I'm kicking off 52 Weeks of GUST with my personal favorite experiment from when I was a kid! This is my go-to experiment for small groups; while it is fairly straightforward, it requires a lot of adult assistance, especially with younger kids. However, nothing can beat the end product -- try out this experiment and see it for yourself!
What's Going On?
Another name for borax is sodium borate, a compound that is easily dissolvable in water (as you have seen from this experiment.) However, dissolving borax in boiling water is different from dissolving it in room temperature or cold water; since water molecules in boiling water move faster and more freely, there is more space for the borax to dissolve.
As the water/borax solution loses heat, these water molecules slow down and are more close together. It can no longer hold the amount of solution that it could when the water was boiling. This is what causes the crystals to build on the pipe cleaner.