Methanol Cannon

Chemistry:	Combustion Reactions, Vortexes
Grade Range:	Elementary School, Middle School, High School
Format:	Stage

The Methanol Cannon is a Science Theatre classic, and works for all ages. This demonstration does produce a large flame, so follow all safety precautions for this demonstration to minimize risk of injury.

Materials

• 5 Gallon Jug with Cork
• Methanol
• Centrifuge Tube
• Tall Matches

Safety Precautions

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

This demonstration requires: safety glasses, fireproof gloves

When performing this demonstration, avoid bringing the bulk container of methanol if possible. Instead, bring a much smaller amount in a 50mL bottle. This will minimize any risk of accidental ignition.

Demonstration

1. Put on the safety glasses. Measure out 5mL of Methanol using the centrifuge tube, and hold it aloft so the audience sees how little you are using. Pour the 5mL into the 5 gallon jug and cork it. Close the methanol container and remove it from the table, having it at least 5 feet from the table.
2. Pick up the jug and start swirling it to vaporize the contents. Explain what you are doing to the audience, and introduce the term Volatile.
3. Have someone standing at the ready to turn off the lights in the room. Put on the gloves, light the long match, and hold it downward so the flame can creep up the stick. Ask for a countdown from 5: at 3, start pulling out the cork, and have the lights turn off at 1. Once the lights are off, pull the cork out completely and drop the match in.
4. After the fire happens, have the lights turn back on and explain the demonstration.

Why This Works

Short Explanation

Methanol is a simple alcohol, and like all alcohols it is volatile. Volatile means that it will quickly vaporize while in the open, even if it isn't warm enough to boil. Alcohols are also very flammable, and release a lot of energy when they burn. This reaction only uses 5 mL of methanol, or about a tablespoon, and we still get a very big flame and a very loud whoosh when we light it! The flame we see is blue because of how hot this reaction is, and the reaction itself is a "clean" combustion reaction, since it only produces water, carbon dioxide and heat!

An interesting additional fact about this reaction is the shape the fire has while burning. Some students might notice that the fire inside the jug is swirling. This happens because of two things: the hot air inside rushing out, and the cool, oxygen rich air rushing in. The air rushing out creates a Vortex, or the "whirlpool" shape, to allow air to rush in and keep the reaction going!

Full Explanation

Methyl alcohol (Methanol) is a simple alcohol with the form CH₃OH. The "methyl" refers to the type of carbon group attached to the hydroxide, and by adding carbon groups we can get other alcohols such as:

Methanol or Methyl Alcohol	Methyl = 1	CH3--OH
Ethanol or Ethyl Alcohol	Ethyl = 2	CH3--CH2--OH
Propanol or Propyl Alcohol	Propyl = 3	CH3--CH2--CH2--OH
Isopropanol or Isopropyl Alcohol	Iso = Isomer	CH3--CH--CH3 CH3--└OH

Alcohols all share a few things in common. They are all Volatile, or readily vaporize at room temperature. This is due to their vary low Heat Capacity, as alcohols only need a small amount of heat to boil. Most importantly, alcohols are highly flammable, and when they burn they release a large amount of energy. This is largely due to how cleanly an alcohol fire burns:

Combustion of General Primary Alcohols

RCH2OH + O2 + Heat Source → R: "Refers" to more CHn

CO2 + H2O + Heat Released

Since the only products are CO₂, H₂O, and heat, this combustion reaction releases a lot of energy with next to no smoke production, and is able to burn quickly. This is why, in order to see the flame, we need to turn off the lights in the room! Since it burns so efficiently, there is no debris that can glow from the heat. Alcohol burns with a blue flame, but since it happens so quickly the flame is nearly impossible to see if the room is bright!

5 mL of methanol weighs about 4 grams, and methanol has an energy density of about 23 MJ/kg. Therefore, our little reaction releases about 90 kJ of energy, which is enough heat energy to make a single cup of tea! If the heat energy could all be converted into kinetic energy, it would be the energy needed for a 155 lb athlete to run at a 78 mph pace!

When ignited, we hear a definite Whoosh from the bottle, and if you watch carefully you may notice the flames inside the jug are spiraling. The sound is easy enough to identify: The air inside the jug is heating up quickly, which causes it to expand and rush out of the jug, causing the Whoosh! However, there is a second part to the noise as well, and it is why the flames appear to spiral. The air that is escaping the jug is also pulling oxygen out with it. This means that the mixture inside the jug could lose some of the oxygen it needs to burn, and would end prematurely. What happens is that a Vortex forms at the mouth of the jug, allowing air to rush both into and out of the jug at same time! A vortex is when a fluid rotates around an axis, such as when you see a spiral of water in a drain. Vortexes allow matter to be transferred efficiently both ways, with one fluid going through the center and the other in the formed spiral. In this case, we see the flames form the spiral on the outside, allowing the heated, expanding air to move out. At the same time, cool, oxygen-rich air can move down the center of the vortex, into the combustion reaction to keep it going!

Additional Information

• This demonstration pairs well with the Nonburning Money, the Candy Conflagration, and the Potassium Permanganate And Glycerin demonstrations
• This demonstration is a part of the Fire and Ice Show