Glow sticks are fun devices that emit light through a chemical reaction (chemiluminescence). Here are glow stick experiment ideas, so you can have fun with the colored light and learn something, too!
Quick Overview of How Glow Sticks Work
It isn’t absolutely necessary to understand the chemistry behind how a glow stick works, but it may help you design more advanced experiments.
A glow stick is a plastic tube that contains a liquid and a glass capsule filled with another liquid. The liquid in the glass capsule is a hydrogen peroxide solution. The fluid outside the tube is diphenyl oxalate, a fluorescent dye, and a base catalyst (usually sodium salicylate). Snapping a glow stick breaks the glass capsule so the two liquids react. The reaction oxidizes diphenyl oxalate into phenol and peroxyacid ester. Peroxyacid ester decomposes to produce carbon dioxide, releasing energy that excites the fluorescent dye so that it releases photons (light). Adjusting the ratio of the chemicals changes how brightly a glow stick glows and how long its light lasts.
Glow Stick Experiment #1: Effect of Temperature
Glow sticks emit light because of a chemical reaction, so the most popular glow stick experiment is testing the effect of temperature on how long a glow stick lasts and how brightly it glows.
Start by applying the scientific method. Make observations of glow sticks and form a prediction of what you think will happen to a glow stick in a cold temperature and hot temperature, compared to room temperature. Conduct an experiment to test the prediction or hypothesis. Snap three glow sticks. Place one in a freezer, leave one at room temperature, and place the other in a bowl of hot water (or other warm location). Compare how brightly each glow stick glows and how long they last.
The Science (Spoiler Alert): Temperature affects the rates of chemical reactions. Usually, temperature speeds the rate of a reaction. This applies to the glow stick reaction, too. At higher temperatures, the reaction releases more energy to excite the fluorescent dye. The glow stick glows more brightly, but the reactions reaches its conclusion quickly. In contrast, cooler temperatures slow the reaction so it lasts longer but produces a dimmer light.
Glow Stick Experiment #2: Exothermic or Endothermic?
A glow stick releases energy in the form of light, so it is an example of an exergonic reaction. Is it also an exothermic (heat-releasing) reaction or is it an endothermic (heat-absorbing) reaction?
For a fun experiment, start with the scientific method. Make observations, make a prediction, and test the prediction with an experiment. If the glow stick reaction was highly exothermic or endothermic, you could simply crack the stick, hold it in your hand, and record whether it gets hot or cold. By this point, you’ve held a glow stick and know it’s neither very hot nor very color. A better approach is to place each stick in an insulated cup of room temperature water with a thermometer and see whether or not the reaction changes the reading.
The Science (Spoiler Alert): Unless your thermometer is very sensitive, you probably did not record a temperature change from the glow stick reaction. It’s an exergonic reaction, but not an exothermic reaction. How is this possible? The answer is pretty technical: the reaction violates the Woodward-Hoffmann rules so the stereochemical conformation that releases heat is a forbidden transition. The simple explanation is that the structure of the dye allows it to absorb energy and release it as light, but it can’t use that energy to change its shape and release heat. (Actually, a glow stick releases a tiny amount of heat, but not enough to really matter.)
Design Your Own Experiment
Some of the coolest science experiments come from asking “what would happen” questions. For example, what do you think would happen if you mixed the contents of a glow stick and a ferrofluid (liquid magnet). Make a prediction, form a hypothesis, and design an experiment to test the hypothesis.
Do you think the two liquids mix so you won’t see the light from the glow stick? Maybe the liquid magnet makes the glow stick brighter. Maybe the two chemicals don’t mix at all and nothing happens.
Do you have a hypothesis? Here’s what happens:
Ideas for fun glow stick experiments include:
- Is carbon dioxide produced by the glow stick reaction?
- Does adding hydrogen peroxide to the glow stick contents make the light glow brighter or affect how long the light lasts?
- Does mixing milk (which is slightly acidic) with glow stick contents affect the reaction?
- Do all the glow stick colors glow the same length of time?
- How does mixing two glow stick colors affect the color of light that is produced? Is it like mixing pigments or like mixing light?
References
- Karukstis, Kerry K.; Van Hecke, Gerald R. (2003-04-10). Chemistry Connections: The Chemical Basis of Everyday Phenomena. Academic Press. ISBN 9780124001510.
- Kuntzleman, Thomas Scott; Rohrer, Kristen; Schultz, Emeric (2012-06-12). “The Chemistry of Lightsticks: Demonstrations To Illustrate Chemical Processes”. Journal of Chemical Education. 89 (7): 910–916. doi:10.1021/ed200328d
- Kuntzleman, Thomas S.; Comfort, Anna E.; Baldwin, Bruce W. (2009). “Glowmatography”. Journal of Chemical Education. 86 (1): 64. doi:10.1021/ed086p64