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Luminol Blood Detection

  Spraying a Luminol solution in a darkened room reveals traces of hidden blood.

Chemicals Required:
Potassium Hydroxide
Hydrogen Peroxide (3% drugstore variety)
Sterile Alcohol Pad

1. Create a 'stock' solution by mixing 0.2 grams of Luminol with 15 grams of Potassium Hydroxide in 250 ml of water.
2. In a clear cup or beaker, mix 10 ml of the stock Luminol solution and 10 ml of the 3% Hydrogen Peroxide.

The Luminol chemiluminescence reaction is used by criminalists to detect traces of blood at crime scenes. In this test, Luminol powder (C8H7O3N3) is mixed with Hydrogen Peroxide (H2O2) and Potassium Hydroxide (KOH) in a spray bottle. The Luminol solution is sprayed where blood might be found. The iron from the hemoglobin in the blood serves as a catalyst for the chemiluminescence reaction that causes Luminol to glow, so a blue glow is produced when the solution is sprayed where there is blood. Only a tiny amount of iron is required to catalyze the reaction. The blue glow lasts for about 30 seconds before it fades, which is enough time to take photographs of the areas so they can be investigated more thoroughly.
You can activate the glow by adding a drop of blood. The blood must be on the alcohol pad. The forensic test is for dried or latent blood, so the reaction between the alcohol and fresh blood is necessary.
If you simply want to view the eerie glow of a Luminol solution, see our other Luminol experiment Here.

Additional Information:
In addition to iron and iron compounds, other substances can catalyze the Luminol reaction. Copper and its compounds, horseradish, and bleach also cause the solution to glow. So, you could substitute any of these materials for the drop of blood or the Potassium Ferricyanide in the demonstration. Similarly, the presence of these chemicals at a crime scene affects testing for blood. If a crime scene was washed in bleach, for example, the whole area would glow when sprayed with Luminol, making it necessary to use a different test to find traces of blood. The iron in the hemoglobin found in blood catalyzes an oxidation reaction in which the Luminol gains oxygen atoms while losing nitrogen and hydrogen. This produces a compound called 3-aminophthalate. The electrons in the 3-aminophthalate are in an excited state. Blue light is emitted as energy is released when the electrons return to the ground state.