PATRIOTIC POUR
INTRODUCTION
This activity uses color and surprise to illustrate
the principle of density. Because of its colorful nature, it is a
nice activity to use with young children. However, the principle
demonstrated also makes it a worthwhile activity for upper elementary age
children. We use this experiment for "Color-full", "Density",
and "Environmental" topics.
PURPOSE
Used with younger children, the color and the
surprise of this activity help to get them excited about the subject of
Science. For children in the upper elementary grades, it is an excellent
demonstration of the principle that different liquids have different densities
and also shows that oil and water are immiscible.
MATERIALS
Milk
Blue Lamp Oil (see NOTE below)
Colorless Corn Syrup dyed red with food coloring
(see NOTE below)
Jar about 1 1/2" in diameter, with no "shoulders";
with screw-on lid
Paper sleeve for the jar that can be slipped
on or off easily
PREPARATION FOR THE ACTIVITY
We keep a packet of nonfat dry milk powder in
the activity packet and make up about one-eighth cup (2 tablespoons) of
milk just prior to class. Regular milk works better if you don't have to worry about spoilage.
To color the corn syrup, heat the corn syrup (lid
off) in your microwave oven for about one minute, or until it becomes more
fluid. Add 10-15 drops of red food coloring to the corn syrup, cap
the bottle, and shake until the food coloring is evenly dispersed throughout
the syrup. You may need to add more food coloring to get a deep red
color.
NOTE: If you are unable to find blue
lamp oil, but red lamp oil is available, you can dye the corn syrup blue.
PROCEDURE
With young children, ask what colors are used
to make green, orange, and purple. Second graders usually know these
combinations, and older first graders do, too. Then ask them what
happens if you add the color white to purple. Many of the children
will know that this will make the purple a lighter purple color.
Show them your three liquids: red corn syrup,
white milk, and blue lamp oil. Tell them that you are going to pour
the three liquids into your jar (which should be hidden inside the paper
sleeve). Pour at least a 1/2" layer of each liquid into the jar,
being careful to use more oil than milk (see NOTE below).
Cap the jar and ask the children what color they will see in the jar.
("Light purple!") Pull the sleeve off the jar, and you will find
the liquids have layered and remain red, white, and blue.
For children in second grade and up, it is even
more surprising if you pour the lamp oil in first, as they expect it to
go to the bottom of the jar and stay there.
Ask the children what will happen if you turn
the jar upside down or place it on its side. Discuss the results.
At this point, they may notice that the white milk and red corn syrup are
beginning to mix. Discuss why these two liquids are mixing, noting
that the blue remains separate.
Finally, the children always want you to shake
the jar. Be sure the top is screwed on tightly and then shake the
jar hard enough to mix the liquids together. Hold the jar up and
observe what happens. Discuss the results.
EXPLANATION
The density of a substance is determined by dividing
its mass by its volume. The liquids stay in layers due to the differences
in density. The corn syrup, a solution of water and a great deal
of sugar, is the most dense (weighs the most for the same volume of liquid)
and thus goes to the bottom of the jar. The lamp oil is the least
dense, and goes to the top, while the milk layer is in between. Even
when poured into the jar first, the lamp oil will go to the top as the
more dense syrup and milk go through and settle underneath the oil layer.
When you change the position of the jar to upside
down and/or on its side, you have done nothing to change the properties
of the liquids, and so the least dense (oil) will still go back to the
top of the more dense liquids.
The corn syrup and milk begin to mix because
they are both water mixtures, while the oil does not like to mix with water,
and so stays separate.
When you shake the liquids together, the liquids
do combine, but the lamp oil layer comes back out on top very quickly,
to the children's delight. NOTE: Some of the milk
and oil will form an emulsion so the oil will be unable to separate.
To avoid this problem, use more oil than milk (about 1 1/2 times as much)
so that not all of the oil will be emulsified and an oil layer will still
separate from the water/corn syrup layer.
ADDITIONAL SUGGESTIONS
For older children, this experiment easily leads
into an environmental discussion regarding oil spills and the importance
of the fact that the oil layer forms on top of the water. If the
oil sank to the bottom of the ocean, lake, etc., much more harm would be
done and clean-up of the oil would be very difficult.
If there is a greater volume of lamp oil than
corn syrup in the jar, young children may have a difficult time understanding
that the oil is still "lighter" than the syrup. They also often surmise
that the milk must be the "heaviest" liquid because it is strong enough
to hold the other two liquids apart. To help them understand that
both volume and mass need to be considered, use 2 common objects with very
different volumes, such as a partially inflated balloon and a baseball,
or a book and a larger piece of foam. Use a simple balance to determine
the mass of each object, so they can see that even though one object is
larger than another, the larger object may still be lighter (and thus less
dense) than the smaller one. (Which weighs more - a pound of feathers
or a pound of lead?) You can also pour a little more corn syrup into
the jar (before you shake the jar to mix the liquids) and let the children
watch as the heavy syrup goes straight through the oil and milk layers
and settles at the bottom. You could illustrate this concept another way,
by dropping a rock in a bucket of water. It will sink to the bottom
immediately, while a chunk of wood of approximately the same size would
quickly bounce back to the top of the water because it is much lighter,
i.e. less dense.
DISPOSAL
Pour as much of the lamp oil as possible back
into your bottle of lamp oil. If a little of the milk/syrup mixture
goes into the bottle, it will sink to the bottom,, remain there, and not
cause any problems when a new oil sample is poured from the bottle.
You may need to use a medicine dropper or a plastic pipette to remove most
of the remaining oil, adding it to the bottle of oil. Dispose of
the remaining very small amount of oil along with the syrup/milk solution
by flushing it down a sink drain.
REFERENCES
Andy Sae, "Red, White, and Blue", Chemical
Magic from the Grocery Store, Eastern New Mexico State University,
Clovis, NM, 1991, pp. 8-9.
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