5 - 18 years
Prep: 20 mins
Activity: 5-10 mins
Youtube ID: KktL6JFaTFg
Customize Activity to Venue
Identify Safety Practices
Introduce Concept of Chemiluminescence
Demonstrate Luminol Reaction
Demonstrate Use of Luminol in Forensics
Here are some key themes to explore with the audience once they've completed the activity. Adjust the details to match the level of your audience.
What makes luminol glow?
When the chemical energy of a reaction is converted to visible light energy, the resulting glow is called “chemiluminescence.” Chemiluminescent reactions are what make glow-sticks and some road safety lights glow.
When luminol is dissolved in a base, such as NaOH, the H+ on its nitrogens are stripped off, leaving a dianion (i.e., a molecule with two negative charges). The dianion forms resonance structures, which stablizes it just long enough to be oxidized by the bleach, which removes the nitrogens to form a dicarboxylate ion and N2.
The oxidized luminol is left with a lot of energy, which it releases as light. Similarly, glow sticks rely on the oxidation of a trichlorosalicylate oxalate ester in a basic solution by hydrogen peroxide.
Luminol and forensics
Hemoglobin, an oxygen-carrying protein in blood, catalyzes the luminol oxidation reaction for a strong glow. Luminol is very sensitive and able to detect trace amounts of blood, even latent blood that has been cleaned or removed.
Luminol also reacts with other oxidizing compounds, such as those found in urine or saliva (even horseradish), so a positive luminol test is usually followed by one that is more specific for blood. Because the application of luminol can dilute any blood that may be present or damage other evidence, other non-destructive techniques are generally used.
Chemiluminescence in nature
When a chemiluminescent reaction occurs in an living organism, the phenomenon is called “bioluminescence.” Bioluminescent organisms include fireflies, some fungi, and certain jellyfish, bacteria, algae, and saltwater fish. These organisms either produce or absorb luciferin, a light-emitting compound.