Big Bang

Better than the test tube pop!.

 

 

 

Category - Chemicals & Reactions

Key Idea - Combustion

 

Purpose - Shows the explosiveness of hydrogen, the reaction between metals and acids and the fact the hydrogen is less dense than air.

Apparatus set up and bubbling, ready for a big bang.

 

Zn  +  HCl  ®  H2­  +  ZnCl
Nature -  Demonstration
Materials -  A conical flask, a rubber stopper with glass tube straight through, 2M hydrochloric acid, granulated zinc (or magnesium ribbon for faster reaction), tripod, strong food tin with small hole punched in bottom, matches, long taper, masking tape
Method - 
  1. Put a strip of tape over the hole in the tin and set it on the tripod with the hole at the top.
  2. Put about 100 ml of hydrochloric acid into the conical flask and drop in a few grams of zinc chips.  Hydrogen should start to bubble straight away.
  3. Seal with the stopper in such a way that the hydrogen will travel into the tin.  Allow to sit for 5 or 10 minutes.
  4. Remove the glass apparatus and light the taper.  Pull back the masking tape to allow the hydrogen to trickle out forming a wick.  Light the hydrogen with the taper.
  5. BIG BANG!
Safety - The tin can jump as a result of the explosion so be sure to keep a clear area around the demonstration.  Make sure you don't leave the hydrogen going too long as the tin can be launched up enough to hit the ceiling (seen it happen!)  2M acid is quite strong so care should be taken with it's use.
Explanation -

Metals react with acids to produce hydrogen (the reaction is shown right).  Hydrogen is a flammable gas and when collected and ignited goes off with a bang. 

Hydrogen being less dense than air will stay in the inverted tin as it tries to rise.  When you remove the tape a "wick" of hydrogen trickles out through the hole.
Notes - This is a larger version of the simple "pop test" done with a piece of magnesium ribbon dropped into a test tube of acid and gently sealed.  If you wait a few moments and put a match to the top of the test tube a noticeable pop is produced.