DENSITY
Density = Mass/Volume
There is a.......  TUTORIAL
There is a....  VIDEO http://genchem.rutgers.edu/density.wmv (175 MB)

Density can be determined by:

A. measuring both the mass and volume,  d =  m/v

B.  by flotation

This experiment will use the first method.

  • MASS.......... will be measured using a balance.

  • VOLUME.... will be measured by:

  • measuring dimensions and using geometry.

For a rectangular solid...... V=(l)(w)(h)
For a cylinder................... V = (3.1416)r2h

  • measuring the volume of liquid displaced by a solid. You will use a 10 mL Graduated Cylinder to make this measurement.
  • indirectly measuring the weight of water displaced and converting this weight to volume using density of water.

To understand this last method, consider the two pictures of the flask below:

The flask on the left contains only solid
The right shows the same flask containing the same solid but filled to the top with distilled water. Air bubbles were carefully removed.

  1. The difference in the two weights of the flask is the weight of distilled water needed to fill the flask when the solid is in the flask.
  2. You will also measure the weight of the empty flask and stopper and the same flask completely filled with water (no air bubbles) and stoppered exactly as on the right. The difference between these two weights will give you the weight of water that fills the flask when it contains no solid.
  3. The difference between the weight of water needed to fill the empty flask and that needed to fill it when it contains the solid is the weight of water displaced by the solid. By measuring the temperature of this distilled water and looking up its density in the "Handbook", you can determine the volume of water displaced.
  4. For a schematic slide presentation, use..... DENSITY TUTORIAL
  5. You may wish to approximate some....... Densities and Masses
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PYCNOMETER

The flask with a one hole stopper, whose mass you are measuring with and without solid and with and without water, is a crude pycnometer. This is a container designed to hold a constant volume and is frequently used to measure densities. The rubber stopper has a hole in it to allow excess liquid out. The picture above on the right has a yellow stripe drawn in at the bottom of the stopper to emphasize a shortcoming of this homemade pycnometer. Commercial pycnometers have a ground glass stopper with a hole rather than a one hole rubber stopper. This always fits in exactly the same way and to the same depth maintaining the constant volume. In your rubber stopper pycnometer, you will have to be careful to put the stopper in to exactly the same depth in each of the measurements where you fill the flask with a liquid! Otherwise you will make an error.


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RWK 1997