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General Safety Guidelines
Answers to Discussion
This activity may be carried out by the students, or if your school does not permit students to work with open flames, the activity may be carried out by the instructor as a demonstration. The two main concepts students can learn from this activity are:
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Molecular structure determines macroscopic properties, and changes in molecular structure bring
about changes in macroscopic properties.
Polymeric molecular structures result in materials with very different properties from those of low-molecular-mass materials.
Background
A molecule of rhombic sulfur is made of eight sulfur atoms arranged in a ring. When rhombic
sulfur is heated above 180°C and is quickly cooled, the rings open and join together
to form long linear chains, like this:
This is called polymeric sulfur, or sometimes thiorubber. Its structure is simply
long linear chains of sulfur atoms. Sulfur in this form is a rubbery solid. The rubber has good
physical properties, but in a few days it reverts to rhombic sulfur. Needless to say, this
polymer isn't very useful. But students will have a good time making it nonetheless.
Preparation
This activity requires little preparation, other than making the materials available to the
students. Make sure the students are aware of the hazards of heating test tubes in open
flames. They should be made aware that they should not hold the test tube with their hands
when heating it, only with tongs, and that an open test tube should never be pointed at anyone
when being heated, to avoid splattering accidents.
Relevant National Science Education Standards
Physical Science — The
activity involves carrying out a chemical reaction. Understanding the changes that the
reaction causes to the molecular structure of the sulfur is essential to the activity,
as is the understanding that macroscopic properties are determined by molecular structure.
Meyer, K.H. Natural and Synthetic High Polymers. New York: Interscience, 1950.
Sorensen, Wayne R., and Campbell, Tod W. Preparative Methods of Polymer Chemistry.
New York: Interscience, 1961.
Tobolsky, A.V., and Eisenberg, A. Journal of the American Chemical Society, 1959,
81, 780.
Watt, Shirley, ed. Polymer Chemistry, Rev. Ed.. Arlington, VA: National Science Teachers
Association, 1997, pp 201–202.
Unifying Concepts and Processes —
The activity involves understanding the sulfur polymerization system and using an
understanding of molecular level changes to explain the behavior of the sulfur on
polymerization, and on depolymerization.
References
Bacon, R.F., and Fanelli, R. Journal of the American Chemical Society, 1943,
65, 639.