This is an experiment that you can try with children. It’s super-fun and very fast, so there’s an immediate payoff, and you can run it many times. You can simply run it with the children or you can teach them a little bit about what’s happening, depending on how old they are and how interested they are. Or you can just have a read and see the results through my camera below 😉
I first did this experiment for a university open day, back when I was teaching prac classes during my first postgraduate degree. The day was devoted to primary school children and it was so much fun to see such wonder and excitement from them.
What will you need?
- a glass dish (I’ve used a tall beaker, but a short flat glass dish works well)
- a styrofoam cup (or quite a few of them!)
- acetone (you can get this from your hardware store, or some pharmacies)
What will you do?
It’s quite simple.
- Pour a small amount of acetone into the dish, about 1cm deep.
- Carefully place your styrofoam cup onto the liquid surface.
- Watch in amazement and delight 🙂
What will you learn?
There are two lessons today. The first is learning about plastics. A styrofoam cup is a type of plastic – a little different to what you might normally consider to be plastic, but all plastics are made of long chains of repeating molecules. Each individual molecule is called a monomer, so when there are many joined together, you have a polymer (you’ve probably heard of polymers?). Plastics are polymers. Styrofoam is different to some other plastics because the long chains are held together quite loosely by non-polar bonds (more on this later). Also, when they make this particular plastic, they make is as a foam (hence the name styrofoam), so there are a lot of air spaces between the molecules.
The second lesson is about polarity and the theory that like-dissolves-like). Let me explain. Molecules either have a charge (polar) or they don’t (non-polar). When the parts of the molecules bind together, they share electrons, and sometimes, one of the atoms attracts more of the electrons than the others. Electrons are negatively charged, so if one side has more electrons, then that side becomes negatively charged. Now that there’s less electrons on the other side, that side becomes positively charged. This is now a polar (or charged) molecule. Water is an example of a charged molecule. The oxygen atom in water attracts more electrons than the hydrogen atoms do, so it becomes a charged molecule. Our styrofoam however, has the charges spread out evenly, it has no charge overall, so it is non-polar.
Oil is another example of a non-polar substance. We all know that water and oil don’t mix (perhaps another experiment another time). This is because of the theory that “like dissolves like”. Polar substances will dissolve in other polar substances. So, this means that water won’t dissolve styrofoam. Remember – water is polar, styrofoam is non-polar, so they won’t dissolve. Now, let’s talk about acetone. This is the chemical we use to remove nail polish, particularly the gel polishes that are popular now. The polish is non-polar and so the acetone will dissolve it because it is also non-polar. Since styrofoam is non-polar and acetone is non-polar, like-dissolves-like and the so the acetone dissolves the styrofoam.
As an extra, since the styrofoam is a foam, there are a lot of air spaces between the molecules so lots of gaps for the acetone to seep in and so the reaction is quite fast. It looks like the cup is melting, but it’s actually dissolving. I remember doing this experiment so many times over the two days, probably dissolving 100 cups. At that time, I used a glass petri dish (flat round dish) and had it sitting on a black laboratory bench. The children were trying to see under the bench to see the cup coming out the other side 🙂 They thought it was magic.
What do you think? Do you think children will be excited by this? I know I still am? Whether you learn something or not, it’s very cool to watch. The acetone looks like it’s boiling around the cup, but it’s just the air escaping from within the foam.
Such a cool experiment! Or is it just me?
x desleyjane
Safety Considerations.
- Do not eat anything in this post – none of it is edible!
- Acetone is flammable and harmful if ingested or inhaled.
- It will dry your skin (acetone dissolves the oils in your skin).
- Do not breathe in the vapours – run this experiment in a well-ventilated area.
Musings of a Frequent Flying Scientist 
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