My goal is to incorporate as many relevant demonstrations into the classroom as possible. Here are photographs of some demonstrations that I have done. Caution: The descriptions of these potentially dangerous demonstrations are incomplete. If you have questions about these demonstrations or suggestions please contact me at campbell@bradley.edu.

No Suds! (water hardness)

This is an easy demonstration if you live in a place like the midwest where hard water is readily available. Acquire some empty 20 oz. soda bottles and fill them halfway: one with hard water, one with deionized water. Add the same amount of soap to both bottle (several drops of inexpensive pine cleaner has worked for me, Ivory soap shavings also work well) and close the lids tightly on the bottles. Shake both bottles about 50 times. Immediately after shaking, the hard water will have more foam on its surface, but this foam quickly breaks, leaving only foam on the deionized (DI) water. The lack of foam on the hard water is due the calcium and/or magnesium ions in the water. These ions bind to the soap molecules in the water, rendering them useless. One result of this is that little or no foam forms on the surface of the water.

References:

Soriano, David S.; Draeger, Jon A. A water treatment experiment (chemical hardness) for nonscience majors. J. Chem Educ. 1993 70 414.

Birch, E. John H. Hardness in water- a demonstration. J. Chem Educ. 1949 26 196.

 

Demonstrating Poisson's Ratios with Chicken Wire

The lateral expansion or contraction of a material as it is stretched can be bescribed by a mathematical relation called the Poisson's ratio. Most materials tend to contract laterally as they are stretched (and have a positive Poisson's ratio), but some materials expand laterally as they are stretched (and have a negative Poisson's ratio). Often a material that has a positive Poisson's ratio can be modified to form a structure that has a negative Poisson's ratio. Chicken wire can be used to demostrate these ratios. Caution: Cut chicken wire can be sharp!

References:

Campbell, D. J.;Querns, M. K. "Using Paper Cutouts to Illustrate Poisson's Ratio." J. Chem. Educ., 2002, 79, 76.

For instructions on how to make fullerene models out of chicken wire, see Murphy, C. J.; Campbell, D. J. "A Chicken Wire Buckyball." Chem. Educator 2000, 5, 1.

ABOVE: Positive Poisson's ratio structures (LEFT) unstreched and (RIGHT) stretched.

ABOVE: Negative Poisson's ratio structures (LEFT) unstreched and (RIGHT) stretched.

 

Balloon in an Airplane (air pressure)

Most everyone who has traveled on an airplane has witnessed some effects of decreased air pressure in the cabin of the plane: ears "pop", poured soda fizzes a little more, and sealed bags swell up. This last observed phenomenon was the basis of a simple experiment run on a long flight from Chicago to Honolulu to estimate the amount of air pressure change. The equipment required is very simple: a typical rubber balloon, a flexible measuring tape (such as one used for clothing measurements), and a permanent felt-tip marker. All of this should present no risk to airline security. Before the plane leaves the ground, inflate the balloon about halfway. DO NOT fully inflate the balloon. If it expands too much when the plane is in the air, the ballon may pop. This not only ruins the experiment, but it may also disturb fellow travel weary paasengers. The flexible measuring tape is used to measure the circumference of the balloon. Since most balloons are not perfectly spherical it is advisable to use the marker to indicate the path of the measuring tape. That way later measurements can be made across the same path. Once set up, the balloon circumference can be measured at any time. One the Chicago to Honolulu trip, a ground circumference was measured to be 52.4 cm and a cruising altitude circumference was measured to be 54.9 cm. Assuming a spherical balloon and that the ground pressure was 1.00 atm, the pressure at cruising altitude would be 0.869 atm.

 

Using the relationship between altitude and pressure described on p.26 of van Loon and Duffy (van Loon, G. W.; Duffy, S. J. Environmental Chemistry: A Global Perspective, Oxford University Press, 2000), a pressure of 0.869 atm relative to a sea-level pressure of 1.00 atm corresponds to an altitude of 4000 feet. Most planes I have been on cruise at a around 35,000 feet, which corresponds to a pressure of 0.294 atm relative to a sea-level pressure of 1.00 atm. Clearly the cabin of the plane is pressurized!

 

Demonstration Pictures: Page 1, Page 2, Page 3, Page 4, Page 5, Page 6, Page 7

 

Link to pictures of LEGO demonstrations

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Last updated 6/10/06

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