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Why didn't my hydrogen/oxygen mixture produce a bang?

Question asked by Shawn Wilson on Dec 10, 2018
Latest reply on Dec 12, 2018 by Steven Cooke

Every year, my kids and I destroy our Halloween pumpkins in a fun way. This year, we made a hydrogen/oxygen mixture from stainless steel plates and a battery charger in a baking soda/water mixture. A funnel captured all the bubbles (not just from the anode or cathode) in an inverted plastic water bottle, which was initially filled with water. Once the bubbles displaced all the water in the bottle, I capped it.


An hour later, to ignite the bottles, we lit some sawdust and lighter fluid in the bottom of the pumpkin.  Once the kids were far away, wearing safety glasses, I tossed the bottle in.  We'd done something similar on a smaller scale with dish soap and water, lighting small amounts of foam with a match.  This produced a satisfying, sharp bang. I had expected the same, only on a larger scale, from the bottles.  Instead, we got a lethargic pop after a moment, then a secondary pop a few seconds later.  I am wondering a few things:

  1. Why 2 bangs? If the first was just the pressure of the heated bottle escaping when it finally melted through (as would happen with normal air in the bottle), I would have expected the second bang to be instantly on the tail of the first.
  2. Is it possible the oxygen and hydrogen settle in the bottle, with the first bang releasing the oxygen from the bottom, and the second being when the hydrogen going off with a scarcity of oxygen?
  3. What else can I do to make this more entertaining?