Frozen Solids

Evangelyn Lilly                William H. Ray 
                               5639 Kimbark Ave.
                               Chicago IL 60637
                               (312) 535-0970

Objectives:

a. To show when water freezes at a temperature of 0oC (32oF), it turns into
   a solid.
b. To show that the water level remains the same before and after the ice has 
   melted.
c. To explain that ice melts at 0oC (32oF). 
d. To demonstrate how ice can be melted without heating it.                     
e. To show that increased pressure lowers the melting point of ice.            

Materials Needed:

   ice cubes, food coloring, two rocks, a glass, wire, pan, cups, salt
   metal forks or spoons, and plastic pop bottles

Strategies: 

    Introduce Frozen Solids:
 a.  Float an ice cube in a glass of water, mixed with food coloring.  Mark the 
   water level with a strip of sticky tape.  Ask the students, can you tell 
   where the water level will be when the ice has melted?  Explain, even though 
   part of the ice cube floats above the surface, the water level in the glass 
   stays the same before and after the ice has melted. 

 b.  Ask, if anyone can tell what will happen if I place a bit if salt in the 
   center of an ice cube?  Demonstrate by putting a pinch of salt in the middle 
   of an ice cube.  Let the ice cube stand for ten minutes.  (During the waiting 
   period, we will start activity c.)  Examine the ice cube after the waiting 
   period.  Ask the students what happened?  The center of the ice cube melted, 
   while the outside of the cube remained frozen.  Explain to the students that 
   ice does not melt until it reaches 0oC (32oF), which is the melting point of 
   ice.  When you add salt, it lowers the melting point of ice.  The ice does 
   not have to reach 0oC (32oF) to melt.  That explains why the center of the 
   ice changes into water, while the outside of the cube remains frozen. 

 c.  Another method of melting ice without heating it is to wind the ends of 
   wire (20cm long) around the two rocks.  Support an ice cube on the mouth of 
   the bottle.  Hang the wire weighted by the rocks over the top of the ice 
   cube.  The students will observe the wire cutting through the ice as the 
   weighted wire exerts pressure on the ice.  The pressure on the ice causes the 
   ice to melt under the wire.  The water then refreezes above the wire.  This 
   is an example of what happens when people ice skate or when people drive on 
   icy streets in winter. 

Performance Assessment:

 a.  The students will explain how the wire is able to cut through the ice and
   refreeze on top in minutes.
 b.  Students will demonstrate that water is more dense than ice, which proves
   why ice will float on water. 
 c.  Students will be able to understand that ice skaters are really skating on 
   water.  After testing the wire that cuts through the ice, students will 
   observe the refreezing of the ice above the wire within minutes.