Ask A Scientist© Chemistry Archive

 > >    name         Holly Rippee
 > >    status       student
 > >    age          14
 > >    EMAIL
 > >    Question -   When you place a foam cup in acetone, the cup melts.  My
 > > question is why?
 >
 > >I know that the acetone is taking the air out of the cup, but how?



The foam cup is made out of polystyrene foam, which is a foam of poly styrene.
This means that there is a chemical styrene which is made into a plastic.  Its
like jello.  Styrene is the jello mix you pour into the bowl.  When you put
the jello into the refrigerator, the jello turns thick.  This is like the
styrene turning into polystyrene. Now somebody comes along and takes this
thick hard stuff, polystyrene and pushs it into the shape of a cup.  (You can
make the jello take the shape of a mold too, maybe some fancy cup, or funny
shapes to eat).

So now you have this polystyrene cup.  But if you come along now and pour on
acetone, it breaks down the connections between the strands of polystyrene.
The cup dissolves.

OK, its not exactly the same thing but if you made a cup out of jello and then
poured in hot water, the jello would dissolve in the  hot water.  The cup
would fall apart.  Its too small for you to see, but little blobs of water are
getting in between the globs of jello, dissolving it, and ruining the cup.
S. Ross
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Actually, the acetone is dissolving the plastic in the cup, and the blow
gas inthe foam is just escaping into the air.  It's exactly the same type
of process as when you put popcorn into water.


                Richard Barrans Jr., Ph.D.
                Chemical Separations Group
                Chemistry Division CHM/200
                Argonne National Laboratory
                9700 South Cass Avenue
                Argonne, IL 60439
                richb@anl.gov

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