Nonburning Money

Chemistry:	Heat Capacity, Alcohol Flammability
Grade Range:	Elementary School, Middle School, High School
Format:	Stage

As with all fire demonstrations, keep a fire extinguisher nearby as a precaution. This demonstration is a favorite among both presenters and students, and is often requested and performed at all grade levels.

Materials

• Nonburning Solution
  • Ethanol or Isopropyl Alcohol
  • Water
  • Table Salt
• Dollar Bill & Cloth
• 2 Small Tubs
• 2 Large Tubs
• Lighter
• Tongs

Safety Precautions

Please read the Fire Safety section of the Demonstration Safety page before performing this demonstration.

This demonstration requires: Safety glasses, small blast shield, fireproof gloves

Demonstration

Preparation

• Prepare the nonburning solution: In a 1 quart bottle, combine the alcohol and the water in equal amounts, making a 50/50 solution. To make the flame more visible, you may want to mix in 2-3 tablespoons of salt, which will make it a bright orange-yellow flame rather than a faint blue flame.

Presentation

1. Set out the tubs (small tubs if using a dollar bill, large tubs if using the cloth) and fill one halfway with water. Fill the other tub with the nonburning solution, enough to cover the bottom of the tub with a thin layer. Close the bottle with the nonburning solution and move it off the table, setting it at least five feet away from the demonstration area. Put the dollar bill or cloth into the solution, and have it soak thoroughly.
2. Explain to the audience that you will be making a fire. Have the students list the three things needed for a fire (oxygen, a fuel source, an ignition source).
3. Explain that you will be using an alcohol, and that alcohols are flammable. Ask the students for ideas on what will happen when you ignite the dollar bill/cloth that is soaked in alcohol. During this time, put on the safety gear and use the tongs to pick up the dollar bill/cloth and hold it over the tub of water.
4. Have students do a countdown, and ignite the dollar bill/cloth. It will burn for several seconds, but then the flame will go out, leaving it intact! dunk it briefly in the water afterwards to cool it down before handling it, and ask the students for ideas on why it didn't burn. Is there something else in the solution?

Why This Works

Short Explanation

Alcohols are extremely flammable, and burn very hot and very quickly. This is because alcohols are Volatile, which means they easily turn into a vapor and mix into the air. This means that we have to be careful about having alcohol near a fire or anything really hot, because if not carefully watched it might ignite! With the Dollar bill/cloth, we had it soaked in a solution that was half alcohol and half water. The water did not stop the alcohol from burning, and it was able to ignite and start burning quickly. However, water has a high Heat Capacity, meaning it can absorb a lot of heat before turning into steam. This means the water was able to absorb all the heat from the alcohol, and kept the dollar bill/cloth safe from the fire!

Full Explanation

Alcohols are organic compounds which readily combust when exposed to a heat source. Alcohols are highly Volatile, meaning that they readily vaporize while at standard pressure and temperature. Alcohols also have a low Heat Capacity, meaning that they can only absorb a small amount of heat before vaporizing or igniting. Alcohols such as ethanol readily decompose and release a large amount of energy when ignited:

Ethanol + 3 O2 (g) (C2H5OH)

→

2 CO2 + 3 H2O + Heat (1 mol ethanol = 12.3 MJ)

One mole of ethanol is only 2.5 cups (0.58 l), and 12.3 MJ is equivalent to the kinetic energy of a flatbed tow truck moving 100 mph (160 km/h)! This fact, as well as the relative ease in igniting ethanol, is why it is now used as a fuel source. Water, unlike alcohols, is not very volatile and has a high heat capacity. The old proverb "A watched pot never boils" draws from the fact that water takes a while to get up to temperature. In fact, to get 2.5 cups of water from room temperature to heat up and vaporize, you would need about 15 MJ of heat energy, which is nearly 25% more than what an equal amount of ethanol can provide! This is what results in the dollar bill or cloth being unscathed and intact!

This demonstration also shows us a technique used in movies. When a stunt requires someone to be "burned alive", the stunt performer will wear a suit which either is padded with water-filled pockets or is heavily soaked in water. That way, when they are covered in the combustible material and ignited, the water will absorb the heat and keep them safe!

Additional Information

• This demonstration pairs well with the Methanol Cannon, and these two can then be used to compare the types of alcohols. Methanol is known as wood alcohol and is used in antifreeze, solvent and some fuels. Methanol is poisonous, and when ingested is broken down into formic acid and formaldehyde, or embalming fluid. Ethanol is the type of alcohol present in wine, beer and other spirits. Ethanol is also used as a fuel in vehicles, and has long been used as antiseptic.
• This demonstration is a part of the Fire and Ice Show