Sometimes, when we add a compound to water or ice, it can
change the freezing temperature of the liquid. The process of lowering the freezing
temperature of a liquid is called freezing point depression.
This is a concept that those who live in areas with very
harsh winters see in action very often. Consider a day when the temperatures
are far below freezing. For these areas, large portions of salt are typically
used to keep roads from icing and making conditions unsafe for drivers. This is
an everyday example of freezing point depression! The salt changes the temperature
at which the water freezes, and cars can continue to drive on the road safely.
At High Touch High Tech, we have an experiment called Ice
Cube Fishing that utilizes this scientific concept while creating a fun game
for children to better understand the concept. During the experiment, string is
added to a cup of ice, and salt is poured in the cup. The salt lowers the
freezing point of water causing the ice to begin to melt. As the ice melts it
becomes colder and the string freezes to the ice, making it possible to “catch”
many pieces of ice with the string.