The Science of Salt and Water: Freezing and Melting Science

Why do we use salt on sidewalks and roads? What exactly does salt do to the snow and ice?  This can be a hard concept to understand, but there are many ways to demonstrate the science of salt and ice.  Here is a simple way to introduce the phenomena of freezing point.

Observing the Changing Temperature

1.  Get two cups.

2.  Place a thermometer in each cup.

3.  Fill the cups with ice.

4.  Place two spoonfuls of salt in one cup.

5.  Shake the cup to get the salt to mix with the ice.

5.  Watch the thermometers carefully for 5 minutes.

Results

The temperature will drop faster in the salt cup.  The picture below contains salt.   The temperature quickly dropped to -10 Celsius.  It can actually drop even further. 

The without salt cup went below zero but did not drop as low as the salt cup.

Salt lowers the freezing point of ice.  When this happens, heat is released, and the temperature drops.  The ice begins to melt because the freezing point has been lowered.

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