The Science of Removing Snow and Ice!

What better Snow Day Activity then to investigate snow!  There are several different materials put onto snow and ice to make our roads and sidewalks safer.  This activity is fun and educational in understanding how to melt snow and ice when temperatures get below 32 degrees Fahrenheit.

You will need: plastic cups, plastic spoons, snow, table salt (sodium chloride), calcium chloride, potassium chloride, and magnesium chloride, water, stop watch.

Now Try this:

  1. Label three plastic cups 1, 2, 3, 4
  2. Place three equal quantities of snow into each plastic cup.
    1. Add 1 teaspoon sodium chloride to cup 1
    2. Add 1 teaspoon calcium chloride to cup 2
    3. Add 1 teaspoon potassium chloride to cup 3
    4. Add 1 teaspoon magnesium chloride to cup 4
    5. Start the stop watch and mix each cup continuously until all the snow has melted.  Note which material melted the snow quicker.
    6. Repeat steps 2 and 3 but with saturated solutions of each added to the snow. (dissolve each into water before adding to the snow).

Note: If you have a thermometer available take the temperatures of each as they melt the snow.

Explanation:

Water freezes at 32 degrees Fahrenheit.  The materials we used to melt snow brings this freezing/melting point of water lower than 32 degrees Fahrenheit.  The following is a table that provides relative temperatures each material lowers this temperature:

Sodium chloride: 18 degrees Fahrenheit

Calcium chloride: -22 degrees Fahrenheit

Potassium chloride: 25 degrees Fahrenheit

Magnesium chloride: -13 degrees Fahrenheit

The science behind the lowering of temperature water is referred to as Freezing Point Depression.  The freezing point depression is dependent upon the type and number of particle present in the water.  Also water must be present in the liquid state in order for these materials to be affective to melting the snow.  Even if a small amount of water is present, just enough to bring these particles into the water solution and thus lowering the freezing point.  When the outside temperatures get too low these materials are not effective because there is no liquid water present.  One option is to deliver these materials as saturated solutions (already in water) onto the snow and ice.

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