Methanol Cannon

Age

Elementary School, Middle School, High School

Format

Stage Show

Materials

   5-gallon jug (Culligan water bottle, available for a few dollars from water-cooler supply companies)
   Rubber stopper for jug
   5 mL of methanol per canon
   Long-necked lighter 

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 Methanol Canon is a very dangerous demonstration and, if not performed safely, can cause serious harm to both the performers and audience. The audience should be seated at least 15 ft away from the canons. Performers must use extreme caution (see Demonstration). The water jug must be taped up (see Preparation). Have a fire extinguisher ready to use if something goes wrong! Methanol is toxic - use gloves to handle it, do not inhale, and consult its MSDS sheet for more information.

Methanol (Methyl Alcohol) MSDS

Preparation

Prepare the water jugs by taping them up, Use clear plastic shipping tape to reinforce the seams in the side of the plastic jug to help prevent shattering during the combustion reaction.

Demonstration

Warn the audience that this demonstration will produce a bright flash and a loud noise, but explain that you are taking many safety precautions.

Add ~5 mL of methanol to the jug and cap it with the rubber stopper. Shake the jug well for about 30 seconds to evaporate the methanol. Remove the rubber stopper and hold a flame to the top of the jug. You may need to slightly insert the flame in to the neck of the jug, but it is extremely important that you not let your hand get so near that the flame touches you! Use a long-necked lighter to keep your hand safe.

If possible, turn out the lights so the audience can see the blue flame more easily. You can light off multiple canons at once for a more impressive effect.

Alternatively, you can build an automatic ignition system into the bottles [2].

What to Say

Start out by warning the audience about the bright flash and loud noise and explaining that you have taken safety precautions - don't try this at home!

Show the audience your 5 mL of methanol - it's a pretty tiny amount of liquid, right? In fact, this tiny bit of liquid holds a ton of energy that is stored in the chemical bonds between the atoms in the molecules. Certain types of chemical reactions release part of the energy from those bonds. Methanol is highly flammable - it can catch fire really easily and participate in a combustion reaction with the oxygen in the air. Let's use this methanol to perform a combustion reaction. We just need a little bit of energy - a spark - to get the reaction going. I'll use this lighter.

Perform the demonstration.

Did you see all of the energy that methanol combustion reaction released? That flame was huge! But how can we use the energy released in a combustion reaction to do useful things? We can certainly use a flame to heat things up, like in a gas stove. If we use the heat from the flame to raise the temperature of a gas, we will cause the gas to expand. This is how a car's engine works - the spark plugs in the engine produce many tiny flames per second using gasoline instead of methanol. Each combustion reaction causes the pressure to rise in your car's cylinder as the gas tries to expand. This produces pressure on the pistons in the engine. The car uses the movement of the piston to cause its tires to turn and to propel you down the road.

Why It Is

For more information about combustion reactions, see Nonburning Money.

5 mL of methanol weighs about 4 grams and methanol has an energy density of about 23 MJ/kg. Therefore our reaction releases about 90 kJ of energy!

Real Life Examples

Combustion reactions power car engines! Spark plugs in a car ignite gasoline, another flammable chemical, to produce small combustion reactions that increase the pressure on the engine's pistons. This happens on a scale much smaller and much faster than in this demonstration - the combustion reactions are produced many times per second in the car. The machinery in the car converts thereby converts the chemical energy stored in the gasoline into mechanical energy to move the car.