Spartan Luminol

Chemistry, Biology:	Chemilluminescence
Grade Range:	Elementary School, Middle School, High School
Format:	Stage

This is a classic Luminol demonstration with the addition of some MSU Spartan pride. The solutions should be prepared at least 8 hours in advance. However, they don't have a long shelf life, so don't rely on any solutions that are 3 months old or older.

Materials

• 2000 mL Vacuum Flask with Tube Cork
• Vacuum Pump
• Spartan "S" Board
• 500 mL Bottle (for Water)

Solution A

• Luminol
• Sodium Carbonate
• Sodium Bicarbonate
• Ammonium Carbonate monohydrate
• Copper (II) Sulfate OR Copper (II) Chloride
• Water
• 1000mL Brown Bottle or similar

Solution B

• Hydrogen Peroxide
• Water
• 1000mL Brown Bottle or similar

Safety Precautions

Please read the Dry Chemical and Liquid Chemical sections of the Demonstration Safety page before performing this demonstration.

This demonstration requires: Safety Glasses, Gloves

Demonstration

Preparation

Solution A: Mix the following chemicals into 500 mL of DI water in order, stirring constantly. Do not add the next chemical until the one prior is fully dissolved. Mix these chemicals either within a dark bottle or in a room with the lights dimmed, as some of them are light sensitive.

• 4.0g Sodium Carbonate
• 0.2g Luminol (3-aminophthalhydrazide)
• 24g Sodium Bicarbonate
• 0.5g Ammonium Carbonate Monohydrate
• 0.4g Copper (II) Sulfate OR 0.25g Copper (II) Chloride

Once all of the chemicals are in solution, add 500mL of DI water to dilute fully. Store in an airtight brown bottle or similar, and label with the Demonstration name, Solution A, and date, as well as your initials.

Solution B: Dilute 5mL of the 30% Hydrogen Peroxide with 1L of DI water. Store in an airtight brown bottle or similar, and label with the Demonstration name, Solution B, and date, as well as your initials.

Presentation

1. Set up the Spartan "S" board, and connect the single ended tube to the tube cork. Put the tube cork on the vacuum flask, and connect it to the vacuum pump.
2. Show the audience the two solutions, and ask them if they have seen fireflies before. Can anyone guess how a firefly lights up? Explain that there is a chemical reaction, much like the one that will happen between the two solutions you have.
3. Put the double ended tube into the two solutions. Explain that the two chemicals will react when they mix and produce light. Ask for a countdown, and at the end flip the switch on the vacuum pump.
4. Watch as the solutions are pulled through the tubing and start to glow! The vacuum pump will pull the solutions pretty quickly, so make sure to watch the bottles for when they run out.
5. After explaining the demonstration, put both of the ends on the double ended tube into the water bottle. Vacuum the water through the tubing to clean it, and then let the vacuum run for a minute to pull air through and dry the tubing. The end solution can be poured safely down a drain.

Why This Works

Short Explanation

Chemilluminescence is when a chemical reaction produces light. The reaction does not have to emit heat, like when a reaction creates fire, but gives off light without being hot. For our reaction, we have a luminol solution mixing with a hydrogen peroxide solution. the hydrogen peroxide reacts with the luminol and causes it to release energy, which it does so by emitting light. If you were to touch the tubes while the reaction happened, they wouldn't be warm at all, even though they are glowing!

This kind of reaction is not very common in chemistry, but it is a reaction that we are all pretty familiar with. Glow sticks use a luminol reaction, by having the two solutions mix together in a small sealed tube. When you crack a glow stick, you are actually breaking a tiny glass tube inside the glow stick. This tube contains a hydrogen peroxide solution, which reacts with the glowing solution around it. Fireflies, or lightning bugs, also use chemilluminescence. When a firefly glows, it has a similar reaction happen inside of its abdomen, which causes a small burst of light. Fireflies create their lights in order to communicate, and each species of firefly uses a different flashing pattern!

Full Explanation

Chemilluminescence is when a reaction produces light without also being exothermic. The release of chemical energy in the reaction excites the electrons in the atoms and molecules, and they go to a higher energy level. The electrons then drop to a lower energy level, emitting a photon in the process. This type of reaction is uncommon, as most reactions that produce light do so by blackbody radiation. Blackbody Radiation is when the electrons in an atom or molecule are excited and go to a higher energy level due to thermal energy. When they drop back to a lower energy level, they produce light.

The Luminol reaction goes through three major steps. When the solutions are first prepared, the sodium carbonate create a basic solution, and luminol reacts with it:

Na2CO3 + H2O	→	2 Na+ + 2 OH- + H2CO3
C8H7O3N3 + 2 OH- (Luminol)	→	C8H5O3N32- + 2 H2O (Luminol Dianion)

It is worth noting that the sodium bicarbonate in solution acts to buffer the carbonic acid (H₂CO₃) being produced, keeping the solution basic.

When the two solutions are mixed, the hydroxide decomposition is catalyzed in a two step reaction by the Copper salt anion:

2 H2O2 + (2 SO42-) or (2 Cl-)	→	2 H2O + (2 SO3- + 2 O2) or (2 ClO-)
2 H2O2 + (2 SO3-) or (2 ClO-)	→	2 H2O + (2 SO42-) or (2 Cl- + 2 O2)

The O₂ produced then reacts with the luminol dianion, replacing the Nitrogen and producing light:

C8H5O3N32- + O2

→

C8H5O5N2- + N2 + Light

Although the peroxide decomposition produces a small amount of heat, it isn't enough to generate the light at the end. The light produced is from the replacement of nitrogen with oxygen, which leaves extra chemical energy in the luminol dianion and excites the electrons on the oxygen. when the electrons release this energy, they release it as light.

This reaction can be found in nature, such as with fireflies using luciferin and the enzyme luciferase to produce light in their abdomens. This reaction is also commonly used as a novelty with glowsticks. Inside a glowstick is a small glass cylinder which contains a peroxide solution. when you bend a glowstick, you break this cylinder and let the peroxide react with the solution around it, producing light!

Additional Information

• This demonstration pairs well the Fluorescent Liquids demonstration, as a way to compare the effects.