hcho15.html

I love winter! I get to go ice skating at my cousin's house. She lives near a pond where we can skate.

When we got there, their driveway was a sheet of ice! But a town truck came by and sprinkled salt on it. The ice melted in no time.
salt truck

That made me wonder about salt and water...if salt can make ice melt, can it keep water from freezing in the first place?

I wanted to know, so I took two plastic cups and filled them with water. I put a tablespoon of salt in one cup, and then put both cups in the freezer.

Can you guess what I found the next day?
Salt can do some really strange things. See for yourself!


	Ice cubes
	2 cups of water
	Thin string or thread
	3 tablespoons salt
	A thermometer (not the kind for taking your body temperature!)

	Fill 2 cups almost to the top with ice and add water.
	Stir both cups of ice water for 30 seconds. Then record the temperature of water in each cup. Be sure to put the thermometer in the water for at least 10 seconds to get an accurate reading.

*Compare the temperature readings.* *What do you notice?*
	Add 3 or 4 tablespoons of salt to one of the cups of ice water and stir. Wait 30 seconds, and record the temperature of water in each cup.
*Is the salty ice water warmer or colder than the plain ice water?*
	Now try this...
	Take an ice cube and lay a piece of string on top of it.
	Sprinkle about half a teaspoon of salt on the top of the ice.
	Watch what happens after the salt is added. After a few minutes, lift the string.
*What happens to the ice cube when you sprinkle the salt on it?* *What do you notice about the ice cube when you lift the string?*

Zero degrees celsius (32 degrees Fahrenheit) is the 'freezing point' of water. At this temperature, water forms ice. It is also the temperature that is warm enough to melt ice.

When you add certain chemicals to water, as you did when you added salt to ice water, you lower the freezing point and the temperature goes down. The temperature is lower because the salt causes the water to lose heat energy.

People add 'antifreeze,' a chemical, to the water in their cars to lower the 'freezing point.' That way, the water won't freeze solid in the winter!