plastic cups, 3 droppers, and 3 different flavoring extracts (vanilla, peppermint, and orange extracts work well).  Here is what you do.  Use the marking pen to write #1, #2, and #3 on each of your balloons.  Do the same with the three plastic cups, and place a dropper in each one.  Have an adult partner pour a small amount of a different flavoring extract into each of the cups, but don’t let them tell you which is which.  It will be up to you to guess which extract is in which balloon.  Use the dropper to place 10 drops of the extract in cup #1 into balloon #1.  Be sure to place the tip of the dropper as far into the balloon as possible before squeezing the dropper bulb so the extract does not get into the neck of the balloon.  Be careful not to get the extract on your hands, or you will end up smelling your hands instead of what is inside the balloon.  Repeat for extracts #2 and #3.

After making sure that there is no extract solution on the lip or neck of the balloon, blow them up, tie off the necks, and shake them a few times.  Blow each balloon up to about the same size.  Try to smell the extract inside balloon #1 by holding the balloon about 30 cm (1 foot) in front of your face in one hand, and using your other hand to fan the air around the balloon towards you.  Slowly move the balloon towards your nose until you begin to smell the extract.  Repeat for balloons #2 and #3.  Confirm with your adult partner that your guesses are correct.  For clean-up, hold each balloon over a sink, have the adult partner cut the knot off of the balloon and drain its contents. Pour any excess extracts down the drain, throw away the deflated balloons and any trash, and wash your hands.

Try these variations.  Compare natural and artificial vanilla flavorings to see if you can tell a difference.  Try inserting cloves or pieces of garlic, nutmeg or onion inside of balloons to see if their scents will pass through the rubber membrane of the balloon. Try substituting snack-size zip-closing plastic bags for the balloons.  So, where is the chemistry here?  To our eyes, the rubber membrane making up the wall of the balloon looks solid, without any holes.  Yet somehow the extracts make it out of the balloons and to your nose.  There are actually millions of holes, of course, but they are very, very tiny.  Air molecules and most scent molecules are small enough to fit through these holes.

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Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
April 2005

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Reference:   Celebrating Chemistry NCW 2004 newspaper, page 8. Facilitator tips found on:
                     www.chemistry.org/portal/resources/ACS/ACSContent/ncw/PDF/ncw_04_facilitatortips.pdf