Monday, December 20, 2010

salt and ice

The other morning, Nora saw her dad salting our icy driveway, and asked why.

I asked her, "Why do YOU think we spread salt on an icy sidewalk? Can you guess?"

She guessed, "The salt melts the ice?"

We decided to see if this were true. I said, "We'll see if ice added to water makes it harder for the water to freeze."

-- We filled two small glass bowls each with 1/2 cup water. To one of these, we added 1 Tbsp salt, and stirred it in. The other, we left plain. We put them both in the freezer for an hour.
-- An hour later, the bowl of plain water (on the right) was frozen about halfway through. The bowl with salt water (on the left) was still mostly liquid, with just a small coating of ice on top. (When I tilted the bowl, the water sloshed all around.)

I explained (after quickly Googling this to make sure I didn't spread misinformation) that salt speeds up the melting of the ice because it can make ice melt at a lower temperature.  Salt also helps keep the ice from re-freezing.....which we saw when we put the salt water in the freezer!

I later came across an experiment where kids can use salt to "glue" an ice cube to a string, and then lift it up. This is exactly the sort of thing that sets my geek heart aflutter.

(I may be a geek, but I'm not a science whiz, so preschool science experiments may be as good as it gets for me. I plan to enjoy this while it lasts, and before I become unable to comprehend any of it.)
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