Floating Squares
Graphite (from a pencil lead) is applied to one side of an index card and a piece of the card is immersed in a beaker containing hexane and water (two layers). The graphite-coated side always faces the hexane layer. When the two liquids are carbon tetrachloride and water the graphite-coated side always faces the carbon tetrachloride.
Keywords
polar, dispersion forces, intermolecular forces, density
Multimedia
Introduction
_Play
movie (7 seconds, 0.4 MB)
Graphite is applied to one side of a paper index card. (The card
is cut into small squares.)
Hexane and water
unlabeled version:
_Play
movie (22 seconds, 1.3 MB)
The square is placed at the interface between two liquids (hexane
and water). The paper orients itself so that the nonpolar
graphite faces the nonpolar hexane and the polar molecules in the
uncoated paper face the polar water.
labeled version: 
_Play
movie (22 seconds, 1.3 MB)
(This is the initial image of the movie instead of the unlabeled
image shown above. The rest of the movie is the same.)
Carbon tetrachloride and water
unlabeled version: 
_Play
movie (31 seconds, 1.7 MB)
The square is placed at the interface between two liquids (carbon tetrachloride and water). The paper orients itself so that the nonpolar graphite faces the nonpolar carbon tetrachloride and the polar molecules in the uncoated paper face the polar water.
labeled version: 
_Play
movie (31 seconds, 1.7 MB)
(This is the initial image of the movie instead of the unlabeled
image shown above. The rest of the movie is the same.)
Discussion
In one version of each the demonstration movies the liquids are NOT labeled.By removing the sound track, the movie can be used for testing and discussion purposes. In the other versions, the liquids are labeled.