A.
Hypothesis
The drop of dish soap, which is a surfactant, had
caused the food coloring to disperse throughout the surface of the milk.
B.
Procedures
1.
Pour
enough milk into three separate pans.
2.
Add
several drops of food coloring to each pan.
3.
Add a
drop of dish soap to the first pan, a drop of alcohol to the second, and a drop
of sesame oil to the third.
4.
Observe
the changes in each pan.
C.
Expectation
Surfactant molecules like dish soap are usually known
to be amphiphilic, meaning they contain both hydrophilic groups (heads) and
hydrophobic groups (tails). As their names suggest, the hydrophilic group of
the molecules actively interacts with water (in this case, milk) and the
hydrophobic group with oil (food coloring), weakening the surface tension of
the milk (by weakening the intermolecular force, the hydrogen bond, existing
between the milk molecules) and eventually blending the food coloring with it,
a phenomenon ostensibly viewed by the observer as ‘spread’.
The hypothesis that the dispersion of the coloring is
attributable to the amphiphilic property of the dish soap may be verified by
adding alcohol and sesame oil, which are substances that are hydrophilic and
hydrophobic respectively, to two separate pans of milk and comparing the
changes. Since neither of the two are amphiphilic, it is very likely that they
do not function as surfactants and consequently not spread the food coloring as
the dish soap did.
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