Introduction

This demo is done most commonly with the copper hydrogen cone apparatus.  After filling the apparatus with hydrogen, the hydrogen gas escaping through the hole in the cap is ignited and burns quietly until enough air mixes with the hydrogen to produce an explosion.

Alternately, a 2 liter plastic soda pop bottle with the bottom cut off and a small hole drilled through the cap, is filled with hydrogen gas and placed on several wooden blocks to allow air to enter the bottom.  The hydrogen gas escaping through the hole in the cap is ignited and burns quietly until enough air mixes with the hydrogen to produce an explosion.

2H2(g) + O2(g) → 2H2O(g)

 To Conduct Demonstration

  1. Hold and invert the bottle, insert the discharge tube from a hydrogen tank up into the neck of the bottle, and flush the bottle with hydrogen gas, Or fill the hydrogen cone in a similar manner.
  2. Remove the hydrogen tube and immediately place the bottle upright on the three wood blocks.  (The cone is already on a stand.)
  3. Using a butane lighter, ignite the hydrogen gas escaping from the small hole in the cap or top of the cone.
  4. The hydrogen gas, being lighter than air, will remain at the top of the bottle and burn for a while as it escapes through the hole in the cap.  When enough air has entered the bottom of the bottle and mixed with the hydrogen (approx. 20 to 40 sec.), an explosion occurs.  The hot expanding gases exit through the open bottom of the bottle.  The bottle usually remains undamaged and can be reused many times.

Note:  If too much time elapses between filling the bottle  or cone with hydrogen gas and lighting it, air will enter the bottle and form an explosive mixture.  The lecturer should not place their face directly over the bottle when lighting it as an accidental explosion will cause the bottle to jump up a few feet in the air.  Ear protection should also be worn as the noise of an explosion close to the demonstrator can be very loud.

Demo Time: 5 - 10 minutes

Safety 

Wear safety goggles and ear protection.  

Reference

Journal of Chemical Education

Acknowledgment

Lora Ruffin and Michael Polk, Summer 2009