`Frozen SolidsEvangelyn Lilly                William H. Ray                                5639 Kimbark Ave.                               Chicago IL 60637                               (312) 535-0970Objectives: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 bottlesStrategies:     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. `