Drano Bombs Away
You can tell the Fourth of July is nigh when the Drano Bombs start to fly. But its no holiday for authorities in the New York City neighborhood of Washington Heights, who are clearing up after local kids set the aluminum-foil-and-drain-cleaner explosives off at a school over the weekend. The New York Daily News reports that fire and police bomb experts found 20 exploded Drano bombs at Public School 178. And a quote in the story suggests hazmat workers were called to clean up the scene.
The Newscripts gang thinks that destroying property and setting off explosives is never a good idea (unless you’ve been trained to set off pyrotechnics like C&EN’s own Elizabeth Wilson and it’s an appropriate occasion). But the Drano bomb incident did get us thinking about the chemistry involved in this particular reaction.
The Interwebs are full of directions to make (and video of) Drano bombs, but the only decent description of the chemistry involved that I could readily find was at a site set up by the University of Siegen, in Germany.
The main reaction that takes place is the that of aluminum with water to generate hydrogen gas and aluminum hydroxide. When conducted in a closed in a soda bottle, this transformation can make a serious boom.
“Under normal circumstances,” notes the Siegen post, “aluminum does not react with water, as an impermeable protective layer composed of aluminum hydroxide either forms within seconds or is already in place.”
Adding sodium hydroxide–the key ingredient in drain cleaner–removes a laver of aluminum oxides that’s built up via passive corrosion. This reaction occurs slowly at first, giving Drano bombers a few seconds to slip away.
Sadly, I suspect that interesting redox reactions are not what the kids in Washington Heights are thinking about when they break into the drain cleaner.