How Does Salt Melt Ice?

Near every doorstep has a bag of salt on it during the winter – at least in places where snow is the norm – for sprinkling over the steps and the walkway.  Meanwhile, trucks drive along spreading salt over the roads.  Brittanica says more than 20 million tonnes of ice are used to melt snow and ice every year.  Zero degrees Celsius is 32 degrees Fahrenheit and it is the freezing point for water H20, turning to ice. The ice molecules and water molecules are interacting when there is a thin layer of water on top of the ice.  Some of the ice is freezing the water, and some of the water is melting the ice. 

When a foreign substance like sand or ionic compound salt is added to ice, the water  molecules cannot attach to make ice as fast when the temperature is zero degrees.  This gives time for the existing ice to melt, providing time for the existing ice to melt, after raising the temperature just slightly.  It causes what is called the “freezing point depression”.  Kissner says, “Salt is the primary component in most of today’s ice melter products. Rock Salt, Calcium Chloride, Magnesium Chloride, and Potassium Chloride all contain a considerable amount of salt in them.”  The salt makes it harder for the water molecules to bond together.  Even though NaCl, regular table salt, will melt the ice, cities use Calcium Chloride CaCl2 a different type of salt, on roads because it can break down into three ions, more than table salt – more ions more melting. 

For an experiment, In one bowl have ice cubes and sprinkle over table salt at the same time in a second bowl have ice cubes and sprinkle over road salt (Calcium Chloride).  Observe to see which bowl melts first.  Always be careful when walking on the ice.  Make sure your boots have good grips on the bottom!

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