««« Contributed by James Palcik
Chemiluminescence is an unusual chemical property in that it allows certain compounds to spontaneously give off light. In this demo, hydrogen peroxide is added to a luminol solution in a darkened room. The resulting chemical reaction produces a blue light that lasts for several minutes.
Curriculum Connection: Grade 10 Chemistry, Academic and Applied; Grade 11 and 12U Chemistry. This activity examines the concept of Energy of Reactions.
- 1 bottle Luminol solution
- 1 bottle Hydrogen peroxide, 6%
Safety Goggles, Gloves, Lab Apron.
- In a darkened room, place approximately 20 mL of luminol solution in a small beaker or similar container.
- Add 1 mL of 6% hydrogen peroxide to the luminol solution and observe.
Many chemical reactions that emit light also emit heat (exothermic). Luminol chemistry produces what is known as “cool” light. In other words, very little (if any) heat is emitted. Luminol in solution normally exists in a ground state. The addition of an oxidizer (hydrogen peroxide in this case), in the presence of a catalyst, causes the luminol molecules to enter an excited state. As the molecules return to the ground state, the energy from the excited state is emitted as light, with virtually immeasurable amounts of heat.
Chemiluminescence should not be confused with phosphorescence (“glow-in-the-dark”). Phosphorescent materials absorb and store energy upon exposure to light and that light energy is released slowly, noticeable when the material is in a dark environment. Chemiluminescent materials do not need to be “charged” with light prior and emit the cool light strictly through chemical reaction.
Chemiluminescent materials are most commonly used in the familiar light sticks, as well as in some medical procedures. One of the more interesting uses for luminol is in forensic investigations. The iron in blood can serve as a catalyst for the luminol reaction and when sprayed on blood evidence at a crime scene, even if an attempt has been made to clean it or it is several years old, will undergo the chemiluminescent reaction and glow.
Dispose of all chemicals in accordance to provincial and Board regulations.
About the author
James Palcik is the owner of Palcik Educational in Ancaster, Ontario. This activity is from the Whiz, Bang, Boom Demos for Science conference session, delivered by James at STAO 2012. Activity from Innovating Science™ by Aldon Corporation, copyright 2008. Used with permission of Palcik Educational.