Spartan Luminol
Age
Elementary School, Middle School, High School
Format
Stage Show
Materials
A-1 and A-2 solutions (see below) Erlenmeyer flash with sidearm and stopper Vacuum pump
Safety Precautions
Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. The chemicals used in this demonstration are safe to go down the drain, as long as you dilute them with water.
Copper (II) Sulfate Pentahydrate MSDS
Copper (II) Chloride Dihydrate MSDS
Preparation
Solution A-1
12.0 g sodium carbonate, dissolved in 1500 mL of DI water 0.6 g Luminol (3-aminophthalhydrazide) THIS COMPOUND IS LIGHT SENSITIVE, THEREFORE STORED IN A PAPER BAG 72.0 g sodium bicarbonate 1.5g ammonium carbonate monohydrate 1.2g copper (II) sulfate pentahydrate OR 0.75 g of copper (II) chloride dihydrate dilute with DI water to 3 L
You will need to shake vigorously or use a stir plate and stir bar to get everything to dissolve. Make sure everything dissolves!
Solution A-2
150 mL 3% hydrogen peroxide Dilute to 3 L with DI water
Demonstration
Use approximately equal amounts of A1 and A2. If taking out into the audience, make sure the solution is stoppered! To run the Spartan S, you need to put one tube into A1 bottle, one tube into A2 bottle (make sure the tubes are clean before you do this, you can run them with water beforehand to make sure). Then, but the stopper on top of a LARGE filter flask and pull a vacuum. WATCH the filter flask to make sure it doesn't get too full of solution. BEFORE you turn off the vacuum, pull out the tubes from A1 and A2, otherwise you will get backwash and it will ruin the rest of your solutions. Put both tubes in a solution of water and pull water through the S to clean it, then pull air.
What to Say
If presented along with several other chemical demonstrations, you may wish to begin by highlighting the novelty of chemiluminesence. Ask the audience what types of things chemical reactions can do. Ask them what types of things they have seen reactions do earlier in your performance, if applicable. They might tell you that reactions can produce heat, as in elephant toothpaste, or eat away at things, as in rip-the-can. Well, chemical reactions can also produce light!
For very young audiences: "Chemiluminescence is a very special type of chemical reaction that produces lots of light. In this case, we are combining a chemical called luminol with one called hydrogen peroxide. Hydrogen peroxide is just the stuff you keep in your bathroom to clean cuts! When you mix these two chemicals, with a few other helper chemicals, the hydrogen peroxide gives energy to the luminol - it makes it excited. It's kind of like how eating a lot of candy gives you energy and makes you bounce around! Luminol is a chemiluminescent chemical, which just means that it likes to get rid of this extra energy by glowing - it makes light!"
This demonstration scales well to more advanced audiences. For high schoolers who may be familiar with the Bohr model, explain how electronic transitions produce photons (see the Why It Is) section and briefly describe why only very special reactions are chemiluminescent.
Why It Is
Chemiluminescence is a rare effect. Most light we see in nature is produced by very hot objects. For instance, the sun and incandescent light bulbs are both very hot objects that emit light through a process called blackbody radiation. In blackbody radiation, thermal energy excites electrons in atoms or molecules to higher energy levels, which then fall back into lower energy levels and use the energy difference to release a photon of light.
Chemiluminescence causes involves transitions causing photons to be released, but the mechanism is very different than blackbody radiation. Rather than heat (thermal energy), chemical reactions provide the energy for electrons to reach higher energy levels in the molecules of a chemiluminescent solution. In this case, the chemical reaction involves the luminol being oxidized by the hydrogen peroxide. A variety of different reactions with luminol can be used, producing different color emission (see Reference 1).
So why don't all exothermic (energy-releasing) reactions produce chemiluminescence? Certain factors must be satisfied. The exothermic reaction must produce a molecule for which excited states can be occupied - not all molecules have these. Moreover, the probability for the molecule to be produced in this excited state must be greater than the probability of it to be produced in the ground state. Finally, the molecule in the resultant solution must be disposed to releasing photons via electronic transitions and must do so at a high rate to produce an easily-visible amount of light. The specific conditions of these characteristics is quite complicated.
Do not confunse chemiluminescence with phosphoresence or fluorescence. In those other processes, light is only emitted following the absorption of light. Phosphorescent or fluorescent reactions do not "glow in the dark," they must be illuminated by photons to then produce photons.
Real Life Examples
Fireflies have enzymes that act on a luciferin substrate to produce their chemiluminescent effect. Many other types of organism, including some bacteria and algea, have similar abilities.
Lightning is also a chemiluminescent effect. It is an electrical discharge in the atmosphere that excites electrons in the gas molecules in air, which then fall back down and produce photons. Lightning also dissassociates diatomic nitrogen and oxygen, which can then release photons when they recombine.