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DENSITY Applications
with Liquids and Solids
DENSITY is a physical property of matter, as each element
and compound has a unique density associated with it. Density
defined in a qualitative manner as the measure of the relative
"heaviness" of objects with a constant volume. For
liquids the density may also vary with the temperature. |
Density Comparison to Water: In chemistry, the density of
many substances is compared to the density of water. Does an
object float on water or sink in the water? If an object such
as a piece of wood floats on water it is less dense than water
vs. if a rock sinks, it is more dense than water. |
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Liquid Density examples based upon differences in
mass or weight per unit volume.
Density of a liquid with a constant volume, varies according
to the weight. The higher the weight, the higher the density.
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Layers of Liquids Demonstrations:
In this series of demonstrations the theme is that a variety
of liquids have different physical properties as shown by their
densities. The most dense liquids will be found on the bottom,
the least dense liquid is on the top. See Table
below.
Layers of Liquids - Demonstrations
with Density
Any objects placed in the liquids will seek their own level
depending upon the density. If an object has a density that is
intermediate in value, the object will float between two layers.
Floating objects in water
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Floating Spheres:
In the case of the floating spheres, the water is the most dense
and hence on the bottom. If the alcohol is very carefully added
to the water with only a minimal mixing, the alcohol will layer
on the top of the water since it is less dense. The oil drops
that are added are more dense than the alcohol so will fall through
the alcohol, but will remain on top of the water. The oil is
less dense than the water. See Table below.
Floating Spheres - Demonstrations
with Density |
Lava Lamp:
The lava lamp in this demo does not actually work on the principle
of original electric lava lamp. In this case, a cylinder is prepared
with water on the bottom and oil floating on the top. Small amounts
of salt are added. Since salt has a high density of 2.16 g/mL,
it forms a coat around some of the oil and causes it to sink,
since it now has a higher density than water. As the salt covered
oil drop rests on the bottom of the water, the salt dissolves
into the water. When all of the salt has dissolved, the oil drop
again rises to the top since it is now again less dense than
the water. See Table below.
Lava Lamp - Demonstrations with
Density |
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Other Demonstration Examples:
Nylon Rope: The adipylchloride or (acid) solution is dissolved
in hexane. The hexane is less dense than the the lower water
solution and thus floats on top of the water. The chemical reaction
occurs right between the two layers. See Table
below.
Deep Purple Magic: In this demo, dichloromethane is added
to water that contains iodine. The density of the dichloromethane
is greater than that of the water, therefore it sinks to the
bottom. During the demo, the iodine is extracted from the water
into the dichloromethane and gives a very deep purple color.
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| Density examples based upon differences
in liquids and solids. The solid has a constant density,
but the density of the liquids varies to give various effects. |
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Ice cubes in different liquids:
In this demo ice cubes are placed into two clear liquids
which appear to be identical. One liquid is water and the ice
cube floats. The other liquid is ethyl alcohol and the ice cube
sinks. The ice cube has a constant density, but its behavior
changes because of the different densities of the liquids. See Table below.
Mysterious Ice - Demonstrations
with Density
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Eggs in different liquids:
Again in this demo, the egg has a constant density, but the
liquids have different densities. If the egg is more dense than
the liquid it will sink as in plain water. If the liquids is
more dense than the egg, it will float as in the case of the
salt water. See Table below.
Egg Densities - sugar water/oil
Floating Eggs - sugar and water - Demonstrations
with Density
In one case, the egg floats in hydrochloric acid because the
bubbles of carbon dioxide attach to the side of the egg and make
it less dense than the water so that it floats.
Smart Eggs - salt water and acid - Demonstrations
with Density
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Liquid Density examples based upon differences in temperature.
There are a number of changes to the structure of water or
any other liquid that occurs with increasing temperature. The
water molecules gain energy which is used to bend and break the
hydrogen bonds. On raising the temperature, the size of ordered
clusters of water molecules decreases, the number of smaller
clusters increases, the number of hydrogen bonds decreases and
the average distance between the water molecules increases.
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Underwater Volcano Demonstration: What makes hot water
rise? As stated above, the hot water has less hydrogen bonds
and the spaces between water molecules increases. The net effect
is to have less mass per unit volume. This translates into a
lower density. The lower density water floats on top of the denser
cold water. In the photo, the hot water is colored with red dye
to make it more visible. |
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Demonstrations
with Density |
Mysterious Ice
Layers of Liquids
Egg Densities - sugar water/oil
Smart Eggs - salt water and acid
Floating Eggs - sugar and water
Floating Spheres
Lava Lamp
Underwater Smoke Stack
Floating objects in water |
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Densities of Common Compounds |
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Substance |
Density
grams per mL |
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Hexane |
0.660 |
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Ethyl Alcohol |
0.789 |
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Rubbing Alcohol |
0.79 |
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Ice |
0.92 |
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Corn oil |
0.93 |
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Water |
1.00 |
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Sea Water (3%) |
1.03 |
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25% Salt water |
1.25 |
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Dichloromethane |
1.3 |
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Corn Syrup |
1.38 |
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Salt |
2.16 |
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