They will need to understand dilution in order to be able to do these experiments in any kind of meaningful way. In this lesson an attempt has been made to relate dilution to the real world. A simple device to measure concentration will be constructed using a light sensor, light source, filter and a meter. What we see as white light is actually made up of light of different colors. The figure to the right represents the visible spectrum.
Coke absorbs more light in the blue end of the spectrum than in the green and red areas.
Since Coke absorbs light in the blue we can get the most response from our sensor if we choose a filter that lets primarily blue light through. This unit will interface with a computer that can then be projected onto a television with the proper adapter. This will give plenty of material to be cut up for class use in this lessons and others. These spectrophotometers can be made ahead of time or allow the students to make their own. If you make them, show how one is made by demo in front of class.