Kristin Tesiny

Title: Chemiluminescence and Chemical light sticks.

http://www.youtube.com/watch?v=UXl8F-eIoiM

Principles Investigated: Chemical reactions producing light and changes in light intensity due to temperature, and bioluminescence in nature.

Standards: 8. Chemical reaction rates depend on factors that influence the frequency of collision of reactant molecules. As a basis for understanding this concept:

b. Students know how reaction rates depend on such factors as concentration, temperature, and pressure.

c. Students know the role a catalyst plays in increasing the reaction rate.

Materials: 3 Chemical light sticks which can be obtained from a party store (Party City) or a SCUBA diving store (Sport Chalet), 3 clear glass containers, hot water (not boiling), cold water with ice, and room temperature water.

Procedure: Take 2 light sticks and bend in half to break the glass container inside of the plastic shell without breaking plastic shell. Shake well. Pass around the classroom to illustrate there is no heat coming from the light sticks. Once the light sticks are glowing then place one light stick in the container containing hot water and place the other light stick in the cold water container with ice. Place the third light stick in room temperature water. Make sure the water is covering the light sticks. Turn down lights and monitor the differences between the three light sticks.

http://www.youtube.com/watch?v=7Ut6fSZ9N-U

Student Prior Knowledge: Students must know that when two or more compounds that the atoms may rearrange themselves in a new compound and either release energy or absorb energy.

Explanation: The light sticks contain an inner glass vial filled with hydrogen peroxide. The outer plastic tube is filled withed phenyl oxalate ester and a dye solution. When the inner vial is broken, the compounds mix and a “cool” chemical reaction where no heat is given off. The rate of the reactions\ can be accelerated or slowed down based on the temperature. When the light stick is placed in ice-cold water the reaction will slow down and the light stick will dim. When the light stick is placed in hot water the reaction will accelerate and glow brighter.

Bioluminescence: Bioluminescence is when chemiluminescence occurs in living organisms. Can you think of any animals that exhibit bioluminescence in nature?

You may think this video is from the movie “Avatar” but bioluminescence occurs right here on planet Earth!

http://www.youtube.com/watch?v=UEzkEElRr6k

http://www.youtube.com/watch?v=huG7Odk_K68

Fireflies are a type of beetle (also known as glow worms in the larval stage) that emits light also known as bioluminescence. The enzyme luciferase acts on the luciferin in the presence of magnesium ions, ATP and oxygen to produce light. As larva, light is produced to warn predators about their bad taste and/or toxicity due to chemicals and as adults it serves as a warning to predators and to attract mates.

Bioluminescence also occurs in plants. Dinoflagellates are small plants that live the ocean and use the same chemical reaction and enzymes as fireflies to produce light. When dinoflagellates are bioluminescent, the ocean and waves can appear to glow!

http://www.youtube.com/watch?v=EN1Yxq8KMsw

Questions:

1. Do all chemical reactions release heat? No, chemiluminescence does not release heat, instead energy is released in the form of light. When the chemical reaction occurs the atom gets excited and the electrons rise to a higher energy level. When the electrons fall down to their normal level, then light is released.

2. Why does the light stick stop glowing? The chemical reaction cannot be stopped once started and the reaction will continue to happen. Once the reaction is done the light stick will not glow. If you want to extend the life of your light stick then place it in the freezer (as illustrated in the demonstration).

3. Why do animals exhibit bioluminescence? Scientists understand five reasons for bioluminescence; camouflage, attraction, repulsion, communication, and illumination.

Bibliography:

http://www.webexhibits.org/causesofcolor/4ADA.html

http://www.stevespanglerscience.com/experiment/light-sticks-the-science-of-liquid-light

http://www.pbs.org/saf/1207/teaching/teaching3.htm

http://wow.osu.edu/experiments/chemistry/lightsticks.html