| 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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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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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. |
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Floating Spheres: |
| 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 |
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Other Demonstration Examples: 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. |
| 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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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. In one case, the egg floats in hydrochloric acid because the
bubbles of carbon dioxide attached to the side of the egg and
make it less dense than the water so that it floats. |
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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. |
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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| 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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The formal definition of density is mass per unit volume. Usually the density is expressed in grams per mL or cc. Mathematically a "per" statement is translated as a division. cc is a cubic centimeter and is equal to a mL Therefore,
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