For our final science project, I introduced the idea of how frost forms. It seemed very timely, as cold was setting in upon us. I got the idea from the very helpful blog, We Made That on how to put it together.
It was really, really easy (and a great project to end on). Take a leftover tin can (I made sure I opened it with child safety opener that doesn’t leave a sharp edge), fill it with ice, sprinkle a lot of sea salt in it, let it do its magic.
This certainly worked more quickly than making it rain, although not quick enough for some of the children. But, such is the nature of our playgroup that they can go play for a bit and come back to see how it is doing. Although Mini-ion #2 was willing to give it a chance and was rewarded with frost on her can. Also, she was waiting until my attention was diverted so she could eat the salt.
The salt lowers the melting point of the ice and causes the surface of the can to be at a below freezing temperature. Then the water vapor in the air around the can condenses and freezes on the can causing the frost. This happens only if the temperature is below freezing, so if you just add the ice to the can with out the salt to lower the melting point you will get condensation on the can but not frost.
When Mini-ion #2 wasn’t eating the salt, the children enjoyed “writing” in the frost and even scraping some off to make it snow!