The Caliper
A Publication for Users of Vernier Products

Innovative Uses

Vernier equipment was used in two recent projects:
• In a flowing-water analogy to radioactive decay, the amount of water in a given vessel, measured by weight by a force sensor, corresponds to the quantity of a radioactive substance. With water flowing at a fixed rate through a capillary tube from one vessel to another, secular equilibrium can be modeled. Stephen J. Fairman, Joseph A. Johnson, and Thomas A. Walkiewicz, "Fluid Flow with Logger Pro," Phys. Teach. 41, 345-350 (Sept. 2003).
• By measuring the rotational period of the tires using an attached magnet and our Magnetic Field sensor, John Buschert was able to accurately measure the power output of a car, including corrections for air drag and rolling friction. John Ross Buschert, "Measuring Horsepower and Torque Curves of a Car," Phys. Teach. 41, 355-361 (Sept. 2003).

Vernier LabPro Goes to Denali

Pete Monte of Forest Grove, Oregon, recently climbed the highest peak in North America, Denali (also known as Mt. McKinley). Pete carried a Vernier LabPro, temperature probe, and a Gas Pressure Sensor all the way to the (20,320 ft, 6,194 m). He recorded temperatures well below freezing (in June), and pressure down to 54 kPa - approximately half of standard atmospheric pressure. Here is a photo of Pete at the top with his LabPro.

A Four-Color Oscillating Reaction: Cerium-Catalyzed Bromate-Malonic Acid Reaction

Not only does this exciting reaction change from green to blue to purple to red, in less than a minute, but then it repeats the four color sequence continuously for over an hour! This very famous reaction is known as the Belousov-Zhabotinsky Reaction, or simply the B-Z reaction.

We thought it might be interesting to see if our sensors could be used to detect the repeating behavior of the chemical reaction. Some of the most interesting results came by using a Stainless Steel Temperature Probe. The results can be seen in these Logger Pro 3 graphs. The first graph shows 20 minutes of data collection, and about 30 cycles of the oscillating reaction. In the second graph, we have zoomed in on 2 cycles, and show where each of the colors appear.

Temperature of the B-Z reaction over 20 minutes

Temperature and color changes of the B-Z reaction over two minutes

These data suggest that the mechanism exhibits a net exothermic process, followed by a somewhat smaller endothermic process, yielding a gradually increasing temperature. What would data from an ORP Sensor, Colorimeter, or pH Sensor look like for this reaction? Try it for yourself!

Flinn Scientific (800-452-1261 or www.flinnsci.com) sells a kit containing all the solutions and instructions needed for this reaction. Order the Fantastic Four-Color Oscillator Chemical Demonstration Kit (order code AP4833). If you wish to prepare your own solutions, instructions can be found in Bassam Shakhashiri’s Chemical Demonstrations: A Handbook for Teachers of Chemistry, University of Wisconsin Press: Madison; 1985; Volume 2, pp 257-261. A very thorough explanation of the reaction mechanism can also be found in the Shakhashiri book.