Rip The Can
Age
Elementary School, Middle School, High School
Format
Hands-on
Materials
Aluminum soda can Iron file or screwdriver for etching ~100 mL of Copper(II) Chloride (Cupric Chloride) solution (approx. 100mL of water per 2g Cupric Chloride) Basin to catch waste Thick safety gloves Goggles Small blast shield (if being presented in close proximity to audience)
Safety Precautions
Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. It is very important to wear thick protective gloves (i.e. gardening gloves) while ripping the can - the edge of the can will be sharp and may slice skin. Cupric chloride is an irritant - do not expose to skin or eyes - wear goggles and gloves. If the audience will be close to the experiment, shield them from accidental spray with a small plexiglass blast shield.
Preparation
Prepare the cupric chloride solution. Because the can will rip more easily the longer the solution has been sitting, you may wish to prepare a pre-made can about 10 or 15 minutes before the performance.
Demonstration
Aluminum soda cans have a plastic lining to separate the soda from the metal. Stick an iron file or screwdriver through the opening at the top of a can to scratch a circle out of the lining near the bottom of a can - this will make an awful sound. Fill the can with ~100 mL of the cupric chloride solution - enough to cover the scratched area. Place the can in the basin in case some solution leaks out. Wait at least 4 min, preferably more than 10 min. Equip protective gloves and goggles and rip the can in half over the basin. Be careful with the sharp edge of the can and do not allow any cupric chloride to splash on the audience.
What to Say
Hello, everyone. You’ll notice that we have a lot of soda cans up here. Does anyone know what soda cans are made of?
Of course, they’re made of aluminum—but that’s not all!
People that work in the packaging industry noticed a problem with storing soda in cans made purely of aluminum. Soda is loaded with an acid called carbonic acid — it’s perfectly safe for you, but it doesn’t react well when it’s mixed with aluminum.
Packagers always have to be very conscious of the chemistry of the foods that will be going in their packages. That’s why all soda cans come with a thin plastic lining that prevents the acid in the soda from reacting with the aluminum.
Look in the can, though; I don’t see any plastic! If it’s clear, how can we tell that it’s there?
Well, we can try scratching off the liner. Then we can expose the bare aluminum to a substance that will react with it. That way, we’ll find if there really is a plastic liner coating the aluminum.
That’s a pretty good idea. Before we do any experiment, we need to put on safety gloves and goggles.
[Put on gloves and goggles. Scratch off a circle off of the inside of a can in front of the kids]
This is a solution of copper chloride. It’s not the same thing as the acid in the soda, but it will react with the aluminum in about the same way. The copper chloride works a lot more quickly than acid so that we can see what happens without waiting too long.
[Pour the mixture into the can. It will take several minutes to degrade the can sufficiently, so have a prepared can from the last demo ready for the audience]
The solution’s already been sitting in this can for a while, let’s use it.
[Pour the solution out from the prepared can]
Normally, I could never rip an aluminum can in half, but now that the aluminum has been weakened by the Copper Chloride, it should be easy.
[Rip the can in half. The audience might not be impressed with how “easy” it is to rip the can, but you can show them the scratched circle where the aluminum has turned a different color]
Look at that! Can you imagine if there was no plastic liner on these cans?
The acid in the soda would tear the can apart while it was sitting on shelves at the store!
Chemistry definitely plays a large role in the packaging industry. I hope all of you learn about the role it plays in other industries at the other booths here today.
Why It Is
Soda contains carbonic acid, which will eat away at the metal in the can if the aluminum is directly expose to it. By scratching away the plastic lining in the can, we can expose the metal on the inside of the can directly to our solution of cupric chloride. The cupric chloride performs a single-replacement reaction with the aluminum:
3CuCl2 (aq) + 2Al (s) > 3AlCl3 (aq) + 3Cu (s)
So the aluminum that used to form the wall of the can ends up in the liquid solution and little bits of solid copper are deposited on the weakened wall of the can.
Real Life Examples
Packaging engineers must consider the effects that food may have on the packages it is stored in. The plastic liner in soda cans exists to protect the aluminum from the acid in the soda. Can you think of any other packages meant to store potentially hazardous or messy products?