A classic chemistry class demonstration is to hold bubbles filled with methane gas or propane gas and light the bubbles on fire. Flames shoot from the teacher's hands and, magically, the teacher is not burned by the flaming inferno in his hand. But don't try this at home, because the teacher used science to ensure he didn't get burned...
I use this demonstration to talk about combustion reactions, natural gas, specific heat of water and many other topics. I also use it as an attention getter and show-stopper because it leaves such an impression on students - they never forget how their teacher lit himself on fire "all in the name of science"!
How to do the Propane or Methane Bubbles Demonstration
I use methane gas because it is available in my classroom lab. You may use propane from a portable canister if methane is not available.
Materials:
-Methane or Propane
-Bubble Solution (recipe below)
-Water
Procedure:
Mix the bubble solution (see below) or use a commercial solution and pour into a glass or beaker. Run a rubber hose from the methane or propane tank and place the end into the glass of bubble solution. Turn on the gas and allow it to bubble until a sizable amount of bubbles are present. Turn off gas.
Wet your hand thoroughly with water (this is what will protect your hand from burning)! Scoop up a handful of bubbles in one hand, hold your hand at or above eye-level (heat and flame rise) and light the bubbles with the lighter.
Precautions: This is fire. It could burn you or the people around you. It could cause things around you to start on fire. It IS fire.
Wetting your hand will keep your hand from burning for a very short amount of time but only if you have a manageable amount of bubbles - too many bubbles will likely burn you.
Homemade Bubble Solution Recipe for making Flaming Soap Bubbles
This homemade bubble solution recipe can be used for any experiment where large sized bubbles are needed or for blowing bubbles just for fun!
Materials
-Distilled Water: 240 ml (1 cup)
-Dawn Dish Soap: 30 ml (2 tablespoons)
-Glycerine: 15 ml (1 tablespoon)
Procedure:
Pour all materials into a glass container and mix thoroughly. Store in a covered container. I store my bubble solution in a jar with a tight lid.
How does the Methane Bubbles Demonstration Work?
This demonstration shows a combustion reaction where oxygen reacts with a fuel (either propane or methane, depending on which is used). The balanced chemical equations for both reactions are shown below
Propane Combustion Reaction - Balanced Chemical Equation
Propane + Oxygen -> Carbon Dioxide + Water
C3H8 + 5O2 -> 3CO2 + 4H2O
Methane Combustion Reaction - Balanced Chemical Equation
Methane + Oxygen -> Carbon Dioxide + Water
CH4 + 2O2 -> CO2 + 2H2O
Is it safe to hold fire bubbles in your hand?
Yes, if done correctly. Be sure to wear googles and a safety apron. Hold the bubbles above eye level because the heat and flames rise from the point of ignition. Be sure to get your hand very wet before doing the demonstration. Water has a high specific heat which means it takes a lot of energy to heat up water. The water on your hand will absorb much of the energy (heat) from the flame as it turns from liquid water to water vapor (gas). But, even with all the safety precautions, this demonstration is potentially very dangerous.
Keep on Learning! ~Craig
