Optional Exercise

An Analytical Study of the Percent Water in Popcorn
This experiment will give you an opportunity to become familiar with the analytical balance. It is extremely important to develop the technique needed to make accurate measurements in the lab. The concept of standard deviation will be applied to your measurements. A standard deviation of one means that there is a 67% assurance that future results will fall in that same range. The importance of doing an experiment more than once will become apparent as your results are combined with the class results.

Corn pops because there is water in the kernel. When the liquid water becomes hot enough, it converts to steam and the kernel “explodes.” Growing conditions greatly affect the amount of water held by the kernel, so it is not an exact amount for each kernel (nonstoichiometric). However, the data are interesting to work with, and you can enjoy the nice smell of popping corn!

The experiment requires you to pop kernels of corn, one at a time, in an Erlenmeyer flask over a Bunsen burner. This is not an easy task, so allow yourself a few practice kernels.

Heat the flask gently over a mild flame, using caution to avoid injury. Drop in a kernel and continue heating, moving the flask gently through the flame. A stirring rod is good for removing the popped kernel before it sticks to the container. Begin when you are confident in your popping ability.
Weigh out ten kernels on an analytical balance. Record the measurements to four places to the right of the decimal. Do not touch the kernel with your fingers after the initial weighing. Use tweezers to move the corn. Use small beakers or baby food jars to keep the kernels separate and labeled.
If the kernels will sit overnight in the lab before they are re-weighed, be certain to place them in sealed containers.
Pop the kernels and re-weigh. Discard kernels that burn or do not pop well. Record your data (see sample data table below). Seven sets of good data are needed.
Calculate the mean percent water in your seven or more good samples. Obtain the absolute difference from this mean and each individual value. Square this difference.

Questions

Compare your results with the classroom results. Where do your data fall in the classroom range?
Work with two other lab groups and recalculate your data using a minimum of 21 samples (from your combined data). Did you standard deviation improve or become greater? Explain?

Reference
Hudson, Kenney, and Watkins, The Laboratory Manual for Chemistry 105/109 and 106/110 (Carroll College, Waukesha, Wisconsin, 1986).

Important Note: The information contained herein is presented in good faith. Teachers should verify their own results prior to the use of these lesson plans in a classroom setting. Use of this document is beyond the control of The Dow Chemical Company (“Dow”), The Dow Chemical Company Foundation (“the Foundation”), the National Science Teachers Association (“NSTA”), and/or the authors. Consequently, Dow, the Foundation, NSTA and/or the authors assume no obligation or liability for the use of these materials or the outcomes of any experiments and make no warranty, express or implied. Safety glasses or goggles should be worn at all times. Other protective clothing should be worn as instructed by the teacher. All materials should be properly disposed of as instructed by the teacher. The user of these materials is solely responsible for compliance with all federal, state and local law(s) concerning appropriate safety and disposal procedures.

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