Chemical Mystery #6: The Case of the Crushed Can

crushed metal can

Have you ever seen experiments, such as the one here, that makes use of air pressure to crush a metal can? Such "can crush" demonstrations can be presented as a neat trick that you can do for your students. See the video below.

What do you suppose is the secret behind this trick? Hint: It has to do with chemistry!

Let me know your thoughts on how you think this experiment is done. I'll post the solution in about a week. 

Join the conversation.

Comments 2

Andres Tretiakov's picture
Andres Tretiakov | Wed, 06/01/2016 - 05:04

Hi Tom,

I think I remember this one but I might be wrong. One can is full of air but (here's the trick) the other is full of carbon dioxide gas (which is denser than air and some gets trapped even when inverting the can). The liquid being poured is a concentrated solution of sodium hydroxide or similar strong base. The carbon dioxide readily dissolves in water to form carbonic acid which reacts with the hydroxide to form a carbonate and water in a neutralization reaction. Since the can is sealed and carbon dioxide is being used up to neutralize the base then atmospheric pressure is able to push on the can, crushing it. The other can containing just air remains the same since the concentration of carbon dioxide is lower. 

This reaction is of great importance to trap CO2 and carbonates and usually lithium hydroxide in it's solid form is used as a scrubber in submarines, fire drills and emergencies and even in spacecrafts to capture waste product of respiration, CO2 from the air. Perhaps the most famous example was the Apollo 13 spacecraft incident were a leak in the oxygen tank was detected and CO2 inside started to quickly build up. Fortunately,  with the help of Houston engineers they managed to build such a scrubber to remove CO2 from the air.

Hope this is OK!

All the best,

and keep the mysteries coming : )


Bob Worley's picture
Bob Worley | Thu, 06/02/2016 - 08:28


I do this with an empty coke bottle (other brands are available). Less expensive than cans. 1M NaOH is what I use.