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