Introduction

This demo is done most commonly with the copper hydrogen cone apparatus which is available in the first glass and wooden cabinet at the front of the demo room.  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)

Supplies

Short List

  •   Copper cone apparatus or plastic pop bottle
  •   Three wood blocks (if using plastic bottle)
  •   Butane lighter or candle and matches
  •   Goggles
  •   Ear plugs

Chemicals

  •   Hydrogen gas    H2(g)

Prior to Lecture  (prep time 5 min.)

  1. Set up the hydrogen cone apparatus, or prepare a soda pop bottle by cutting off the bottom and drilling a 3mm diameter hole in the cap.  Metal caps, if available, are more durable than plastic.  Cut three small wood blocks that can be used to support the bottle from the open bottom end in an upright position while allowing air to enter. (The bottle apparatus for this demo is available in the black closet opposite the hood in the demo room.)
  2. Provide the lecturer with the above apparatus, a butane lighter, a hydrogen tank, safety goggles, and ear protection.

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 and Disposal

Wear safety goggles and ear protection.  There are no chemical wastes requiring disposal.