Dr. Campbell's Favorite Demos III

Demonstrations Page 4 - Density

Scroll down to view photographs and short descriptions of some of the demonstrations in the list below.

WARNING – Use at your own risk! We cannot guarantee the accuracy or the safety of these activities. Some of these activities are far more dangerous than others. The contributors and Bradley University do not assume any responsibility for these activities or their results. If you have questions, corrections, or comments please do not hesitate to contact Dean Campbell (campbell@bumail.bradley.edu) at Bradley University.

Ferrofluid Demonstrations
Refrigerator Magnet Demonstrations
Polydimethysiloxane Demonstrations
LEGO® Brick Chemistry and Nanotechnology Demonstrations

Soda Can Density
Cans of regular soda will sink in water; cans of diet soda will float in water. This density difference has been attributed to sugar concentration in the sodas (regular soda is more dense because it contains sugar; diet soda is less dense because it contains little or no sugar). Special thanks to Karen Campbell for assistance with the photography.

LEFT TO RIGHT: Cans of regular Coke®, Diet Coke®, Diet Dr. Pepper®, and Dr. Pepper®. Blue food coloring has been added to the water to make it more visible.

More information:
Herrick, Richard S.; Nestor, Lisa P.; Benedetto, David A. Using Data Pooling to measure the density of sodas: An introductory Discovery Experiment J. Chem Educ. 1999 76 1411.

Henderson, Susan K.; Fenn, Carol A.; Domijan, John D. Determination of Sugar Content in Commercial Beverages by Density: A Novel Experiment for General Chemistry Courses J. Chem Educ. 1998 75 1122.

A Floating Bowling Ball?
My 11-pound bowling ball will actually float in water. I use this as an illustration that a heavy object is NOT necessarily a dense object. According to some rough calculations, a 12-pound ball has about the density of water and a 13-pound ball should sink. Special thanks to Dr. Doris Kolb for the use of her demo tank.


"Lava" Lamps
Stacy Swanson assisted in preparing these descriptions.

A Real "Lava" Lamp

This lamp was purchased, not homemade. You can see our version of the lava lamp below.

ABOVE (LEFT): A lava lamp can take several hours to heat up the solid "lava"

(MIDDLE): After 90 minutes of heating, a few small spheres emerge. The wire coil found in the bottom of the container helps break the surface tension of descending bubbles.

(RIGHT): Three and a half hours later, the lava is fully heated. You can see the "blobs" sliding past each other, but they do not coalesce until they reach the bottom of the lamp. Without the wire coil, this lava would not coalesce to form the mesmerizing blobs we all know and love.

A Homemade "Lava" Lamp

We set out to find a perfect homemade recipe that could be used in the lab to illustrate a variety of physical and chemical properties such as convection, solubility, surface tension, thermal expansion and density. After searching the net for recipes, we tried a mixture of mineral oil (lava) and isopropyl alcohol. This gave us reasonable results, but the isopropyl alcohol evaporates quickly and with heating it evaporates even more quickly. So, we tried the mixture shown above. It is a saturated sodium chloride/water solution with silicone oil as the lava. We used iodine to tint the silicone oil purple. A 60 watt light bulb was used to heat the solution, and a wire coil from a heating element was placed in the bottom of the beaker to help break the surface tension of the silicone oil so new blobs can form. As the light bulb heats the silicone oil, the density of the oil becomes less than the salt water and the oil rises to the top. We shielded the top of the beaker from the light to keep a temperature differential so that the lava would cool and become more dense. The density of the silicone oil becomes greater than the salt water and the silicone oil sinks. When picking ingredients, the densities need to be similar, and the coefficient of thermal expansion for the lava should be high relative to the surrounding liquid. Ideally, the mixture should be placed in a sealed container to prevent evaporation. Another homemade recipie and a bit of lava lamp history can be found at: www.oozinggoo.com

BELOW: A homemade lava lamp.

More history of lava lamps can be found at:

www.straightdope.com/classics/a2_359.html

www.uspto.gov/patft/index.html (you can see the original US patent (#3387396) through this search engine)