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see also:
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Light sticks
Demonstration Notes, Warnings, Safety Information, The luminol solutions and the contents of a light stick are reasonably safe. The light stick should not be opened because of broken glass remaining inside.
There are three components of a lightstick. There need to be two chemicals that interact to release energy and also a fluorescent dye to accept this energy and convert it into light. Although there is more than one recipe for a lightstick, a common commercial lightstick uses a solution of hydrogen peroxide that is kept separate from a solution of a phenyl oxalate ester together with a fluorescent dye. The color of the fluorescent dye is what determines the resulting color of the lightstick when the chemical solutions are mixed. The basic premise of the reaction is that the reaction between the two chemicals releases enough energy to excite the electrons in the fluorescent dye. This causes the electrons to jump to a higher energy level and then fall back down and release light.
Specifically, the chemical reaction works like this: The hydrogen peroxide oxidizes the phenyl oxalate ester, to form phenol and an unstable peroxyacid ester. The unstable peroxyacid ester decomposes, resulting in phenol and a cyclic peroxy compound. The cyclic peroxy compound decomposes to carbon dioxide. This decomposition reaction releases the energy that excites the dye.
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simple experiments, see also
SimpleScience
EXPERIMENT 9. CHEMILUMINESCENCE ( from
http://mattson.creighton.edu/O2/ )
Equipment
Microscale Gas Chemistry Kit
Chemicals
O2(g), 60 mL KOH pellets, 4 g Luminol, 0.1 g DMSO (dimethylsulfoxide), 10 mL
Suitability
classroom demonstration
Applications, Topics, Purpose
forms of energy, chemiluminescence
Precaution
Read the safety information available for DMSO, dimethylsulfoxide! Wear gloves. Avoid dermal contact.
Instructions
Measure out 4 g KOH pellets and 0.1 g luminol and set them aside for use later. You will also need 10 mL DMSO. Generate oxygen and wash the gas twice. Remove the plunger, dump out the vial cap, add the solid KOH and luminol through the syringe mouth and reinsert the plunger to its previous mark (about 60 mL.) Because O2 has a similar density to that of air, O2 loss is not excessive if you work quickly and replace the plunger as soon as possible. Remove the syringe cap and draw 10 mL of DMSO into the syringe and 2 - 5 mL H2O. Darken the room. Shake the solution and it will emit a blue chemiluminescent glow which will last for a very long time, depending on the amount of shaking. We have had the system last 48 hours.
Clean-up: Do not reuse this syringe. DMSO must be disposed of properly. One effective method that we have used is to remove the plunger and dump in 30 mL of absorbent cat litter, reinsert the plunger, remove the excess air, and recap. Place capped syringe containing dmso and cat litter in a sealed food storage bag and place in the trash. Check state regulations.
Teaching tips
1. Relate the demonstration to light sticks.
Questions
1. What are the three ways in which a chemical reaction can give off energy?
2. What are other examples of chemiluminescence?
3. Why does shaking the syringe make the light brighter?
4. Why does the reaction eventually stop?
--
RachelWingfield - 10 Jun 2004
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