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Anyone who has played with finger paints knows that if you mix enough different colors together, you end up with a black mess. Mixing different colors of light, however, yields quite a different result. When all the colors of visible light are combined, you can end up with white!
To understand how this works, consider the primary colors of both light and pigment. Red light is the name given to visible light (visible electromagnetic radiation) with a wavelength of about 600 nm (.0000006 meters). Red paint, in contrast, is made from a pigment which absorbs all visible light, except red. When light hits a mirror, nearly all the colors are reflected equally. When light strikes red paint, only the red light is reflected. Other colors are absorbed by the paint. In other words, an apple looks red because the pigments in its skin reflect only red light.
Paint pigments are designed to systematically absorb and reflect different colors of visible light. In this way, scientists and artists are able to produce just about any color of the rainbow. If the primary colors of pigment (red, yellow, and blue) are mixed together, all the colors of visible light will be absorbed and we will see black.
The primary colors of light, however, are quite different. When they are combined, we perceive white light. Many light sources emit white light. In actuality, these sources are emitting nearly all the colors of visible light. When we see each of these light waves together, we perceive the color white.
6 light sticks: 2 red, 2 green, and 2 blue
4 small (~50 ml) beakers or clear plastic cups
2 white paper towels
1 sharp pocket knife or X-acto knife (not incl.)
This demonstration should be performed in a dark room (the darker the better). In practice, the demonstration produces enough light to work by, so we usually make the room completely dark.
While the chemicals contained within lights sticks are reported to be non-toxic, this demonstration
should only be attempted in an appropriate, properly equipped, laboratory environment. Goggles and
gloves should be worn at all times. Also, be aware that the chemicals contained with the light sticks
can stain clothing.
The chemicals contained within light sticks may be safely washed down the drain with water. All
glass and plastic should be disposed of properly.
Light sticks contain a small glass ampule, which must be broken to activate. This glass is extremely
fine and sharp, and breaks into small slivers. Extra special care must be taken to avoid touching this glass. Do not pour the chemical within the light sticks onto your hand, or place your hand in the chemical after it has been poured into a beaker. The glass is extremely difficult to see (especially in the dark) and it is probably that some glass will remain in the liquid even after it has been decanted.
Sarquis, Mickey and Jerry Sarquis. Fun with Chemistry – A Guidebook of K-12 Activities, Volume 1. Institute for Chemical Education: Madison, WI; pp. 163-166.
Shakhashiri, Bassam Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 1. The University of Wisconsin Press: Madison, WI; pp. 146-152.
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Students can plan and conduct an investigation with the Light Sticks to describe and classify different kinds of materials by their observable properties.
Students can plan and conduct an investigation with the Light Sticks to develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen.
Students can use the Light Sticks to conduct an investigation to determine whether the mixing of two or more substances results in new substances.
Students can use the Light Sticks to develop and use a model to describe how waves are reflected, absorbed, or transmitted through various materials.
Students can use the Light Sticks to construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the Periodic Table and knowledge of the patterns of chemical properties.
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