Chemiluminescence

Demonstration – Oxidation of Luminol

Materials:

2L of distilled water

4.0g of anhydrous sodium carbonate

24.0 g of sodium bicarbonate (baking soda)

50 mL of 3% hydrogen peroxide

0.1 g luminol

0.1 g bovine hemoglobin

0.005g fluorescein disodium salt

2L beaker

Spatula

Magnetic stirrer

Large stirring bar (2 to 3 cm)


Safety: Wear gloves, safety goggles, and a lab apron/lab coat at all times in both the preparation and the performance of the demonstration.


Demo Preparation:

Solution A:

  1. Pour 1.5L of distilled water into the 2L beaker.

  2. Add 4.0g of sodium carbonate and 24.0g of sodium bicarbonate to the beaker.

  3. Stir to dissolve.

  4. Add 50 ML of 3% hydrogen peroxide and dilute to 1800 mL with distilled water.


Powder B:

  1. Mix 0.1 g bovine hemoglobin with 0.1g of luminol.


Powder C:

  1. Take 0.05g of Powder B and mix it with .005g of fluorescein.


Performance of demo:


  1. Place the beaker containing Solution A onto a magnetic stirrer and place the stir bar into the solution.

  2. Adjust the stirring speed to form a slight vortex, 2-3 cm in depth.

  3. Turn off the lights.

  4. Sprinkle about 0.04g of Powder B into the vortex.

  5. Then, sprinkle about 0.04g of Powder C near the walls of the beaker.


Disposal:

Contents can be flushed down the drain.







Discussion:

Chemiluminescence is light created by a chemical reaction. The electrons in the atom absorb energy from the chemical reaction, causing them to go to an excited state. The electrons return to the ground state since the excited state is unstable, releasing a photon of light- the glow that we see. Different colors result from different wavelengths of light. Students may have heard of luminol before from watching criminal investigation shows such as Forensic Files or CSI. The oxidation of luminol is similar to the reactions that occur in fireflies. When a chemical reaction produces light in an organism, we call this bioluminescence. Luminol, 5-amino-2,3-dihydrophthalazine-1,4-dione, is pictured below:


image taken from http://www.sigmaaldrich.com/catalog/search/TablePage/16187804



The chemiluminescence of luminol is an oxidation reaction represented in general terms by the below equation:




(image derived from http://www.practicalchemistry.org/experiments/chemiluminescence-cold-light,62,EX.html and altered to match generic reaction from reference)


There are several variations of this demonstration, but all involve the above general chemical equation, the oxidation of luminol to the aminophthalate ion, producing light energy. Depending on the media used, various mechanisms for the reaction take place. In this demonstration, the reactants used are in powder form to produce the colorful “tornado” effect. The activator for the reaction is an iron(II) complex found in the bovine hemoglobin.


Reference:

Shakhashiri, Bassam. Chemical Demonstrations. Volume 1. University of Wisconsin Press: Madison, 1983. pg. 156-167.