For many, the sound of bangs from crackers marks the start of Christmas dinner. Share this article about the chemistry behind the cracker with your students so that, before they don their paper hat and tuck into their turkey this year, they can inform their family exactly how crackers work.

 

The chemistry behind how Christmas crackers work

 

The bang you hear when you pull a Christmas cracker is caused by a small explosion. The explosive used is normally silver fulminate which has the formula AgCNO. It is a compound which contains four different elements: silver (Ag), carbon (C), nitrogen (N) and oxygen (O).

The name comes from the Latin word fulminare, to be struck by lightning, which is how you would feel if you came into contact with too much of it!

Silver fulminate is very explosive and so extremely dangerous. So dangerous, in fact, that it has very little practical use – apart from being used in crackers. A few milligrams of it in a pile would self-detonate without the need for any flame just because of the weight of it on itself. For this reason, only a small amount is used in your cracker.

But, if such a small amount is used in a cracker than where does the heat needed come from to detonate it?

Inside the cracker is the snap. This consists of two strips of card. One strip of card is covered in silver fulminate and the other has a small piece of sandpaper. These ends are glued together. When you pull the cracker the ends brush against each other. It is the friction from the sandpaper that creates the heat needed to cause the explosion and that satisfying bang.

 Further Festive Science

Students can see how science has answered another Christmas question by watching the Free video – Why Rudolph’s nose is red.