Sublimation

Amelia D. Witherspoon          Mays Academy
                               1800 West Garfield
                               Chicago IL 60609
                               (312) 535-9395

Objectives:

These objectives are directed toward intermediate and upper grades.
1.  The student will be able to describe the process of sublimation.
2.  The student will be able to describe the process of deposition (which is 
    sometimes called sublimation).
    Note:  Deposition is the reverse operation where the vaporized air 
    condenses and re-forms the solid.  

Materials Needed:

1.  Toilet bowl freshener.
2.  Moth balls.
3.  Two 100 mL beakers.
4.  Two 150 mL beakers.
5.  Clear, shallow dish or pan.
6.  Ice.
7.  Thermometer.

    Optional Materials:

1.  Iodine - dangerous (must be cooled and concealed)
2.  Solid air freshener
3.  Hot plate

Procedure:

1.  Place a few small lumps of toilet bowl freshener in the bottom of the 150 mL
    beaker.
2.  Place a few moth balls in the bottom of the second 150 mL beaker.
3.  Put the 100 mL beakers inside of the 150 mL beakers.  They should fit nicely 
    inside of each other.  However, the smaller beakers should not touch the 
    bottom of the larger ones.
4.  Use a fume hood.
5.  Fill the small beakers three-fourths full with ice.  Be sure that no ice 
    gets into the larger beakers.
6.  Fill the shallow dish or pan about one-third full with hot water (one or
    two dishes may be used).
7.  It might prove better to use the hot plate to heat the water and then 
    place the apparatus in the water bath for faster results. 
8.  Measure the temperature of the water bath and adjust it by adding cold 
    water until the temperature of the water bath is about 60 degrees C.
    (You may experiment with a water bath temperature from 50-70 degrees C). 
9.  Place the sublimation apparatus in the shallow dish.
10. Observe what happens to the toilet bowl freshener and the moth balls 
    (solids).


Reaction:  

The heat from the water bath causes the solids to vaporize (sublime).  The cold, 
smaller beakers cause the vaporized solids to condense and re-form solids 
back to their original form (crystals). 

Notes for the Teacher:

Teachers and students must use safety glasses while doing this experiment.  
Teachers and students must use tongues to handle solids.  If no fume hood is 
available, do this experiment outside.  The fumes could be damaging to you and
students with upper respiratory problems.  Another solid that will sublime 
easily is solid iodine (use small amounts).  This solid could be used as a 
demonstration.  If you use cheap toilet-bowl deodorizers that contain 
p-dichlorobenzene (also found in some types of moth balls), be careful, this 
substance is toxic.  Lastly, teachers and students must wear a lab coat or 
apron.        

Reference:

Borgford, Christie L. and Summerlin, Lee R. Chemical Activities:  Teacher 
   Edition.  American Chemical Society, Washington, D.C.  1988.