Saturday, February 16, 2013
Winter Ice Melt Palooza!
Learn why salt helps to melt ice using different types of salt.
Appropriate Age Level
5+ (some concepts can be 3+)
Freezing Point - The temperature at which a liquid becomes a solid
Temperature - a physical measurement of the hotness or coolness of something
Freezing Point depression - when the freezing point of something is lowered by a solute
Colligative Property - a property of a substance that depends on the number of particles present instead of type of particle.
Solution - a homogeneous mixture of solute and solvent that is in one phase (liquid, solid, gas)
Solvent - A substance that dissolves a solute.
Solute - A substance, usually a solid, dissolved into another substance, usually a liquid.
Liquid- a state of matter that is characterized by taking up a definite volume but having no particular shape
Solid - state of matter that is characterized by being structurally rigid and resistance to change
Table Salt - NaCl
Magnesium Chloride MgCl2
Calcium Chloride CaCl2
1. Either find a block of ice outside, or freeze some water in a plastic container.
2. Explain how ice is frozen water and a solid and how its freezing point is at 32F or 0C. When water is not frozen it is in the liquid state.
3. On a surface that you don't mind getting wet, take some table salt and add it to the block of ice in one area. Attempt to stir in the salt into the ice. Notice how the salt, the solute, melts the ice, the solvent. It essentially lowers its freezing point of the ice. (If the student wants to know more, it essentially breaks the hydrogen bonds required to keep the ice in solid form by the salt molecules coming in and wanting to share the same space and transferring electrons.)
4. If you have Magnesium Chloride and/or Calcium Chloride on hand you can add a spoonful of each to other parts of the block. (You could probably add some different food colorings to differentiate the different materials if you would like more wow!) If you have a thermometer on hand you can check out the differences in temperature of the solution melts. The MgCl2 will depress the freezing point of ice to 5F. While table salt only depresses it until 15F. Calcium chloride depresses it until -20F. While if you are doing this experiment inside the temperatures gotten will not be at these exact levels you should be able to see some difference.
5. Explain that the differences of the freezing points arrise from freezing point depression being a colligative property and the differences in size of the molecules, where NaCl is the smallest, CaCl2 is the largest, makes a difference in melt points.