Fat, Sugar, and Protein Experiment

When you look on a package you can read the calories per serving, but you may wonder how these calculations are made. In most cases the material is carefully dried and then a specific amount of the material is burned in a special piece of lab equipment that will measure the amount of heat produced as the material burns. This is real "burning" not exactly like "metabolism" in the body. In class we would try to simulate this process with a very simple demonstration. We would take a large "real" cork (not a hard rubber kind) and place the wider end down on the lab table and then push a large pin into the center of the cork so that the point was upward (not down). This would allow you to put some type of "fat", "protein", or sugar on the point of the pin later.

Now you would need large pieces of walnuts, marshmallows, and pure wool yarn (not a synthetic). The yarn would be the protein, the walnut would contain the fatty oil and the marshmallow would contain mostly sugar. You will need to have a triple beam balance scale or some other very accurate scale. You would want to get one piece of walnut that would weigh exactly one gram. You want one gram of marshmallow and one gram of wool. (You will have to kind of ball up the wool.)

You would need three large test tubes, test tube rack, matches or lighter, and water. Place the three test tubes in the test tube rack and fill each half way full of water, They must be filled to the same level and they must be the same size test tubes. You must use goggles for eye protection and you will want a test tube holder. You would put the 1 gram of marshmallow on the head of the pin and then you would light it with a match. You hold the test tube over the burning marshmallow, time how long it burns and if possible measure the temperature of the water as soon as it stops burning. (Be careful to follow all safety rules and also be careful that you don't set off the fire alarm because of the burning material.) The water heats up and you would record the temperature.

You would do this same experiment with one gram of wool and again with one gram of walnut. The walnut should burn for a very long time and could even bring the water to the boiling point. (Be carful because the boiling water can spray out of the tube so don't point the tube toward anyone.) The experiment will dramatically show how walnuts have a great deal of stored energy in the form of fatty oils. Students would probably think that the marshmallow would have the most energy potential. The might even think that the wool will not burn - it will.

If you can measure an exact amount of grams of water into the test tubes, this is even better. It takes one calorie of heat to raise one gram of water one degree on the Celsius scale. Once the temperature of the water reaches boiling, it will no longer be able to register changes in temperature because it would simply change to steam.

You should try this experiment on your own first to be certain you can get each step accomplished properly: then you can use it as a demonstration. In my class I would do this in the front of the classroom. I would move the first students back out of the way and would still not point the test tube in their direction. Sometimes I would have a student hold the test tube (with a test tube holder) in the burning material and would have another student check the temperature (Each student would have goggles and a lab coat on during the process.) Don't push to hard on the walnut or it will break, the marshmallow sometimes melts off the pin, and the wool sometimes unwinds as it burns. Despite all of this it is a great demonstration. Even just recording the length of time each burns will give a good concept of the energy potential.