This experiment, #5 in the series, is not actually one that we did during chemistry camp, but we did it during a Passover science event back in April, and it was fun enough that I decided to talk about it on the blog.
It turns out that salt can melt ice, which is not surprising to anyone who lives in New England and has used salt to melt all kinds of walkways, staircases, and other exterior surfaces all winter long. Why does this work? Well, the melting temperature of the ice is lowered when salt is added, which is a phenomenon referred to as “melting point depression.”
(Incidentally, salt also raises the boiling point of water, in a phenomenon called “boiling point elevation,” which has effects in cases where you are boiling pasta, especially at high altitudes.)
But why does that help ice melting, you may be wondering? Shouldn’t that make the ice EVEN HARDER to melt? Technically, yes, but because it turns out that the ice is almost always covered in a thin layer of water. Once you make that water salty, it will refreeze at a slower rate than the surrounding ice, and cause the water to stay in a liquid form.
What kinds of experiments can you do with this? It turns out that we can do neon watercolors, by using neon paint in frozen ice blocks, and neon paints in salt water droppers. Dropping the salty water onto the salt-free frozen blocks resulted in melting in channels, crevices, and other cool patterns. We were even able to use a black light to truly visualize those exciting colors!
Check out the links below to find out more information about using salt to melt ice:
And about fun science projects you can do based on these effects: